WO2022095939A1 - Gnss接收机和卫星捕获跟踪方法 - Google Patents

Gnss接收机和卫星捕获跟踪方法 Download PDF

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WO2022095939A1
WO2022095939A1 PCT/CN2021/128796 CN2021128796W WO2022095939A1 WO 2022095939 A1 WO2022095939 A1 WO 2022095939A1 CN 2021128796 W CN2021128796 W CN 2021128796W WO 2022095939 A1 WO2022095939 A1 WO 2022095939A1
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time
satellite
gnss
receiver
module
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PCT/CN2021/128796
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English (en)
French (fr)
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李志成
赵岩
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展讯通信（上海）有限公司
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/35—Constructional details or hardware or software details of the signal processing chain
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/25—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS
    • G01S19/256—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS relating to timing, e.g. time of week, code phase, timing offset
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/28—Satellite selection

Definitions

  • the invention belongs to the technical field of satellite acquisition and tracking, and in particular relates to a GNSS receiver and a satellite acquisition and tracking method.
  • GNSS Global Navigation Satellite System, Global Navigation Satellite System
  • GNSS system the full name of Global Navigation Satellite System, includes GPS (Global Positioning System, Global Positioning System) of the United States, GLONASS (Global Navigation Satellite System, Global Navigation Satellite System) of Russia, BDS (BeiDou Satellite Navigation System, Beidou Satellite) of China navigation system) and the European Union's Galileo (Galileo) satellite navigation system.
  • GPS Global Positioning System, Global Positioning System
  • GLONASS Global Navigation Satellite System, Global Navigation Satellite System
  • BDS BeiDou Satellite Navigation System, Beidou Satellite
  • Galileo Galileo
  • the hardware part of GNSS receiver mainly includes RF front-end circuit, acquisition engine and tracking engine.
  • the RF front-end circuit is used to receive the signal from the GNSS satellite. After the signal is amplified, filtered, down-converted, etc., an intermediate frequency signal suitable for analog conversion is generated and sent to the capture engine.
  • the acquisition engine usually contains a certain number of acquisition channels, and each channel is used to search and acquire specific satellite signals.
  • the tracking engine completely strips the intermediate frequency carrier and pseudo-random code from the navigation message from the satellite signal searched by the acquisition engine.
  • the positioning solution module is a pure software module, which uses the satellite information decoded by the tracking engine to finally calculate the terminal's position, speed and precise time information.
  • the GNSS receiver includes an antenna, a radio frequency front end, a baseband processor and a processor, wherein the baseband processor includes an acquisition engine module and a tracking engine module. And a co-processing for performing baseband related software processing and positioning calculations.
  • the signal-in-space arriving at the antenna is downconverted, filtered, and digitized in the front-end section. This process ultimately generates the desired intermediate frequency data, typically represented as real and complex components (ie, I (in-phase) and Q (quadrature) components).
  • the capture engine module includes a real number component capture channel, a complex number component capture channel and a local code generator.
  • the real number component capture channel includes a real number component accumulator, a real number component integrator and dumper
  • the complex number component capture channel includes a complex number component accumulator and a complex number component integrator.
  • the GNSS receiver generates the C/A locally. A copy of the code is performed, and a correlation operation is performed with the signal of the IQ branch to achieve code alignment. According to the autocorrelation properties of C/A codes, when the local replica and the input signal are aligned, their correlation operation will generate a peak. The code delay/Doppler frequency corresponding to this peak gives a good estimate of the initial tracking engine tracking loop.
  • the tracking engine module includes code tracking channel, carrier tracking channel and auxiliary carrier module.
  • the GNSS receiver tracks them by replicating the C/A codes and continuously adjusting their code delay and carrier phase to ensure synchronization with the incoming signal.
  • the receiver implements a code tracking loop and a carrier tracking loop to achieve synchronization with the input signal.
  • Integrate and Dump A module that accumulates the correlator output and provides its in-phase I and quadrature Q components.
  • Discriminator Processes the output of the correlator to provide measurable quantities (eg carrier phase information).
  • Filter Filter the output of the discriminator to reduce noise.
  • NCO Numerically Controlled Oscillator converts filter output to Doppler frequency and available correction factor for code delay
  • the integrator and dumper the module that accumulates the correlator output and provides its in-phase I and quadrature Q components.
  • the discriminator is used to process the output of the correlator to provide measurable quantities (eg carrier phase information). Filters are used to filter the output of the discriminator to reduce noise.
  • a numerically controlled oscillator is used to convert the filter output into available correction factors for Doppler frequency and code delay.
  • the carrier loop jitter is much less than the code loop jitter, so the measured value in the carrier loop can be used to eliminate the dynamic characteristics of the code loop line of sight (LOS, Line of sight), reduce the order of the code loop filter and its bandwidth.
  • This architecture is often referred to as an auxiliary carrier module.
  • the acquisition engine occupies more chip area than other modules (such as the tracking engine), which has a significant impact on the overall cost of the chip.
  • the acquisition engine mainly carries the search for satellite signals. Due to its large search range, it is often necessary to perform a full-range code domain search and a wide-range frequency scan.
  • the capture engine is computationally intensive and consumes a lot of battery capacity.
  • the power consumption of the tracking engine is significantly lower than that of the capture engine.
  • the technical problem to be solved by the present invention is to provide a GNSS receiver and a satellite acquisition and tracking method in order to overcome the defects of large occupied area and large power consumption of the acquisition engine in the prior art GNSS receiver.
  • the present invention provides a GNSS receiver, comprising a cellular communication module and a GNSS module;
  • the GNSS module includes a tracking engine and a navigation solution module
  • the cellular communication module is used to parse the signal frame to obtain the frame edge, the navigation calculation module is used to record the first local time according to the frame edge, the cellular communication module is also used to obtain the corresponding first GPS time according to the frame edge, and the cellular communication module also uses To estimate the frequency offset to obtain the clock drift corresponding to the local clock;
  • the cellular communication module is also used to obtain the optimized GPS time according to the first GPS time and the signal transmission delay, and send the optimized GPS time to the navigation calculation module.
  • the signal transmission delay is required for the signal to be transmitted from the base station to the GNSS receiver. time;
  • the navigation calculation module is also used to obtain the current time according to the first local time, the optimized GPS time, and the second local time, and the second local time is the local time corresponding to the optimized GPS time received by the GNSS module;
  • the navigation calculation module is also used to obtain the acquisition parameters of the satellite according to the current time, clock drift, and satellite navigation messages;
  • the tracking engine makes satellite acquisitions based on the acquisition parameters.
  • the signal transmission delay is the signal transmission delay
  • (X 1 , Y 1 , Z 1 ) represent the coordinates corresponding to the position of the base station
  • (X 2 , Y 2 , Z 2 ) represent the coordinates corresponding to the approximate position of the GNSS receiver
  • c represents the speed of light.
  • the navigation calculation module obtains pseudoranges, Doppler raw observation quantities, and satellite positions according to satellite ranging signals and satellite navigation messages;
  • the navigation calculation module obtains the position, speed and second GPS time Tgps of the GNSS receiver according to the pseudorange, Doppler original observation, and the position of the satellite;
  • the navigation calculation module performs filter estimation according to the cellular network time and the third GPS time Tgps_1 to obtain the system deviation ⁇ T.
  • the navigation calculation module performs filter estimation based on the following linear model:
  • ⁇ is the cellular network time to be estimated, represents the corresponding time change rate, ⁇ is the model error, T s represents the measurement time interval; ⁇ Measurement is Tgps_1, ⁇ represents the observation error;
  • a time-dependent Kalman filter is constructed based on a linear model, and ⁇ and ⁇ are estimated by ⁇ Measurement Obtain the ⁇ estimation error of the filtered output as the system bias ⁇ T.
  • the navigation calculation module estimates the code phase of the satellite according to the following formula:
  • T transmit T Receiver - ⁇ T travel - ⁇ T SatClkBias ;
  • T transmit represents the estimated transmission time of the satellite signal
  • T Receiver represents the current time
  • ⁇ T travel is the time required for the satellite signal to propagate from the satellite to the GNSS receiver
  • ⁇ T SatClkBias is the clock drift information of the satellite.
  • the navigation calculation module determines the precise position, velocity and time information of the GNSS receiver based on the least squares method or the Kalman filter algorithm.
  • the invention also provides a satellite acquisition and tracking method.
  • the satellite acquisition and tracking method is realized based on a GNSS receiver, and the GNSS receiver includes a cellular communication module and a GNSS module;
  • the GNSS module includes a tracking engine and a navigation solution module
  • the satellite capture and tracking method includes the following steps:
  • the cellular communication module parses the signal frame to obtain the frame edge, the navigation calculation module records the first local time according to the frame edge, the cellular communication module obtains the corresponding first GPS time according to the frame edge, and the cellular communication module estimates the frequency offset to obtain the corresponding local clock the clock drift;
  • the cellular communication module obtains the optimized GPS time according to the first GPS time and the signal transmission delay, and sends the optimized GPS time to the navigation calculation module, and the signal transmission delay is the time required for the signal to be transmitted from the base station to the GNSS receiver;
  • the navigation calculation module obtains the current time according to the first local time, the optimized GPS time, and the second local time, and the second local time is the local time corresponding to the optimized GPS time received by the GNSS module;
  • the navigation calculation module obtains the acquisition parameters of the satellite according to the current time, clock drift and satellite navigation message
  • the tracking engine makes satellite acquisitions based on the acquisition parameters.
  • the signal transmission delay is the signal transmission delay
  • (X 1 , Y 1 , Z 1 ) represent the coordinates corresponding to the position of the base station
  • (X 2 , Y 2 , Z 2 ) represent the coordinates corresponding to the approximate position of the GNSS receiver
  • c represents the speed of light.
  • the step of obtaining the system deviation ⁇ T includes:
  • the navigation calculation module obtains pseudoranges, Doppler raw observations, and satellite positions according to satellite ranging signals and satellite navigation messages;
  • the navigation calculation module obtains the position, speed and second GPS time Tgps of the GNSS receiver according to the pseudorange, Doppler original observation, and the position of the satellite;
  • the navigation calculation module performs filter estimation according to the cellular network time and the third GPS time Tgps_1 to obtain the system deviation ⁇ T.
  • the navigation calculation module performs filter estimation based on the following linear model:
  • ⁇ is the cellular network time to be estimated, represents the corresponding time change rate, ⁇ is the model error, T s represents the measurement time interval; ⁇ Measurement is Tgps_1, ⁇ represents the observation error;
  • a time-dependent Kalman filter is constructed based on a linear model, and ⁇ and ⁇ are estimated by ⁇ Measurement Obtain the ⁇ estimation error of the filtered output as the system bias ⁇ T.
