A capture-to-tracking control method for weak satellite navigation signals

Abstract

The present invention relates to a capture-to-tracking control method applicable to weak satellite navigation signals. After each successful capture and before switching to closed-loop tracking, the following steps are executed: S1. Perform short-time coherent integration with an integration duration of T / 2 and store the short-time coherent integration result, where T is the pseudo-code period of the satellite navigation signal; S2. Perform cross-product and dot-product operations to obtain the cross-product C for a single pseudo-code period and the dot-product D for a single pseudo-code period; S3. Perform non-coherent accumulation on the cross-product C for a single pseudo-code period and the dot-product D for a single pseudo-code period to obtain the cross-product non-coherent accumulation value and the dot-product non-coherent accumulation value; S4. Calculate the frequency discrimination error Δf k ; S6. Use the estimated frequency difference Δf k to correct the Doppler value of the satellite signal provided in the capture stage, obtain the initial carrier offset value for closed-loop tracking, and configure the local carrier frequency of the tracking channel accordingly; S7. Configure the tracking channel to output the coherent integration result once per pseudo-code period, end the above capture-to-tracking open-loop estimation control process, and start the closed-loop tracking process.

Description

Technical Field

[0001] The invention belongs to the technical field of satellite navigation and relates to a weak signal capture and tracking control method. Background Art

[0002] In satellite navigation receiver processing, the accuracy of the capture frequency is limited by factors such as the sweep step selection of the capture algorithm or the selection of the coherent integration length, which sometimes leads to a large residual frequency deviation after capture. If the residual frequency deviation from capture to tracking is too large and exceeds the traction range of the receiver tracking loop, the tracking loop of the receiver will not work properly, resulting in problems such as loss of capture to tracking lock or false lock, affecting the performance of the receiver. In addition, the use of frequency-expanded short coherent integration tracking will cause large frequency and phase errors of the receiver in a weak signal environment due to the short coherence time, resulting in problems such as instability of the initial tracking loop and a long convergence time. Therefore, to solve the above problems, a capture-to-tracking control method suitable for strong and weak signals is needed. Summary of the invention

[0003] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art, to overcome the shortcomings of the prior art, to provide a capture-to-tracking control method suitable for weak signals, to improve the capture-to-tracking frequency estimation accuracy under weak signals, to increase the capture-to-tracking success probability, and to accelerate the convergence speed of the carrier tracking loop.

[0004] The technical solution of this method is: a capture-to-tracking control method applicable to weak satellite navigation signals, characterized in that the following steps are performed before switching to closed-loop tracking after each successful capture:

[0005] S1. Configure the correlator of the tracking channel to use the local pseudo code instantaneous path to perform short-time coherent integration of the external input satellite navigation baseband signal with an integration time of T / 2 and store the short-time coherent integration result, where T is the pseudo code period of the satellite navigation signal;

[0006] S2, performing cross product and dot product operations on the in-phase short-time coherent integration value result ip_pre and the orthogonal short-time coherent integration value result qp_pre of the first half of each pseudo code cycle and the in-phase short-time coherent integration value result ip and the orthogonal short-time coherent integration value result qp of the second half of each pseudo code cycle to obtain a single pseudo code cycle cross product C and a single pseudo code cycle dot product D;

[0007] S3, performing incoherent accumulation on a single pseudocode period cross product C and a single pseudocode period dot product D to obtain a cross product incoherent accumulation value and a dot product incoherent accumulation value;

[0008] S4. Calculate the frequency discrimination error Δf based on the cross product incoherent accumulation value and the dot product incoherent accumulation value k ;

[0009] S6, using the estimated frequency difference Δf k Correct the satellite signal Doppler value provided in the acquisition phase to obtain the initial carrier offset value for closed-loop tracking, and configure the local carrier frequency of the tracking channel accordingly;

[0010] S7, configuring the tracking channel to output a coherent integration result once in each pseudo code period, ending the above capture-to-tracking open-loop estimation control process, and starting a closed-loop tracking process.

[0011] Preferably, the calculation formula of the cross product C of the single pseudo code period is:

[0012] C = qp×ip_pre-ip×qp_pre.

[0013] Preferably, the calculation formula of the dot product D of the single pseudo code period is:

[0014] D = ip × ip_pre + qp × qp_pre.

[0015] Preferably, the calculation formula of the cross product incoherent accumulation value Y is as follows:

[0016]

[0017] Wherein, N is the number of incoherent accumulations.

[0018] Preferably, the calculation formula of the dot product incoherent accumulation value X is:

[0019]

[0020] Wherein, N is the number of incoherent accumulations.

[0021] Preferably, the frequency discrimination error Δf k The calculation formula is as follows:

[0022]

[0023] Preferably, the correction method of step S6 is:

[0024] Δf=Δf Acqu +Δf k

[0025] Where Δf Acqu The navigation satellite acquisition Doppler value provided to the acquisition module.

