Navigation signal high-sensitivity lock losing recapturing method

Abstract

The invention relates to the field of satellite navigation, and provides a navigation signal high-sensitivity lock losing recapturing method, which realizes tracking satellite Doppler estimation and reliability estimation by using a normal positioning resolving result, and inputs prior information by using the result as recapturing input prior information. Coherent integration time, FFT calculation points and incoherent integration time in a recapture search process are flexibly configured, and a carrier-to-noise ratio success threshold of recapture search is matched, so that the sensitivity of signal lock loss recapture is remarkably improved, and meanwhile, normal level quick lock loss recapture is considered through a lock loss recapture algorithm based on capture, so that the reliability of signal lock loss recapture is improved. The overall performance of a satellite navigation receiver is improved, the application experience is improved, and the application range is expanded.

Description

Technical Field

[0001] The invention relates to the field of satellite navigation, and in particular to a navigation signal loss-and-recapture method with high sensitivity. Background Art

[0002] The market demand for satellite navigation and location services is growing year by year. In particular, digital application scenarios such as smart wearables, smart transportation, and smart communities are closely related to satellite navigation applications. Satellite navigation applications have entered all aspects of social activities.

[0003] In satellite navigation applications, the receiver's signal level is often reduced due to complex application scenarios including urban buildings, trees, etc. Satellite navigation receivers need to achieve signal tracking in the above scenarios through high-sensitivity tracking. At the same time, bridges, tunnels, electromagnetic interference, etc. will cause signal loss. However, due to the low signal level, the traditional signal recapture algorithm based on signal sliding code cannot achieve low-level signal recapture. Starting the capture module to achieve signal recapture with a high-sensitivity capture algorithm will increase the signal recapture time. These problems will reduce the overall performance of the satellite navigation receiver and reduce the application experience. Therefore, it is necessary to invent a navigation signal high-sensitivity loss and recapture method. Summary of the invention

[0004] The present invention aims to solve the deficiencies of the prior art and provide a navigation signal loss-and-recapture method with high sensitivity, while also taking into account a fast recapture algorithm of a normal level.

[0005] The technical solution adopted by the present invention is:

[0006] A navigation signal high-sensitivity loss-of-lock recapture method comprises the following steps:

[0007] Step 1: The receiver captures, pulls, coarsely tracks and finely tracks the satellite navigation signal, and performs navigation message synchronization, message demodulation, satellite information solution and observation quantity extraction based on the signal tracking result to complete the positioning solution; then, the noise power corresponding to the satellite navigation signal is estimated in real time, the pseudo code phase of the tracking channel at the observation quantity sampling time is latched in real time, the Doppler of the satellite navigation signal received by the receiver is estimated in real time, and the reliability of the satellite Doppler estimation value is evaluated;

[0008] Step 2: During the operation of the receiver, the signal level is detected in real time. If the signal is not lost, step 1 is repeated. If the signal is lost, the receiver enters the signal recapture coarse search state in step 3.

[0009] Step 3, in the signal recapture coarse search state, start the signal loss recapture workflow based on the tracking channel, add the satellite to the list of satellites to be captured and start the loss recapture workflow assisted by the capture module; then execute steps 4 and 9 synchronously;

[0010] Step 4, in the signal loss and recapture based on the tracking channel, configure the loss and recapture control parameters corresponding to the loss and recapture coarse search, including: configuring the coherent integration time, the number of valid input points for FFT calculation, the number of FFT calculation points after zero padding, the number of incoherent accumulations, the recapture search Doppler center, the Doppler search frequency grid range, the number of pseudo-phase searches, the pseudo-code phase search range, the search success carrier-to-noise ratio threshold, the recapture search counter threshold and the search timeout threshold;

[0011] Step 5, adjusting the recapture search Doppler and pseudo code phase according to the set parameters; wherein, starting from the set Doppler and pseudo code phase center, the adjustment is performed once each time this step is performed, and after the set Doppler and pseudo code phase range is searched, the search is restarted from the set center;

[0012] Step 6, accumulate the energy of all correlator results in the tracking channel according to the set recapture parameters, calculate the signal power, and find the maximum signal power, record the correlator position corresponding to the maximum power and the frequency position corresponding to the maximum frequency, and calculate the current signal-to-noise ratio based on the maximum signal power and noise power;

[0013] Step 7, if the recapture signal carrier-to-noise ratio does not exceed the threshold, the recapture search counter is reset to zero, and the process goes to step 5. If the recapture signal carrier-to-noise ratio exceeds the threshold, the recapture search counter is incremented by 1.

