GNSS pseudolite system

Abstract

The present application discloses a GNSS pseudo-satellite system for generating and broadcasting time-frequency synchronized GNSS pseudo-satellite signals based on a GNSS system. The system includes at least one main base station and at least three sub-base stations. Any one of the at least one main base station includes a main base station GNSS signal processing unit, a main base station time-frequency synchronization unit, a main base station signal generation unit, a main base station synchronization reference signal receiving unit, a main base station loop processing unit, and a main base station reference signal generation unit. Any one of the at least three sub-base stations includes a sub-base station time-frequency synchronization unit, a sub-base station signal generation unit, a sub-base station synchronization reference signal receiving unit, a sub-base station loop processing unit, and a sub-base station reference signal generation unit. The signals emitted by the main base station and sub-base stations of the GNSS pseudo-satellite system of the present application have time-frequency synchronization characteristics, which can help the user terminal achieve accurate dynamic positioning.

Description

Technical Field

[0001] The present application relates to the field of navigation technology, and in particular to a GNSS pseudo-satellite system. Background Art

[0002] With the continued development of the Global Navigation Satellite System (GNSS), high-precision navigation, positioning, and timing services have become essential infrastructure for modern society, playing a key role in national economic and social development. However, traditional satellite-based GNSS positioning technology faces two key challenges: 1. Limited service coverage. Satellite signals are blocked indoors, in urban canyons, under bridges and tunnels, and in areas with weak signal coverage, such as underground and at the North and South Poles. This makes it difficult to provide reliable services and meet the needs of users worldwide. 2. Inadequate availability and security. The radio spectrum is very crowded and subject to numerous interferences. Therefore, satellite signals cannot provide secure and reliable services in complex electromagnetic environments.

[0003] To supplement and enhance GNSS, expand its service scope, improve usability and security, and meet user needs in a wider range of scenarios, pseudolite technology has been proposed. Existing pseudolite positioning technologies primarily include standalone pseudolite technology and synchronous pseudolite technology. In standalone pseudolite technology, precise time synchronization is achieved between pseudolites through wired or wireless means. Independent pseudolite ranging signals are broadcast in specific frequency bands. Pseudolite positioning terminals perform joint processing based on the pseudorange / carrier measurements from multiple pseudolites to achieve high-precision positioning. Standalone pseudolite technology offers flexible networking deployment, high positioning accuracy, and strong anti-interference capabilities, making it suitable for a wide range of applications. However, its reliance on dedicated receiving terminals limits its widespread adoption and application. In synchronous pseudolite technology, real GNSS signals received by a receiving antenna or GNSS signals generated by a multi-channel GNSS signal simulator are amplified and forwarded to provide positioning signals in areas with weak GNSS coverage. GNSS positioning terminals use the forwarded GNSS signals to achieve positioning. In this case, the receiver's location is the receiving antenna's location or the user's location simulated by the simulator. Synchronous pseudolites are based on the method of forwarding / simulating GNSS signals. They are highly compatible with GNSS and have wide applicability. However, they cannot provide dynamic user locations.

[0004] Therefore, there is a need for a GNSS pseudolite system that can solve the above-mentioned problems existing in the existing pseudolite technology, and the GNSS pseudolite system does not require the addition of a dedicated receiving terminal and provides dynamic user positions. Summary of the Invention

[0005] In view of this, the present application proposes a GNSS pseudolite system to at least solve the above-mentioned existing technical problems.

[0006] According to an embodiment of the present application, a GNSS pseudo-satellite system is used to generate and broadcast a time-frequency synchronized GNSS pseudo-satellite signal based on a GNSS system. The GNSS pseudo-satellite system includes at least one main base station and at least three sub-base stations. Any one of the at least one main base station includes a main base station GNSS signal processing unit, a main base station time-frequency synchronization unit, and a main base station signal generation unit. Any one of the at least three sub-base stations includes a sub-base station time-frequency synchronization unit and a sub-base station signal generation unit, wherein:

[0007] The master base station GNSS signal processing unit receives and processes GNSS signals from the GNSS system and outputs receiver clock compensation parameters and GNSS satellite ephemeris orbit parameters.

[0008] The master base station time and frequency synchronization unit receives the receiver clock difference compensation parameter and obtains and outputs the master base station clock compensation parameter based on the receiver clock difference compensation parameter.

[0009] The master base station signal generation unit receives the master base station clock compensation parameter and the GNSS satellite ephemeris orbit parameter, and generates and broadcasts a master base station synchronization reference signal on a first frequency point and a master base station GNSS pseudo-satellite signal on a second frequency point according to the master base station clock compensation parameter and the GNSS satellite ephemeris orbit parameter;

[0010] The sub-base station time and frequency synchronization unit receives the master base station synchronization reference signal and outputs the sub-base station clock compensation parameter and the GNSS satellite ephemeris orbit parameter,

[0011] The sub-base station signal generation unit receives the sub-base station clock compensation parameter and the GNSS satellite ephemeris orbit parameter, and generates and broadcasts a sub-base station synchronization reference signal on the first frequency point and a sub-base station GNSS pseudo-satellite signal on the second frequency point according to the sub-base station clock compensation parameter and the GNSS satellite ephemeris orbit parameter;

[0012] The master base station time and frequency synchronization unit includes a master base station synchronization reference signal receiving unit, a master base station loop processing unit and a master base station reference signal generating unit, wherein the master base station synchronization reference signal receiving unit receives and outputs the sub-base station synchronization reference signal; the master base station loop processing unit receives the sub-base station synchronization reference signal and receives the master base station synchronization reference signal from the master base station reference signal generating unit, and obtains and outputs a first phase difference measurement value and a first frequency difference measurement value between the master base station synchronization reference signal and the sub-base station synchronization reference signal observed by the master base station based on the master base station synchronization reference signal and the sub-base station synchronization reference signal; the master base station reference signal generating unit receives the first phase difference measurement value and the first frequency difference measurement value and broadcasts the first phase difference measurement value and the first frequency difference measurement value through the master base station synchronization reference signal; and

[0013] The sub-base station time and frequency synchronization unit includes a sub-base station synchronization reference signal receiving unit, a sub-base station loop processing unit and a sub-base station reference signal generating unit, wherein the sub-base station synchronization reference signal receiving unit receives and outputs the main base station synchronization reference signal; the sub-base station loop processing unit receives the main base station synchronization reference signal and receives the sub-base station synchronization reference signal from the sub-base station reference signal generating unit, and obtains the first phase difference measurement value and the first frequency difference measurement value from the main base station synchronization reference signal and obtains the second phase difference measurement value and the second frequency difference measurement value between the sub-base station synchronization reference signal and the main base station synchronization reference signal observed by the sub-base station based on the sub-base station synchronization reference signal and the main base station synchronization reference signal, and also jointly processes the first phase difference measurement value and the first frequency difference measurement value as well as the second phase difference measurement value and the second frequency difference measurement value to obtain and output the sub-base station clock compensation parameter, so that all main base station synchronization reference signals are time and frequency synchronized with all sub-base station synchronization reference signals;

[0014] The main base station signal generation unit also generates and broadcasts a main base station GNSS pseudo-satellite signal based on the main base station synchronization reference signal and the sub-base station synchronization reference signal, and the sub-base station signal generation unit also generates and broadcasts a sub-base station GNSS pseudo-satellite signal based on the sub-base station synchronization reference signal and the main base station synchronization reference signal, thereby generating and broadcasting a main base station GNSS pseudo-satellite signal and a sub-base station GNSS pseudo-satellite signal that are time-frequency synchronized.

