Method and apparatus for an OFDM-based local positioning system

Abstract

The present invention provides a method and apparatus for determining the location of a mobile station (also referred to herein as a mobile object) by utilizing modified Wi-Fi signals, transmitting and receiving Wi-Fi signals by a plurality of base stations, receiving signals transmitted by these base stations (which have known coordinates and are located in the vicinity of the mobile station), and calculating the location coordinates of the mobile station (also referred to herein as a mobile object) based on the signals.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to radionavigation, and more particularly to determining the position of an object when global positioning satellite system signals are unavailable. [Background technology]

[0002] Determining the current position and motion parameters of a moving object (e.g., a moving vehicle) using a radio navigation system is a long-standing problem, and there are many known solutions using a variety of techniques.

[0003] In some cases, this determination can be made using differential ranging, a technique frequently used in various satellite positioning systems, such as the American Global Positioning System (GPS), the Russian GLONASS, and the European GALILEO. However, indoor GNSS signal reception, such as in deep mines, canyons, and other impenetrable terrain, and / or in densely populated urban areas, can be limited by the limited line-of-sight of the satellites in such navigation systems, significantly reducing the system's effectiveness in determining position.

[0004] To address these issues, technologies exist that use pseudo-satellite signals to determine vehicle position and achieve a certain level of navigation accuracy. For example, U.S. Patent Nos. 6,449,558, 7,495,614, 7,859,462, and 8,675,561 disclose various technologies using pseudo-satellite signals. Alternatively, many technologies utilize hybrid positioning devices that utilize both GNSS signals and other signals provided by terrestrial base stations to determine position (e.g., U.S. Patent Nos. 8,738,035 and 6,449,558). The advantages of such systems are wider coverage of the target area and improved position accuracy. However, such systems are highly complex and expensive to implement, and because they function as a positioning system rather than a data transmission system, they suffer from reduced communication channel throughput. Furthermore, these potential limitations are compounded by the fact that work to develop positioning and data transmission systems for mobile devices is crucial to ensuring the required levels of positioning accuracy and data communication.

[0005] To overcome some of the aforementioned limitations, many positioning techniques (e.g., fingerprinting) use Wi-Fi access points (hereinafter, "APs") to measure the strength of received signals and then compare the measured strength with a known spatial power distribution. Such fingerprinting techniques are disclosed, for example, in U.S. Patent Nos. 7,515,578, 8,155,673, and 8,838,151. These technical solutions can be used for both determining the location of mobile subscribers / customers and transmitting and receiving data via Wi-Fi networks. Several alternative technical solutions that provide both positioning and data transmission are also disclosed, such as U.S. Patent Publication Nos. 2015 / 0087331, 2015 / 0099536, and 2015 / 0172863, respectively, in which signals are transmitted over the information channel of a Wi-Fi network. However, these known methods cannot provide highly accurate estimates of coordinates (e.g., centimeter-level measurements) and present numerous technical implementation challenges, making them difficult to implement.

[0006] Other technical solutions for position determination (e.g., as disclosed in U.S. Patent Nos. 7,515,578, 7,916,661, and 8,155,673) utilize specific information from ground maps, Wi-Fi AP distribution, and / or coverage zones and received signal strength to identify the location of a mobile user. Furthermore, other known positioning devices (e.g., those disclosed in U.S. Patent Publication Nos. 2012 / 0075145 and 2013 / 0093619) utilize phase differences between signals received by antennas spaced at predetermined intervals to identify the location of a mobile object.

[0007] No. 7,859,462 describes another known positioning technique in which multiple reference transmitters generate and transmit in-phase navigation signals, which are received by a rover, and the rover's position is calculated by determining the delay time associated with the received signals. However, due to the low throughput of the communication channel, this technique cannot be directly used to transmit information between the reference transmitters and the mobile receiver / rover.

[0008] Therefore, improved techniques are needed to determine the current position and motion parameters of a mobile object when GNSS signal reception is impossible or insufficient to provide the required positioning accuracy. Summary of the Invention

[0009] A method for determining a location of a mobile station includes exchanging Wi-Fi signals between a mobile station and a plurality of base stations. The Wi-Fi signals are comprised of a plurality of Orthogonal Frequency Division Multiplexing (OFDM) communication signals. A location of the mobile station is determined based on the OFDM communication signals. The Wi-Fi signals are transmitted via a dual-polarized or triple-polarized antenna. In one embodiment, determining the location of the mobile station based on the OFDM communication signals is further based on the polarization of the OFDM communication signals. The OFDM communication signals may be generated based on a pseudo-noise sequence. A mobile station location determination system includes a mobile station and a plurality of base stations. In one embodiment, the system is configured to determine the location of the mobile station using the above procedure. A mobile station is also described, comprising a processor and a memory storing computer program instructions for determining the location of the mobile station. [Brief explanation of the drawings]

[0010] In the drawings, the same reference numerals represent the same components in different figures. The same numerals with different letter suffixes represent different instances of the same component and / or signal.

