Positioning system for wireless electric vehicle charging

Abstract

Apparatus, systems, and methods of wireless network communication, and in particular, to establishing communications between an electric vehicle and a wireless charging station.

Description

000469-0016-WO1 Positioning System for Wireless Electric Vehicle Charging CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional ApplicationNo.63 / 692,558,filed September 9, 2024. The disclosures of each of the foregoing applications are incorporated by reference herein in their entirety. BACKGROUND

[0002] This application relates to wireless network communication, and in particular, toestablishing communications between an electric vehicle and a wireless charging station.

[0003] Wireless power transfer (WPT) for charging electric vehicles is described in detailin patents such as U.S. Patents 8,933,594, titled “Wireless energy transfer for vehicles,” and 9,561,730, titled “Wireless power transmission in electric vehicles,” which are incorporated here by reference in their entirety. More specifically, these patents refer to inductive WPT between a ground-based unit of a wireless charging station and a vehicle-based unit, herein also simply referred to as the ground unit and the vehicle unit, respectively.

[0004] Efficient and regulatory compliant WPT for electric vehicles requires a WPT coil inthe vehicle unit to be aligned with a WPT coil in the ground unit within a specified tolerance zone. Some standards specify a tolerance zone of + / - 75 mm in x-direction (vehicle longitudinal axis) and + / - 100 mm in y-direction (vehicle lateral axis). Therefore, one aspect of WPT for charging electric vehicles to be addressed is assisting a user or an autonomous driving system to park and align the vehicle within the relatively tight tolerance zone sometimes also referred to as “charging spot”. Such park assist system may also include guidance of the user or the autonomous driving system in steering the vehicle towards the ground unit.

[0005] A further aspect of WPT for electric vehicle charging to be addressed isestablishing wireless communications between the vehicle and the wireless charging station the vehicle is attempting for being charged from. Standard compliant WPT for electric vehicles, requires the wireless charging station to communicate with the vehicle via awireless communication network for purposes of WPT system control and other WPT-related functions (e.g., for the safety of the system). This communication is based on WiFi IEEE 802.11x using standardized protocols enabling interoperability. Establishing wireless communications may be particularly difficult in a parking facility with multiple wireless charging stations at which multiple EVs may be attempting to park at the same time. It is necessary to disambiguate the connections – that is, make sure that each vehicle is in communication with the wireless charging station it is attempting to use for charging, and not another e.g., neighboring station. This disambiguation is part of a process referred to as pairing and shall ensure that a wireless communication node (e.g., a WiFi client) associated to the vehicle communicates with a wireless communication node (e.g., a WiFi access point) associated to the right wireless charging station.

[0006] Guidance, alignment, and pairing principally rely on determining a positionalrelationship between the vehicle unit and the ground unit of the wireless charging station the vehicle is attempting to use for charging. SUMMARY

[0007] Afirst general aspect includes a ground unit for charging an electric vehicle, theground unit comprising a ground position detection, PD, unit. The ground PD unit is configured to transmitfirst and second magneticfield signals to be used by a vehicle PD unit to determine a positional relationship between a vehicle unit and the ground unit based on thefirst and second magneticfield signals, wherein thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axisdirection; thefirst magneticfield signal is a binary modulated carrier signal modulatedaccording to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on-intervals and substantially absent in off-intervals; and the second magneticfield signal is transmitted during off-intervals of thefirst magneticfield signal.

[0008] Optionally, in embodiments of thefirst general aspect, thefirst axis direction maycorrespond to a longitudinal axis direction of a parking space.

[0009] Optionally, in embodiments of thefirst general aspect, thefirst and secondmagneticfield signals may be transmitted in quadrature and at a same carrier frequency.

[0010] Optionally, in embodiments of thefirst general aspect, presence of thefirstmagneticfield signal during on-intervals may represent a binary one, and substantial absence of thefirst magneticfield signal during off-intervals may represent a binary zero.

[0011] Optionally, in embodiments of thefirst general aspect, a phase of the secondmagneticfield signal may alternate betweenfirst and second phases across successive off- intervals of thefirst magneticfield signal.

[0012] Optionally, in embodiments of thefirst general aspect, thefirst phase may differfrom the second phase by 180 degrees.

[0013] Optionally, in embodiments of thefirst general aspect, thefirst phase may be 90degrees and the second phase may be 270 degrees compared to a phase of thefirst magneticfield signal.

[0014] Optionally, in embodiments of thefirst general aspect, a magnitude of the secondmagneticfield signal may be less than a magnitude of thefirst magneticfield signal.

[0015] Optionally, in embodiments of thefirst general aspect, the binary modulatedcarrier signal may be Manchester encoded.

[0016] Optionally, in embodiments of thefirst general aspect, the binary modulatedcarrier signal may convey data.

[0017] Optionally, in embodiments of thefirst general aspect, thefirst magneticfieldsignal may induce afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal may induce a second voltage signal into the one or more receiver coils of the vehicle PD unit. The inducedfirst and second voltages may be used by the vehicle PD unit to: measure thefirst and second voltage signals, and determine a position of the vehicle unit relative to the ground unit based on the measuredfirst and second voltage signals.

[0018] Optionally, in embodiments of thefirst general aspect, thefirst and secondmagneticfield signals may be used by the vehicle PD unit to determine a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determine the position and orientation of the vehicle unit relative to the ground unit.

[0019] A second general aspect includes a vehicle unit for electric vehicle charging, thevehicle unit comprising a vehicle position detection, PD, unit. The vehicle PD unit is configured to receivefirst and second magneticfield signals from a ground PD unit and determine a positional relationship between the vehicle unit and the ground unit based onthefirst and second magneticfield signals, wherein thefirst magneticfield signal resultsfrom a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axis direction; thefirst magneticfield signal is a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on-intervals and substantially absent in off-intervals; and the second magneticfield signal is received during off-intervals of thefirst magneticfield signal.

[0020] Optionally, in embodiments of the second general aspect, thefirst axis directionmay correspond to a longitudinal axis direction of a parking space.

[0021] Optionally, in embodiments of the second general aspect, thefirst and secondmagneticfield signals may be transmitted in quadrature and at a same carrier frequency.

[0022] Optionally, in embodiments of the second general aspect, presence of thefirstmagneticfield signal during on-intervals may represent a binary one; and substantial absence of thefirst magneticfield signal during off-intervals may represent a binary zero.

[0023] Optionally, in embodiments of the second general aspect, a phase of the secondmagneticfield signal may alternate betweenfirst and second phases across successive off- intervals of thefirst magneticfield signal.

[0024] Optionally, in embodiments of the second general aspect, thefirst phase maydiffer from the second phase by 180 degrees.

[0025] Optionally, in embodiments of the second general aspect, thefirst phase may be90 degrees and the second phase may be 270 degrees compared to a phase of thefirst magneticfield signal.

[0026] Optionally, in embodiments of the second general aspect, a magnitude of thesecond magneticfield signal may be less than a magnitude of thefirst magneticfield signal.

[0027] Optionally, in embodiments of the second general aspect, the binary modulatedcarrier signal may be Manchester encoded.

[0028] Optionally, in embodiments of the second general aspect, the binary modulatedcarrier signal may convey data.

[0029] Optionally, in embodiments of the second general aspect, thefirst magneticfieldsignal may induce afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal may induce a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the vehicle PD unit may be configured to use the inducedfirst and second voltages to: measure thefirst and second voltage signals, and determine a position of the vehicle unit relative to the ground unit based on the measured first and second voltage signals.

[0030] Optionally, in embodiments of the second general aspect, the vehicle PD unit maybe configured to use thefirst and second magneticfield signals to: determine a magnitude and an angle of each of thefirst and second magneticfield signals with respect to anorientation of the vehicle unit; and determine the position and orientation of the vehicleunit relative to the ground unit.

[0031] A third general aspect includes a wireless power transfer, WPT, system for electricvehicle charging, the WPT system comprising: a ground unit comprising a ground position detection, PD, unit and a vehicle unit comprising a vehicle PD unit. The ground PD unit is configured to transmitfirst and second magneticfield signals to the vehicle PD unit, wherein thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis directionthat is perpendicular to thefirst axis direction; thefirst magneticfield signal is a binarymodulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on-intervals and substantially absent in off-intervals; the second magneticfield signal is transmitted during off-intervals of thefirst magneticfield signal. The vehicle PD unit is configured to receive thefirst and second magneticfield signals; and the vehicle PD unit is configured to determine a positional relationship between the vehicle unit and the ground unit based on thefirst and second magneticfield signals.

[0032] Optionally, in embodiments of the third general aspect, thefirst axis direction maycorrespond to a longitudinal axis direction of a parking space.

[0033] Optionally, in embodiments of the third general aspect, thefirst and secondmagneticfield signals are transmitted in quadrature and at a same carrier frequency.

[0034] Optionally, in embodiments of the third general aspect, presence of thefirstmagneticfield signal during on-intervals may represent a binary one; and substantial absence of thefirst magneticfield signal during off-intervals may represent a binary zero.

[0035] Optionally, in embodiments of the third general aspect, a phase of the secondmagneticfield signal may alternate betweenfirst and second phases across successive off- intervals of thefirst magneticfield signal.

[0036] Optionally, in embodiments of the third general aspect, thefirst phase may differfrom the second phase by 180 degrees.

[0037] Optionally, in embodiments of the third general aspect, thefirst phase may be 90degrees and the second phase may be 270 degrees compared to a phase of thefirst magneticfield signal.

[0038] Optionally, in embodiments of the third general aspect, a magnitude of thesecond magneticfield signal may be less than a magnitude of thefirst magneticfield signal.

[0039] Optionally, in embodiments of the third general aspect, the binary modulatedcarrier signal may be Manchester encoded.

[0040] Optionally, in embodiments of the third general aspect, the binary modulatedcarrier signal may convey data.

[0041] Optionally, in embodiments of the third general aspect, thefirst magneticfieldsignal may induce afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal may induce a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the vehicle PD unit may be configured to use the inducedfirst and second voltages to: measure thefirst and second voltage signals, and determine a position of the vehicle unit relative to the ground unit based on the measured first and second voltage signals.

[0042] Optionally, in embodiments of the third general aspect, the vehicle PD unit may beconfigured to use thefirst and second magneticfield signals to: determine a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determine the position and orientation of the vehicle unit relative to the ground unit.

[0043] A fourth general aspect includes a method of controlling a wireless power transfer,WPT, system for electric vehicle charging, the WPT system comprising a ground unit comprising a ground position detection, PD, unit and a vehicle unit comprising a vehicle PD unit. The method comprises: transmitting, by the ground PD unit,first and second magnetic field signals to be used by the vehicle PD unit, wherein thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axisdirection; modulating, by the ground PD unit, thefirst magneticfield signal to generate abinary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on-intervals and substantially absent in off-intervals; transmitting, by the ground PD unit, the second magneticfield signal during off-intervals of thefirst magneticfield signal; receiving, by the vehicle PD unit, the first and second magneticfield signals; and determining, by the vehicle PD unit, a positional relationship between the vehicle unit and the ground unit based on thefirst and second magneticfield signals.

[0044] Optionally, in embodiments of the fourth general aspect, thefirst axis directionmay correspond to a longitudinal axis direction of a parking space.

[0045] Optionally, in embodiments of the fourth general aspect, thefirst and secondmagneticfield signals may be transmitted in quadrature and at a same carrier frequency.

[0046] Optionally, in embodiments of the fourth general aspect, presence of thefirstmagneticfield signal during on-intervals may represent a binary one; and substantial absence of thefirst magneticfield signal during off-intervals may represent a binary zero.

[0047] Optionally, in embodiments of the fourth general aspect, a phase of the secondmagneticfield signal may alternate betweenfirst and second phases across successive off- intervals of thefirst magneticfield signal.

[0048] Optionally, in embodiments of the fourth general aspect, thefirst phase may differfrom the second phase by 180 degrees.

[0049] Optionally, in embodiments of the fourth general aspect, thefirst phase may be 90degrees and the second phase may be 270 degrees compared to a phase of thefirst magneticfield signal.

[0050] Optionally, in embodiments of the fourth general aspect, a magnitude of thesecond magneticfield signal may be less than a magnitude of thefirst magneticfield signal.

[0051] Optionally, in embodiments of the fourth general aspect, the binary modulatedcarrier signal may be Manchester encoded.

[0052] Optionally, in embodiments of the fourth general aspect, the binary modulatedcarrier signal may convey data.

[0053] Optionally, in embodiments of the fourth general aspect, thefirst magneticfieldsignal may induce afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal may induce a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the determining, by the vehicle PD unit, may comprises: measuring thefirst and second voltage signals, and determining a position of thevehicle unit relative to the ground unit based on the measuredfirst and second voltage signals.

[0054] Optionally, in embodiments of the fourth general aspect, the determining, by thevehicle PD unit, may comprise determining a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determining the position and orientation of the vehicle unit relative to the ground unit.

[0055] Afifth general aspect includes a method of controlling a ground unit for electricvehicle charging, the ground unit comprising a ground position detection, PD, unit. The method comprises transmitting, by the ground PD unit,first and second magneticfield signals to be used by a vehicle PD unit, wherein thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axis direction; modulating, by the ground PD unit, thefirst magneticfield signal to generate a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on-intervals and substantially absent in off-intervals; and transmitting, by the ground PD unit, the second magneticfield signal during off-intervals of thefirst magneticfield signal.

[0056] Optionally, in embodiments of thefifth general aspect, thefirst axis direction maycorrespond to a longitudinal axis direction of a parking space.

[0057] Optionally, in embodiments of thefifth general aspect, thefirst and secondmagneticfield signals may be transmitted in quadrature and at a same carrier frequency.

[0058] Optionally, in embodiments of thefifth general aspect, the presence of thefirstmagneticfield signal during on-intervals may represent a binary one; and substantial absence of thefirst magneticfield signal during off-intervals may represent a binary zero.

[0059] Optionally, in embodiments of thefifth general aspect, a phase of the secondmagneticfield signal may alternate betweenfirst and second phases across successive off- intervals of thefirst magneticfield signal.

[0060] Optionally, in embodiments of thefifth general aspect, thefirst phase may differfrom the second phase by 180 degrees.

[0061] Optionally, in embodiments of thefifth general aspect, thefirst phase may be 90degrees and the second phase may be 270 degrees compared to a phase of thefirst magneticfield signal.

[0062] Optionally, in embodiments of thefifth general aspect, a magnitude of the secondmagneticfield signal may be less than a magnitude of thefirst magneticfield signal.

[0063] Optionally, in embodiments of thefifth general aspect, the binary modulatedcarrier signal may be Manchester encoded.

[0064] Optionally, in embodiments of thefifth general aspect, the binary modulatedcarrier signal may convey data.

[0065] Optionally, in embodiments of thefifth general aspect, thefirst magneticfieldsignal may induce afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal may induce a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the inducedfirst and second voltages may be used by the vehicle PD unit for: measuring thefirst and second voltage signals, and determining a position of the vehicle unit relative to the ground unit based on the measuredfirst and second voltage signals.

[0066] Optionally, in embodiments of thefifth general aspect, thefirst and secondmagneticfield signals may be used by the vehicle PD unit for: determining a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determining the position and orientation of the vehicle unit relative to the ground unit.

[0067] A sixth general aspect includes a method of controlling a vehicle unit for electricvehicle charging, the vehicle unit comprising a vehicle position detection, PD, unit. The method comprises: receiving, by the vehicle PD unit,first and second magneticfield signals from a ground PD unit, wherein: thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magneticmoment in a second axis direction that is perpendicular to thefirst axis direction, thefirst magneticfield signal is a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, thefirst magneticfield signal is present in on-intervals and substantially absent in off-intervals, and the second magneticfield signal is received during off-intervals of thefirst magneticfield signal; and determining, by the vehicle PD unit, a positional relationship between the vehicle unit and the ground unit based on thefirst and second magneticfield signals.

[0068] Optionally, in embodiments of the sixth general aspect, thefirst axis direction maycorrespond to a longitudinal axis direction of a parking space.

[0069] Optionally, in embodiments of the sixth general aspect, thefirst and secondmagneticfield signals may be transmitted in quadrature and at a same carrier frequency.

[0070] Optionally, in embodiments of the sixth general aspect, presence of thefirstmagneticfield signal during on-intervals may represent a binary one; and substantial absence of thefirst magneticfield signal during off-intervals may represent a binary zero.

[0071] Optionally, in embodiments of the sixth general aspect, a phase of the secondmagneticfield signal may alternate betweenfirst and second phases across successive off- intervals of thefirst magneticfield signal.

[0072] Optionally, in embodiments of the sixth general aspect, thefirst phase may differfrom the second phase by 180 degrees.

[0073] Optionally, in embodiments of the sixth general aspect, thefirst phase may be 90degrees and the second phase may be 270 degrees compared to a phase of thefirst magneticfield signal.

[0074] Optionally, in embodiments of the sixth general aspect, a magnitude of the secondmagneticfield signal may be less than a magnitude of thefirst magneticfield signal.

[0075] Optionally, in embodiments of the sixth general aspect, the binary modulatedcarrier signal is Manchester encoded.

[0076] Optionally, in embodiments of the sixth general aspect, the binary modulatedcarrier signal may convey data.

[0077] Optionally, in embodiments of the sixth general aspect, thefirst magneticfieldsignal may induce afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal may induce a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the determining may comprise: measuring thefirst and second voltage signals, and determining a position of the vehicle unit relative to the ground unit based on the measuredfirst and second voltage signals.

[0078] Optionally, in embodiments of the sixth general aspect, the determining maycomprise: determining a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determining the positionand orientation of the vehicle unit relative to the ground unit.

[0079] A seventh general aspect includes a vehicle unit for electric vehicle charging, thevehicle unit comprising a vehicle position detection, PD, unit, configured to: acquire a multi- parking space layout for a plurality of parking spaces and a frequency re-use pattern for transmission of beacon signals; receive afirst beacon signal at afirst frequency from afirst ground unit disposed in afirst parking space from among the plurality of parking spaces; receive a second beacon signal at a second frequency from a second ground unit disposed in a second parking space from among the plurality of parking spaces; determine afirst distance between the vehicle unit and thefirst ground unit based on a magnitude of thefirst beacon signal using a magnitude vs distance function; determine a second distance between the vehicle unit and the second ground unit based on a magnitude of the second beaconsignal using the magnitude vs distance function; and determine a positional relationshipbetween the vehicle unit and thefirst ground unit based on the determined distances, the acquired multi-parking space layout, and the acquired frequency re-use pattern, wherein the positional relationship is determined using lateration.

[0080] Optionally, in embodiments of the seventh general aspect, the vehicle PD unit maybe configured to: receive a third beacon signal at a third frequency from a third ground unit disposed in a third parking space from among the plurality of parking spaces, wherein thesecond and third ground units are disposed on opposite sides of thefirst ground unit; and determine a third distance between the vehicle unit and the third ground unit based on a magnitude of the third beacon signal using the magnitude vs distance function, wherein the positional relationship is determined using trilateration.

[0081] Optionally, in embodiments of the seventh general aspect, the vehicle PD unit maybe configured to: receive a fourth beacon signal at a fourth frequency from a fourth ground unit disposed in a fourth parking space, from among the plurality of parking spaces, adjacent to one of the second and third parking spaces; and determine a fourth distance between the vehicle unit and the fourth ground unit based on a magnitude of the fourth beacon signal, wherein the positional relationship is determined using multilateration.

[0082] Optionally, in embodiments of the seventh general aspect, the multi-parking spacelayout may be a predetermined parking space layout and the frequency re-use pattern may be a predetermined frequency re-use pattern.

[0083] Optionally, in embodiments of the seventh general aspect, the multi-parking spacelayout and the frequency re-use pattern may be communicated to the vehicle PD unit via a radio network.

[0084] Optionally, in embodiments of the seventh general aspect, the vehicle PD unit maybe further configured to: determine a global position of the vehicle unit using a globalpositioning system; and select one of a set of predetermined multi-parking space layoutsand frequency re-use patterns based on the determined global position.

[0085] Optionally, in embodiments of the seventh general aspect, the multi-parking spacelayout may include a parking space width.

[0086] Optionally, in embodiments of the seventh general aspect, the multi-parking spacelayout used to determine a parking space width; and the vehicle PD unit is configured todetermine the parking space width using overdetermination of multilateration.

[0087] Optionally, in embodiments of the seventh general aspect, the vehicle PD unit maybe configured to: determine distances between the vehicle unit and the respective ground units at two or more vehicle positions as the vehicle unit moves along a trajectory towardsthefirst ground unit; and determine the parking space width based on the distances determined at the two or more positions.

[0088] Optionally, in embodiments of the seventh general aspect, the beacon signals maybe magneticfield signals.

[0089] Optionally, in embodiments of the seventh general aspect, the vehicle PD unit maycomprise one or more receiver coils; the magneticfield signals may induce respective voltage signals into the one or more receiver coils; and the vehicle PD unit may be configured to: measure the voltage signals; and determine at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals.

[0090] Optionally, in embodiments of the seventh general aspect, thefirst beacon signalmay be received by the vehicle PD unit asfirst and second magneticfield signals from the first ground unit; the second beacon signal may be received by the vehicle PD unit asfirstand second magneticfield signal from an adjacent ground unit; thefirst magneticfieldsignals may result from a magnetic moment in afirst axis direction of the ground units; and the second magneticfield signals may result from a magnetic moment in a second axis direction of the ground units.

[0091] Optionally, in embodiments of the seventh general aspect, thefirst axis directionmay correspond to a longitudinal axis direction of a parking space.

[0092] Optionally, in embodiments of the seventh general aspect, the vehicle PD unit maycomprises one or more receiver coils; thefirst magneticfield signals may induce respective first voltage signals into the one or more receiver coils; the second magneticfield signals may induce respective second voltage signals into the one or more receiver coils; and the vehicle PD unit may be configured to: measure thefirst and second voltage signals; and determine at least one of a position and an orientation of the vehicle unit relative to the first ground unit based on the measuredfirst and second voltage signals.

[0093] An eights general aspect includes afirst ground unit, from among a set of groundunits, for electric vehicle charging, thefirst ground unit comprising afirst ground PD unit,wherein the set of ground units are configured according to a frequency re-use pattern, and thefirst ground PD unit is configured to: transmit, for use by a vehicle PD unit to determine a positional relationship between a vehicle unit and thefirst ground unit using lateration: the frequency re-use pattern for transmitting afirst beacon signal by thefirst ground unit disposed in afirst parking space from, among a plurality of parking spaces, and for transmitting a second beacon signal by a second ground unit, from among the set of ground units, disposed in a second parking space, from among the plurality of parking spaces; and a multi-parking space layout for the plurality of parking spaces.

[0094] Optionally, in embodiments of the eighth general aspect, the multi-parking spacelayout may be a predetermined parking space layout and the frequency re-use pattern may be a predetermined frequency re-use pattern.

[0095] Optionally, in embodiments of the eighth general aspect, the multi-parking spacelayout and the frequency re-use pattern may be transmitted to the vehicle PD unit via a radio network.

[0096] Optionally, in embodiments of the eighth general aspect, the multi-parking spacelayout may include a parking space width.

[0097] Optionally, in embodiments of the eighth general aspect, the multi-parking spacelayout may be used to determine a parking space width; and the parking space width may be determined by the vehicle PD unit using overdetermination.

[0098] Optionally, in embodiments of the eighth general aspect, the beacon signals maybe magneticfield signals.

[0099] Optionally, in embodiments of the eighth general aspect, the magneticfieldsignals may induce respective voltage signals into one or more receiver coils of the vehicle PD unit; and the magneticfield signals may be used by the vehicle PD unit to: measure the voltage signals; and determine at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals.

[0100] A ninth general aspect includes a wireless power transfer, WPT, system for electricvehicle charging, the WPT system comprising: afirst ground unit disposed in afirst parkingspace from among a plurality of parking spaces, wherein thefirst ground unit comprises a first ground position detection, PD, unit; a second ground unit disposed in a second parking space from among the plurality of parking spaces, wherein the second ground unit comprises a second ground PD unit; and a vehicle unit comprising a vehicle PD unit, wherein: thefirst ground PD unit is configured to transmit afirst beacon signal at afirst frequency to be used by the vehicle PD unit to determine a positional relationship between the vehicle unit and thefirst ground unit; the second ground PD unit is configured to transmit a second beacon signal at a second frequency to be used by the vehicle PD unit to determine the positional relationship between the vehicle unit and thefirst ground unit; and the vehicle PD unit is configured to: receive thefirst beacon signal transmitted at thefirst frequency by thefirst ground PD unit; receive the second beacon signal transmitted at the second frequency by the second ground PD unit; acquire a multi-parking space layout for the plurality of parking spaces and a frequency re-use pattern for transmission of the beacon signals; determine afirst distance between the vehicle unit and thefirst ground unit based on a magnitude of thefirst beacon signal using a magnitude vs distance function; determine a second distance between the vehicle unit and the second ground unit based on a magnitude of the second beacon signal using the magnitude vs distance function; and determine the positional relationship between the vehicle unit and thefirst ground unit based on the determined distances, the acquired multi-parking space layout, and the acquired frequency re-use pattern, wherein the positional relationship is determined using lateration.

[0101] Optionally, in embodiments of the ninth general aspect, the vehicle PD unit maybe configured to: receive a third beacon signal at a third frequency from a third ground unit disposed in a third parking space from among the plurality of parking spaces, wherein the second and third ground units are disposed on opposite sides of thefirst ground unit; and determine a third distance between the vehicle unit and the third ground unit based on a magnitude of the third beacon signal using the magnitude vs distance function, wherein the positional relationship is determined using trilateration.

[0102] Optionally, in embodiments of the ninth general aspect, the vehicle PD unit maybe configured to: receive a fourth beacon signal at a fourth frequency from a fourth ground unit disposed in a fourth parking space, from among the plurality of parking spaces, adjacentto one of the second and third parking spaces; and determine a fourth distance between the vehicle unit and the fourth ground unit based on a magnitude of the fourth beacon signal, wherein the positional relationship is determined using multilateration.

[0103] Optionally, in embodiments of the ninth general aspect, the multi-parking spacelayout may be a predetermined parking space layout and the frequency re-use pattern may be a predetermined frequency re-use pattern.

[0104] Optionally, in embodiments of the ninth general aspect, the multi-parking spacelayout and the frequency re-use pattern may be communicated to the vehicle PD unit via a radio network.

[0105] Optionally, in embodiments of the ninth general aspect, the vehicle PD unit maybe further configured to: determine a global position of the vehicle unit using a globalpositioning system; and select one of a set of predetermined multi-parking space layoutsand frequency re-use patterns based on the determined global position.

[0106] Optionally, in embodiments of the ninth general aspect, the multi-parking spacelayout may include a parking space width.

[0107] Optionally, in embodiments of the ninth general aspect, the multi-parking spacelayout may be used to determine a parking space width; and the vehicle PD unit may be configured to determine the parking space width using overdetermination of multilateration.

[0108] Optionally, in embodiments of the ninth general aspect, the vehicle PD unit maybe configured to: determine distances between the vehicle unit and the respective ground units at two or more vehicle positions as the vehicle unit moves along a trajectory towards thefirst ground unit; and determine the parking space width based on the distances determined at the two or more positions.

[0109] Optionally, in embodiments of the ninth general aspect, the beacon signals maybe magneticfield signals.

[0110] Optionally, in embodiments of the ninth general aspect, the vehicle PD unit maycomprises one or more receiver coils; the magneticfield signals may induce respective voltage signals into the one or more receiver coils; and the vehicle PD unit may be configured to: measure the voltage signals; and determine at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals.