[0015] In the GNSS pseudo-satellite system according to an embodiment of the present application, the main base station loop processing unit further performs joint processing on the first phase difference measurement value and the first frequency difference measurement value, as well as the second phase difference measurement value and the second frequency difference measurement value, in the received sub-base station synchronization reference signal and the main base station synchronization reference signal to obtain and output a first frequency difference estimation value and a first clock difference estimation value at the first frequency point between the main base station synchronization reference signal and the sub-base station synchronization reference signal; the main base station reference signal generation unit receives the first frequency difference estimation value and the first clock difference estimation value and obtains a first compensation value at the second frequency point based on the first frequency difference estimation value and the first clock difference estimation value; and the main base station signal generation unit generates a carrier and a pseudo code of the main base station GNSS pseudo-satellite signal based on the first compensation value, thereby generating the main base station GNSS pseudo-satellite signal; and

[0016] The sub-base station loop processing unit also obtains and outputs the second frequency difference estimation value and the second clock difference estimation value at the first frequency point between the sub-base station synchronization reference signal and the main base station synchronization reference signal based on the joint processing of the first phase difference measurement value and the first frequency difference measurement value and the second phase difference measurement value and the second frequency difference measurement value. The sub-base station reference signal generation unit receives the second frequency difference estimation value and the second clock difference estimation value and obtains the second compensation value at the second frequency point based on the second frequency difference estimation value and the second clock difference estimation value. The sub-base station signal generation unit generates the carrier and pseudo code of the sub-base station GNSS pseudo-satellite signal based on the second compensation value and thus generates the sub-base station GNSS pseudo-satellite signal.

[0017] In the GNSS pseudo-satellite system according to the embodiment of the present application, the first phase differential measurement value includes the ranging code phase differential measurement value measured by the main base station and the carrier phase differential measurement value measured by the main base station; the second phase differential measurement value includes the ranging code phase differential measurement value measured by the sub-base station and the carrier phase differential measurement value measured by the sub-base station.

[0018] In the GNSS pseudo-satellite system according to the embodiment of the present application,

[0019] The ranging code phase differential measurement value measured by the primary base station is obtained by:

[0020] c·(δt s -δt m )=-(ρ m,s -ρ m,m )+r-(d s -d m )+σ;

[0021] The carrier phase differential measurement value measured by the master base station is obtained by:

[0022] c·(δt s -δt m )=-(L m,s -L m,m )·λ1+r-(d s -d m )+σ;

[0023] The ranging code phase differential measurement value of the sub-base station is obtained by:

[0024] c·(δt s -δt m )=-(ρ s,s -ρ s,m )-r-(d s -d m )+σ;

[0025] The carrier phase differential measurement value of the sub-base station is obtained by:

[0026] c·(δt s -δt m )=-(L s,s -L s,m )·λ1-r-(d s -d m )+σ,

[0027] in:

[0028] c represents the speed of light,

[0029] δt s represents the clock difference of the sub-base station,

[0030] δt m represents the clock difference of the main base station,

[0031] ρ m,s It represents the pseudo-range observation value of the sub-base station measured by the main base station,

[0032] ρ m,m represents the pseudorange observation value of the main base station measured by the main base station,

[0033] ρ s,s represents the pseudorange observation value of the sub-base station measured by the sub-base station,

[0034] ρ s,m represents the pseudorange observation value of the main base station measured by the sub-base station,

[0035] r represents the distance between the sub-base station and the main base station,

[0036] d sIndicates the hardware delay of the sub-base station,

[0037] d m Indicates the hardware delay of the primary base station.

[0038] σ represents the measurement noise,

[0039] L m,s Indicates the carrier observation value of the sub-base station measured by the main base station,

[0040] L m,m Indicates the carrier observation value of the main base station measured by the main base station,

[0041] L s,s represents the carrier observation value of the sub-base station measured by the sub-base station,

[0042] L s,m Indicates the carrier observation value of the main base station measured by the sub-base station,

[0043] λ1 represents the nominal wavelength of the synchronization reference signal, which corresponds to the nominal frequency of the synchronization reference signal.

[0044] In the GNSS pseudo-satellite system according to the embodiment of the present application,

[0045] The average ranging code phase difference is calculated by:

[0046]

[0047] The average carrier phase difference is calculated by:

[0048]

[0049] Obtaining a clock deviation of the sub-base station relative to the main base station according to the average ranging code phase difference and the average carrier phase difference;

[0050] A sub-base station clock compensation parameter is obtained according to the clock deviation of the sub-base station relative to the main base station.

[0051] In the GNSS pseudolite system according to the embodiment of the present application, the sub-base station time and frequency synchronization unit obtains the sampling rate correction required by the sub-base station signal generation unit by:

[0052] Get the carrier frequency differential measurement value of the sub-base station Δf1 = f 1,s -f 1,m , where Δf1 represents the frequency difference between the synchronization reference signal of the sub-base station and the master base station measured by the sub-base station, f 1,s represents the sub-base station synchronization reference signal frequency measured by the sub-base station, f 1,m Indicates the master base station synchronization reference signal frequency measured by the sub-base station,

[0053] The sampling rate correction is calculated based on the carrier frequency differential measurement, and the calculation formula is: fs fix =(f 1,s -f 1,m )*f s / f1, where fs fix is the sampling rate correction, f s is the sampling rate used to generate the signal, and f1 is the nominal frequency of the synchronization reference signal.

[0054] In the GNSS pseudolite system according to the embodiment of the present application, the main base station and the sub-base station implement time-frequency synchronization of the main base station GNSS pseudolite signal and the sub-base station GNSS pseudolite signal according to the following:

[0055] Based on the frequency difference estimate value of f1, a clock sampling rate compensation estimate value is obtained through frequency domain conversion, and then a frequency difference compensation value of f2 is obtained through inverse frequency domain conversion. Based on the frequency difference compensation value of f2, the main base station signal generation unit and the sub-base station signal generation unit generate the f2 carrier in real time;

[0056] Based on the clock error estimate of f1 and the sampling rate compensation estimate, the sampling rate compensation algorithm is used to obtain the cumulative step value of the pseudo code generator. Based on the pseudo code step value, the main base station signal generation unit and the sub-base station signal generation unit generate GNSS pseudo code and modulation code signals in the time domain in real time.

