Method and configuration for determining at least one distance between antennas

Abstract

A method for determining at least one distance between antenna pairs. The method includes self-measurement, a first bi-directional transmission at a first time interval, a first uni-directional transmission at a second time interval, a second bi-directional transmission at a third time interval, and a second uni-directional transmission at a fourth time interval. The method also includes determining phase information based on the performed transmissions and determining distance information regarding the at least one distance.

Description

Technical Field

[0001] The present invention generally relates to wireless communication and distance measurement. More specifically, the present invention relates to determining at least one distance between a pair of antennas based on a plurality of transmissions performed at selected time intervals. Background of the Invention

[0002] Distance measurement may generally be utilized for various useful applications. For example, the distance between one or more transmitting devices and a receiving device may be determined and used for positioning purposes. When high positioning accuracy is required, such as in a Real-Time Kinematic (RTK) Global Navigation Satellite System (GNSS), methods involving the measurement of the phase of the received signal are used.

[0003] Conventional wireless positioning methods, such as GNSS and Long Range Navigation (LORAN), utilize only downlink or one-way transmissions. Therefore, signals are transmitted only unidirectionally from a transmitter (e.g., a satellite) to a receiver (e.g., a ground mobile unit). In such carrier phase techniques, to achieve high precision, it is necessary to measure the relative phase between signals received from a plurality of different transmitters. Additionally, it is necessary to solve the integer ambiguity (IA) problem (e.g., RTK in GNSS, etc.). A rapid solution (not in minutes but in seconds, etc.) of the IA problem in RTK GNSS requires interference-free simultaneous reception from a large number of transmitters (satellites). This is generally impossible in a complete ground measurement system because dozens of pseudo-satellites / access points / base stations need to be visible in the Line of Sight (LOS) simultaneously. Also, in satellite-based solutions, obstacles in the sky direction of the line of sight and reflections of radio waves from buildings in large cities, etc., also significantly degrade the measurement accuracy and the information obtained therefrom.

[0004] The most accurate wireless distance measurements are still generally based on carrier phase technology. However, to directly measure the distance between two wireless units (wireless links) using such technology, it is necessary for the wireless units to be completely phase coherent in advance, which can be costly in terms of setup. This is especially true when cables are required or when bidirectional transmission is used. Note that by having each wireless unit transmit a signal at the same frequency and received by the other wireless unit, it is possible to evaluate the distance between a pair of wireless units without prior phase synchronization.

[0005] Unlike GNSS, etc., bidirectional transmission may be able to achieve phase-based positioning with a very small number of infrastructure elements. However, the drawback of using bidirectional transmission is that there are problems from the perspectives of resources and scalability. In the worst case, solutions involving bidirectional transmission require two separate broadband transmissions for each link. This also means that all units, such as mobile units to be tracked or positioned, must also transmit and receive signals repeatedly for accurate positioning determination.

[0006] Complete measurement data regarding the signal is required from both units participating in the bidirectional phase transmission scheme. When a mobile unit needs to perform measurements regarding a large number of links that change rapidly and related transmissions from many antennas, the fact that complete measurement data is required from both units can be a problem for the mobile unit. There may be a need to frequently transmit a large amount of information to the distance calculation unit via the wireless link. Also, when data communication is interrupted, the waiting time for positioning, etc., may become long.

[0007] In a terrestrial system, it is desirable to provide a solution that accurately and efficiently determines distance with few resources and without requiring bidirectional measurements on all measurement links. Summary of the Invention

[0008] The object of the present invention is to mitigate at least some of the problems in the prior art. This object is achieved by various embodiments of a method for determining a distance and related configurations for determining a distance. Determining a distance may refer to determining a numerical value of the distance. Or, it may refer to determining one or more variables indicating the distance, which variables can be used to calculate the numerical value of the distance.

[0009] According to a first aspect of the present invention, there is provided a method for determining at least one distance between a plurality of antenna pairs. Here, each antenna is associated with a radio unit, and the method comprises: performing self-measurements through at least a part of the antennas at a selected first time interval, and determining self-measurement phase information for each antenna participating in the self-measurements; performing a first bi-directional transmission between a first plurality of antenna pairs at the first time interval, and determining first bi-directional phase information for each antenna pair participating in the first bi-directional transmission; obtaining clock rate and Doppler frequency related information for the first plurality of antenna pairs; using the self-measurement phase information, the first bi-directional phase information, and the clock rate and Doppler frequency related information to determine antenna branch phase response data of the antennas of the first plurality of antenna pairs, and absolute clock offset data between a plurality of radio units associated with the first plurality of antenna pairs; performing a first uni-directional transmission between a second plurality of antenna pairs at a selected second time interval, and determining first uni-directional phase information for each antenna pair participating in the first uni-directional transmission; determining distance information between the second plurality of antenna pairs based on the determined first uni-directional phase information, the antenna branch phase response data, and the absolute clock offset data; Execute a second bi-directional transmission among a third plurality of antenna pairs at a selected third time interval, and for each antenna pair participating in the second bi-directional transmission, determine second bi-directional phase information; Track clock offset variations among the plurality of wireless units based on the second bi-directional phase information, the clock rate, and Doppler frequency related information; Execute a second uni-directional transmission among the second plurality of antenna pairs at a selected fourth time interval, and for each antenna pair participating in the second uni-directional transmission, determine second uni-directional phase information; Update distance information among the second plurality of antenna pairs based on the determined second uni-directional phase information, the tracked clock offset variations, and the antenna branch phase response data; Including.

[0010] The present invention also provides a system for determining at least one distance among a plurality of antenna pairs. This system includes at least one processor and at least two wireless units each associated with at least one antenna. And this system Execute self-measurement through at least a part of the antennas at a selected first time interval, and for each antenna participating in the self-measurement, determine self-measurement phase information; Execute a first bi-directional transmission among a first plurality of antenna pairs at the first time interval, and for each antenna pair participating in the first bi-directional transmission, determine first bi-directional phase information; Obtain clock rate and Doppler frequency related information of the first plurality of antenna pairs; Using the self-measurement phase information, the first bi-directional phase information, and the clock rate and Doppler frequency related information, determine antenna branch phase response data of the antennas of the first plurality of antenna pairs, and absolute clock offset data among the plurality of wireless units associated with the first plurality of antenna pairs; Execute a first unidirectional transmission between a second plurality of antenna pairs at a selected second time interval, and for each antenna pair participating in the first unidirectional transmission, determine first unidirectional phase information; Determine distance information between the second plurality of antenna pairs based on the determined first unidirectional phase information, antenna branch phase response data, and the absolute clock offset data; Execute a second bidirectional transmission between a third plurality of antenna pairs at a selected third time interval, and for each antenna pair participating in the second bidirectional transmission, determine second bidirectional phase information; Track clock offset variations between the plurality of wireless units using the second bidirectional phase information and the clock rate and Doppler frequency related information; Execute a second unidirectional transmission between the second plurality of antenna pairs at a selected fourth time interval, and for each antenna pair participating in the second unidirectional transmission, determine unidirectional phase information; Update the distance information between the second plurality of antenna pairs based on the determined unidirectional phase information, the tracked clock offset variations, and the antenna branch phase response data; Is configured to perform.

[0011] One aspect of the present invention relates to a computer program product as recited in the claims.

[0012] The present invention is based on a plurality of transmissions performed using different numbers of antenna pairs at selected time intervals. These transmissions may be utilized to determine various types of phase information. These phase information may be utilized to determine the information selected at the selected time interval. It is for determining distance information when the distance between the antenna pairs of the system has to be determined, and the determination of the distance information is performed without the need to execute transmissions between all the antenna pairs of the system at each time interval and can obtain accurate distance information such as up to 0.1 mm accuracy.

[0013] Distance measurement based on two-way transmission has an integer ambiguity (IA) of half a wavelength, while the distance determined based on one-way transmission has an integer ambiguity of one wavelength. Therefore, IA has a periodicity of half a wavelength in two-way transmission and one wavelength in one-way transmission. Therefore, IA may be easier to eliminate in one-way transmission. It is advantageous that the distance can be determined by one-way transmission between antennas.

[0014] The determination of the phase delay / phase response of the antenna branch is data that may be required for accurate distance determination and may be obtained as part of the process being executed in some embodiments of the method according to the present invention. Therefore, a dedicated calibration circuit for obtaining this data may not be necessary. A separate calibration circuit may increase the cost of the system and may typically interfere with the main functions of the system, such as positioning or communication.

[0015] The first time interval may be longer than the second time interval and the third time interval. The second time interval may be longer than the third time interval. The third time interval may be longer than the fourth time interval.

[0016] The first time interval may typically be between 1 second and 10 seconds. The first time interval may be determined by the stability of the hardware. For example, it may be determined by how fast the phase response of the active components of the antenna receiving branch or the antenna transmitting branch changes. These changes may be tracked by the transmission in the first time interval.

[0017] The second time interval may be, for example, between 0.5 seconds and 2 seconds. The second time interval may be selected to maintain the correct IA at one or more distances determined through the first one-way transmission.

[0018] The third time interval may be, for example, between 20 ms and 150 ms. The third time interval may be determined by the stability of the oscillator of the wireless unit and the operating frequency. With a high-quality oven-controlled crystal oscillator (OCXO) or oven-controlled MEMS oscillator (OCMO), when the radio frequency (RF) operating frequency is 5 - 6 GHz, the second time interval may be on the order of 50 ms, for example, 20 ms - 100 ms. At a frequency of 2.45 GHz, 100 ms, 150 ms, etc. can be used as the third time interval.