[0014] Step 8: If the recapture search counter does not reach the threshold, keep the current search pseudo code phase and Doppler and repeat step 6; if the threshold is exceeded, that is, the signal recapture is successful, then enter the coarse tracking state and jump to step 1; if the recapture timeout is detected, exit the recapture workflow and jump to step 1;

[0015] Step 9: In the lost-lock recapture work based on the capture module, the capture and recapture are executed cyclically according to the list to be captured. After detecting that the current satellite is captured successfully, the recapture carrier phase and pseudo code phase are adjusted according to the capture result, and the tracking channel is transferred to the lost-lock recapture fine search state;

[0016] Step 10: Configure the lock-loss recapture control parameters corresponding to the lock-loss recapture precise search, and jump to step 5.

[0017] Furthermore, in step 1, the Doppler of the satellite navigation signal received by the receiver is estimated in real time, and the reliability of the satellite Doppler estimation is evaluated. The specific process is: based on the positioning solution result, the precise local position is obtained, and the Doppler of the satellite navigation signal is obtained after correcting the satellite clock error, local clock drift, earth rotation effect and relativistic effect errors. At the same time, the reliability of the satellite Doppler estimation is evaluated based on whether the satellite participates in the solution, whether the precise error correction is completed and the time information of participating in the solution. The evaluation results include three levels: reliable, basically reliable and unreliable.

[0018] Furthermore, in step 5, the strategy for adjusting the recapture search Doppler and pseudo-code phase is frequency first and phase later, specifically: configure the initial value of the pseudo-code phase according to the configured signal search Doppler center, and start the signal loss of lock coarse search; for the current pseudo-code phase search value, complete the search of all Doppler frequency grids; adjust the Doppler to the configured search Doppler center, adjust the pseudo-code phase, and search all Doppler frequency grids; after all Doppler frequency grids and pseudo-code phase searches are completed, adjust them to the set carrier and pseudo-code phase center, and repeat the above search process until the signal search is successful or the recapture search times out.

[0019] Furthermore, the specific process of step 9 is: record the capture Doppler and pseudocode phase, calculate the signal pseudocode phase difference based on the pseudocode phase information latched by the observation quantity in step 1 and the capture pseudocode information, use the signal pseudocode phase difference to adjust the local phase pseudocode to the capture result pseudocode phase, adjust the search Doppler center to the capture Doppler result, mark the capture assist as valid, and switch the tracking channel to the lost lock recapture precision search state.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention can significantly improve the sensitivity of signal loss-of-lock recapture by flexibly configuring the coherent integration time, FFT calculation points, and incoherent integration time in the recapture search process, in conjunction with the recapture search carrier-to-noise ratio success threshold. At the same time, the capture-based loss-of-lock recapture algorithm takes into account normal level fast loss-of-lock recapture, thereby improving the overall performance of the satellite navigation receiver, enhancing the application experience, and expanding the scope of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flowchart of the signal unlocking and recapture process of the present invention.

[0023] Figure 2 This is an overall working block diagram of the receiver of the present invention.

[0024] Figure 3 This is a signal working state transfer relationship diagram of the present invention.

[0025] Figure 4 It is a schematic diagram of the search strategy of Doppler and pseudo code phase in the recapture process of the present invention.

[0026] Figure 5 It is a schematic diagram of the signal energy accumulation time during the recapture process of the present invention. DETAILED DESCRIPTION

[0027] Figure 1For the entire workflow of the present invention, the receiver needs to first complete normal signal reception and positioning solution, and after detecting signal loss, realize signal loss and recapture based on the solution of the present application. Steps 4 to 8 realize a high-sensitivity loss and recapture workflow based on the tracking channel, and the synchronized steps 9 to 10 and steps 5 to 8 realize fast signal loss and recapture based on the assistance of the capture module.