[0057] The main base station signal generating unit and the sub-base station signal generating unit modulate the generated f2 carrier and pseudo code and broadcast them.

[0058] In the GNSS pseudo-satellite system according to the embodiment of the present application, the master base station signal generation unit further receives the GNSS satellite ephemeris orbit parameters, and generates pseudo-code phase and carrier phase corrections at the start and end times of the GNSS pseudo-satellite signal based on the GNSS satellite ephemeris orbit parameters, and corrects the pseudo-code phase and carrier phase of the master base station GNSS pseudo-satellite signal by using the pseudo-code phase and carrier phase corrections at the start and end times so that the pseudo-code phase and carrier phase of the master base station GNSS pseudo-satellite signal are consistent with the pseudo-code phase and carrier phase of the GNSS signal, respectively.

[0059] The sub-base station signal generation unit also receives the GNSS satellite ephemeris orbit parameters, and generates pseudo-code phase and carrier phase corrections at the start and end times of the GNSS pseudo-satellite signal based on the GNSS satellite ephemeris orbit parameters, and corrects the pseudo-code phase and carrier phase of the sub-base station GNSS pseudo-satellite signal by using the pseudo-code phase and carrier phase corrections at the start and end times so that the pseudo-code phase and carrier phase of the sub-base station GNSS pseudo-satellite signal are consistent with the pseudo-code phase and carrier phase of the GNSS signal, respectively.

[0060] In the GNSS pseudolite system according to the embodiment of the present application, the main base station and the sub-base station implement orbit compensation of the main base station GNSS pseudolite signal and the sub-base station GNSS pseudolite signal according to the following:

[0061] Obtaining an equivalent GNSS time of the start time and the end time of the generation of GNSS pseudolite signals by the main base station signal generation unit and the sub-base station signal generation unit, wherein the equivalent GNSS time of the start time is obtained by calculating the clock difference, and the equivalent GNSS time of the end time needs to compensate for the time advance / lag caused by clock drift;

[0062] Based on the equivalent GNSS time of the start moment and the equivalent GNSS time of the end moment, the atmospheric transmission delay caused by the GNSS signal passing through the ionosphere and troposphere, as well as the signal transmission delay caused by the GNSS satellite clock error and clock drift, are compensated, and the GNSS transmission start time and end time in the GNSS pseudolite signal are calculated;

[0063] Based on the start time and end time of the GNSS transmission moment, control parameters for the main base station signal generation unit and the sub-base station signal generation unit to generate GNSS pseudo-satellite signals are accurately calculated.

[0064] According to the GNSS pseudo-satellite system of the embodiment of the present application, the GNSS pseudo-satellite signals generated by multiple base stations (including at least one main base station and at least three sub-base stations) achieve high-precision signal time-frequency synchronization. Since the signals of different base stations have time-frequency synchronization characteristics, the GNSS positioning user terminal receives GNSS pseudo-satellite signals transmitted by more than four base stations, which can achieve seamless and compatible positioning. At the same time, the arrival time of the multiple pseudo-satellite signals received by the GNSS positioning user terminal is related to its position. Therefore, based on the GNSS pseudo-satellite signal of the base station, the terminal has the ability of dynamic positioning, and can further be combined with the satellite-based GNSS satellite signal for positioning. The GNSS pseudo-satellite system has the advantages of not requiring the addition of a dedicated receiving terminal and being able to provide accurate dynamic user positions. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] For purposes of illustration and not limitation, the present application will now be described in terms of its preferred embodiments, particularly with reference to the accompanying drawings, in which:

[0066] Figure 1 Schematic diagram of an application scenario of a GNSS pseudo-satellite system according to an embodiment of the present application;

[0067] Figure 2 Schematic diagram of the structure of a main base station in a GNSS pseudo-satellite system according to an embodiment of the present application;

[0068] Figure 3 Schematic diagram of the structure of a sub-base station in a GNSS pseudo-satellite system according to an embodiment of the present application;

[0069] Figure 4A Schematic diagram of test results of pseudorange single difference and true range single difference of a GNSS pseudolite system according to an embodiment of the present application;

[0070] Figure 4B Schematic diagram of test results of pseudorange single difference and carrier single difference of a GNSS pseudolite system according to an embodiment of the present application;

[0071] Figure 5 Schematic diagram of positioning results of a GNSS pseudo-satellite system according to an embodiment of the present application. DETAILED DESCRIPTION

[0072] The following will clearly and completely describe the technical solution of this application in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0073] In this application, GNSS stands for Global Navigation Satellite System (GNSS), and is hereinafter referred to as GNSS or GNSS system. GNSS pseudolites are ground-based devices that are stationary, mimicking satellites in the sky and capable of transmitting GNSS signals. These pseudolites transmit GNSS-like radio navigation signals to users, enabling enhanced navigation.

[0074] The GNSS pseudo-satellite system according to the embodiment of the present application is used to generate and broadcast a GNSS pseudo-satellite signal with time and frequency synchronization based on the GNSS system, such as Figure 1 As shown, the GNSS pseudo-satellite system includes at least one main base station 10 and at least three sub-base stations 20. It should be explained that Figure 1The GNSS pseudo-satellite system includes one main base station and four sub-base stations, which is for example only and not limiting. According to the embodiment of the present application, the GNSS pseudo-satellite system includes at least four base stations, which can achieve precise positioning, thereby helping the user terminal to achieve navigation function.