[0011] [Figure 1] FIG. 1 illustrates a network including mobile devices communicating with one or more of a plurality of wireless access points. [Figure 2] FIG. 2 shows a signal transmission graph according to an embodiment. [Figure 3] FIG. 3 shows the components of a Master Station (MSTA) including a transmit antenna with two orthogonal polarizations. [Figure 4] FIG. 4 shows the components of a slave station (SSTA) including a transmit antenna and a receive antenna using two orthogonal polarizations. [Figure 5] FIG. 5 shows the components of a Rover (Mobile) Station (RSTA) including an antenna using two orthogonal polarizations. [Figure 6] FIG. 6 shows the components of a Master Station (MSTA) including a transmit antenna with three orthogonal polarizations. [Figure 7] FIG. 7 shows the components of a slave station (SSTA) including transmit and receive antennas using three orthogonal polarizations. [Figure 8] FIG. 8 shows the components of a Rover Station (RSTA) including antennas using three orthogonal polarizations. [Figure 9] FIG. 9 shows components for generating navigation signals for two antennas using a pseudo-noise sequence (PNS) generator and a digital mixer in one embodiment. [Figure 10] FIG. 10 shows components for generating navigation signals for three antennas using pseudo-noise sequence (PNS) generators and digital mixers in one embodiment. [Figure 11] FIG. 11 shows eight tracking channels on a receiver using phase and delay measurements. [Figure 12] FIG. 12 shows the spectrum of an orthogonal frequency division multiplexed (OFDM) signal output in one embodiment. [Figure 13] FIG. 13 shows a graph of the spectrum of a 12.5 MHz signal using eight subcarriers in one embodiment. [Figure 14] FIG. 14 shows a graph of the spectrum of a 3.125 MHz signal using eight subcarriers in one embodiment. [Figure 15] FIG. 15 shows a graph of the spectrum of a 3.125 MHz signal using 16 subcarriers in one embodiment. [Figure 16]FIG. 16 shows a graph of the spectrum of a 3.125 MHz signal using 32 subcarriers in one embodiment. [Figure 17] FIG. 17 shows a graph of the spectrum of a 12.5 MHz signal using eight subcarriers in one embodiment. [Figure 18] FIG. 18 shows a graph of the spectrum of a 12.5 MHz signal using eight subcarriers in one embodiment. [Figure 19] FIG. 19 shows a graph of the spectrum of a 12.5 MHz signal using 16 subcarriers in one embodiment. [Figure 20] FIG. 20 shows a spectral representation of a signal in an embodiment. [Figure 21] FIG. 21 is a signal graph illustrating the difference in subcarrier phase estimates in an embodiment. [Figure 22] FIG. 22 shows the estimated position of a rover mobile station in an embodiment. [Figure 23] FIG. 23 shows a graph of the positioning error of the estimated position of a rover mobile station in an embodiment. [Figure 24] FIG. 24 shows the estimated position of a rover mobile station in an embodiment. [Figure 25] FIG. 25 shows a graph of the positioning error of the estimated position of a rover mobile station in an embodiment. [Figure 26] FIG. 26 shows a high-level schematic diagram of a computer that may be used to implement the various devices described herein. DETAILED DESCRIPTION OF THE INVENTION

[0012] According to an embodiment of the present invention, position determination is achieved by modifying Wi-Fi access point and station signals emitted by a master (i.e., guiding) base station, combining them with slave (i.e., guided) stations with known coordinates, and processing the signals received from these base stations at the mobile station (or user) to calculate a desired position.

[0013] This is described in more detail below, and in that description (and associated figures) acronyms and abbreviations are used, including: Media Access Control (MAC); Master Station / Master Access Point (MSTA / MAP); Orthogonal Frequency Division Multiplexing (OFDM); Physical Layer (PHY); Pseudo Noise Sequence (PNS); Rover (Mobile) Station (RSTA); Slave (Fixed) Station (SSTA); User Station (USTA); and Wireless Local Area Network (WLAN).

[0014] Specifically, various embodiments provide a method and apparatus for determining the location of a mobile station (e.g., a rover) by utilizing modified Wi-Fi signals (e.g., compliant with the IEEE 802.11 protocol), transmitting and receiving Wi-Fi signals by multiple base stations, receiving the signals transmitted by these base stations (having known coordinates and located in proximity to the mobile station), measuring delay and phase differences at the mobile station received from a different set of base stations, and calculating location coordinates of the mobile station (also referred to herein as a mobile) using the delay and phase differences. In one embodiment, the location of the mobile station is determined based on orthogonal frequency division multiplexing (OFDM) communication signals. In one embodiment, the OFDM communication signals are included in the multiple Wi-Fi signals. The location of the mobile station may be further determined based on the polarization of the OFDM communication signals. The OFDM communication signals may be based on pseudo-noise sequences as described herein.

[0015] The calculation of location coordinates is facilitated by exchanging (i.e., transmitting and receiving) Wi-Fi signals generated by a guiding (i.e., master) base station and guided (i.e., slave) stations arranged relative to each other in a predetermined manner. The master base station and slave stations periodically transmit signals in the form of frames with an assigned structure according to a predetermined time sequence. The structure of the transmitted frames includes specially generated symbol sequences used for mobile location. Service information required for the location determination operation is transmitted in fields of the preamble header and in the selected / available information fields of such frames.