  • the step of obtaining the capture parameters of the satellite includes:
  • the navigation solver module estimates the code phase of the satellite according to the following formula:
  • T transmit T Receiver - ⁇ T travel - ⁇ T SatClkBias ;
  • T transmit represents the estimated transmission time of the satellite signal
  • T Receiver represents the current time
  • ⁇ T travel is the time required for the satellite signal to propagate from the satellite to the GNSS receiver
  • ⁇ T SatClkBias is the clock drift information of the satellite.
  • the satellite capture and tracking method further includes the following steps:
  • the navigation calculation module determines the precise position, velocity and time information of the GNSS receiver based on the least squares method or the Kalman filter algorithm.
  • the positive improvement effect of the invention is that the invention can effectively improve the satellite acquisition speed, reduce the chip area of the GNSS receiver and reduce the power consumption of the GNSS receiver.
  • FIG. 1 is a schematic structural diagram of a GNSS receiver according to Embodiment 1 of the present invention.
  • FIG. 2 is a schematic structural diagram of a GNSS module of a GNSS receiver according to Embodiment 1 of the present invention.
  • FIG. 3 is a flowchart of a satellite acquisition and tracking method according to Embodiment 3 of the present invention.
  • the GNSS receiver 9 includes a cellular communication module 5 and a GNSS module 6 .
  • the cellular communication module 5 communicates with the base station 1 through the first antenna 3 .
  • the GNSS module 6 communicates with the satellite 2 via the second antenna 8 .
  • the cellular communication module 5 and the GNSS module 6 share a TCXO (Temperature Compensate X'tal (crystal) Oscillator temperature compensation crystal oscillator) 10 as a clock source.
  • TCXO Tempoture Compensate X'tal (crystal) Oscillator temperature compensation crystal oscillator
  • the GNSS module 6 includes a radio frequency front end 103 , a tracking engine 104 and a navigation calculation module 105 .
  • the radio frequency front end 103 receives the signal from the satellite 2 through the second antenna 8, and performs operations such as amplifying, filtering, and down-converting the signal to generate an intermediate frequency signal.
  • the tracking engine 104 directly processes the signal through the auxiliary information, completely strips the carrier and the pseudo-random code from the navigation message, and obtains the corresponding bit stream of the navigation message.
  • the navigation calculation module 105 performs frame synchronization and decoding calculation on the navigation message obtained by the tracking engine to obtain satellite-related information (including position, speed, clock error, etc.)
  • the Ler frequency shift observation value is finally calculated by the least square method or Kalman filtering operation to obtain the position, velocity and time information of the GNSS receiver.
  • the precise auxiliary information required by the aforementioned tracking engine for satellite acquisition includes precise time information, satellite navigation messages, and approximate position information of the receiver.
  • the cellular communication module 5 can provide precise time information, and the AGNSS (Aided-GNSS, Assisted GNSS) server 107 can provide the general position information of the receiver, satellite navigation messages and other related information.
  • the GNSS receiver stores receiver status, satellite message information, etc. in the non-volatile memory 108 .
  • the cellular communication module 5 cannot provide accurate time assistance information and cannot directly capture satellites through the tracking engine.
  • the software capture engine module 109 is activated to capture satellites.
  • the software capture engine module 109 runs in DDR (Double Rate Synchronous Dynamic Random Access) memory 110 . Therefore, it does not consume any RAM (Random Access Memory) or ROM (Read-Only Memory) space of the GNSS chip.
  • DDR Double Rate Synchronous Dynamic Random Access
  • the GNSS receiver of this embodiment performs satellite acquisition and tracking with reference to the following steps:
  • Step S1 the cellular communication module parses the signal frame to obtain the frame edge, the navigation calculation module records the first local time according to the frame edge, the cellular communication module obtains the corresponding first GPS time according to the frame edge, and the cellular communication module performs frequency. Bias estimation to get the clock drift corresponding to the local clock.
  • Step S2 the cellular communication module obtains the optimized GPS time according to the GPS time and the signal transmission delay, and sends the optimized GPS time to the navigation calculation module.
  • the signal transmission delay is the time required for the signal to be transmitted from the base station to the GNSS receiver.
  • Step S3 the navigation calculation module obtains the current time according to the first local time, the optimized GPS time, and the second local time.
  • the second local time is the local time corresponding to the optimized GPS time received by the GNSS module.
  • Step S4 the navigation calculation module obtains the acquisition parameters of the satellite according to the current time, clock drift, and satellite navigation message.
  • Step S5 the tracking engine performs satellite acquisition according to the acquisition parameters.
  • the GNSS receiver 9 After the GNSS receiver 9 receives the start command, it starts to execute the GNSS start process, and requests the cellular communication module 5 for time information and assistance information.
  • auxiliary information There are two sources of auxiliary information here. One is to fetch directly from non-volatile memory 108 . This method is usually used in GNSS warm-start mode. Another source is the AGNSS server 107 .
  • the terminal product is in the form of a single GNSS module, the AGNSS request is directly completed by the GNSS module 6; in another optional embodiment, if the terminal product is a mobile phone, a wearable device For products with AP (application processor), the AGNSS service is completed by the AP.
  • AP application processor
  • the AP After the AP receives the auxiliary information sent by the server, it transmits it through UART (Universal Asynchronous Receiver/Transmitter, Universal Asynchronous Receiver/Transmitter) or other methods. Give GNSS module 6.
  • the auxiliary information includes rough time information, position information, ephemeris parameters and other information.
  • the cellular communication module 5 When the cellular communication module 5 receives the time request from the GNSS module 6, in step S1, the cellular communication module 5 parses the signal frame to obtain the frame edge, and generates an interrupt signal at the edge of the signal frame and sends it to the GNSS module 6 for navigation calculation module 105. Since the GNSS module 6 and the cellular communication module 5 are directly connected by hardware (such as through GPIO (General-purpose input/output, general-purpose input/output), etc.), the time delay of the interrupt signal transmission is negligible, so the interrupt signal and the signal corresponding to the frame edge.
  • GPIO General-purpose input/output, general-purpose input/output
  • the navigation calculation module 105 of the GNSS module 6 After the navigation calculation module 105 of the GNSS module 6 receives the interruption signal, the navigation calculation module 105 records the first local time Tg1 according to the interruption signal, and waits for the time information transmitted by the software channel.
  • the cellular communication module 5 obtains the corresponding first GPS time T1 according to the frame edge, and the cellular communication module 5 performs frequency offset estimation to obtain the clock drift clkDrift corresponding to the local clock TCXO and the corresponding ambiguity.
  • the signal transmission delay deltaT is the time required for the signal to be transmitted from the base station to the GNSS receiver 9 .
  • the size of deltaT depends on the distance between the receiver and the base station.
  • the specific calculation method of deltaT refers to the following formula:
  • (X 1 , Y 1 , Z 1 ) are the coordinates corresponding to the base station position
  • (X 2 , Y 2 , Z 2 ) are the coordinates corresponding to the approximate position of the GNSS receiver 9
  • c is the speed of light.
  • the introduction of deltaT can effectively improve the accuracy. For example, when the distance between the base station and the GNSS receiver 9 is 3 km (kilometers), ignoring deltaT will bring about an error of 10 chips.
  • the coordinates corresponding to the base station position are known.
  • the method of obtaining the approximate position of the GNSS receiver 9 is: the GNSS receiver 9 measures the downlink pilot signals of different base stations, and obtains TOA (Time of Arrival, time of arrival) of the downlink pilots of different base stations ) or TDOA (Time Difference of Arrival, time difference of arrival), according to the measurement results and the coordinates of the base station position, the triangular formula estimation algorithm is used to calculate the approximate position of the GNSS receiver 9.
  • TOA Time of Arrival, time of arrival
  • TDOA Time Difference of Arrival, time difference of arrival
  • the operation of the cellular communication module 5 to demodulate the time starts after the cellular communication network completes the network setup.
  • the cellular communication module 5 obtains the optimized GPS time T2 and transmits the GPS time T2 to the navigation calculation module 105 of the GNSS module 6 .
  • step S3 the navigation calculation module 105 obtains the current time T Receiver according to the first local time Tg1, the optimized GPS time T2, and the second local time Tg2, and the second local time Tg2 is the optimized GPS time Tg2 received by the GNSS module 6.
  • T Receiver T2+(Tg2-Tg1).
  • the GNSS module 6 has obtained the precise time information (the current time T Receiver ), the clock drift of the local clock clkDrift, the rough position information and the satellite navigation message. This information is sufficient to estimate satellite acquisition parameters, including code phase and Doppler shift.
  • step S4 the navigation calculation module 105 estimates the code phase of the satellite according to the following formula:
  • T transmit T Receiver - ⁇ T travel - ⁇ T SatClkBias ;
  • T transmit is the estimated satellite signal transmission time. Since the length of a periodic signal of the GNSS satellite C/A code is 1023 chips, the duration is 1 millisecond. When the precise transmission time is obtained, the precise chip position can be calculated by only considering the part less than milliseconds;
  • ⁇ T travel is the time it takes for the satellite signal to travel from the satellite to the receiver, which can be calculated from the satellite position parsed by the message and the rough receiver position. Since the receiver position error obtained through base station positioning is usually within 500 meters, the chip estimation error introduced by the receiver position error is usually less than 10 chips in the worst case, and this part can be considered in the satellite acquisition range.
  • ⁇ T SatClkBias is the clock drift information of the satellite, which can be directly demodulated from the satellite message.
  • the Doppler shift can be calculated from the Doppler effect of the satellite and the receiver, and the effect of the clock drift of the receiver's local clock needs to be considered.
  • the speed of the satellite can be calculated directly from the information given in the navigation message, the speed of the receiver can be replaced by a rough estimate, and the ambiguity is taken into account in the Doppler frequency search range.
  • the tracking engine is directly activated to capture satellites. Because the estimated parameters are relatively accurate, the tracking engine can usually quickly capture satellite signals, and provide the demodulated information as observations to the navigation solution module. The navigation solution module finally determines the precise position, speed and time information of the receiver through the least square method or Kalman filtering algorithm.
  • the time accuracy of base station 1 is of the same order of magnitude as GNSS.
  • the time synchronization requirement is 10us; when base station 1 is a TD-SCDMA base station, the time synchronization requirement is 3u; when base station 1 is an LTE base station, the time synchronization requirement is 1us or even on the order of microseconds.
  • the accuracy requirements for the base station system in this embodiment can be well satisfied.
  • each base station is equipped with a GNSS receiver 9 as a reference source for the time reference.
  • the GNSS receiver 99 includes both the cellular communication module 5 and the GNSS module 6 .
  • the cellular communication module 5 receives the signal frame from the base station 1, and analyzes to obtain the time information corresponding to the edge of the signal frame.