[0111] Optionally, in embodiments of the ninth general aspect, thefirst beacon signalmay be received by the vehicle PD unit asfirst and second magneticfield signals from the first ground unit; the second beacon signal may be received by the vehicle PD unit asfirstand second magneticfield signals from an adjacent ground unit; thefirst magneticfieldsignals may result from a magnetic moment in afirst axis direction of the ground units; and the second magneticfield signals may result from a magnetic moment in a second axis direction of the ground units.

[0112] Optionally, in embodiments of the ninth general aspect, thefirst axis directionmay correspond to a longitudinal axis direction of a parking space.

[0113] Optionally, in embodiments of the ninth general aspect, the vehicle PD unit maycomprises one or more receiver coils; thefirst magneticfield signals may induce respective first voltage signals into the one or more receiver coils; the second magneticfield signals may induce respective second voltage signals into the one or more receiver coils; and the vehicle PD unit may be configured to: measure thefirst and second voltage signals; and determine at least one of a position and an orientation of the vehicle unit relative to the first ground unit based on the measuredfirst and second voltage signals.

[0114] A tenth general aspect includes a method of controlling a wireless power transfer,WPT, system for electric vehicle charging, the WPT system comprising: afirst ground unit disposed in afirst parking space from among a plurality of parking spaces, wherein thefirst ground unit comprises afirst ground position detection, PD, unit; a second ground unit disposed in a second parking space from among the plurality of parking spaces, wherein the second ground unit comprises a second ground PD unit; and a vehicle unit comprising a vehicle PD unit, wherein the method comprises: transmitting, by thefirst ground PD unit, afirst beacon signal at afirst frequency to be used by the vehicle PD unit to determine apositional relationship between the vehicle unit and thefirst ground unit; transmitting, bythe second ground PD unit, a second beacon signal at a second frequency to be used by the vehicle PD unit to determine the positional relationship between the vehicle unit and the first ground unit; receiving, by the vehicle PD unit, thefirst beacon signal from thefirst ground PD unit; receiving, by the vehicle PD unit, the second beacon signals from the second ground PD unit; acquiring, by the vehicle PD unit, a multi-parking space layout for the plurality of parking spaces and a frequency re-use pattern for transmission of the beacon signals; determining, by the vehicle PD unit, afirst distance between the vehicle PD unit and thefirst ground PD unit based on a magnitude of thefirst beacon signal using a magnitude vs distance function; determining, by the vehicle PD unit, a second distance between the vehicle PD unit and the second ground PD unit based on a magnitude of the second beacon signal using the magnitude vs distance function; and determining, by the vehicle PD unit, a positional relationship between the vehicle unit and thefirst ground unit based on the determined distances, the acquired multi-parking space layout, and the acquired frequency re-use pattern, wherein the positional relationship is determined using lateration positioning.

[0115] Optionally, in embodiments of the tenth general aspect, 109. the method maycomprise: receiving, by the vehicle PD unit, a third beacon signal at a third frequency from a third ground unit disposed in a third parking space from among the plurality of parking spaces, wherein the second and third ground units are disposed on opposite sides of the first ground unit; and determining, by the vehicle PD unit, a third distance between the vehicle unit and the third ground unit based on a magnitude of the third beacon signal using the magnitude vs distance function, wherein the positional relationship is determined using trilateration.

[0116] Optionally, in embodiments of the tenth general aspect, the method maycomprise: receiving, by the vehicle PD unit, a fourth beacon signal at a fourth frequency from a fourth ground unit disposed in a fourth parking space, from among the plurality of parking spaces, adjacent to one of the second and third parking spaces; and determining, by the vehicle PD unit, a fourth distance between the vehicle unit and the fourth ground unitbased on a magnitude of the fourth beacon signal, wherein the positional relationship is determined using multilateration.

[0117] Optionally, in embodiments of the tenth general aspect, the multi-parking spacelayout may be a predetermined parking space layout and the frequency re-use pattern may be a predetermined frequency re-use pattern.

[0118] Optionally, in embodiments of the tenth general aspect, the multi-parking spacelayout and the frequency re-use pattern may be communicated to the vehicle PD unit via a radio network.

[0119] Optionally, in embodiments of the tenth general aspect, the method maycomprise: determining, by the vehicle PD unit, a global position of the vehicle unit using aglobal positioning system; and selecting, by the vehicle PD unit, one of a set ofpredetermined multi-parking space layouts and frequency re-use patterns based on the determined global position.

[0120] Optionally, in embodiments of the tenth general aspect, the multi-parking spacelayout may include a parking space width.

[0121] Optionally, in embodiments of the tenth general aspect, the multi-parking spacelayout may be used to determine a parking space width; and the method may comprises: determining, by the vehicle PD unit, the parking space width using overdetermination of multilateration.

[0122] Optionally, in embodiments of the tenth general aspect, the method maycomprise: determining, by the vehicle PD unit, distances between the vehicle unit and the respective ground units at two or more vehicle positions as the vehicle unit moves along a trajectory towards thefirst ground unit; and determining, by the vehicle PD unit, the parking space width based on the distances determined at the two or more positions.

[0123] Optionally, in embodiments of the tenth general aspect, the beacon signals maybe magneticfield signals.

[0124] Optionally, in embodiments of the tenth general aspect, the vehicle PD unit maycomprise one or more receiver coils; the magneticfield signals may induce respective voltage signals into the one or more receiver coils; and the method may comprise: measuring, by the vehicle PD unit, the voltage signals; and determining, by the vehicle PD unit, at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals.

[0125] Optionally, in embodiments of the tenth general aspect, thefirst beacon signalmay be received by the vehicle PD unit asfirst and second magneticfield signals from the first ground unit; the second beacon signal may be received by the vehicle PD unit asfirstand second magneticfield signal from an adjacent ground unit; thefirst magneticfieldsignals may result from a magnetic moment in afirst axis direction of the ground units; and the second magneticfield signals may result from a magnetic moment in a second axis direction of the ground unit.

[0126] Optionally, in embodiments of the tenth general aspect, thefirst axis directionmay correspond to a longitudinal axis direction of a parking space.

[0127] Optionally, in embodiments of the tenth general aspect, the vehicle PD unit maycomprises one or more receiver coils; thefirst magneticfield signals may induce respective first voltage signals into the one or more receiver coils; the second magneticfield signals may induce respective second voltage signals into the one or more receiver coils; and the method may comprise: measuring, by the vehicle PD unit, thefirst and second voltage signals; and determining, by the vehicle PD unit, at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measuredfirst and second voltage signals.

[0128] An eleventh general aspect includes a method of controlling a vehicle unit forelectric vehicle charging, the vehicle unit comprising a vehicle position detection, PD, unit, the method comprising: acquiring a multi-parking space layout for a plurality of parking spaces and a frequency re-use pattern for transmission of beacon signals; receiving afirst beacon signal at afirst frequency from afirst ground unit disposed in afirst parking space from among the plurality of parking spaces; receiving a second beacon signal at a secondfrequency from a second ground unit disposed in a second parking space from among the plurality of parking spaces; determining afirst distance between the vehicle unit and thefirst ground unit based on a magnitude of thefirst beacon signal using a magnitude vs distance function; determining a second distance between the vehicle unit and the second ground unit based on a magnitude of the second beacon signal using the magnitude vs distancefunction; and determining a positional relationship between the vehicle unit and thefirstground unit based on the determined distances, the acquired multi-parking space layout, and the acquired frequency re-use pattern, wherein the positional relationship is determined using lateration.

[0129] Optionally, in embodiments of the eleventh general aspect, the method maycomprise: receiving, by the vehicle PD unit, a third beacon signal at a third frequency from a third ground unit disposed in a third parking space from among the plurality of parking spaces, wherein the second and third ground units are disposed on opposite sides of the first ground unit; and determining, by the vehicle PD unit, a third distance between the vehicle unit and the third ground unit based on a magnitude of the third beacon signal using the magnitude vs distance function, wherein the positional relationship is determined using trilateration.

[0130] Optionally, in embodiments of the eleventh general aspect, the method maycomprise: receiving, by the vehicle PD unit, a fourth beacon signal at a fourth frequency from a fourth ground unit disposed in a fourth parking space, from among the plurality of parking spaces, adjacent to one of the second and third parking spaces; and determining, by the vehicle PD unit, a fourth distance between the vehicle unit and the fourth ground unit based on a magnitude of the fourth beacon signal, wherein the positional relationship is determined using multilateration.

[0131] Optionally, in embodiments of the eleventh general aspect, the multi-parkingspace layout may be a predetermined parking space layout and the frequency re-use pattern may be a predetermined frequency re-use pattern.

[0132] Optionally, in embodiments of the eleventh general aspect, the multi-parkingspace layout and the frequency re-use pattern may be communicated to the vehicle PD unit via a radio network.

[0133] Optionally, in embodiments of the eleventh general aspect, the method maycomprise: determining, by the vehicle PD unit, a global position of the vehicle unit using aglobal positioning system; and selecting, by the vehicle PD unit, one of a set ofpredetermined multi-parking space layouts and frequency re-use patterns based on the determined global position.

[0134] Optionally, in embodiments of the eleventh general aspect, the multi-parkingspace layout may include a parking space width.

[0135] Optionally, in embodiments of the eleventh general aspect, the multi-parkingspace layout may be used to determine a parking space width; and the method may comprise: determining, by the vehicle PD unit, the parking space width using overdetermination of multilateration.

[0136] Optionally, in embodiments of the eleventh general aspect, the method maycomprises: determining, by the vehicle PD unit, distances between the vehicle unit and the respective ground units at two or more vehicle positions as the vehicle unit moves along a trajectory towards thefirst ground unit; and determining, by the vehicle PD unit, the parking space width based on the distances determined at the two or more positions.

[0137] Optionally, in embodiments of the eleventh general aspect, the beacon signalsmay be magneticfield signals.

[0138] Optionally, in embodiments of the eleventh general aspect, the vehicle PD unitmay comprises one or more receiver coils; the magneticfield signals may induce respective voltage signals into the one or more receiver coils; and the method may comprise: measuring, by the vehicle PD unit, the voltage signals; and determining, by the vehicle PD unit, at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals.

[0139] Optionally, in embodiments of the eleventh general aspect, thefirst beacon signalmay be received by the vehicle PD unit asfirst and second magneticfield signals from the first ground unit; the second beacon signal may be received by the vehicle PD unit asfirstand second magneticfield signals from an adjacent ground unit; thefirst magneticfieldsignals may result from a magnetic moment in afirst axis direction of the ground units; and the second magneticfield signals may result from a magnetic moment in a second axis direction of the ground units.

[0140] Optionally, in embodiments of the eleventh general aspect, thefirst axis directionmay correspond to a longitudinal axis direction of a parking space.

[0141] Optionally, in embodiments of the eleventh general aspect, the vehicle PD unitmay comprise one or more receiver coils; thefirst magneticfield signals may inducerespectivefirst voltage signals into the one or more receiver coils; the second magneticfieldsignals may induce respective second voltage signals into the one or more receiver coils; and the method may comprise: measuring, by the vehicle PD unit, thefirst and second voltage signals; and determining, by the vehicle PF unit, at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measuredfirst and second voltage signals.

[0142] A twelfth general aspect includes a method of controlling afirst ground unit, fromamong a set of ground units, for electric vehicle charging, thefirst ground unit comprising a first ground position detection, PD, unit, wherein the set of ground units are configuredaccording to a frequency re-use pattern, and the method comprises: transmitting, for use bya vehicle PD unit to determine a positional relationship between a vehicle unit and thefirst ground unit using lateration: the frequency re-use pattern for transmitting afirst beacon signal by thefirst ground unit disposed in afirst parking space from, among a plurality of parking spaces, and for transmitting a second beacon signal by a second ground unit, from among the set of ground units, disposed in a second parking space from, among the plurality of parking spaces; and a multi-parking space layout for the plurality of parking spaces.

[0143] Optionally, in embodiments of the twelfth general aspect, the multi-parking spacelayout may be a predetermined parking space layout and the frequency re-use pattern may be a predetermined frequency re-use pattern.

[0144] Optionally, in embodiments of the twelfth general aspect, the multi-parking spacelayout and the frequency re-use pattern may be transmitted to the vehicle PD unit via a radio network.

[0145] Optionally, in embodiments of the twelfth general aspect, the multi-parking spacelayout may include a parking space width.

[0146] Optionally, in embodiments of the twelfth general aspect, the multi-parking spacelayout may be used to determine a parking space width.

[0147] Optionally, in embodiments of the twelfth general aspect, the beacon signals maybe magneticfield signals.

[0148] Optionally, in embodiments of the twelfth general aspect, the magneticfieldsignals may induce respective voltage signals into one or more receiver coils of the vehicle PD unit for determining at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals.

[0149] A thirteenth general aspect includes a ground unit for electric vehicle charging,the ground unit comprising a ground position detection, PD, unit, wherein: the ground PD unit is configured to: generate and transmit a modulated beacon signal for use by a vehicle PD unit to determine a position of a vehicle unit with respect to the ground unit, wherein: the modulated beacon signal comprises a time-series of pulses, a shape of the pulses is defined based on a pulse shape function, each pulse has a pulse magnitude selected from a set of pulse magnitudes, the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated by the pulserate or an integer multiple thereof, the pulse shape function is configured to reduceemissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at eachfrequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide a spectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency.

[0150] Optionally, in embodiments of the thirteenth general aspect, the carrier signalmay comprise positional information of the ground unit; the modulated beacon signal may comprise a residual carrier component of the carrier signal with a magnitude sufficient to determine the position of the vehicle PD unit; and the residual component may be used by the vehicle PD unit to determine the position of the vehicle PD unit.

[0151] Optionally, in embodiments of the thirteenth general aspect, the modulatedbeacon signal may be afirst modulated beacon signal, the carrier signal may be afirst carrier signal, and the carrier frequency of thefirst carrier signal may be afirst frequency; thefirst frequency may be different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal may comprise pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal.

[0152] Optionally, in embodiments of the thirteenth general aspect, both thefirstfrequency and the second frequency may be selected from the set of frequencies allocated within the predetermined frequency band.

[0153] Optionally, in embodiments of the thirteenth general aspect, the predeterminedfrequency band may be afirst frequency band; and the second frequency may be selected from another set of frequencies allocated within a second frequency band different than the first frequency band.

[0154] Optionally, in embodiments of the thirteenth general aspect, the modulatedbeacon signal may convey data intended to be received and demodulated by the vehicle PD unit.

[0155] Optionally, in embodiments of the thirteenth general aspect, the pulse shapefunction may provide a signal-to-inter-symbol interference ratio greater than 20 dB.

[0156] Optionally, in embodiments of the thirteenth general aspect, the pulse shapefunction may be a raised-cosine function in the time domain.

[0157] Optionally, in embodiments of the thirteenth general aspect, the raised-cosinefunction may comprise an adjustment factor; and the ground PD unit may be configured to define the shape of the pulses based on the adjustment factor.

[0158] Optionally, in embodiments of the thirteenth general aspect, the set of pulsemagnitudes may comprise a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero.

[0159] Optionally, in embodiments of the thirteenth general aspect, the spectral notchmay be devoid of frequency components of the modulated beacon signal.

[0160] Optionally, in embodiments of the thirteenth general aspect, the time-series ofpulses may be encoded using Manchester coding.

[0161] A fourteenth general aspect includes a vehicle unit for electric vehicle charging,the vehicle unit comprising a vehicle position detection, PD, unit, configured to receive a modulated beacon signal from a ground PD unit of a ground unit and determine a position of the vehicle unit with respect to the ground unit based on the modulated beacon signal, wherein: the modulated beacon signal comprises a time-series of pulses, a shape of the pulses is defined based on a pulse shape function, each pulse has a pulse magnitude selected from a set of pulse magnitudes, the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated bythe pulse rate or an integer multiple thereof, the pulse shape function is configured toreduce emissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at each frequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide aspectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency.

[0162] Optionally, in embodiments of the fourteenth general aspect, the carrier signalmay comprise positional information of the ground unit; the modulated beacon signal may comprise a residual carrier component of the carrier signal with a magnitude sufficient to determine the position of the vehicle PD unit; and the residual component may be used by the vehicle PD unit to determine the position of the vehicle PD unit.

[0163] Optionally, in embodiments of the fourteenth general aspect, the modulatedbeacon signal may be afirst modulated beacon signal, the carrier signal may be afirst carrier signal, and the carrier frequency of thefirst carrier signal may be afirst frequency; thefirst frequency may be different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal may comprise pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal.

[0164] Optionally, in embodiments of the fourteenth general aspect, both thefirstfrequency and the second frequency may be selected from the set of frequencies allocated within the predetermined frequency band.

[0165] Optionally, in embodiments of the fourteenth general aspect, the predeterminedfrequency band may be afirst frequency band; and the second frequency may be selected from another set of frequencies allocated within a second frequency band different than the first frequency band.

[0166] Optionally, in embodiments of the fourteenth general aspect, the modulatedbeacon signal may convey data intended to be received and demodulated by the vehicle PD unit.

[0167] Optionally, in embodiments of the fourteenth general aspect, the pulse shapefunction may provide a signal-to-inter-symbol interference ratio greater than 20 dB.

[0168] Optionally, in embodiments of the fourteenth general aspect, the pulse shapefunction may be a raised-cosine function in the time domain.

[0169] Optionally, in embodiments of the fourteenth general aspect, the raised-cosinefunction may comprise an adjustment factor; and the shape of the pulses may be based on the adjustment factor.

[0170] Optionally, in embodiments of the fourteenth general aspect, the set of pulsemagnitudes may comprise a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero.

[0171] Optionally, in embodiments of the fourteenth general aspect, the spectral notchmay be devoid of frequency components of the modulated beacon signal.

[0172] Optionally, in embodiments of the fourteenth general aspect, the time-series ofpulses may be encoded using Manchester coding.

[0173] In afifteenth general aspect, a wireless power transfer, WPT, system for electricvehicle charging, the WPT system comprising: a ground unit comprising a ground position detection, PD, unit and a vehicle unit comprising a vehicle PD unit, wherein the ground PD unit is configured to: generate and transmit a modulated beacon signal for use by the vehicle PD unit to determine a position of the vehicle unit with respect to the ground unit, wherein: the modulated beacon signal comprises a time-series of pulses, a shape of the pulses is defined based on a pulse shape function, each pulse has a pulse magnitude selected from a set of pulse magnitudes, the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated by the pulserate or an integer multiple thereof, the pulse shape function is configured to reduceemissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at each frequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide a spectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency, and wherein the vehicle PD unit is configured to: receive amodulated beacon signal to determine the position of the vehicle unit with respect to the ground unit.

[0174] Optionally, in embodiments of thefifteenth general aspect, the carrier signal maycomprise positional information of the ground unit; the modulated beacon signal may comprise a residual carrier component of the carrier signal with a magnitude sufficient to determine the position of the vehicle PD unit; and the residual component may be used by the vehicle PD unit to determine the position of the vehicle PD unit.

[0175] Optionally, in embodiments of thefifteenth general aspect, the modulated beaconsignal may be afirst modulated beacon signal, the carrier signal may be afirst carrier signal, and the carrier frequency of thefirst carrier signal may be afirst frequency; thefirst frequency may be different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal may comprise pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal.

[0176] Optionally, in embodiments of thefifteenth general aspect, both thefirstfrequency and the second frequency may be selected from the set of frequencies allocated within the predetermined frequency band.

[0177] Optionally, in embodiments of thefifteenth general aspect, the predeterminedfrequency band may be afirst frequency band; and the second frequency may be selected from another set of frequencies allocated within a second frequency band different than the first frequency band.

[0178] Optionally, in embodiments of thefifteenth general aspect, the modulated beaconsignal may convey data intended to be received and demodulated by the vehicle PD unit.

[0179] Optionally, in embodiments of thefifteenth general aspect, the pulse shapefunction may provide a signal-to-inter-symbol interference ratio greater than 20 dB.

[0180] Optionally, in embodiments of thefifteenth general aspect, the pulse shapefunction may be a raised-cosine function in the time domain.

[0181] Optionally, in embodiments of thefifteenth general aspect, the raised-cosinefunction may comprise an adjustment factor; and the ground PD unit may be configured to define the shape of the pulses based on the adjustment factor.

[0182] Optionally, in embodiments of thefifteenth general aspect, the set of pulsemagnitudes may comprise a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero.

[0183] Optionally, in embodiments of thefifteenth general aspect, the spectral notch maybe devoid of frequency components of the modulated beacon signal.

[0184] Optionally, in embodiments of thefifteenth general aspect, the time-series ofpulses may be encoded using Manchester coding.

[0185] A sixteenth general aspect includes a method of controlling a wireless powertransfer, WPT, system for electric vehicle charging, the WPT system comprising a ground unit comprising a ground position detection, PD, unit and a vehicle unit comprising a vehicle PD unit, wherein the method comprises: generating and transmitting, by the ground PD unit, a modulated beacon signal for use by the vehicle PD unit to determine a position of the vehicle unit with respect to the ground unit, wherein: the modulated beacon signal comprises a time-series of pulses, a shape of the pulses is defined based on a pulse shape function, each pulse has a pulse magnitude selected from a set of pulse magnitudes, the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated by the pulse rate or an integer multiple thereof, the pulse shape function is configured to reduce emissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at each frequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide a spectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency; and receiving, by the vehicle PD unit, a modulated beacon signal to determine the position of the vehicle unit with respect to the ground unit.

[0186] Optionally, in embodiments of the sixteenth general aspect, the carrier signal maycomprise positional information of the ground unit; the modulated beacon signal may comprise a residual carrier component of the carrier signal with a magnitude sufficient to determine the position of the vehicle PD unit; and the residual component may be used by the vehicle PD unit to determine the position of the vehicle PD unit.

[0187] Optionally, in embodiments of the sixteenth general aspect, the modulatedbeacon signal may be afirst modulated beacon signal, the carrier signal may be afirst carrier signal, and the carrier frequency of thefirst carrier signal may be afirst frequency; thefirst frequency may be different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal may comprise pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal.

[0188] Optionally, in embodiments of the sixteenth general aspect, both thefirstfrequency and the second frequency may be selected from the set of frequencies allocated within the predetermined frequency band.

[0189] Optionally, in embodiments of the sixteenth general aspect, the predeterminedfrequency band maybe afirst frequency band; and the second frequency may be selected from another set of frequencies allocated within a second frequency band different than the first frequency band.

[0190] Optionally, in embodiments of the sixteenth general aspect, the modulatedbeacon signal may convey data intended to be received and demodulated by the vehicle PD unit.

[0191] Optionally, in embodiments of the sixteenth general aspect, the pulse shapefunction may provide a signal-to-inter-symbol interference ratio greater than 20 dB.

[0192] Optionally, in embodiments of the sixteenth general aspect, the pulse shapefunction may be a raised-cosine function in the time domain.

[0193] Optionally, in embodiments of the sixteenth general aspect, the raised-cosinefunction may comprises an adjustment factor; and the method may comprise: defining, by the ground PD unit, the shape of the pulses based on the adjustment factor.

[0194] Optionally, in embodiments of the sixteenth general aspect, the set of pulsemagnitudes may comprise a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero.

[0195] Optionally, in embodiments of the sixteenth general aspect, the spectral notchmay be devoid of frequency components of the modulated beacon signal.

[0196] Optionally, in embodiments of the sixteenth general aspect, the time-series ofpulses may be encoded using Manchester coding.

[0197] A seventeenth general aspect includes a method of controlling a ground unit forelectric vehicle charging, the ground unit comprising a ground position detection, PD, unit, the method comprising: generating and transmitting a modulated beacon signal for use by a vehicle PD unit to determine a position of a vehicle unit with respect to the ground unit, wherein: the modulated beacon signal comprises a time-series of pulses, a shape of the pulses is defined based on a pulse shape function, each pulse has a pulse magnitude selected from a set of pulse magnitudes, the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated bythe pulse rate or an integer multiple thereof, the pulse shape function is configured toreduce emissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at each frequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide a spectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency.

[0198] Optionally, in embodiments of the seventeenth general aspect, the carrier signalmay comprise positional information of the ground unit; the modulated beacon signal may comprise a residual carrier component of the carrier signal with a magnitude sufficient todetermine the position of the vehicle PD unit; and the residual component may be used by the vehicle PD unit to determine the position of the vehicle PD unit.

[0199] Optionally, in embodiments of the seventeenth general aspect, the modulatedbeacon signal may be afirst modulated beacon signal, the carrier signal may be afirst carrier signal, and the carrier frequency of thefirst carrier signal may be afirst frequency; thefirst frequency may be different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal may comprise pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal.

[0200] Optionally, in embodiments of the seventeenth general aspect, both thefirstfrequency and the second frequency may be selected from the set of frequencies allocated within the predetermined frequency band.

[0201] Optionally, in embodiments of the seventeenth general aspect, the predeterminedfrequency band may be afirst frequency band; and the second frequency may be selected from another set of frequencies allocated within a second frequency band different than the first frequency band.

[0202] Optionally, in embodiments of the seventeenth general aspect, the modulatedbeacon signal may convey data intended to be received and demodulated by the vehicle PD unit.

[0203] Optionally, in embodiments of the seventeenth general aspect, the pulse shapefunction may provide a signal-to-inter-symbol interference ratio greater than 20 dB.

[0204] Optionally, in embodiments of the seventeenth general aspect, the pulse shapefunction may be a raised-cosine function in the time domain.

[0205] Optionally, in embodiments of the seventeenth general aspect, the raised-cosinefunction may comprise an adjustment factor; and the method may comprises: defining, by the ground PD unit, the shape of the pulses based on the adjustment factor.

[0206] Optionally, in embodiments of the seventeenth general aspect, the set of pulsemagnitudes may comprise a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero.

[0207] Optionally, in embodiments of the seventeenth general aspect, the spectral notchmay be devoid of frequency components of the modulated beacon signal.

[0208] Optionally, in embodiments of the seventeenth general aspect, the time-series ofpulses may be encoded using Manchester coding.

[0209] An eighteenth general aspect includes a method of controlling a vehicle unit forelectric vehicle charging, the vehicle unit comprising a vehicle position detection, PD, unit, the method comprising: receiving a modulated beacon signal from a ground PD unit of a ground unit; and determining a position of the vehicle unit with respect to the ground unit based on the modulated beacon signal, wherein: the modulated beacon signal comprises a time-series of pulses, a shape of the pulses is defined based on a pulse shape function, each pulse has a pulse magnitude selected from a set of pulse magnitudes, the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated by the pulse rate or an integer multiple thereof, the pulse shape function is configured to reduce emissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at each frequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide a spectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency.

[0210] Optionally, in embodiments of the eighteenth general aspect, the carrier signalmay comprise positional information of the ground unit; the modulated beacon signal may comprise a residual carrier component of the carrier signal with a magnitude sufficient to determine the position of the vehicle PD unit; and the method may comprise: determining, by the vehicle PD unit, the position of the vehicle PD unit based on the residual component.

[0211] Optionally, in embodiments of the eighteenth general aspect, the modulatedbeacon signal may be afirst modulated beacon signal, the carrier signal may be afirst carrier signal, and the carrier frequency of thefirst carrier signal may be afirst frequency; thefirst frequency may be different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal may comprise pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal.

[0212] Optionally, in embodiments of the eighteenth general aspect, both thefirstfrequency and the second frequency may be selected from the set of frequencies allocated within the predetermined frequency band.

[0213] Optionally, in embodiments of the eighteenth general aspect, the predeterminedfrequency band may be afirst frequency band; and the second frequency may be selected from another set of frequencies allocated within a second frequency band different than the first frequency band.

[0214] Optionally, in embodiments of the eighteenth general aspect, the modulatedbeacon signal may convey data intended to be received and demodulated by the vehicle PD unit.