[0019] The fourth time interval may be between 5 ms and 20 ms. The fourth time interval may be determined by the RF frequency and the rate of change occurring in the environment, or the rate of change of the distance or speed occurring between the antenna pairs being considered. For example, consider a configuration related to a warehouse where there are multiple automatic guided vehicles (AGVs) operating at 5 - 6 GHz. However, the AGVs are coupled to the wireless unit, and the distance between the antennas of different AGVs and / or the distance between the antenna of the AGV and the antenna of the fixed wireless unit is determined. At this time, the fourth time interval can typically be about 10 ms.

[0020] The present invention can make it possible to determine the distance data between antenna pairs at selected time intervals by combining the frequently occurring second one-way transmission (at time intervals when the distance is determined) with additional transmissions that occur less frequently than the second one-way transmission (including at least two-way transmission and the first one-way transmission).

[0021] It is possible to obtain distance determination accuracy comparable to that of distance determination using a complete two-way transmission at the time intervals when the distance is determined, and moreover, fewer resources are used (only one-way transmission is required at these time intervals).

[0022] A plurality of antennas and a plurality of distances being determined between antenna pairs enable a positioning / position tracking application.

[0023] The accuracy required for clock offset data to utilize only one-way transmission for distance determination is extremely high. If the radio frequency is 5 GHz or higher, it is only a fraction of picoseconds. This problem has hindered the opportunity to use only one-way transmission in distance determination. However, the present invention provides a method that can utilize one-way transmission in combination with accurate information regarding the clock differences between a plurality of radio units of a plurality of antennas included in an antenna pair. This can be made possible by a configuration in which a first two-way transmission for a first plurality of antenna pairs in a first time interval is combined with and applied to a second two-way transmission for a third plurality of antenna pairs in a third time interval, and the distance can be evaluated using only one-way transmission in a fourth time interval for a second plurality of antenna pairs.

[0024] By performing a first two-way transmission in a selected first time interval, the first two-way transmission may be utilized to determine absolute clock offset data such that the associated integer ambiguity (IA) in the clock offset is resolved. The absolute clock offset data may represent the absolute difference in time units (such as seconds) between the local clocks of the radio units associated with the antenna pair under consideration.

[0025] Next, in order to track the change of the clock offset, a second bi-directional transmission may be performed at a third time interval shorter than the first time interval. Here, it is known that the IA does not change among a plurality of second bi-directional transmissions performed at the third time interval. Therefore, these plurality of second bi-directional transmissions may be used to update or check the relevant clock phase difference (at the measured radio frequency). Since this is done at the third time interval, information regarding how the absolute clock offset has changed can be obtained. Thus, the second bi-directional transmission and the tracked clock offset data can be used to track the clock offset between the antennas at the selected third time interval.

[0026] The obtained information regarding the phase difference and time difference (including the clock offset data of its change) between (local oscillators (LOs) of) a plurality of radio units may be directly used in a positioning algorithm or may be used to maintain a determined time / phase relationship in the system. Many prior art wireless systems may utilize the system backhaul for time synchronization between wireless units. In such systems, another fixed reference is always required for synchronization. However, the backhaul is usually based on optical fiber communication technology, and the time synchronization accuracy is at most on the order of nanoseconds.

[0027] For example, in a cellular communication system, the required accuracy is at the picosecond level. The time synchronization accuracy on the nanosecond time scale is not suitable for phase-coherent transmission where the required accuracy is at the picosecond level. Furthermore, many of the prior art methods require a line-of-sight (LoS) between wireless units in order to function properly. Factors such as weather conditions can also affect the accuracy of a system that utilizes known methods for determining the phase difference between local oscillators of wireless units. However, according to the present invention, clock offset data with an accuracy of less than picoseconds can be obtained without a backhaul and can be effectively used for distance determination. Since multiple wireless units are used, the above-described method is not affected by whether there is a line-of-sight between antennas. Only the ability to transmit and receive signals between wireless units is required.

[0028] Therefore, the present invention is suitable for a terrestrial distance determination system. Conversely, the prior art methods do not have sufficient accuracy for distance determination achievable in a terrestrial system (at least with respect to the accuracy of clock offset data). There are also methods that have an accuracy better than the above-described 1 nanosecond time synchronization accuracy, but these are generally for a fixed wireless link between two wireless units and are not suitable for synchronization of a large number of wireless units including mobile wireless units.

[0029] Depending on the embodiment, since high-precision clock offset and geometric phase length data (between the transmission and reception antennas) can be obtained, the present invention can enable the integration of cooperative multi-point transmission (CoMP) between wireless units. Here, the same wireless components and antennas used to obtain the clock offset data (i.e., the same ones participating in the bidirectional transmission) can be utilized to provide communication services using CoMP. The frequency used for the communication service and the frequency used for the determination and tracking of the clock offset may be somewhat different. For example, adjacent frequency bands may be used to avoid interference. However, the frequencies used can be close enough to each other such that the cable phase length, clock offset information, and the obtained geometric path phase length have sufficient accuracy for coherent CoMP transmission and reception. For example, on the one hand, the frequency used for communication and, on the other hand, the frequency used for the determination of the clock offset and path length may be adjacent. To succeed in CoMP, a phase accuracy of 10 to 20 degrees at the carrier frequency used for communication would be sufficient.

[0030] The first one-way transmission performed in the second time interval may be utilized to determine the distance integer ambiguity, along with the antenna branch phase response and the absolute clock offset data, and may then be utilized to determine the distances between the second plurality of antenna pairs. Thereafter, the second one-way transmission may be performed more frequently in the fourth time interval than the first one-way transmission. The second one-way transmission may be performed using fewer frequencies (i.e., using fewer resources) than the first one-way transmission. The fourth time interval may be selected such that the IA related to the distance is known not to change between measurements.

[0031] The second plurality of antenna pairs may include all the antenna pairs for which the distances are to be determined. In a system or method in which the distances between all antenna pairs are determined, the second plurality of antenna pairs may include all the antenna pairs.

[0032] According to some embodiments, the system or method is associated with at least three fixed radio units and at least one mobile / movable radio unit. In this case, the method can be used to determine the position of each mobile radio unit relative to at least a part of the fixed units. Here, the antenna can be considered to be either fixed or movable.

[0033] In particular, in the case of multiple mobile radio units, the number of the second plurality of antenna pairs may include only fewer antenna pairs than can be considered in total including all radio units. This is because the distance between the antennas of different mobile radio units is not necessarily determined. Of course, if desired, the distance between the antennas of the mobile radio unit can also be determined (precisely, the distance between its antennas can also be determined).

[0034] When the second part of the plurality of antennas is associated with the mobile radio unit, the one-way transmission may include a transmission in which, for an antenna pair including at least one antenna in the second part, the transmission is sent from the antenna in the second part and received by the other antenna of the antenna pair. In this way, it is not necessary to transmit the phase measurement information (or the data determined therefrom) from the mobile unit to the processing unit. As a result, signal measurements at the mobile radio unit can be significantly reduced. At the mobile radio unit, it may be sufficient to only receive transmissions for the purpose of determining clock offset data or tracking clock offsets. Thereby, with a high-quality local oscillator, it is possible to reduce the required uplink measurement data by orders of magnitude.

[0035] The method or system may also be relevant only to fixed wireless units or wireless units that are originally considered fixed but may move slightly. In that case, the distance between the antennas may be determined to determine the changes that occur. This can advantageously work, for example, in a structural integrity monitoring application where changes in the distance between radios / antennas installed at selected locations in a building indicate, for example, whether maintenance work is required. Another application area is, for example, a fixed wireless unit installed on a port lighting mast. The mast may sway in the wind, and the position of the fixed wireless unit installed on the lighting mast may be continuously determined, for example, with reference to a truly fixed reference unit, such as at the base of the light mast.

[0036] In some embodiments, the method may further include, in the starting step, performing at least two sets of preliminary bidirectional transmissions between a first plurality of antenna pairs (two signals having the same frequency), and for each of the antenna pairs participating in the preliminary bidirectional transmissions, determining a preliminary set of bidirectional phase information. Preferably, in this embodiment, the method includes determining information regarding a preliminary clock rate of the wireless unit with respect to the first plurality of antenna pairs based on the two sets of preliminary bidirectional phase information, and / or determining information regarding the Doppler frequency of the first plurality of antenna pairs based on the two sets of preliminary bidirectional phase information.

[0037] The determination of the information regarding the preliminary clock rate of the wireless unit related to the first plurality of antenna pairs and / or the information regarding the Doppler frequency of the first plurality of antenna pairs may be determined or obtained using other methods.

[0038] The third plurality of antenna pairs may include only a smaller number of antenna pairs than the first or second plurality of antenna pairs. Also, the third plurality of antenna pairs includes at least one antenna per radio unit. By using a smaller number of antenna pairs in the third plurality of antennas, the required resources can be reduced while determining the distance with the desired accuracy. Therefore, the transmission of the third plurality of antenna pairs and the related data determination may be sufficient with only one other radio unit involved per radio unit. That is, each radio unit only needs to report the measured reception phase value for at least one other radio unit, and does not need to report for all other radio units, and at least, it only needs to report for a smaller number of radio units than may be required in relation to the first plurality of antenna pairs.