  • the cellular communication module 5 detects the edge of the signal frame, it generates a trigger signal, and communicates with the GNSS module 6 through a direct hardware connection.
  • the GNSS module 6 records the time when the signal is triggered by the local clock. The delay of the hardware connection is very small and can be ignored.
  • the GNSS module 6 and the cellular communication module 5 share the TCXO as a clock source.
  • the GNSS module 6 receives the ranging signal from the satellite 2 through the second antenna 8, and the precise time information of the receiver can be obtained through PVT calculation.
  • the GNSS module 6 can calculate the GNSS time corresponding to the signal trigger time through the local clock, and track the time error of the cellular communication module 5 in real time in combination with the time obtained by the cellular communication module 5 .
  • the GNSS receiver of this embodiment utilizes the time assistance provided by the cellular network module and the ephemeris assistance provided by the AGNSS server, omitting the acquisition engine module in the traditional GNSS receiver, which can not only reduce the cost by reducing the chip area of the GNSS receiver, but also The overall power consumption of the GNSS receiver can also be reduced. At the same time, satellite acquisition through the tracking engine is faster, thereby improving GNSS positioning performance.
  • This embodiment provides a GNSS receiver.
  • the GNSS receiver of this embodiment is substantially the same as the GNSS receiver of Embodiment 1, except that the navigation calculation module 105 introduces a system deviation ⁇ T in the process of acquiring the current time.
  • the base station's reference is not GNSS time
  • the above estimation may contain a systematic deviation; or the base station's clock reference is GNSS time, but the base station may introduce a system deviation when GNSS time is synchronized with cellular network signal modulation. is ⁇ T.
  • ⁇ T system deviation
  • the following formula is used to obtain the current time T Receiver :
  • To2 represents the compensated GPS time
  • T2 represents the optimized GPS time
  • Tg2 represents the second local time
  • T1 represents the first GPS time
  • ⁇ T represents the system deviation
  • the process of further obtaining the system deviation ⁇ T is as follows:
  • the GNSS receiver By receiving GNSS satellite ranging signals and satellite navigation messages, the GNSS receiver composes pseudoranges, Doppler original observations, and obtains satellite position information; based on pseudoranges, Doppler original observations, and satellite positions , calculate the position, velocity and second GPS time Tgps of the current GNSS receiver through the least squares algorithm or the Kalman filter algorithm;
  • Tgps_1 Tgps-(Tg2-Tg1);
  • the filter estimate is based on the following linear model:
  • ⁇ is the cellular network time to be estimated (in GPS time), Represents the corresponding time rate of change, ⁇ is the model error (usually assumed to be Gaussian white noise), and T s represents the measurement time interval (or measurement frequency).
  • ⁇ Measurement is the GPS time obtained by the GNSS module (ie, the third GPS time Tgps_1 ), and ⁇ represents the observation error.
  • a time-dependent Kalman filter is constructed (for the specific method of constructing the Kalman filter, please refer to Mo Xianglin, Du Jianhong, "An Adaptive OFDM Frequency Offset Estimation Method", Fudan Journal (Natural Science Edition) ), Vol. 44, No. 1, 2005), estimating ⁇ and The ⁇ estimation error of the filtered output is the system deviation ⁇ T that needs to be solved.
  • the GNSS receiver 9 includes a cellular communication module 5 and a GNSS module 6 .
  • the cellular communication module 5 communicates with the base station 1 through the first antenna 3 .
  • the GNSS module 6 communicates with the satellite 2 via the second antenna 8 .
  • the cellular communication module 5 and the GNSS module 6 share a TCXO (Temperature Compensate X'tal (crystal) Oscillator temperature compensation crystal oscillator) 10 as a clock source.
  • TCXO Tempoture Compensate X'tal (crystal) Oscillator temperature compensation crystal oscillator
  • the GNSS module 6 includes a radio frequency front end 103 , a tracking engine 104 and a navigation calculation module 105 .
  • the radio frequency front end 103 receives the signal from the satellite 2 through the second antenna 8, and performs operations such as amplifying, filtering, and down-converting the signal to generate an intermediate frequency signal.
  • the tracking engine 104 directly processes the signal through the auxiliary information, completely strips the carrier and the pseudo-random code from the navigation message, and obtains the corresponding bit stream of the navigation message.
  • the navigation calculation module 105 performs frame synchronization and decoding calculation on the navigation message obtained by the tracking engine to obtain satellite-related information (including position, speed, clock error, etc.)
  • the Ler frequency shift observation value is finally calculated by the least square method or Kalman filtering operation to obtain the position, velocity and time information of the GNSS receiver.
  • the precise auxiliary information required by the aforementioned tracking engine for satellite acquisition includes precise time information, satellite navigation messages, and approximate position information of the receiver.
  • the cellular communication module 5 can provide precise time information, and the AGNSS (Aided-GNSS, Assisted GNSS) server 107 can provide the general position information of the receiver, satellite navigation messages and other related information.
  • the GNSS receiver stores receiver status, satellite message information, etc. in the non-volatile memory 108 .
  • the cellular communication module 5 cannot provide accurate time assistance information and cannot directly capture satellites through the tracking engine.
  • the software capture engine module 109 is activated to capture satellites.
  • the software capture engine module 109 runs in DDR (Double Rate Synchronous Dynamic Random Access) memory 110 . Therefore, it does not consume any RAM (Random Access Memory) or ROM (Read-Only Memory) space of the GNSS chip.
  • DDR Double Rate Synchronous Dynamic Random Access
  • the GNSS receiver of this embodiment performs satellite acquisition and tracking with reference to the following steps:
  • Step S1 the cellular communication module parses the signal frame to obtain the frame edge, the navigation calculation module records the first local time according to the frame edge, the cellular communication module obtains the corresponding first GPS time according to the frame edge, and the cellular communication module performs frequency. Bias estimation to get the clock drift corresponding to the local clock.
  • Step S2 the cellular communication module obtains the optimized GPS time according to the GPS time and the signal transmission delay, and sends the optimized GPS time to the navigation calculation module.
  • the signal transmission delay is the time required for the signal to be transmitted from the base station to the GNSS receiver.
  • Step S3 the navigation calculation module obtains the current time according to the first local time, the optimized GPS time, and the second local time.
  • the second local time is the local time corresponding to the optimized GPS time received by the GNSS module.
  • Step S4 the navigation calculation module obtains the acquisition parameters of the satellite according to the current time, clock drift, and satellite navigation message.
  • Step S5 the tracking engine performs satellite acquisition according to the acquisition parameters.
  • the GNSS receiver 9 After the GNSS receiver 9 receives the start command, it starts to execute the GNSS start process, and requests the cellular communication module 5 for time information and assistance information.
  • auxiliary information There are two sources of auxiliary information here. One is to fetch directly from non-volatile memory 108 . This method is usually used in GNSS warm-start mode. Another source is the AGNSS server 107 .
  • the terminal product is in the form of a single GNSS module, the AGNSS request is directly completed by the GNSS module 6; in another optional embodiment, if the terminal product is a mobile phone, a wearable device For products with AP (application processor), the AGNSS service is completed by the AP.
  • AP application processor
  • the AP After the AP receives the auxiliary information sent by the server, it transmits it through UART (Universal Asynchronous Receiver/Transmitter, Universal Asynchronous Receiver/Transmitter) or other methods. Give GNSS module 6.
  • the auxiliary information includes rough time information, position information, ephemeris parameters and other information.
  • the cellular communication module 5 When the cellular communication module 5 receives the time request from the GNSS module 6, in step S1, the cellular communication module 5 parses the signal frame to obtain the frame edge, and generates an interrupt signal at the edge of the signal frame and sends it to the GNSS module 6 for navigation calculation module 105. Since the GNSS module 6 and the cellular communication module 5 are directly connected by hardware (such as through GPIO (General-purpose input/output, general-purpose input/output), etc.), the time delay of the interrupt signal transmission is negligible, so the interrupt signal and the signal corresponding to the frame edge.
  • GPIO General-purpose input/output, general-purpose input/output
  • the navigation calculation module 105 of the GNSS module 6 After the navigation calculation module 105 of the GNSS module 6 receives the interruption signal, the navigation calculation module 105 records the first local time Tg1 according to the interruption signal, and waits for the time information transmitted by the software channel.
  • the cellular communication module 5 obtains the corresponding first GPS time T1 according to the frame edge, and the cellular communication module 5 performs frequency offset estimation to obtain the clock drift clkDrift corresponding to the local clock TCXO and the corresponding ambiguity.
  • the signal transmission delay deltaT is the time required for the signal to be transmitted from the base station to the GNSS receiver 9 .
  • the size of deltaT depends on the distance between the receiver and the base station.
  • the specific calculation method of deltaT refers to the following formula:
  • (X 1 , Y 1 , Z 1 ) are the coordinates corresponding to the base station position
  • (X 2 , Y 2 , Z 2 ) are the coordinates corresponding to the approximate position of the GNSS receiver 9
  • c is the speed of light.
  • the introduction of deltaT can effectively improve the accuracy. For example, when the distance between the base station and the GNSS receiver 9 is 3 km (kilometers), ignoring deltaT will bring about an error of 10 chips.
  • the coordinates corresponding to the base station position are known.
  • the method of obtaining the approximate position of the GNSS receiver 9 is: the GNSS receiver 9 measures the downlink pilot signals of different base stations, and obtains TOA (Time of Arrival, time of arrival) of the downlink pilots of different base stations ) or TDOA (Time Difference of Arrival, time difference of arrival), according to the measurement results and the coordinates of the base station position, the triangular formula estimation algorithm is used to calculate the approximate position of the GNSS receiver 9.
  • TOA Time of Arrival, time of arrival
  • TDOA Time Difference of Arrival, time difference of arrival
  • the operation of the cellular communication module 5 to demodulate the time starts after the cellular communication network completes the network setup.
  • the cellular communication module 5 obtains the optimized GPS time T2 and transmits the GPS time T2 to the navigation calculation module 105 of the GNSS module 6 .
  • step S3 the navigation calculation module 105 obtains the current time T Receiver according to the first local time Tg1, the optimized GPS time T2, and the second local time Tg2, and the second local time Tg2 is the optimized GPS time Tg2 received by the GNSS module 6.
  • T Receiver T2+(Tg2-Tg1).
  • the GNSS module 6 has obtained the precise time information (the current time T Receiver ), the clock drift of the local clock clkDrift, the rough position information and the satellite navigation message. This information is sufficient to estimate satellite acquisition parameters, including code phase and Doppler shift.