[0215] Optionally, in embodiments of the eighteenth general aspect, the pulse shapefunction may provide a signal-to-inter-symbol interference ratio greater than 20 dB.

[0216] Optionally, in embodiments of the eighteenth general aspect, the pulse shapefunction may be a raised-cosine function in the time domain.

[0217] Optionally, in embodiments of the eighteenth general aspect, the raised-cosinefunction may comprise an adjustment factor; and the shape of the pulses may be based on the adjustment factor.

[0218] Optionally, in embodiments of the eighteenth general aspect, the set of pulsemagnitudes may comprise a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero.

[0219] Optionally, in embodiments of the eighteenth general aspect, the spectral notchmay be devoid of frequency components of the modulated beacon signal.

[0220] Optionally, in embodiments of the eighteenth general aspect, the time-series ofpulses may be encoded using Manchester coding.

[0221] It will be understood that, in one or more of the above aspects, thefirst groundunit may be a target ground unit, thefirst ground PD unit may be a target ground PD unit, thefirst parking space may be a target parking space, the second ground unit may be an adjacent ground unit, the second ground PD unit may be an adjacent ground PD unit, and the second parking space may be an adjacent parking space. BRIEF DESCRIPTION OF THE DRAWINGS

[0222] Fig. 1 illustrates an example parking facility with multiple wireless chargingstations for use by electric vehicles.

[0223] FIG. 2 is a hierarchical block diagram of an example wireless power transfer systemfor wireless electric vehicle charging.

[0224] FIG. 3A shows an example parking space and a parking scenario illustrating apositional relationship between a vehicle and a wireless charging station in a ground-based coordinate system.

[0225] FIG. 3B shows an example parking space and a parking scenario illustrating apositional relationship between a wireless charging station and a vehicle in a vehicle-based coordinate system.

[0226] FIG. 4 shows a multiple parking space facility providing a plurality of wirelesscharging stations illustrating an example parking scenario with a vehicle.

[0227] FIG. 5A shows frequency allocations in a portion of low frequency radio spectrum.

[0228] FIG. 5B shows frequency allocations in another portion of low frequency radiospectrum.

[0229] FIG. 6A illustrates an example single-axis magneticfield generator comprising amulti-turn coil and a ferrite structure.

[0230] FIG. 6B illustrates another example single-axis magneticfield generator comprisinga multi-turn coil and a ferrite structure.

[0231] FIG. 6C illustrates a further example single-axis magneticfield generatorcomprising a multi-turn coil and a ferrite structure.

[0232] FIG. 6D illustrates an example double-axis magneticfield generator comprisingtwo orthogonal multi-turn coils and a ferrite structure.

[0233] FIG. 7A illustrates an example double-axis magneticfield sensor comprising twoorthogonal multi-turn coils and a ferrite structure.

[0234] FIG. 7B illustrates another example double-axis magneticfield sensor comprisingtwo orthogonal multi-turn coils and a ferrite structure.

[0235] FIG. 7C illustrates a principle of magneticfield sensing using the double-axismagnetic-field sensor of FIG.7A rotated with respect to a direction of a magneticfield.

[0236] FIG. 7D illustrates locus curves of voltages induced into the coils of the double-axismagnetic-field sensor of FIG.7A.

[0237] FIG. 8A displays a magnetic vectorfield obtained by measuring a voltage vector atdiscrete grid points over a predefined area.

[0238] FIG. 8B displays another magnetic vectorfield obtained by measuring a voltagevector at discrete grid points over the predefined area.

[0239] FIG. 8C displays a further magnetic vectorfield obtained by measuring a voltagevector at discrete grid points over the predefined area.

[0240] FIG. 9A illustrates a principle of position determination based on double-axismagneticfield generation and phase-synchronized double-axis magneticfield sensing using absolute phase synchronization.

[0241] FIG. 9B illustrates the principle of position determination based on double-axismagneticfield generation and phase-asynchronous doble-axis magneticfield sensing.

[0242] FIG. 10 illustrates an example frame structure referring to a physical layer model.

[0243] FIG. 11A illustrates a base-band elementary pulse based on a raised-cosinefunction in time domain.

[0244] FIG. 11B illustrates a sequence of base-band elementary pulses of FIG.11A in timedomain.

[0245] FIG. 11C illustrates a Wiener-Khinchin power density spectrum of a sequence ofbase-band elementary pulses of FIG.11A.

[0246] FIG. 11D illustrates an ensemble of Wiener-Khinchin power density spectra of FIG.11C spaced in frequency by twice a modulation rate.

[0247] FIG. 12A illustrates an increase in wanted receive signal level and interferencelevel as a function of a vehicle position.

[0248] FIG. 12B illustrates an increase in the wanted receive signal level and interferenceplus noise level as a function of the vehicle position.

[0249] FIG. 13 illustrates an effect of pulse shaping in an example scenario with amodulation spectrum in a lower frequency band and in a higher frequency band.

[0250] FIG. 14 illustrates an example discrete-frequency spectrum as it may be producedby a Fast Fourier Transform.

[0251] FIG. 15 illustrates an example implementation of a modulated double-axismagneticfield beacon transmission for conveying data.

[0252] FIG. 16A is a schematic diagram illustrating an example implementation of aportion of a double-axis magneticfield beacon receiver including a matchedfilter.

[0253] FIG. 16B illustrates an example sequence of complex samples as output by thematchedfilter of the receiver of FIG.16A.

[0254] FIG. 16C illustrates another example sequence of complex samples as output bythe matchedfilter of the receiver of FIG.16A.

[0255] FIG. 16D illustrates a further example sequence of complex samples as output bythe matchedfilter of the receiver of FIG.16A. DETAILED DESCRIPTION

[0256] Wireless inductive charging of electric vehicles (EV) may provide numerousbenefits such as improved convenience, safety, and reliability. It eliminates cabling that is often impedimental for pedestrians and prone for wear out, vandalism, and pollution. It can preserve urban aesthetics without compromising functionality and provide a suitable solution for autonomous parking. It may increase availability of parked vehicles for vehicle- to-grid (V2G) power transfer e.g., to stabilize the electricity grid as the demand for fluctuating renewable energy increases.

[0257] Fig. 1 illustrates an example of a parking facility 100 providing wireless chargingservices. Two wireless charging-enabled vehicles, 102a, 102b integrating WPT vehicle units 130a, 130b are each parked over a WPT ground unit, 120a, 120b. Both vehicle unit and ground unit include a WPT coil (not shown) sometimes also referred to as an induction coil configured to wirelessly transfer power based on the Faraday induction principle. In some implementations, the ground units are surface mount on thefloor. In other implementations, the ground units areflush mount with thefloor or buried in the ground (e.g., in the asphalt). The power converters 110a, 110b convert power received by WPT vehicle units 130a, 130b to a form suitable for charging the vehicle’s traction battery (not shown). In some examples and as described in Patent US 9,561,730, the power converters 140a, 140b may be integrated with power converters used for plug-in charging of the vehicle, commonly called on-board chargers (OBC.), or other on-board vehicle components. The WPT ground units 120a, 120b are shown linked to external power converters 110a, 110b, each connected to a power supply bus 118. In some implementations, the power converters 110a, 110b are configured and mounted as a “wall box”. In other implementations, the power converters or parts thereof are integrated into the WPT ground units. The power supply bus 118 is in turn connected to a central power distribution unit 114. In some implementations and operations, the central power distribution unit receivespower from a power utility 112 sometimes referred to as “power grid” and provides DC power to the bus 118, and the power converters 110a, 110b are inverters, such as the multi- level inverter described in U.S. Application Publication 2024-0136944,filed October 13, 2023, and incorporated here by reference. The power converters 110a, 110b, provide low- frequency (LF) power signals, such as the 85 kHz signals used for WPT according to the SAE J2954 standard, to the WPT ground units 120a, 120b, to turn into LF magneticfields for WPT. In other examples, the power distribution unit 114 provides the LF signals directly to each WPT ground unit, and power converters 110a, 110b are simpler or not present. In yet other examples, the power distribution unit 114 and bus 118 are not present, and the power converters 110a, 110b are each connected directly to the power utility 112 and convert AC power from the utility to LF power for wireless power transfer. The combination of a WPT ground unit (e.g., 120a), a power converter (e.g., 110a), and any other ground-side electronics (not shown) constitutes a wireless charging station (e.g., 104a) as indicated in FIG.1. In some cases, the WPT ground units 120a, 120b are also referred to as Ground Assembly Resonators (GAR) or ground assembly pads, and the wireless charging station is also referred to as a Ground Assembly (GA) or Electric Vehicle Supply Equipment (EVSE). Analogously, the WPT vehicle units 130a, 130b are sometimes referred to as Vehicle Assembly Resonators (VAR) or vehicle assembly pads and the combination of a WPT vehicle unit (e.g., 130a) and a power converter (e.g., 140a) and any other vehicle-side electronics (not shown) constitutes a Vehicle Assembly (VA) (e.g., 106a). Each of the power connections shown may be bi-directional, allowing the vehicles to discharge power from their batteries to the power utility 112 in a vehicle-to-grid (V2G), or other load in a vehicle-to-home (V2H), vehicle-to-vehicle (V2V) or similar arrangement (generally V2x).

[0258] FIG. 1 also illustrates vehicles 102a, 102b, and power distribution unit 114providing wireless communication units 146a, 146b, and 116, respectively. The wireless communication unit 116 may be configured to wirelessly communicate with the vehicles 102a and 102b e.g., based on a WiFi IEEE 802.11x standard. In SAE standard conformant wireless charging systems, this communication is used for exchanging data between the GA and VA for purposes of WPT control and safety. Further, the power distribution unit 114 provides an interface 119 configured to communicate with external entities (e.g., a charging operation center) via a communication backhaul (not shown). This backhaul may rely onradio communications (e.g., via communication unit 116), power line communications (e.g., via power utility 112), or any other line communications includingfiber optical. In the example parking facility 100, wireless communication unit 116 is configured to serve multiple vehicles. In other parking facilities, each of the wireless charging stations 104a, 104b provide a wireless communication unit (not shown) configured to communicate with the respective vehicles 102a, 102b.

[0259] Beside the WPT coil, the WPT ground units 120a, 120b or the WPT vehicle units130a, 130b, or both may include various sensors and detection systems (not shown). For example, they may include systems for detecting a positional relationship between the vehicle unit and the ground unit. The positional relationship is needed to guide the vehicle to the charging spot, to mutually align the vehicle-side and groundside WPT coils within the specified tolerance, and for pairing of a vehicle with a wireless charging station as needed toestablish communication between the right entities in multiple vehicle multiple chargingstation scenarios. The ground unit may also include sensors and detection systems todetermine presence of a foreign object that has the potential to heat up by inductionheating or any hazardous events caused by an incandescent object on the surface of the ground unit. Further, it may include sensors and a detection system for determining presence of a living object e.g., a hand of a person or animals approaching a critical space beneath the vehicle where electromagneticfield exposure exceeds certain limits (e.g., based on IEEE or ICNIRP guidelines). Moreover, the ground unit may include sensors and a detection system for determining a presence of the vehicle or a type of the vehicle. In some implementations, sensors and detection systems or parts thereof may be external to the ground unit or vehicle unit.

[0260] FIG. 2 is a hierarchical block diagram of an example WPT system 200 for wirelesselectric vehicle charging. At the top hierarchy level, the system 200 comprises a GA 204 and a VA 206 that may refer to the wireless charging station 104a and the VA 106a, respectively, of FIG.1. The next lower level shows the GA 204 composed of a GA power conversion & control unit 210 and a WPT ground unit 220 (e.g., 120a of FIG.1) and various connectionsbetween these blocks. Splitting the GA into two blocks implies implementations where theGA power conversion & control unit and the ground unit are physically separated (as illustrated in FIG.1) and interconnected via a several meters long multiwire cable hereinreferred to as GA feeder cable (not shown). However, it should not exclude implementations where the GA power conversion & control unit is entirely or partially integrated in the ground unit forming one physical unit with a common housing (not shown).

[0261] At the third level, the GA power conversion & control unit includes a GA powerconverter 212 (e.g., 110a of FIG.1), a GA controller 214, and a GA wireless communication unit 216 (e.g., 132a of FIG.1). The ground unit 220 integrates a GA WPT coil 222 as well as various functions as needed for Foreign Object Detection (FOD), Living Object Detection (LOD), Vehicle Detection (VD), and Position Detection (PD) as previously discussed with reference to FIG.1. In the example of FIG.2, these functions are provided by a FOD unit 224, a LOD unit 226, and a GA PD unit 228, each configured and connected to the GA controller for exchanging data and control. In some implementations such as described in Patent US 11,914,094 and incorporated here by reference, these functions share or partially share onecommon hardware platform referred to as a multi-purpose detection system.

[0262] In an implementation conforming with the SAE standard, the GA wirelesscommunication unit 216 is a WiFi Access Point providing an air interface to a Wireless Local Area Network (WLAN) of a parking facility. Certain parking facilities (e.g., parking facility 100 of FIG.1) provide a central WiFi access point associated to multiple GAs. In such implementations, the GA wireless communication unit 216 is external to the GA 204. In another implementation, the GA wireless communication unit is integral part of the ground unit 220.

[0263] The GA WPT coil 222 may include a tuning & impedance matching network (notshown) forming a resonant circuit and the ground-unit is referred to as the GAR as previously mentioned. In other implementations, the tuning & impedance matching network or parts thereof are included in the GA power converter 212. Further, the GA controller 214 interfaces to the GA power converter 212 and the GA wireless communication unit 216 for data exchange and system control. It also provides a data interface 219 (e.g., Ethernet) tocommunicate with a system external entity e.g., via a backbone network as mentioned withreference to FIG.1. Moreover, the GA power converter 212 disposes a power interface 218 for feeding or receiving AC or DC power as discussed with reference to FIG.1.

[0264] At the second level, FIG.2 shows the VA 206 composed of a WPT vehicle unit 230(e.g., 106a of FIG.1) connected to a VA power conversion & control unit 240. At a third level, the VA power conversion & control unit 240 comprises a VA power converter 242 (e.g., 108a of FIG.1), a VA controller 244, and a VA wireless communication unit 246 (e.g., 132a of FIG. 1). The vehicle unit 230 comprises a VA WPT coil 232 and a VA PD unit 238, the vehicle-side counterpart of the GA PD unit 228 interfacing with the VA controller for data exchange and control. Splitting the VA into two blocks implies implementations where the VA power conversion & control unit and the vehicle unit are physically separated (as illustrated in FIG. 1) and interconnected via a multiwire cable herein referred to as VA feeder cable (not shown). However, this should not exclude implementations where the VA power conversion & control unit 240 is entirely or partially integrated in the vehicle unit 230 forming one physical unit with a common housing (not shown).

[0265] In a standard-conforming implementation, the VA wireless communication unit246 is a WiFi Client. As with the GA wireless communication unit, the VA wireless communication unit may be external to the VA 206, e.g., mounted anywhere on the vehicle or parts or it may be partially or fully integrated into the vehicle unit.

[0266] In some implementations, the VA WPT coil 232 includes a tuning & impedancematching network (not shown) forming a resonant circuit and the vehicle unit is referred to as the VAR as previously mentioned. Further, the VA controller interfaces to the VA power converter and the VA wireless communication unit for data exchange and control. It also provides a line communication interface 249, e.g., a CAN bus interface to communicate with an external vehicle onboard entity. Moreover, the VA power converter disposes a power interface 248 for feeding or receiving DC power as previously discussed with reference to FIG.1.

[0267] FIG. 3A shows an example parking space and a parking scenario 300A illustrating apositional relationship between a vehicle unit 330 (e.g., 106a of FIG.1 or 230 of FIG.2) and a ground unit 320 (e.g., 104a of FIG.1 or 220 of FIG.2) as it may be needed for guidance, alignment, and pairing. FIG.3A represents this positional relationship in a ground-based coordinate system defined by perpendicular x- y-, and z-axes and having its origin O in the ground unit 320. The x- and y-axes (also referred to as the horizontal axes) span a parallelplane to a parking space defined by road markings 308. The z-axis (vertical axis) points towards the zenith assuming a right-hand oriented coordinate system. The x-axis is aligned in parallel to a longitudinal axis of the parking space pointing towards the rear of the parking space.

[0268] The vehicle unit 330 mounted on a vehicle 302 may also be associated with avehicle-based coordinate system defined by perpendicular x'-, y'-, and z’-axes and having its origin O’ in the vehicle unit. The x’- and y’-axes span a plane substantially parallel to the parking space, depending on a tilt of the vehicle-unit relative to thefloor, while the z’-axis essentially points towards the zenith assuming a right-hand oriented coordinate system. The x’-axis is assumed aligned with a longitudinal axis of the vehicle pointing in driving direction.

[0269] The origins O and O’ may correspond to a magnetic center point of the groundunit and the vehicle unit, respectively, as explained in U.S. Patent 11,394,253 incorporated here by reference. In some implementations, the vertical coordinate (e.g., z or z’) is omitted in a positional relationship as needed for purposes of guidance and alignment. However, it may be used in a process of determining a positional relationship e.g., if a z-height of the vehicle unit 330 matters.

[0270] In a ground-based coordinate system omitting z, the positional relationshipbetween the vehicle unit 330 and the ground unit 320 may be defined by the position of the origin O’ also denoted P and an angle of rotation φ measured from the dashed line parallel to the x-axis as indicated in FIG.3A. Using Cartesian coordinates, the position P may be represented by a vector r = (xp, yp). In a polar representation, P may be defined by a distance d = square root of (xp2+ yp2) and an angle α = arctan (yp / xp) measured from the x-axis. The angle φ is herein also referred to as the vehicle rotation relative to the parking space. The position P and angle φ are herein also referred to as the pose of the vehicle unit or simply, the pose of the vehicle.

[0271] FIG. 3B shows an example parking space and a parking scenario 300B illustratingthe same positional relationship between a ground unit 320 (e.g., 104a of FIG.1) and a vehicle unit 330 (e.g., 106a of FIG.1) represented in a vehicle-based coordinate systemdefined by perpendicular x’- y’-, and z’-axes and having its origin O’ as described above with reference to FIG.3A.

[0272] The ground unit 320 is associated with the ground-based coordinate systemdefined by perpendicular x-, y-, and z-axes and having its origin O in the ground unit and aligned with road markings 308 as described above with reference to FIG.3A. In the vehicle- based coordinate system omitting z’, the positional relationship between the ground unit 320 and the vehicle unit 330 may be defined by the position of the origin O also denoted P’ and an angle of rotation φ’ measured from the dashed line parallel to the x’-axis as indicated in FIG.3B. Using Cartesian coordinates, the position P’ may be represented by a vector r’ = (xp’, yp’). In a polar representation, P’ may be defined by a distance d’ = square root of (xp‘2+ yp‘2) and an angle α’ = arctan (yp’ / xp’) measured from the x-axis. The angle φ’ is herein also referred to as the rotation of the ground unit relative to the vehicle. While the distances d’ and d are identical, the angles α’ and α generally differ. The position P’ and angle φ’ are herein also referred to as the pose of the ground-unit or simply, the pose of the parking space.

[0273] In some implementations of a guidance and alignment system, e.g., using agraphical user interface (GUI) abord the vehicle, the pose of the vehicle unit is represented in a ground-based coordinate system. In other implementations, the pose of the ground unit is displayed in a vehicle-based coordinate system. Various implementations of the vehicle onboard GUI are disclosed in Patent US 10,343,535 incorporated herein as reference. In an example implementation of a guidance and alignment system, the pose of the vehicle unit 330 is determined in a ground-based coordinate system and then mathematically transformed into the pose of the ground-unit 320 as described in Patent US 10,343,537 incorporated herein as reference.

[0274] FIG. 4 shows a parking facility 400 illustrating an example multiple parking spacescenario with multiple vehicles 402a, 402b, 402c. Parking spaces are outlined by road markings 408. Parking spaces are equipped with wireless charging stations (GAs) referring to GAs 404a, 404b, 404c, 404d, 404e. The plurality of GAs is sometimes also referred to as ground infrastructure. The GAs include respective WPT ground units 420a, 420b, 420c, 420d, 420e suitably positioned in the parking spaces and connected to respective GA powerconversion & control units 410a, 410b, 410c, 410d, 410e implemented in some examples as “wall boxes” as described with reference to FIG.2. Further, each ground unit integrates a GA PD unit (e.g., GA PD unit 228 of FIG.2, not shown) configured to interact with a vehicle-side counterpart for determining a positional relationship. Moreover, the GAs provide a respective GA wireless communication unit 416a, 416b, 416c, 416d, 416e configured to communicate with vehicles (e.g., 402a, 402b, 402c). FIG.4 also shows a central GA wireless communication unit 416 (e.g., 116 of FIG.1) as part of the ground infrastructure connected to each of the GAs (connections not shown). In some implementations, the central communication unit is configured as a communication node of a backbone network (not shown). In other implementations, it is configured to communicate with vehicles (e.g., 402a, 402b, 402c).

[0275] Further, FIG. 4 indicates that the vehicles 402a, 402b, 402c are equipped with VAs406a, 406b, 406c. The VAs include respective WPT vehicle units 430a, 430b, 430c suitably mounted on the vehicles and connected to respective VA power conversion & control units (e.g., 240 of FIG.2, not shown) as described with reference to FIG.2. Further, each vehicle unit integrates a VA PD unit (e.g., VA PD unit 238 of FIG.2, not shown) configured to interact with the ground-side counterpart for determining the positional relationship. Moreover, the VAs provide a respective VA wireless communication unit 446a, 446b, 446c configured to communicate with any of the GA wireless communication units (e.g., 416a, 416b, 416c, 416d, 416e).

[0276] In another aspect, FIG. 4 displays the vehicles 402a and 402b heading towards theground unit 420b and 420d, respectively, and vehicle 402c parked over the ground unit 420e e.g., for charging. From the perspective of the vehicle 402a, the ground unit 420b is herein also referred to as the target ground unit and the GA 404b as the target GA. From the perspective of the ground unit 420b, the vehicle 402a is also referred to as the vehicle attempting for being charged from. Likewise, the GA 404d and its ground unit 420d are referred to as the target GA and the target ground unit, respectively, of the vehicle 402b, which in turn may also be referred to as the vehicle attempting for being charged from GA 404d.

[0277] As mentioned with reference to FIG. 1, standard-compliant WPT for electricvehicles requires wireless communications between a target GA (e.g., GA 404b) and a vehicle (e.g., 402a). In a multiple parking space multiple vehicle scenario such as illustrated in FIG.4 by example, it is necessary to assure that the VA (e.g., 406a) is actually communicating with the target GA (e.g., 404b), and not another neighboring GA (e.g., 404d). The VA may establish wireless network communications with a GA of an adjacent parking space, falsely determining that it has established communication with its target GA. When the VA requests power and does not receive it (because it is in communication with the wrong GA), the VA may not detect the source of the problem. Likewise, the GA of the adjacent parking space may detect a fault because it is attempting to provide power and recognizing no load. This problem may be referred to as “cross-connect.” In addition to the primary function of providing power to a vehicle being impossible in a cross-connect situation, additional functions such as PD for guidance and alignment, FOD, and LOD may not operate properly, if at all, when wireless communications are not established between the VA and its target GA.

[0278] As previously mentioned, guidance, alignment, and pairing in the examplemultiple parking space scenario illustrated in FIG.4 requires the VA (e.g., VA 406a) to disambiguate between the target GA (e.g., GA 404b) and neighboring GAs (e.g., 404a, 404c, 404d, 404e). Pairing for wireless communications (e.g., via WiFi) additionally requires the VA to disambiguate between the GA wireless communication unit (e.g., 446b) associated to the target GA and the GA wireless communication units associated to neighboring GAs. Alternatively, it requires the GA (e.g., 104b) to disambiguate the vehicle (e.g., 402a), attempting for being charged from other vehicles (e.g., 402a, 402c) as well as the associated VA wireless communication unit (e.g., 446a) from the VA communication units associated to other vehicles.

[0279] Moreover, guidance and alignment may require PD to periodically determine apositional relationship between the vehicle unit (e.g., 430a) and the ground unit (e.g., 420b) in a suitable coordinate system, at a suitable update rate as mentioned in U.S. Patent 10,411,524, and over a suitable distance range. In some implementations, guidance starts at a distance of 5 m and positions are determined at a rate of 10 per second. At a distance of 1 m, the update rate may be increased e.g., to 20 per second for alignment.

[0280] Various approaches to PD using different means such as quasi-static magnetic nearfields (MF), optical, quasi-optical, ultra-wideband (UWB) based on electromagnetic or ultrasonic waves are discussed e.g., in Patents US 10,343,535 and US 10,139,238. While optical, quasi-optical, and ultra-wideband techniques may be impaired by dielectric materials such as water, snow, ice, and dirt, quasi-static magnetic nearfields have almost no interaction with these materials. Therefore, the use of quasi-static magnetic nearfields can provide a robust and reliable PD solution for indoor and outdoor parking spaces, also suitable for integration inflush-mount or buried ground units. Moreover, using quasi-static magnetic nearfields is advantageous as thefield strength decays with the third power of distance, thus providing a pronounced distance effect. This is a prerequisite for accurate ranging and disambiguation between the target GA (e.g., 404b) and neighboring GAs (e.g., 404a, 404c, 404d, 404e). This feature also helps to reduce potential interference emanating from the neighboring GAs concurrently generating magneticfields. In a distance range limited by the parking space boundaries, magneticfields (MF) alternating with a low frequency (e.g., < 1 MHz) may be considered as quasi-static magnetic nearfields.

[0281] Methods of pairing using magnetic nearfields are disclosed e.g., in Patent US9,505,314. The underlying principle of pairing is based on comparing (e.g., determining a correlation) between information conveyed by the MF and information transmitted via the wireless communication link (e.g., WiFi). This principle requires the MF being modulated in some form. In some implementations, the MF conveys an identifier (ID) that unambiguously relates to an ID transmitted over the wireless communication link (e.g., via communication units 216 and 246 of FIG.2). A low frequency (LF) magneticfield used for PD and signaling of information are herein also referred to as a beacon MF.

[0282] In some implementations, such as disclosed in Patent US 10,343,535, one or morebeacon MFs are generated by the ground-unit, while beacon MF sensing and signal processing is performed in the vehicle unit. Applied to the system of FIG.2, the GA PD unit 228 and the VA PD unit 238 are configured as a beacon transmitter and a beacon receiver, respectively. This configuration enables PD directly on the vehicle not requiring position data to be communicated to the vehicle as opposed to a reversely transmitting system with the transmitter on the vehicle and the receiver on ground. In a reverse transmittingimplementation with the VA PD unit being the beacon transmitter, the position data has tobe communicated from the GA to the VA via the wireless communication link. In implementations relying on WiFi, it may occur that a WiFi connection cannot be established in due time, e.g., before the vehicle has approached a distance (e.g., 5 m) where PD is needed for guidance. Moreover, when WiFi frequency channels are highly congested, a WiFi link may be prone to latency and jitter compromising guidance and alignment.

[0283] In one aspect, determining a positional relationship including an x,y-position andangle of rotation φ of the vehicle (e.g., in the ground-based coordinate system of FIG. 3A)may require multiple MF generators and multiple MF sensors. In some implementations, one or more generators are integrated at a different position in the ground unit or are configured to generate a magnetic moment in a different orthogonal axis direction (e.g., in an x- and y- axis direction with reference to FIG.3A). The same may apply to the MF sensors. In some implementations, one or more sensors are configured to sense the MF in a different orthogonal axis direction (e.g., in an x’-, y’-direction with reference to FIG.3A).