[0016] Figure 1 shows a master station (MSTA) 12 in communication with a user station (USTA) 11. MSTA 12 also communicates with slave station 0 (SSTA0) 14, SSTA1 15, and SSTAN 16. The devices shown in Figure 1 exchange multiple Wi-Fi signals and orthogonal frequency division multiplexing communication signals. Note that the number of slave stations can be configured arbitrarily to cover areas of different sizes.

[0017] A mobile station, Rover Station (RSTA) 13, communicates with MSTA 12, SSTA0 14, SSTA1 15, and SSTAN 16. In one embodiment, as shown in Figure 1, MSTA 12 communicates with other devices using IEEE 802.11 communications, indicated by double-headed arrows.

[0018] MSTA 12 transmits navigation signals (e.g., signals used to determine the position of a mobile object such as RSTA 13) to SSTA0 14, SSTA1 15, SSTAN 16, and RSTA 13, as shown by the solid single arrows radiating from MSTA 12 toward SSTA0 14, SSTA1 15, SSTAN 16, and RSTA 13, respectively.

[0019] RSTA 13 receives navigation signals from each of SSTA0 14, SSTA1 15, and SSTAN 16, as indicated by the dashed single arrows pointing to RSTA 13.

[0020] Navigation signals transmitted from MSTA 12 to each of SSTA0 14, SSTA1 15, and SSTAN 16 instruct the receiving devices to transmit navigation signals to RSTA 13. In one embodiment, Wi-Fi signals constitute the navigation signals and are exchanged between the devices shown in Figure 1. Based on the navigation signals received by RSTA 13, the device determines its location using measured phase delays and phase differences.

[0021] FIG. 2 shows a signal graph 200 identifying the timing of signals transmitted from the device shown in FIG. 1. Navigation signals are transmitted from MSTA (MAP) in timing interval 0 (TS0). Navigation signals are then transmitted sequentially from SSTA0, SSTA1, and SSTAN in timing intervals TS1, TS2, and TS3, respectively. Note that there can be "N" number of slave stations transmitting navigation signals. After "N" slave stations have transmitted their navigation signals, RSTA transmits 802.11 data d in timing interval TS N+3. The sequence of navigation signals is then repeated indefinitely.

[0022] In one embodiment, the MSTA uses a transmit antenna with two orthogonal polarizations as shown in FIG. 3 for MSTA 12A, or in another embodiment, three orthogonal polarizations as shown in FIG. 6 for MSTA 12B. Each SSTA uses transmit and receive antennas with two orthogonal polarizations as shown in FIG. 4 for SSTA 14A in one embodiment, or three orthogonal polarizations as shown in FIG. 7 for SSTA 14B in another embodiment. The RSTA uses receive antennas with two orthogonal polarizations as shown in FIG. 5 for RSTA 13A in one embodiment, or three orthogonal polarizations as shown in FIG. 8 for RSTA 13B in another embodiment. Using different orthogonal polarizations at the transmit and receive antennas facilitates the implementation of more independent receive channels for tracking MSTA and SSTA signals. Using different orthogonal PNSs makes it easier to determine which antenna and which subcarrier the MSTA signal and each SSTA signal are transmitted from. Details of these embodiments are described below.

[0023] 3 illustrates an MSTA 12A configured, in one embodiment, to transmit from two orthogonal polarization antennas, each transmitting a different orthogonal pseudo-noise sequence (PNS). A media access control (MAC) and physical layer (PHY) communication module 121 receives and transmits IEEE 802.11 communications from other devices, as shown in FIG. 1. The MAC and PHY communication module 121 communicates with an OFDM Nav signal generator 122. Control signals are transmitted and received between the MAC and PHY communication module 121 and the OFDM Nav signal generator 122. In response to the control signals, the OFDM Nav signal generator 122 transmits an OFDM navigation signal to a dual-polarized transmit (Tx) antenna 123. The MSTA (MAP) navigation signal is transmitted from the dual-polarized transmit (Tx) antenna 123 in response to the OFDM navigation signal.

[0024] FIG. 4 illustrates an SSTA0 14A configured, in one embodiment, to transmit using two orthogonal polarizations, each transmitting a different orthogonal PNS. A MAC and PHY communication module 141 communicates with an OFDM Nav signal generator 142. Control signals are transmitted and received between the MAC and PHY communication module 141 and the OFDM Nav signal generator 142. In response to the control signals, the OFDM Nav signal generator 142 transmits OFDM navigation signals to a dual-polarized transmit (Tx) antenna 143, which in turn transmits SSTA navigation signals in response. An MSTA signal tracking channel 144 communicates with the OFDM signal generator 142. The MSTA signal tracking channel 144 and the OFDM signal generator 142 transmit and receive control signals to and from each other. A dual-polarized RX antenna 145 receives the MSTA (MAP) navigation signals and transmits OFDM navigation signals to the MSTA signal tracking channel 144 in response. It should be noted that while FIG. 4 shows components used in SSTA0 14A, the same components may be used in SSTA1 15, SSTAN 16, and any number of other SSTAs.

