Method and apparatus for generating and distributing radio signal correction data

Abstract

A method and apparatus for generating and distributing signal correction data for use by GNSS receivers. In embodiments, a method for performing signal processing in a radio signal receiver and a moving antenna that moves about a known, fixed location, includes: receiving radio signals from a plurality of transmitters using the moving antenna, where the antenna is moving relative to the received radio signals; performing motion compensated correlation of the signals to generate motion compensated correlation results; determining a measured pseudorange from the receiver and each of the plurality of transmitters; determining a difference between the pseudorange and an expected pseudorange for each transmitter, where the difference represents an atmospheric delay experienced by the signals as the signals propagate from each transmitter to the receiver; and transmitting the delay to a correction data server to be used to generate correction data that is distributed to at least one GNSS receiver.

Description

METHOD AND APPARATUS FOR GENERATING AND DISTRIBUTING RADIO SIGNAL CORRECTION DATABACKGROUNDField

[0001] Embodiments of the present invention generally relate to radio signal receivers and, in particular, to a method and apparatus for generating and distributing radio signal correction data.Description of the Related Art

[0002] Positioning signal receivers such as receivers for global satellite navigation systems (GNSS) signals have become ubiquitous in mobile devices and vehicles. A GNSS receiver (e.g., receivers for GPS, GLONASS, GALILEO, BEIDOU, etc. satellite signals or a combination thereof) receive signals from satellites, process the received signals and determine the position of the receiver from information contained in the received signals.

[0003] To determine a position, the GNSS receiver determines the distance to each satellite that is in view above the receiver. This distance is known as a pseudorange. The receiver knows the location of each satellite from ephemeris data supplied to the receiver. The accuracy of the pseudorange varies with unknown signal propagation delays caused by the atmosphere (e.g., tropospheric and ionospheric delays) as well as errors and biases in satellite clock and orbit information. Such pseudorange inaccuracy causes inaccuracy in the position calculation, e.g., at best unaided GNSS accuracy is about 2 m.

[0004] In real-time kinematic (RTK) positioning systems and / or Precise Point Positioning (PPP) systems various common errors, including atmospheric delays and satellite related errors, are corrected to improve the position calculation. An RTK system places RTK reference stations at surveyed locations. These reference stations comprise highly accurate GNSS receivers and complex antennas that enable the position uncertainty to be reduced to as little as about 2.5 cm. The RTK reference stations transmit signal correction data (typically, through the cell telephone networkPATENTAttorney Docket No.: FPP0044WOor via satellite ground link) to roving GNSS receivers that operate within about a 35 km radius of a reference station. Within the operating radius of a reference station, the roving receiver uses the correction data to correct for common errors, including atmospheric delays, within the signal processing. In addition, other correction data including satellite clock errors, satellite orbit errors and / or satellite biases may be provided to the RTK system by the GNSS operator and then distributed to the GNSS receivers. Specifically, the receiver compensates for the atmospheric delays (and other anomalies) through adjustment of GNSS observables such as the pseudoranges, carrier phase and / or code phase. The use of correction data in this manner enables the roving receiver to achieve high position accuracy that is on the order of the accuracy at the reference station, e.g., up to about 2.5 cm.

[0005] Unfortunately, RTK and PPP systems are expensive and complex. In addition, RTK systems find limited use within urban environments where multipath interference impacts the operation and accuracy of the RTK reference stations’ ability to accurately determine atmospheric delays.

[0006] Therefore, there is a need in the art for a method and apparatus for generating and distributing radio signal correction data using inexpensive reference stations that accurately operate in urban environments.SUMMARY

[0007] Embodiments of the present invention generally relate to a method and apparatus for generating and distributing radio signal correction data as shown in and / or described in connection with at least one of the figures.

[0008] Various features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout.PATENTAttorney Docket No.: FPP0044WOBRIEF DESCRIPTION OF THE DRAWINGS

[0009] So that the manner in which the features of the present invention can be understood in detail, a particular description of the invention, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0010] FIG. 1 depicts a block diagram of a system for generating and distributing correction data in accordance with at least one embodiment of the invention;

[0011] FIG. 2 is a functional block diagram of a reference station in accordance with at least one embodiment of the invention;

[0012] FIG. 3 is a functional block diagram of a correction data server in accordance with at least one embodiment of the invention;

[0013] FIG. 4 depicts a flow diagram of a method of generating correction data in accordance with at least one embodiment of the invention;

[0014] FIG. 5 depicts a flow diagram of a method of processing and distributing correction data in accordance with at least one embodiment of the invention; and

[0015] FIG. 6 depicts a flow diagram of a method of using correction data in a GNSS receiver in accordance with at least one embodiment of the invention.DETAILED DESCRIPTION

[0016] Embodiments of the present invention comprise apparatus and methods of generating and distributing radio signal correction data for radio signal receivers. Such receivers include receivers used in positioning systems (e.g., GNSS receivers).