[0284] FIGs.5A and 5B show radio spectrum portions 500A and 500 B ranging from 9 kHzto 90 kHz and 90 kHz to 158 kHz, respectively, as indicated by vertical scales. Morespecifically, FIGs. 5A and 5B show a frequency allocation in a left column and correspondinggeneral radio applications in a center column both referring to the geographic region 1 as defined by the International Radio Telecommunications Union (ITU-R). Region 1 comprises Europe, Africa, Middle East, and Northern parts of Asia. Except for frequencies > 148.5 kHz, the allocations in Region 2 (North & South America) and Region 3 (Southern parts of Asia and Australia) look similar, therefore not shown herein. The right column shows spectrum users that are considered relevant regarding coexistence with LF MF-based PD in Region 1 but not exclusively.

[0285] The left column of FIGs.5A and 5B contains incumbent radio services that havebeen allocated on a primary and secondary basis by the ITU. The center column includes applications of the respective services as well as so-called “underlay applications” of unallocated spectrum users referring to the European Table of Frequency Allocations and Applications (ECA Table). These underlay applications are able to share the frequency bands with the applications of the allocated radio services in such a way they are not causing interference nor request protection against interference. In the radio spectrum portions500A and 500 B, the ECA table includes only two underlay applications referred to as “active medical implants” and “inductive applications”, though medical implants operating in this frequency range are also inductive applications. The columns of FIGs.5A and 5B are subdivided into frequency bands as the combination of allocations, applications, or users in adjacent bands differ.

[0286] A category of inductive applications are Short Range Devices (SRD) as defined e.g.,by the ITU-R for license exempt operation in the designated bands. In Europe, SRD can be operated under constraints as specified by the European Norm EN 300330. In the U.S., SRD are referred to as “unlicensed radio frequency devices” and are regulated by the FederalCommunications Commission (FCC) in FCC Part 15. SRD include applications for radiocommunications, radio identification of objects, and radio determination of position, velocity, and other characteristics of an object. Examples of inductive SRD applications are Radio Frequency Identification (RFID), Electronic Article Surveyance (EAS), Radio telemetry, Near Field Communications (NFC), automotive Passive Keyless Entry (PKE), vehicle immobilizers, avalanche victim detectors, balise systems for railways, and active implantable medical devices.

[0287] It may be appreciated that LF MF beaconing for PD conveying ID data (e.g., forpairing) meets the definition of an inductive SRD for radio determination and identification applications as regulated by the EN 300330 and FCC Part 15. For LF inductive applications, the EN 300330 is more restrictive than its FCC counterpart since it specifies tight emission limits for frequencies above 148.5 kHz. This is due to the adjacent longwave broadcast band specific to ITU-R Region 1. Broadcast to domestic listeners and car radios generally requires better protection from interference caused by underlay applications as compared to the services operating below 148.5 kHz mainly governed by Land & Maritime Military (L&MM) applications. The EN 300330 emission mask, the nearfield and range requirements as previously discussed with reference to FIG.4 may restrict LF MF beaconing to frequencies < 148.5 kHz.

[0288] Further, the third column of FIG. 5A includes WPT for EV charging as a spectrumuser being relevant for LF MF-based PD. WPT is also an inductive application but regulated by FCC Part 18 and CISPR 11 standards (CISPR: International Special Committee on RadioInterference). WPT operating frequency bands as presently standardized are 79 – 90 kHz for light-duty vehicles, 19 – 25 kHz, 36 – 40 kHz, and 55 – 65 kHz for heavy-duty vehicles. Though concurrent PD and WPT operation on the same vehicle may be excluded, an LF MF- based PD system must be capable of operating in presence of MF emissions emanating from active WPT installed on adjacent parking spaces. In certain scenarios e.g., as illustrated in FIG.4 by vehicle 402a, the aggregated WPT signals as received by the beacon receiver of VA PD unit (e.g., 238 of FIG.2) may exceed the level of the beacon MF by 50 dB or more. To handle such input signal dynamics in an economically designed beacon receiver, a spacing between any of the WPT frequencies and the beacon frequency of >20% may be required (e.g., >18 kHz for 90 kHz WPT).

[0289] Moreover, the third column of FIG.5A includes frequencies of the Standardfrequency & Time (SF&T) and the European Radio Ripple Control (EFR) services. The SF&T service provides synchronization to an installed base of millions of radio-controlled clocks (RCC). In Central Europe, RCCs receive the SF&T signal at 77.5 kHz broadcast by a high-power longwave transmitter station located in Mainflingen, Germany. RCC receivers are typically low-cost consumer devices providing limited off-frequency (blocking) immunity. The EFR service remotely controls electricity meters (e.g., tariff control) and street lighting in certain areas of Central and Eastern Europe. The frequency shift keyed (FSK) EFR signals with a spectral bandwidth of approximately 500 Hz are also transmitted from high power longwave stations at locations and on frequencies as indicated in FIG.5B. A majority of both RCC and EFR receivers are installed in public and domestic zones. Many of them may potentially be collocated with a WPT system integrating a beacon transmitter within a radius of less than 10 m. The EN 300330 specifies somewhat lower emission limits in narrow slots around carrier frequencies of these services. Conversely, there exist areas surrounding any of this high-power longwave transmitter stations where the LF beacon receiver may have to cope with a strong SF&T or EFR signal at the receiver’s input in addition to the WPT signals as discussed above. To achieve interference-free coexistence, some spacing (e.g., 5% or 6.5 kHz at 129.1 kHz) between any of the SF&T or EFR frequencies and the beacon frequency may be required.

[0290] Concerning the U.S., FCC part 15 lists a range 90 to 110 kHz as a restricted band ofoperation. However, Part 15 neither mentions any reason nor defines emission limits specificfor this band. According to FIG.5B, this band is allocated to Fixed and Radio Navigation services. In the U.S., it was used by the LORAN C navigation system for maritime and aeronautical purposes until its operation was terminated in 2010 for economical, strategic, and technical reasons. However, the band remained restricted likely due to its historical use or other non-disclosed governmental applications.

[0291] Further, FIG. 5B shows a narrow band between 135.7 and 137.8 kHz allocated tothe Amateur Radio Service. This band also known as the “2200 m band” is permitted to be used by Radio Amateurs on a secondary basis in all ITU-R regions under the constraint of a maximum effective isotropic radiated power (EIRP) of 1 W. Amateurs use very slow telegraphy modes and long wire (e.g., Beverage) antennas providing directivity enabling transatlantic radio communication mainly for experimentation and exploration purposes. Alternatively, Amateurs use high power (e.g., 200 W) feed into an “electrically short” antenna (short compared to the wavelength) providing low radiation efficiency butgenerating high reactive electromagnetic nearfields in the surrounding. Therefore, co-frequency sharing with LF MF-based PD in collocation scenarios may result in interference in both directions. The relatively high noise levels in urban areas and space requirements for the antenna however restrict the use of this band to stations located in rural areas. Due to these restrictions, the activity in this band is comparatively low and so the likelihood of collocation. Nevertheless, use of this band for LF MF-based PD may not be recommended if friendly coexistence is aimed.

[0292] Access control systems such as Passive Keyless Entry (PKE) are another underlayapplication sharing frequencies in the LF radio spectrum 500A and 500B. Automotive PKE systems are potentially closely collocated with wireless EV charging and thus with LF MF- based PD. PKE enabled vehicles periodically send an LF wake-up signal to an electronic car key (key fob) when approaching the vehicle’s PKE transmitter. Upon receipt of the wake-up signal, ID and security data is exchanged between the car key and the vehicle on an Ultra High Frequency (UHF) channel. For LF wake-up signaling, PKE systems typically use 20 kHz, 125 kHz, or 134 kHz as carrier frequency as indicated in the right column of FIGs.5A and 5B. PKE key fobs are commonly low-cost consumer devices providing limited off-frequency (blocking) immunity. Depending on the signal-to-interference ratio (SIR) and the frequency offset, interference from LF MF beaconing for PD may reduce the wake-up radius and thusthe PKE user experience. A critical scenario can be found illustrated in FIG.4 by parked vehicle 402c and the ground unit 420d installed on an adjacent parking space. The distance between ground unit and key fob (not shown) may be as short as 1.5 m when the key fob is at the normal wake-up distance (e.g., 1 m) from the front door handle of parked vehicle402c integrating a PKE LF transmitter. The interference potential may be substantiallyreduced if a frequency spacing of 10 kHz between LF MF beaconing and PKE is maintained.

[0293] Longwave (LW) sound broadcast is a further radio service to be considered. Thisservice is allocated on a primary basis in the ITU-R Region 1 as shown in the left column of FIG.5B. Over the last three decades, LW sound broadcast has been more and more ousted to niche applications. Nevertheless, it still holds some relevance, especially for transmitting certain programs in remote areas, less developed geographic regions, or countries that have censored Internet access due to political reasons. Listeners are mostly residential or automobile, thus may potentially be collocated with wireless EV charging. Therefore, FIG.5B lists Romanian state-owned Radio Antena Satelor transmitting at 153 kHz as a relevant spectrum user. During dark hours, the sky wave signal of this radio station located in Bra^ov, Romania can reach as far as Western Europe on a regular basis.

[0294] To protect LW sound broadcast reception, the EN 300330 defines relatively lowlimits for wanted emissions above 148.5 kHz. Moreover, standard EMC test procedures specify use of a 9 kHz bandwidthfilter (CISPRfilter) for frequencies at and above 150 kHz. Thisfilter intends to mimic the selectivity curve of a typical consumer AM broadcast receiver but provides little suppression of emissions just below 148.5 kHz. Therefore, LF MF beaconing at frequencies above 145 kHz for purposes of guidance up to a range e.g., 5 m (also referred herein to as “long range”) may be difficult to achieve under constraints given by the EN 300330.

[0295] Taking all of above restrictions and considerations into account, only a small pieceof spectrum may be available for LF MF beaconing with a transmit level sufficient for guidance. However, for alignment at ranges e.g., < 1 m (also referred to as “short range”) requiring substantially lower transmit levels, there may exist more options to accommodate LF MF beaconing. The present SAE J2954 / 1 standard defines MF beacon signals essentially occupying afirst range from 110 to 119 kHz for long-range guidance and a second rangefrom 140 to 148 kHz for short-range alignment as indicted in FIG.5B by respective bands 510 and 520 herein also referred to as long-range band and short-range band.

[0296] FIGs.6A to 6C illustrate example single-axis MF generators 600A, 600B, 600C,respectively, each comprising a multi-turn coil 606 wound around a ferrite structure 604 suitably disposed on an electrically conductive (e.g., Aluminum) back plate 602. In some implementations, the ferrite structure 604 and the backplate 602 are shared with the GA WPT coil and form an integral part of the ground unit (e.g., 420b of FIG.4). The single-axisMF generators are oriented and configured to generate an alternating magnetic moment in arespective x-, y-, z-axis direction, if driven by a respective alternating current as indicated inFIGs.6A to 6C as Ix, Iy, Iz. The x-, y-, z-axis may refer to the axis of the ground-based coordinate system of FIG.3A. The MFs as generated by the single-axis generators 600A, 600B, 600C may also refer herein as to an x-MF, y-MF, z-MF, respectively. For a sinusoidal excitation at angular frequency ω, the currents may be defined as functions of time twith Iˆx , Iˆy, Iˆz denoting the peak amplitudes of the respective current.

[0297] FIG. 6D illustrates an example double-axis MF generator 600D comprisingorthogonally arranged multi-turn coils 606a, 606b, each wound around the ferrite structure 604. The double-axis MF generator is oriented and configured to generate an alternating magnetic moment in the x- and y-axis direction if driven by currents Ix, Iy.

[0298] To sense the x- and y-MF separately, some implementations use a frequencydivision multiplexing (FDM) scheme generating the x- and y-MF concurrently but at differentfrequencies (e.g., ωx, ωy). Other implementations use a time division multiplexing (TDM) scheme generating the x- and y-MF in different time slots (e.g., tx, ty) but at the same frequency ω. In yet other implementations, a code division multiplexing (CDM) scheme is applied for generating the x- and y-MF e.g., using different spreading codes cx, cy. Thevarious multiplexing schemes for MF beaconing are also disclosed and discussed in Patent US 11,394,253.

[0299] FIG. 7A illustrates an example double-axis MF sensor 700A comprised oforthogonally arranged multi-turn coils 706a, 706b, each wound around a ferrite structure 704. The ferrite structure is suitably disposed on an electrically conductive (e.g., Aluminum) back plate 702. In some implementations, the ferrite structure 704 and the backplate 702 are shared with a VA WPT coil (not shown) and form an integral part of the vehicle unit (e.g., 430a of FIG.4). The double-axis MF sensor is oriented and configured to sense the alternating MF in an x’-, y’-axis direction by measuring induced voltages Vx’, Vy’at respective coil terminals as indicated in FIG.7A. The x’-, y’-axis as indicated in FIG.7A may correspond with the axis of the vehicle-based coordinate system of FIG.3B. (Note that FIG.7A is a bottom view explaining the x’-axis reversal.) In case of double-axis sensing of MFs as transmitted by a double-axis MF generator (e.g., 600D of FIG.6D), the voltages induced into the x’- and y’-coils by the x-and y-MF are referred to as Vxx’, Vxy’, Vyx’, Vyy’, respectively.

[0300] FIG. 7B illustrates another example implementation of a double-axis MF sensor700B comprised of orthogonally arranged multi-turn coils 707a, 707b. The sensor 700B differs from the sensor 700A in that each of the coils 707a, 707b are wound across the diagonal of the ferrite structure 704. The sensor 700B is oriented and configured to sense the MF in a u’-, v’-axis direction by measuring induced voltages Uu’, Uv’ at respective coil terminals as indicated in FIG.7B. The u’-, v’-axis form a coordinate system rotated by 45° with respect to a vehicle-based coordinate system as defined in of FIG.3B having the same origin O’. (Note that FIG.7B is a bottom view turning the sense of the u’- and x’-axis.) Defining vectors V = [Vx’, Vy’]Tand U = [Uu’, Uv’]Twith reference to sensors 700A and 700B, respectively, and assuming a homogenous MF, it may be shown that the implementations 700A and 700B are equivalent and related by a linear coordinate transformation as follows:where R(π / 4) denotes the π / 4- (45°)-rotation matrix defined as

[0301] Alternative implementations of multiple-axis MF generators and sensors e.g.,based on sets of co-planar coils are disclosed and discussed in Patent US 9,739,844. More practical implementation, integration, and fabrication aspects of multiple-axis MF generators and sensors (e.g., generator 600D of FIG.6D, sensor 700 of FIG.7) are disclosed and discussed in Patent EP3298615.

[0302] FIG. 7C illustrates a principle of MF sensing using the double-axis MF sensor 700A.It shows the sensor 700A in presence of an alternating MF represented by a snapshot of a magneticflux density vector B(t) at an instant. The vector oscillates from one direction as shown by B(t) to the opposite direction with a peak magnitude Bˆ. FIG.7C also indicates voltages Vx’(t), Vy’(t) as induced into the respective x’-, y’-coils 706a, 706b. The sensor 700A is shown aligned to an associated vehicle-based coordinate system as defined in FIG.3Bwhose x’-axis forms an angle θ with the MF vector B(t). Analytically, B(t) of a MF sinusoidallyvarying at an angular frequency ω may be expressed in terms of an x’- and y’-component as functions of time tTheflux density vector B(t) is related by some function to the drive current of the MF generator (e.g., 600A of FIG.6A) e.g.,This function depends on the position of the sensor relative to the generator. Assuming asubstantially homogenous MF in the area of the sensor and applying Faraday’s induction law to Equations (6) and (7), the voltages induced into the x’-, y’-coils having transducer factors kx’, kymay be expressed as functions of timeEquation (10) includes a phase angle δ referred to as phase imbalance that may occur in a practical implementation e.g., due to parasitic capacitances. In LF implementation of the sensor 700A the phase imbalance δ may be negligibly small. Neglecting δ, above equations show both induced voltages shifted in phase by 90° relative to B(t) as they relate to thefirst derivative of B(t). Based on Equations (9), (10), the peak amplitudes of the induced voltage signals may be expressed asThe factorsare herein referred to as transducer factors of the sensor. A sensor 700A satisfyingis herein referred to as an isotropic sensor and Equation (13) as the isotropy condition. In some implementations, the sensor (e.g., 600A) itself may be anisotropic and isotropy is achieved by a correction in the voltage measurement based on a calibration of the sensor in a homogenous MF.

[0303] FIG. 7D illustrates the induced voltage vector V(t) (shown as a snapshot at aninstant) moving (circulating) along an elliptical locus curve 722 in a 2D voltage vector space(voltage vector plane) 700D having axis vx’, vy’. FIG.7D also displays the sinusoidal waveforms 720a, 720b of Vx’(t), Vy’(t) describing the locus curve 722 (also referred to as Lissajousfigure) if projected onto the respective vx’-, vy’-axis. The locus curve is shown with a small ellipticity as it may result from a tiny phase imbalance δ as previously discussed and also indicated in FIG.7D for the waveform 720b. With a perfectly phase balanced sensor 600A, the locus curve 722 would degenerate to a straight line (zero ellipticity). The long axis of the ellipse ranges from V^y’, V^x’to an antipodal point -V^y’, -V^x’forming an angle θ’ with the vx’-axis. As evident from Equations (11) and (12), the angle θ’ obtained from an isotropic sensor equals θ, thus being indicative of the orientation of the sensor’s x’-axis with respect to the MF vector B(t).

[0304] In general, a vector is defined by a magnitude and a direction with respect to acoordinate system. The direction in turn may be subdivided into an orientation and a sense (polarity). Using this concept, the vector V(t) as obtained from a phase balanced sensor (e.g., 600A of FIG.6A) may be described as an oscillating magnitude peaking at V^ = [V^ x’2 + V^ y’2]1 / 2, (14)with a constant orientation and a polarity that isflipping after every half period. Therefore, disregarding time, the direction of V(t) is ambiguous, meaning that there are two potentialsolutions for the sensor’s direction relative to the MF, namely θ and θ + 180°. Navigating in aMF may however require magnitude, orientation, and sense to be consistently determined at any point in a predetermined space similarly to using a compass in the earth’s static MF. While the peak magnitude V^ and the orientation of V(t) may be obtained, determining its sense may be more challenging. More specifically, it may require measuring V(t) at specific times in synchronism e.g., with the drive current I(t) as defined in Equation (8). In an example implementation, the polarity of the vector V(t) is determined in time intervals or portions thereof where thefirst derivative dI(t) / dt is positive. This may require either highly stable time bases (e.g., atomic clocks) at both generator and sensor-side (e.g., in GA PD unit 228 and VA PD unit 238) or a supplementary wireless synchronization link configured to synchronize the measurement of V(t) with respect to the phase of I(t). The ambiguity problem inherent to navigation in alternating MFs and how to deal with is also subject of Patents US 11,394,253 and US 10,343,537. US 11,394,253 also concludes that a supplementary phase synchronization may require out-of-band transmission. Conversely stated, phase synchronization to reliably resolve polarity ambiguity in low SNR conditions may not be feasible by narrowband signaling under bandwidth constraints given, e.g., by band 510 of FIG.5B.

[0305] FIG. 8A displays a vectorfield 800A obtained by measuring a 2D voltage vector Vxat discrete grid points spaced by 20 cm over an area ranging from x = -500 to 0 cm and y = - 150 to 150 cm referring to a ground-based coordinate system as defined in FIG.3A and as indicated in FIG.8A by an x-, y-axis. The components of Vx denoted by Vxx’, Vxy’ refer to the voltages induced into the x’-, y’-coils of an isotropic double-axis MF sensor (e.g., 700A of FIG.7A) by a sinusoidally alternating MF. The MF is generated by an x-MF generator 820A(e.g., 600A of FIG.6A) producing a magnetic moment in the x-axis direction when driven by a current ix(t) as indicated in FIG.8A and defined e.g., by Equation (1) at a frequency e.g., in the long-range band 510 of FIG.5B. The generator is suitably disposed in a parking space outlined by road markings 808 with its magnetic center in the origin O of the ground-based coordinate system. More specifically, the voltages are measured with the MF sensor mounted on a caster-wheel trolley and with the x’-axis maintained aligned with the x-axis defined as zero rotation (φ = 0). Moreover, voltages are measured in time-synchronism with the drive current ix(t) as discussed with reference to FIG.7D. The components Vxx’, Vxy’may refer to a peak or root mean square (RMS) value including a polarity (signed value). It may be appreciated that vectors Vxmay be indicative of 2D (horizontal) MF vectors Bxin terms of magnitude and direction at least in those regions where the MF is substantially homogenous over the area of the sensor. Due to the 3rdpower law decay of magnetic nearfields, the vector magnitude may vary by several orders of magnitudes if the sensor is moved e.g., over the x-range as defined above. To ease visualization of the vectorfield 800A, the magnitudes of the displayed Vx are specially scaled as described below with reference to FIGs.8B, 8C. The void regions to the left of the generator 820A are due to the wheels of the measurement trolley not permitting drive over the MF generator 820A (ground unit).

[0306] More precisely, FIG. 8A displays two vectorfields 802A and 804A in comparison asshown more clearly by a zoom-in view 810A at a grid point selected by example. The vector field 802A may refer to an ideal (non-distorted) vectorfield as measured on a homogenous electrically conductive ground, while thefield 804A represents an actual (distorted) vector field as measured in a real parking space on a ferroconcrete ground using the same generator 820A. In fact, iron structures to reinforce concrete grounds and walls such as typical for underground or multi-story car parks may alter the MF patterns in terms of vector magnitude and direction. The cause of such distortion effects are discussed in Patent US 10,029,577 in more detail. Experience has shown that MF distortion may become significant typically at a range of 2.5 m and beyond where they may substantially compromise a MF- based PD.

[0307] Accordingly, FIGs. 8B, 8C display vectorfields 800B, 800C of 2D voltage vectors Vy,Vz as measured at the same grid points using the same double-axis sensor as for Vx however in presence of a respective y-, z-MF generated by respective y-, z-MF generators 820B, 820C(e.g., 600B, 600C of FIGs 6B, 6C) using the same set-up and conditions as for measuring Vx. The vectorfields 800B, 800C also refer to isotropic double-axis sensing at zero rotation (φ = 0), measuring components Vyx’, Vyy’and Vzx’, Vzy’in time-synchronism with a respective drive current iy(t), iz(t) as indicated in FIGs.8B, 8C and defined e.g., by Equations (2) and (3). It may be appreciated that the vectors Vy, Vzmay be indicative of 2D (horizontal) MF vectors By, Bzin terms of magnitude and direction at least in those regions where the MF is substantially homogenous over the area of the sensor. The void regions as shown in FIGs.8B, 8C refer to areas where no measurements are available for reasons explained above. As in FIG.8A, the vectorfields 800B, 800C include ideal (non-distorted) vectorfields 802B, 802C and actually measured (distorted) vectorfields 804B, 804C in comparison as also shown more clearly by respective zoom-in views 810B, 810C at grid points selected by example.

[0308] As vectors Vx, the vectors Vy, Vz are scaled for purposes of visualization andcomparison. At each grid point, the scale factor is derived from the magnitude of an overall 4D vector composed of Vx and Vy, excluding Vz. More precisely, the ideal 4D vectors 802A, 802B and the measured 4D vectors 804A, 804B are scaled (normalized) in magnitude by a common factor so that the larger of the two has unity magnitude resulting in a grid point specific scale factor. The same grid point specific scale factor is then also applied to Vz. Since Vz is not part of the normalization, its magnitude “explodes” at certain points where Vx and Vy tend to vanish (e.g., as indicated by long arrows in a peripheral area of the generator 820C). This particular scaling intends to reveal the much faster decay of the magnitude |Vz| compared to |Vx| and |Vy| with increasing distance from the respective generator.

[0309] Contemplating the Vx vectorfield 800A in FIG. 8A, it may be appreciated that thex-MF can principally be used for guiding the vehicle (e.g., 402a of FIG.4) into the alignment range by following the directions as given by Vx. This may be particularly true, if road markings 808 can serve as an aid to approach the ground unit in a “cone”-like lane 812 around the x-axis as indicated by dashed lines and to align the vehicle substantially inparallel to the parking space. By strictly following the directions of Vx, the vehicle wouldmove on a path (trajectory) whose tangent vectors align with Vx. This path is also known as a field line. Followingfield lines in a direction of an increasing magnitude |Vx| will always lead to thefield source (generator 820A) and thus into the alignment range. Moreover, determining |Vx| along the driving trajectory may serve to estimate a remaining distance tothe generator 820A, which may be useful to control the vehicle speed and to determine transition into the alignment range. It may be appreciated that this approach to guidance only requires determining magnitude and orientation of Vx. Vector polarity requiring phase synchronous voltage measurement as discussed above may not be needed.

[0310] In another implementation, guidance is based on double-axis sensing of the y-MFas exemplary illustrated by the Vyvectorfield 800B of FIG.8B. In this implementation, the vehicle (e.g., 402a of FIG.4) may follow a path known as an orthogonal trajectory to thefield lines of the Vyvectorfield. An orthogonal trajectory intersects each of a plurality offield lines with an angle of 90°. However, the magnitude |Vy| in the lane 812 may be half of |Vx| as generated by an x-MF generator with equal magnetic moment. Comparing vectorfields 804A, 804B more thoroughly also reveals that the ferroconcrete environment may affect (distort) Vxand Vydifferently (e.g., due to anisotropy). This may be observed e.g., around x = -450 cm, y = -100 cm where vectors 804B, 802B are unequally directed as opposed to vectors 804A, 802A pointing substantially into the same direction.

[0311] In a further implementation, guidance is based on double-axis sensing of the z-MFas exemplary illustrated by the Vzvectorfield 800C of FIG.8C. Thisfield and particularly the ideal (non-distorted)field 802C is a substantially radialfield with substantially straightfield lines ending up at the z-MF generator 820C. Followingfield lines in direction of increasing |Vz| will always lead to the z-MF generator 820C and thus into the alignment range. However, thoroughly inspecting the vectorfield 800C reveals more deviation between vectors 802C, 804C than between vectors 802A, 804A as generated by a horizontally polarized MF source.

[0312] From above discussions, it may be concluded that within lane 812 x-MF beaconingis preferable as it provides higherfield levels than y-MF beaconing and less distortion than the z-MF. Single-axis MF beaconing may be considered as a low complexity solution that may not provide true position information (e.g., x,y-position and rotation angle φ in the ground- based coordinate system of FIG.3A) but some sort of pseudo position information that may be useful for guidance. Such approaches are also disclosed in Patents US 11,491,882, US 10,090,885, US 9,739,844, and US 10,566,839 (e.g., using an x-MF).

[0313] In certain conditions, pseudo position information as obtained from single-axis MFbeaconing may not satisfy user expectations or requirements for an automated parking system. Such conditions may include missing or badly visible landmarks or road markings (e.g., 408 of FIG.4) e.g., outdoors due to snow or darkness, a badly visibleflush-mount ground unit, etc. Guidance in such conditions may require determining a full positional relationship (full-PD) including e.g., x,y-coordinates and rotation angle φ. As previously mentioned with reference to FIG.4, full-PD may be performed using double-axis MF generation and double-axis MF sensing e.g., by using the generator 600D of FIG.6D and sensor 700A of FIG.7A. Various approaches and implementations of multi-axis MF generation and sensing are disclosed and discussed in Patents US 10,343,535, US 10,090,885, US 9,739,844, US 11,394,253, US 10,566,839, US 10,343,537, and US 10,029,577.