[0025] 5 shows an RSTA 13A configured to receive signals using an antenna with two orthogonal polarizations in one embodiment. A MAC and PHY communication module 131 communicates with an MSTA and SSTAs signal tracking channel 132. The MAC and PHY communication module and the MSTA and SSTAs signal tracking channel 132 each transmit and receive control signals to and from each other. The MSTA and SSTAs signal tracking channel 132 receives SSTA navigation signals from a dual-polarized RX antenna 133. It should be noted that the dual-polarized RX antenna 133 receives MSTA (MAP) navigation signals and multiple SSTA navigation signals from multiple SSTAs.

[0026] FIG. 6 illustrates an MSTA 12B configured, in one embodiment, to transmit over an antenna using three orthogonal polarizations, each transmitting a different orthogonal pseudo-noise sequence (PNS). A media access control (MAC) and physical layer (PHY) communication module 121 receives and transmits IEEE 802.11 communications from other devices, as shown in FIG. 1. The MAC and PHY communication module 121 communicates with an OFDM Nav signal generator 122. Control signals are transmitted and received between the MAC and PHY communication module 121 and the OFDM Nav signal generator 122. In response to the control signals, the OFDM Nav signal generator 122 transmits an OFDM navigation signal to a triple-polarized transmit (Tx) antenna 123. An MSTA (MAP) navigation signal is transmitted from the dual-polarized transmit (Tx) antenna 123 in response to the OFDM navigation signal.

[0027] FIG. 7 illustrates an SSTA0 14B configured, in one embodiment, to transmit using three orthogonal polarizations, each transmitting a different orthogonal PNS. A MAC and PHY communication module 141 communicates with an OFDM Nav signal generator 142. Control signals are transmitted and received between the MAC and PHY communication module 141 and the OFDM Nav signal generator 142. In response to the control signals, the OFDM Nav signal generator 142 transmits OFDM navigation signals to a triple-polarized transmit (Tx) antenna 143, which in turn transmits SSTA navigation signals in response. An MSTA signal tracking channel 144 communicates with the OFDM signal generator 142. The MSTA signal tracking channel 144 and the OFDM signal generator 142 transmit and receive control signals to and from each other. A dual-polarized RX antenna 145 receives MSTA (MAP) navigation signals and transmits OFDM navigation signals to the MSTA signal tracking channel 144 in response. It should be noted that while FIG. 7 shows components used in SSTA0 14, the same components may be used in SSTA1 15, SSTAN 16, and any number of other SSTAs.

[0028] 8 shows an RSTA 13B configured to receive signals using an antenna with three orthogonal polarizations in one embodiment. The MAC and PHY communication module 131 communicates with an MSTA and SSTAs signal tracking channel 132. The MAC and PHY communication module and the MSTA and SSTAs signal tracking channel 132 transmit and receive control signals to and from each other. The MSTA and SSTAs signal tracking channel 132 receives SSTA navigation signals from a triple-polarized RX antenna 133. Note that the dual-polarized RX antenna 133 receives MSTA (MAP) navigation signals and multiple SSTA navigation signals from multiple SSTAs.

[0029] 9 and 10 show additional details of the components used to generate the transmit signals via two antennas (FIG. 9) or three antennas (FIG. 10).

[0030] 9 shows the components for generating the signals output from the two antennas. Timing control 1421 receives a control signal and, in response, generates control signals that are sent to PNS generator for antenna 1 1422 and PNS generator for antenna 2 1424. In response to the received control signal, PNS generator for antenna 1 1422 generates PNSs for multiple subcarriers that are sent to digital mixer for orthogonal frequencies 1423. OFDM navigation signals for the Tx antenna are output from digital mixer for orthogonal frequencies 1423. In response to the received control signal, PNS generator for antenna 2 1424 generates PNSs for multiple subcarriers. OFDM navigation signals for the Tx antenna are output from digital mixer for orthogonal frequencies 1425.

[0031] FIG. 10 shows components for generating signals output from three antennas. Timing control 1421 receives a control signal and, in response, generates control signals that are sent to PNS generator for antenna 1 1422, PNS generator for antenna 2 1424, and PNS generator for antenna 3 1426. In response to the received control signal, PNS generator for antenna 1 1422 generates PNSs for multiple subcarriers that are sent to digital mixer for orthogonal frequencies 1423. OFDM navigation signals for the Tx antenna are output from digital mixer for orthogonal frequencies 1423. In response to the received control signal, PNS generator for antenna 2 1424 generates PNSs for multiple subcarriers. OFDM navigation signals for the Tx antenna are output from digital mixer for orthogonal frequencies 1425. PNS generator for antenna 3 1426 generates PNSs for multiple subcarriers. OFDM navigation signals for the Tx antenna are output from digital mixer for orthogonal frequencies 1427.

[0032] In one embodiment, using different orthogonal polarizations for the transmit and receive antennas allows for the implementation of more independent receive channels for tracking MSTA and SSTA signals. Different orthogonal PNSs are used to determine from which antenna and on which subcarrier the MSTA signal and each SSTA signal are transmitted.