[0017] Embodiments of the invention comprise a plurality of motion compensated correlation reference stations (also referred to as a SUPERCORRELATION™ GNSSPATENTAttorney Docket No.: FPP0044WO(S-GNSS®) reference station) coupled through a communications network to a correction data server. SUPERCORRELATION™ and S-GNSS® are trademarks of Focal Point Positioning Ltd. The S-GNSS reference stations are positioned in known, fixed locations and use a stationary SUPERCORRELATION™ technique to process received GNSS radio signals to extract common error correction data, e.g., atmospheric delays, from the received signals. Other correction data such as, but not limited to, satellite orbit errors, satellite clock errors, and / or satellite biases that are available for the GNSS operators. The SUPERCORRELATION™ technique is used to receive GNSS signals in challenging environments (e.g., urban environments, attenuated signal environments, spoofing environments) and facilitate determining very accurate pseudoranges to line-of-sight (LOS) satellites. Since the reference stations know their locations and the location of the LOS satellites from the satellite ephemeris, the pseudoranges are processed to determine the correction data, including atmospheric delays experienced by the signals as they propagate from the satellites to the reference stations. Alternatively, rather than compute the correction data locally, the received GNSS signals may be transmitted from the reference stations to a remote location for processing to compute the correction data.

[0018] Each reference station comprises a standard, inexpensive GNSS receiver that is capable of executing the motion compensated correlation process. To generate motion at a stationary reference station, the reference station comprises a simple, inexpensive antenna (e.g., monopole patch antenna) that is set in motion on a moving platform. For example, the antenna (or the antenna and receiver) is attached to a rotating platform where the axis of rotation is located at the fixed, known location. The stationary SUPERCORRELATION™ technique is described in commonly assigned US Patent Publication No. US20240014549A1, published 11 January 2024, entitled “Method and Apparatus for Processing Radio Signals,” which is herein incorporated by reference herein in its entirety. By using motion compensated correlation, the reference station may accurately operate in an urban environment where multipath interference is prevalent.PATENTAttorney Docket No.: FPP0044WO

[0019] The plurality of S-GNSS reference stations transmit the correction data (or the received GNSS signals) through the communications network to a correction data server. The server processes the data (or signals) to form a correction data map covering an area between the reference stations. In one embodiment, the correction data map may be transmitted through the communications network to at least one GNSS receiver. The GNSS receiver extracts correction data from the map that is relevant to the receiver’s estimated position and uses the correction data to process received satellite signals. The use of the correction data enables the GNSS receiver to significantly improve its computed position accuracy. In alternative embodiments, the GNSS receiver may request correction data related to its location and the correction data server sends the relevant correction data rather than send an entire correction data map or a portion of a map.

[0020] FIG. 1 depicts a block diagram of a system 100 for generating and distributing correction data in accordance with at least one embodiment of the invention. The system 100 comprise a plurality of motion compensated correlation reference stations (also referred to as a SUPERCORRELATION™ GNSS (S-GNSS®) reference station) 102-1, 102-2,... 102-N (collectively referred to as reference stations 102) coupled through a communications network 106 to a correction data server 108. The communications network 106 comprises, but is not limited to, satellite communications network, internet network, wide area network, local area network, and / or combinations of one or more such networks. The correction data reference stations 102 are positioned in known locations. The positions may be known by placing the stations 102 at surveyed markers, through use of an RTK positioning system to accurately position the stations 102, or some other known procedure for providing accurate position information to the reference station 102.

[0021] Each S-GNSS reference station 102 uses a stationary SUPERCORRELATION™ technique (also referred to as a stationary motion compensated correlation technique) to process received GNSS radio signals to extract common error correction data, e.g., atmospheric delays, from the receivedPATENTAttorney Docket No.: FPP0044WOsignals. The SUPERCORRELATION™ technique is used to receive GNSS signals in challenging environments (e.g., urban environments, attenuated signal environments, spoofing environments) and facilitate determining very accurate pseudoranges. In one embodiment, within an urban environment, the reference stations are spaced about 10 km apart from one another. In other environments, the stations may be spaced about at shorter or longer distances. The motion compensated correlation technique enables the reference station to accurately discriminate the angle of arrival of the received signals. In this manner, the reference stations 102 are capable of improving the reception of signals from line-of-sight (LOS) satellites (i.e., satellites directly transmitting to the reference station 102 without reflection) and attenuating the reception of signals from non-line-of-sight (NLOS) satellites (and / or GNSS spoofers). The receiver may receive a LOS signal and a NLOS signal from the same satellite and, using S-GNSS, select to receive the LOS signal and attenuate the NLOS signal. As such, the S-GNSS reference stations 102 are capable of operating in urban environments and attenuated signal environments.