[0314] The fundamental principle of PD based on double-axis generation and sensing isillustrated in FIG.9A showing eight selected points A to H of a double vectorfield 900A composed of voltage vector pairs Vx, Vy in a ground-based coordinate system with origin O as defined in FIG.3A. The vector pairs Vx, Vyas shown qualitatively may result from double- axis generation e.g., using generator 600D of FIG.6D with its magnetic center positioned at O and double-axis sensing e.g., using sensor 700 of FIG.7 with zero rotation (φ = 0) providing vector components Vxx’, Vxy’ and Vyx’, Vyy’. FIG.9A also indicates magnetic moments mx, my produced by the double-axis generator in respective x-, y-axis direction assuming |mx| = |my|. To separate voltage components Vxx’, Vxy’ from Vyx’, Vyy’, a multiplexing scheme (e.g., FDM) may apply as previously discussed with reference to FIG.6D. Further, the direction (polarity) of vectors Vx, Vy relate to the respective magnetic moments mx, my, assuming phase synchronous voltage measurement as previously discussed with reference to FIG.7. FIG.9A also indicates quadrants 1 to 4 as relevant for the following considerations.

[0315] Contemplating the double-vectorfield 900A at points A to H, it can be found thatvector pairs generally distinguish by |Vx|, |Vy|, and an angle ϑ between Vx, Vy, except at diametric points e.g., A and E, B and F, etc. due to symmetries in the MF pattern. Points H and D are characterized by an obtuse-angle (ϑ > 90°), points B and F by an acute-angle (ϑ <90°), x-axis points A and E by ϑ = 90° and |Vx| > |Vy|, and y-axis points C and G by ϑ = 90° and|Vx| < |Vy|. It may be appreciated that these features also apply to any other point inrespective quadrants 1 to 4 including the x- and y-axis. For an ideally isotropic sensor, these features are also invariant to any sensor rotation φ.

[0316] In some implementations, above features in vector pairs Vx, Vy are used forguidance in quadrants 2 and 3 based on full-PD including x,y-coordinates and rotation angle φ. Limiting guidance to quadrants 2 and 3 (left half plane) excluding the alignment range and areas near the y-axis, the x,y-position and rotation angle φ may be unambiguously determined at any point. The principles and implementations of PD based on multi-axis MF generation and sensing are described and discussed e.g., in US 10,343,537 in more detail.

[0317] FIG. 9B illustrates a double vectorfield 900B composed of vector pairs Vx, Vywhose polarity is indeterminate (ambiguous) as resulting when the voltage components Vxx’, Vxy’and Vyx’, Vyy’are measured asynchronously with respect to the phase of the generator’s drive currents. This ambiguity is represented in FIG.9B by vectors Vx, Vyand anti-vectors -Vx,-Vy pointing in opposite direction resulting in four potential options (combinations) of vectorpairs comprising two pairs forming an acute angle ϑ and two pairs forming an obtuse angle ϑ. It may be appreciated that the angle ϑ is no longer useful to discriminate between quadrant 2 and 3. If by chance e.g., vector Vxand anti-vector -Vywere measured at point H forming an acute angle, quadrant 3 would be falsely selected. However, if by chance e.g., anti-vectors -Vx, -Vy were detected yielding an obtuse angle, quadrant 2 would be correctly selected. This example at point H demonstrates that vector polarity ambiguity may result in quadrant ambiguity, but also shows that determining the polarity of Vx relative to the polarity of Vy rather than their absolute polarity (e.g., related to the polarity of the magnetic moments mx, my) may suffice to unambiguously determine the quadrant.

[0318] The effects of vector polarity ambiguity and how to deal with it are extensivelydiscussed in US 10,343,537. Detecting the correct relative vector polarity requires measuring the voltage components Vyx’, Vyy’ of Vy in synchronism with respect to the phase of the x-MF or vice versa. This may be referred to as measuring in relative phase synchronism. Relative phase synchronization may generally be less demanding and less critical than absolute phase synchronization (e.g., based on the generator’s drive currents). As opposed to absolute phase synchronization, relative phase synchronization may be accomplished using in-band signaling.

[0319] In an example implementation based on the FDM scheme as described withreference to FIG.6D, relative phase synchronization is provided by driving the x- and y-coil of the MF generator (e.g., 600D of FIG.6D) with a “two-tone” current signalThe “double-tone” x-MF as generated by Ix(t) conveys time synchronization information, which may be used for synchronously measuring the voltage components Vxx’, Vxy’, Vyx’, Vyy’ in a relative sense so that the relative polarities are correctly detected. More specifically, measuring the voltage components refers to specific times tm where the phase difference Δω tm modulo 2π between Ix1(t) and Ix2(t) amounts to afixed value (e.g., zero). To fully exploit the available MF signals, Vx may be determined based on the “double-tone” x-MF as sensed by the sensor (700A of FIG.7A). It may be appreciated that in this FDM implementation, the x- and y-MFs cannot be confused, provided that frequency stability of MF generation and the frequency-selective voltage measurement is high enough to properly separate and determine all induced voltage components.

[0320] In an implementation based on the TDM scheme as described with reference toFIG.6D, relative phase synchronization is provided by exciting the x-coil of the MF generator (e.g., 600D of FIG.6D) with a current Ix(t) = Iˆxcos(ωt) in odd time slots and the y-coil with a current Iy(t) = Iˆycos(ωt) in even time slots with the same angular frequency ω. An odd and a consecutive even time slot together may be referred to as a frame. Assuming framesynchronization, the vectors Vx and Vy are measured in consecutive time slots spaced in timeby Tscorresponding to a slot period, which is half of the frame period 2Ts. Assuming ω and Tsderived from the same time base (e.g., time base of GA PD unit 228 of FIG.2), the timespacing Tsdirectly translates to afixed and known phase offset ω Ts, if Vxand Vyhave the same polarity. If Vxand Vyhave opposite polarity, a phase offset Δω Ts+ π results.

[0321] Since x- and y-MF signals are not distinguishable per se, they may not provide ameans for frame synchronization. In an example implementation, this problem is solved inanalogy to the triple-frequency FDM implementation as described above by extending the double-slot frame to a triple-slot frame. More specifically, the x-coil is driven by a current Ix1(t) in afirst time slot and a current Ix2(t) shifted in phase (e.g., by π / 2) relative to Ix1(t) in a second time slot, while the y-coil is excited with a current Iy(t) in a third time slot e.g., as follows:where n = 0, 1, 2, 3,… denotes a frame counter. It may be appreciated that the phase shift in the x2-MF signal may suffice to unambiguously establish frame synchronization.

[0322] In alternative TDM implementations, the x1- and x2-MF signals are distinguishedby a different peak amplitude (I^x1 ≠ I^x2) or by a different angular frequency (ωx1 ≠ ωx2).Various implementations of multi-axis MF beaconing based on FDM, TDM, CDM providingmeans for relative phase synchronization are disclosed in US 11,394,253.

[0323] As already mentioned with reference to FIG. 4, there is a potential risk ofinterference if beacon signals are concurrently transmitted by neighboring ground units (e.g., 420a to 420e) in an uncoordinated manner. This is particularly true if the ground units (integrating e.g., GA PD unit 228 of FIG.2) are configured to support guidance at distances larger than 2 m. To reduce the risk of interference, ground units installed in neighboring parking spaces must share the available spectral resource in some coordinated manner. Sharing may be accomplished in time, frequency, or both as suggested in US 10,343,535, applying known schemes based on frequency division, time division, or code division.

[0324] Patents US 10,090,885 and US 10,343,535 disclose single-axis MF beaconingemploying a frequency division scheme using a simple frequency re-use pattern based on a set of e.g., four frequencies f0, f1, f2, f3. In some implementations, these frequencies are manually assigned to neighboring ground units at time of installation or systemconfiguration in a repetitive fashion similar to cellular radio networks. Separation betweenthe different MF beaconing frequencies may be as small as 1 kHz, also depending on the modulation rate as needed to transmit pairing data (e.g., an ID) as previously mentioned with reference to FIG.4.

[0325] Using a time division scheme, neighboring ground units may share a singlecommon operating frequency by transmitting in different time slots using a simple slot re- use pattern based on a set of e.g., four time slots t0, t1, t2, t3. Some implementations use a common time reference for all ground units and the time slots are manually assigned e.g., as described above for the frequency division scheme. In other implementations not requiring a common time reference, each ground unit of a multi-parking facility (e.g., 400 of FIG.4) provides a receiver (not shown) configured to receive one or more neighboring beacon signals and a circuit (not shown) to synchronize its beacon transmission in a manner to avoid interference. Since self-synchronizing networks based on synchronization propagation tend to self-oscillate, this implementation involves a risk of periodic slot reallocations and mutual interference.

[0326] A code division scheme using a spread spectrum technology may not require time-synchronously operating ground units. Considering however the limited spectrum as given e.g., by the long-range band 510 of FIG.5B, the available bandwidth may be too scarce for achieving a processing gain as needed to sufficiently mitigate interference from adjacent ground units. This may be particularly true if the transmission is data modulated.

[0327] In a further aspect and as previously discussed, WiFi pairing requires at least oneof the beacon signals as transmitted by a beacon transmitter (not shown) of a GA PD unit (e.g., 228 of FIG.2) being data modulated. In some implementations, data modulation is also used to convey system specific information for configuring and parametrizing the VA PD unit (e.g., 238 of FIG.2) to appropriately process the received beacon signals. Further, overheadinformation for purposes of synchronization, error correction, error detection, and security may be added.

[0328] Beacon transmission conveying data may be structured in a sequence of frames.FIG.10 illustrates an example repetitive frame structure 1000 referring to the physical layer of an OSI model. An example frame 1002 comprises a modulated section 1010 (indicated in FIG.10 by shaded section) corresponding to a time duration Tmodand a non-modulated continuous-wave (CW) section 1020 of duration TCW. FIG.10 also indicates the total frame duration (frame period) TF= Tmod+ TCW. The example modulated section comprises a preamble 1012, a message 1014, and a cyclic redundancy check sequence (CRC) 1016. The entire data contained in the modulated section 1010 may also be referred to as a physical layer data packet.

[0329] In some implementations, the preamble 1012 is configured to reliably detectpresence of a beacon signal and to synchronize the beacon receiver of a VA PD unit (e.g., 238 of FIG.2) in terms of start of frame and modulation symbol timing. Therefore, the preamble is also referred to as a “synchronization sequence”. In one implementation, the preamble 1012 is a pseudo-random sequence (e.g., an “m”-sequence). In another implementation, the preamble is one of a set of predefined sequences (e.g., Gold- sequences) selected based on auto- and cross-correlation properties. The set of preambles is used for signaling specific information e.g., an applicable transmission format, if the VA PD unit has to support different beacon transmission standards. The message 1014 may include specific information such as transmit levels, system control data, type of ground unit (e.g., surface mount,flush mount), characteristics of the beacon MF pattern, ground types (e.g., ferroconcrete, asphalt), etc. Further, it may include pairing data such as an SSID or a derivative thereof of the WiFi access point and an ID of the GA. The CRC 1016 is used to detect a corrupt message 1014 containing one or more erroneously decoded bits. The CRC may be based on a generator polynomial as known in the art. Present SAE J2954 / 1 standard defines a data packet 1010 of an overall size of 176 bits (22 Bytes) comprising a 64-bit preamble 1012, a 96-bit message 1014, and a 16-bit CRC 1016.

[0330] In an implementation, each frame 1002 comprises the entire message 1014, thusretransmitted in each frame. In another implementation, the message 1014 is partitionedinto several frames and retransmitted in a longer (multiple frame) cycle referred to as a super frame (not shown). In a further implementation, afirst part of the message 1014 (e.g., including time critical information) is retransmitted in every frame and a second part of the message is partitioned into several frames, thus retransmitted in every super frame. Retransmitting time critical information in every frame may ensure low latency.

[0331] The non-modulated CW section 1020 may serve the VA PD unit (e.g., 238 of FIG.2) to perform PD for guidance and alignment. The CW section permits narrowbandfiltering in the beacon receiver of VA PD unit (e.g., 238 of FIG.2) providing enough processing gain to accurately measure the voltage components at the terminals of a double-axis MF sensor (e.g., 700A of FIG.7A). A beacon transmission format comprising an amplitude or phase modulated section for purposes of synchronization and pairing, and a non-modulated section dedicated for PD is also disclosed and discussed in U.S. Patent 11,394,253.

[0332] In an implementation, the modulated section 1010 is amplitude modulated e.g.,using binary amplitude shift keying (ASK) leaving a residual carrier wave containing at least half of the total signal power. ASK with 100% modulation depth, also known as ON-OFF keying (OOK), provides a residual carrier with half of the total signal power assuming 50% ON time. The residual carrier in the modulated section 1010 may additionally be used by the VA PD unit (e.g., 238 of FIG.2) to improve PD. This implementation enables unrestricted use of the beacon transmission for PD, e.g., if the specified position update rate is higher than the frame rate.

[0333] In another implementation in accordance with present SAE J2954 / 1 standard, themodulated section 1010 includes the entire frame 1002 and is binary ASK (e.g., OOK) modulated leaving a residual carrier, entirely omitting the CW section 1020. This implementation may result in a shorter frame period TF and thus in lower latency for data decoding at a given data rate.

[0334] In a further implementation, the modulated section 1010 is phase modulated e.g.,using binary phase shift keying (PSK) also referred to as antipodal signaling. PSK provides a 3 dB lower threshold SNR but cancels out the carrier wave. Therefore, the modulated section 1010 may not be used for PD unless the transmitted data is known. However, once thethreshold SNR is exceeded and data can be decoded, the receiver may use this data to restore the carrier, a technique known as decision feedback carrier recovery. Before the threshold SNR is reached, PD may solely rely on the CW section 1020. Afterwards, the VA PD unit (e.g., 238 of FIG.2) may use both the modulated and non-modulated sections. In some implementations, this may apply at distances < 2.5 m.

[0335] The voltages as measured at a MF sensor (e.g., 700A of FIG. 7A) by means of theresidual carrier in the modulated section 1010 may vary depending on the distribution of binary “ones” and “zeros”. This may be particularly true if the message 1014 contains long strings of binary zeros or binary ones. Therefore, some implementations employ Manchester coding as known in the art to reduce a variance (fluctuation) in the measured voltages. According to the IEEE 802.3 convention, Manchester encoding applied to OOK translates a logical “1” into an off-to-on (positive) transition, while a logical “0” converts to an on-to-off (negative) transition. It may be appreciated that this encoding scheme is very effective to produce almost perfectly balanced on-off sequences, regardless of the logical bit pattern. However, it doubles the modulation bandwidth, thus lowers spectral efficiency.

[0336] In some implementations, the beacon transmission is based on Manchesterencoded OOK leaving a residual carrier and the frames 1002 are entirely modulated (omitting any CW section) to reduce the variance in in the measured voltages and to enable unrestricted use of the beacon transmission for PD as previously discussed.

[0337] Further, some implementations use hard keying for data modulation, which maybe considered as composed of a time-series of rectangular-shaped elementary pulses p(t). Assuming Manchester encoding, this time-series of pulses may be expressed aswhere Tb denotes the logical bit period, i the logical bit counter, and bi ∈ [0,1] the value ofthe i-th logical bit. In frequency domain, hard keying produces wide modulation sidebands (spectral skirts) with a slow decay following a 1 / x law. Hard keying may cause undesirable out-of-band emissions and interference from beacon signals transmitted by neighboring ground units e.g., if a frequency division scheme is employed as previously discussed with reference to FIG.4.

[0338] Therefore, some implementations employ pulse shaping to reduce out-of-bandemissions and interference (e.g., inter-GA interference) as suggested in Patent US 11,394,253 B2. Shaping of a rectangular pulse p(t) may be accomplished in various ways employing known shaping or window functions satisfying certain requirements in time and frequency domain. A class of pulse shaping functions with interesting properties are basedon a “raised-cosine” function in time-domain. The grade of shaping can be controlled by aparameter β also referred to as “roll-off factor”. Using base-band representation, the generic raised-cosine shaped elementary pulse p(t;β) as a function of time t and parameter β may be defined asSubstituting p(t) in Equation (21) by p(t;β) of Equation (22) yields the corresponding time- series of raised-cosine shaped base-band pulses sm(t;β), also referred to as modulation signal.

[0339] FIG. 11A displays a base-band elementary pulse p(t;β) 1100A for different roll-offfactors β as indicated. It may be appreciated that the pulse area (the integral) remains constant as β varies in the range 0 < β < 1, while its duration including tails varies in the range from Tb / 2 to Tb.

[0340] FIG. 11B displays the Manchester encoded modulation signal sm(t;β) 1100B basedon the elementary pulse p(t;β) for a logical bit sequence ‘0’, ’0’, ‘1’, ‘1’, ‘0’, ‘0’ and for the three different roll-off factors β as indicated in FIG.11A.

[0341] FIG. 11C displays a power density spectrum Φsm(f;β) 1100C of a base-bandmodulation signal sm(t) for three different roll-off factors β as indicated. The spectrum 1100C is shown on a logarithmic scale (dB scale) and excludes the zero-frequency component (Dirac function) representing the residual carrier in the base-band. More precisely, the spectrum 1100C refers to the Wiener-Khinchin power density spectrum defined as the Fourier transform of the autocorrelation function of a random binary process including Manchester encoding and pulse shaping. The random binary process may be defined as a sequence ofbits whose next bit is a ‘0’ or ‘1’ with equal probability, independent of previous bits. The resulting base-band spectrum 1100C is composed of spectral sidelobes offirst, second, and higher order of the lower and upper modulation sidebands with spectral notches in between at |f| = 0, 2 / Tb, 4 / Tb, 6 / Tb, etc. It can be shown that the notch at f = 0 is produced by Manchester encoding, while the spectral notches at |f| > 0 are double zeros produced by both Manchester encoding and the raised-cosine-shaped elementary pulse p(t;β) for any β in range 0 ≤ β ≤ 1. Otherwise stated, Manchester encoding in combination with raised- cosine pulse shaping produces very pronounced and relatively broad spectral notches. FIG. 11C also demonstrates the impact of the roll-off factor β on the higher order modulation sidelobes. With β = 0.3, the 4-th and 5-th order sidelobes reduce by > 10 dB and > 20 dB, respectively. There exist other classes of pulse shaping functions (e.g., trapezoidal functions) satisfying certain symmetry properties as needed to provide zeros in the frequency domain. However, these functions may not be as effective in reducing sidelobes as the raised-cosine function.

[0342] The data modulated beacon signal in the operating frequency band (e.g., 510 ofFIG.5B) may be represented aswith f0denoting the carrier frequency. The signal s(t) may be representative for the drive current Ix(t) of coil 606 with reference to FIG.6A. The power density spectrum Φsm(f;β) of a process s(t) (not shown) is obtained by shifting the spectrum 1100C by f0so that the zero- frequency becomes the carrier frequency f0. This frequency shift translates spectral notches to frequencies| |

[0343] In an example implementation, the residual carrier in the beacon signal s(t) is usedfor measuring the voltage components as induced into the orthogonal coils of a MF sensor (e.g., 700A of FIG.7A) by employing narrow-bandfiltering in the beacon receiver of a VA PD unit (e.g., 238 of FIG.2) as previously discussed with reference to FIG.10. It may be appreciated that the notch at |f – f0| = 0 due to Manchester encoding reduces an impact of data modulation on a PD performance (PD error) by reducing a variance of the measured voltages.

[0344] In an example implementation based on a frequency division scheme, a frequencyre-use pattern is employed to discriminate between beacon signals concurrently transmitted by neighboring ground units (e.g., 420a to 420e of FIG.4) as previously described in the context of FIGs.4 and 9B. The set of frequencies comprises a number of frequencies (e.g., f1, f2, f3, f4) referring to the carrier frequencies of respective beacon signals (e.g., s1(t), s2(t), s3(t), s4(t)). These frequencies are also referred herein as to channel frequencies. Further, beacon transmitters of GA PD units (e.g., 228 of FIG.2) of neighboring ground units are configured to transmit data at the same speed with a logical bit rate 1 / Tb. Moreover, and as far as possible under the limitations given by the frequency reuse pattern, beacon transmitters of neighboring ground units use a different channel frequency selected from a set of frequencies spaced by 2 / Tbor a multiple thereof so that residual carriers will fall into spectral zeros as described above. This particular implementation may reduce interference on the residual carrier component as used for PD. More specifically, it may reduce a “noise” component on the voltages as frequency-selectively measured at the MF sensor (e.g., 700A of FIG.7A).

[0345] FIG. 11D shows a base-band representation of an ensemble of Wiener-Khinchinpower density spectra 1100D of four modulated beacon signals s(t) that are offset in frequency by -6 / Tb, -2 / Tb, 2 / Tb, 6 / Tb. The power density spectra expressed as Φsm(f + 6 / Tb), x-MF, Φsm(f – 2 / Tb), Φsm(f – 6 / Tb) and displayed in logarithmic (dB) scales refer to a rectangular modulation waveform sm(t) with β = 0. The ensemble of spectra 1100D illustrates an example implementation dividing available spectral resources (e.g., band 510 of FIG.5B) in four beaconing channels with respective carrier frequencies f1, f2, f3, f4 spaced by 4 / Tb. Using this frequency spacing, 1storder sidelobes of all beacon transmissions become disjunct and their residual carriers fall into spectral notches of any of the modulation sidebands.

[0346] To accommodate four beaconing channels with frequencies f1, f2, f3, f4 spaced by4 / Tb under the bandwidth constraint as given by the long-range band 510 of FIG.5B, present SAE J2954 / 1 standard specifies a transmission speed Rb = 500 logical bit / s (Tb = 2 ms) resulting in a frequency spacing of 2 kHz and a frame length TF of 352 ms assuming the packet size of 176 bits as presently specified by SAE.

[0347] Returning to FIG.4, the ground units 420a to 420e of the multi-parking facility 400may be assigned to frequencies f1, f2, f3, f4,f1, respectively, according to a repetitive 1:4 frequency re-use pattern. Further, the onboard beacon receiver of VA PD unit (e.g., 238 of FIG.2) of vehicle 402a may be tuned to the frequency (e.g., f2) of the wanted beacon signal transmitted by the target ground unit (e.g., 420b). Assuming all ground units concurrently transmitting, the wanted beacon signal may be interfered by one or more unwanted emissions from neighbor ground units (e.g., 420a, 420c). Further, assuming a channel frequency spacing of 4 / Tbas shown in FIG.11D by example, neighbor channel interference is only caused by second and higher order sidelobes. In some implementations, neighbor channel interference but also out-of-band emissions is lowered using pulse shaping (e.g., raised-cosine with β > 0 with reference to FIG.11A) to further suppress higher order sidelobes of the spectra 1100D. However, raised-cosine pulse shaping in time domain may also cause inter-symbol interference in the beacon receiver of VA PD unit (e.g., 238 of FIG. 2). Inter-symbol interference is a form of disturbance in which subsequent pulses (representing symbols e.g., bits) interfere with one another causing symbol detection errors. This may happen if subsequent pulses substantially overlap such as illustrated in FIG.11B for raised-cosine pulse shaping with β = 0.7. Therefore, in some implementations, the roll-off factor β represents a tradeoff between neighbor channel interference and inter-symbol interference.

[0348] As the vehicle 402a is approaching its target ground unit 420b, the level of thewanted beacon signal as received by the beacon receiver of VA PD unit (e.g., 238 of FIG.2) at f2 will steadily increase. However, interference potentially produced by neighboring ground units will also mount to some extent as the vehicle advances. This general increase in received levels for a vehicle moving along an x-axis (ref. FIG.3A) from x = -5 m to 0.5 m is graphically displayed in FIG.12A by a family of computed curves 1200A. More specifically, FIG.12A shows the wanted signal level S(x) (excluding the residual carrier component) and the aggregated interference I(x;β) as a function of the x-position of the MF sensor (e.g., 700A of FIG.7a) in a log-log plot on a relative dB scale. The three curves I(x;β) refer to three different pulse shaping roll-off factors β as indicated in FIG.12B and defined with reference to FIGs.10 and 11A. Computations are based on a simplified model assuming a multiple parking scenario comprising nine neighbor ground units e.g., 420a, 420c, 420d, 420e andsome more of an adjacent row (not shown) opposite of road marking 408, each transmitting a beacon signal and acting as an uncorrelated interference source. Further, the model assumes ground units are spaced by 2.5 m in x- and y-direction and sharing spectrum using a 1:4 frequency re-use pattern with a channel frequency spacing of 4 / Tb, a magnetic dipole field pattern for each beacon signal, a 3rdpower law (60 dB per decade) path loss model for distances > 0.5 m, and a double-axis MF sensor (e.g., 700A of FIG.7A) with rotation angle φ = 0 providing maximum coupling between the x-coil of ground unit 420b and the x’-coil of vehicle unit 430a. Moreover, it assumes the Wiener-Khinchin spectrum Φsm(f) of FIG.11C for the interfering signals, which may be considered representative for an average over many realizations of real transmit spectra. The beacon receiver is modelled by afilter matched to the Manchester bipolar elementary pulse providing maximum SNR in additive white Gaussian noise (AWGN). However, the model neglects inter-symbol interference as it may be experienced for larger roll-off factors e.g., β > 0.5.

[0349] As evident from FIG.11D and the assumed scenario, the sum interference I(x;β) ismainly composed of neighbor channel interference produced by sidelobes of 2ndor higher order but also of co-channel interference from a more distal ground unit (not shown) re- using the same frequency f2. The difference between S(x) and I(x;β) refers to the Signal-to- Interference ratio (SIR) increasing from 10.2 dB at x = -5 m to 18.9 dB at x = -2.5 m as indicated in FIG.12. Moreover, FIG.12 shows a small improvement in SIR of 0.8 dB at x = -5 m if a raised-cosine pulse shaping with β = 0.7 is applied.

[0350] In another aspect, the receive signal and thermal noise level and eventually theresulting SNR are considered. The RMS voltage Vx’ induced into the x’-coil of an example MF sensor (e.g., 700A of FIG.7A) by an SAE standard compliant x-MF may be found to be = 2.2 μV (= 6.7 dBμV) per turn referring to a position x = -5 m, y = 0, and rotation φ = 0 and a ferroconcrete ground theoretically increasing the receive signal strength at x = - 5m by about 6 dB. This voltage may be representative for a MF sensor integrated into a vehicle unit (e.g., 430a of FIG.4) configured for a z1-class as specified by the SAE J2954 / 1 standard. The z1- class defines the smallest form factor for the VA WPT coil and thus the smallest MF sensor representing a worst case in terms of receive voltage. For an OOK modulated beacon signal with roll-off factor β = 0, this voltage level refers to the ON state. For β > 0, it applies to the ON state excluding the roll-off periods, which may be referred to as the peak envelope.Further, it may be appreciated that binary OOK can be decomposed into a CW component and a binary PSK (bipolar) modulated component. For β = 0, these components are equal in amplitude and power at any time. For β > 0, this is only true for the peak envelope, resulting in somewhat lower average power for the bipolar modulated component if a peak envelop constrain applies. In the example MF sensor, the peak envelope RMS voltage of the received bipolar modulated component amounts to Vx’= 1.1 μV (= 0.7 dBμV) per turn.

[0351] In an example implementation of the beacon receiver of VA PD unit (e.g., 238 ofFIG.2), the receiver intrinsic thermal noise in the frequency band 510 of FIG.5B is equivalent to a noise voltage spectral density of 59 nVHz-1 / 2at the terminals of the x’-coil. This so-called “input referred noise” is normally governed by the receiver’s preamplifier (e.g., a low-noise amplifier). Assuming the wanted signal voltage per turn and the noise voltage density as given above, an SNR of -4.9 dB at the matchedfilter’s output would result at x = -5 m. In theory, this SNR may be increased using a multi-turn x’-coil. In a practical and economical implementation, a single-turn x’-coil may however already represent a design limit considering protection of the receiver’s front-end against the high voltages induced when WPT is active.