[0075] In the GNSS pseudo-satellite system according to the embodiment of the present application, the internal structures of the main base station 10 and the sub-base station 20 are respectively as follows: Figure 2 and Figure 3As shown. Any of the at least one master base station 10 includes a master base station GNSS signal processing unit 101, a master base station time and frequency synchronization unit 102, and a master base station signal generation unit 103, and any of the at least three sub-base stations includes a sub-base station time and frequency synchronization unit 202 and a sub-base station signal generation unit 203. Among them, the master base station GNSS signal processing unit 101 receives and processes GNSS signals from the GNSS system and outputs receiver clock compensation parameters and GNSS satellite ephemeris orbit parameters. The master base station time and frequency synchronization unit 102 receives the receiver clock compensation parameters and obtains and outputs the master base station clock compensation parameters based on the receiver clock compensation parameters. The master base station signal generation unit 103 receives the master base station clock compensation parameters and GNSS satellite ephemeris orbit parameters, and generates and broadcasts the master base station synchronization reference signal on the first frequency point and the master base station GNSS pseudo-satellite signal on the second frequency point based on the master base station clock compensation parameters and GNSS satellite ephemeris orbit parameters. The sub-base station time and frequency synchronization unit 202 receives the master base station synchronization reference signal and outputs the sub-base station clock compensation parameters and GNSS satellite ephemeris orbit parameters. The sub-base station signal generation unit 203 receives the sub-base station clock compensation parameters and the GNSS satellite ephemeris orbit parameters, and generates and broadcasts the sub-base station synchronization reference signal at the first frequency point and the sub-base station GNSS pseudo-satellite signal at the second frequency point based on the sub-base station clock compensation parameters and the GNSS satellite ephemeris orbit parameters. The master base station time and frequency synchronization unit 102 includes a master base station synchronization reference signal receiving unit 104, a master base station loop processing unit 105, and a master base station reference signal generation unit 106. The master base station synchronization reference signal receiving unit 104 receives and outputs the sub-base station synchronization reference signal. The master base station loop processing unit 105 receives the sub-base station synchronization reference signal and receives the master base station synchronization reference signal from the master base station reference signal generation unit 106, and obtains and outputs a first phase difference measurement value and a first frequency difference measurement value between the master base station synchronization reference signal and the sub-base station synchronization reference signal based on the master base station synchronization reference signal and the sub-base station synchronization reference signal. The master base station reference signal generation unit 106 receives the first phase difference measurement value and the first frequency difference measurement value and broadcasts the first phase difference measurement value and the first frequency difference measurement value via the master base station synchronization reference signal. The sub-base station time and frequency synchronization unit 202 includes a sub-base station synchronization reference signal receiving unit 201, a sub-base station loop processing unit 204, and a sub-base station reference signal generation unit 205. The sub-base station synchronization reference signal receiving unit 201 receives and outputs the master base station synchronization reference signal.The sub-base station loop processing unit 204 receives the master base station synchronization reference signal and receives the sub-base station synchronization reference signal from the sub-base station reference signal generation unit 205, and obtains a first phase difference measurement value and a first frequency difference measurement value from the master base station synchronization reference signal, and obtains a second phase difference measurement value and a second frequency difference measurement value between the sub-base station synchronization reference signal observed by the sub-base station and the master base station synchronization reference signal based on the sub-base station synchronization reference signal and the master base station synchronization reference signal, and further jointly processes the first phase difference measurement value and the first frequency difference measurement value as well as the second phase difference measurement value and the second frequency difference measurement value to obtain and output the sub-base station clock compensation parameter, so that all master base station synchronization reference signals are synchronized in time and frequency with all sub-base station synchronization reference signals. The master base station signal generation unit 103 also generates and broadcasts the master base station GNSS pseudo-satellite signal based on the master base station synchronization reference signal and the sub-base station synchronization reference signal. In addition, the sub-base station signal generation unit 203 also generates and broadcasts a sub-base station GNSS pseudo-satellite signal based on the sub-base station synchronization reference signal and the main base station synchronization reference signal, thereby generating and broadcasting a time-frequency synchronized main base station GNSS pseudo-satellite signal and a sub-base station GNSS pseudo-satellite signal. The main base station loop processing unit 105 also jointly processes the first phase difference measurement value and the first frequency difference measurement value, as well as the second phase difference measurement value and the second frequency difference measurement value in the received sub-base station synchronization reference signal and the main base station synchronization reference signal to obtain and output a first frequency difference estimate value and a first clock difference estimate value at a first frequency point between the main base station synchronization reference signal and the sub-base station synchronization reference signal. The main base station reference signal generation unit 106 receives the first frequency difference estimate value and the first clock difference estimate value and obtains a first compensation value at a second frequency point based on the first frequency difference estimate value and the first clock difference estimate value, and the main base station signal generation unit 103 generates a carrier and a pseudo code of the main base station GNSS pseudo-satellite signal based on the first compensation value, thereby generating a main base station GNSS pseudo-satellite signal. The sub-base station loop processing unit 204 further obtains and outputs a second frequency difference estimate and a second clock difference estimate at the first frequency point between the sub-base station synchronization reference signal and the master base station synchronization reference signal based on joint processing of the first phase difference measurement value and the first frequency difference measurement value, as well as the second phase difference measurement value and the second frequency difference measurement value. The sub-base station reference signal generation unit 205 receives the second frequency difference estimate and the second clock difference estimate and obtains a second compensation value at the second frequency point based on the second frequency difference estimate and the second clock difference estimate. The sub-base station signal generation unit 203 generates a carrier and a pseudo code of the sub-base station GNSS pseudo-satellite signal based on the second compensation value, thereby generating the sub-base station GNSS pseudo-satellite signal.

[0076] According to the GNSS pseudo-satellite system of the embodiment of the present application, the first phase differential measurement value may include the ranging code phase differential measurement value measured by the main base station and the carrier phase differential measurement value measured by the main base station; the second phase differential measurement value may include the ranging code phase differential measurement value measured by the sub-base station and the carrier phase differential measurement value measured by the sub-base station.

[0077] The ranging code phase differential measurement value measured by the primary base station can be obtained as follows:

[0078] c·(δt s -δt m )=-(ρ m,s -ρ m,m )+r-(d s -d m )+σ;

[0079] The carrier phase differential measurement value measured by the master base station can be obtained as follows:

[0080] c·(δt s -δt m )=-(L m,s -L m,m )·λ1+r-(d s -d m )+σ;

[0081] The ranging code phase differential measurement value measured by the sub-base station can be obtained as follows:

[0082] c·(δt s -δt m )=-(ρ s,s -ρ s,m )-r-(d s -d m )+σ;

[0083] The carrier phase differential measurement value of the sub-base station can be obtained as follows:

[0084] c·(δt s -δt m )=-(L s,s -L s,m )·λ1-r-(d s -d m )+σ,

[0085] in:

[0086] c represents the speed of light,

[0087] δt s represents the clock difference of the sub-base station,

[0088] δt mrepresents the clock difference of the main base station,

[0089] ρ m,s It represents the pseudo-range observation value of the sub-base station measured by the main base station,

[0090] ρ m,m represents the pseudorange observation value of the main base station measured by the main base station,

[0091] ρ s,s represents the pseudorange observation value of the sub-base station measured by the sub-base station,

[0092] ρ s,m represents the pseudorange observation value of the main base station measured by the sub-base station,

[0093] r represents the distance between the sub-base station and the main base station,

[0094] d s Indicates the hardware delay of the sub-base station,

[0095] d m Indicates the hardware delay of the primary base station.