[0022] Since the reference stations 102 know their locations and the location of the LOS satellites from satellite ephemeris, each reference station 102 determines what the pseudorange should be (i.e., an expected pseudorange). Through processing the received signals, the reference stations 102 compute pseudoranges to the LOS satellites (i.e., the measured pseudoranges). The difference between the expected pseudorange and the measured pseudorange represents the common errors which can be used as correction data. This difference is the signal delay caused when the signals pass through the atmosphere (e.g., tropospheric and ionospheric delays collectively referred to as atmospheric delays). Additional correction data may be supplied to the correction data server 108 via the communications network 106 by other correction data sources 110 and distributed to the GNSS receivers 104. Such additional correction data includes, but is not limited to, satellite orbit error, satellite clock errors and / or satellite biases that are made available from the GNSS operators.PATENTAttorney Docket No.: FPP0044WO

[0023] In other embodiments, where the location of reflecting surface(s) is known, e.g., three-dimensional (3D) building map, the NLOS signals may be used for determining the atmospheric delay. For example, with knowledge of the location of the satellite and knowledge of the reflector location, the pseudorange of the reflected NLOS signal path is determined. The difference between the expected reflected signal pseudorange and the measured reflected signal pseudorange represents the atmospheric delay.

[0024] The plurality of S-GNSS reference stations 102 transmit the correction data through the communications network 106 to the correction data server 108. The server 108 processes the data as described in detail below to form a correction data map covering an area between the reference stations 102. In one embodiment, the correction data map (or a portion of the map) may be transmitted through the communications network 106 to at least one GNSS device 104-1, 104-2,... 104-N (collectively referred to as GNSS devices 104). In some embodiments, the GNSS devices 104 may be S-GNSS devices, i.e., containing GNSS receivers that are capable of performing motion compensated correlation. The at least one GNSS device 104 extracts correction data from the map that is relevant to its estimated position and uses the correction data to process received satellite signals. The use of the correction data enables the at least one GNSS device 104 to significantly improve the accuracy of its position computation. In other embodiments, the at least one GNSS device 104 may request correction data related to its estimated location from the server 108 and the correction data server 108 sends the relevant correction data rather than send an entire correction data map or a portion of a map.

[0025] FIG. 2 is a functional block diagram of a reference station 102 in accordance with at least one embodiment of the invention. In one embodiment, each reference station 102 comprises a standard, inexpensive GNSS receiver 250 that is capable of executing the motion compensated correlation process. To generate motion at a stationary reference station, the reference station 102 comprises a simple, inexpensive antenna (e.g., monopole patch antenna) 200 that is set in motion on anPATENTAttorney Docket No.: FPP0044WOactuator 201, e.g., a moving platform that imparts, for example, circular motion to the antenna 200. In one embodiment, the antenna 200 (or receiver and antenna together) rotates at a known velocity around an axis that is located at a fixed, known location. The antenna motion is relative to the received GNSS signals (i.e., relative to the transmitters). The stationary SUPERCORRELATION™ technique is described in commonly assigned US Patent Publication No. US20240014549A1, published 11 January 2024, entitled “Method and Apparatus for Processing Radio Signals,” which is herein incorporated by reference herein in its entirety.

[0026] In one exemplary embodiment, the GNSS receiver 250 comprises a front end 202, support circuits 204, motion module 208, at least one processor 206 and memory 210. The front end 202 is generally coupled to the moving antenna 200. In some embodiments, the antenna and receiver together are attached to the actuator 201 to cause the antenna to move relative to the received GNSS signals and the transmitter(s). The SUPERCORRELATION™ technique operates based upon determining a component of motion of the signal receiving antenna 200 that is in the direction of the source (e.g., GNSS satellite) of a received signal. Any mention of motion herein refers to the motion of the antenna 200 with respect to the stationary GNSS receiver 250.

[0027] The receiver’s front end 202 downconverts, filters, and samples (digitizes) the received signals in a manner that is well-known to those skilled in the art. The output of the receiver front end 202 is a digital signal containing signal data. The signal data of interest for performing motion compensation is a deterministic code, e.g., Gold code, used by the processor 206 to synchronize the receiver 250 to the GNSS transmission.

[0028] The at least one processor 206 may be any form of processor or combination of processors including, but not limited to, central processing units, microprocessors, microcontrollers, field programmable gate arrays, graphics processing units, digital signal processors, and the like. The support circuits 204 mayPATENTAttorney Docket No.: FPP0044WOcomprise well-known circuits and devices facilitating functionality of the processor(s). The support circuits 204 may comprise one or more of, or a combination of, power supplies, clock circuits, analog to digital converters, communications circuits, cache, displays, filters, and / or the like.

[0029] The memory 210 comprises one or more forms of non-transitory computer readable media including one or more of, or any combination of, read-only memory or random-access memory. The memory 210 stores software and data including, for example, GNSS signals 216 (and / or representations of those signals), signal processing software 212, and a motion model 218. The memory 210 may also store a receiver position estimate 220, correction data 222 (e.g., atmospheric delays, satellite bias, satellite clock error, satellite orbit errors, and various additional data used to perform the SUPERCORRELATION™ processing and pseudorange correction. In some embodiments, the correction data 222 may be determined at the correction data server (108 in FIG. 1) as described below. The signal processing software 212 comprises motion compensated correlation software 214 that is executed to perform the SUPERCORRELATION™ technique.