[0352] In a further aspect, the receive signal-to-noise + interference power ratio (SNIR) isconsidered. The SNIR may be expressed in terms of the SNR and the SIR asThe increase of the wanted signal level (excluding the residual carrier component) and the sum of thermal noise and interference for a vehicle moving along the x-axis (ref. FIG.3A) from x = -5 m to 0.5 m is graphically displayed in FIG.12B by a family of computed curves 1200B in a log-log plot on a relative dB scale. The underlying SNR as a function of x is obtained by matched to the SNR at x = -5 m extrapolated to x = -0.5 m applying the 3rd power law for the MF strength as previously mentioned. The underlying SIR(x,β) correspondsto the curves 1200A of FIG. 12A. The three curves N + I(x;β) refer to the roll-off factors β asindicated in FIG.12B. For β = 0, the SNIR increases from -5 dB at x = -5 to 12.1 dB at x = 2.5 m.

[0353] From FIG. 12B, it may be concluded that the SNIR is mainly determined by thethermal noise. In this predominantly noise-limited transmission, pulse shaping has little effect on the SNIR in the beacon receiver using a matchedfilter. In contrast, the SNIR tends to slightly reduce when β is increased while maintaining the peak envelope. This can be explained by the small average power loss as previously discussed. However, pulse shaping may effectively reduce out-of-band emissions (e.g., higher order sidebands) falling into the frequency band 520 of FIG.5B that may be used for alignment as previously mentioned with reference to FIG.5B. Present SAE J2954 / 1 standard defines carrier frequencies for generating a long-range beacon MF for guidance and multiple short-range beacon MFs (not shown) for alignment in respective bands 510 and 520 of FIG.5B. It also specifies voltages induced into a standardized MF sensor (e.g., 700B of FIG.7B) by the long-range and short- range beacon MFs. In the alignment range, the voltages induced by the short-range MFs in a level range useful for alignment may be 15 to 40 dB lower compared to the voltage produced by the long-range MF.

[0354] FIG. 13 illustrates an example scenario 1300 in the spectral domain by spectrum1310 and 1312 of a modulated beacon signal with a standardized carrier frequency of 117.5 kHz in the long-range band 510 differing by a roll-off factor and by a spectrum 1320 of a modulated beacon signal with a standardized carrier frequency of 142 kHz in the short-range band 520. The example spectra 1310 and 1312 are provided for β = 0 and β = 0.1, while the example spectrum 1320 is shown for β = 0.1 with a 20 dB lower spectral densityrepresenting an average in the range as mentioned above. This example anticipates apotential risk of the received short-range signal being interfered by high order modulation sidelobes of the long-range beacon signal if no pulse shaping (β = 0) is applied. In contrast, the spectrum 1312 for β = 0.1 suggests a substantial increase of the SIR in the band 520 by > 30 dB from a minor pulse shaping.

[0355] Returning to FIG.12B and assuming a vehicle 402a approaching ground unit 420balong the x-axis with reference to FIGs.4 and 3A, there will be afirst point where the SNIR exceeds a threshold needed to establish frame and symbol synchronization using the preamble 1012 as previously described with reference to FIG.10. Then, there will be a second point where the SNIR exceeds a minimum required SNIR to correctly decode the message 1014. In some receiver implementations, the threshold SNIR for a Bit Error Rate(BER) < 10-4can be found in the range from 7 to 10 dB. Using previous numerical assumptions, this threshold may be exceeded somewhere between x = - 3 and -2.7 m. In the worst-case, depending on the frame epoch, it may last a couple of frame periods (e.g., 2TF= 704 ms) until the entire message 1014 has successfully passed the CRC 2016. Assuming a vehicle speed of 1 m / s, this may happen somewhere between x = -2.3 and 2 m. This numerical example shows that latency can matter particularly in implementations where some data of message 1014 is needed for guidance and alignment (e.g., transmit levels, type of ground unit, etc.) as previously mentioned with reference to FIG.10. Early decoding of the message 1014 may also be needed for non-PD purposes e.g., to inform the user whether the targeted parking space is reserved or barred or to initiate WiFi pairing e.g., if WiFi communication is needed before the vehicle has reached itsfinal parking position. Therefore, a short frame length TFomitting a CW section and a compact message 1014 repeated in every frame may be advantageous.

[0356] Returning to FIG.4, a VA PD unit (e.g., 238 of FIG.2) of vehicle 402a entering aparking space of the parking facility 400 providing charging services may not know the beaconing channel frequency associated to the ground unit 420b in advance. In other parking facilities, the VA PD unit may not even know presence of an operational charging infrastructure. Therefore, the VA PD unit of vehicle 402a is initially in a receiving mode configured to detect any potential beacon signal (e.g., in the long-range band 510 of FIG.5B) indicating presence of a GA and supporting guidance. In some implementations, the VA PD unit is in an inactive (or standby) mode when the vehicle is driving at a speed exceeding a threshold speed (e.g., 2 m / s). However, as soon as the vehicle speed drops below the threshold, the receive mode is activated. In other implementations, the VA PD unit transitions into receive mode as soon as a WiFi network (e.g., a WiFi access point of the parking facility 400) is detected. This policy may apply e.g., for purposes of energy saving or to reduce a false detection probability.

[0357] In an implementation with reference to FIG. 10, the VA PD unit may be configuredto detect presence of a beacon signal transmitted according to the frame structure 1000 by means of its unmodulated (CW) section 1020. In absence of the CW section, it may be configured to detect the OOK modulated beacon signal by means of its residual carrier component using frequency-selective processing e.g., employing a 20 Hzfilter tuned to itscarrier frequency. Assuming a standard compliant beacon MF, such narrow-bandfiltering may enable reliably detecting presence of a beacon signal at a distance of 5 m or more from its MF source employing threshold detection.

[0358] In a further example, with reference to the parking facility 400 of FIG. 4, thebeacon channel frequency of the target ground unit 420b may initially be unknown when the vehicle 402a turns into the parking space. As previously described e.g., with reference to FIGs.9B and 11D, four long-range beacon channel frequencies f1, f2, f3, f4may be assigned to ground units 420a to 420e according to a repetitive 1:4 frequency re-use pattern. Parking in the multiple parking facility 400 may require the beacon receiver of a VA PD unit (e.g., 238 of FIG.2) to monitor all of the four beacon frequency channels. Additionally, there may be an uncertainty due to a frequency error in both GA PD unit (e.g., 228 of FIG.2) and VA PD unit. Present SAE J2954 / 1 standard specifies a carrier frequency accuracy of + / -25 ppm for any beacon signal as transmitted by the ground-based infrastructure. A larger tolerance of + / -50 ppm may be assumed for an economically designed beacon receiver, resulting in a maximum relative frequency offset of + / -9 Hz in the worst case for the long-range band.

[0359] In an implementation, a bank of four narrow-bandfilters tuned to respectivefrequencies f1, f2, f3, f4 is used to monitor the long-range band. In another implementation, additional narrow-bandfilters slightly offset in frequency are used to cope with the frequency offset as discussed above. In a further implementation, the bank of narrow-band filters is realized in a digital processor (not shown) as part of the beacon receiver using a discrete Fourier transform (e.g., a Fast Fourier Transform, FFT) as disclosed e.g., in Patent US 10,090,885.

[0360] FIG. 14 displays an example discrete frequency spectrum 1400 on a relative dBscale as it may be produced by a fast Fourier transform (FFT) after the vehicle 402a has turned into the parking space and is moving towards ground unit 420 with reference to FIG. 4. The spectrum 1400 illustrates a plurality of discrete frequency outputs also referred to as frequency bins. Further the spectrum 1400 assumes an FFT being configured in a manner so that four frequency bins 1410 of the plurality of bins match the nominal carrier frequencies f1, f2, f3, f4 as indicated in FIG.14, disregarding a potential frequency offset as discussed above. The magnitudes of the bins 1410 at frequencies f1, f2, f3, f4 may be indicative of thevoltage Vx’as induced by the residual carrier of a respective modulated beacon MF into the x’-coil 706a of MF sensor 700A with reference to FIG.7A. In general, the magnitudes include a superimposed noise component, depending on the SNR. The magnitude of the plurality of bins (e.g., bin 1420) excluding the bins 1410 generally represent noise plus interference as received at respective bin frequencies. Assuming ground units 420a to 420e assigned to frequencies f1, f2, f3, f4according to a repetitive pattern, the magnitude of the bin 1410 at f2may be indicative of the level of the beacon signal as received from the target ground unit 420b. As the vehicle is advancing towards the ground unit 420b, the magnitude of bin 1410 at f2will increase faster than the magnitudes of the other bins 1410 revealing the wanted beacon signal of the target ground unit. At some point, this beacon signal may be selected as “winner” or “survivor” to be used for PD (guidance). This process may be referred to as beacon discrimination.

[0361] In an example implementation, a VA PD unit (e.g., 238 of FIG. 2) starts beacondiscrimination as soon as the magnitude of one of the bins 1420 exceeds a threshold. The threshold may be a dynamic threshold that is computed based on a mean level of noise plus interference as determined from the plurality of bins (e.g., bin 1420) excluding bins 1410. Inanother implementation, the VA PD unit starts beacon discrimination as soon as a ratio of amaximum magnitude bin 1410 and the mean noise plus interference level meet certain criteria as described above. The VA PD unit then uses the at least one of a distance, position, and pose to discriminate the wanted beacon (e.g., of ground unit 420b of FIG.4) unit from the other beacons (e.g., of ground unit 420a of FIG.4). In yet a further implementation, the beacon receiver of the VA PD unit also performs a correlation of at least one received beacon signal with a local replica of the 64-bit preamble 1012 as periodically transmitted in each frame 1002 with reference to FIG.10. In a further implementation, the VA PD unit monitors the FFT spectrum 1400 associated to afirst coil (e.g. an x’-coil 706a of FIG.7A) and to a second coil (e.g., y’-coil 706b of FIG.7A) and uses both spectra 1400 for beacon discrimination. In yet another implementation, the beacon receiver is configured to perform a complex output FFT for each of thefirst and second coil receive signal. The VA PD unit then uses the complex bins of both FFTs for determining an angle of the beacon MF vector for each received beacon signal meeting a threshold criterion.

[0362] In some examples, a VA PD unit (e.g., 238 of FIG. 2) determines at least one of adistance, position, and pose with reference to FIGs.3A, 3B of the vehicle unit relative to the ground units whose received beacon signals. The VA PD unit then uses a correlation result to verify validity of the beacon signal as selected in one of the beacon discrimination processes as described above. This procedure may prevent the VA PD unit from using an invalid signal for PD. An invalid signal may be a CW interference accidentally falling into one of the bins 1410. Beacon discrimination approaches are also disclosed in Patents US 10,090,885, US 10,139,238, and US 10,090,885.

[0363] In some implementations and with reference to FIG. 4, a VA PD unit (e.g., 238 ofFIG.2) uses beacon signals as received from all ground units in range for purposes of PD rather than discriminating wanted from unwanted beacons. More specifically, beacon signals as received from the target ground unit (e.g., 420b) and ground units on adjacent parking spaces (e.g., 420a and 420c) are used for determining of a position of the vehicle unit (e.g., 430a) relative to the target ground unit. In some implementations, at least two beacon signals meeting certain criteria (e.g., signal strength, SNR) are selected for PD.

[0364] In some implementations, the position of the vehicle unit is determinedfirst byestimating distances between the vehicle unit and the selected ground units based on the received beacon signals and second by using a geometric method commonly referred to as lateration (e.g., bilateration) or multilateration (e.g., trilateration) as known in the art. Distances may be estimated by the receive level (magnitude) of the respective beacon signal using a known magnitude vs. distance relation. For magnetic nearfields, a 3rd power distance law as previously used to compute the curves 1200A of FIG.12A may apply at distances > 1 m. In implementations using the double-axis MF sensor 700A of FIG.7A, the receive level of the beacon signal e.g., with carrier frequency f2 may be indicative of the vector magnitude (norm) of the induced voltage components Vx’ and Vy’ as selectively measured at f2. In implementations using the sensor 700A and an FFT as previously described with reference to FIG.14, the magnitude of the received beacon signal at f2 may be obtained from a corresponding output bin 1410 of Vx’ and a corresponding output bin 1410 of Vy’.

[0365] Lateration or multilateration may require a priori knowledge of a multi-parkingspace layout including a parking space width. The multi-parking space layout may include one of a 90°-parking, an angled (e.g., 45°) parking, and a 0°-parking. An example 90°-parking is illustrated in FIG.4. In an angled parking, parking spaces adjoin on a long side with an offset. In 0°-parking, parking spaces adjoin on a short side as typical for curbside parking. The 0°-parking maneuver is also referred to as parallel parking. In a homogenously arranged parking lot, the multi-parking space layout including the parking space width defines a lateration or multilateration base as required for determining a relative position between the vehicle unit (e.g., 430a) and the target ground unit (e.g., 420b).

[0366] Further, lateration or multilateration may require a suitable frequency re-usepattern based on four or more frequencies as previously described with reference to FIG.4. In a suitable re-use pattern, the frequencies are assigned to parking spaces in a manner such that no two frequencies are the same in any group of four or more adjacent parking spaces. An adjacent parking space may be defined as a parking space whose ground unit is in a second or third shortest distance from the vehicle unit when the vehicle is positioned in an area at the entrance of the target parking space. This entrance area may be most relevant for lateration-based PD as previously discussed. It may be appreciated that a frequency re- use pattern as defined above principally permits disambiguation of the ground units disposed on the left and right adjacent parking space if the vehicle PD unit knows the general frequency re-use pattern. However, there is no need to know the exact frequency assignment. An example of a suitable frequency re-use pattern is provided with reference to FIG.4.

[0367] In absence of a priori knowledge of the parking space width, the VA PD unit mayuse a standard parking space width as default lateration base. In implementations based on trilateration using beacons signals transmitted by ground units (adjacent ground units) disposed on the left and right adjacent parking space, the trilateration base and the position are jointly determined using overdetermination inherent in trilateration. This method assumes equal spacing between adjacent ground units. In another implementation, the VA PD unit extracts the lateration or trilateration base from a series of consecutive distance measurements performed at different way points on the trajectory as the vehicle is moving towards the target ground unit. In a further implementation, the VA PD unit determines theparking space layout including the parking space width from the series of consecutive distance measurements and overdetermination as described above. In yet another implementation, the vehicle PD unit acquires a priori knowledge about the multi-parking space layout including the parking space width via a radio network (e.g., WiFi) using the VA wireless communication unit 246 of FIG.2. In yet a further implementation, the vehicle uses a global navigation system (e.g., GPS) to determine its position and acquires a priori knowledge about the multi-parking space layout including the parking space width from a vehicle onboard memory or an online data bank based on this position.

[0368] In some implementations, multilateration is used for full-PD including x, y, φ atdistances > 2.5 m from the ground unit 420b where single-ground unit PD based on double- axis MF beaconing becomes unreliable as previously discussed with reference to FIGs.7A, 8A. In other implementations, multilateration is used to support and enhance single-ground unit PD based on double-axis MF beaconing over the entire distance range as specified for guidance. In further implementations, multilateration is used to enhance determining a pseudo-position (pseudo-PD) based on single-axis MF beaconing as previously described with reference to FIGs 8A to 8C.

[0369] In a further aspect of standardization and interoperability, a legacy PD standardfor long-range guidance may support pseudo-PD based on single-axis MF beaconing. For enhanced user experience and autonomous parking e.g., in more difficult conditions as previously addressed with reference to FIGs.8A to 8C, a later PD standard for guidance may also support double-axis MF beaconing for full-PD (e.g., x, y, φ). To ensure interoperability at any time, the legacy standard may be required to ensure forward compatibility of legacy VA PD units (e.g., 238 for FIG.2) with double-axis MF beaconing without being compromised by the additional MF. Conversely, the later standard may be required to ensure backward compatibility of later VA PD units supporting double-axis MF beaconing with legacy single- axis MF beaconing without being compromised by the missing MF.

[0370] These requirements of interoperability limit the variety of potential approaches todouble-axis MF beaconing. Various MF multiplexing schemes based on FDM, TDM, CDM are recapitulated with reference to FIG.6D. FIG.15 illustrates an example implementation concept of a double-axis MF beacon transmission 1500 comprising a data modulated x-MFsignal and a y-MF signal with reference to FIGs.8A, 8B, respectively. This implementation combines OOK, TDM, and quadrature modulation. More specifically, FIG.15 illustrates this concept by means of four time domain signals comprising a binary pulse waveform 1502 representing an example sequence of logical data bits, a modulation pulse waveform 1504 as resulting after Manchester encoding, and modulated carrier signals 1506, 1508 as resulting after OOK and quadrature modulation and as used to drive a respective x- and y- coil of a double-axis MF generator (e.g., 600D of FIG.6D). As evident from FIG.15, the y-MF signal is transmitted in the OFF intervals of the x-MF signal at the same carrier frequency. In other words, the x- and y-MF signals are complementary sharing time with a 1:1 ratio. Further, the x- and y-MF signals are transmitted in quadrature meaning that the carrier of the y-MF signal is shifted in phase by 90° relative to the carrier of the x-MF signal. Additionally, the y-MF signal may be transmitted at a lower level than the x-MF signal. Moreover, its polarity alters from logical bit to logical bit resulting in a 90° / 270° PSK (bipolar) modulated y-MF signal. Mathematically, the transmitted x- and y-MF signals may be expressed asrespectively, where Ax and Ay denote the respective carrier amplitudes, ωc the angular carrier frequency, p(t) the elementary pulse, Tb the logical bit period, i the logical bit counter,and bi ∈ [0,1] the value of the i-th logical bit. In some implementations, the elementarypulse p(t) is shaped by a raised-cosine function with roll-off factor β resulting in a pulse p(t;β) as defined by Equation (22).

[0371] As previously described with reference to FIG.10, the legacy standard defines aset of preambles 1012 for signaling the applicable transmission format from a GA PD unit (e.g., 228 of FIG.2) to a VA PD unit (e.g., 238 of FIG.2). To meet the forward compatibility requirement as discussed above, the legacy standard defines a preamble #1 for the legacy single-axis MF beaconing and a set of spare preambles #2, #3, #4 for other transmission formats (e.g., double-axis MF beaconing) specified in a later standard. Though a legacy GA PD unit may only transmit preamble #1, forward compatibility may require a legacy VA PDunit to correlate the received signal with all preambles defined in the legacy standard e.g., for purposes of frame synchronization as described with reference to FIG.10.

[0372] Backward compatibility requires the y-MF signal as needed for double-axis MFbeaconing to be transmitted in a manner to ensure virtually uncompromised reception of the x-MF signal by legacy VA PD units with respect to both demodulating data and detecting coil voltages as needed for pseudo PD. This requirement should be fulfilled regardless of the legacy beacon receiver implementation.

[0373] In a low complexity implementation, the beacon receiver may employ non-coherent detection of the Manchester encoded OOK signal. Non-coherent detection is sometimes also referred to as energy detection. In some implementations, the beacon receiver detects and compares the energy as received in an ON interval with the energy detected in an associated OFF interval to determine whether the received data is a logical ‘1’ or a logical ‘0’. It may be appreciated that transmitting the y-MF signal in the OFF intervals of the x-MF signal may potentially compromise a performance of non-coherent detection in legacy receivers (e.g., increase a minimum required SNR for error free data decoding). Therefore, the y-MF signal is required to be transmitted at a substantially lower level. However, transmitting the y-MF signal at lower level potentially reduces the range of double- axis MF beaconing. Therefore, the y-MF transmit level as specified by a later standard may represent a trade-off between performance degradation of low complexity legacy beacon receivers and double-axis MF beaconing range.

[0374] In an example operation in accordance with a later standard and with reference toFIGs.3A, 6D, 8A, 8B, the x- and y-coil current levels of the MF generator 600D are adjusted to produce a magnitude output vector |Vy| that is 10-times (20 dB) smaller than a magnitude output vector |Vx| at a double-axis MF sensor (e.g., 700A of FIG.7A) positioned at a distance > 2.5 m on the x-axis. This level ratio may result in a performance degradation of 1 dB in a legacy receiver employing simple energy detection. Reapplying the 3rdpower distance law and a maximum range of 5 m for x-axis MF beaconing, the SNR-limited range of y-axis MF beaconing and thus of double-axis MF beaconing may be found around 2.3 m. It may be appreciated that this SNR-limited range matches the range limited by MF distortion effects as previously discussed with reference to FIG.8A. In this example operation and withreference to FIG.4, the vehicle 402a approaching the ground unit 420b may initially rely on single-axis MF beaconing beginning at x = -5 m and then changing to full-PD using double- axis MF beaconing at x = -2.3 m.

[0375] In a more sophisticated implementation, the legacy beacon receiver may employcoherent detection for data demodulation by synchronizing on the residual carrier phase of the OOK modulated x-MF signal. In this implementation, the residual carrier may serve for both PD and phase synchronization. To preserve backward compatibility with this category of legacy beacon receivers, the complementary OOK modulated y-MF signal is transmitted in a manner to suppress its residual carrier component and to reduce an impact on coherent data demodulation. In the implementation of FIG.15 and as defined by Equation (26), the residual carrier is suppressed by transmitting y-MF pulses with an alternating polarity, while the impact on coherent data demodulation is reduced by transmitting the y-MF pulses in quadrature (shifted in phase by 90°) to the x-MF signal. These features may also be needed in beacon receiver implementations according to the later standard.

[0376] FIG. 16A is a schematic diagram illustrating an example implementation of aportion of a dual-branch MF beacon receiver 1600A comprised of a u’-branch and a v’- branch electrically connected to the respective u’-coil 706a and v’-coil 706b of the double- axis MF sensor 700B with reference to FIG.7B. The u’-branch as shown in FIG.16A is composed of an analog amplifier 1602a electrically connected to the u’-coil 706a, an analog- to-digital converter (ADC) 1604a electrically connected to the output of the amplifier 1602a, an FFT processor 1606a electrically connected to the output of the ADC 1604a and providing a discrete-time output denoted by Vxu’, a receiver matchedfilter 1608a also electrically connected to the output of the ADC 1604a, a y-sample extractor 1610a electrically connected to the output of the receiver matchedfilter 1608a, and a y-sample remodulator andfilter 1612a electrically connected to the output of the y-sample extractor 1610a and providing a discrete-time output denoted by Vyu’. Likewise, the v’-branch is composed of an analog amplifier 1602b, an ADC 1604b, an FFT processor 1606b providing a discrete-time output denoted by Vxv’, a receiver matchedfilter 1608b, a y-sample extractor 1610b, and a y- sample remodulator andfilter 1612b providing a discrete-time output Vyv’. The blocks of the v’-branch are electrically connected analogously to the u’-branch. The receiver matched filters 1608a, 1608b and FFT processors 1606a, 1606b may correspond to the matchedfilterand FFT as described with reference to FIGs.12A and 14, respectively. With reference to FIG. 7B, the outputs denoted by Vxu’, Vyu’, Vxv’, Vyv’are complex samples composed of a real and imaginary part indicative of the amplitude and phase of the voltages induced into the u’- and v’-coil 706a, 706b by the x- and y-MF signal. Further, the y-sample extractors 1610a, 1610b are controlled by logical bit decisions biwith i ∈ [0,1,2,…] e.g., as sequentially output by a data decoder (not shown) as part of the beacon receiver. The y-sample remodulator and filter blocks 1612 are provided with an alternating bipolar sequence (-1)i= 1,-1, 1,-1, 1,-1, ... for purposes as further explained in the context of FIG.16B. FIG.16A also indicates orthogonal magneticfield vectors Hxand Hy(with a smaller magnitude) as representative for the x- and y-MF e.g., at x = -2.5 m, y = 0.

[0377] FIGs.16B, 16C, 16D are diagrams illustrating example sequences of complexsamples 1600B, 1600C, 1600D as output by the receiver matchedfilter 1608a in different conditions and with the double-axis MF sensor 700B positioned e.g., at x = -2.5 m, y = 0, and φ = 0 with reference to FIG.3A. The diagrams display the complex output samples in a complex plane having a real and imaginary axis corresponding to an in-phase (I) and quadrature (Q) component. More specifically, the sequences of samples 1600A, 1600B, 1600C refer to a beacon receiver that is perfectly synchronized with respect to both symbol- timing and carrier phase using to the x-MF component of a double-axis MF beacon signal as defined by Equations (25) and (26). Though only shown and described for the u’-branch of the beacon receiver, FIGs.16B, 16C, 16D would also apply to its v’-branch.

[0378] FIG. 16B shows the sequence of complex output samples 1600B in absence ofnoise, inter-channel interference, and inter-symbol interference (e.g., roll-off factor β = 0) as previously discussed in the context of FIG.11D. The samples 1600B ideally map onto three distinct points denoted by Vxu’, Vyu’, V-yu’ that are indicative of the voltages induced into the u’-coil by the x-MF and by the y-MF signal with a positive and a negative polarity, respectively. As shown in FIG.16B, the Vxu’-samples (x-samples) map onto the I-axis, while the Vyu’- and V-yu’-samples (y-samples) fall onto antipodal points on the Q-axis and closer to the origin because the y-MF signal is transmitted at lower level, in quadrature, and with an alternating polarity as previously discussed.

[0379] In the example implementation of FIG.1600A, the y-sample extractor 1610aextracts y-samples from the sequence of samples 1600B as output by the matchedfilter 1608a using logical bit decisions as output by the data decoder (not shown) following a Manchester coding convention. For a transmit signal encoded according to IEEE 802.3, a sample pair associated to a logical ‘0’ would start with an x-sample and end with a y-sample. For a logical ‘1’ it is vice-versa. With reference to FIG.12B, an approaching vehicle (e.g., 402a of FIG.4) at x = -2.5 m has already passed the point where the SNIR exceeds the threshold to correctly decode the data and thus to correctly extract the y-samples.

[0380] The y-sample remodulator andfilter 1612a then inverts every second y-sampleusing a remodulation sequence that is a local replica of the transmitted bipolar sequence (e.g., 1,-1, 1,-1, 1,… ). Remodulation rectifies the sequence of y-samples. In some implementations, the remodulation sequence is synchronized with the received signal using the preamble 1012 with reference to FIG.10. This process of remodulation is sometimes also referred to as carrier recovery. Finally, the block 1612a performs narrowband noise filtering as needed for PD similarly as previously discussed for the x-MF signal with reference to FIG.14. In absence of noise and interference, the y-samples as output by block 1612a would only display two distinct points (not shown), one on the I-axis indicative of Vxu’ and one on the Q-axis indicative of Vyu’. While Vxu’ is positive by definition, Vyy’ may be positive or negative, depending on the relative polarity between the x- and y-MF signal as sensed by the u’-coil. As previously discussed with reference to FIGs.9A and 9B, the sign of the y-sample on the Q-axis is essential for full-PD including x, y, φ.

[0381] FIG. 16C assumes a raised-cosine pulse shaping with β > 0 resulting in some inter-symbol interference (crosstalk) due to pulse overlap in time-domain as previously discussed. In other words, and with reference to FIG.12, an x-MF pulse tail may infringe into an adjacent time slot where a y-MF pulse is transmitted and vice-versa. This crosstalk may cause the three points Vxu’, Vyu’, V-yu’ to scatter as exemplarily illustrated in FIG.16C. Scattering is most prominent on Vyu’, V-yu’ since the y-MF signal is weaker. It may be appreciated that y-remodulation andfiltering (1610a, 1610b) potentially eliminates any biasing of the y-samples and reduces scattering both caused by crosstalk. Moreover, thanks to the quadrature transmission of the x- and y-MF signals, any residual scattering is predominantly in the I-axis direction not impacting the Q-component of the y-samples asneeded for PD. This feature of crosstalk cancellation may also apply to the detection and processing of the x-samples. It enables use of overlapping pulse shaping in double-axis MF beaconing according to the implementation as described herein e.g., to reduce spectral sidelobes as previously described with reference to FIG.13.

