A high-sensitivity lock-loss recapturing method for navigation signals

Abstract

The application relates to the field of satellite navigation and provides a high-sensitivity lock-loss recapturing method of a navigation signal. Normal positioning calculation results are used to realize Doppler estimation and reliability estimation of a tracking satellite, and the results are used as prior information of recapturing input. By flexibly configuring coherent integration time, FFT calculation point number and non-coherent integration time in a recapturing search process, and cooperating with a recapturing search carrier-to-noise ratio success threshold, the sensitivity of signal lock-loss recapturing is obviously improved. Meanwhile, the lock-loss recapturing algorithm based on capture considers normal level fast lock-loss recapturing, improves the overall performance of a satellite navigation receiver, improves application experience and expands the application range.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of satellite navigation, in particular to a high-sensitivity lock loss recapture method of navigation signal. BACKGROUND

[0002] The market demand of satellite navigation and location service is growing year by year, especially in smart wear, intelligent transportation, smart community and other digital application scenarios, which are closely related to satellite navigation application. Satellite navigation application has entered all aspects of social activities.

[0003] In satellite navigation application, the receiver often causes the signal level to decrease due to the shielding of complex application scenarios including city buildings, trees, etc. The satellite navigation receiver needs to realize signal tracking in the above-mentioned scenarios through high-sensitivity tracking. At the same time, the signal may be lost due to bridges, tunnels, electromagnetic interference, etc. However, due to the low signal level, the traditional signal recapture algorithm based on signal sliding code cannot realize the recapture of low-level signal, and starting the capture module to capture the signal with high-sensitivity capture algorithm will increase the time consumption of signal recapture. These problems will reduce the overall performance of the satellite navigation receiver and reduce the application experience. Therefore, it is necessary to invent a high-sensitivity lock loss recapture method of navigation signal. SUMMARY

[0004] The present application aims to solve the problems of the prior art and provide a high-sensitivity lock loss recapture method of navigation signal, which also takes into account the fast recapture algorithm of normal level.

[0005] The technical scheme adopted by the present application is as follows:

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

[0007] Step 1, the receiver captures, drags, coarsely tracks and finely tracks the satellite navigation signal, and performs navigation text synchronization, text demodulation, satellite information solution and observation extraction based on the signal tracking result, and completes the positioning solution; then, the noise power corresponding to the satellite navigation signal is estimated in real time, the code phase of the tracking channel at the observation 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, the receiver detects the signal level in real time during the working process, and if the signal is not lost, step 1 is repeated, and if the signal is lost, step 3 signal recapture coarse search state is entered;

[0009] Step 3, in the signal recapture coarse search state, the signal lock loss recapture work flow based on the tracking channel is started, the satellite is added to the list of satellites to be captured, and the lock loss recapture work flow based on the capture module is started. Then, step 4 and step 9 are executed synchronously;

[0010] Step 4, in the signal lock-in loss recapture based on the tracking channel, the corresponding lock-in loss recapture control parameters of the lock-in loss recapture coarse search are configured, including: configuring the coherent integration time length, the FFT calculation effective input point number, the FFT calculation point number after zero padding, the non-coherent accumulation number, the recapture search Doppler center, the Doppler search frequency bin range, the pseudo-phase search number, 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, the recapture search Doppler and pseudo-code phase are adjusted according to the set parameters; wherein, taking the set Doppler and pseudo-code phase center as the starting point, the recapture search Doppler and pseudo-code phase are adjusted once every time this step is executed, and after the set Doppler and pseudo-code phase range is searched, the recapture search Doppler and pseudo-code phase are searched again from the set center.

[0012] Step 6, the energy accumulation is performed on all correlator results in the tracking channel according to the set recapture parameters, the signal power is calculated, and the maximum signal power is found, the correlator position corresponding to the maximum power and the frequency position corresponding to the maximum frequency are recorded, and the current signal carrier-to-noise ratio is calculated according to the maximum signal power and the noise power.

[0013] Step 7, if the recapture signal carrier-to-noise ratio does not exceed the threshold, the recapture search counter is set to zero, and step 5 is entered; if the recapture signal carrier-to-noise ratio exceeds the threshold, the recapture search counter is increased by 1.