[0033] FIG. 11 shows the components configured for a receiver using eight tracking channels. For example, if each antenna transmits different orthogonal PNS signals on two orthogonal subcarriers, using two antennas with orthogonal polarizations at the transmitter and the same antenna at the receiver, under multipath conditions, the receiver can obtain 2 × 2 × 2 = 8 tracking channels by measuring the phase and delay due to different multipath effects. As the number of antennas and subcarriers increases, the number of channels with different multipath effects increases depending on the shape of reflectors and the multipath correlation intervals generated in the area in which the system operates. FIG. 11 shows how timing control 1421 receives and transmits control signals related to tracking. Timing control 1421 transmits and receives control signals from PNS generator 1422 for antenna 1 and PNS generator 1424 for antenna 2. PNS generator 1422 for antenna 1 generates PNS signals for multiple subcarriers and sends them to digital mixer 1423 for orthogonal frequencies. PNS generator 1424 for antenna 2 generates PNSs for multiple subcarriers and sends them to digital mixer 1425 for orthogonal frequencies. Digital mixer 1423 for orthogonal frequencies sends PNS1, the subcarrier 1 signal, and PNS2, the subcarrier 2 signal to TX antenna 1 1426. Digital mixer 1425 for orthogonal frequencies sends PNS3, the subcarrier 1 signal, and PNS4, the subcarrier 2 signal to TX antenna 2 1428. TX antenna 1 sends subcarriers to RX antenna 1 and RX antenna 2. TX antenna 2 also sends subcarriers to RX antenna 1 and RX antenna 2. In response to the received subcarrier signals, RX antenna 1 sends PNS1, the subcarrier 1 signal, PNS2, the subcarrier 2 signal, PNS3, the subcarrier 1 signal, and PNS4, the subcarrier 2 signal. In response to the received subcarrier signals, RX Antenna 2 transmits PNS1, the subcarrier 1 signal, PNS2, the subcarrier 2 signal, PNS3, the subcarrier 1 signal, and PNS4, the subcarrier 2 signal.

[0034] Figures 12 to 19 show graphs of the spectra of the OFDM signals output from the digital mixers 1423, 1425, and 1427 shown in Figures 9, 10, and 11. In each graph of Figures 12 to 19, the signal represented by a solid black line represents the total signal input to the corresponding TX antenna.

[0035] Figure 12 shows a graph of the spectrum generated using a Gold code 12.5 MHz Type 1 signal with two subcarriers and dF = 25 MHz in one embodiment. Signal 1202 is the total signal input to the corresponding Tx antenna.

[0036] Figure 13 shows a graph of the spectrum generated using a Gold-coded 12.5 MHz Type 2 signal with 8 subcarriers and dF = 3.125 MHz. Signal 1302 is the total signal input to the corresponding Tx antenna.

[0037] Figure 14 shows a graph of the spectrum generated using a Gold-coded 3.125 MHz Type 1 signal with 8 subcarriers and dF = 3.125 MHz. Signal 1402 is the total signal input to the corresponding Tx antenna.

[0038] Figure 15 shows a graph of the spectrum generated using a Gold-coded 3.125 MHz Type 2 signal with 16 subcarriers and dF = 3.125. Signal 1502 is the total signal input to the corresponding Tx antenna.

[0039] Figure 16 shows a graph of the spectrum generated using a Gold Code 3.125 MHz Type 3 signal with 32 subcarriers and dF = 1.5625 MHz. Signal 1602 is the total signal input to the corresponding Tx antenna.

[0040] Figure 17 shows a graph of the spectrum generated using the Kasami algorithm for a 12.5 MHz Type 1 signal with 8 subcarriers and dF = 3.125. Signal 1702 is the total signal input to the corresponding Tx antenna.

[0041] Figure 18 shows a graph of the spectrum generated using the Kasami algorithm for a 12.5 MHz Type 1 signal with 8 subcarriers and dF = 6.25 MHz. Signal 1802 is the total signal input to the corresponding Tx antenna.

[0042] Figure 19 shows a graph of the spectrum generated using the Kasami algorithm on a 12.5 MHz Type 2 signal with 16 subcarriers and dF = 3.125. Signal 1902 is the total signal input to the corresponding Tx antenna.

[0043] An advantage of the positioning method using modified Wi-Fi access point and station signals described herein is that it is possible to filter out erroneous measurements using one of several different algorithms such as QLL, COLL, CoOp, vector tracking, or for example the following algorithm:

[0044] In this algorithm, the positioning system uses base stations at known coordinate points. These base stations transmit signals that are received and processed by the rover. The rover receives signals from multiple base stations and calculates its current position and / or velocity using range differencing or other known methods.

[0045] In the simplest case, where phase measurements are performed and only relative coordinates are required, the navigation signals are purely harmonic signals. Additional details are disclosed in the literature, see, for example, Joon Wayn Cheong et al., "Characterizing the Signal Structure of Locata's Pseudolite based Positioning System," International Satellite Positioning Systems Association IGNSS Symposium 2009, Holiday Inn Surfers Paradise, Qld, Australia, 1-3 December 2009; Barnes J., Rizos C., Wang J., Small D., Voigt G & Gambale N. (2003) Locata: "A New Positioning Technology for High Precision Indoor and Outdoor Positioning," Abstracts of the International Symposium on GPS / GNSS, 9-18 2003; and Locata, Inc. Each of the Technology Briefs http: / / wvvw.locata.com / wpcontent / uploads / 2014 / 07 / Locata-Technology-Brief-vBJuly-2014-Final 1 .pdf is incorporated herein by reference in its entirety.

