High-speed code GNSS (Global Navigation Satellite System) tracking starting method

Abstract

The invention belongs to the field of GNSS (Global Navigation Satellite System), and particularly relates to a high-speed code GNSS tracking starting method. The method comprises the following steps that: in a high code rate mode, each satellite starts a tracking channel ahead of N half chip time; performing accumulation judgment on the signals of the 2N + 1 half chips after the starting moment to obtain 2N + 1 integral results; wherein within the accumulated judgment time, the loop is in an open-loop state tracking mode; according to 2N + 1 integral results, starting boundary information is adjusted at a time, and satellite signals are tracked; performing algorithm judgment on the 2N + 1 integral results, and if the judgment is passed, determining that the tracking starting is successful; otherwise, tracking starting fails, and waiting for next starting; according to the method, the success rate of high-bit-rate loop tracking starting can be effectively improved, and the precision of the position and speed of the target calculated through subsequent joint calculation is also obviously improved.

Description

Technical Field

[0001] The invention belongs to the field of GNSS, and in particular relates to a high-speed code GNSS tracking start method. Background Art

[0002] With the completion and operation of my country's BeiDou system and the rapid development of other GNSS (global navigation satellite system) systems (US GPS, Russian GLONASS, European Galileo), the availability of the system has greatly increased. Among them, high-speed codes (code rates exceeding 5MHz) account for the majority of full-frequency systems. Since traditional tracking is started after successful capture and then waiting for software response, the longer the processing time, the greater the tracking boundary error obtained, and the duration of each code chip of the high-speed code is very short (1us~2us), the increase in error will significantly reduce the success rate of tracking and locking. Therefore, how to ensure the normal tracking and locking of high-code rate satellites is an important issue that needs to be solved in engineering applications.

[0003] In view of this, the present invention uses multiple real-time tracking channels on the basis of traditional tracking, automatically and continuously starts the same satellite, and then uses signal processing to effectively improve the tracking and locking success rate to solve engineering problems in actual use. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a high-speed code GNSS tracking start method, which includes:

[0005] S1: In high bit rate mode, each satellite starts the tracking channel N half-chip times in advance;

[0006] S2: make cumulative decisions on the signals of 2N+1 half chips after the start time, and obtain 2N+1 integral results; wherein, during the cumulative decision time, the loop is in an open-loop tracking mode;

[0007] S3: adjust the start boundary information at one time according to the 2N+1 integration results to achieve tracking of satellite signals;

[0008] S4: Make an algorithmic decision on the 2N+1 integral results. If the decision is passed, the tracking start is successful; otherwise, the tracking start fails and waits for the next start.

[0009] Preferably, the process of making an accumulation decision on the signal of 2N+1 half chips after the start time includes:

[0010] Set the signal integration time length according to the signal strength;

[0011] The integral accumulation time length is divided into coherent accumulation time and incoherent accumulation time;

[0012] The signal is accumulated and calculated according to the coherent accumulation time and the incoherent accumulation time to obtain 2N+1 integration results.

[0013] Furthermore, the process of setting the integral accumulation time length of the signal according to the signal strength includes: dividing the signal into a strong signal and a weak signal according to the signal-to-noise ratio of the signal; setting the integral accumulation time of the strong signal to 20 milliseconds, and setting the integral accumulation time of the weak signal to 200 milliseconds.

[0014] Furthermore, the process of splitting the integral accumulation time length into coherent accumulation time and incoherent accumulation time includes: the coherent accumulation time of the strong signal and the weak signal is set to 1 millisecond, the incoherent accumulation time of the strong signal is set to 20 milliseconds, and the incoherent accumulation time of the weak signal is set to 200 milliseconds.

[0015] Preferably, the process of adjusting the start boundary information at one time according to 2N+1 integration results includes: obtaining the maximum value position in the 2N+1 integration results, and calculating the delay time according to the maximum value position; selecting the channel corresponding to the maximum value position as the optimal tracking channel, and resetting the remaining channels; sending the delay time to the tracking channel to adjust the start boundary information at one time.

[0016] Preferably, the process of making algorithmic decisions on the 2N+1 integral results includes:

[0017] Select the maximum value of the integral result from 2N+1 integral results;

[0018] Calculate the average value of all integral results whose distance from the maximum integral result position is greater than 3;

[0019] Calculate the ratio of the maximum value to the average value. If the ratio is greater than the preset threshold, the tracking startup is successful; otherwise, the tracking startup fails and waits for the next startup.

[0020] The beneficial effects of the present invention are as follows: the present invention calculates the integral results of multiple time delays in parallel, and the maximum tolerance range is 64 0.5 chips. Compared with the prior art, the present invention expands the error tolerance range, improves the tracking and starting efficiency of high code rate signals, and can effectively improve the starting probability of high code rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of the high-speed code GNSS tracking startup method in the present invention. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] According to calculation and evaluation, for a signal with a code rate of 10MHz, taking the BDS B3 frequency point as an example, a Doppler error of 500Hz after capture and lasting for 124 milliseconds will cause a tracking boundary error of 0.5chip. A larger dynamic range and an increased tracking response time will cause this error to increase sharply, thereby significantly increasing the probability of tracking and locking failure. To this end, the present invention proposes a high-speed code GNSS tracking startup method, such as Figure 1 As shown, the method includes:

[0024] S1: In high bit rate mode, each satellite starts the tracking channel N half-chip times in advance.