[0014] Step 8, if the recapture search counter does not reach the threshold, the current search pseudo-code phase and Doppler are kept, and step 6 is repeated; if the threshold is exceeded, i.e. the signal recapture is successful, the coarse tracking state is entered, and step 1 is jumped to; if the recapture timeout is detected, the recapture workflow is exited, and step 1 is jumped to.

[0015] Step 9, in the lock-in loss recapture work based on the acquisition module, the acquisition recapture is executed in a loop according to the to-be-acquired list, after the acquisition of the current satellite is detected to be successful, the recapture carrier phase and pseudo-code phase are adjusted according to the acquisition result, and the tracking channel is transferred to the lock-in loss recapture fine search state.

[0016] Step 10, the corresponding lock-in loss recapture control parameters of the lock-in loss recapture fine search are configured, and step 5 is jumped to.

[0017] Further, 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 value is evaluated, and the specific process is: the accurate local position is obtained based on the positioning solution result, and the satellite navigation signal Doppler is obtained after the satellite clock error, the local clock drift, the earth rotation effect and the relativistic effect error are corrected, and the reliability of the satellite Doppler estimation value is evaluated according to whether the current satellite participates in the solution, whether the accurate error correction is completed and the time information of participating in the solution, and the evaluation result includes three levels of reliable, basically reliable and unreliable.

[0018] Further, in step 5, the strategy of adjusting the search Doppler and the code phase is first frequency and then phase, specifically: according to the configured signal search Doppler center, the code phase initial value is configured, and the signal lock loss coarse search is started; for the current code phase search value, all Doppler frequency grid searches are completed; the Doppler is adjusted to the configured search Doppler center, the code phase is adjusted, and all Doppler frequency grids are searched; after all Doppler frequency grids and code phase searches are completed, the set carrier and code phase center are adjusted, and the above search process is repeated until the signal search is successful or the recapture search is timed out.

[0019] Further, the specific process of step 9 is: recording the capture Doppler and code phase, calculating the signal code phase difference value according to the code phase information and the capture code information latched in step 1, adjusting the local phase code to the capture result code phase by using the signal code phase difference value, adjusting the search Doppler center to the capture Doppler result, marking the capture auxiliary effective, and switching the tracking channel to the lock loss recapture fine search state.

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

[0021] The present application can significantly improve the sensitivity of signal lock loss recapture by flexibly configuring the coherent integration time, FFT calculation point number, and non-coherent integration time in the recapture search process, and cooperating with the recapture search carrier-to-noise ratio success threshold, and at the same time, the normal level fast lock loss recapture is considered through the lock loss recapture algorithm based on capture, the overall performance of the satellite navigation receiver is improved, the application experience is improved, and the application range is expanded. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The present application is a signal lock loss recapture workflow diagram.

[0023] Figure 2 The present application is a receiver overall working block diagram.

[0024] Figure 3 The present application is a signal working state transition relationship diagram.

[0025] Figure 4 The present application is a search strategy diagram of Doppler and code phase in the recapture process.

[0026] Figure 5 The present application is a signal energy accumulation time diagram in the recapture process. DETAILED DESCRIPTION

[0027] Figure 1For the whole workflow of the application, the receiver and the need to complete the signal normal reception and positioning solution first, after detecting the signal loss, the signal lock recapture is realized based on the scheme of the application, steps 4-8 realize the high sensitivity lock loss recapture workflow based on the tracking channel, and the synchronous steps 9-10 and steps 5-8 realize the fast signal lock loss recapture based on the capture module auxiliary.

[0028] Figure 2 For the receiver architecture realized by the application, all the working modules of the normal workflow and the recapture workflow are included.

[0029] Figure 3 For the receiver state transition relationship involved in the scheme of the application, the channel idle indicates that there is no successfully received signal at present, the traction, coarse tracking and fine tracking are the normal working states of the receiver, and the recapture coarse search and recapture fine search are the lock loss recapture working states of the receiver.

[0030] Figure 4 The recapture Doppler and pseudo code phase search mode realized by the scheme of the application is realized in the order of Doppler and pseudo code, and after all the 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 realized by the scheme of the application realizes high sensitivity recapture search of the signal in the way of coherent integration, FFT calculation and non-coherent accumulation.