  • step S4 the navigation calculation module 105 estimates the code phase of the satellite according to the following formula:
  • T transmit T Receiver - ⁇ T travel - ⁇ T SatClkBias ;
  • T transmit is the estimated satellite signal transmission time. Since the length of a periodic signal of the GNSS satellite C/A code is 1023 chips, the duration is 1 millisecond. When the precise transmission time is obtained, the precise chip position can be calculated by only considering the part less than milliseconds;
  • ⁇ T travel is the time it takes for the satellite signal to travel from the satellite to the receiver, which can be calculated from the satellite position parsed by the message and the rough receiver position. Since the receiver position error obtained through base station positioning is usually within 500 meters, the chip estimation error introduced by the receiver position error is usually less than 10 chips in the worst case, and this part can be considered in the satellite acquisition range.
  • ⁇ T SatClkBias is the clock drift information of the satellite, which can be directly demodulated from the satellite message.
  • the Doppler shift can be calculated from the Doppler effect of the satellite and the receiver, and the effect of the clock drift of the receiver's local clock needs to be considered.
  • the speed of the satellite can be calculated directly from the information given in the navigation message, the speed of the receiver can be replaced by a rough estimate, and the ambiguity is taken into account in the Doppler frequency search range.
  • the tracking engine is directly activated to capture satellites. Because the estimated parameters are relatively accurate, the tracking engine can usually quickly capture satellite signals, and provide the demodulated information as observations to the navigation solution module. The navigation solution module finally determines the precise position, speed and time information of the receiver through the least square method or Kalman filtering algorithm.
  • the time accuracy of base station 1 is of the same order of magnitude as GNSS.
  • the time synchronization requirement is 10us; when base station 1 is a TD-SCDMA base station, the time synchronization requirement is 3u; when base station 1 is an LTE base station, the time synchronization requirement is 1us or even on the order of microseconds.
  • the accuracy requirements for the base station system in this embodiment can be well satisfied.
  • each base station is equipped with a GNSS receiver 9 as a reference source for the time reference.
  • the GNSS receiver 99 includes both the cellular communication module 5 and the GNSS module 6 .
  • the cellular communication module 5 receives the signal frame from the base station 1, and analyzes to obtain the time information corresponding to the edge of the signal frame.
  • the cellular communication module 5 detects the edge of the signal frame, it generates a trigger signal, and communicates with the GNSS module 6 through a direct hardware connection.
  • the GNSS module 6 records the time when the signal is triggered by the local clock. The delay of the hardware connection is very small and can be ignored.
  • the GNSS module 6 and the cellular communication module 5 share the TCXO as a clock source.
  • the GNSS module 6 receives the ranging signal from the satellite 2 through the second antenna 8, and the precise time information of the receiver can be obtained through PVT calculation.
  • the GNSS module 6 can calculate the GNSS time corresponding to the signal trigger time through the local clock, and track the time error of the cellular communication module 5 in real time in combination with the time obtained by the cellular communication module 5 .
  • the satellite acquisition and tracking method of this embodiment utilizes the time assistance provided by the cellular network module and the ephemeris assistance provided by the AGNSS server, omitting the acquisition engine module in the traditional GNSS receiver, and can not only reduce the cost by reducing the chip area of the GNSS receiver , and can also reduce the overall power consumption of the GNSS receiver. At the same time, satellite acquisition through the tracking engine is faster, thereby improving GNSS positioning performance.
  • This embodiment provides a satellite acquisition and tracking method.
  • the satellite acquisition and tracking method in this embodiment is substantially the same as the satellite acquisition and tracking method in Embodiment 3, except that in step S3, a system deviation ⁇ T is introduced in the process of acquiring the current time.
  • the base station's reference is not GNSS time
  • the above estimation may contain a systematic deviation; or the base station's clock reference is GNSS time, but the base station may introduce a system deviation when GNSS time is synchronized with cellular network signal modulation. is ⁇ T.
  • ⁇ T system deviation
  • the following formula is used to obtain the current time T Receiver :
  • To2 represents the compensated GPS time
  • T2 represents the optimized GPS time
  • Tg2 represents the second local time
  • T1 represents the first GPS time