[0046] The main context for this algorithm is local positioning radio systems operating in a strong multipath environment when signals are transmitted from a reference (base) station.

[0047] When multipath signals exist in the measurement radio channel, not only does it cause fading effects in the received signal, but it also causes uncontrollable signal phase jumps, the latter of which has a significant impact on the accuracy of the phase measurement and, consequently, the accuracy of the rover's current position.

[0048] Experimental measurements of the total phase of the signals from two receivers under multipath reception conditions show significant jumps in the total phase, which leads to an increase in the error in determining the current position. These jumps represent anomalous behavior of the total phase, caused by multipath reception of the signals from each base station.

[0049] The core of the algorithm is a method and its implementation device for reducing the impact of uncontrollable received signal phase jumps that occur during radio wave propagation in multipath channels on the accuracy of local and global positioning system position determinations based on phase measurement methods.

[0050] A positioning system typically includes several reference (base) stations Tx1...TxN with known coordinates, which transmit navigation radio signals with a predetermined structure.

[0051] The mobile unit (rover) receives navigation signals from base stations, processes them, and then determines its current position and speed. Known methods, such as range-difference methods, can be used to solve the navigation task. To determine the coordinates of a mobile unit on a plane, at least three base stations are required. To determine coordinates in three-dimensional space, four base stations are required.

[0052] In fact, in many cases, the number of base stations that a rover can "see" may exceed the minimum number required to solve the task of determining the rover's current location.

[0053] Modern navigation and positioning systems utilize code and phase measurements, which can significantly improve coordinate estimation, allowing total positioning errors to be significantly smaller than the carrier wavelength.

[0054] However, in reality, especially in local positioning systems, multipath signals exist, where the signal received by the rover's receiver is the sum of the direct signal and signals reflected from nearby objects.

[0055] The latter signals have different path lengths to the receiving point and therefore different phase delays. Furthermore, they may also have different amplitudes. Rover movement changes the phase difference between these signals, and at certain times (instantaneous moments) they may be out of phase. If the signal levels are very close, the composite signal may "fade", i.e. the signal level may drop or go to zero. In this case, when the signal reaches a minimum value, uncontrollable hopping changes occur in the total signal phase.

[0056] For example, multipath effects can be mitigated by using two separate antennas receiving the signal with different polarizations, usually with antennas that share a common phase center.

[0057] It uses multipath propagation of signals from two transmitters and reception to two independent antennas with a common phase center, where the transmitters can operate at different carrier frequencies, allowing for more efficient multipath suppression.

[0058] When a signal reflects off a nearby object, its polarization changes, so using antennas with different polarizations can eliminate signal fading at both receiving antennas simultaneously.

[0059] A similar effect occurs when signals are received from two or more transmitters, with the benefits relating to both different antenna polarizations and different transmitter frequencies.

[0060] Therefore, the use of different polarization antennas and receiving signals at different carrier frequencies of transmitters can lay the foundation for building a multipath-resistant positioning system.

[0061] Considering the above, reducing the effects of multipath on phase measurements in a navigation-positioning radio system works as follows.

[0062] Base stations with known coordinates and positioned in a predetermined manner in space transmit navigation signals with different pseudorandom codes.

[0063] A radio signal transmitted from the base station is received by a multi-channel correlation receiver in the mobile station.

[0064] The differential delay and phase of signals received from a set of different base stations is measured.

[0065] The current movement position is calculated based on the measured phase difference and delay difference.

[0066] To transmit navigation signals, base stations use radio channels that distinguish not only the code used but also several other parameters, such as carrier frequency, polarization type, spatial position, etc.

[0067] The number of radio channels exceeds the number of channels required to perform navigation measurements.

[0068] Radio signals from several base stations are received at a mobile station.

[0069] An estimate of the current overall phase of the received signal is generated for each radio channel of the multi-channel correlation receiver.

[0070] The rate of change, eg, the speed or acceleration of change of the current total phase of the received signal, is controlled at the output of each channel of the multi-channel correlation receiver.

[0071] If an abnormal change in total phase (see Figure 11) exists in the channel, the result of estimating the current total phase of the received signal in a given channel is excluded from the original data for solving the navigation task.

[0072] In one embodiment, if the base station transmits navigation signals of different polarization types, these signals are received at a mobile station equipped with multiple antennas using the same phase center and different polarization types, and the signal from the output of each antenna is sent to the input of a corresponding channel of a multi-channel correlation receiver.

[0073] Furthermore, abnormal changes in the current total phase of the received signal are detected based on the square or absolute value of the first or second increment of the current total phase exceeding a preset threshold level / value for each channel. The required numerical threshold can also be determined based on experimental or simulation measurements during the phase measurement calibration process. Because abnormal changes in the total phase can move in both decreasing and increasing directions, it is reasonable to compare the absolute value characteristic of the rate of change of the total phase with the threshold. For example, the square or absolute value of the first or second increment of the current total phase can be used.