[0028] Figure 2 The schematic diagram of the receiver architecture implemented in the present invention includes all the working modules of the normal working process and the recapture working process.

[0029] Figure 3 This is a receiver working state transition relationship diagram involved in the solution of the present invention, wherein channel idle indicates that no signal is currently successfully received, traction, coarse tracking and fine tracking are normal working states of the receiver, and recapture coarse search and recapture fine search are receiver lost lock recapture working states.

[0030] Figure 4 The recapture Doppler and pseudo code phase search method implemented by the solution of the present invention is implemented in a Doppler first and pseudo code second manner, and after all polling is completed, the search is repeated from the set Doppler center and pseudo code center.

[0031] Figure 5 The recapture signal energy accumulation scheme implemented by the present invention adopts coherent integration, FFT calculation and incoherent accumulation to realize high-sensitivity recapture search of signals.

[0032] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments. It should be clear that the embodiments described below are partial embodiments of the present application, rather than all embodiments.

[0033] like Figure 1 As shown, a navigation signal high-sensitivity loss-of-lock recapture method comprises the following steps:

[0034] Step 1: The receiver first realizes normal signal reception. The working principle is as follows: Figure 2 As shown, the working status involves Figure 3 Channel idle, traction, coarse tracking, and fine tracking.

[0035] The receiver must first realize navigation signal capture, signal pulling, signal coarse tracking and signal fine tracking, and based on the signal tracking results, realize navigation message synchronization, message demodulation, satellite information solution and observation quantity extraction, complete real-time positioning solution, and obtain the receiver position, speed and time information;

[0036] During the operation of the receiver, it is necessary to estimate the noise power P of the navigation signal in real time. N, used to calculate the carrier-to-noise ratio of the search signal when losing lock and recapture; latch the local pseudo-code phase information CP of the tracking channel at the moment of observation meas , used to calculate and adjust the local pseudo code phase deviation CP based on the capture result when losing lock and recapture diff .

[0037] During the operation of the receiver, it is necessary to estimate the Doppler of the satellite signal received by the receiver in real time, evaluate the reliability of the satellite Doppler estimation value, and estimate the relative Doppler information between the current satellite and the receiver based on the solution results. In the estimation process, it is necessary to compensate for satellite clock error, local clock drift, earth rotation effect, relativistic effect and other error terms to obtain accurate satellite Doppler information DOP. est , used as a frequency reference when losing lock and recapture; at the same time, the reliability S of the satellite is estimated R , S R A value of 2 indicates that the signal estimation result is reliable, a value of 1 indicates that the estimation is basically reliable, and a value of 0 indicates that it is unreliable;

[0038] The calculation formula is as follows:

[0039]

[0040] In the formula,

[0041] S reliable =S track +S solve

[0042]

[0043] Where S track is based on the signal stable tracking time T lock Calculated, S solve It is based on whether the satellite participates in the solution calculation normally.

[0044] Step 2: Detect the signal level during the receiver operation. If the signal is not lost, repeat step 1. If the signal is lost, enter step 3 signal recapture coarse search state;

[0045] like Figure 3 As shown, the signal loss judgment basis is that the signal carrier-to-noise ratio is lower than the receiver tracking working threshold.

[0046] Step 3: In the signal recapture coarse search state, start the signal loss-of-lock recapture workflow based on the tracking channel, and use the energy accumulation time in the search process to flexibly configure the high-sensitivity loss-of-lock recapture; add the satellite to the list of satellites to be captured to start the loss-of-lock recapture workflow based on the capture module, and realize the rapid loss-of-lock recapture of normal level signals; the signal state transfer relationship is as follows: Figure 3 As shown; then execute step 4 and step 9 synchronously.