  • ⁇ T represents the system deviation
  • the process of further obtaining the system deviation ⁇ T is as follows:
  • the GNSS receiver By receiving GNSS satellite ranging signals and satellite navigation messages, the GNSS receiver composes pseudoranges, Doppler raw observations, and obtains satellite position information;
  • Tgps_1 Tgps-(Tg2-Tg1);
  • the filter estimate is based on the following linear model:
  • ⁇ is the cellular network time to be estimated (in GPS time), Represents the corresponding time rate of change, ⁇ is the model error (usually assumed to be Gaussian white noise), and T s represents the measurement time interval (or measurement frequency).
  • ⁇ Measurement is the GPS time obtained by the GNSS module (ie, the third GPS time Tgps_1 ), and ⁇ represents the observation error.
  • a time-dependent Kalman filter is constructed (for the specific method of constructing the Kalman filter, please refer to Mo Xianglin, Du Jianhong, "An Adaptive OFDM Frequency Offset Estimation Method", Fudan Journal (Natural Science Edition) ), Vol. 44, No. 1, 2005), estimating ⁇ and The ⁇ estimation error of the filtered output is the system deviation ⁇ T that needs to be solved.

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Abstract

一种GNSS接收机（9）和卫星（2）捕获跟踪方法，其中GNSS接收机（9）包括蜂窝通信模块（5）、GNSS模块（6）；GNSS模块（6）包括跟踪引擎（104）、导航解算模块（105）；蜂窝通信模块（5）用于解析信号帧以得到帧边缘，导航解算模块（105）用于根据帧边缘记录第一本地时间，蜂窝通信模块（5）还用于根据帧边缘得到对应的第一GPS时间（S1）；蜂窝通信模块（5）还用于根据第一GPS时间和信号传输时延得到优化的GPS时间（S2）；导航解算模块（105）还用于得到当前时间（S3）；导航解算模块（105）还用于得到卫星（2）的捕获参数（S4）；跟踪引擎（104）根据捕获参数进行卫星（2）捕获（S5）。能够有效提升卫星（2）捕获速度、减少GNSS接收机（9）的芯片面积和降低GNSS接收机（9）的功耗。

Description

GNSS接收机和卫星捕获跟踪方法
本申请要求申请日为2020年11月4日的中国专利申请202011218804.0的优先权。本申请引用上述中国专利申请的全文。
技术领域
本发明属于卫星捕获跟踪技术领域，尤其涉及一种GNSS接收机和卫星捕获跟踪方法。
背景技术
在这个万物互联的时代，位置服务已经是人们日常生活中不可或缺的一部分。对手机、物联网装置和可穿戴设备而言没有定位信息是无法想象的。而在位置服务中，GNSS(Global Navigation Satellite System，全球导航卫星系统)扮演了一个非常重要的角色。
GNSS系统，全称为全球导航卫星系统，包含美国的GPS(Global Positioning System，全球定位系统)、俄罗斯的GLONASS(Global Navigation Satellite System，全球导航卫星系统)，中国的BDS(BeiDou Satellite Navigation System，北斗卫星导航系统)和欧盟的Galileo(伽利略)卫星导航系统等。GNSS接收机通过接收多颗卫星发射的无线测距信号来实现实时的定位、授时和导航等功能。
通常而言，GNSS接收机硬件部分主要包含射频前端电路、捕获引擎和跟踪引擎。射频前端电路是用于接收从来自GNSS卫星的信号，该信号后经过放大、滤波、下变频等操作产生适合模拟转换的中频信号后发送给捕获引擎。捕获引擎通常包含一定数量的捕获通道，每个通道用于对特定卫星信号进行搜索捕获。跟踪引擎从捕获引擎搜索到的卫星信号中把中频载波和伪随机码彻底从导航电文上剥离下来。定位解算模块是纯软件模块，利用跟踪引擎解码后得到的卫星信息，最终计算得到终端的位置、速度以及精确的时间信息。
GNSS接收机包括天线、射频前端、基带处理器和处理器，其中，基带处理器包括捕获引擎模块、跟踪引擎模块。以及一个协处理，用于执行基带相关软件处理及定位计算。在典型的GNSS接收机实现中，到达天线的空间信号在前端部分被下变频，滤波和数字化。该过程最终生成所需中频数据，通常表示为实数和复数分量(即I(同相)和Q(正交)分量)。
捕获引擎模块包括实数分量捕获通道、复数分量捕获通道和本地码生成器，实数分 量捕获通道包括实数分量累加器、实数分量积分与转储器，复数分量捕获通道包括复数分量累加器、复数分量积分与转储器，实数分量累加器连接所述实数分量积分与转储器，所述实数分量积分与转储器，复数分量累加器连接复数分量积分与转储器，本地码生成器将本地码根据码延迟进行调整，该码延迟表示将本地码与输入信号进行相关运算之前对码进行移位的量，输入信号被分为实数分量数据和复数分量数据，GNSS接收机在本地生成C/A码的副本，并分别与IQ分路的信号进行相关运算来实现码的对齐。根据C/A码的自相关特性，当本地副本和输入信号对齐时，它们的相关运算会生成一个峰值。该峰值相对应的码延迟/多普勒频率给出了初始化跟踪引擎跟踪环路的良好估计。
跟踪引擎模块包括码跟踪通道、载波跟踪通道和辅助载波模块。为了从输入信号中提取信息，GNSS接收机通过复制C/A码并连续调整其码延迟和载波相位来跟踪它们，以确保与输入信号的同步。在最常见的实现中，接收器实现码跟踪环路和载波跟踪环路，以实现与输入信号的同步。
积分与转储(I&D)：累积相关器输出并提供其同相I和正交Q分量的模块。
鉴别器(discriminator)：处理相关器的输出以提供可测量的数量(例如载波相位信息)。
过滤器(Filter)：过滤鉴别器的输出以减少噪声。
NCO：数控振荡器将滤波器输出转换为多普勒频率和码延迟的可用校正因子
其中，积分与转储器，用于累积相关器输出并提供其同相I和正交Q分量的模块。鉴别器用于处理相关器的输出以提供可测量的数量(例如载波相位信息)。过滤器用于过滤鉴别器的输出以减少噪声。数控振荡器用于将滤波器输出转换为多普勒频率和码延迟的可用校正因子。
其中，载波环抖动比码环抖动要少得多，因此可以使用载波环中的测量值来消除码环路视线方向(LOS，Line of sight)的动态特性，降低码循环滤波器的阶数及其带宽。这种架构通常被称为辅助载波模块。
在目前的GNSS接收机(包括芯片及模块)设计中，捕获引擎相对于其他模块(如跟踪引擎)占据了更多的芯片面积，对芯片的总体成本有举足轻重的影响。
此外，捕获引擎主要承载着对卫星信号的搜索，由于其搜索范围大，往往要进行全范围的码域搜索以及大范围的频率扫描。捕获引擎运算量极大，从而消耗了大量的电池容量。而跟踪引擎的功耗则明显低于捕获引擎。
发明内容
本发明要解决的技术问题是为了克服现有技术的GNSS接收机中捕获引擎的占据面 积较大、消耗功耗较大的缺陷，提供一种GNSS接收机和卫星捕获跟踪方法。
本发明是通过下述技术方案来解决上述技术问题：
本发明提供一种GNSS接收机，包括蜂窝通信模块、GNSS模块；
GNSS模块包括跟踪引擎、导航解算模块；
蜂窝通信模块用于解析信号帧以得到帧边缘，导航解算模块用于根据帧边缘记录第一本地时间，蜂窝通信模块还用于根据帧边缘得到对应的第一GPS时间，蜂窝通信模块还用于进行频偏估计以得到本地时钟对应的钟漂；
蜂窝通信模块还用于根据第一GPS时间和信号传输时延得到优化的GPS时间，并将优化的GPS时间发送至导航解算模块，信号传输时延为信号从基站传输到GNSS接收机所需要的时间；
导航解算模块还用于根据第一本地时间、优化的GPS时间、第二本地时间得到当前时间，第二本地时间为GNSS模块接收到优化的GPS时间对应的本地时间；
导航解算模块还用于根据当前时间、钟漂、卫星导航电文得到卫星的捕获参数；
跟踪引擎根据捕获参数进行卫星捕获。
较佳地，信号传输时延
Figure PCTCN2021128796-appb-000001
其中，(X 1，Y 1，Z 1)表征基站的位置对应的坐标，(X 2，Y 2，Z 2)表征GNSS接收机的概略位置对应的坐标，c表征光速。
较佳地，当前时间T Receiver＝T2+(Tg2-Tg1)，T2＝T1+deltaT；其中，T2表征优化的GPS时间，Tg2表征第二本地时间，T1表征第一GPS时间。
较佳地，当前时间T Receiver＝To2+(Tg2-Tg1)，T2＝T1+deltaT，To2＝T2+△T；其中，To2表征补偿的GPS时间，T2表征优化的GPS时间，Tg2表征第二本地时间，T1表征第一GPS时间，△T表征系统偏差。
较佳地，导航解算模块根据卫星测距信号和卫星导航电文获取伪距、多普勒原始观测量、卫星的位置；
导航解算模块根据伪距、多普勒原始观测量、卫星的位置获取GNSS接收机的置位、速度和第二GPS时间Tgps；
导航解算模块获取蜂窝信号帧边缘对应的第三GPS时间Tgps_1＝Tgps–(Tg2-Tg1)；
导航解算模块根据蜂窝网络时间和第三GPS时间Tgps_1进行滤波估计以得到系统偏差△T。
较佳地，导航解算模块基于如下线性模型进行滤波估计：
Figure PCTCN2021128796-appb-000002
τ Measurement(t)＝τ(t)+ε τ(t)；
其中，τ是待估计的蜂窝网络时间，
Figure PCTCN2021128796-appb-000003
表示相应的时间变化率，ω为模型误差，T s表示测量时间间隔；τ Measurement取值为Tgps_1，ε表示观测误差；
基于线性模型构造一时间相关的卡尔曼滤波器，通过τ Measurement估计τ及
Figure PCTCN2021128796-appb-000004
获取滤波输出的τ估计误差作为系统偏差△T。
较佳地，导航解算模块根据以下公式估计卫星的码相位：
T transmit＝T Receiver-ΔT travel-ΔT SatClkBias；
其中，T transmit表征估计的卫星信号的发射时间，T Receiver表征当前时间，ΔT travel为卫星信号从卫星传播到GNSS接收机所需要的时间，ΔT SatClkBias为卫星的钟漂信息。
较佳地，导航解算模块基于最小二乘法或者卡尔曼滤波算法确定GNSS接收机的精确的位置、速度及时间信息。
本发明还提供一种卫星捕获跟踪方法，卫星捕获跟踪方法基于一GNSS接收机实现，GNSS接收机包括蜂窝通信模块、GNSS模块；
GNSS模块包括跟踪引擎、导航解算模块；
卫星捕获跟踪方法包括以下步骤：
蜂窝通信模块解析信号帧以得到帧边缘，导航解算模块根据帧边缘记录第一本地时间，蜂窝通信模块根据帧边缘得到对应的第一GPS时间，蜂窝通信模块进行频偏估计以得到本地时钟对应的钟漂；