[0032] The technical scheme of the application will be described in detail below with reference to the drawings and specific embodiments. It should be clear that the embodiments described below are part of the embodiments of the application, not all of the embodiments.

[0033] As shown in Figure 1 , a high-sensitivity lock loss recapture method for navigation signals includes the following steps:

[0034] Step 1, the receiver first realizes normal reception of the signal, and the working principle is as shown in Figure 2 , the working state involves Figure 3 channel idle, traction, coarse tracking, fine tracking.

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

[0036] During the operation of the receiver, the noise power P N, for calculating the carrier-to-noise ratio of the search signal when performing reacquisition after losing lock; and meas , for calculating and adjusting the local pseudo-code phase offset CP based on the acquisition result when performing reacquisition after losing lock diff .

[0037] During the operation of the receiver, the Doppler of the satellite signal received by the receiver needs to be estimated in real time, and the reliability of the estimated Doppler of the satellite needs to be evaluated. According to the calculation result, the relative Doppler information between the current satellite and the receiver is estimated. In the estimation process, the satellite clock error, the local clock drift, the effect of the earth rotation, the relativistic effect and other error terms need to be compensated to obtain accurate satellite Doppler information DOP est , for serving as a frequency reference when performing reacquisition after losing lock; and R R S = 2 indicates that the signal estimation result is reliable, S = 1 indicates that the estimation is basically reliable, and S = 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] Wherein, S track is calculated based on the stable tracking time T lock of the signal, and S solve is calculated based on whether the current satellite normally participates in the calculation.

[0044] Step 2, detecting the signal level during the operation of the receiver, repeating step 1 if the signal is not lost, and entering step 3 if the signal loses lock.

[0045] As shown in Figure 3 , the signal loss judgment is based on the fact that the carrier-to-noise ratio of the signal is lower than the tracking working threshold of the receiver.

[0046] Step 3, in the signal reacquisition coarse search state, starting the signal loss reacquisition working process based on the tracking channel, using the energy accumulation time in the flexible configuration search process to realize high-sensitivity loss reacquisition; adding the satellite to the list of satellites to be acquired to start the loss reacquisition working process based on the acquisition module, and realizing fast loss reacquisition of the normal level signal; the signal state transition relationship is as shown in Figure 3 ; then steps 4 and 9 are executed synchronously. ​

[0047] Step 4, configure the corresponding lost lock recapture control parameters of the coarse search of lost lock recapture, as follows:

[0048] (1) Configure the energy accumulation time according to the target recapture signal sensitivity, which consists of three parts: coherent integration time M, corresponding to time unit ms; FFT calculation effective input point number K, corresponding to time unit Mms, zero padding FFT calculation point number K1, in order to improve the Doppler resolution in the search process, set Non-coherent accumulation number N, time unit MKms; total energy accumulation time is NKMms, 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, set N = 5, K = 4, K1 = 16, M = 10, which can realize signal recapture sensitivity of-155dBm, single search Doppler range of 200Hz, and Doppler resolution of 12.5Hz.

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

[0053] Taking Beidou B1C as an example, N d may be set to 2.

[0054] (3) Configure the pseudo code phase search center and range, based on the search Doppler, set the pseudo code search center CP center , set the pseudo code search range N c , unit: CP step , wherein N corrTo track the number of channel correlators, where 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 f is the pseudocode rate of the signal. sig The carrier frequency of the signal;

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

[0059] (4) Configure the carrier-to-noise ratio threshold CN0 for successful reacquisition search based on the target reacquisition signal sensitivity. thd Set the recapture search counter CNT search Success threshold CNT thd ;

[0060] Taking Beidou B1C as an example, CN0 can be set. thd =16dB, achieving a signal reacquisition sensitivity of -155dBm, CNT setting thd =2, meaning that when searching for the same pseudocode phase and the same Doppler value, exceeding the carrier-to-noise ratio threshold twice consecutively indicates a successful reacquisition search.

[0061] (5) Configure the coarse search timeout threshold T based on the maximum unlock time of the received signal. timeout ;

[0062] Taking Beidou B1C as an example, T can be set timeout =185s, ensuring that signal recapture can still be achieved 3 minutes after signal loss.