[0096] σ represents the measurement noise,

[0097] L m,s Indicates the carrier observation value of the sub-base station measured by the main base station,

[0098] L m,m Indicates the carrier observation value of the main base station measured by the main base station,

[0099] L s,s represents the carrier observation value of the sub-base station measured by the sub-base station,

[0100] L s,m Indicates the carrier observation value of the main base station measured by the sub-base station,

[0101] λ1 represents the nominal wavelength of the synchronization reference signal, which corresponds to the nominal frequency of the synchronization reference signal.

[0102] Then, the average ranging code phase difference can be obtained by:

[0103]

[0104] And, the average carrier phase difference can be obtained as follows:

[0105]

[0106] The clock deviation δt of the sub-base station relative to the main base station is calculated based on the average ranging code phase difference and the average carrier phase difference. (s) ;

[0107] According to the clock deviation δt of the sub-base station relative to the main base station (s) Calculate the clock compensation parameters of the sub-base station.

[0108] In the GNSS pseudolite system according to the embodiment of the present application, the sub-base station time and frequency synchronization unit 202 can obtain the sampling rate correction required by the sub-base station signal generation unit 203 by:

[0109] Get the carrier frequency differential measurement value of the sub-base station Δf1 = f 1,s -f 1,m , where Δf1 represents the frequency difference between the synchronization reference signal of the sub-base station and the master base station measured by the sub-base station, f 1,s represents the sub-base station synchronization reference signal frequency measured by the sub-base station, f 1,m Indicates the master base station synchronization reference signal frequency measured by the sub-base station,

[0110] The sampling rate correction is calculated based on the carrier frequency differential measurement. The calculation formula is: fs fix =(f 1,s -f 1,m )*f s / f1, where fs fix is the sampling rate correction, f s is the sampling rate used to generate the signal, and f1 is the nominal frequency of the synchronization reference signal.

[0111] In the GNSS pseudolite system according to the embodiment of the present application, the main base station 10 and the sub-base station 20 can achieve time and frequency synchronization of the main base station GNSS pseudolite signal and the sub-base station GNSS pseudolite signal according to the following:

[0112] Based on the frequency difference estimation value of f1, a clock sampling rate compensation estimation value is obtained through frequency domain conversion, and then a frequency difference compensation value of f2 is obtained through inverse frequency domain conversion. Based on the frequency difference compensation value of f2, the main base station signal generation unit 103 and the sub-base station signal generation unit 203 generate the f2 carrier in real time;

[0113] Based on the clock error estimate value of f1 and the sampling rate compensation estimate value, the sampling rate compensation algorithm is used to obtain the cumulative step value of the pseudo code generator. Based on the pseudo code step value, the main base station signal generation unit 103 and the sub-base station signal generation unit 203 generate the GNSS pseudo code and modulation code signal in the time domain in real time.

[0114] The main base station signal generating unit 103 and the sub-base station signal generating unit 203 modulate the generated f2 carrier and pseudo code and broadcast them.

[0115] In the GNSS pseudo-satellite system according to the embodiment of the present application, the master base station signal generation unit 103 may further receive GNSS satellite ephemeris orbital parameters, and generate pseudo-code phase and carrier phase corrections for the start and end times of the GNSS pseudo-satellite signal based on the GNSS satellite ephemeris orbital parameters, and correct the pseudo-code phase and carrier phase of the master base station GNSS pseudo-satellite signal using the pseudo-code phase and carrier phase corrections at the start and end times so that the pseudo-code phase and carrier phase of the master base station GNSS pseudo-satellite signal are consistent with the pseudo-code phase and carrier phase of the GNSS signal, respectively. The sub-base station signal generation unit 203 may further receive GNSS satellite ephemeris orbital parameters, and generate pseudo-code phase and carrier phase corrections for the start and end times of the GNSS pseudo-satellite signal based on the GNSS satellite ephemeris orbital parameters, and correct the pseudo-code phase and carrier phase of the sub-base station GNSS pseudo-satellite signal using the pseudo-code phase and carrier phase corrections at the start and end times so that the pseudo-code phase and carrier phase of the sub-base station GNSS pseudo-satellite signal are consistent with the pseudo-code phase and carrier phase of the GNSS signal, respectively.

[0116] In the main base station loop processing unit 105 and the sub-base station loop processing unit 204, in order to eliminate the influence of measurement noise and achieve higher frequency synchronization stability, alpha filtering can be used to filter the differential measurement values ​​of the carrier frequencies of multiple epochs. The phase cumulative differential measurement value is obtained after time integration and input into a classic second-order phase-locked loop. The loop system function is as follows.

[0117]

[0118] Among them, w n is called the characteristic frequency, and a2 is called the damping coefficient. These two parameters determine the performance of the second-order loop. Considering that the measurement noise level is related to the frequency stability of the crystal oscillator, and the base station is generally in a static and undisturbed state, the typical loop filter parameter configuration ( B L =0.53w n ), the loop bandwidth can be kept relatively small, thereby ensuring the stability of the signal synchronization frequency between the master base station and the slave base station. The filter loop output can be used as the input of the subsequent signal generation unit to form a loop.

[0119] As can be seen from the above, in the GNSS pseudo-satellite system according to the embodiment of the present application, the main base station first obtains the clock error and clock drift parameters of its local clock in real time, and then calculates its main base station clock compensation parameters, and then generates the main base station synchronization reference signal and the main base station GNSS pseudo-satellite signal based on the main base station clock compensation parameters and the GNSS satellite ephemeris orbit parameters. At the same time, the main base station also performs loop processing, receives the synchronization reference signals of itself and the sub-base station, obtains differential measurement values ​​such as carrier and pseudo-range between the main base station and the sub-base station, and broadcasts the differential measurement values ​​through the synchronization reference signal for the sub-base station to complete two-way differential time synchronization. The sub-base station receives the synchronization reference signals of the main base station and itself, and calculates the frequency phase difference between itself and the synchronization reference signal of the main base station in real time based on the differential measurement method of loop processing, and calculates the clock compensation parameters of the sub-base station through the time-frequency synchronization algorithm, and then adjusts and compensates the frequency phase information of the sub-base station synchronization reference signal and the sub-base station GNSS pseudo-satellite signal generated by its sub-base station in real time according to the sub-base station clock compensation parameters and the GNSS satellite ephemeris orbit parameters, obtains the sub-base station GNSS pseudo-satellite signal and broadcasts it. In addition, the main base station and sub-base station can use the same crystal oscillator to drive the internal receiver and transmitter, and eliminate the hardware delay between the transmitter and receiver channels of the base station by calibrating the delay.