蜂窝通信模块根据第一GPS时间和信号传输时延得到优化的GPS时间，并将优化的GPS时间发送至导航解算模块，信号传输时延为信号从基站传输到GNSS接收机所需要的时间；
导航解算模块根据第一本地时间、优化的GPS时间、第二本地时间得到当前时间，第二本地时间为GNSS模块接收到优化的GPS时间对应的本地时间；
导航解算模块根据当前时间、钟漂、卫星导航电文得到卫星的捕获参数；
跟踪引擎根据捕获参数进行卫星捕获。
较佳地，信号传输时延
Figure PCTCN2021128796-appb-000005
其中，(X 1，Y 1，Z 1)表征基站的位置对应的坐标，(X 2，Y 2，Z 2)表征GNSS接收机的概略位置对应的坐标，c表征光速。
较佳地，当前时间T Receiver＝T2+(Tg2-Tg1)，T2＝T1+deltaT；其中，T2表征优化的GPS时间，Tg2表征第二本地时间，T1表征第一GPS时间。
较佳地，当前时间T Receiver＝To2+(Tg2-Tg1)，T2＝T1+deltaT，To2＝T2+△T； 其中，To2表征补偿的GPS时间，T2表征优化的GPS时间，Tg2表征第二本地时间，T1表征第一GPS时间，△T表征系统偏差。
较佳地，获取系统偏差△T的步骤包括：
导航解算模块根据卫星测距信号和卫星导航电文获取伪距、多普勒原始观测量、卫星的位置；
导航解算模块根据伪距、多普勒原始观测量、卫星的位置获取GNSS接收机的置位、速度和第二GPS时间Tgps；
导航解算模块获取蜂窝信号帧边缘对应的第三GPS时间Tgps_1＝Tgps–(Tg2-Tg1)；
导航解算模块根据蜂窝网络时间和第三GPS时间Tgps_1进行滤波估计以得到系统偏差△T。
较佳地，导航解算模块基于如下线性模型进行滤波估计：
Figure PCTCN2021128796-appb-000006
τ Measurement(t)＝τ(t)+ε τ(t)；
其中，τ是待估计的蜂窝网络时间，
Figure PCTCN2021128796-appb-000007
表示相应的时间变化率，ω为模型误差，T s表示测量时间间隔；τ Measurement取值为Tgps_1，ε表示观测误差；
基于线性模型构造一时间相关的卡尔曼滤波器，通过τ Measurement估计τ及
Figure PCTCN2021128796-appb-000008
获取滤波输出的τ估计误差作为系统偏差△T。
较佳地，得到卫星的捕获参数的步骤包括：
导航解算模块根据以下公式估计卫星的码相位：
T transmit＝T Receiver-ΔT travel-ΔT SatClkBias；
其中，T transmit表征估计的卫星信号的发射时间，T Receiver表征当前时间，ΔT travel为卫星信号从卫星传播到GNSS接收机所需要的时间，ΔT SatClkBias为卫星的钟漂信息。
较佳地，卫星捕获跟踪方法还包括以下步骤：
导航解算模块基于最小二乘法或者卡尔曼滤波算法确定GNSS接收机的精确的位置、速度及时间信息。
本发明的积极进步效果在于：本发明能够有效提升卫星捕获速度、减少GNSS接收机的芯片面积和降低GNSS接收机的功耗。
附图说明
图1为本发明的实施例1的GNSS接收机的结构示意图。
图2为本发明的实施例1的GNSS接收机的GNSS模块的结构示意图。
图3为本发明的实施例3的卫星捕获跟踪方法的流程图。
具体实施方式
下面通过实施例的方式进一步说明本发明，但并不因此将本发明限制在所述的实施例范围之中。
实施例1
本实施例提供一种GNSS接收机。参照图1，该GNSS接收机9包括蜂窝通信模块5、GNSS模块6。蜂窝通信模块5通过第一天线3与基站1通信。GNSS模块6通过第二天线8与卫星2通信。蜂窝通信模块5和GNSS模块6共用TCXO(Temperature Compensate X'tal(crystal)Oscillator温度补偿晶体振荡器)10作为时钟源。
参照图2，GNSS模块6包括射频前端103、跟踪引擎104及导航解算模块105。射频前端103通过第二天线8接收来自卫星2的信号，并对信号进行放大、滤波、下变频等操作产生中频信号。跟踪引擎104通过辅助信息，直接对信号进行处理，把载波和伪随机码彻底从导航电文上剥离下来，并获取相应的导航电文比特流。导航解算模块105对跟踪引擎获取的导航电文，进行帧同步及解码计算得到卫星相关信息(包括位置、速度、钟差等)，然后根据载波、伪随机码的相关信息得到伪距和多普勒频移观测值，利用最小二乘法或者卡尔曼滤波运算最终计算得到GNSS接收机的位置、速度以及时间信息。
前述跟踪引擎进行卫星捕获时所需要精确辅助信息，包含精确的时间信息、卫星导航电文以及接收机概略的位置信息。蜂窝通信模块5可以提供精确的时间信息，而AGNSS(Aided-GNSS，辅助GNSS)服务器107则可以提供接收机概略的位置信息、卫星导航电文等相关信息。此外，为了提供GNSS接收机快速启动及减少GNSS接收机和AGNSS服务器107数据交互的频度，GNSS接收机把接收机状态、卫星电文信息等存储到非易失性存储器108中。在蜂窝通信网络无信号的环境下，蜂窝通信模块5无法提供精确的时间辅助信息，无法直接通过跟踪引擎进行卫星捕获，此时，则启动软件捕获引擎模块109来实现对卫星的捕获。作为备份解决方案，软件捕获引擎模块109运行在DDR(双倍速率同步动态随机)存储器110中。因此，它不会消耗GNSS芯片的任何RAM(Random Access Memory，随机存取存储器)或ROM(Read-Only Memory，只读存储器)空间。
参照图3，本实施例的GNSS接收机参照以下步骤进行卫星捕获跟踪：
步骤S1、蜂窝通信模块解析信号帧以得到帧边缘，导航解算模块根据所述帧边缘记录第一本地时间，蜂窝通信模块根据所述帧边缘得到对应的第一GPS时间，蜂窝通信模块进行频偏估计以得到本地时钟对应的钟漂。
步骤S2、蜂窝通信模块根据GPS时间和信号传输时延得到优化的GPS时间，并将优化的GPS时间发送至导航解算模块。信号传输时延为信号从基站传输到GNSS接收机所需要的时间。
步骤S3、导航解算模块根据第一本地时间、优化的GPS时间、第二本地时间得到当前时间。第二本地时间为GNSS模块接收到优化的GPS时间对应的本地时间。
步骤S4、导航解算模块根据当前时间、钟漂、卫星导航电文得到卫星的捕获参数。
步骤S5、跟踪引擎根据捕获参数进行卫星捕获。
具体实施时，当GNSS接收机9接收到启动命令后，开始执行GNSS启动流程，并向蜂窝通信模块5请求时间信息，以及请求辅助信息。这里的辅助信息来源分为两个。一个是直接从非易失性存储器108中获取。此方法通常用于GNSS热启动的模式。另一个来源是AGNSS服务器107。在一种可选的实施方式中，如果终端产品为GNSS单模块形态，则AGNSS请求由GNSS模块6直接完成；在另一种可选的实施方式中，如果终端产品为手机、可穿戴式设备等带有AP(应用处理器)的产品，AGNSS服务则由AP完成，AP收到服务器下发的辅助信息后，再通过UART(Universal Asynchronous Receiver/Transmitter，通用异步收发传输器)或者其他方式传输给GNSS模块6。如上所述辅助信息包含粗略的时间信息、位置信息和星历参数等信息。
当蜂窝通信模块5接收到GNSS模块6的时间请求后，在步骤S1中，蜂窝通信模块5解析信号帧以得到帧边缘，并在该信号帧边缘生产中断信号发送给GNSS模块6的导航解算模块105。由于GNSS模块6和蜂窝通信模块5通过硬件直连(如通过GPIO(General-purpose input/output，通用输入输出)等)，中断信号传输的时间延迟可忽略不计，所以，该中断信号与该信号帧边缘相对应。
GNSS模块6的导航解算模块105接收到该中断信号后，导航解算模块105根据中断信号记录第一本地时间Tg1，并等待软件通路传输过来的时间信息。蜂窝通信模块5根据帧边缘得到对应的第一GPS时间T1，蜂窝通信模块5进行频偏估计以得到本地时钟TCXO对应的钟漂clkDrift及相应的模糊度。
然后，在步骤S2中，蜂窝通信模块5根据第一GPS时间T1和信号传输时延deltaT得到优化的GPS时间T2。其中，T2＝T1+deltaT。
信号传输时延deltaT为信号从基站传输到GNSS接收机9所需要的时间。deltaT的大小取决于接收机和基站的距离。deltaT的具体计算方式参照以下公式：
Figure PCTCN2021128796-appb-000009
其中，(X 1，Y 1，Z 1)为基站位置对应的坐标，(X 2，Y 2，Z 2)为GNSS接收机9的概 略位置对应的坐标，c为光速。deltaT的引入，可以有效提高精度。例如，基站与GNSS接收机9的距离为3km(千米)的时候，忽略deltaT会带来10个码片的误差。
在基站设置完成后，基站位置对应的坐标即为已知。
在一种可选的实施方式中，获取GNSS接收机9的概略位置的方式为：GNSS接收机9测量不同基站的下行导频信号，得到不同基站下行导频的TOA(Time of Arrival，到达时刻)或TDOA(Time Difference of Arrival，到达时间差)，根据该测量结果并结合基站位置的坐标，采用三角公式估计算法，计算得到GNSS接收机9的概略位置，技术细节可以参考《蜂窝网无线定位》(电子工业出版社，2002，范平志、邓平、刘林)。
在一种可选的实施方式中，为了加速GNSS定位时间，蜂窝通信模块5解调时间的操作从蜂窝通信网络完成驻网后就开始进行。
蜂窝通信模块5得到优化的GPS时间T2，则将GPS时间T2传输至GNSS模块6的导航解算模块105。
接下来，在步骤S3中，导航解算模块105根据第一本地时间Tg1、优化的GPS时间T2、第二本地时间Tg2得到当前时间T Receiver，第二本地时间Tg2为GNSS模块6接收到优化的GPS时间T2对应的本地时间。T Receiver＝T2+(Tg2-Tg1)。
此时，GNSS模块6已经得到精确的时间信息(当前时间T Receiver)、本地时钟的钟漂clkDrift、概略的位置信息以及卫星导航电文。这些信息已经足够用于估计卫星的捕获参数，包括码相位及多普勒频移等。
然后，在步骤S4中，导航解算模块105根据以下公式估计卫星的码相位：
T transmit＝T Receiver-ΔT travel-ΔT SatClkBias；
其中：T transmit为估计的卫星信号发射时间。由于GNSS卫星C/A码一个周期信号长度为1023个码片，时长为1毫秒。当得到精确的发射时间后，只考虑少于毫秒的部分，就可以计算得到精确的码片位置；
ΔT travel为卫星信号从卫星传播到接收机所需要的时间，可以通过电文解析到的卫星位置和粗略的接收机位置计算得到。由于通过基站定位获取到的接收机位置误差通常在500米内，故而接收机位置误差引入的码片估计误差最恶劣的情况通常也不足10个码片，此部分可在卫星捕获范围中加以考虑。
ΔT SatClkBias为卫星的钟漂信息，可以直接从卫星的电文中解调得到。
多频勒频移可以通过卫星和接收机的多普勒效应计算得到，同时还需要考虑接收机本地时钟的钟漂影响。卫星的速度可以根据导航电文给出的信息直接计算得到，接收机的速度可以用粗略的估计值代替，模糊度则在多普勒频率搜索范围中加以考虑。
利用上述估计的卫星捕获参数直接启动跟踪引擎进行卫星的捕获。由于估计的参数较为精确，通常跟踪引擎可以快速捕获到卫星信号，并将解调后的信息作为观测量提供给导航解算模块。导航解算模块通过最小二乘法或者卡尔曼滤波算法最终确定接收机精确的位置、速度及时间信息。
基站1的时间精度和GNSS在同一量级。当基站1为CDMA基站和CDMA 2000基站时，时间同步的要求是10us；当基站1为TD-SCDMA基站时，时间同步要求为3u；当基站1为LTE基站时，时间同步要求为1us甚至是微秒量级。对于类似精度量级的基站系统，可以很好的满足本实施例对基站系统的精度要求。以CDMA系统为例，每一个基站都搭载GNSS接收机9，作为时间基准的参考源。GNSS接收机99同时包含蜂窝通信模块5及GNSS模块6。蜂窝通信模块5接收来自基站1的信号帧，并解析得到信号帧边缘对应的时间信息。在蜂窝通信模块5检测到信号帧边缘的同时，产生触发信号，并通过硬件直连与GNSS模块6进行通信，GNSS模块6通过本地时钟记录信号触发的时刻。硬件连接的时延很小，可以忽略不计。GNSS模块6和蜂窝通信模块5共用TCXO作为时钟源。同时，GNSS模块6通过第二天线8接收来自卫星2的测距信号，通过PVT解算可以得到接收机精确的时间信息。GNSS模块6通过本地时钟可以推算出在信号触发时刻对应的GNSS时间，并结合蜂窝通信模块5得到的时间，实时跟踪蜂窝通信模块5的时间误差。