[0047] Step 4: Configure the lock-loss recapture control parameters corresponding to the lock-loss recapture coarse search, as follows:

[0048] (1) Configure the energy accumulation time according to the target recapture signal sensitivity. The energy accumulation time consists of three parts: the coherent integration time M, corresponding to the time unit ms; the number of effective input points for FFT calculation K, corresponding to the time unit Mms; the number of FFT calculation points after zero padding K1. To improve the Doppler resolution during the search process, set The number of non-coherent accumulations is N, and the time unit is MKms; the total energy accumulation time is NKMms, and the corresponding single search Doppler range is DOP step , Doppler resolution is: DOP resolution , the calculation formula is as follows:

[0049] DOP step =1000 / N(Hz)

[0050] DOP resolution =1000 / (N·K1)(Hz)

[0051] Taking Beidou B1C as an example, setting N=5, K=4, K1=16, and M=10 can achieve a signal recapture sensitivity of -155dBm, a single search Doppler range of 200Hz, and a Doppler resolution of 12.5Hz.

[0052] (2) Configure the Doppler search center and search range: If the capture result is valid, set the Doppler search center DOP center Configured to capture Doppler DOP acq If the capture result is invalid, configure the Doppler search center DOP when the estimation result is reliable or basically reliable. center The estimated result DOP in step 3 est , when the estimation result is unreliable, configure the Doppler search center DOP center DOP of the first-order filtering result of the current tracking channel loop loop ; Configure Doppler search range to N d , unit: DOP step ;

[0053] Taking Beidou B1C as an example, you can set N d =2.

[0054] (3) Configure the pseudo code phase search center and range. Set the pseudo code search center CP based on the search Doppler. center , set the pseudo code search range N c , unit: CP step , where N corrTo track the number of channel correlators, d is the channel correlator interval; the calculation formula is:

[0055] CP center =DOP center ·R s / f sig

[0056] CP step =N corr ·d

[0057] R s is the pseudo code rate of the signal, f sig is the carrier frequency of the signal;

[0058] Taking Beidou B1C as an example, you can set N c =4,N corr =5, d=0.5.

[0059] (4) Configure the recapture search success carrier-to-noise ratio threshold CN0 according to the target recapture signal sensitivity thd , set the recapture search counter CNT search The success threshold of CNT thd ;

[0060] Taking Beidou B1C as an example, you can set CN0 thd =16dB, the signal recapture sensitivity is -155dBm, set CNT thd =2, that is, when searching for the same pseudo code phase and the same Doppler value, exceeding the carrier-to-noise ratio threshold twice in a row indicates that the recapture search is successful.

[0061] (5) Configure the coarse search timeout threshold T according to the maximum unlocking time of the received signal timeout ;

[0062] Taking Beidou B1C as an example, you can set T timeout = 185s, ensuring that the signal can be recaptured 3 minutes after the signal is lost.

[0063] Step 5, adjusting the recapture search Doppler and pseudo code phase according to the set parameters;

[0064] The adjustment strategy of recapture search Doppler and pseudo code phase is frequency first and then phase, and Doppler search is used to control DOP. cur = 0 and pseudo code search control CP cur = 0 to start recapture search. When the current search needs to be adjusted, follow Figure 4 The adjustment is performed according to the process shown in the figure, where the single Doppler adjustment amount is DOP step , Doppler search range: DOP range , the pseudo code single adjustment amount is CP step, the pseudo code search range is: CP range , the calculation formulas are as follows:

[0065]

[0066] Taking Beidou B1C as an example, combined with the parameters set in step 5, the Doppler single adjustment amount is 200Hz, the Doppler search range is: ±500Hz, the pseudo code single adjustment amount is 2.5chips, and the pseudo code search range is: ±11.25chips.

[0067] Step 6, according to the set coherent integration accumulation time N, FFT calculation effective input points K, FFT calculation points K1 after zero padding, and non-coherent accumulation times M, all correlator results in the tracking channel are accumulated. The accumulation process is as follows: Figure 5 As shown; the energy array P of all correlators and all frequency points is calculated sig [N corr ][K1], find the maximum signal power P sig,max , record the maximum power corresponding to the correlator position N corr,max , the frequency position corresponding to the maximum frequency K1 max , according to the maximum signal power P max and noise power P N Calculate the current signal-to-noise ratio CN0 cur , the calculation formula is as follows:

[0068]

[0069] Step 7: If the carrier-to-noise ratio of the recaptured signal is CN0 cur Does not exceed the recapture carrier-to-noise ratio threshold CN0 thd , then the recapture search counter CNT search Clear to zero and go to step 5, adjust the search Doppler and pseudo code phase and continue searching; carrier-to-noise ratio CN0 cur Whether it exceeds the set recapture carrier-to-noise ratio threshold CN0 thd If the threshold is exceeded, CNT search Add 1 and continue with the next steps.