[0063] Step 5: Adjust the reacquisition search Doppler and pseudocode phase according to the set parameters;

[0064] The recapture search Doppler and pseudocode phase adjustment strategy is to adjust the frequency first and then the phase, using Doppler search to control the DOP. cur =0 and pseudocode search control CP cur =0 initiates a recapture search. When the current search needs adjustment, it follows... Figure 4 The process shown is adjusted, where the single Doppler adjustment amount is DOP. step The Doppler search range is: DOP range The pseudocode's single adjustment amount is CP. step, the pseudo code search range is: CP range , the calculation formula is as follows:

[0065]

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

[0067] Step 6, according to the set coherent integration accumulation time N, the effective input point number K of FFT calculation, the zero-filled FFT calculation point number K1, and the incoherent accumulation number M, the energy accumulation of all correlator results in the tracking channel is carried out, and the accumulation process is as shown in Figure 5 ; the energy array P sig [N corr ][K1] of all correlators and all frequency points is calculated, the maximum signal power P sig,max is found, and the correlator position N corr,max corresponding to the maximum power, the frequency position K1 max corresponding to the maximum frequency, the maximum signal power P max and the noise power P N are calculated. cur The calculation formula is as follows:

[0068]

[0069] Step 7, if the recapture signal carrier-to-noise ratio CN0 cur does not exceed the recapture carrier-to-noise ratio threshold CN0 thd , the recapture search counter CNT search is cleared, and step 5 is entered to continue searching after adjusting the search Doppler and pseudo code phase; whether the carrier-to-noise ratio CN0 cur exceeds the set recapture carrier-to-noise ratio threshold CN0 thd , if it exceeds the threshold, CNT search is added by 1, and the subsequent steps are continued to be executed.

[0070] Step 8, judge whether the current recapture search counter CNT search exceeds the set threshold CNT thd , if it does not exceed the threshold, the current search pseudo code phase and Doppler are repeated step 6, if it exceeds the threshold, the signal recapture is successful, and the coarse tracking state is entered, and jumps to step 1; if the recapture timeout is detected, the recapture work flow is exited, and jumps to step 1.

[0071] Step 9: In the reacquisition process based on the acquisition module, perform acquisition and reacquisition cyclically according to the list of satellites to be acquired. After successful acquisition of this satellite, record the acquisition Doppler result (DOP). acq Based on the pseudo-code phase information CP latched by the observation in step 1 meas And capturing pseudocode information CP acq The phase difference CP of the pseudocode signal was calculated. diff The corresponding calculation formula is as follows:

[0072] CP diff =CP meas -CP acq

[0073] Based on the acquisition results, adjust the recapture carrier phase and pseudocode phase, and switch the tracking channel into the lock-out recapture fine search state.

[0074] Step 10: Configure the lock-out recapture control parameters corresponding to the lock-out recapture fine search, then proceed to step 5.

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

[0076] Taking 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 to achieve a signal recapture sensitivity of -133dBm and no longer perform Doppler search.

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

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

[0080] (4) Configure success threshold and set CN0 thd =30dB, achieving a signal reacquisition sensitivity of -133dBm, CNT is set. thd =2, meaning that when searching for the same pseudocode phase and the same Doppler value, exceeding the carrier-to-noise ratio threshold twice consecutively indicates a successful reacquisition search;

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

[0082] The navigation signal high-sensitivity lock loss recapture method of the embodiment of the application uses normal positioning solution results to realize Doppler estimation and reliability estimation of a tracking satellite, and uses the same as prior information for recapture input. By flexibly configuring coherent integration time, FFT calculation point number, non-coherent integration time in the recapture search process, and cooperating with a recapture search carrier-to-noise ratio success threshold, the sensitivity of signal lock loss recapture can be significantly improved. At the same time, the lock loss recapture algorithm based on capture also takes into account normal level fast lock loss recapture, improves the overall performance of a satellite navigation receiver, improves application experience, and expands the application range. Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the application and not to limit the application. Although the application has been described in detail with reference to the examples, it should be understood by those skilled in the art that the technical solutions of the application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the application, and they should be included in the scope of the claims of the application.