[0120] Based on the above process, the GNSS pseudo-satellite signals generated by multiple base stations (including at least one main base station and at least three sub-base stations) in the GNSS pseudo-satellite system according to the embodiment of the present application achieve high-precision signal time-frequency synchronization. Since the signals of different base stations have time-frequency synchronization characteristics, the GNSS positioning user terminal receives GNSS pseudo-satellite signals transmitted by more than 4 base stations, which can achieve seamless and compatible positioning. At the same time, the arrival time of multiple pseudo-satellite signals received by the GNSS positioning user terminal is related to its position. Therefore, based on the GNSS pseudo-satellite signal of the base station, the terminal has the ability of dynamic positioning, and can also be further combined with the satellite-based GNSS satellite signal for joint positioning.

[0121] Even after achieving time and frequency synchronization, the GNSS pseudo-satellite signals from each base station still exhibit some discrepancies with the GNSS signals from the satellites. This is because satellite GNSS signals propagate through the ionosphere and troposphere, incurring significant propagation delays. Furthermore, the satellites are in motion, so their pseudo-range, carrier wave, and Doppler measurements exhibit time-varying characteristics, dependent on the satellite's relative motion relative to the user. This can lead to confusion in positioning results, making it impossible to properly output information such as the user's position and velocity.

[0122] In order to ensure that the GNSS pseudo-satellite signals received by the user terminal from each base station are basically consistent with the signal parameter representation of the GNSS signal actually received from the satellite, and to maintain the same space-time reference frame so that the two can be seamlessly compatible, an orbit compensation algorithm can also be introduced into the GNSS pseudo-satellite system according to the embodiment of the present application. The GNSS satellite orbit can be accurately extrapolated using the GNSS broadcast ephemeris / precise ephemeris combined with the long-term orbit prediction algorithm. When the signal generation units of the main base station and the sub-base station have achieved time-frequency synchronization, they can estimate the position of the satellite at any virtual transmission time and calculate the theoretical propagation delay of the signal. Ultimately, the distance difference corresponding to the current generation time and the virtual transmission time is consistent with the theoretical propagation delay, thereby determining the pseudo-code phase and carrier phase corrections for the generation start and end times. Based on these correction parameters, the pseudo-code generator and carrier generator parameters are fine-tuned to accurately control the ranging code and carrier of the generated GNSS pseudo-satellite signal to achieve consistency with the GNSS satellite signal parameters.

[0123] In the GNSS pseudolite system according to the embodiment of the present application, the main base station 10 and the sub-base station 20 implement orbit compensation of the main base station GNSS pseudolite signal and the sub-base station GNSS pseudolite signal according to the following:

[0124] Based on the measurement parameters of the time-frequency synchronization algorithm, the equivalent GNSS time t of the start time of the main base station signal generation unit 103 and the sub-base station signal generation unit 203 generating the GNSS pseudo-satellite signal is obtained. k and the equivalent GNSS time t of the termination moment k +1 , where the equivalent GNSS time at the start time is t k The equivalent GNSS time t at the end time is obtained by calculating the clock difference. k+1 The time advance / lag caused by clock drift needs to be compensated;

[0125] Based on t k and t k+1 , compensate for the atmospheric transmission delay caused by the ionosphere and troposphere of the GNSS signal and the signal transmission delay caused by the GNSS satellite clock error and clock drift, and calculate the GNSS transmission time start time τ in the GNSS pseudo-satellite signal generated by the main base station signal generation unit 103 and the sub-base station signal generation unit 203 k and termination time τ k+1 , where τ is calculated k and τ k+1The process can be implemented through the fixed point iteration method, which is as follows: Step 1. Initialize the signal transmission time based on the average signal propagation time of GNSS satellites, which is generally around 70 to 110 ms; Step 2. Extrapolate the satellite position at the corresponding time using the orbit prediction algorithm; Step 3. Calculate the pseudorange observation value based on the satellite position and satellite clock error, clock drift, user reference position and GNSS time to obtain the new signal transmission time; Step 4. Repeat Step 2 to Step 4 until the iterative convergence condition is reached;

[0126] Based on the GNSS transmission start time τ in the generated GNSS pseudo-satellite signal k and termination time τ k+1 , accurately calculate the control parameters of the main base station signal generating unit 103 and the sub-base station signal generating unit 203 to generate the GNSS pseudo-satellite signal, wherein: using τ k and τ k+1 The difference is divided by the number of sampling points to obtain the accurate pseudo code NCO (Numerical Controlled Oscillator) and carrier NCO correction value.

[0127] The beneficial effect of the GNSS pseudo-satellite system according to the embodiment of the present application is that it can provide multi-source GNSS pseudo-satellite signals with high-precision time and frequency synchronization, thereby achieving the beneficial effect of providing dynamic user location without adding a dedicated receiving terminal.

[0128] Figure 4A and Figure 4B The test results of the pseudorange single difference and true range single difference of the GNSS pseudolite system according to the embodiment of the present application are shown.

[0129] The test site was an indoor parking lot. Seven wireless transceiver base stations were placed around the site, with one serving as the master base station and the other six as slave base stations, ensuring a common line of sight between them. Two commercial GNSS receivers were installed at the center of the site as user terminals to receive the GNSS pseudo-satellite signals transmitted by the seven base stations and obtain raw observations of the GNSS signals, including pseudorange, carrier, Doppler, and carrier-to-noise ratio, as well as positioning results.

[0130] During the test, each base station operates simultaneously to generate synchronization reference signals and GNSS pseudo-satellite signals. The signal generation unit in each base station only runs the frequency synchronization algorithm without adding the orbit compensation algorithm. Figure 4A and Figure 4BAs shown, the pseudorange single difference and carrier single difference measurements of the GNSS pseudolite system used in the present application are stable near the true value, with very low noise. Specifically, the pseudorange single difference accuracy is better than 1.4m, and the carrier single difference accuracy is better than 0.8mm. This shows that the GNSS pseudolite system used in the present application can generate high-precision time-frequency synchronized GNSS pseudolite signals in real time, with a time synchronization accuracy of less than 100ps, far exceeding the positioning and timing accuracy of conventional single-point positioning of the GNSS system (>10ns, 5-10m).

[0131] Figure 5 A schematic diagram of the positioning results of the GNSS pseudo-satellite system according to an embodiment of the present application is shown. The figure is a screenshot of the positioning result display interface. The upper right corner of the picture shows the positioning data (longitude, latitude, altitude, etc.) of the GNSS receiver, and the left side of the picture shows the signal strength and reception status of the GNSS pseudo-satellite signal received by the GNSS receiver.

[0132] The system of seven wireless transceiver base stations mentioned above is still used. Each base station operates simultaneously to generate a synchronization reference signal and a GNSS pseudo-satellite signal. The signal generation unit in each base station runs a frequency synchronization algorithm to obtain information such as the synchronization time, frequency correction, and sampling rate correction of the signal generation. Then, an orbit compensation algorithm is used to calculate the transmission time, sampling rate, code phase, time step value, carrier phase, and time step value of the corresponding satellite signal based on the synchronization time, frequency correction, and sampling rate correction, thereby generating a GNSS signal in a synchronous orbit.