[0070] Step 8: Determine the current recapture search counter CNT search Whether it exceeds the set threshold CNT thd If the threshold is not reached, the current search pseudo code phase and Doppler are maintained and step 6 is repeated. If the threshold is exceeded, the signal is recaptured successfully, the state is switched to coarse tracking, and the process is skipped to step 1. If a recapture timeout is detected, the recapture workflow is exited and the process is skipped to step 1.

[0071] Step 9: In the recapture work based on the capture module, the capture and recapture are executed according to the list to be captured. After detecting that the satellite is successfully captured, the capture Doppler result DOP is recorded. acq , according to the pseudo code phase information CP latched by the observation in step 1 meas and capture pseudo code information CP acq Calculate the signal pseudo code phase difference CP diff , the corresponding calculation formula is as follows:

[0072] CP diff =CP meas -CP acq

[0073] Adjust the recapture carrier phase and pseudo code phase according to the capture result, and switch the tracking channel to the unlocked recapture precise search state.

[0074] Step 10: Configure the lock-loss recapture control parameters corresponding to the lock-loss recapture precise search, and jump to step 5.

[0075] The calculation method and content of the configured parameters are the same as those in step 4, but the specific values ​​are different, as follows:

[0076] Take Beidou B1C as an example.

[0077] (1) Configure the energy accumulation time according to the target recapture signal sensitivity, set N = 1, K = 1, K1 = 8, M = 10, and the signal recapture sensitivity can be -133dBm, and Doppler search is no longer performed;

[0078] (2) Configure and search range, set N d =2;

[0079] (3) Configure the pseudo code phase search center and range, set N c =1,N corr =5, d=0.5;

[0080] (4) Configure the success threshold and set CN0 thd =30dB, the signal recapture sensitivity is -133dBm, set CNT thd =2, that is, when searching for the same pseudo code phase and the same Doppler value, exceeding the carrier-to-noise ratio threshold twice in a row indicates that the recapture search is successful;

[0081] (5) Configure the recapture timeout and set T timeout =4s.

[0082] A navigation signal high-sensitivity loss-of-lock recapture method in an embodiment of the present invention utilizes normal positioning solution results to realize tracking satellite Doppler estimation and reliability estimation, and uses this as recapture input prior information. By flexibly configuring the coherent integration time, FFT calculation points, and incoherent integration time in the recapture search process, and cooperating with the recapture search carrier-to-noise ratio success threshold, the sensitivity of signal loss-of-lock recapture can be significantly improved. At the same time, the capture-based loss-of-lock recapture algorithm also takes into account the normal level fast loss-of-lock recapture, thereby improving the overall performance of the satellite navigation receiver, enhancing the application experience, and expanding the scope of application. Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present application and are not limiting. Although the present application is described in detail with reference to examples, ordinary technicians in this field should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present application, which should be included in the scope of the claims of the present application.

[0083] Parts not disclosed in the present invention belong to the common knowledge in the art.