[0030] Satellite-based positioning systems utilize encoded digital signals including a deterministic digital code to facilitate signal acquisition, e.g., Gold codes. Such a digital code is determined by the receiver 250 and repeatedly broadcast by the transmitter to enable a receiver to acquire and process transmitted signals. Using such deterministic codes combined with an accurate motion model of the receiver, embodiments of the invention are useful to enable the receiver 250 to improve its position computation accuracy and / or signal reception. The technique for improving radio signal reception using receiver motion compensated signal correlation is known as SUPERCORRELATION™ and is described in commonly assigned US patent 9,780,829, issued 3 October 2017; US patent 10,321,430, issued 11 June 2019; US patent 10,816,672, issued 27 October 2020; US patent 11,808,865, issued 7 November 2023; US patent 11,474,258, issued 18 October 2022; US patent publication 2024 / 0045077, published 8 February 2024, and US Patent PublicationPATENTAttorney Docket No.: FPP0044WO2024 / 0014549, published 11 January 2024, which are hereby incorporated herein by reference in their entireties. The motion model 218 is known from the controlled motion imparted by the actuator 201 to the antenna 200 (or the receiver-antenna combination). The motion, e.g., circular motion around an axis at a controlled velocity, is defined by the motion module 208 and controlled by the processor 206.

[0031] In operation, the at least one processor 206 accesses the buffered GNSS signals 216 and the at least one processor 206 correlates the received code from each satellite with locally generated codes to produce correlation results. The correlation results are processed as is well-known in the art to generate position information 220, e.g., the correlation results are used to determine pseudoranges for each satellite and the pseudoranges are processed to compute the receiver position 220. The at least one processor 206 performs the SUPERCORRELATION™ processing to provide signals (phasor sequences) to phase adjust the complex correlation results such that the coherent integration period is extended, e.g., extended to one or more seconds, to improve signal reception and angle of arrival discrimination. The phasor sequence is a time sequence of phase offsets where each phasor in the sequence adjusts the phase of a complex signal sample. The adjustment may be performed by adjusting the phase of each sample of the received signals, the locally generated signals or the correlation results themselves. The least computationally intensive adjustment process adjusts the phase of the complex correlation results.

[0032] In some embodiments, the GNSS signals may have been fully or partially processed before being buffered as part of the data. For example, the partially processed signals may include downconverted, filtered, and / or sampled GNSS signals. Fully processed signals may include complex correlation results.

[0033] The motion model 218 is used by the at least one processor 206 to generate phasor sequences that are used to motion compensate the complex correlation results. The phasor sequences comprise a sequence of phase offsets to be madePATENTAttorney Docket No.: FPP0044WOover time, e.g., across a received signal, to compensate for phase changes that occur over time due to movement of the antenna. In one embodiment, the motion module 208 defines the motion to be imparted to the antenna 200 and uses the at least one processor 206 to generate control signals causing the actuator 201 to move the antenna 200 in a predictable manner, e.g., a constant rotational speed about a central axis. In one embodiment, the motion may comprise the velocity and heading (i.e., a motion model 218) of the antenna rotating at a radius offset from a central axis.

[0034] As is described in detail below, the SUPERCORRELATION™ technique determines which satellites are sending signals without reflection or significant attenuation, i.e., the satellites that are line-of-sight (LOS) to the receiver antenna. These LOS signals are selected for processing to determine the atmospheric delays experienced by the signals. The atmospheric delays may be computed within the receiver 250 and sent to the correction data server 108 or the received LOS GNSS signals may be transmitted to the correction data server 108 for processing. For example, rather than compute the correction data locally, the received GNSS signals (or data derived from or representing the GNSS signals such as measured pseudoranges, signal correlation results and the like) may be transmitted from the S-GNSS reference stations to a remote location (e.g., a correction data server) for processing to compute the correction data. Whether the receiver 250 performs the atmospheric delay processing or not depends on the computing power of the receiver’s processor 206. Various techniques for computing atmospheric delays are described below with respect to FIG. 6.

[0035] In other embodiments, where the location of reflecting surface(s) is known, e.g., three-dimensional (3D) building map, the NLOS signals may be used for determining the atmospheric delay. For example, with knowledge of the location of the satellite and knowledge of the reflector location, the pseudorange of the reflected NLOS signal path is determined. The difference between the expected reflected signal pseudorange and the measured reflected signal pseudorange represents the atmospheric delay.PATENTAttorney Docket No.: FPP0044WO

[0036] FIG. 3 is a functional block diagram of a correction data server 108 in accordance with at least one embodiment of the invention. In one exemplary embodiment, the correction data server 108 comprises a processor 300, support circuits 302, and memory 304.

[0037] The at least one processor 300 may be any form of processor or combination of processors including, but not limited to, central processing units, microprocessors, microcontrollers, field programmable gate arrays, graphics processing units, digital signal processors, and the like. The support circuits 302 may comprise well-known circuits and devices facilitating functionality of the processor(s). The support circuits 302 may comprise one or more of, or a combination of, power supplies, clock circuits, analog to digital converters, communications circuits, cache, displays, filters, and / or the like. The support circuits 302 provide an interface to the communications network 106.