[0133] The GNSS pseudo-satellite signal of the base station is received by a GNSS commercial receiver, and the original observation values ​​such as pseudo-range, carrier, Doppler and real-time positioning results of the GNSS pseudo-satellite signal of the base station are obtained. Figure 5 As shown on the left, the GNSS receiver successfully identifies and stably receives GNSS pseudo-satellite signals from 6 visible base stations. Figure 5 As shown on the right, the GNSS receiver successfully achieves real-time positioning, and its positioning result is consistent with the preset user location. This demonstrates that the GNSS pseudolite system according to the embodiment of the present application, after further introducing the orbit compensation algorithm, can achieve compatibility with GNSS signals and achieve high-precision pseudolite positioning consistent with the GNSS positioning framework.

[0134] The above specific embodiments do not constitute a limitation on the scope of protection of this application. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application shall be included within the scope of protection of this application.

Claims

1. A GNSS pseudo-satellite system for generating and broadcasting time-frequency synchronized GNSS pseudo-satellite signals based on a GNSS system, wherein the GNSS pseudo-satellite system comprises at least one main base station (10) and at least three sub-base stations (20), wherein any one of the at least one main base station (10) comprises a main base station GNSS signal processing unit (101), a main base station time-frequency synchronization unit (102), and a main base station signal generation unit (103), and wherein any one of the at least three sub-base stations comprises a sub-base station time-frequency synchronization unit (202) and a sub-base station signal generation unit (203), wherein: The main base station GNSS signal processing unit (101) receives and processes GNSS signals from the GNSS system and outputs receiver clock error compensation parameters and GNSS satellite ephemeris orbit parameters. The master base station time and frequency synchronization unit (102) receives the receiver clock difference compensation parameter and obtains and outputs the master base station clock compensation parameter based on the receiver clock difference compensation parameter. The master base station signal generating unit (103) receives the master base station clock compensation parameter and the GNSS satellite ephemeris orbit parameter, and generates and broadcasts a master base station synchronization reference signal at a first frequency point and a master base station GNSS pseudo-satellite signal at a second frequency point according to the master base station clock compensation parameter and the GNSS satellite ephemeris orbit parameter; The sub-base station time and frequency synchronization unit (202) receives the master base station synchronization reference signal and outputs the sub-base station clock compensation parameter and the GNSS satellite ephemeris orbit parameter, The sub-base station signal generating unit (203) receives the sub-base station clock compensation parameter and the GNSS satellite ephemeris orbit parameter, and generates and broadcasts the sub-base station synchronization reference signal at the first frequency point and the sub-base station GNSS pseudo-satellite signal at the second frequency point according to the sub-base station clock compensation parameter and the GNSS satellite ephemeris orbit parameter; The master base station time and frequency synchronization unit (102) includes a master base station synchronization reference signal receiving unit (104), a master base station loop processing unit (105) and a master base station reference signal generating unit (106), wherein the master base station synchronization reference signal receiving unit (104) receives and outputs the sub-base station synchronization reference signal; the master base station loop processing unit (105) receives the sub-base station synchronization reference signal and receives the master base station synchronization reference signal from the master base station reference signal generating unit (106), and obtains and outputs a first phase difference measurement value and a first frequency difference measurement value between the master base station synchronization reference signal and the sub-base station synchronization reference signal observed by the master base station based on the master base station synchronization reference signal and the sub-base station synchronization reference signal; the master base station reference signal generating unit (106) receives the first phase difference measurement value and the first frequency difference measurement value and broadcasts the first phase difference measurement value and the first frequency difference measurement value through the master base station synchronization reference signal; and The sub-base station time and frequency synchronization unit (202) includes a sub-base station synchronization reference signal receiving unit (201), a sub-base station loop processing unit (204) and a sub-base station reference signal generating unit (205), wherein the sub-base station synchronization reference signal receiving unit (201) receives and outputs the master base station synchronization reference signal; the sub-base station loop processing unit (204) receives the master base station synchronization reference signal and receives the sub-base station synchronization reference signal from the sub-base station reference signal generating unit (205), and obtains the first phase difference measurement value and the first frequency difference measurement value from the master base station synchronization reference signal and obtains the second phase difference measurement value and the second frequency difference measurement value between the sub-base station synchronization reference signal and the master base station synchronization reference signal observed by the sub-base station based on the sub-base station synchronization reference signal and the master base station synchronization reference signal, and further jointly processes the first phase difference measurement value and the first frequency difference measurement value and the second phase difference measurement value and the second frequency difference measurement value to obtain and output the sub-base station clock compensation parameter, so that all master base station synchronization reference signals are synchronized in time and frequency with all sub-base station synchronization reference signals; The main base station signal generation unit (103) further generates and broadcasts a main base station GNSS pseudo-satellite signal based on the main base station synchronization reference signal and the sub-base station synchronization reference signal, and the sub-base station signal generation unit (203) further generates and broadcasts a sub-base station GNSS pseudo-satellite signal based on the sub-base station synchronization reference signal and the main base station synchronization reference signal, thereby generating and broadcasting a main base station GNSS pseudo-satellite signal and a sub-base station GNSS pseudo-satellite signal that are time-frequency synchronized; The main base station loop processing unit (105) further performs joint processing on the first phase difference measurement value and the first frequency difference measurement value, as well as the second phase difference measurement value and the second frequency difference measurement value, in the received sub-base station synchronization reference signal and the main base station synchronization reference signal to obtain and output a first frequency difference estimation value and a first clock difference estimation value at the first frequency point between the main base station synchronization reference signal and the sub-base station synchronization reference signal, the main base station reference signal generation unit (106) receives the first frequency difference estimation value and the first clock difference estimation value and obtains a first compensation value at the second frequency point based on the first frequency difference estimation value and the first clock difference estimation value, and the main base station signal generation unit (103) generates a carrier and a pseudo code of the main base station GNSS pseudo satellite signal based on the first compensation value, thereby generating the main base station GNSS pseudo satellite signal; and The sub-base station loop processing unit (204) further obtains and outputs a second frequency difference estimation value and a second clock difference estimation value at the first frequency point between the sub-base station synchronization reference signal and the master base station synchronization reference signal based on the joint processing of the first phase difference measurement value and the first frequency difference measurement value and the second phase difference measurement value and the second frequency difference measurement value; the sub-base station reference signal generation unit (205) receives the second frequency difference estimation value and the second clock difference estimation value and obtains a second compensation value at the second frequency point based on the second frequency difference estimation value and the second clock difference estimation value; and the sub-base station signal generation unit (203) generates a carrier and a pseudo code of the sub-base station GNSS pseudo-satellite signal based on the second compensation value, thereby generating the sub-base station GNSS pseudo-satellite signal. The master base station signal generating unit (103) further receives the GNSS satellite ephemeris orbit parameters, generates pseudo code phase and carrier phase corrections at the start and end times of the GNSS pseudo satellite signal based on the GNSS satellite ephemeris orbit parameters, and corrects the pseudo code phase and carrier phase of the master base station GNSS pseudo satellite signal using the pseudo code phase and carrier phase corrections at the start and end times so that the pseudo code phase and carrier phase of the master base station GNSS pseudo satellite signal are consistent with the pseudo code phase and carrier phase of the GNSS signal, respectively. The sub-base station signal generating unit (203) further receives the GNSS satellite ephemeris orbit parameters, and generates pseudo-code phase and carrier phase corrections at the start and end times of the GNSS pseudo-satellite signal based on the GNSS satellite ephemeris orbit parameters, and corrects the pseudo-code phase and carrier phase of the sub-base station GNSS pseudo-satellite signal by using the pseudo-code phase and carrier phase corrections at the start and end times so that the pseudo-code phase and carrier phase of the sub-base station GNSS pseudo-satellite signal are consistent with the pseudo-code phase and carrier phase of the GNSS signal, respectively.