[0026] The value range of the non-coherent accumulation times N in step S3 is 10-20.

[0027] The advantages of the present invention compared with the prior art are:

[0028] (1) The present invention adopts a software processing method to achieve the goal of greatly improving the frequency accuracy of the capture-to-tracking process without increasing the existing capture resources, improving the accuracy of frequency estimation in a weak signal environment, and taking a shorter time, which will not affect the subsequent normal closed-loop tracking. The robustness of the loop capture and tracking is improved, and the continuity, effectiveness and reliability of the receiver operation are ensured;

[0029] (2) The method of the present invention has simple steps and procedures, takes a short time, and will not affect the subsequent normal closed-loop tracking.

[0030] (3) The method provided by the present invention can estimate the frequency error of ±500Hz of signals above -138dBm, improve the frequency estimation accuracy of capture-to-tracking under weak signals, increase the probability of successful capture-to-tracking, and accelerate the convergence speed of the carrier tracking loop. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a flowchart of a capture-to-tracking control method applicable to weak signals according to an embodiment of the present invention.

[0032] Figure 2 It is a principle diagram of a frequency estimator based on dot cross product incoherent accumulation according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention is described in detail below with reference to the accompanying drawings.

[0034] In order to solve the problem that the capture accuracy does not meet the tracking requirements under weak signals, an open-loop frequency estimation module combining short-time coherence and multiple incoherent accumulations is added before the closed-loop tracking of the loop. The capture frequency error can be estimated in a shorter time, and the tracking loop can be compensated before switching to normal closed-loop tracking control.

[0035] The present invention provides a capture-to-tracking control method applicable to satellite navigation weak signals. The method performs the following steps before switching to closed-loop tracking after each successful capture:

[0036] S1. Configure the correlator of the tracking channel to use the local pseudo code instantaneous path to perform short-time coherent integration of the external input satellite navigation baseband signal with an integration time of T / 2 and store the short-time coherent integration result, where T is the pseudo code period of the satellite navigation signal;

[0037] S2, performing cross product and dot product operations on the in-phase short-time coherent integration value result ip_pre and the orthogonal short-time coherent integration value result qp_pre of the first half of each pseudo code cycle and the in-phase short-time coherent integration value result ip and the orthogonal short-time coherent integration value result qp of the second half of each pseudo code cycle to obtain a single pseudo code cycle cross product C and a single pseudo code cycle dot product D;

[0038] The calculation formula of the cross product C of the single pseudo code period is:

[0039] C = qp×ip_pre-ip×qp_pre.

[0040] The calculation formula of the dot product D of the single pseudo code period is:

[0041] D = ip × ip_pre + qp × qp_pre.

[0042] S3, performing incoherent accumulation on a single pseudocode period cross product C and a single pseudocode period dot product D to obtain a cross product incoherent accumulation value and a dot product incoherent accumulation value;

[0043] The calculation formula of the cross product incoherent accumulation value Y is as follows:

[0044]

[0045] Wherein, N is the number of incoherent accumulations.

[0046] The calculation formula of the dot product incoherent accumulation value X is:

[0047]

[0048] Wherein, N is the number of incoherent accumulations.

[0049] S4. Calculate the frequency discrimination error Δf based on the cross product incoherent accumulation value and the dot product incoherent accumulation value k ;

[0050] The frequency discrimination error Δf k The calculation formula is as follows:

[0051]

[0052] S6, using the estimated frequency difference Δf k Correct the satellite signal Doppler value provided in the acquisition phase to obtain the initial carrier offset value for closed-loop tracking, and configure the local carrier frequency of the tracking channel accordingly;

[0053] S7, configuring the tracking channel to output a coherent integration result once in each pseudo code period, ending the above capture-to-tracking open-loop estimation control process, and starting a closed-loop tracking process.

[0054] The correction method of step S6 is:

[0055] Δf=Δf Acqu +Δf k

[0056] Where Δf Acqu The navigation satellite acquisition Doppler value provided to the acquisition module.

[0057] The non-coherent accumulation number N is related to the sensitivity of the signal to be received. Generally, N=20, which can adapt to signal tracking above -140dBm.

[0058] Example:

[0059] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0060] like Figure 1 As shown in the figure, it is a flow chart of the capture-to-tracking control method for weak signals implemented by the present invention. It is necessary to call Figure 1 The specific steps are described as follows:

[0061] S1. After successful capture, the tracking channel is turned on and configured to output the coherent integration result once every 0.5 milliseconds.