[0083] Parts not disclosed in the application belong to the known technology in the art.

Claims

1. A high-sensitivity re-acquisition method for navigation signals after lock-off, characterized in that, Includes the following steps: Step 1: The receiver acquires, pulls, coarsely tracks, and finely tracks the satellite navigation signal, and performs navigation message synchronization, message demodulation, satellite information calculation, and observation extraction based on the signal tracking results to complete the positioning calculation; 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 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 estimate 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, Step 3, signal reacquisition and coarse search state, is entered. Step 3: In the signal recapture coarse search state, start the signal lock-off recapture workflow based on the tracking channel, add the satellite to the list of satellites to be captured, and start the lock-off recapture workflow assisted by the capture module. Then execute steps 4 and 9 simultaneously; Step 4: In the signal lock-out recapture based on the tracking channel, configure the lock-out recapture control parameters corresponding to the coarse search for lock-out recapture, including: configuring the coherent integration duration, the number of valid input points for FFT calculation, the number of FFT calculation points after zero padding, the number of non-coherent accumulations, the Doppler center for recapture search, the Doppler search frequency range, the number of pseudo-phase searches, the pseudo-code phase search range, the carrier-to-noise ratio threshold for successful search, the recapture search counter threshold, and the search timeout threshold; Step 5: Adjust the Doppler and pseudocode phase of the reacquisition search according to the set parameters; wherein, starting from the set center of the Doppler and pseudocode phase, this step is adjusted once for each execution, and after the set range of Doppler and pseudocode phase is completed, 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, 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 carrier-to-noise ratio based on the maximum signal power and noise power. Step 7: If the carrier-to-noise ratio of the recaptured signal does not exceed the threshold, set the recapture search counter to zero and proceed to step 5. If the carrier-to-noise ratio of the recaptured signal exceeds the threshold, increment the recapture search counter by 1. Step 8: If the reacquisition search counter has not reached the threshold, maintain the current search pseudocode phase and Doppler and repeat step 6; if the threshold is exceeded, i.e. the signal reacquisition is successful, switch to coarse tracking state and jump to step 1; if a reacquisition timeout is detected, exit the reacquisition workflow and jump to step 1. Step 9: In the lock-down reacquisition operation based on the acquisition module, the acquisition and reacquisition are performed cyclically according to the list to be acquired. After the satellite is successfully acquired, the reacquisition carrier phase and pseudo-code phase are adjusted according to the acquisition results, and the tracking channel is switched to the lock-down reacquisition fine search state. Step 10: Configure the lock-out recapture control parameters corresponding to the lock-out recapture fine search, then proceed to step 5.

2. The high-sensitivity re-acquisition method for navigation signals 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 estimate is evaluated. The specific process is as follows: the accurate local position is obtained based on the positioning solution result, and the Doppler of the satellite navigation signal is obtained after correcting for errors caused by satellite clock bias, local clock drift, Earth rotation effect and relativistic effect. At the same time, the reliability of the satellite Doppler estimate is evaluated based on whether the satellite participated in the solution, whether the accurate error correction was completed, and the time information of participation in the solution. The evaluation results include three levels: reliable, basically reliable, and unreliable.

3. The high-sensitivity re-acquisition method for navigation signals according to claim 1, characterized in that, In step 5, the strategy for adjusting the reacquisition search Doppler and pseudo-code phase is frequency first, then phase. Specifically: configure the initial value of the pseudo-code phase based on the configured signal search Doppler center, and start the coarse search for signal loss; 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 to the set carrier and pseudo-code phase center, and repeat the above search process until the signal search is successful or the reacquisition search times out.

4. The high-sensitivity re-acquisition method for navigation signals according to claim 1, characterized in that, Step 9 is as follows: Record the captured Doppler and pseudocode phase. Calculate the signal pseudocode phase difference based on the pseudocode phase information latched in Step 1 and the captured pseudocode information. Use the signal pseudocode phase difference to adjust the local phase pseudocode to the captured result pseudocode phase. Adjust the search Doppler center to the captured Doppler result. Mark the capture assist as effective. Switch the tracking channel to the re-capture fine search state after loss of lock.

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