[0382] FIG. 16D illustrates scattering of the matchedfilter output sequence 1600D due tocrosstalk (β > 0) and uncorrelated additive noise as it may be present in a real transmission channel. As opposed to crosstalk, additive noise will cause additionally scattering of the three points Vxu’, Vyu’, V-yu’in I- and Q-direction. However, it may be appreciated that the crosstalk cancellation effect will remain in noisy conditions as long as the beacon receiver is able to reliably phase- and time-synchronize on the double-axis MF signal and to correctly extract the y-samples as previously described.

[0383] In some implementations, the samples Vxu’, Vyu’, Vxv’, Vyv’ are output by therespective blocks 1606a, 1612a, 1606b, 1616b at a rate of 10 per second and are consideredas a vector V (e.g., a voltage vector). A vehicle position may be determined in afirst step bytransforming the measured vector V to a rotation invariant vector A and in a second step byfinding the best match of the vector A with a reference vector Arefof a stored vector map (Look-up Table). A point of best match may be used as an initial x,y-position estimate. In athird step, the rotation angle φ may be estimated byfinding the best match with a set ofrotationally transformed versions of a reference vector Vref selected from another stored vector map at the estimated x,y-position. The stored vector maps of Aref and Vref may be individual for a VA PD unit, vehicle type, and vehicle installation and may be produced and downloaded by the vehicle manufacturer as part of the system software. Such or similar PD processes are disclosed e.g., in Patents US 10,090,885, US 10,343,537, and US10,029,577.

[0384] Embodiments are also defined in the following items:Items: 1. A ground unit for charging an electric vehicle, the ground unit comprising a ground position detection, PD, unit, wherein: the ground PD unit is configured to transmitfirst and second magneticfield signals to be used by a vehicle PD unit to determine a positional relationship between a vehicle unit and theground unit based on thefirst and second magneticfield signals, wherein thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axis direction; thefirst magneticfield signal is a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on- intervals and substantially absent in off-intervals; and the second magneticfield signal is transmitted during off-intervals of thefirst magneticfield signal. 2. The ground unit of item 1, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space. 3. The ground unit of item 1 or item 2, wherein thefirst and second magneticfield signals are transmitted in quadrature and at a same carrier frequency. 4. The ground unit of any preceding item, wherein: presence of thefirst magneticfield signal during on-intervals represents a binary one; and substantial absence of thefirst magneticfield signal during off-intervals represents a binary zero. 5. The ground unit of any preceding item, wherein a phase of the second magneticfield signal alternates betweenfirst and second phases across successive off-intervals of thefirst magneticfield signal. 6. The ground unit of item 5, wherein thefirst phase differs from the second phase by 180 degrees. 7. The ground unit of item 5, wherein thefirst phase is 90 degrees and the second phase is 270 degrees compared to a phase of thefirst magneticfield signal. 8. The ground unit of any preceding item, wherein a magnitude of the second magneticfield signal is less than a magnitude of thefirst magneticfield signal.9. The ground unit of any preceding item, wherein the binary modulated carrier signal is Manchester encoded. 10. The ground unit of any preceding item, wherein the binary modulated carrier signal conveys data. 11. The ground unit of any preceding item, wherein: thefirst magneticfield signal induces afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal induces a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the inducedfirst and second voltages are used by the vehicle PD unit to: measure thefirst and second voltage signals, and determine a position of the vehicle unit relative to the ground unit based on the measuredfirst and second voltage signals. 12. The ground unit of any preceding item, wherein thefirst and second magneticfield signals are used by the vehicle PD unit to: determine a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determine the position and orientation of the vehicle unit relative to the ground unit. 13. A vehicle unit for electric vehicle charging, the vehicle unit comprising a vehicle position detection, PD, unit, wherein: the vehicle PD unit is configured to receivefirst and second magneticfield signals from a ground PD unit and determine a positional relationship between the vehicle unit and the ground unit based on thefirst and second magneticfield signals, wherein thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axis direction; thefirst magneticfield signal is a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on- intervals and substantially absent in off-intervals; and the second magneticfield signal is received during off-intervals of thefirst magneticfield signal.14. The vehicle unit of item 13, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space. 15. The vehicle unit of item 13 or item 14, wherein thefirst and second magneticfield signals are transmitted in quadrature and at a same carrier frequency. 16. The vehicle unit of any of items 13 to 15, wherein: presence of thefirst magneticfield signal during on-intervals represents a binary one; and substantial absence of thefirst magneticfield signal during off-intervals represents a binary zero. 17. The vehicle unit of any of items 13 to 15, wherein a phase of the second magneticfield signal alternates betweenfirst and second phases across successive off-intervals of thefirst magneticfield signal. 18. The vehicle unit of item 17, wherein thefirst phase differs from the second phase by 180 degrees. 19. The vehicle unit of item 17, wherein thefirst phase is 90 degrees and the second phase is 270 degrees compared to a phase of thefirst magneticfield signal. 20. The vehicle unit of any of items 13 to 19, wherein a magnitude of the second magneticfield signal is less than a magnitude of thefirst magneticfield signal. 21. The vehicle unit of any of items 13 to 20, wherein the binary modulated carrier signal is Manchester encoded. 22. The vehicle unit of any of items 13 to 21, wherein the binary modulated carrier signal conveys data. 23. The vehicle unit of any of items 13 to 22, wherein: thefirst magneticfield signal induces afirst voltage signal into one or more receiver coils of the vehicle PD unit;the second magneticfield signal induces a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the vehicle PD unit is configured to use the inducedfirst and second voltages to: measure thefirst and second voltage signals, and determine a position of the vehicle unit relative to the ground unit based on the measuredfirst and second voltage signals. 24. The vehicle unit of any of items 13 to 23, wherein the vehicle PD unit is configured to use the first and second magneticfield signals to: determine a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determine the position and orientation of the vehicle unit relative to the ground unit. 25. A wireless power transfer, WPT, system for electric vehicle charging, the WPT system comprising: a ground unit comprising a ground position detection, PD, unit and a vehicle unit comprising a vehicle PD unit, wherein: the ground PD unit is configured to transmitfirst and second magneticfield signals to the vehicle PD unit, wherein thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axis direction; thefirst magneticfield signal is a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on- intervals and substantially absent in off-intervals; the second magneticfield signal is transmitted during off-intervals of thefirst magneticfield signal; the vehicle PD unit is configured to receive thefirst and second magneticfield signals; and the vehicle PD unit is configured to determine a positional relationship between the vehicle unit and the ground unit based on thefirst and second magneticfield signals. 26. The WPT system of item 25, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space. 27. The WPT system of item 25 or item 26, wherein thefirst and second magneticfield signals are transmitted in quadrature and at a same carrier frequency.28. The WPT system of any of items 25 to 27, wherein: presence of thefirst magneticfield signal during on-intervals represents a binary one; and substantial absence of thefirst magneticfield signal during off-intervals represents a binary zero. 29. The WPT system of any of items 25 to 28, wherein a phase of the second magneticfield signal alternates betweenfirst and second phases across successive off-intervals of thefirst magnetic field signal. 30. The WPT system of item 29, wherein thefirst phase differs from the second phase by 180 degrees. 31. The WPT system of item 29, wherein thefirst phase is 90 degrees and the second phase is 270 degrees compared to a phase of thefirst magneticfield signal. 32. The WPT system of any of items 25 to 31, wherein a magnitude of the second magneticfield signal is less than a magnitude of thefirst magneticfield signal. 33. The WPT system of any of items 25 to 32, wherein the binary modulated carrier signal is Manchester encoded. 34. The WPT system of any of items 25 to 33, wherein the binary modulated carrier signal conveys data. 35. The WPT system of any of items 25 to 34, wherein: thefirst magneticfield signal induces afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal induces a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the vehicle PD unit is configured to use the inducedfirst and second voltages to: measure thefirst and second voltage signals, and determine a position of the vehicle unit relative to the ground unit based on the measuredfirst and second voltage signals.36. The WPT system of any of items 25 to 35, wherein the vehicle PD unit is configured to use thefirst and second magneticfield signals to: determine a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determine the position and orientation of the vehicle unit relative to the ground unit. 37. A method of controlling a wireless power transfer, WPT, system for electric vehicle charging, the WPT system comprising a ground unit comprising a ground position detection, PD, unit and a vehicle unit comprising a vehicle PD unit, wherein the method comprises: transmitting, by the ground PD unit,first and second magneticfield signals to be used by the vehicle PD unit, wherein thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axis direction; modulating, by the ground PD unit, thefirst magneticfield signal to generate a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on-intervals and substantially absent in off- intervals; transmitting, by the ground PD unit, the second magneticfield signal during off-intervals of thefirst magneticfield signal; receiving, by the vehicle PD unit, thefirst and second magneticfield signals; and determining, by the vehicle PD unit, a positional relationship between the vehicle unit and the ground unit based on thefirst and second magneticfield signals. 38. The method of item 37, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space. 39. The method of item 37 or item 38, wherein thefirst and second magneticfield signals are transmitted in quadrature and at a same carrier frequency. 40. The method of any of items 37 to 39, wherein: presence of thefirst magneticfield signal during on-intervals represents a binary one; and substantial absence of thefirst magneticfield signal during off-intervals represents a binary zero.41. The method of any of items 37 to 40, wherein a phase of the second magneticfield signal alternates betweenfirst and second phases across successive off-intervals of thefirst magneticfield signal. 42. The method of item 41, wherein thefirst phase differs from the second phase by 180 degrees. 43. The method of item 41, wherein thefirst phase is 90 degrees and the second phase is 270 degrees compared to a phase of thefirst magneticfield signal. 44. The method of any of items 37 to 43, wherein a magnitude of the second magneticfield signal is less than a magnitude of thefirst magneticfield signal. 45. The method of any of items 37 to 44, wherein the binary modulated carrier signal is Manchester encoded. 46. The method of any of items 37 to 45, wherein the binary modulated carrier signal conveys data. 47. The method of any of items 37 to 46, wherein: thefirst magneticfield signal induces afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal induces a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the determining, by the vehicle PD unit, comprises: measuring thefirst and second voltage signals, and determining a position of the vehicle unit relative to the ground unit based on the measuredfirst and second voltage signals. 48. The method of any of items 37 to 47, wherein the determining, by the vehicle PD unit, comprises: determining a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; anddetermining the position and orientation of the vehicle unit relative to the ground unit. 49. A method of controlling a ground unit for electric vehicle charging, the ground unit comprising a ground position detection, PD, unit, wherein the method comprises: transmitting, by the ground PD unit,first and second magneticfield signals to be used by a vehicle PD unit, wherein thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axis direction; modulating, by the ground PD unit, thefirst magneticfield signal to generate a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on-intervals and substantially absent in off- intervals; and transmitting, by the ground PD unit, the second magneticfield signal during off-intervals of thefirst magneticfield signal. 50. The method of item 49, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space. 51. The method of item 49 or item 50, wherein thefirst and second magneticfield signals are transmitted in quadrature and at a same carrier frequency. 52. The method of any of items 49 to 51, wherein: presence of thefirst magneticfield signal during on-intervals represents a binary one; and substantial absence of thefirst magneticfield signal during off-intervals represents a binary zero. 53. The method of any of items 49 to 52, wherein a phase of the second magneticfield signal alternates betweenfirst and second phases across successive off-intervals of thefirst magneticfield signal. 54. The method of item 53, wherein thefirst phase differs from the second phase by 180 degrees.55. The method of item 53, wherein thefirst phase is 90 degrees and the second phase is 270 degrees compared to a phase of thefirst magneticfield signal. 56. The method of any of items 49 to 55, wherein a magnitude of the second magneticfield signal is less than a magnitude of thefirst magneticfield signal. 57. The method of any of items 49 to 56, wherein the binary modulated carrier signal is Manchester encoded. 58. The method of any of items 49 to 57, wherein the binary modulated carrier signal conveys data. 59. The method of any of items 49 to 58, wherein: thefirst magneticfield signal induces afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal induces a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the inducedfirst and second voltages are used by the vehicle PD unit for: measuring thefirst and second voltage signals, and determining a position of the vehicle unit relative to the ground unit based on the measuredfirst and second voltage signals. 60. The method of any of items 49 to 59, wherein thefirst and second magneticfield signals are used by the vehicle PD unit for: determining a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determining the position and orientation of the vehicle unit relative to the ground unit. 61. A method of controlling a vehicle unit for electric vehicle charging, the vehicle unit comprising a vehicle position detection, PD, unit, wherein the method comprises: receiving, by the vehicle PD unit,first and second magneticfield signals from a ground PD unit, wherein:thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axis direction, thefirst magneticfield signal is a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, thefirst magneticfield signal is present in on-intervals and substantially absent in off- intervals, and the second magneticfield signal is received during off-intervals of thefirst magneticfield signal; and determining, by the vehicle PD unit, a positional relationship between the vehicle unit and the ground unit based on thefirst and second magneticfield signals. 62. The method of item 61, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space. 63. The method of item 61 or item 62, wherein thefirst and second magneticfield signals are transmitted in quadrature and at a same carrier frequency. 64. The method of any of items 61 to 63, wherein: presence of thefirst magneticfield signal during on-intervals represents a binary one; and substantial absence of thefirst magneticfield signal during off-intervals represents a binary zero. 65. The method of any of items 61 to 64, wherein a phase of the second magneticfield signal alternates betweenfirst and second phases across successive off-intervals of thefirst magneticfield signal. 66. The method of item 65, wherein thefirst phase differs from the second phase by 180 degrees. 67. The method of item 65, wherein thefirst phase is 90 degrees and the second phase is 270 degrees compared to a phase of thefirst magneticfield signal.68. The method of any of items 61 to 67, wherein a magnitude of the second magneticfield signal is less than a magnitude of thefirst magneticfield signal. 69. The method of any of items 61 to 68, wherein the binary modulated carrier signal is Manchester encoded. 70. The method of any of items 61 to 69, wherein the binary modulated carrier signal conveys data. 71. The method of any of items 61 to 70, wherein: thefirst magneticfield signal induces afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal induces a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the determining comprises: measuring thefirst and second voltage signals, and determining a position of the vehicle unit relative to the ground unit based on the measuredfirst and second voltage signals. 72. The method of any of items 61 to 71, wherein the determining comprises: determining a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determining the position and orientation of the vehicle unit relative to the ground unit. 73. A vehicle unit for electric vehicle charging, the vehicle unit comprising a vehicle position detection, PD, unit, configured to: acquire a multi-parking space layout for a plurality of parking spaces and a frequency re-use pattern for transmission of beacon signals; receive afirst beacon signal at afirst frequency from afirst ground unit disposed in afirst parking space from among the plurality of parking spaces; receive a second beacon signal at a second frequency from a second ground unit disposed in a second parking space from among the plurality of parking spaces; determine afirst distance between the vehicle unit and thefirst ground unit based on a magnitude of thefirst beacon signal using a magnitude vs distance function;determine a second distance between the vehicle unit and the second ground unit based on a magnitude of the second beacon signal using the magnitude vs distance function; and determine a positional relationship between the vehicle unit and thefirst ground unit based on the determined distances, the acquired multi-parking space layout, and the acquired frequencyre-use pattern, wherein the positional relationship is determined using lateration.74. The vehicle unit of item 73, wherein the vehicle PD unit is configured to: receive a third beacon signal at a third frequency from a third ground unit disposed in a third parking space from among the plurality of parking spaces, wherein the second and third ground units are disposed on opposite sides of thefirst ground unit; and determine a third distance between the vehicle unit and the third ground unit based on a magnitude of the third beacon signal using the magnitude vs distance function, wherein the positional relationship is determined using trilateration. 75. The vehicle unit of item 73 or item 74, wherein the vehicle PD unit is configured to: receive a fourth beacon signal at a fourth frequency from a fourth ground unit disposed in a fourth parking space, from among the plurality of parking spaces, adjacent to one of the second and third parking spaces; and determine a fourth distance between the vehicle unit and the fourth ground unit based on a magnitude of the fourth beacon signal, wherein the positional relationship is determined using multilateration. 76. The vehicle unit of any of items 73 to 75, wherein the multi-parking space layout is a predetermined parking space layout and the frequency re-use pattern is a predetermined frequency re-use pattern. 77. The vehicle unit of any of items 73 to 76, wherein the multi-parking space layout and the frequency re-use pattern are communicated to the vehicle PD unit via a radio network. 78. The vehicle unit of any of items 73 to 77, wherein the vehicle PD unit is further configured to: determine a global position of the vehicle unit using a global positioning system; and select one of a set of predetermined multi-parking space layouts and frequency re-use patterns based on the determined global position.79. The vehicle unit of any of items 73 to 78, wherein the multi-parking space layout includes a parking space width. 80. The vehicle unit of any of items 75 to 78, wherein: the multi-parking space layout is used to determine a parking space width; and the vehicle PD unit is configured to determine the parking space width using overdetermination of multilateration. 81. The vehicle unit of item 80, wherein the vehicle PD unit is configured to: determine distances between the vehicle unit and the respective ground units at two or more vehicle positions as the vehicle unit moves along a trajectory towards thefirst ground unit; and determine the parking space width based on the distances determined at the two or more positions. 82. The vehicle unit of any of items 73 to 81, wherein the beacon signals are magneticfield signals. 83. The vehicle unit of item 82, wherein the vehicle PD unit comprises one or more receiver coils; the magneticfield signals induce respective voltage signals into the one or more receiver coils; and the vehicle PD unit is configured to: measure the voltage signals; and determine at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals. 84. The vehicle unit of any of items 73 to 81, wherein: thefirst beacon signal is received by the vehicle PD unit asfirst and second magneticfield signals from thefirst ground unit; the second beacon signal is received by the vehicle PD unit asfirst and second magneticfield signal from an adjacent ground unit; thefirst magneticfield signals result from a magnetic moment in afirst axis direction of the ground units; andthe second magneticfield signals result from a magnetic moment in a second axis direction of the ground units. 85. The vehicle unit of item 84, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space. 86. The vehicle unit of item 84 or item 85, wherein: the vehicle PD unit comprises one or more receiver coils; thefirst magneticfield signals induce respectivefirst voltage signals into the one or more receiver coils; the second magneticfield signals induce respective second voltage signals into the one or more receiver coils; and the vehicle PD unit is configured to: measure thefirst and second voltage signals; and determine at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measuredfirst and second voltage signals. 87. Afirst ground unit, from among a set of ground units, for electric vehicle charging, thefirst ground unit comprising afirst ground PD unit, wherein the set of ground units are configured according to a frequency re-use pattern, and thefirst ground PD unit is configured to: transmit, for use by a vehicle PD unit to determine a positional relationship between a vehicle unit and thefirst ground unit using lateration: the frequency re-use pattern for transmitting afirst beacon signal by thefirst ground unit disposed in afirst parking space from, among a plurality of parking spaces, and for transmitting a second beacon signal by a second ground unit, from among the set of ground units, disposed in a second parking space, from among the plurality of parking spaces; and a multi-parking space layout for the plurality of parking spaces. 88. Thefirst ground unit of item 87, wherein the multi-parking space layout is a predetermined parking space layout and the frequency re-use pattern is a predetermined frequency re-use pattern. 89. Thefirst ground unit of item 87 or item 88, wherein the multi-parking space layout and the frequency re-use pattern are transmitted to the vehicle PD unit via a radio network.90. Thefirst ground unit of any of items 87 to 89, wherein the multi-parking space layout includes a parking space width. 91. Thefirst ground unit of any of items 87 to 90, wherein: the multi-parking space layout is used to determine a parking space width; and the parking space width is determined by the vehicle PD unit using overdetermination. 92. Thefirst ground unit of any of items 87 to 91, wherein the beacon signals are magneticfield signals. 93. Thefirst ground unit of item 92, wherein: the magneticfield signals induce respective voltage signals into one or more receiver coils of the vehicle PD unit; and the magneticfield signals are used by the vehicle PD unit to: measure the voltage signals; and determine at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals. 94. A wireless power transfer, WPT, system for electric vehicle charging, the WPT system comprising: afirst ground unit disposed in afirst parking space from among a plurality of parking spaces, wherein thefirst ground unit comprises afirst ground position detection, PD, unit; a second ground unit disposed in a second parking space from among the plurality of parking spaces, wherein the second ground unit comprises a second ground PD unit; and a vehicle unit comprising a vehicle PD unit, wherein: thefirst ground PD unit is configured to transmit afirst beacon signal at afirst frequency to be used by the vehicle PD unit to determine a positional relationship between the vehicle unit and thefirst ground unit; the second ground PD unit is configured to transmit a second beacon signal at a second frequency to be used by the vehicle PD unit to determine the positional relationship between the vehicle unit and thefirst ground unit; and the vehicle PD unit is configured to: receive thefirst beacon signal transmitted at thefirst frequency by thefirst ground PD unit;receive the second beacon signal transmitted at the second frequency by the second ground PD unit; acquire a multi-parking space layout for the plurality of parking spaces and a frequency re-use pattern for transmission of the beacon signals; determine afirst distance between the vehicle unit and thefirst ground unit based on a magnitude of thefirst beacon signal using a magnitude vs distance function; determine a second distance between the vehicle unit and the second ground unit based on a magnitude of the second beacon signal using the magnitude vs distance function; and determine the positional relationship between the vehicle unit and thefirst ground unit based on the determined distances, the acquired multi-parking space layout, and the acquired frequency re-use pattern, wherein the positional relationship is determined using lateration. 95. The WPT system of item 94, wherein the vehicle PD unit is configured to: receive a third beacon signal at a third frequency from a third ground unit disposed in a third parking space from among the plurality of parking spaces, wherein the second and third ground units are disposed on opposite sides of thefirst ground unit; and determine a third distance between the vehicle unit and the third ground unit based on a magnitude of the third beacon signal using the magnitude vs distance function, wherein the positional relationship is determined using trilateration. 96. The WPT system of item 94 or item 95, wherein the vehicle PD unit is configured to: receive a fourth beacon signal at a fourth frequency from a fourth ground unit disposed in a fourth parking space, from among the plurality of parking spaces, adjacent to one of the second and third parking spaces; and determine a fourth distance between the vehicle unit and the fourth ground unit based on a magnitude of the fourth beacon signal, wherein the positional relationship is determined using multilateration. 97. The WPT system of any of items 94 to 96, wherein the multi-parking space layout is a predetermined parking space layout and the frequency re-use pattern is a predetermined frequency re-use pattern.98. The WPT system of any of items 94 to 97, wherein the multi-parking space layout and the frequency re-use pattern are communicated to the vehicle PD unit via a radio network. 99. The WPT system of any of items 94 to 98, wherein the vehicle PD unit is further configured to: determine a global position of the vehicle unit using a global positioning system; and select one of a set of predetermined multi-parking space layouts and frequency re-use patterns based on the determined global position. 100. The WPT system of any of items 94 to 99, wherein the multi-parking space layout includes a parking space width. 101. The WPT system of any of items 96 to 99, wherein: the multi-parking space layout is used to determine a parking space width; and the vehicle PD unit is configured to determine the parking space width using overdetermination of multilateration. 102. The WPT system of item 101, wherein the vehicle PD unit is configured to: determine distances between the vehicle unit and the respective ground units at two or more vehicle positions as the vehicle unit moves along a trajectory towards thefirst ground unit; and determine the parking space width based on the distances determined at the two or more positions. 103. The WPT system of any of items 94 to 102, wherein the beacon signals are magneticfield signals. 104. The WPT system of item 103, wherein the vehicle PD unit comprises one or more receiver coils; the magneticfield signals induce respective voltage signals into the one or more receiver coils; and the vehicle PD unit is configured to: measure the voltage signals; and determine at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals.105. The WPT system of any of items 94 to 102, wherein: thefirst beacon signal is received by the vehicle PD unit asfirst and second magneticfield signals from thefirst ground unit; the second beacon signal is received by the vehicle PD unit asfirst and second magneticfield signals from an adjacent ground unit; thefirst magneticfield signals result from a magnetic moment in afirst axis direction of the ground units; and the second magneticfield signals result from a magnetic moment in a second axis direction of the ground units. 106. The WPT system of item 105, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space. 107. The WPT system of item 105 or item 106, wherein: the vehicle PD unit comprises one or more receiver coils; thefirst magneticfield signals induce respectivefirst voltage signals into the one or more receiver coils; the second magneticfield signals induce respective second voltage signals into the one or more receiver coils; and the vehicle PD unit is configured to: measure thefirst and second voltage signals; and determine at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measuredfirst and second voltage signals. 108. A method of controlling a wireless power transfer, WPT, system for electric vehicle charging, the WPT system comprising: afirst ground unit disposed in afirst parking space from among a plurality of parking spaces, wherein thefirst ground unit comprises afirst ground position detection, PD, unit; a second ground unit disposed in a second parking space from among the plurality of parking spaces, wherein the second ground unit comprises a second ground PD unit; and a vehicle unit comprising a vehicle PD unit, wherein the method comprises:transmitting, by thefirst ground PD unit, afirst beacon signal at afirst frequency to be used by the vehicle PD unit to determine a positional relationship between the vehicle unit and thefirst ground unit; transmitting, by the second ground PD unit, a second beacon signal at a second frequency to be used by the vehicle PD unit to determine the positional relationship between the vehicle unit and thefirst ground unit; receiving, by the vehicle PD unit, thefirst beacon signal from thefirst ground PD unit; receiving, by the vehicle PD unit, the second beacon signals from the second ground PD unit; acquiring, by the vehicle PD unit, a multi-parking space layout for the plurality of parking spaces and a frequency re-use pattern for transmission of the beacon signals; determining, by the vehicle PD unit, afirst distance between the vehicle PD unit and thefirst ground PD unit based on a magnitude of thefirst beacon signal using a magnitude vs distance function; determining, by the vehicle PD unit, a second distance between the vehicle PD unit and the second ground PD unit based on a magnitude of the second beacon signal using the magnitude vs distance function; and determining, by the vehicle PD unit, a positional relationship between the vehicle unit and thefirst ground unit based on the determined distances, the acquired multi-parking space layout,and the acquired frequency re-use pattern, wherein the positional relationship is determined usinglateration positioning. 109. The method of item 108, wherein to the method comprises: receiving, by the vehicle PD unit, a third beacon signal at a third frequency from a third ground unit disposed in a third parking space from among the plurality of parking spaces, wherein the second and third ground units are disposed on opposite sides of thefirst ground unit; and determining, by the vehicle PD unit, a third distance between the vehicle unit and the third ground unit based on a magnitude of the third beacon signal using the magnitude vs distance function, wherein the positional relationship is determined using trilateration. 110. The method of item 108 or item 109, wherein the method comprises: receiving, by the vehicle PD unit, a fourth beacon signal at a fourth frequency from a fourth ground unit disposed in a fourth parking space, from among the plurality of parking spaces, adjacent to one of the second and third parking spaces; anddetermining, by the vehicle PD unit, a fourth distance between the vehicle unit and the fourth ground unit based on a magnitude of the fourth beacon signal, wherein the positional relationship is determined using multilateration. 111. The method of any of items 108 to 110, wherein the multi-parking space layout is a predetermined parking space layout and the frequency re-use pattern is a predetermined frequency re-use pattern. 112. The method of any of items 108 to 111, wherein the multi-parking space layout and the frequency re-use pattern are communicated to the vehicle PD unit via a radio network. 113. The method of any of items 108 to 112, wherein the method comprises: determining, by the vehicle PD unit, a global position of the vehicle unit using a global positioning system; and selecting, by the vehicle PD unit, one of a set of predetermined multi-parking space layouts and frequency re-use patterns based on the determined global position. 114. The method of any of items 108 to 113, wherein the multi-parking space layout includes a parking space width. 115. The method of any of items 110 to 114, wherein: the multi-parking space layout is used to determine a parking space width; and the method comprises: determining, by the vehicle PD unit, the parking space width using overdetermination of multilateration. 116. The method of item 115, wherein the method comprises: determining, by the vehicle PD unit, distances between the vehicle unit and the respective ground units at two or more vehicle positions as the vehicle unit moves along a trajectory towards thefirst ground unit; and determining, by the vehicle PD unit, the parking space width based on the distances determined at the two or more positions.117. The method of any of items 108 to 116, wherein the beacon signals are magneticfield signals. 118. The method of item 117, wherein the vehicle PD unit comprises one or more receiver coils; the magneticfield signals induce respective voltage signals into the one or more receiver coils; and the method comprises: measuring, by the vehicle PD unit, the voltage signals; and determining, by the vehicle PD unit, at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals. 119. The method of any of items 108 to 116, wherein: thefirst beacon signal is received by the vehicle PD unit asfirst and second magneticfield signals from thefirst ground unit; the second beacon signal is received by the vehicle PD unit asfirst and second magneticfield signal from an adjacent ground unit; thefirst magneticfield signals result from a magnetic moment in afirst axis direction of the ground units; and the second magneticfield signals result from a magnetic moment in a second axis direction of the ground unit. 120. The method of item 119, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space. 121. The method of item 119 or item 120, wherein: the vehicle PD unit comprises one or more receiver coils; thefirst magneticfield signals induce respectivefirst voltage signals into the one or more receiver coils; the second magneticfield signals induce respective second voltage signals into the one or more receiver coils; and the method comprises: measuring, by the vehicle PD unit, thefirst and second voltage signals; and determining, by the vehicle PD unit, at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measuredfirst and second voltage signals.122. A method of controlling a vehicle unit for electric vehicle charging, the vehicle unit comprising a vehicle position detection, PD, unit, the method comprising: acquiring a multi-parking space layout for a plurality of parking spaces and a frequency re- use pattern for transmission of beacon signals; receiving afirst beacon signal at afirst frequency from afirst ground unit disposed in afirst parking space from among the plurality of parking spaces; receiving a second beacon signal at a second frequency from a second ground unit disposed in a second parking space from among the plurality of parking spaces; determining afirst distance between the vehicle unit and thefirst ground unit based on a magnitude of thefirst beacon signal using a magnitude vs distance function; determining a second distance between the vehicle unit and the second ground unit based on a magnitude of the second beacon signal using the magnitude vs distance function; and determining a positional relationship between the vehicle unit and thefirst ground unit based on the determined distances, the acquired multi-parking space layout, and the acquired frequency re-use pattern, wherein the positional relationship is determined using lateration. 123. The method of item 122, wherein the method comprises: receiving, by the vehicle PD unit, a third beacon signal at a third frequency from a third ground unit disposed in a third parking space from among the plurality of parking spaces, wherein the second and third ground units are disposed on opposite sides of thefirst ground unit; and determining, by the vehicle PD unit, a third distance between the vehicle unit and the third ground unit based on a magnitude of the third beacon signal using the magnitude vs distance function, wherein the positional relationship is determined using trilateration. 124. The method of item 122 or item 123, wherein the method comprises: receiving, by the vehicle PD unit, a fourth beacon signal at a fourth frequency from a fourth ground unit disposed in a fourth parking space, from among the plurality of parking spaces, adjacent to one of the second and third parking spaces; and determining, by the vehicle PD unit, a fourth distance between the vehicle unit and the fourth ground unit based on a magnitude of the fourth beacon signal, wherein the positional relationship is determined using multilateration.125. The method of any of items 122 to 123, wherein the multi-parking space layout is a predetermined parking space layout and the frequency re-use pattern is a predetermined frequency re-use pattern. 126. The method of any of items 122 to 125, wherein the multi-parking space layout and the frequency re-use pattern are communicated to the vehicle PD unit via a radio network. 127. The method of any of items 122 to 126, wherein the method comprises: determining, by the vehicle PD unit, a global position of the vehicle unit using a global positioning system; and selecting, by the vehicle PD unit, one of a set of predetermined multi-parking space layouts and frequency re-use patterns based on the determined global position. 128. The method of any of items 122 to 127, wherein the multi-parking space layout includes a parking space width. 129. The method of any of items 124 to 127, wherein: the multi-parking space layout is used to determine a parking space width; and the method comprises: determining, by the vehicle PD unit, the parking space width using overdetermination of multilateration. 130. The method of item 129, wherein the method comprises: determining, by the vehicle PD unit, distances between the vehicle unit and the respective ground units at two or more vehicle positions as the vehicle unit moves along a trajectory towards thefirst ground unit; and determining, by the vehicle PD unit, the parking space width based on the distances determined at the two or more positions. 131. The method of any of items 122 to 130, wherein the beacon signals are magneticfield signals. 132. The method of item 131, wherein the vehicle PD unit comprises one or more receiver coils;the magneticfield signals induce respective voltage signals into the one or more receiver coils; and the method comprises: measuring, by the vehicle PD unit, the voltage signals; and determining, by the vehicle PD unit, at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals. 133. The method of any of items 122 to 130, wherein: thefirst beacon signal is received by the vehicle PD unit asfirst and second magneticfield signals from thefirst ground unit; the second beacon signal is received by the vehicle PD unit asfirst and second magneticfield signals from an adjacent ground unit; thefirst magneticfield signals result from a magnetic moment in afirst axis direction of the ground units; and the second magneticfield signals result from a magnetic moment in a second axis direction of the ground units. 134. The method of item 133, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space. 135. The method of item 133 or item 134, wherein: the vehicle PD unit comprises one or more receiver coils; thefirst magneticfield signals induce respectivefirst voltage signals into the one or more receiver coils; the second magneticfield signals induce respective second voltage signals into the one or more receiver coils; and the method comprises: measuring, by the vehicle PD unit, thefirst and second voltage signals; and determining, by the vehicle PF unit, at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measuredfirst and second voltage signals. 136. A method of controlling afirst ground unit, from among a set of ground units, for electric vehicle charging, thefirst ground unit comprising afirst ground position detection, PD, unit, wherein the set of ground units are configured according to a frequency re-use pattern, and the method comprises:transmitting, for use by a vehicle PD unit to determine a positional relationship between a vehicle unit and thefirst ground unit using lateration: the frequency re-use pattern for transmitting afirst beacon signal by thefirst ground unit disposed in afirst parking space from, among a plurality of parking spaces, and for transmitting a second beacon signal by a second ground unit, from among the set of ground units, disposed in a second parking space from, among the plurality of parking spaces; and a multi-parking space layout for the plurality of parking spaces. 137. The method of item 136, wherein the multi-parking space layout is a predetermined parking space layout and the frequency re-use pattern is a predetermined frequency re-use pattern. 138. The method of item 136 or item 137, wherein the multi-parking space layout and the frequency re-use pattern are transmitted to the vehicle PD unit via a radio network. 139. The method of any of items 136 to 138, wherein the multi-parking space layout includes a parking space width. 140. The method of any of items 136 to 139, wherein: the multi-parking space layout is used to determine a parking space width. 141. The method of any of items 136 to 140, wherein the beacon signals are magneticfield signals. 142. The method of item 141, wherein: the magneticfield signals induce respective voltage signals into one or more receiver coils of the vehicle PD unit for determining at least one of a position and an orientation of the vehicle unit relative to thefirst ground unit based on the measured voltage signals. 143. A ground unit for electric vehicle charging, the ground unit comprising a ground position detection, PD, unit, wherein: the ground PD unit is configured to: generate and transmit a modulated beacon signal for use by a vehicle PD unit to determine a position of a vehicle unit with respect to the ground unit, wherein: the modulated beacon signal comprises a time-series of pulses,a shape of the pulses is defined based on a pulse shape function, each pulse has a pulse magnitude selected from a set of pulse magnitudes, the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated by the pulse rate or an integer multiple thereof, the pulse shape function is configured to reduce emissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at each frequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide a spectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency. 144. The ground unit of item 143, wherein: the carrier signal comprises positional information of the ground unit; the modulated beacon signal comprises a residual carrier component of the carrier signal with a magnitude sufficient to determine the position of the vehicle PD unit; and the residual component is used by the vehicle PD unit to determine the position of the vehicle PD unit. 145. The ground unit of item 143 or item 144, wherein: the modulated beacon signal is afirst modulated beacon signal, the carrier signal is afirst carrier signal, and the carrier frequency of thefirst carrier signal is afirst frequency; thefirst frequency is different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal comprises pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal. 146. The ground unit of item 145, wherein both thefirst frequency and the second frequency are selected from the set of frequencies allocated within the predetermined frequency band. 147. The ground unit of item 145, wherein: the predetermined frequency band is afirst frequency band; andthe second frequency is selected from another set of frequencies allocated within a second frequency band different than thefirst frequency band. 148. The ground unit of any of items 143 to 147, wherein the modulated beacon signal conveys data intended to be received and demodulated by the vehicle PD unit. 149. The ground unit of any of items 143 to 148, wherein the pulse shape function provides a signal-to-inter-symbol interference ratio greater than 20 dB. 150. The ground unit of any of items 143 to 149, wherein the pulse shape function is a raised- cosine function in the time domain. 151. The ground unit of item 150, wherein: the raised-cosine function comprises an adjustment factor; and the ground PD unit is configured to define the shape of the pulses based on the adjustment factor. 152. The ground unit of any of items 143 to 151, wherein the set of pulse magnitudes comprises a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero. 153. The ground unit of any of items 143 to 152, wherein the spectral notch is devoid of frequency components of the modulated beacon signal. 154. The ground unit of any of items 143 to 153, wherein the time-series of pulses is encoded using Manchester coding. 155. A vehicle unit for electric vehicle charging, the vehicle unit comprising a vehicle position detection, PD, unit, configured to receive a modulated beacon signal from a ground PD unit of a ground unit and determine a position of the vehicle unit with respect to the ground unit based on the modulated beacon signal, wherein: the modulated beacon signal comprises a time-series of pulses, a shape of the pulses is defined based on a pulse shape function, each pulse has a pulse magnitude selected from a set of pulsemagnitudes, the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated by the pulse rate or an integer multiple thereof, the pulse shape function is configured to reduce emissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at each frequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide a spectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency. 156. The vehicle unit of item 155, wherein: the carrier signal comprises positional information of the ground unit; the modulated beacon signal comprises a residual carrier component of the carrier signal with a magnitude sufficient to determine the position of the vehicle PD unit; and the residual component is used by the vehicle PD unit to determine the position of the vehicle PD unit. 157. The vehicle unit of item 155 or item 156, wherein: the modulated beacon signal is afirst modulated beacon signal, the carrier signal is afirst carrier signal, and the carrier frequency of thefirst carrier signal is afirst frequency; thefirst frequency is different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal comprises pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal. 158. The vehicle unit of item 157, wherein both thefirst frequency and the second frequency are selected from the set of frequencies allocated within the predetermined frequency band. 159. The vehicle unit of item 157, wherein: the predetermined frequency band is afirst frequency band; andthe second frequency is selected from another set of frequencies allocated within a second frequency band different than thefirst frequency band. 160. The vehicle unit of any of items 155 to 159, wherein the modulated beacon signal conveys data intended to be received and demodulated by the vehicle PD unit. 161. The vehicle unit of any of items 155 to 160, wherein the pulse shape function provides a signal-to-inter-symbol interference ratio greater than 20 dB. 162. The vehicle unit of any of items 155 to 161, wherein the pulse shape function is a raised- cosine function in the time domain. 163. The vehicle unit of item 162, wherein: the raised-cosine function comprises an adjustment factor; and the shape of the pulses is based on the adjustment factor. 164. The vehicle unit of any of items 155 to 163, wherein the set of pulse magnitudes comprises a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero. 165. The vehicle unit of any of items 155 to 163, wherein the spectral notch is devoid of frequency components of the modulated beacon signal. 166. The vehicle unit of any of items 155 to 165, wherein the time-series of pulses is encoded using Manchester coding. 167. A wireless power transfer, WPT, system for electric vehicle charging, the WPT system comprising: a ground unit comprising a ground position detection, PD, unit and a vehicle unit comprising a vehicle PD unit, wherein the ground PD unit is configured to: generate and transmit a modulated beacon signal for use by the vehicle PD unit to determine a position of the vehicle unit with respect to the ground unit, wherein: the modulated beacon signal comprises a time-series of pulses, a shape of the pulses is defined based on a pulse shape function, each pulse has a pulse magnitude selected from a set of pulse magnitudes,the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated by the pulse rate or an integer multiple thereof, the pulse shape function is configured to reduce emissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at each frequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide a spectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency, and wherein the vehicle PD unit is configured to: receive a modulated beacon signal to determine the position of the vehicle unit with respect to the ground unit. 168. The WPT system of item 167, wherein: the carrier signal comprises positional information of the ground unit; the modulated beacon signal comprises a residual carrier component of the carrier signal with a magnitude sufficient to determine the position of the vehicle PD unit; and the residual component is used by the vehicle PD unit to determine the position of the vehicle PD unit. 169. The WPT system of item 167 or item 168, wherein: the modulated beacon signal is afirst modulated beacon signal, the carrier signal is afirst carrier signal, and the carrier frequency of thefirst carrier signal is afirst frequency; thefirst frequency is different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal comprises pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal. 170. The WPT system of item 169, wherein both thefirst frequency and the second frequency are selected from the set of frequencies allocated within the predetermined frequency band. 171. The WPT system of item 169, wherein:the predetermined frequency band is afirst frequency band; and the second frequency is selected from another set of frequencies allocated within a second frequency band different than thefirst frequency band. 172. The WPT system of any of items 167 to 171, wherein the modulated beacon signal conveys data intended to be received and demodulated by the vehicle PD unit. 173. The WPT system of any of items 167 to 172, wherein the pulse shape function provides a signal-to-inter-symbol interference ratio greater than 20 dB. 174. The WPT system of any of items 167 to 173, wherein the pulse shape function is a raised- cosine function in the time domain. 175. The WPT system of item 174, wherein: the raised-cosine function comprises an adjustment factor; and the ground PD unit is configured to define the shape of the pulses based on the adjustment factor. 176. The WPT system of any of items 167 to 175, wherein the set of pulse magnitudes comprises a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero. 177. The WPT system of any of items 167 to 176, wherein the spectral notch is devoid of frequency components of the modulated beacon signal. 178. The WPT system of any of items 167 to 177, wherein the time-series of pulses is encoded using Manchester coding. 179. A method of controlling a wireless power transfer, WPT, system for electric vehicle charging, the WPT system comprising a ground unit comprising a ground position detection, PD, unit and a vehicle unit comprising a vehicle PD unit, wherein the method comprises: generating and transmitting, by the ground PD unit, a modulated beacon signal for use by the vehicle PD unit to determine a position of the vehicle unit with respect to the ground unit, wherein:the modulated beacon signal comprises a time-series of pulses, a shape of the pulses is defined based on a pulse shape function, each pulse has a pulse magnitude selected from a set of pulse magnitudes, the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated by the pulse rate or an integer multiple thereof, the pulse shape function is configured to reduce emissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at each frequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide a spectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency; and receiving, by the vehicle PD unit, a modulated beacon signal to determine the position of the vehicle unit with respect to the ground unit. 180. The method of item 179, wherein: the carrier signal comprises positional information of the ground unit; the modulated beacon signal comprises a residual carrier component of the carrier signal with a magnitude sufficient to determine the position of the vehicle PD unit; and the residual component is used by the vehicle PD unit to determine the position of the vehicle PD unit. 181. The method of item 179 or item 180, wherein: the modulated beacon signal is afirst modulated beacon signal, the carrier signal is afirst carrier signal, and the carrier frequency of thefirst carrier signal is afirst frequency; thefirst frequency is different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal comprises pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal. 182. The method of item 181, wherein both thefirst frequency and the second frequency are selected from the set of frequencies allocated within the predetermined frequency band.183. The method of item 181, wherein: the predetermined frequency band is afirst frequency band; and the second frequency is selected from another set of frequencies allocated within a second frequency band different than thefirst frequency band. 184. The method of any of items 179 to 183, wherein the modulated beacon signal conveys data intended to be received and demodulated by the vehicle PD unit. 185. The method of any of items 179 to 184, wherein the pulse shape function provides a signal- to-inter-symbol interference ratio greater than 20 dB. 186. The method of any of items 179 to 185, wherein the pulse shape function is a raised-cosine function in the time domain. 187. The method of item 186, wherein: the raised-cosine function comprises an adjustment factor; and the method comprises: defining, by the ground PD unit, the shape of the pulses based on the adjustment factor. 188. The method of any of items 179 to 187, wherein the set of pulse magnitudes comprises a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero. 189. The method of any of items 179 to 188, wherein the spectral notch is devoid of frequency components of the modulated beacon signal. 190. The method of any of items 179 to 189, wherein the time-series of pulses is encoded using Manchester coding. 191. A method of controlling a ground unit for electric vehicle charging, the ground unit comprising a ground position detection, PD, unit, the method comprising: generating and transmitting a modulated beacon signal for use by a vehicle PD unit to determine a position of a vehicle unit with respect to the ground unit, wherein:the modulated beacon signal comprises a time-series of pulses, a shape of the pulses is defined based on a pulse shape function, each pulse has a pulse magnitude selected from a set of pulse magnitudes, the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated by the pulse rate or an integer multiple thereof, the pulse shape function is configured to reduce emissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at each frequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide a spectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency. 192. The method of item 191, wherein: the carrier signal comprises positional information of the ground unit; the modulated beacon signal comprises a residual carrier component of the carrier signal with a magnitude sufficient to determine the position of the vehicle PD unit; and the residual component is used by the vehicle PD unit to determine the position of the vehicle PD unit. 193. The method of item 191 or item 192, wherein: the modulated beacon signal is afirst modulated beacon signal, the carrier signal is afirst carrier signal, and the carrier frequency of thefirst carrier signal is afirst frequency; thefirst frequency is different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal comprises pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal. 194. The method of item 193, wherein both thefirst frequency and the second frequency are selected from the set of frequencies allocated within the predetermined frequency band. 195. The method of item 193, wherein:the predetermined frequency band is afirst frequency band; and the second frequency is selected from another set of frequencies allocated within a second frequency band different than thefirst frequency band. 196. The method of any of items 191 to 195, wherein the modulated beacon signal conveys data intended to be received and demodulated by the vehicle PD unit. 197. The method of any of items 191 to 196, wherein the pulse shape function provides a signal- to-inter-symbol interference ratio greater than 20 dB. 198. The method of any of items 191 to 197, wherein the pulse shape function is a raised-cosine function in the time domain. 199. The method of item 198, wherein: the raised-cosine function comprises an adjustment factor; and the method comprises: defining, by the ground PD unit, the shape of the pulses based on the adjustment factor. 200. The method of any of items 191 to 199, wherein the set of pulse magnitudes comprises a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero. 201. The method of any of items 191 to 200, wherein the spectral notch is devoid of frequency components of the modulated beacon signal. 202. The method of any of items 191 to 200, wherein the time-series of pulses is encoded using Manchester coding. 203. A method of controlling a vehicle unit for electric vehicle charging, the vehicle unit comprising a vehicle position detection, PD, unit, the method comprising: receiving a modulated beacon signal from a ground PD unit of a ground unit; and determining a position of the vehicle unit with respect to the ground unit based on the modulated beacon signal, wherein: the modulated beacon signal comprises a time-series of pulses, a shape of the pulses is defined based on a pulse shape function,each pulse has a pulse magnitude selected from a set of pulse magnitudes, the pulses are modulated on a carrier signal having a carrier frequency selected from a set of frequencies allocated within a predetermined frequency band, the pulses are transmitted at a pulse rate, the frequencies are separated by the pulse rate or an integer multiple thereof, the pulse shape function is configured to reduce emissions of the ground PD unit at frequencies outside of the predetermined frequency band compared to a rectangular pulse configured to provide a spectral notch at each frequency allocated within the same predetermined frequency band excluding a corresponding carrier frequency, and the pulse shape function is configured to provide a spectral notch at each frequency allocated within the predetermined frequency band excluding the carrier frequency. 204. The method of item 203, wherein: the carrier signal comprises positional information of the ground unit; the modulated beacon signal comprises a residual carrier component of the carrier signal with a magnitude sufficient to determine the position of the vehicle PD unit; and the method comprises: determining, by the vehicle PD unit, the position of the vehicle PD unit based on the residual component. 205. The method of item 203 or item 204, wherein: the modulated beacon signal is afirst modulated beacon signal, the carrier signal is afirst carrier signal, and the carrier frequency of thefirst carrier signal is afirst frequency; thefirst frequency is different than a second frequency selected for a second carrier signal of a second modulated beacon signal concurrently transmitted by another ground unit near the ground unit; and the second modulated beacon signal comprises pulses with a shape defined based on the same pulse shape function as used for thefirst modulated beacon signal. 206. The method of item 205, wherein both thefirst frequency and the second frequency are selected from the set of frequencies allocated within the predetermined frequency band. 207. The method of item 205, wherein:the predetermined frequency band is afirst frequency band; and the second frequency is selected from another set of frequencies allocated within a second frequency band different than thefirst frequency band. 208. The method of any of items 203 to 207, wherein the modulated beacon signal conveys data intended to be received and demodulated by the vehicle PD unit. 209. The method t of any of items 203 to 208, wherein the pulse shape function provides a signal- to-inter-symbol interference ratio greater than 20 dB. 210. The method of any of items 203 to 209, wherein the pulse shape function is a raised-cosine function in the time domain. 211. The method of item 210, wherein: the raised-cosine function comprises an adjustment factor; and the shape of the pulses is based on the adjustment factor. 212. The method of any of items 203 to 211, wherein the set of pulse magnitudes comprises a non-zero-magnitude and a zero-magnitude that represent a binary set comprising a logical one and a logical zero. 213. The method of any of items 203 to 212, wherein the spectral notch is devoid of frequency components of the modulated beacon signal. 214. The method of any of items 203 to 213, wherein the time-series of pulses is encoded using Manchester coding.