本实施例的GNSS接收机利用蜂窝网络模块提供的时间辅助以及AGNSS服务器提供星历辅助，省略了传统GNSS接收机中的捕获引擎模块，不但可以通过减少GNSS接收机的芯片的面积来降低成本，还可以降低GNSS接收机整体功耗。同时，通过跟踪引擎进行卫星捕获速度更快，从而提升了GNSS定位性能。
实施例2
本实施例提供一种GNSS接收机。本实施例的GNSS接收机与实施例1的GNSS接收机大致相同，区别在于，导航解算模块105在获取当前时间的过程中引入系统偏差△T。
如果基站的基准不是GNSS时间的话，上述估计有可能含有一个系统偏差；或者基站的时钟基准是GNSS时间，但是基站在做GNSS时间与蜂窝网络信号调制进行同步操作时，可能引入一个系统偏差，记为△T。对包含系统偏差的情况下，则采用如下公式获得来当前时间T Receiver：
T Receiver＝To2+(Tg2-Tg1)，T2＝T1+deltaT，To2＝T2+△T；
其中，To2表征补偿的GPS时间，T2表征优化的GPS时间，Tg2表征第二本地时 间，T1表征第一GPS时间，△T表征系统偏差。
在得到第一GPS时间T1、优化的GPS时间系统T2、第一本地时间Tg1、第二本地时间Tg2等之后，进一步获取系统偏差△T的过程如下：
GNSS接收机通过接收GNSS卫星测距信号和卫星导航电文，组成伪距、多普勒原始观测量，以及解得卫星的位置信息；根据伪距、多普勒原始观测量、卫星的位置等信息，通过最小二乘算法或卡尔曼滤波算法，计算当前GNSS接收机的位置、速度及第二GPS时间Tgps；
然后，根据本地时间差，推算出蜂窝信号帧边缘对应的第三GPS时间Tgps_1：
Tgps_1＝Tgps–(Tg2-Tg1)；
最后，对同一时刻的蜂窝网络时间及GNSS模块得到的GPS时间(第三GPS时间Tgps_1)进行滤波估计。滤波估计基于如下线性模型：
Figure PCTCN2021128796-appb-000010
τ Measurement(t)＝τ(t)+ε τ(t)；
其中，τ是待估计的蜂窝网络时间(以GPS时来表示)，
Figure PCTCN2021128796-appb-000011
表示相应的时间变化率，ω为模型误差(通常假定为高斯白噪声)，T s表示测量时间间隔(或称之为测量频率)。τ Measurement为GNSS模块得到的GPS时(即第三GPS时间Tgps_1)，ε表示观测误差。通过如上模型，构造一个时间相关的卡尔曼滤波器(构造该卡尔曼滤波器的具体方式可参考莫祥林，杜建洪，“一种自适应的OFDM频偏估计方法”，复旦学报(自然科学版)，第44卷第一期，2005)，通过τ Measurement来估计τ及
Figure PCTCN2021128796-appb-000012
滤波输出的τ估计误差即为需要求解的系统偏差△T。
本实施例的GNSS接收机进行卫星捕获跟踪的其他步骤可参照实施例1实现，此处不再赘述。
实施例3
本实施例提供一种卫星捕获跟踪方法。该卫星捕获跟踪方法基于一种GNSS接收机实现。参照图1，该GNSS接收机9包括蜂窝通信模块5、GNSS模块6。蜂窝通信模块5通过第一天线3与基站1通信。GNSS模块6通过第二天线8与卫星2通信。蜂窝通信模块5和GNSS模块6共用TCXO(Temperature Compensate X'tal(crystal)Oscillator温度补偿晶体振荡器)10作为时钟源。
参照图2，GNSS模块6包括射频前端103、跟踪引擎104及导航解算模块105。射频前端103通过第二天线8接收来自卫星2的信号，并对信号进行放大、滤波、下变频等操作产生中频信号。跟踪引擎104通过辅助信息，直接对信号进行处理，把载波和伪 随机码彻底从导航电文上剥离下来，并获取相应的导航电文比特流。导航解算模块105对跟踪引擎获取的导航电文，进行帧同步及解码计算得到卫星相关信息(包括位置、速度、钟差等)，然后根据载波、伪随机码的相关信息得到伪距和多普勒频移观测值，利用最小二乘法或者卡尔曼滤波运算最终计算得到GNSS接收机的位置、速度以及时间信息。
前述跟踪引擎进行卫星捕获时所需要精确辅助信息，包含精确的时间信息、卫星导航电文以及接收机概略的位置信息。蜂窝通信模块5可以提供精确的时间信息，而AGNSS(Aided-GNSS，辅助GNSS)服务器107则可以提供接收机概略的位置信息、卫星导航电文等相关信息。此外，为了提供GNSS接收机快速启动及减少GNSS接收机和AGNSS服务器107数据交互的频度，GNSS接收机把接收机状态、卫星电文信息等存储到非易失性存储器108中。在蜂窝通信网络无信号的环境下，蜂窝通信模块5无法提供精确的时间辅助信息，无法直接通过跟踪引擎进行卫星捕获，此时，则启动软件捕获引擎模块109来实现对卫星的捕获。作为备份解决方案，软件捕获引擎模块109运行在DDR(双倍速率同步动态随机)存储器110中。因此，它不会消耗GNSS芯片的任何RAM(Random Access Memory，随机存取存储器)或ROM(Read-Only Memory，只读存储器)空间。
参照图3，本实施例的GNSS接收机参照以下步骤进行卫星捕获跟踪：
步骤S1、蜂窝通信模块解析信号帧以得到帧边缘，导航解算模块根据所述帧边缘记录第一本地时间，蜂窝通信模块根据所述帧边缘得到对应的第一GPS时间，蜂窝通信模块进行频偏估计以得到本地时钟对应的钟漂。
步骤S2、蜂窝通信模块根据GPS时间和信号传输时延得到优化的GPS时间，并将优化的GPS时间发送至导航解算模块。信号传输时延为信号从基站传输到GNSS接收机所需要的时间。
步骤S3、导航解算模块根据第一本地时间、优化的GPS时间、第二本地时间得到当前时间。第二本地时间为GNSS模块接收到优化的GPS时间对应的本地时间。
步骤S4、导航解算模块根据当前时间、钟漂、卫星导航电文得到卫星的捕获参数。
步骤S5、跟踪引擎根据捕获参数进行卫星捕获。
具体实施时，当GNSS接收机9接收到启动命令后，开始执行GNSS启动流程，并向蜂窝通信模块5请求时间信息，以及请求辅助信息。这里的辅助信息来源分为两个。一个是直接从非易失性存储器108中获取。此方法通常用于GNSS热启动的模式。另一个来源是AGNSS服务器107。在一种可选的实施方式中，如果终端产品为GNSS单模块形态，则AGNSS请求由GNSS模块6直接完成；在另一种可选的实施方式中，如果终端产品为手机、可穿戴式设备等带有AP(应用处理器)的产品，AGNSS服务则由AP完 成，AP收到服务器下发的辅助信息后，再通过UART(Universal Asynchronous Receiver/Transmitter，通用异步收发传输器)或者其他方式传输给GNSS模块6。如上所述辅助信息包含粗略的时间信息、位置信息和星历参数等信息。
当蜂窝通信模块5接收到GNSS模块6的时间请求后，在步骤S1中，蜂窝通信模块5解析信号帧以得到帧边缘，并在该信号帧边缘生产中断信号发送给GNSS模块6的导航解算模块105。由于GNSS模块6和蜂窝通信模块5通过硬件直连(如通过GPIO(General-purpose input/output，通用输入输出)等)，中断信号传输的时间延迟可忽略不计，所以，该中断信号与该信号帧边缘相对应。
GNSS模块6的导航解算模块105接收到该中断信号后，导航解算模块105根据中断信号记录第一本地时间Tg1，并等待软件通路传输过来的时间信息。蜂窝通信模块5根据帧边缘得到对应的第一GPS时间T1，蜂窝通信模块5进行频偏估计以得到本地时钟TCXO对应的钟漂clkDrift及相应的模糊度。
然后，在步骤S2中，蜂窝通信模块5根据第一GPS时间T1和信号传输时延deltaT得到优化的GPS时间T2。其中，T2＝T1+deltaT。
信号传输时延deltaT为信号从基站传输到GNSS接收机9所需要的时间。deltaT的大小取决于接收机和基站的距离。deltaT的具体计算方式参照以下公式：
Figure PCTCN2021128796-appb-000013
其中，(X 1，Y 1，Z 1)为基站位置对应的坐标，(X 2，Y 2，Z 2)为GNSS接收机9的概略位置对应的坐标，c为光速。deltaT的引入，可以有效提高精度。例如，基站与GNSS接收机9的距离为3km(千米)的时候，忽略deltaT会带来10个码片的误差。
在基站设置完成后，基站位置对应的坐标即为已知。
在一种可选的实施方式中，获取GNSS接收机9的概略位置的方式为：GNSS接收机9测量不同基站的下行导频信号，得到不同基站下行导频的TOA(Time of Arrival，到达时刻)或TDOA(Time Difference of Arrival，到达时间差)，根据该测量结果并结合基站位置的坐标，采用三角公式估计算法，计算得到GNSS接收机9的概略位置，技术细节可以参考《蜂窝网无线定位》(电子工业出版社，2002，范平志、邓平、刘林)。
在一种可选的实施方式中，为了加速GNSS定位时间，蜂窝通信模块5解调时间的操作从蜂窝通信网络完成驻网后就开始进行。
蜂窝通信模块5得到优化的GPS时间T2，则将GPS时间T2传输至GNSS模块6的导航解算模块105。
接下来，在步骤S3中，导航解算模块105根据第一本地时间Tg1、优化的GPS时间 T2、第二本地时间Tg2得到当前时间T Receiver，第二本地时间Tg2为GNSS模块6接收到优化的GPS时间T2对应的本地时间。T Receiver＝T2+(Tg2-Tg1)。
此时，GNSS模块6已经得到精确的时间信息(当前时间T Receiver)、本地时钟的钟漂clkDrift、概略的位置信息以及卫星导航电文。这些信息已经足够用于估计卫星的捕获参数，包括码相位及多普勒频移等。
然后，在步骤S4中，导航解算模块105根据以下公式估计卫星的码相位：
T transmit＝T Receiver-ΔT travel-ΔT SatClkBias；
其中：T transmit为估计的卫星信号发射时间。由于GNSS卫星C/A码一个周期信号长度为1023个码片，时长为1毫秒。当得到精确的发射时间后，只考虑少于毫秒的部分，就可以计算得到精确的码片位置；
ΔT travel为卫星信号从卫星传播到接收机所需要的时间，可以通过电文解析到的卫星位置和粗略的接收机位置计算得到。由于通过基站定位获取到的接收机位置误差通常在500米内，故而接收机位置误差引入的码片估计误差最恶劣的情况通常也不足10个码片，此部分可在卫星捕获范围中加以考虑。
ΔT SatClkBias为卫星的钟漂信息，可以直接从卫星的电文中解调得到。
多频勒频移可以通过卫星和接收机的多普勒效应计算得到，同时还需要考虑接收机本地时钟的钟漂影响。卫星的速度可以根据导航电文给出的信息直接计算得到，接收机的速度可以用粗略的估计值代替，模糊度则在多普勒频率搜索范围中加以考虑。
利用上述估计的卫星捕获参数直接启动跟踪引擎进行卫星的捕获。由于估计的参数较为精确，通常跟踪引擎可以快速捕获到卫星信号，并将解调后的信息作为观测量提供给导航解算模块。导航解算模块通过最小二乘法或者卡尔曼滤波算法最终确定接收机精确的位置、速度及时间信息。
基站1的时间精度和GNSS在同一量级。当基站1为CDMA基站和CDMA 2000基站时，时间同步的要求是10us；当基站1为TD-SCDMA基站时，时间同步要求为3u；当基站1为LTE基站时，时间同步要求为1us甚至是微秒量级。对于类似精度量级的基站系统，可以很好的满足本实施例对基站系统的精度要求。以CDMA系统为例，每一个基站都搭载GNSS接收机9，作为时间基准的参考源。GNSS接收机99同时包含蜂窝通信模块5及GNSS模块6。蜂窝通信模块5接收来自基站1的信号帧，并解析得到信号帧边缘对应的时间信息。在蜂窝通信模块5检测到信号帧边缘的同时，产生触发信号，并通过硬件直连与GNSS模块6进行通信，GNSS模块6通过本地时钟记录信号触发的时刻。硬件连接的时延很小，可以忽略不计。GNSS模块6和蜂窝通信模块5共用TCXO 作为时钟源。同时，GNSS模块6通过第二天线8接收来自卫星2的测距信号，通过PVT解算可以得到接收机精确的时间信息。GNSS模块6通过本地时钟可以推算出在信号触发时刻对应的GNSS时间，并结合蜂窝通信模块5得到的时间，实时跟踪蜂窝通信模块5的时间误差。