2. The GNSS pseudolite system according to claim 1, wherein: The first phase differential measurement value includes a ranging code phase differential measurement value measured by the primary base station and a carrier phase differential measurement value measured by the primary base station; The second phase differential measurement value includes a ranging code phase differential measurement value measured by the sub-base station and a carrier phase differential measurement value measured by the sub-base station.

3. The GNSS pseudo-satellite system according to claim 2, wherein: The ranging code phase differential measurement value measured by the primary base station is obtained by: c·(δt s -δt m )=-(ρ m，s -r m，m )+r-(d s -d m )+σ; The carrier phase differential measurement value measured by the master base station is obtained by: c·(δt s -δt m )=-(L m，s -L m，m )·λ1+r-(d s -d m )+σ; The ranging code phase differential measurement value of the sub-base station is obtained by: c·(δt s -δt m )=-(ρ s，s -r s，m )-r-(d s -d m )+σ; The carrier phase differential measurement value of the sub-base station is obtained by: c·(δt s -δt m )=-(L s，s -L s，m )·λ1-r-(d s -d m )+σ, in, c represents the speed of light, δt s represents the clock difference of the sub-base station, δt m represents the clock difference of the main base station, ρ m，s It represents the pseudo-range observation value of the sub-base station measured by the main base station, ρ m，m represents the pseudorange observation value of the main base station measured by the main base station, ρ s，s represents the pseudorange observation value of the sub-base station measured by the sub-base station, ρ s，m represents the pseudorange observation value of the main base station measured by the sub-base station, r represents the distance between the sub-base station and the main base station, d s Indicates the hardware delay of the sub-base station, d m Indicates the hardware delay of the primary base station. σ represents the measurement noise, L m，s Indicates the carrier observation value of the sub-base station measured by the main base station, L m，m Indicates the carrier observation value of the main base station measured by the main base station, L s，s represents the carrier observation value of the sub-base station measured by the sub-base station, L s，m Indicates the carrier observation value of the main base station measured by the sub-base station, λ1 represents the nominal wavelength of the synchronization reference signal, which corresponds to the nominal frequency of the synchronization reference signal.

4. The GNSS pseudolite system according to claim 3, wherein: The average ranging code phase difference is obtained by: The average carrier phase difference is obtained by: Obtaining a clock deviation of the sub-base station relative to the main base station according to the average ranging code phase difference and the average carrier phase difference; A sub-base station clock compensation parameter is obtained according to the clock deviation of the sub-base station relative to the main base station.

5. The GNSS pseudolite system according to claim 4, wherein: The sub-base station time-frequency synchronization unit (202) obtains the sampling rate correction amount required by the sub-base station signal generation unit (203) by: Get the carrier frequency differential measurement value of the sub-base station Δf1 = f 1，s -f 1，m , where Δf1 represents the frequency difference between the synchronization reference signal of the sub-base station and the main base station measured by the sub-base station, f 1，s represents the sub-base station synchronization reference signal frequency measured by the sub-base station, f 1，m Indicates the master base station synchronization reference signal frequency measured by the sub-base station, The sampling rate correction is calculated based on the carrier frequency differential measurement, and the calculation formula is: fs fix =(f 1，s -f 1，m )*f s / f1, where fs fix is the sampling rate correction, f s is the sampling rate used to generate the signal, and f1 is the nominal frequency of the synchronization reference signal.

6. The GNSS pseudolite system according to claim 5, wherein: The main base station (10) and the sub-base station (20) achieve time-frequency synchronization of the main base station GNSS pseudo-satellite signal and the sub-base station GNSS pseudo-satellite signal according to the following: Based on the frequency difference estimation value of f1, a clock sampling rate compensation estimation value is obtained through frequency domain conversion, and then through frequency domain inverse conversion, a frequency difference compensation value of f2 is obtained; based on the frequency difference compensation value of f2, a main base station signal generation unit (103) and a sub-base station signal generation unit (203) generate an f2 carrier in real time; Based on the clock error estimation value of f1 and the sampling rate compensation estimation value, the pseudo code generator cumulative step value is obtained through a sampling rate compensation algorithm; based on the pseudo code step value, the main base station signal generation unit (103) and the sub-base station signal generation unit (203) generate the GNSS pseudo code and modulation code signal in the time domain in real time; The main base station signal generating unit (103) and the sub-base station signal generating unit (203) modulate the generated f2 carrier and pseudo code and broadcast them.

7. The GNSS pseudolite system according to claim 6, wherein: The main base station (10) and the sub-base station (20) implement orbit compensation of the main base station GNSS pseudo-satellite signal and the sub-base station GNSS pseudo-satellite signal according to the following: Obtaining the equivalent GNSS time of the start moment and the equivalent GNSS time of the end moment of the generation of the GNSS pseudo-satellite signal by the main base station signal generating unit (103) and the sub-base station signal generating unit (203), wherein the equivalent GNSS time of the start moment is obtained by calculating the clock difference, and the equivalent GNSS time of the end moment needs to compensate for the time advance / lag caused by clock drift; Based on the equivalent GNSS time of the start moment and the equivalent GNSS time of the end moment, the atmospheric transmission delay caused by the GNSS signal passing through the ionosphere and troposphere, as well as the signal transmission delay caused by the GNSS satellite clock error and clock drift, are compensated, and the GNSS transmission start time and end time in the GNSS pseudolite signal are calculated; Based on the start time and end time of the GNSS transmission moment, control parameters for generating GNSS pseudo-satellite signals by a main base station signal generating unit (103) and a sub-base station signal generating unit (203) are accurately calculated.

Images