[0039] The second plurality of antenna pairs may be the same as the first plurality of antenna pairs. Or, (preferably as a subset of the first plurality of antenna pairs), it may include only a smaller number of pairs than the first plurality of antenna pairs.

[0040] The first bi-directional transmission and the first uni-directional transmission may each be performed using at least three different frequencies having a selected difference between the frequencies. Also, the at least three frequencies are spaced apart by a selected interval of at least 200 MHz or more, more preferably 500 MHz or more, from each other. Further, the transmission may include one or more frequencies that are considered to be in at least two non-overlapping different frequency ranges, and the ranges have a selected difference.

[0041] Advantageously, the difference between the highest frequency and the lowest frequency may preferably be at least 200 MHz, and most preferably at least 500 MHz. These frequency ranges can be completely different radio bands. For example, the higher frequency band may be the 5 GHz RLAN band or the new 6 GHz unlicensed band, and the lower frequency band may be the 2.4 GHz ISM band. That is, a frequency difference of more than 3 GHz is possible. Thus, the frequency ranges may be separated, for example, by 500 MHz to 5 GHz.

[0042] The second bidirectional transmission and the second unidirectional transmission may be performed using fewer frequencies than the first bidirectional transmission and the first unidirectional transmission. Sometimes only one frequency is sufficient. Therefore, the second bidirectional transmission may be performed using at least fewer resources than the first bidirectional transmission. Also, the second unidirectional transmission may be performed using at least fewer resources than the first unidirectional transmission.

[0043] Advantageously, the first bidirectional transmission and the first unidirectional transmission are only required to be performed less frequently than the lighter second bidirectional transmission and second unidirectional transmission. The execution of the transmission may also be related to the resources required in relation to the relevant determination of the data being executed (e.g., phase information).

[0044] The first bidirectional transmission and the first unidirectional transmission may be used to determine distance information and absolute clock offset data including the resolved integer ambiguity.

[0045] The absolute clock offset data may be determined for each pair of participating radio units based on performing the first bidirectional transmission. Here, determining based on performing the first bidirectional transmission means a) performing a first offset bidirectional transmission between radio units using a first offset signal including a selected first offset frequency; b) determining first offset phase information regarding a first offset signal received by the wireless unit; c) determining a first offset phase difference as a difference between the first offset phase information determined for each of the wireless units belonging to the wireless unit pair, and preferably correcting the first offset phase difference for the phase response of the antenna branch, the difference in clock rate, and the influence of the Doppler frequency; d) performing second and subsequent offset bi-directional transmissions between at least one wireless unit pair using second and subsequent offset signals including the selected second and subsequent offset frequencies; e) determining second and subsequent offset phase information regarding the second and subsequent offset signals received by the wireless unit; f) determining a second and subsequent offset phase difference as a difference between the second and subsequent phase information determined for each of the wireless units belonging to the wireless unit pair, and preferably correcting the second and subsequent offset phase difference for the phase response of the antenna branch, the difference in clock rate, and the influence of the Doppler frequency; g) determining a difference between the first offset phase difference and the second and subsequent offset phase differences, or a difference between the offset phase difference determined at the highest or lowest offset signal frequency and a subsequent phase difference; h) determining at least one clock offset variable indicating an estimated value of the clock offset between the wireless units within the wireless unit pair based on the difference determined in step g; i) determining an estimated maximum error of the determined clock offset variable based at least on the maximum error of the first offset phase difference and the maximum error of the second and subsequent offset phase differences; j) determining whether the maximum error of the clock offset variable enables uniquely determining the clock offset by determining a set of candidate clock offset values obtained by the variation of the clock offset corresponding to an integral number of half-cycle periods at the first offset frequency or subsequent offset frequencies, the set of clock offset values being limited by the estimated maximum error of the determined clock offset variable; k) if it is determined that the clock offset cannot be uniquely determined, repeating steps d-j using a next selected offset frequency that is different from the first offset frequency by a value greater than the difference between the first offset frequency and the second offset frequency or the previously used offset frequency; including.

[0046] Since the magnitude of the error of the determined clock offset is small, the determination of the clock offset data may remain essentially unaffected by the slow movement of the unit, such as the slow movement like the swaying of a lamppost. The movement of one or more wireless units may be considered, and the movement may be compensated through models and / or measurements to normalize or equalize the reference frame of the clock offset determination measurement.

[0047] The present invention may enable the determination or evaluation of the distance between antennas where the instantaneous bandwidth of the used frequency of the transmission signal is narrow (for example, as narrow as 40 MHz or 10 kHz). The present invention provides a method and configuration that can be implemented at low cost, whereby an inexpensive narrowband receiver can be utilized.

[0048] Since the operating bandwidth of the present invention is narrow, the system may operate in a frequency band / range where high transmission power is allowed. Therefore, better range and accuracy are possible compared to, for example, a UWB-based time synchronization system that needs to operate at very low transmission power. The band that can be used with the present invention may be, for example, a 5 GHz RLAN (where transmission power of 100 mW or 1 W is possible), or a WIA band (where transmission power of 400 mW is possible). Accordingly, the power used for transmitting one or more signals (for example, a primary signal and / or an auxiliary signal) may be tens of mW or more, for example, 20 mW or more, or 50 mW or more, or 80 mW or more, etc.

[0049] According to the present invention, it may also be possible to easily adapt the narrow band used, for example, between WiFi network channels.

[0050] Preferably, at least a part of the signal is transmitted as a broadcast so that the transmitted signal is received by at least a part of the antenna that is not performing the transmission.

[0051] In some embodiments, one of the wireless units may be set as a reference wireless unit, and the reference wireless unit may look at the clock offsets of all other wireless units.

[0052] When multiple wireless units are used to determine multiple clock offsets according to an embodiment of the present invention, time and / or resources may be saved. In a conventional system having multiple wireless units, measurements are performed in relation to each wireless link, that is, each pair of wireless units transmits a signal individually to each of the remaining wireless units. For example, in a system or configuration with 10 wireless units, 45 bidirectional signals should be utilized, and thereby at least a total of 90 transmissions should be made. However, in the present invention, the clock offset between each wireless unit can be determined with only 10 transmissions, significantly reducing the resources and time required for measurement and / or transmission.

[0053] According to some embodiments, each of the wireless units that perform transmission may transmit at least one signal in a predetermined time slot and in a predetermined order.

[0054] The novel features considered to be characteristic of the present invention are particularly set forth in the appended claims. However, the configurations, operating methods, additional objects, and advantages of the present invention will be best understood from the following detailed description of specific exemplary embodiments read in conjunction with the accompanying drawings.

[0055] As will be understood by those skilled in the art, the considerations presented above with respect to various embodiments of the method can be readily applied mutatis mutandis to embodiments of the apparatus, and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Next, the present invention will be described in more detail with reference to exemplary embodiments in accordance with the accompanying drawings.

Figure 1

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Figure 8

[0057] Figure 1 shows a system 100 according to an embodiment of the present invention. The system 100 has at least two wireless units, here a first wireless unit 104 and a second wireless unit 106. Each wireless unit has at least one antenna. The first wireless unit in Figure 1 has a first antenna 108 and a second antenna 110, and the second wireless unit 106 has at least a first antenna 112 and a second antenna 114.

[0058] The system 100 also comprises at least one processing device 102 or is connected to the processing device 102. The wireless units 104, 106 may have a processing unit, and / or the wireless units 104, 106 may be connected to the processing unit 102 by wire or wirelessly. The processing device 102 may receive data from the wireless units 104, 106.

[0059] The processing device 102 and the wireless units 108, 110 can be powered, for example, using PoE (Power-over-Ethernet), direct main power supply, battery, solar panel, or a mechanical generator (such as a wind turbine blade).

[0060] The system is configured to determine at least one distance between pairs of the antennas 108, 110, 112, 114. For example, the system 100 in Figure 1 may be configured to determine the distances between four different antenna pairs. In Figure 2, these distances, when the antennas of the wireless unit are the first antenna k and the second antenna l, the phase length Corresponding to TIFF2025519283000002.tif811, for example, the distance D k,l may be represented as.

[0061] The transmission and timing of signals, and the information determined based on the transmitted signals will be described later.

[0062] It should be noted that not all antennas of a wireless unit need to transmit signals, nor is the ability to transmit even essential. For example, if wireless units 104 and 106 have four antennas 108, 110, 112, and 114, and two of those antennas are involved in transmission, there are a sufficient number of equations to derive all the unknowns.

[0063] Antennas 108, 110, 112, and 114 can each transmit their respective signals in their respective time slots. However, it is also possible for two or more antennas of a wireless unit to transmit simultaneously in one time slot using frequency division (where different frequencies are transmitted by the antennas) or code division (where each antenna uses a different scrambling code). Also, multiple antennas of a wireless unit can transmit the exact same signal simultaneously if there is no risk of interference with each other, for reasons such as spatial separation.

[0064] Each signal transmitted is a radio frequency (RF) signal, preferably a sine wave, but can be any signal modulated by known techniques. The duration of the signal can be, for example, 10 - 10000 μs depending on, for example, the length of the distance between the antennas / wireless units, the time interval between transmissions, and / or the quality of the local oscillators provided in wireless units 104 and 106. The duration of the signal can be, for example, about 100 μs.

[0065] Normally, the signal frequency is different from the frequency of the local oscillator. Also, phase measurement is often done in a digital baseband using, for example, a fast Fourier transform. This is essentially equivalent to measuring the phase with respect to a local oscillator that is considered to operate at the signal frequency for simplicity.