[0038] The memory 304 comprises one or more forms of non-transitory computer readable media including one or more of, or any combination of, read-only memory or random-access memory. The memory 304 stores software and data including, for example, correction data generation software 306, atmospheric delays 308, GNSS signals 310, a correction data map 312, and correction data 314. The atmospheric delays 308 and / or the GNSS signals 310 may be provided by the S-GNSS reference stations 102 via the communications network 106. The S-GNSS reference stations 102 may provide the GNSS signals 310 from satellites to the correction data server 108 such that the server 108 may calculate the atmospheric delays 308 at each of the stations 102 from the GNSS signals 310. Alternatively, the stations may locally compute the atmospheric delays 308 and transmit the atmospheric delays 308 through the communications network 106 to the correction data server 108. Additionally, the correction data 314 may include additional correction data including, but not limited to, satellite orbit error, satellite clock error, and / or satellite biases, that are made available from GNSS operators.PATENTAttorney Docket No.: FPP0044WO

[0039] In operation, the correction data server 108 executes the correction data generation software 306 to process the atmospheric delays 308 to generate the correction data map 312. The correction data map 312 is a model of the atmospheric delays in a geographic region between the S-GNSS stations 102. In one embodiment, the server 108 transmits the correction data map 312 through the communications network 106 to the GNSS devices 104 to enable the devices to determine their local correction data for use by the GNSS devices 104 as described in detail below. In other embodiments, the GNSS devices 104 may request correction data related to its specific position estimate and the satellites from which the receiver is currently receiving signals. The server 108 transmits the specific correction data to the requesting device.

[0040] FIG. 4 depicts a flow diagram of a method 400 of operation of the at least one S-GNSS reference station 102 in accordance with at least one embodiment of the invention. As described above, the S-GNSS reference station 102 has a known location and a moving antenna. The method 400 begins at 402 and proceeds to 404 where the S-GNSS reference station 102 receives GNSS signals. Using a motion compensated correlation technique (also known as SUPERCORRELATION™), at 406, the method 400 determines the satellite signals that are transmitted directly from the satellite to the receiver without reflection (i.e., LOS or direct satellite signals).

[0041] At 406, the received GNSS signals are processed using the SUPERCORRELATION™ technique to motion compensate the correlation results. During this process, the SUPERCORRELATION™ procedure generates a plurality of phasor sequence hypotheses related to the motion information. Each phasor sequence hypothesis comprises a phase estimate that varies with motion parameters of the receiver. The signal processing correlates a local code encoded in a local signal with a code encoded in the received RF signal. The phasor sequence hypotheses are used to adjust, at a sub-wavelength accuracy, the complex carrier phase of the local signal. Such adjustment or compensation may be performed by adjusting a local oscillator signal, the received signal(s), or the correlation result. The signals and / orPATENTAttorney Docket No.: FPP0044WOcorrelation results comprise complex signal samples having in-phase (I) and quadrature phase (Q) components. The method applies each phase offset in the phasor sequence to a corresponding complex sample in the signals and / or correlation results. For each received signal, the process correlates the received signals with a set (plurality) of phasor sequence hypotheses containing estimates of a phase offset necessary to accurately correlate the received signals. All the hypotheses are tested to find the hypothesis that provides the best or optimal correlation result magnitude.

[0042] The motion estimates are typically hypotheses of the motion in a direction of interest such as in the direction of the satellite that transmitted the received signal, e.g., along the signal propagation path. As with all GNSS receivers, the satellite positions are known to the reference station through known ephemeris data. A comparison of correlation results over the direction hypotheses enables the method 400 to narrow the search space when processing subsequently received signals. Consequently, subsequent compensation is performed over a narrow search space.

[0043] In one embodiment, if a signal from a given satellite was received previously, the set of hypotheses for the newly received signal include a group of phasor sequence hypotheses using the expected Doppler and Doppler rate and / or last Doppler and last Doppler rate used in receiving the prior signal from that particular satellite. The hypotheses values may be centered around the last values used or the last values used additionally offset by a prediction of further offset based on the expected receiver motion. The method 400 correlates each received signal with that signal’s set of hypotheses. The hypotheses are used as parameters to form the phase-compensated phasors to phase compensate the correlation process. As such, the phase compensation may be applied to the received signals, the local frequency source (e.g., an oscillator), or the correlation result values. The result of the correlation process is a plurality of phase-compensated correlation results - one phase-compensated correlation result value for each hypothesis for each received signal.PATENTAttorney Docket No.: FPP0044WO

[0044] The method 400 processes the correlation results to find the “best” or optimal result for each received signal. In one embodiment, the method 400 produces a joint correlation output as a function (e.g., summation) of the plurality of correlation results resulting from all the hypotheses and received transmitter signals. The joint correlation output may be a single value or a plurality of values that represent the parameter hypotheses (preferred hypotheses) that provide an optimal or best correlation output. In general, a cost function is applied to each set of correlation values for each received signal to find the optimal correlation output corresponding to a preferred hypothesis or hypotheses.