[0074] The technical implementation of the proposed method can be realized as a single antenna receiver with redundancy of all phase estimates to improve the accuracy of the local coordinate estimation.

[0075] The navigation signals from the reference station are received by the antenna and then fed to a general multi-channel correlation receiver, which generates a current total phase estimate for each measurement channel at its output. These estimates are then fed to the corresponding inputs of the navigation task block / navigation task solution block, which generates an estimate of the rover's current position (absolute or relative, depending on the task being solved). Furthermore, the current total phase estimate for each measurement channel from the corresponding output of the multi-channel correlation receiver is fed to the input of a block corresponding to the current total phase change rate estimation for the corresponding channel 1...N. If the total phase change rate exceeds a threshold, a threshold exceedance signal is generated. The output of the corresponding channel 1...N change rate estimation block is connected to the corresponding input of the channel selection block, which generates a signal corresponding to the channel number that exceeded the threshold. The number of these measurement channels is fed, for example, to the N+1 input of the navigation task block via a data bus line. The current total phase estimate for the specified channel is corrected according to information based on the solution of the navigation task in the relevant step.

[0076] An embodiment of a block for estimating the rate of change of the total phase 1...N is shown, including a block for calculating the first or second increment of the current total phase, and a block for taking the square or absolute value of the resulting phase increment.

[0077] An abnormal change in the current total phase of the received signal on each radio channel is detected based on the square or absolute value of the first or second increment of the current total phase exceeding a predetermined threshold level.

[0078] The channel selection block works as follows: the values ​​calculated by the rate of change estimation block for each channel 1...N are sent to its input. These values ​​are compared with the threshold values ​​for each channel in the threshold units 1...N, and the outputs of the threshold units that exceed the threshold generate a logical 0, and the other outputs generate a logical 0. The channel number generation block generates at its output the data about the channel numbers that exceed the threshold.

[0079] An embodiment of the proposed method includes a multi-antenna receiver with full phase estimation redundancy to improve the accuracy of the local coordinate estimation.

[0080] The function of a multi-antenna receiver is similar to that of the single-antenna receiver described above, but because more independent receive channels are available, it is able to more effectively compensate for the effects of multipath when receiving radio signals.

[0081] The rejection of erroneous measurements in complex multipath environments improves the positioning accuracy of RSTA due to the redundancy of the measurements generated.

[0082] The methods and apparatus described herein are implemented in an aircraft hangar. In one embodiment, the methods and apparatus use the detection algorithms and multipath rejection described above.

[0083] Due to the large number of cycle slips in the phase estimate of a single transmitter signal, such methods may not be useful for centimeter-level positioning, so redundancy was created in the transmitted signal. In this frequency range, within a bandwidth of up to 50 MHz, an OFDM signal with pseudorandom Gold codes was generated because multipath is frequency selective. The spectral representation of this signal is shown in Figure 20. To increase redundancy, all available combinations of orthogonal polarizations at the transmitter and receiver were also used. Figure 20 also shows the spectral representation of an OFDM signal using Gold PRN. Each subcarrier is modulated with the same Gold code, resulting in a sum of 2002 subcarriers.

[0084] Phase estimation using an OFDM signal using Gold's PRN is performed independently for each subcarrier. However, if the phase estimate is converted to a metric, it is possible to implement an algorithm to detect cycle slips in the estimate using a catcher based on the total phase estimate. Implementing the algorithm requires calculating the total phase difference between all subcarrier pairs, then, at each point in time, selecting the phase estimate for the subcarrier that is currently not affected by multipath. Implementing this algorithm requires calculating the total phase difference between all subcarrier pairs, then, at each point in time, selecting the phase estimate for the subcarrier that is currently not affected by multipath. These operations must be performed separately for each transmitter at the receiver. This results in an estimate of the total phase increment, from which most of the cycle slips are removed. Figure 21 shows the difference in phase estimates between subcarriers. It can be seen that this parameter contains only noise and cycle slips, since the effects of RF, motion, and other hardware are identical in both subcarriers and cancel each other out.

[0085] When this algorithm was applied to experimental data from a hangar, the algorithm achieved a root mean square (RMS) of 2D position of approximately 10 cm, as shown in Figures 22 to 25 .

[0086] 22 shows a graph of the estimated position of a Rover Mobile Station (RSTA) traveling in a circular orbit in one embodiment in which the algorithm is used. Circular path 2202 is the actual traveling path, and substantially circular path 2204 is the estimated traveling path determined by the systems and methods described herein.

[0087] Figure 23 shows a graph of the estimated position error of the RSTA traveling on a circular orbit as shown in Figure 22. Figures 22 and 23 show a single run of the RSTA along a circular orbit, and show that the 2D RMS is less than 10 cm.

[0088] 24 shows a graph of the estimated position of an RSTA traveling in multiple circular orbits in one embodiment where the algorithm is used. The circular path 2402 is the actual path traveled, and the other substantially circular graphs are estimated paths traveled determined by the systems and methods described herein.