[0066] In some cases, due to hardware or bandwidth limitations, the frequencies of the signals used are considered to be composed of a plurality of different non-overlapping frequency ranges, each corresponding to an individual transceiver chain having a predetermined bandwidth. In this case, the frequency range includes a maximum bandwidth of, for example, 50 Hz - 100 kHz, preferably 10 - 100 kHz, when only one signal is transmitted in the range, or 5 - 100 MHz, preferably 10 - 50 MHz, for example 40 MHz, when a plurality of signals are transmitted in the range.

[0067] When using a plurality of frequency ranges, for example, the difference between the first frequency range and the second frequency range is at least 150 MHz, preferably at least 200 MHz, and most preferably at least 500 MHz. For example, when two frequency bands are in completely different radio bands such as the 2.4 GHz ISM, 5 GHz RLAN / ISM, 6 GHz unlicensed band, etc., the difference between the first frequency range and the second frequency range can even be 3 GHz or more.

[0068] FIG. 2 is a flowchart of a method according to an embodiment of the present invention, showing the execution of measurement / transmission frames at selected time intervals.

[0069] The method may include, in a starting step, performing at least two sets of preliminary bi-directional transmissions between a first plurality of antenna pairs (202). However, this starting step is not essential. The starting step may be performed only once in the method or may be performed at a selected time, but at a frequency less than the fourth time interval.

[0070] The preliminary two-way transmission may include transmitting at least first and second preliminary signals at each of the transmission antennas 108, 110, 112, 114. Here, these first and second preliminary signals have the same frequency. That is, each antenna transmits a pair of at least one same signal twice. The above-mentioned preliminary signals may be transmitted in a predetermined time slot by each of the antennas participating in the above-mentioned starting step. The first and second preliminary two-way transmissions may be performed, for example, within 1 - 2 milliseconds.

[0071] The preliminary two-way transmission may include two-way transmission between a selected antenna pair (and at each of the radio links having antennas included in the antenna pair whose distance is to be determined). At this time, each of the radio units 104, 106 associated with the antennas included in the first plurality of antenna pairs has at least one of the antennas 108, 110, 112, 114 participating in the preliminary two-way transmission. The signal can be received at all antennas of the non-transmitting antenna (non-transmitting antenna), for example, the non-transmitting radio unit (non-transmitting radio unit). Or it can be received at at least one antenna of the non-transmitting radio unit. It is sufficient to determine only the phase information of one receiving antenna.

[0072] The preliminary two-way transmission may include further transmission. For example, it may include each antenna participating in the preliminary two-way transmission transmitting at least a third preliminary signal and a fourth preliminary signal having the same frequency as the third preliminary signal. The frequencies used for the preliminary two-way transmission may all be included in a relatively narrow frequency range, such as between 10 - 50 MHz, for example.

[0073] The starting step may also include determining a preliminary set of two-way phase information for each antenna pair participating in the preliminary two-way transmission.

[0074] The starting step may then include determining information regarding a preliminary clock rate of the first plurality of antennas (204) based on two sets of preliminary bidirectional phase information, and determining information regarding a Doppler frequency of the first plurality of antenna pairs based on the two sets of preliminary bidirectional phase information.

[0075] At 206, self-measurement may be performed through at least a part of antennas 108, 110, 112, 114 at a selected first time interval. The first time interval may be, for example, 1 - 10 seconds. The self-measurement may be performed by all the antennas of the system or by the antennas included in at least the first plurality of antenna pairs. Then, self-measurement phase information may be determined for each antenna participating in the self-measurement.

[0076] The antennas 108, 110, 112, 114 performing the self-measurement are configured to transmit at least one signal received by other antennas included in the same radio units 104, 106. The self-measurement can also be expressed as being performed by the radio units 104, 106. That is, each radio unit participating in the self-measurement transmits a signal via each of its antennas, and the signal is received by all the other non-transmitting antennas of the radio unit. Alternatively, the self-measurement may include transmission of a signal by an antenna of the radio unit and reception of a sample of the transmitted signal by the same (transmitting) antenna. This will be further described later.

[0077] Regarding self-measurement of receiving a signal by non-transmitting antennas within the same radio unit, for each radio unit 104, 106 participating in the self-measurement, with reference to radio unit i having antennas k, l, each unit measures the following quantities during self-measurement at frequency f m as follows. TIFF2025519283000003.tif13170

[0078] Here TIFF2025519283000004.tif817 is the self-phase (phase of the signal at reception) of radio unit i measured by transmission using antenna k and reception using antenna l. θ i Tk is the phase length (from the DAC to the antenna) of transmission antenna branch k. θ i Rl is the phase length (from the antenna to the ADC) of reception antenna branch l. TIFF2025519283000005.tif811 is the phase length of the coupling between antenna k and antenna l at the measurement frequency f m For a radio unit with four antennas, this results in 12 measurement values for each of radio units 104, 106, and is described by Equation (1) respectively.

[0079] Coupling phase term TIFF2025519283000006.tif811 can be understood to be very stable. These can be determined using the calibration procedure described later in this specification, but are assumed to be known at present. Branch terms θ i Tk and θ i Rl are not so stable. This is because the antenna branches contain active electronic components such as amplifiers and mixers. However, it can be considered constant on the time scale of seconds or minutes.

[0080] In 208, the first bi-directional transmission may be performed between the first plurality of antenna pairs at the first time interval, and the first bi-directional phase information may be determined for each antenna pair. The first bi-directional transmission may be performed between all radio links involved in distance determination. For example, all radio units 104, 106 associated with the antennas included in the first plurality of antenna pairs may each have antennas 108, 110, 112, 114 participating in the first bi-directional transmission.

[0081] "Phase information" may represent the phase of the received signal relative to the local oscillator of the received radio unit. "Bidirectional phase information" may represent the phase information determined for a signal transmitted by a first antenna (of a first radio unit) and received by a second antenna (of a second radio unit), and the phase information determined for a corresponding signal having the same frequency, transmitted by the second antenna and received by the first antenna.

[0082] "Phase difference" may represent the difference between two phases determined by bidirectional phase information.

[0083] The first bidirectional transmission may be performed using a plurality of frequencies. These frequencies are sufficient for the associated IA to be uniquely determined, or are sufficient for the correct clock offset value to be uniquely determined from a set of candidate values for the clock offset. For example, at least two frequencies in two different frequency ranges may be used. These frequency ranges are described elsewhere in this specification.

[0084] Self-measurement and the first bidirectional transmission may be performed simultaneously, or may be performed at different times in separate time slots.

[0085] At 210, the antenna branch phase response data of the antennas of the first plurality of antenna pairs, and the absolute clock offset between the radio units associated with the first plurality of antenna pairs, are determined using self-measured phase information, first bidirectional phase information, and clock rate and Doppler frequency related information. The clock offset also includes information regarding the IA (estimated value) of the clock offset.

[0086] Considering a pair of radio units i and j, two sets of pairwise measurements can be made. The first is the case where radio unit i transmits with antenna k and radio unit j receives with antenna l, and the second is the case where radio unit j transmits with antenna l and radio unit i receives with antenna k. TIFF2025519283000007.tif13170TIFF2025519283000008.tif13170

[0087] Here TIFF2025519283000009.tif823 is the phase of the received signal measured by the receiving unit i at the transmission time t i with respect to the clock of the radio unit j, which is θ i C (t i ) and θ j C (t i ) is the phase of the local oscillator at t i , which is θ T and θ R are the same as described above. TIFF2025519283000010.tif817 is the phase length of the link between the phase centers of the radio node i antenna k and the radio node j antenna l. Since all quantities are always at the frequency f m , this dependency is omitted in the following equations. Since the channel is the same in the reverse direction, note that it is TIFF2025519283000011.tif823.

[0088] One of the instrumental terms of each unit (e.g., θ i T0 in equations (2) and (3)), or the phase length of the transmission branch 0, can be normalized to zero. This means that the clock solution of any radio node refers to the antenna 0 phase center at the time of transmission, rather than the LO oscillator output. With such an agreement, all other instrumental terms of a particular radio node should be understood as follows. That is, considering an ideal radio unit (or a radio unit equivalent to such an arrangement) in which all major components (including the sampler) connected to all receiving antennas (RX) are arranged at their phase centers, θ i C (t i ) - θ i Tkis the transmission phase at the phase center of antenna k, and θ i Rk + θ i C (t j ) is the phase of the local oscillator at the phase center of antenna k.

[0089] Assuming that the clock has a constant speed ((d 2 θ C ) / (dt 2 ) = 0) and the Doppler TIFF2025519283000012.tif1313 is also constant, a difference is formed. TIFF2025519283000013.tif20170 Here, Δt = t j - t i .

[0090] System 100 is configured to obtain clock rate and Doppler frequency related information for a first plurality of antenna pairs. This information may be obtained from an external source or may be pre-known.

[0091] However, in some embodiments, if the clock rate difference and Doppler are not known, they may be determined through a system configured to perform at least two sets of preliminary two-way transmissions among the first plurality of antenna pairs in the starting step. For each pair of antennas participating in the preliminary two-way transmission, a set of preliminary two-way phase information may be determined.