[0045] For example, assuming all other receiver parameters are known except receiver motion direction, the method 400 tests hypotheses with various phasor sequences that compensate for phase changes due to each direction hypothesis. The correct phasor sequence hypothesis that represents the accurate direction estimate will produce the highest correlation result magnitude for a given received signal. By processing the received signals from different satellites, the correlation results will converge upon hypotheses representing the true antenna motion direction as well as the direction from which the signal has been transmitted (e.g., the transmission angle of arrival).

[0046] With knowledge of the angle of arrival and the satellite ephemeris defining the height of the satellite above the horizon, the method 400 may discriminate amongst satellite signals to identify the LOS satellites and their signals. In other embodiments, the method 400 may use a 3DMA (3D-mapping-aiding) map to determine if any satellites are obscured by buildings. The signals from the obscured satellites will be considered NLOS and will not be used to determine the correction data.

[0047] If additional receiver parameters (e.g., clock frequency and / or frequency rate) are unknown or not accurately known, those parameter offsets may also be expressed as phasor hypotheses and tested to optimize the correlation output acrossPATENTAttorney Docket No.: FPP0044WOmultiple parameters at once. These parameter offsets are used to correct inaccuracies in, for example, the receiver clock.

[0048] At 408, the method 400 may optionally determine the atmospheric delays from the GNSS signals it has received. Since the S-GNSS station has a known location and the station knows the location of each satellite from the satellite ephemeris, the atmospheric delay may be computed as the difference between the expected pseudorange and the measured pseudorange. This computation is performed for each LOS signal (or NLOS signal when reflector location is known). Other techniques may be used to determine the atmospheric delay experienced by each received signal as described below with reference to FIG. 5.

[0049] At 410, the method 400 transmits either the GNSS signals (or representations of the signals) or the computed atmospheric delays for each satellite as well as the station location to the correction data server. At 412, the method 400 queries whether the method 400 should continue receiving and processing signals. If the query is affirmatively answered, the method 400 proceeds along path 416 to receive and process additional GNSS signals. If the query at 412 is negatively answered, the method 400 proceeds to 414 and ends.

[0050] FIG. 5 depicts a flow diagram of a method 500 of processing and distributing correction data using the correction data server 108 in accordance with at least one embodiment of the invention. The method 500 begins at 502 and proceeds to 504 where the method 500 receives either the GNSS signals to be used in the atmospheric delay calculation or the atmospheric delays that were computed by the plurality of S-GNSS reference stations 102. At 506, the method 500 stores the information it has received from the S-GNSS reference station 102.

[0051] At 508, the method 500 computes a correction data map using the information it has received from the S-GNSS reference stations 102. If the method 500 has received the GNSS signals without the computed atmospheric delays, the method 500 computes the atmospheric delays associated with each of the S-GNSSPATENTAttorney Docket No.: FPP0044WOsignals prior to computing the correction data map. The correction data map includes a model of the atmospheric delays across the geographic region between S-GNSS reference stations 102. In essence, the method 500 interpolates the atmospheric delays in the region between S-GNSS reference stations 102 from the computed atmospheric delays for each of the S-GNSS reference stations 102.

[0052] More specifically, the method 500 uses the S-GNSS reference stations 102 as a distributed network of noisy sensors and crowd sources the atmospheric delay data. In one embodiment, GNSS signals from both L1 (1575.42 MHz) and L5 (1176 MHz) frequencies from each satellite are collected and processed to determine atmospheric delay data. An embodiment may use the technique described in Smith, J. et al., “Mapping the Ionosphere with Millions of Phones,” Code Ocean, https: / / doi.org / 10.24433 / CO.9149928.v1 (2024). This technique analyzes dual frequency GNSS signal data from smartphones to determine the total electron content (TEC) within the ionosphere along a propagation path between the visible GNSS satellites and the smartphones. The electron density in the propagation path delays the propagation of the GNSS signal. The technique produces a TEC map for a region of the atmosphere above the smartphones. The TEC map may be used to produce an atmospheric delay map, i.e., the relationship between electron density and ionospheric delay is well known. Embodiments of the invention ensure that the TEC mapping technique only uses LOS satellite signals (or NLOS signals when the reflector location is known) received at the reference stations and reduces the effects of multipath on the TEC / atmospheric delay calculations. This in turn enables more accurate local delay maps to be generated using data from few S-GNSS reference stations - the various embodiments described herein do not require “millions of phones” to produce an accurate TEC and / or atmospheric delay map.

[0053] Other techniques may be used to analyze the GNSS signals to determine atmospheric delays rather than creating TEC maps. For example, a measured pseudorange may be compared to an expected pseudorange for a particular satellite. The difference between the expected and measured pseudoranges represents thePATENTAttorney Docket No.: FPP0044WOatmospheric delay. In other embodiments, for a given satellite, signal measurements may be performed on one or more frequencies (e.g., L1 and / or L5) to compute the atmospheric delay. When using dual frequencies, the difference in propagation time of a signal using each frequency (time of flight) is indicative of the atmospheric delay (e.g., the difference between propagation time of an L1 signal and an L5 signal). By crowd sourcing the processing across many S-GNSS reference stations, the impact of device biases (e.g., differential code bias (DBC)) are suppressed enabling computation of accurate atmospheric delays.