[0062] S2, read the instantaneous path coherent integration value of the in-phase path ip and the quadrature path qp in 0.5 milliseconds;

[0063] S3, read the 0.5 millisecond count mark, the first 0.5 millisecond count mark within 1 millisecond is 1, and the last 0.5 millisecond count mark is 0;

[0064] S4, when the 0.5 millisecond count mark is 1, store the current integration result and record it as ip_pre and qp_pre, record the information and return to step S2, and wait for the next integration result. When the 0.5 millisecond count mark is 0, store the current integration result and record it as ip and qp, and go to step S5;

[0065] S5. Calculate using stored ip_pre, qp_pre, ip, qp:

[0066] 1 ms cross product: C = qp × ip_pre - ip × qp_pre;

[0067] 1 millisecond dot product: D = ip × ip_pre + qp × qp_pre;

[0068] S6. Perform non-coherent accumulation of the 1 millisecond cross product C and the dot product D, with the number of accumulations being 20 and the time consuming being 20 milliseconds. Obtain:

[0069] 20 times cross product incoherent accumulation value:

[0070] 20 times of incoherent accumulation of dot products:

[0071] S7. Calculate the frequency discrimination error using 20 times of dot cross product incoherent accumulation value:

[0072] Where T = 0.5 milliseconds;

[0073] S8. Obtain Δf k is the estimated value of the residual frequency offset after capture. k The initial carrier offset of closed-loop tracking is corrected to: Δf = Δf Acqu +Δf k ; where Δf Acqu The acquisition Doppler value provided to the acquisition module.

[0074] S9. After completing the above correction, the tracking channel is configured to output a coherent integration result every 1 millisecond, ending the above capture-to-tracking open-loop estimation control process and entering a normal closed-loop tracking process.

[0075] Steps (5) to (7) are Figure 2 Specific implementation steps of the dot cross product incoherent frequency estimator schematic diagram, where DT = 1 millisecond, N = 20 times.

[0076] In summary, this embodiment uses the correlator, i.e., the coherent output of 0.5 milliseconds before and after the time path, to perform dot product and cross product operations, and then performs 20 incoherent accumulations of the dot product and cross product of 1 millisecond to perform frequency discrimination calculation. The above method can estimate the frequency error of ±500Hz of the signal above -138dBm, improve the frequency estimation accuracy of capture-to-tracking under weak signals, increase the probability of successful capture-to-tracking, and accelerate the convergence speed of the carrier tracking loop.

[0077] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A capture-to-tracking control method for weak satellite navigation signals, characterized in that After each successful capture, before switching to closed-loop tracking, perform the following steps: S1. The correlator of the tracking channel is configured to use the local pseudo code instantaneous path to perform short-time coherent integration of the external input satellite navigation baseband signal with an integration time of T / 2 and store the short-time coherent integration result, where T is the pseudo code period of the satellite navigation signal; S2, performing cross product and dot product operations on the in-phase short-time coherent integration value result ip_pre and the orthogonal short-time coherent integration value result qp_pre of the first half of each pseudo code cycle and the in-phase short-time coherent integration value result ip and the orthogonal short-time coherent integration value result qp of the second half of each pseudo code cycle to obtain a single pseudo code cycle cross product C and a single pseudo code cycle dot product D; S3, performing incoherent accumulation on a single pseudocode period cross product C and a single pseudocode period dot product D to obtain a cross product incoherent accumulation value and a dot product incoherent accumulation value; S4. Calculate the frequency discrimination error Δf based on the cross product incoherent accumulation value and the dot product incoherent accumulation value k ; S6, using the estimated frequency difference Δf k Correct the satellite signal Doppler value provided in the acquisition phase to obtain the initial carrier offset value for closed-loop tracking, and configure the local carrier frequency of the tracking channel accordingly; S7, configuring the tracking channel to output a coherent integration result once in each pseudo code period, ending the above capture-to-tracking open-loop estimation control process, and starting a closed-loop tracking process.

2. A capture-to-tracking control method suitable for weak signals according to claim 1, characterized in that The calculation formula of the cross product C of the single pseudo code period is: C = qp×ip_pre-ip×qp_pre.

3. A capture-to-tracking control method suitable for weak signals according to claim 1, characterized in that The calculation formula of the dot product D of the single pseudo code period is: D = ip × ip_pre + qp × qp_pre.

4. A capture-to-tracking control method suitable for weak signals according to claim 1, characterized in that The calculation formula of the cross product incoherent accumulation value Y is as follows: Wherein, N is the number of incoherent accumulations.

5. The capture-to-tracking control method for weak signals according to claim 1, characterized in that The calculation formula of the dot product incoherent accumulation value X is: Wherein, N is the number of incoherent accumulations.

6. The capture-to-tracking control method for weak signals according to claim 1, characterized in that The frequency discrimination error Δf k The calculation formula is as follows:

7. The capture-to-tracking control method for weak signals according to claim 1, characterized in that The correction method of step S6 is: Δf=Δf Acqu +Δf k Where Δf Acqu The navigation satellite acquisition Doppler value provided to the acquisition module.

8. The capture-to-tracking control method for weak signals according to claim 1, characterized in that The value range of the non-coherent accumulation times N in step S3 is 10-20.

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