[0092] Here, the clock rate difference and Doppler may be obtained by solving the following set of equations. In the following equations, T is the time between two sets of two-way preliminary transmissions. TIFF2025519283000014.tif16170TIFF2025519283000015.tif16170

[0093] Solve for the clock rate and Doppler frequency, and set the reference clock to zero (θ0 CAfter (=0), that is, after selecting one of the radio units as the reference unit, all other clock phases (or equivalently, the phases of the local oscillators) and the phase lengths of the antenna branches can be solved from the equation groups (1) and (4). It should be noted that to solve the equations, the true phase rather than the periodic phase should be used. As an example, if there are four antennas in one radio unit and two radio units, 24 equations can be obtained from the equation group (1) and 16 equations can be obtained from the equation group (4). The number of unknowns in this case is 15. By creating these equations and using methods such as Gaussian elimination, it can be found that the number of linearly independent equations included in these two equation groups is also 15, and the unknowns can be obtained.

[0094] The above measurements and solutions are for one frequency point f m . As described below, these can be repeated (or performed simultaneously) for any number of frequency points. Thereby, the clock difference between the radio units (the clock difference in time units, not the phase difference of the local oscillators) can be measured. Also, the branch phase responses and delays for all antenna branches can be measured and used to determine the true (aperiodic) phases required for the linear equations.

[0095] The absolute clock offset data may be determined based on performing a first bidirectional transmission for each pair of participating radio units. Here, determining based on performing the first bidirectional transmission means a) performing a first offset bidirectional transmission between the radio units using a first offset signal including the selected first offset frequency; b) determining first offset phase information regarding the first offset signal received by the radio unit; c) determining a first offset phase difference as the difference between the first offset phase information determined for each of the radio units belonging to the radio unit pair; d) Using second and subsequent offset signals including the selected second and subsequent offset frequencies, performing second and subsequent offset bi-directional transmission between at least one pair of radio units; e) Determining second and subsequent offset phase information regarding the second and subsequent offset signals received by the radio unit; f) Determining a second and subsequent offset phase difference as a difference between the second and subsequent phase information determined for each of the radio units belonging to the pair of radio units; g) Determining a difference between the first offset phase difference and the second and subsequent offset phase difference, or a difference between the offset phase difference determined at the highest or lowest offset signal frequency and a subsequent phase difference; h) Based on the difference determined in step g, determining at least one clock offset variable indicating an estimated value of the clock offset between radio units within the pair of radio units; i) Determining an estimated maximum error of the determined clock offset variable based at least on the maximum error of the first offset phase difference and the maximum error of the second and subsequent offset phase differences; j) By a step of determining a set of candidates for clock offset values obtained by variations in the clock offset corresponding to variations in an integer number of half-cycle periods at the first offset frequency or subsequent offset frequencies, determining whether the maximum error of the clock offset variable enables the clock offset to be uniquely determined, wherein the set of clock offset values is limited by the estimated maximum error of the determined clock offset variable; k) If it is determined that the clock offset cannot be uniquely determined, repeating steps d-j using a selected next offset frequency that is different from the first offset frequency by a value greater than the difference between the first offset frequency and the second offset frequency or a previously used offset frequency; including.

[0096] As described above, it is possible to select a plurality of offset frequencies to be used, which are each composed of frequencies considered to be in different frequency ranges.

[0097] At 212, the first one-way transmission may be performed between the second plurality of antenna pairs at a selected second time interval. The second time interval may be, for example, 0.5 - 2 seconds. The first one-way transmission may be used to determine the first one-way phase information. For each relevant antenna pair of the radio units 104, 106, the second plurality of antenna pairs may participate in the first one-way transmission such that the antennas included in the second plurality of antenna pairs transmit or receive at least one signal with another radio unit. A particular radio unit may be selected to perform the transmission. For example, a mobile radio unit may be selected to only receive.

[0098] The time intervals considered, especially the first and second time intervals, may be changed, for example, every cycle if it is determined to be advantageous. These time intervals, or the procedures performed at the specified time intervals, may be performed, for example, in response to a request. For example, if the channel is occupied by another system and the distance IA has slipped by one cycle or more, and the procedures to be performed at the fourth time interval have been missed consecutively several times, such a slip may be a factor in the appropriate selection of other time intervals. In 3D positioning involving multiple antennas, such a slip may be detected from the residuals in the position solution and may be used to execute the procedures related to the second time interval when necessary. This also applies to the procedures performed in the first time interval and may also be executed on demand.

[0099] When only measuring the distance between two antennas purely, there may be no way to detect such an IA slip, and it may be necessary to perform the procedures regularly at the first and second time intervals.

[0100] The first one-way transmission may be performed using a plurality of frequencies. These frequencies are sufficient for the associated IA to be uniquely determined, or are sufficient for the correct distance value to be uniquely determined from a set of candidate distance values. For example, in this case, at least two frequencies in two different frequency ranges may be used.

[0101] Next, at 214, based on the determined first one-way phase information, and also based on the determined clock offset and branch phase response, distance information between a second plurality of antenna pairs is determined. The determination of the distance information may include resolving integer ambiguity, i.e., resolving the uncertainty of the number of full wavelengths associated with the determined distance.

[0102] When the clock offset, clock phase, and branch phase response are measured through the first two-way transmission, the true geometric phase of the radio path between the antenna phase centers can be determined through one-way transmissions (the first and second one-way transmissions used separately) and the determined one-way phase information, and also by transforming Equation (2). TIFF2025519283000016.tif13170

[0103] The actual length of the link (referring to the distance between the antennas) can be estimated based on the geometric phase and knowledge of the number of wavelengths between the phase centers of the antennas. The number of wavelengths can be obtained from geometric phase measurements performed over a sufficient number of frequencies to resolve the integer ambiguity. This will be described in detail later.

[0104] A sufficient approximation of the Doppler estimate required in Equation (4) can be tracked by calculating the difference in successive geometric phases: TIFF2025519283000017.tif16170where Δt is the time interval between adjacent second one-way phase measurements. Similarly, a suitable accuracy approximation of the clock rate estimate can be obtained from the clock offset: TIFF2025519283000018.tif16170

[0105] For equations (8) and (9) to hold, the Doppler rate and the clock rate must be small enough to avoid phase ambiguity during the measurement interval. Otherwise, it may be necessary to use a more sophisticated estimation means such as a Kalman filter initialized with the values obtained from equations (5) and (6).

[0106] As described above, the phase θ of the clock i C (t i ,f m ) and the geometric path length TIFF2025519283000019.tif823 can be determined from equations (1) to (4) and equation (7) respectively for one measurement frequency. With such single-frequency phase values alone, it is not possible to determine the absolute clock offset τ of the radio unit i with respect to the reference unit i in seconds, or to determine the absolute distance D kl between antenna k and antenna l. However, there are simple relationships between them. TIFF2025519283000020.tif13170TIFF2025519283000021.tif13170

[0107] Here c is the speed of light, and θ i C (t i ,f m ) and TIFF2025519283000022.tif823 is given in radians. Therefore, if M and N (integer ambiguity) can be determined, even from a single frequency, τ i and D kl can be derived. The method for determining these is to perform phase measurements at a plurality of different frequencies. For example, assume the first and second selected frequencies, frequencies f1 and f2 are used. Omitting the time relationship, from equations (10) and (11), TIFF2025519283000023.tif13170TIFF2025519283000024.tif13170Here, N1 and N2 (or M1 and M2) respectively correspond to the integer ambiguities at frequencies f1 and f2.

[0108] When deformed, TIFF2025519283000025.tif16170TIFF2025519283000026.tif16170

[0109] Since N and M must be integers, for a given phase measurement, only a set of discrete values for τ i and D kl are possible, and these respectively correspond to one value of 1 - N2 or M1 - M2. These can be considered as a set of candidate values for the clock offset and a set of candidate values for the distance. The difference between such consecutive discrete values is 1 / (f1 - f2) for τ i and c / (f1 - f2) for D kl . If there is a large a priori uncertainty in the values of τ i and D kl , a small difference f1 - f2 must be used so that there is only one candidate value within the range of the uncertainty. Different values can be used for f1 and f2 to determine τ i and D kl because these uncertainties are naturally different. The maximum value of the frequency difference is as follows. TIFF2025519283000027.tif13170TIFF2025519283000028.tif13170

[0110] Here, Δτ i and ΔD kl are respectively the a priori uncertainties of the clock offset and the distance. For example, the uncertainty of τ i is, for example, 1 microsecond and can be easily achieved with a synchronization sequence commonly used in wireless communication. Therefore, τ iFor [it], it suffices to have at most one candidate value within the known range. This can be achieved by setting the measurement frequency such that |f1 - f2| < 1 MHz. Similarly, for example, if it is known that the distance is 100 m or less, for D kl for [it], it suffices to have only one possible value within the range of 0 to 100 m. For that, |f1 - f2| must be less than 3 MHz.

[0111] τ i and D kl The values of [them] are obtained by solving equations (14) and (15) using the measured values at frequencies f1 and f2 and fitting the range of a priori uncertainties. These are the clock offset variable τ i 12 and the distance variable D kl 12 expressed as. There are also uncertainties arising from the uncertainties in both measurements of the clock phase Δθ i C and the geometric phase TIFF2025519283000029.tif811. TIFF2025519283000030.tif16170TIFF2025519283000031.tif16170

[0112] These are derived from the assumption that the sum of the uncertainties in the phase differences is twice the uncertainty of a single phase measurement, and equations (14) and (15). This uncertainty is based on the estimated maximum error in the determined phase information and can be used to obtain the estimated maximum error in the determined phase difference. The estimated maximum error of the phase-related information can limit the set of candidate values of the distance or the set of candidate values of the clock offset through the corresponding error margin.