[0054] At 510, the method 500 transmits the map, a portion of the map, or individual delays extracted from the map to the GNSS devices 104. In some embodiments, the correction data may also include satellite clock errors, satellite orbit errors and / or satellite bias. The GNSS devices 104 use the correction data to improve the navigation solution as described below. At 512, the method 500 queries whether the method should process additional received GNSS signals and / or atmospheric delays. If the query is answered affirmatively, the method proceeds along 516 to 504. If the query is negatively answered, the method 500 proceeds to 514 and ends.

[0055] FIG. 6 depicts a flow diagram of a method 600 of using correction data in a GNSS device 104 in accordance with at least one embodiment of the invention. The method 600 begins at 602 and proceeds to 604 where the method 600 receives correction data from correction data server 108. In one embodiment, the correction data may comprise the entire map for the region in which the GNSS device is located and the GNSS device extracts the correction data that is pertinent to its location from the map. In another embodiment, the server transmits only a portion of a correction data map that is relevant to the GNSS device and the GNSS device extracts the correction data for its particular location estimate. In a further embodiment, the correction data server may send only specific correction data that is relevant to a particular GNSS device. Such specific data may be sent upon a given GNSS device requesting correction data. Which of these embodiments to use depends on thePATENTAttorney Docket No.: FPP0044WOamount of memory available within the GNSS device and / or the amount of processing power available within the GNSS device.

[0056] At 606, the method 600 uses the correction data it has received from the correction data server 108 to adjust the GNSS observable, e.g., at least one of the measured pseudoranges to each satellite, the carrier phase or the code phase. For example, remove the delay by shortening the measured pseudorange. At 608, the method 600 uses the adjusted observables to calculate the position of the GNSS device 104. The use of observables to calculate a position and / or velocity is performed using a well-known navigation solution. In this manner, the method 600 is capable of computing a highly accurate position because of the use of the correction data.

[0057] At 610, the method 600 queries whether the method 600 should continue to compute additional positions for the GNSS device 104. If the query is affirmatively answered, the method 600 proceeds along path 614 to update the position of the device104. If the query is negatively answered, the method 600 proceeds to 612 where it ends.

[0058] Here multiple examples have been given to illustrate various features and are not intended to be so limiting. Any one or more of the features may not be limited to the particular examples presented herein, regardless of any order, combination, or connections described. In fact, it should be understood that any combination of the features and / or elements described by way of example above are contemplated, including any variation or modification which is not enumerated, but capable of achieving the same. Unless otherwise stated, any one or more of the features may be combined in any order.

[0059] As above, figures are presented herein for illustrative purposes and are not meant to impose any structural limitations, unless otherwise specified. Various modifications to any of the structures shown in the figures are contemplated to be within the scope of the invention presented herein. The invention is not intended to be limited to any scope of claim language.PATENTAttorney Docket No.: FPP0044WO

[0060] Where “coupling” or “connection” is used, unless otherwise specified, no limitation is implied that the coupling or connection be restricted to a physical coupling or connection and, instead, should be read to include communicative couplings, including wireless transmissions and protocols.

[0061] Any block, step, module, or otherwise described herein may represent one or more instructions which can be stored on a non-transitory computer readable media as software and / or performed by hardware. Any such block, module, step, or otherwise can be performed by various software and / or hardware combinations in a manner which may be automated, including the use of specialized hardware designed to achieve such a purpose. As above, any number of blocks, steps, or modules may be performed in any order or not at all, including substantially simultaneously, i.e., within tolerances of the systems executing the block, step, or module.

[0062] Where conditional language is used, including, but not limited to, “can,” “could,” “may” or “might,” it should be understood that the associated features or elements are not required. As such, where conditional language is used, the elements and / or features should be understood as being optionally present in at least some examples, and not necessarily conditioned upon anything, unless otherwise specified.

[0063] Where lists are enumerated in the alternative or conjunctive (e.g., one or more of A, B, and / or C), unless stated otherwise, it is understood to include one or more of each element, including any one or more combinations of any number of the enumerated elements (e.g. A, AB, AC, ABC, ABB, etc.). When “and / or” is used, it should be understood that the elements may be joined in the alternative or conjunctive.

[0064] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

PATENTAttorney Docket No.: FPP0044WOClaims:

1. A method for performing signal processing in a radio signal receiver and a moving antenna that moves about a known, fixed location, comprising:receiving radio signals from a plurality of transmitters using the moving antenna, where the antenna is moving relative to the received radio signals;performing motion compensated correlation of the received radio signals to generate motion compensated correlation results;determining a measured pseudorange from the radio signal receiver and each of the plurality of transmitters;determining a difference between the measured pseudorange and an expected pseudorange for each transmitter of the plurality of transmitters, where the difference represents an atmospheric delay experienced by the radio signals as the radio signals propagate from each transmitter to the radio signal receiver; and transmitting the atmospheric delay to a correction data server to be used to generate correction data that is distributed to at least one GNSS receiver.