本实施例的卫星捕获跟踪方法利用蜂窝网络模块提供的时间辅助以及AGNSS服务器提供星历辅助，省略了传统GNSS接收机中的捕获引擎模块，不但可以通过减少GNSS接收机的芯片的面积来降低成本，还可以降低GNSS接收机整体功耗。同时，通过跟踪引擎进行卫星捕获速度更快，从而提升了GNSS定位性能。
实施例4
本实施例提供一种卫星捕获跟踪方法。本实施例的卫星捕获跟踪方法与实施例3的卫星捕获跟踪方法大致相同，区别在于，在步骤S3中，在获取当前时间的过程中引入系统偏差△T。
如果基站的基准不是GNSS时间的话，上述估计有可能含有一个系统偏差；或者基站的时钟基准是GNSS时间，但是基站在做GNSS时间与蜂窝网络信号调制进行同步操作时，可能引入一个系统偏差，记为△T。对包含系统偏差的情况下，则采用如下公式获得来当前时间T Receiver：
T Receiver＝To2+(Tg2-Tg1)，T2＝T1+deltaT，To2＝T2+△T；
其中，To2表征补偿的GPS时间，T2表征优化的GPS时间，Tg2表征第二本地时间，T1表征第一GPS时间，△T表征系统偏差。
在得到第一GPS时间T1、优化的GPS时间系统T2、第一本地时间Tg1、第二本地时间Tg2等之后，进一步获取系统偏差△T的过程如下：
GNSS接收机通过接收GNSS卫星测距信号和卫星导航电文，组成伪距、多普勒原始观测量，以及解得卫星的位置信息；
根据伪距、多普勒原始观测量、卫星的位置等信息，通过最小二乘算法或卡尔曼滤波算法，计算当前GNSS接收机的位置、速度及第二GPS时间Tgps；
然后，根据本地时间差，推算出蜂窝信号帧边缘对应的第三GPS时间Tgps_1：
Tgps_1＝Tgps–(Tg2-Tg1)；
最后，对同一时刻的蜂窝网络时间及GNSS模块得到的GPS时间(第三GPS时间Tgps_1)进行滤波估计。滤波估计基于如下线性模型：
Figure PCTCN2021128796-appb-000014
τ Measurement(t)＝τ(t)+ε τ(t)；
其中，τ是待估计的蜂窝网络时间(以GPS时来表示)，
Figure PCTCN2021128796-appb-000015
表示相应的时间变化率，ω为模型误差(通常假定为高斯白噪声)，T s表示测量时间间隔(或称之为测量频率)。τ Measurement为GNSS模块得到的GPS时(即第三GPS时间Tgps_1)，ε表示观测误差。通过如上模型，构造一个时间相关的卡尔曼滤波器(构造该卡尔曼滤波器的具体方式可参考莫祥林，杜建洪，“一种自适应的OFDM频偏估计方法”，复旦学报(自然科学版)，第44卷第一期，2005)，通过τ Measurement来估计τ及
Figure PCTCN2021128796-appb-000016
滤波输出的τ估计误差即为需要求解的系统偏差△T。
本实施例的其他步骤可参照实施例3实现，此处不再赘述。
虽然以上描述了本发明的具体实施方式，但是本领域的技术人员应当理解，这仅是举例说明，本发明的保护范围是由所附权利要求书限定的。本领域的技术人员在不背离本发明的原理和实质的前提下，可以对这些实施方式做出多种变更或修改，但这些变更和修改均落入本发明的保护范围。

Claims (16)

  1. 一种GNSS接收机，其特征在于，包括蜂窝通信模块、GNSS模块；
    所述GNSS模块包括跟踪引擎、导航解算模块；
    所述蜂窝通信模块用于解析信号帧以得到帧边缘，所述导航解算模块用于根据所述帧边缘记录第一本地时间，所述蜂窝通信模块还用于根据所述帧边缘得到对应的第一GPS时间，所述蜂窝通信模块还用于进行频偏估计以得到本地时钟对应的钟漂；
    所述蜂窝通信模块还用于根据所述第一GPS时间和信号传输时延得到优化的GPS时间，并将所述优化的GPS时间发送至所述导航解算模块，所述信号传输时延为信号从基站传输到所述GNSS接收机所需要的时间；
    所述导航解算模块还用于根据第一本地时间、优化的GPS时间、第二本地时间得到当前时间，所述第二本地时间为所述GNSS模块接收到所述优化的GPS时间对应的本地时间；
    所述导航解算模块还用于根据所述当前时间、所述钟漂、卫星导航电文得到卫星的捕获参数；
    所述跟踪引擎根据所述捕获参数进行卫星捕获。
  2. 如权利要求1所述的GNSS接收机，其特征在于，所述信号传输时延
    Figure PCTCN2021128796-appb-100001
    Figure PCTCN2021128796-appb-100002
    其中，(X 1，Y 1，Z 1)表征所述基站的位置对应的坐标，(X 2，Y 2，Z 2)表征所述GNSS接收机的概略位置对应的坐标，c表征光速。
  3. 如权利要求2所述的GNSS接收机，其特征在于，所述当前时间T Receiver＝T2+(Tg2-Tg1)，T2＝T1+deltaT；其中，T2表征所述优化的GPS时间，Tg2表征所述第二本地时间，T1表征所述第一GPS时间。
  4. 如权利要求2所述的GNSS接收机，其特征在于，所述当前时间T Receiver＝To2+(Tg2-Tg1)，T2＝T1+deltaT，To2＝T2+△T；其中，To2表征补偿的GPS时间，T2表征所述优化的GPS时间，Tg2表征所述第二本地时间，T1表征所述第一GPS时间，△T表征系统偏差。
  5. 如权利要求4所述的GNSS接收机，其特征在于，所述导航解算模块根据卫星测距信号和所述卫星导航电文获取伪距、多普勒原始观测量、所述卫星的位置；
    所述导航解算模块根据所述伪距、所述多普勒原始观测量、所述卫星的位置获取所述GNSS接收机的置位、速度和第二GPS时间Tgps；
    所述导航解算模块获取蜂窝信号帧边缘对应的第三GPS时间Tgps_1＝Tgps–(Tg2-Tg1)；
    所述导航解算模块根据蜂窝网络时间和第三GPS时间Tgps_1进行滤波估计以得到所述系统偏差△T。
  6. 如权利要求5所述的GNSS接收机，其特征在于，所述导航解算模块基于如下线性模型进行滤波估计：
    Figure PCTCN2021128796-appb-100003
    τ Measurement(t)＝τ(t)+ε τ(t)  ；
    其中，τ是待估计的蜂窝网络时间，
    Figure PCTCN2021128796-appb-100004
    表示相应的时间变化率，ω为模型误差，T s表示测量时间间隔；τ Measurement取值为Tgps_1，ε表示观测误差；
    基于所述线性模型构造一时间相关的卡尔曼滤波器，通过τ Measurement估计τ及
    Figure PCTCN2021128796-appb-100005
    获取滤波输出的τ估计误差作为所述系统偏差△T。
  7. 如权利要求1所述的GNSS接收机，其特征在于，所述导航解算模块根据以下公式估计所述卫星的码相位：
    T transmit＝T Receiver-ΔT travel-ΔT SatClkBias；
    其中，T transmit表征估计的卫星信号的发射时间，T Receiver表征所述当前时间，ΔT travel为所述卫星信号从所述卫星传播到所述GNSS接收机所需要的时间，ΔT SatClkBias为所述卫星的钟漂信息。
  8. 如权利要求1所述的GNSS接收机，其特征在于，所述导航解算模块基于最小二乘法或者卡尔曼滤波算法确定所述GNSS接收机的精确的位置、速度及时间信息。
  9. 一种卫星捕获跟踪方法，其特征在于，所述卫星捕获跟踪方法基于一GNSS接收机实现，所述GNSS接收机包括蜂窝通信模块、GNSS模块；
    所述GNSS模块包括跟踪引擎、导航解算模块；
    所述卫星捕获跟踪方法包括以下步骤：
    所述蜂窝通信模块解析信号帧以得到帧边缘，所述导航解算模块根据所述帧边缘记录第一本地时间，所述蜂窝通信模块根据所述帧边缘得到对应的第一GPS时间，所述蜂窝通信模块进行频偏估计以得到本地时钟对应的钟漂；
    所述蜂窝通信模块根据所述第一GPS时间和信号传输时延得到优化的GPS时间，并将所述优化的GPS时间发送至所述导航解算模块，所述信号传输时延为信号从基站传输到所述GNSS接收机所需要的时间；
    所述导航解算模块根据第一本地时间、优化的GPS时间、第二本地时间得到当前时 间，所述第二本地时间为所述GNSS模块接收到所述优化的GPS时间对应的本地时间；
    所述导航解算模块根据所述当前时间、所述钟漂、卫星导航电文得到卫星的捕获参数；
    所述跟踪引擎根据所述捕获参数进行卫星捕获。
  10. 如权利要求9所述的卫星捕获跟踪方法，其特征在于，所述信号传输时延
    Figure PCTCN2021128796-appb-100006
    Figure PCTCN2021128796-appb-100007
    其中，(X 1，Y 1，Z 1)表征所述基站的位置对应的坐标，(X 2，Y 2，Z 2)表征所述GNSS接收机的概略位置对应的坐标，c表征光速。
  11. 如权利要求10所述的卫星捕获跟踪方法，其特征在于，所述当前时间T Receiver＝T2+(Tg2-Tg1)，T2＝T1+deltaT；其中，T2表征所述优化的GPS时间，Tg2表征所述第二本地时间，T1表征所述第一GPS时间。
  12. 如权利要求10所述的卫星捕获跟踪方法，其特征在于，所述当前时间T Receiver＝To2+(Tg2-Tg1)，T2＝T1+deltaT，To2＝T2+△T；其中，To2表征补偿的GPS时间，T2表征所述优化的GPS时间，Tg2表征所述第二本地时间，T1表征所述第一GPS时间，△T表征系统偏差。
  13. 如权利要求12所述的卫星捕获跟踪方法，其特征在于，获取所述系统偏差△T的步骤包括：
    所述导航解算模块根据卫星测距信号和所述卫星导航电文获取伪距、多普勒原始观测量、所述卫星的位置；
    所述导航解算模块根据所述伪距、所述多普勒原始观测量、所述卫星的位置获取所述GNSS接收机的置位、速度和第二GPS时间Tgps；
    所述导航解算模块获取蜂窝信号帧边缘对应的第三GPS时间Tgps_1＝Tgps–(Tg2-Tg1)；
    所述导航解算模块根据蜂窝网络时间和第三GPS时间Tgps_1进行滤波估计以得到所述系统偏差△T。
  14. 如权利要求13所述的卫星捕获跟踪方法，其特征在于，所述导航解算模块基于如下线性模型进行滤波估计：
    Figure PCTCN2021128796-appb-100008
    τ Measurement(t)＝τ(t)+ε τ(t)  ；
    其中，τ是待估计的蜂窝网络时间，
    Figure PCTCN2021128796-appb-100009
    表示相应的时间变化率，ω为模型误差，T s表示测量时间间隔；τ Measurement取值为Tgps_1，ε表示观测误差；
    基于所述线性模型构造一时间相关的卡尔曼滤波器，通过τ Measurement估计τ及
    Figure PCTCN2021128796-appb-100010
    获取滤波输出的τ估计误差作为所述系统偏差△T。
  15. 如权利要求9所述的卫星捕获跟踪方法，其特征在于，得到所述卫星的捕获参数的步骤包括：
    所述导航解算模块根据以下公式估计所述卫星的码相位：
    T transmit＝T Receiver-ΔT travel-ΔT SatClkBias；
    其中，T transmit表征估计的卫星信号的发射时间，T Receiver表征所述当前时间，ΔT travel为所述卫星信号从所述卫星传播到所述GNSS接收机所需要的时间，ΔT SatClkBias为所述卫星的钟漂信息。
  16. 如权利要求9所述的卫星捕获跟踪方法，其特征在于，
    所述卫星捕获跟踪方法还包括以下步骤：
    所述导航解算模块基于最小二乘法或者卡尔曼滤波算法确定所述GNSS接收机的精确的位置、速度及时间信息。
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