[0113] From equations (10) and (11), the clock phase θ i C (f1) (or the geometric phase TIFF2025519283000032.tif817 that matches τi (or D kl )'s candidate values are found to repeat at intervals of 1 / f1 (or c / f1). τ obtained from Equation (18) or (19) i 12 or D kl 12 If the uncertainty in is smaller than these repetition intervals, i.e., if the following holds Determine N or M from TIFF2025519283000033.tif16170TIFF2025519283000034.tif16170 and τ from Equations (10) and (11) i or D kl The final estimated value of can be obtained. That is, in this case, an appropriate clock offset value or an appropriate distance value can be uniquely selected from the set of candidate values (i.e., only one value that meets the determined error margin remains).

[0114] However, if the uncertainty is larger and the clock offset value or distance value cannot be uniquely selected, measurements can be repeated at a subsequent selected frequency (e.g., a third frequency f3 farther from the first frequency f1 than the second frequency f2, i.e., |(f1 - f3)| > |(f1 - f2)|). However, the difference |(f1 - f3)| cannot be arbitrarily increased. This is because Equations (16) and (17) must hold to prevent phase ambiguity. By using Equations (16) - (19), the necessary conditions for the distance at the new frequency f3 can be set. TIFF2025519283000035.tif16170TIFF2025519283000036.tif16170 This process is repeated using subsequent new frequencies f3, f4,... (in place of f2) until the conditions of (20) and (21) are met.

[0115] As an example, when the phase measurement error is 5 degrees and |(f1 - f2)| = 1 MHz is used, from Equation (18), the maximum uncertainty τ iAbout 30 nanoseconds can be obtained. However, when the highest measurement frequency f1 is 5.8 GHz, from Equation (20), it can be seen that the uncertainty is less than 1 / 5.8 GHz = 170 picoseconds. Therefore, the third frequency to be found will be at most about 30 MHz away from f1 (from Equation 16). For example, it is 5.77 GHz. Assuming the same phase measurement accuracy (5 degrees), a new measured value θ i C (f3) can be obtained. Since this is still worse than the required accuracy of 170 picoseconds, a new frequency that satisfies condition (16) is found. Since the current condition is |(f1 - f4)| < 1 GHz, for example, f4 = 5.4 GHz can be safely selected. Thereby, τ i has an uncertainty of 55 picoseconds. This is sufficient to use Equation (10) to obtain the final estimated value of τ i . The accuracy of this measurement is already 5 picoseconds (from Equation 18 with f2 = 0).

[0116] In a practical implementation, f1, f2, and f3 may be transmitted in a single frequency band (or the first frequency band) with a bandwidth of only 30 MHz, and the fourth frequency may be transmitted in another band (the second frequency band). The fourth frequency may be transmitted simultaneously with f1, f2, and f3, or may be transmitted subsequently to these. In a low-cost transmitter with a very narrow bandwidth, all four frequencies can be transmitted in a high-speed sequence (for example, on the order of 200 microseconds). However, in order to form an accurate phase difference with separate transmissions, a relatively excellent oscillator is still required.

[0117] The discussion regarding the selection of the second or subsequent frequencies can also be considered from the perspective of the selection of the second or subsequent frequency ranges. In a narrowband device that can transmit only one frequency at a time, there is no need to include the consideration of frequency ranges in the consideration of the second and subsequent frequencies. For example, in a widerband system with a bandwidth of 40 MHz, two or more signals with different frequencies can be transmitted simultaneously within one range. In this case, further distant frequencies should be transmitted in another frequency range. A system with two parallel wideband transceivers may be utilized. In that case, signals can be transmitted and received simultaneously in two frequency ranges. Also, a more expensive system with a bandwidth of, for example, 500 MHz can be adopted. In this case, all signals can be transmitted in one large frequency band. Thus, the concept of the frequency range will depend on the hardware implementation.

[0118] In 216, the second bi-directional transmission may be performed between a third plurality of antenna pairs at a selected third time interval. The number of the third plurality of antenna pairs is preferably less than that of the first or second plurality of antennas. And for each of the antenna pairs participating in the second bi-directional transmission, second bi-directional phase information is determined. The second bi-directional transmission may be performed using only one frequency.

[0119] The above-described integer ambiguity determination protocol for clock offset may be performed through the first bi-directional transmission in the selected first time interval. The system 100 may be configured to track, for example, the clock offset between the first radio unit 104 and the second radio unit 106 so that the IA does not change. This tracking may be done through the second bi-directional transmission in the selected third time interval. The second bi-directional phase information may be used to determine the phase difference in order to repeatedly determine clock offset information indicating the change in the clock offset between the first radio unit and the second radio unit.

[0120] To determine the change in clock offset, it is sufficient to measure the clock offset phase at one or two frequencies (to withstand strong fading events that can occur at one frequency). Since the antenna branch phase response is measured by using two-way measurements over multiple frequencies and solving equations (1) to (4), the update of the clock phase between radio units can be calculated from the following equation. TIFF2025519283000037.tif32170

[0121] This is obtained by transforming equation (4). Since the branch phase responses are known for all antennas, the mutual clock offset phase θ j C (t i ) - θ i C (t i ) between any two radio units can be obtained by using one antenna pair between these radio units. By performing this between different pairs of radio units, it is clear that the clock phase θ j C (t i ) of any radio unit with respect to the reference unit can be determined and tracked. (The reference unit has its clock offset set to zero.) Note that for some units, especially for all mobile units, it is advantageous to perform this two-way one-frequency or two-frequency measurement with only one fixed radio unit. This is because the amount of measurement data transmitted from the mobile unit is minimized.

[0122] The repetition interval (the third time interval) of the clock offset update measurement needs to be made small enough so that the phase error of the clock offset does not exceed an appropriate value, for example, does not exceed 7 degrees. An accuracy of 7 degrees is sufficient to determine the distance with an accuracy of 1 millimeter at a frequency of 5 GHz. A typical value for the third time interval is 20 - 50 ms for a high-quality oven-controlled MEMS oscillator.

[0123] Therefore, based on the second bidirectional phase information and the information regarding the Doppler frequency, the change in the clock offset between the radio units can be tracked (218). The clock rate may be updated using the change in the clock offset.

[0124] In the above process, the antenna coupling phase term in Equation (1) TIFF2025519283000038.tif817 was assumed to be known. The antenna coupling phase term can be measured using calibration measurements where the positions and orientations of the two radio units 104, 106 relative to each other are known. For example, if there are four antennas 108, 110, 112, 114 at both radio units, there are 16 known distances between the antenna phase centers. This distance corresponds to the known phase lengths m at each frequency f corresponding to TIFF2025519283000039.tif817. The process of determining the antenna coupling term TIFF2025519283000040.tif817 can be as follows. 1) Set TIFF2025519283000041.tif817 to 0. 2) Calculate TIFF2025519283000042.tif817 using Equations (1)-(3) and Equation (7), and compare this with a known value (known from the known distance between the antenna phase centers by the calibration procedure). TIFF2025519283000042.tif817 is calculated using Equations (1)-(3) and Equation (7), and compared with a known value (known from the known distance between the antenna phase centers by the calibration procedure). 3) Adjust TIFF2025519283000043.tif817 and return to 2) until a reasonable match is achieved, for example, RMS within 5 - 10 degrees for all TIFF2025519283000044.tif817 is achieved.

[0125] At 220, a second one-way transmission is performed between a second plurality of antenna pairs at a selected fourth time interval. And for each of the antenna pairs participating in the second one-way transmission, second one-way phase information is determined. The second one-way transmission may be performed using only one frequency.

[0126] As already described in relation to the absolute clock offset, if integer ambiguities for both the clock offset and the distance are determined (see the procedures performed in relation to the first and second time intervals), to provide updated clock offset information and thus updated distance information, the IA only needs to track changes in both the clock offset and the distance assuming the IA remains known.

[0127] Similar to what was discussed in relation to the clock offset, when the IA determines all the distances between a second plurality of antenna pairs, the geometric phase To obtain a new estimate for TIFF2025519283000045.tif823, Equation (7) is used and new one-way measurements at one, two, or a few frequencies may be used. If there is no risk of significant fast fading, in principle one frequency is sufficient. If there is a line of sight (LOS) between the antennas, the fading is small and one frequency should work well enough. The repetition interval of the one-way distance update measurement, i.e., the fourth time interval, should be narrow enough so that there is no risk that the geometric phase estimate deviates by more than one cycle (i.e., more than 2π). A typical value for a moving vehicle such as a car or an automated guided vehicle is, for example, 10 milliseconds.

[0128] The rate and Doppler estimates required in Equation (24) can be easily obtained from the observed rates of change of the updated clock offset phase and the geometric phase information, as shown in Equations (8) and (9).

[0129] In this way, the distance information between the second plurality of antenna pairs is updated (222) based on the determined second one-way phase information, the tracked clock offset variation, and the antenna branch phase response data. At least a part of the determined distance coincides with what has already been determined in step 214, but may be updated or tracked in step 222. Also, the distance updated in 222 may include or be able to refer to information related to the relative positions of the antennas.

[0130] In some embodiments, it may be advantageous to determine distance information in a wireless unit associated with a mobile antenna. In this case, a separate (position-fixed) processor 102 may periodically transmit data regarding the clock offset and the antenna branch phase response information to the wireless unit associated with the mobile antenna. In this case, the wireless unit itself may also have a processing unit 102 to determine the distance according to Equation (7) based on its own measurements of the distance phase. If the position-fixed processor 102 also reports the position information of the position-fixed wireless unit, the processor of the mobile wireless unit can also determine the position information of the mobile unit.