2. The method of claim 1, wherein the generated correction data includes a correction data map covering an area between a plurality of the radio signal receivers.

3. The method of claim 1 or 2, wherein the radio signal receiver is a GNSS receiver.

4. The method of any of claims 1 -3, further comprising identifying one or more line of sight signals from the received signals, and / or identifying one or more non line of sight (NLOS) signals reflected from reflecting surfaces at known locations and using the one or more NLOS signals and the known locations to determine atmospheric delay.PATENTAttorney Docket No.: FPP0044WO5. The method of any of claims 1 -4, wherein the motion compensated correlation is performed only on received radio signals that are transmitted from one or more line of sight transmitters.

6. The method of any of claims 1-5, wherein performing motion compensated correlation includes generating a plurality of phasor sequence hypotheses, wherein each phasor sequence hypothesis comprises a phase estimate that varies with parameters of the radio signal receiver, and correlating the received radio signals with the plurality of phasor sequence hypotheses.

7. The method of claim 6, wherein the parameters of the radio signal receiver include at least one of motion parameters, clock frequency, or frequency rate.

8. The method of claim 6, wherein for a received signal that was previously received from a transmitter, the plurality of phasor sequence hypotheses for the received signal include a group of phasor sequence hypotheses using an expected Doppler and Doppler rate and / or previous Doppler and Doppler rate used in receiving the previously received signal from the transmitter.

9. The method of claim 6, further comprising processing the motion compensated correlation results to produce a joint correlation output as a function of the motion compensated correlation results resulting from all of the plurality of phasor sequence hypotheses and received radio signals, wherein the joint correlation output represents an optimal correlation output.

10. The method of claim 9, wherein processing the motion compensated correlation results include applying a cost function to correlation values for each received signal to find the optimal correlation output corresponding to one or more preferred hypothesis.PATENTAttorney Docket No.: FPP0044WO11. Apparatus for generating correction date in a radio signal receiver having and a moving antenna that moves about a known, fixed location, comprising at least one processor and at least one non-transient computer readable medium for storing instructions that, when executed by the at least one processor, causes the apparatus to perform operations comprising:receiving radio signals from a plurality of transmitters using the moving antenna, where the antenna is moving relative to the received radio signals;performing motion compensated correlation of the received radio signals to generate motion compensated correlation results;determining a measured pseudorange from the radio signal receiver and each of the plurality of transmitters;determining a difference between the measured pseudorange and an expected pseudorange for each transmitter of the plurality of transmitters, where the difference represents an atmospheric delay experienced by the radio signals as the radio signals propagate from each transmitter to the radio signal receiver; and transmitting the atmospheric delay to a correction data server to be used to generate correction data that is distributed to at least one GNSS receiver.

12. The apparatus of claim 11, wherein the generated correction data includes a correction data map covering an area between a plurality of the radio signal receivers.

13. The apparatus of claim 11 or 12, wherein the radio signal receiver is a GNSS receiver.

14. The apparatus of any of claims 11-13, wherein the operations further comprise identifying one or more line of sight signals from the received signals, and / or identifying one or more non line of sight (NLOS) signals reflected from reflecting surfaces at known locations and using the one or more NLOS signals and the known locations to determine atmospheric delay.PATENTAttorney Docket No.: FPP0044WO15. The apparatus of any of claims 11-14, wherein the motion compensated correlation is performed only on received radio signals that are transmitted from one or more line of sight transmitters.

16. The apparatus of any of claims 11-15, wherein performing motion compensated correlation includes generating a plurality of phasor sequence hypotheses, wherein each phasor sequence hypothesis comprises a phase estimate that varies with parameters of the radio signal receiver, and correlating the received radio signals with the plurality of phasor sequence hypotheses.

17. The apparatus of claim 16, wherein the parameters of the radio signal receiver include at least one of motion parameters, clock frequency, or frequency rate.

18. The apparatus of claim 16, wherein for a received signal that was previously received from a transmitter, the plurality of phasor sequence hypotheses for the received signal include a group of phasor sequence hypotheses using an expected Doppler and Doppler rate and / or previous Doppler and Doppler rate used in receiving the previously received signal from the transmitter.

19. The apparatus of claim 16, wherein the operations further comprise processing the motion compensated correlation results to produce a joint correlation output as a function of the motion compensated correlation results resulting from all the plurality of phasor sequence hypotheses and received radio signals, wherein the joint correlation output represents an optimal correlation output.

20. The apparatus of claim 19, wherein processing the motion compensated correlation results include applying a cost function to correlation values for eachPATENTAttorney Docket No.: FPP0044WOreceived signal to find the optimal correlation output corresponding to one or more preferred hypothesis.

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