Claims

1. What is claimed is:

1. A ground unit for charging an electric vehicle, the ground unit comprising a ground position detection, PD, unit, wherein: the ground PD unit is configured to transmitfirst and second magneticfield signals to be used by a vehicle PD unit to determine a positional relationship between a vehicle unit and the ground unit based on thefirst and second magneticfield signals, wherein thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axis direction; thefirst magneticfield signal is a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on- intervals and substantially absent in off-intervals; and the second magneticfield signal is transmitted during off-intervals of thefirst magneticfield signal.

2. The ground unit of claim 1, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space.

3. The ground unit of claim 1 or claim 2, wherein thefirst and second magneticfield signals are transmitted in quadrature and at a same carrier frequency.

4. The ground unit of any preceding claim, wherein: presence of thefirst magneticfield signal during on-intervals represents a binary one; and substantial absence of thefirst magneticfield signal during off-intervals represents a binary zero.

5. The ground unit of any preceding claim, wherein a phase of the second magneticfield signal alternates betweenfirst and second phases across successive off-intervals of thefirst magneticfield signal.

6. The ground unit of claim 5, wherein thefirst phase differs from the second phase by 180 degrees.

7. The ground unit of claim 5, wherein thefirst phase is 90 degrees and the second phase is 270 degrees compared to a phase of thefirst magneticfield signal.

8. The ground unit of any preceding claim, wherein a magnitude of the second magneticfield signal is less than a magnitude of thefirst magneticfield signal.

9. The ground unit of any preceding claim, wherein the binary modulated carrier signal is Manchester encoded.

10. The ground unit of any preceding claim, wherein the binary modulated carrier signal conveys data.

11. The ground unit of any preceding claim, wherein: thefirst magneticfield signal induces afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal induces a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the inducedfirst and second voltages are used by the vehicle PD unit to: measure thefirst and second voltage signals, and determine a position of the vehicle unit relative to the ground unit based on the measuredfirst and second voltage signals.

12. The ground unit of any preceding claim, wherein thefirst and second magneticfield signals are used by the vehicle PD unit to: determine a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determine the position and orientation of the vehicle unit relative to the ground unit.

13. A vehicle unit for electric vehicle charging, the vehicle unit comprising a vehicle position detection, PD, unit, wherein: the vehicle PD unit is configured to receivefirst and second magneticfield signals from a ground PD unit and determine a positional relationship between the vehicle unit and the ground unit based on thefirst and second magneticfield signals, wherein thefirst magneticfield signal resultsfrom a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axis direction; thefirst magneticfield signal is a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on- intervals and substantially absent in off-intervals; and the second magneticfield signal is received during off-intervals of thefirst magneticfield signal.

14. The vehicle unit of claim 13, wherein thefirst axis direction corresponds to a longitudinal axis direction of a parking space.

15. The vehicle unit of claim 13 or claim 14, wherein thefirst and second magneticfield signals are transmitted in quadrature and at a same carrier frequency.

16. The vehicle unit of any of claims 13 to 15, wherein: presence of thefirst magneticfield signal during on-intervals represents a binary one; and substantial absence of thefirst magneticfield signal during off-intervals represents a binary zero.

17. The vehicle unit of any of claims 13 to 15, wherein a phase of the second magneticfield signal alternates betweenfirst and second phases across successive off-intervals of thefirst magnetic field signal.

18. The vehicle unit of claim 17, wherein thefirst phase differs from the second phase by 180 degrees.

19. The vehicle unit of claim 17, wherein thefirst phase is 90 degrees and the second phase is 270 degrees compared to a phase of thefirst magneticfield signal.

20. The vehicle unit of any of claims 13 to 19, wherein a magnitude of the second magneticfield signal is less than a magnitude of thefirst magneticfield signal.

21. The vehicle unit of any of claims 13 to 20, wherein the binary modulated carrier signal is Manchester encoded.

22. The vehicle unit of any of claims 13 to 21, wherein the binary modulated carrier signal conveys data.

23. The vehicle unit of any of claims 13 to 22, wherein: thefirst magneticfield signal induces afirst voltage signal into one or more receiver coils of the vehicle PD unit; the second magneticfield signal induces a second voltage signal into the one or more receiver coils of the vehicle PD unit; and the vehicle PD unit is configured to use the inducedfirst and second voltages to: measure thefirst and second voltage signals, and determine a position of the vehicle unit relative to the ground unit based on the measuredfirst and second voltage signals.

24. The vehicle unit of any of claims 13 to 23, wherein the vehicle PD unit is configured to use thefirst and second magneticfield signals to: determine a magnitude and an angle of each of thefirst and second magneticfield signals with respect to an orientation of the vehicle unit; and determine the position and orientation of the vehicle unit relative to the ground unit.

25. A wireless power transfer, WPT, system for electric vehicle charging, the WPT system comprising: a ground unit comprising a ground position detection, PD, unit and a vehicle unit comprising a vehicle PD unit, wherein: the ground PD unit is configured to transmitfirst and second magneticfield signals to the vehicle PD unit, wherein thefirst magneticfield signal results from a magnetic moment in afirst axis direction and the second magneticfield signal results from a magnetic moment in a second axis direction that is perpendicular to thefirst axis direction; thefirst magneticfield signal is a binary modulated carrier signal modulated according to an on-off keying, OOK, modulation scheme, wherein thefirst magneticfield signal is present in on- intervals and substantially absent in off-intervals; the second magneticfield signal is transmitted during off-intervals of thefirst magneticfield signal; the vehicle PD unit is configured to receive thefirst and second magneticfield signals; andthe vehicle PD unit is configured to determine a positional relationship between the vehicle unit and the ground unit based on thefirst and second magneticfield signals.

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