[0131] The processing of information can also be performed in the complex domain. In this case, the argument of the complex number represents the phase to be considered. For example, as will be understood by those skilled in the art, the equations considered herein can also be described in the complex domain. The processing of information may be performed in an order different from that proposed herein.

[0132] The order in which the transmissions of the wireless unit are assigned to time slots may vary between the superframes further introduced below. For example, the order may be reversed every other superframe. This will of course affect the way the equations are described. All possible variations should be understood to be within the scope of the present disclosure.

[0133] Figure 3 depicts how the first bidirectional transmission can be used to determine absolute clock offset information. Here, an appropriate clock offset value can be selected from a set of candidate clock offset values. Figure 3 shows, on a graph of offset phase difference determined as a function of the transmission signal frequency, the offset phase difference that may be determined in one use case scenario according to an embodiment of the present invention, and lines corresponding to a set of candidate clock offset values. Here, two frequency ranges are considered. There are two offset signals in each range.

[0134] The numbers, lines, and calculated values in Figure 3 are merely illustrative and are intended to provide a visual aid in explaining the present invention. The exact depicted values may be possible, for example, if the absolute clock offset is only about 200 picoseconds. However, the principle is the same for any clock offset.

[0135] The depicted points 302 and 304 may correspond to the first offset phase difference and the second offset phase difference, respectively. In this example, the first and second offset signals (having frequencies f1 and f2, respectively) are being transmitted. The first and second offset signals may be considered to be constituted by the first frequency range f a . An exemplary first frequency range f a extends over a frequency range of about 40 MHz.

[0136] The points 308 and 310 may correspond to the third offset phase difference and the fourth offset phase difference, respectively. In this example, the third and fourth offset signals (having frequencies f3 and f4, respectively) are being transmitted. These offset signals may be considered to be constituted by the second frequency range f b . An exemplary second frequency range f b extends over a frequency range of about 40 MHz.

[0137] The first and second frequency ranges f a , fb They may have the same bandwidth or different bandwidths from each other. However, advantageously, both the first and second frequency bands are narrow enough to enable the use of either a narrowband receiver (see WiFi receiver) or an Internet of Things (IoT) receiver operating on coin cells.

[0138] The first frequency range f a and the second frequency range f b In the example of FIG. 3, the difference Δf therebetween is about 550 MHz. The frequency of the primary signal may be greater than or less than the frequency of the auxiliary signal, but it is desirable that there is a frequency difference or a frequency range difference Δf of sufficient magnitude to determine a clock offset value that is considered appropriate.

[0139] In some embodiments of the present invention, the signal may be transmitted in a third and possibly fourth and subsequent narrow bands in addition to the first band or the first frequency range f a and the second band or the second frequency range f b . An intentional selection of the frequency range may be made, or the offset signal may be transmitted without a frequency range selection or determination being made during the selection of the offset signal frequency. By the subsequent selection of the frequency in step k described above, ultimately, the transmitted offset signal is considered to include frequencies in two different non-overlapping frequency ranges.

[0140]

[0141] ​When considering the offset phase difference as a function of the transmission frequency, the set of candidate clock offset values can be understood to correspond to the integer ambiguity lines on the graph. This is shown in FIG. 3. The set of candidate IA values (values of N) or the set of candidate clock offset values is shown as the integer ambiguity lines intersecting the first offset phase difference 302. A line having a slope corresponding to the determined clock offset variable is shown as 316. This is IA = 0 (the best provisional match). This line also determines the values of N1 - N2. The adjacent candidates are IA = +1 (318) and IA = -1 (314), corresponding respectively to the clock offset difference when the half-cycle period is larger in the measurement frequency range and the clock offset difference when the half-cycle period is smaller. All of these are within the error limits 2Δθ around the first and second offset phase difference measurement values indicated by error bars. i C and thus are part of the set of candidate IA values or clock offset values after transmission of the first and second offsets.

[0142] The integer ambiguity line IA = 0 may be determined as the line passing through two of the determined offset phase differences, or as the line having the best least-squares fit for a plurality of offset phase difference points.

[0143] In the example of FIG. 3, it can be observed that the appropriate integer ambiguity values are not limited to one possible clock offset value after transmission of the first and second offset signals, and that the third and fourth offset signals or frequencies (corresponding to offset phase differences 308 and 310) may be selected to limit the set of candidate values of the clock offset.

[0144] In FIG. 3, it can be seen that the appropriate integer ambiguity values are the values corresponding to the integer ambiguity lines that fit within the measurement error 2Δθ. i C This limits the set of candidate values of the clock offset, which in this example results in IA = 0 corresponding to line 316.

[0145] The above description related to FIG. 3 and the clock offset may also be applicable to distance determination based on a first one-way transmission. The determined first one-way phase information can thus be shown on a graph of the determined phase as a function of the transmission signal frequency. Such a graph shows candidates for the determined one-way phase information and lines corresponding to a set of candidate distance values. Similarly, the transmission frequency and the number of transmissions used can be selected such that an appropriate distance value is uniquely selected from the set of candidate distance values.

[0146] The processes a)-k) described above can be adapted for the case of distance determination based on a first one-way transmission, except that it is a set of candidate distance values determined based on one-way phase information having the corresponding error values described above.

[0147] The following differences can be applied to the determination of distance. · Instead of performing offset two-way transmission, distance one-way transmission is performed. · Instead of determining offset phase information, distance phase information regarding the distance signal received by the radio unit is determined. · Instead of determining the offset phase difference, the determined distance phase is corrected only for the clock offset between radio units within a pair and the associated antenna branch phase response. · Instead of determining the difference between offset phase differences, the difference between the corresponding distance phases is determined. · Instead of determining a clock offset variable, a distance variable is determined. · Instead of determining the estimated maximum error of the determined clock offset variable, the estimated maximum error of the distance variable is determined using the corresponding maximum error of the distance phase. · Instead of determining at least one set of clock offset candidate values, at least one set of distance candidate values is obtained through variations in distance corresponding to variations in integer wavelengths at at least one of the first or subsequent operating frequencies.

[0148] FIG. 4 shows an example of how transmission is performed in an embodiment of the present invention including four radio units RU1, RU2, RU3, and RU4. One of these radio units (RU4) may be a mobile radio unit. Individual antennas of the radio units are not depicted in FIG. 4 and are not considered.

[0149] FIG. 4 shows transmission and reception by radio units RU1, RU2, RU3, and RU4. These are performed in steps 202, 208, 212, 216, and 220 (see the method steps introduced in FIG. 2).

[0150] FIG. 4 also introduces that steps 202, 216, and 220 are performed as light measurements, and steps 208 and 212 include full measurements. The terms "light" and "full" refer to the number of different frequencies at which transmission is performed. In light measurements, a smaller number of frequencies are utilized than in full measurements. As disclosed previously, in full measurements, at least four different frequencies may be involved. (Or, sufficient frequencies may be involved to select appropriate clock offset values and / or distance values, i.e., sufficient to resolve integer ambiguities.) However, in light measurements, one or two to three different frequencies may be involved. Of course, each of all steps can also be performed using, for example, more than four frequencies, but in order to save resources, in certain steps, fewer frequencies may be sufficient.

[0151] FIG. 5 shows an exemplary embodiment of radio units 104 and 106. In this example, the radio units each have four antennas 502, 504, 506, and 508 (antenna reference numerals are depicted only for the first radio unit 104). The antennas are integrated into the radio units. The dotted line marked TIFF2025519283000046.tif811 shows various pairs of antennas that are considered and the associated distances between them.

[0152] Figure 6 shows yet another exemplary embodiment of wireless units 104, 106. In this example too, each wireless unit comprises four antennas respectively. However, these antennas are provided as separate antennas respectively, here antennas 602, 604, 606, 608. (Note that the antenna reference numerals are drawn only for the first wireless unit 104.) The estimated distances can be the same as those depicted in Figure 5, that is, the possible pairs of antennas that can be considered include all antennas 602, 604, 606, 608 of wireless units 104, 106.

[0153] One possible way to self-calibrate (which means to perform self-measurement) such wireless units is to use the leakage through the antenna switch instead of the signals coupled to other antennas.

[0154] During transmission through the antenna and during self-measurement, the switch is in the transmit (TX) position. When receiving signals from other wireless units using the antenna, the switch is in the receive (RX) position. Since the switch is a small device with excellent stability over time, the coupling term (for antenna k) through the switch TIFF2025519283000047.tif817 can be expected to be constant.

[0155] In such a configuration, when θ i Tk (f m ) is set to zero, Equation (1) becomes as follows. TIFF2025519283000048.tif13170

[0156] For each antenna, θ i Tk (f mSetting to zero means that, at the time of transmission, the clock of the radio unit is individually normalized to the phase center of each antenna. That is, the radio unit will effectively have a virtual clock for each transmitting antenna instead of a single clock. Suppose two such radio units are measuring / receiving transmission signals from each other (i.e., performing two-way transmission), and for such measurements, assume that each is using only one antenna (radio unit i uses antenna k and radio unit j uses antenna l). When determining the Doppler term and the clock rate term as described previously, Equation (4) is simplified as follows. TIFF2025519283000049.tif13170

[0157] Here, assuming that TIFF2025519283000050.tif817 is calibrated, θ i Rk and θ j Rl can be easily obtained from the self-measured values and Equation (8). Note that the index of the antenna for which the clock is normalized is added to the clock phase term. It can be seen that the clock offset between radio units i and j can be determined for the antenna pair kl.