Claims

1. A navigation signal high-sensitivity lock-loss recapture method, characterized in that: The following steps are involved: Step 1: The receiver captures, pulls, coarsely tracks and finely tracks the satellite navigation signal, and performs navigation message synchronization, message demodulation, satellite information solution and observation quantity extraction based on the signal tracking result to complete the positioning solution; Then, the noise power corresponding to the satellite navigation signal is estimated in real time, the pseudo code phase of the tracking channel at the observation sampling time is locked in real time, the Doppler of the satellite navigation signal received by the receiver is estimated in real time, and the reliability of the satellite Doppler estimation value is evaluated; Step 2: During the operation of the receiver, the signal level is detected in real time. If the signal is not lost, step 1 is repeated. If the signal is lost, the receiver enters the signal recapture coarse search state in step 3. Step 3: In the signal recapture coarse search state, start the signal loss recapture workflow based on the tracking channel, add the satellite to the list of satellites to be captured and start the loss recapture workflow based on the acquisition module assistance; Then execute steps 4 and 9 synchronously; Step 4, in the signal loss and recapture based on the tracking channel, configure the loss and recapture control parameters corresponding to the loss and recapture coarse search, including: configuring the coherent integration time, the number of valid input points for FFT calculation, the number of FFT calculation points after zero padding, the number of incoherent accumulations, the recapture search Doppler center, the Doppler search frequency grid range, the number of pseudo-phase searches, the pseudo-code phase search range, the search success carrier-to-noise ratio threshold, the recapture search counter threshold and the search timeout threshold; Step 5, adjusting the recapture search Doppler and pseudo code phase according to the set parameters; wherein, starting from the set Doppler and pseudo code phase center, the adjustment is performed once each time this step is performed, and after the set Doppler and pseudo code phase range is searched, the search is restarted from the set center; Step 6, accumulate the energy of all correlator results in the tracking channel according to the set recapture parameters, calculate the signal power, and find the maximum signal power, record the correlator position corresponding to the maximum power and the frequency position corresponding to the maximum frequency, and calculate the current signal-to-noise ratio based on the maximum signal power and noise power; Step 7, if the recapture signal carrier-to-noise ratio does not exceed the threshold, the recapture search counter is reset to zero, and the process goes to step 5. If the recapture signal carrier-to-noise ratio exceeds the threshold, the recapture search counter is incremented by 1. Step 8: If the recapture search counter does not reach the threshold, keep the current search pseudo code phase and Doppler and repeat step 6; if the threshold is exceeded, that is, the signal recapture is successful, then enter the coarse tracking state and jump to step 1; if the recapture timeout is detected, exit the recapture workflow and jump to step 1; Step 9: In the lost-lock recapture work based on the capture module, the capture and recapture are executed cyclically according to the list to be captured. After detecting that the current satellite is captured successfully, the recapture carrier phase and pseudo code phase are adjusted according to the capture result, and the tracking channel is transferred to the lost-lock recapture fine search state; Step 10: Configure the lock-loss recapture control parameters corresponding to the lock-loss recapture fine search, and jump to step 5.

2. A navigation signal high-sensitivity loss-of-lock recapture method according to claim 1, characterized in that: In step 1, the Doppler of the satellite navigation signal received by the receiver is estimated in real time, and the reliability of the satellite Doppler estimation is evaluated. The specific process is: based on the positioning solution result, the precise local position is obtained, and the Doppler of the satellite navigation signal is obtained after correcting the satellite clock error, local clock drift, earth rotation effect and relativistic effect errors. At the same time, the reliability of the satellite Doppler estimation is evaluated based on whether the satellite participates in the solution, whether the precise error correction is completed and the time information of participating in the solution. The evaluation results include three levels: reliable, basically reliable and unreliable.

3. The navigation signal high-sensitivity loss-of-lock recapture method according to claim 1, characterized in that: In step 5, the strategy for adjusting the recapture search Doppler and pseudo-code phase is frequency first and phase later, specifically: configure the initial value of the pseudo-code phase according to the configured signal search Doppler center, and start the signal loss of lock coarse search; for the current pseudo-code phase search value, complete the search of all Doppler frequency grids; adjust the Doppler to the configured search Doppler center, adjust the pseudo-code phase, and search all Doppler frequency grids; after all Doppler frequency grids and pseudo-code phase searches are completed, adjust them to the set carrier and pseudo-code phase center, and repeat the above search process until the signal search is successful or the recapture search times out.

4. A navigation signal high-sensitivity loss-of-lock recapture method according to claim 1, characterized in that: The specific process of step 9 is: record the capture Doppler and pseudo code phase, calculate the signal pseudo code phase difference based on the pseudo code phase information latched by the observation quantity in step 1 and the capture pseudo code information, use the signal pseudo code phase difference to adjust the local phase pseudo code to the capture result pseudo code phase, adjust the search Doppler center to the capture Doppler result, mark the capture assist as valid, and switch the tracking channel to the lost lock recapture precision search state.

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