[0089] Figure 25 shows a graph of the estimated position error of the RSTA traveling multiple circular orbits as shown in Figure 24. Figures 24 and 25 show that only a small amount of tracking error accumulates / stores over multiple runs along the orbit. Error storage / accumulation can be a phenomenon specific to local positioning systems.

[0090] In one embodiment, a computer may be used to implement various devices (e.g., a master station, a user station, a slave station, a rover station) and to perform various methods and operations described herein. A high-level block diagram of such a computer is shown in FIG. 26. Computer 2602 includes a processor 2604 that controls the overall operation of computer 2602 by executing computer program instructions that define such operations. The computer program instructions are stored in storage 2612 or other computer-readable medium (e.g., magnetic disk, CD-ROM, etc.) and are loaded into memory 2610 when execution of the computer program instructions is required. Thus, the methods and operations described herein are defined by computer program instructions stored in memory 2610 and / or storage 2612 and controlled by processor 2604 executing the computer program instructions. For example, the computer program instructions may be implemented as computer-executable code programmed by one skilled in the art to perform the algorithms defined by the methods and operations described herein. Thus, by executing the computer program instructions, processor 2604 performs the algorithms defined by the methods and operations described herein. The computer 2602 also includes one or more network interfaces 2606 for communicating with other devices over a network. The computer 2602 also includes input / output devices 2608 (such as a display, keyboard, mouse, speakers, buttons, etc.) that allow a user to interact with the computer 2602. Those skilled in the art will recognize that an actual computer implementation may include other components, and that Figure 26 is a high-level representation of some of the components of such a computer for purposes of explanation.

[0091] The foregoing detailed description should be understood in all respects to be illustrative and representative, and not restrictive, and the scope of the inventive concepts disclosed herein should be interpreted in accordance with the broadest scope permitted by patent law. It should be understood that the embodiments shown and described herein are merely illustrative of the principles of the inventive concepts, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the inventive concepts. Those skilled in the art could implement various other feature combinations without departing from the scope and spirit of the inventive concepts.

Claims

1. 1. A method for determining a location of a mobile station, comprising: exchanging a plurality of Wi-Fi signals between the mobile station and a plurality of base stations, the Wi-Fi signals including a plurality of Orthogonal Frequency Division Multiplexing (OFDM) communication signals; determining a location of the mobile station based on the OFDM communication signals.

2. The method of claim 1 , wherein the Wi-Fi signal is transmitted via a dual-polarized antenna.

3. The method of claim 1 , wherein the Wi-Fi signal is transmitted via a tri-polarized antenna.

4. 3. The method of claim 2, wherein determining the location of the mobile station based on the OFDM communication signal is further based on the polarization of the OFDM communication signal.

5. The method of claim 3 , wherein determining the location of the mobile station based on the OFDM communication signals is further based on the polarization of the OFDM communication signals.

6. The method of claim 4 , wherein the OFDM communication signal is based on a pseudo-noise sequence.

7. The method of claim 5 , wherein the OFDM communication signal is based on a pseudo-noise sequence.

8. A mobile station and a plurality of base stations, exchanging a plurality of Wi-Fi signals between the mobile station and the plurality of base stations, the Wi-Fi signals including a plurality of Orthogonal Frequency Division Multiplexing (OFDM) communication signals; A system configured to determine a location of the mobile station based on the OFDM communication signal.

9. The system of claim 8 , wherein the Wi-Fi signal is transmitted via a dual-polarized antenna.

10. The system of claim 8 , wherein the Wi-Fi signal is transmitted via a tri-polarized antenna.

11. 10. The system of claim 9, wherein determining the location of the mobile station based on the OFDM communication signal is further based on the polarization of the OFDM communication signal.

12. 11. The system of claim 10, wherein determining the location of the mobile station based on OFDM communication signals is further based on polarization of the OFDM communication signals.

13. The system of claim 11 , wherein the OFDM communication signal is based on a pseudo-noise sequence.

14. The system of claim 12 wherein the OFDM communication signal is based on a pseudo-noise sequence.

15. A mobile station, a processor; a memory storing computer program instructions that, when executed by the processor, cause the processor to perform operations; receiving a plurality of Wi-Fi signals from a plurality of base stations, the Wi-Fi signals including a plurality of orthogonal frequency division multiplexing (OFDM) communication signals; A mobile station that determines a location of the mobile station based on the OFDM communication signal.

16. 16. The mobile station of claim 15, wherein the Wi-Fi signal is transmitted via a dual-polarized antenna.

17. 16. The mobile station of claim 15, wherein the Wi-Fi signal is transmitted via a tri-polarized antenna.

18. 17. The mobile station of claim 16, wherein determining the location of the mobile station based on the OFDM communication signal is further based on the polarization of the OFDM communication signal.

19. 20. The mobile station of claim 17, wherein determining the location of the mobile station based on the OFDM communication signal is further based on polarization of the OFDM communication signal.

20. 20. The mobile station of claim 18, wherein the OFDM communication signal is based on a pseudo-noise sequence.

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