[0158] Figure 7 depicts one exemplary use case where nine radio units RU1, RU2, RU3, RU4, RU5, RU6, RU7, RU8, RU9 each have four separate external antennas 602, 604, 606, 608. This figure depicts the distances between the antenna pairs that can be determined. Here, the antenna pairs whose distances from each other are determined do not include all the antenna pairs that could theoretically be obtained with the depicted hardware.

[0159] FIG. 8 shows a measurement frame 802 and time slots 804 according to an embodiment. Each measurement frame 802 has a selected number of time slots 804. The number of time slots 804 in each frame 802 may be different, but typically, for one system 100, the number of time slots in each frame may correspond to the number of radio units 102, 104.

[0160] The measurement frame 802 may be arranged in a superframe 806. Each superframe 806 may include a selected number of frames 802. Each superframe may include a different number of frames 802. The plurality of frames may be used for measurements at various frequencies, for example, so that the local oscillators of the radio units have time to settle to a new frequency. Although the superframe has various numbers of measurement frames, the start time of each superframe occurs regularly at a fourth time interval.

[0161] As described above, the present invention has been described with reference to the foregoing embodiments, and some advantages of the present invention have been shown. The present invention is not limited to these embodiments, but includes the spirit and scope of the inventive concept and all possible embodiments within the scope of the following claims.

[0162] Unless otherwise explicitly stated, the features described in the dependent claims can be freely combined with each other.

Claims

1. A method for determining at least one distance between multiple pairs of antennas, wherein each antenna is associated with a radio unit, and the method is Performing self-measurements through at least a portion of the antenna at a selected first time interval, and determining self-measurement phase information for each antenna that participated in the self-measurement; Perform a first bidirectional transmission between a first number of antenna pairs at the first time interval, and determine first bidirectional phase information for each antenna pair that participated in the first bidirectional transmission; To obtain information related to the clock rate and Doppler frequency of the first set of antenna pairs; Using the self-measured phase information, the first bidirectional phase information, and the clock rate and Doppler frequency related information, the antenna branch phase response data of the antennas of the first plurality of antenna pairs, and the absolute clock offset data between the plurality of radio units associated with the first plurality of antenna pairs are determined; Perform a first one-way transmission between a second set of antenna pairs at a selected second time interval, and determine first one-way phase information for each antenna pair that participated in the first one-way transmission; Based on the first unidirectional phase information determined above, antenna branch phase response data, and absolute clock offset data, distance information between the second plurality of antenna pairs is determined; Perform a second bidirectional transmission between a third set of antenna pairs at a selected third time interval, and determine second bidirectional phase information for each antenna pair that participated in the second bidirectional transmission; Tracking the clock offset variation between the plurality of wireless units based on the second bidirectional phase information and the clock rate and Doppler frequency related information; Perform a second one-way transmission between the second plurality of antenna pairs at a selected fourth time interval, and determine second one-way phase information for each antenna pair that participated in the second one-way transmission; Based on the second unidirectional phase information determined above, the tracked clock offset variation, and the antenna branch phase response data, distance information between the second plurality of antenna pairs is updated; Methods that include...

2. The method according to claim 1, wherein the first time interval is longer than the second time interval and the third time interval, preferably the second time interval is longer than the third time interval and the third time interval is longer than the fourth time interval.

3. The method according to claim 1, wherein the first time interval is 1 to 10 seconds, the second time interval is 0.5 to 2 seconds, the third time interval is 20 to 150 ms, and the fourth time interval is 5 to 20 ms.

4. The method according to claim 1, wherein the first bidirectional transmission and the first unidirectional transmission are used to determine distance information and absolute clock offset data including a resolved integer ambiguity.

5. The method according to claim 1, wherein the transmitting wireless unit transmits at least one signal in a predetermined order within a predetermined time slot.

6. The method according to claim 1, wherein the second plurality of antenna pairs includes all antenna pairs whose distance is determined.

7. The method according to claim 1, wherein at least a first portion of the antenna is fixed and at least a second portion of the antenna is movable.

8. The method according to claim 1, further comprising in the commencement step, performing at least two sets of preliminary bidirectional transmissions between the first plurality of antenna pairs, and determining a preliminary set of bidirectional phase information for each of the antenna pairs participating in the preliminary bidirectional transmissions.

9. The method according to claim 8, comprising determining information regarding the preliminary clock rate of the radio unit relating to the first plurality of antenna pairs based on the two sets of preliminary bidirectional phase information.

10. The method according to claim 8, comprising determining information regarding the Doppler frequencies for the first plurality of antenna pairs based on the two sets of preliminary bidirectional phase information.

11. The method according to claim 1, wherein the third plurality of antenna pairs comprises fewer antenna pairs than the first or second plurality of antenna pairs, and the third plurality of antenna pairs comprises at least one antenna for each wireless unit.

12. The method according to claim 1, wherein each of the third plurality of antenna pairs includes at least one antenna in each of the radio units associated with the antennas included in the first plurality of antennas.

13. The method according to claim 1, wherein the first bidirectional transmission and the first unidirectional transmission are each performed using at least three different frequencies with a selected difference between them, and the at least three frequencies extend to a selected frequency range, preferably at least 200 MHz and more preferably 500 MHz and above.

14. The method according to claim 1, wherein the second bidirectional transmission and the second unidirectional transmission are performed using fewer frequencies than the first bidirectional transmission and the first unidirectional transmission, preferably using only one or two frequencies.

15. The method according to claim 1, wherein the absolute clock offset data is determined for each pair of participating wireless units based on performing the first bidirectional transmission, and the determination is based on performing the first bidirectional transmission. a) Performing a first offset bidirectional transmission between radio units using a first offset signal that includes a selected first offset frequency; b) Determining the first offset phase information relating to the first offset signal received by the wireless unit; c) Determining the first offset phase difference as the difference between the first offset phase information determined for each of the radio units belonging to the radio unit pair; d) Performing a second or subsequent offset bidirectional transmission between at least one pair of radio units using a second or subsequent offset signal that includes the selected second or subsequent offset frequency; e) Determining the second and subsequent offset phase information for the second and subsequent offset signals received by the wireless unit; f) Determining the second and subsequent offset phase differences as the difference between the second and subsequent phase information determined for each of the radio units belonging to the radio unit pair; g) Determining the difference between the first offset phase difference and the second and subsequent offset phase differences, or the difference between the offset phase difference determined at the highest or lowest offset signal frequency and the subsequent phase differences; h) Determine at least one clock offset variable that indicates an estimated clock offset between radio units in a pair of radio units, based on the difference determined in step g; i) The estimated maximum error of the determined clock offset variable is determined based at least on the maximum error of the first offset phase difference and the maximum error of the second and subsequent offset phase differences; j) Determining whether the maximum error of the clock offset variable allows for a unique determination of the clock offset, by determining a set of candidate clock offset values ​​obtained by variations in the clock offset corresponding to an integer number of half-cycle periods of variation in the first offset frequency or subsequent offset frequencies, wherein the set of clock offset values ​​is limited by the estimated maximum error of the determined clock offset variable; k) If it is determined that the clock offset cannot be uniquely determined, repeat steps d-j using the next selected offset frequency which differs from the first offset frequency by a value greater than the difference between the first offset frequency and the second offset frequency or a previously used offset frequency; Methods that include...

16. A system for determining at least one distance between multiple antenna pairs, the system comprising at least one processor and at least two radio units, each associated with at least one antenna, Performing self-measurements through at least a portion of the antenna at a selected first time interval, and determining self-measurement phase information for each antenna that participated in the self-measurement; Perform a first bidirectional transmission between a first number of antenna pairs at the first time interval, and determine first bidirectional phase information for each antenna pair that participated in the first bidirectional transmission; To obtain information related to the clock rate and Doppler frequency of the first set of antenna pairs; Using the self-measured phase information, the first bidirectional phase information, and the clock rate and Doppler frequency related information, the antenna branch phase response data of the antennas of the first plurality of antenna pairs, and the absolute clock offset data between the plurality of radio units associated with the first plurality of antenna pairs are determined; Perform a first one-way transmission between a second set of antenna pairs at a selected second time interval, and determine first one-way phase information for each antenna pair that participated in the first one-way transmission; Based on the first unidirectional phase information determined above, antenna branch phase response data, and absolute clock offset data, distance information between the second plurality of antenna pairs is determined; Perform a second bidirectional transmission between a third set of antenna pairs at a selected third time interval, and determine second bidirectional phase information for each antenna pair that participated in the second bidirectional transmission; Tracking the clock offset variation between the plurality of wireless units using the second bidirectional phase information and the clock rate and Doppler frequency related information; Perform a second one-way transmission between the second plurality of antenna pairs at a selected fourth time interval, and determine second one-way phase information for each antenna pair that participated in the second one-way transmission; Based on the determined unidirectional phase information, the tracked clock offset variation, and the antenna branch phase response data, the distance information between the second plurality of antenna pairs is updated; A system configured to perform a task.

17. A computer program comprising program code configured to cause the system to perform the method described in any one of claims 1 to 15 when executed by the system's processing means.

18. A system comprising processing means and storage means, wherein the storage means stores a computer program, and the computer program, when executed by the processing means, is configured to cause the system to perform the method described in any one of claims 1 to 15.

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