[0025] In high bit rate mode, each satellite starts the tracking channel N half-chip times before the millisecond boundary point where the traditional tracking method needs to start the tracking channel.

[0026] S2: Make an accumulation decision on the signal of 2N+1 half code chips after the start time to obtain 2N+1 integration results; wherein, during the accumulation decision time, the loop is in the open-loop state tracking mode.

[0027] The baseband hardware logic starts the calculation engine shared by all the tracking channels for the high bit rate start-up. The calculation engine supports parallel calculation of 64 channels that need to be judged in total; the calculation engine makes cumulative judgments on the signals of 2N+1 half-code chips after the start-up time. Specifically:

[0028] The integral accumulation time length of the signal, i.e., the accumulation decision time, is set according to the signal strength. If the signal strength is strong, the integral accumulation time length is set short; if the signal strength is weak, the integral accumulation time length is set long. Preferably, the integral accumulation time length of the signal with strong signal strength can be set to 20 milliseconds, and the integral accumulation time length of the signal with weak signal strength can be set to 200 milliseconds. The strength of the signal is determined by the signal-to-noise ratio obtained when the signal is captured.

[0029] The integral accumulation time length is divided into coherent accumulation time and incoherent accumulation time; preferably, the coherent accumulation time of the strong signal and the weak signal is set to 1 millisecond, the incoherent accumulation time of the strong signal is set to 20 milliseconds, and the incoherent accumulation time of the weak signal is set to 200 milliseconds.

[0030] The signal is accumulated and calculated according to the coherent accumulation time and the incoherent accumulation time to obtain 2N+1 integration results.

[0031] During the cumulative decision time, the loop does not make adjustments and is in open-loop tracking mode.

[0032] S3: Adjust the start boundary information at one time according to the 2N+1 integration results to achieve tracking of satellite signals.

[0033] The process of adjusting the startup boundary information includes: obtaining the maximum value position among 2N+1 integral results, calculating the delay time according to the maximum value position, for example, the Kth maximum, then the corresponding delay time is (-N+(K-1) / 2)*chip; selecting the channel corresponding to the maximum value position as the optimal tracking channel, and resetting the remaining channels; sending the delay time to the tracking channel to adjust the startup boundary information once, and starting loop tracking according to the startup boundary information.

[0034] S4: Make an algorithmic judgment on the 2N+1 integral results. If the judgment is passed, the tracking start is successful. Otherwise, the tracking start fails and waits for the next start.

[0035] Select the maximum value of the integral result from 2N+1 integral results.

[0036] Calculate the average value of all integration results whose distance from the maximum value position of the integration result is greater than 3. For example, the maximum value position of the integration result is the Kth one, and the spacing between each result in the 2N+1 results is 0.5 chip. The integration results whose distance from the maximum value position of the integration result is greater than 3, that is, the integration results whose distance from the maximum value position of the integration result is greater than 1.5 chips, add the integration results before the k-3 position and the integration results after the K+3 position (a total of 2N+1-7=2N-6) and then average them to get the average value.

[0037] Set the preset threshold, calculate the ratio of the maximum value to the average value, if the ratio is greater than the preset threshold, the tracking start is judged to be successful, otherwise the tracking start fails, the current start tracking is considered invalid, the channel is reset, and wait for the next start. Threshold judgment can solve the problem of the current start signal being too weak or the captured information being false information, and reduce the probability of incorrect start tracking.

[0038] By executing the above-mentioned tracking start steps, the present invention can effectively improve the success rate of high-code rate loop tracking start, and the accuracy of the position and speed of the target subsequently jointly calculated is also significantly improved.

[0039] The above embodiments further illustrate the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above embodiments are only preferred implementation modes of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-speed code GNSS tracking startup method, characterized in that: include: S1: In high bit rate mode, each satellite starts the tracking channel N half-chip times in advance; S2: make an accumulation decision on the signal of 2N+1 half chips after the start time, and obtain 2N+1 integration results; wherein, during the accumulation decision time, the loop is in the open-loop state tracking mode; S3: adjust the start boundary information at one time according to the 2N+1 integration results to achieve tracking of satellite signals; S4: Make an algorithmic decision on the 2N+1 integral results. If the decision is passed, the tracking start is successful; otherwise, the tracking start fails and waits for the next start.

2. A high-speed code GNSS tracking start method according to claim 1, characterized in that: The process of making an accumulation decision on the signal of 2N+1 half chips after the start time includes: Set the signal integration time length according to the signal strength; The integral accumulation time length is divided into coherent accumulation time and incoherent accumulation time; The signal is accumulated and calculated according to the coherent accumulation time and the incoherent accumulation time to obtain 2N+1 integration results.

3. A high-speed code GNSS tracking start method according to claim 2, characterized in that: The process of setting the integral accumulation time length of the signal according to the signal strength includes: dividing the signal into a strong signal and a weak signal according to the signal-to-noise ratio of the signal; setting the integral accumulation time of the strong signal to 20 milliseconds, and setting the integral accumulation time of the weak signal to 200 milliseconds.

4. A high-speed code GNSS tracking start method according to claim 2, characterized in that: The process of splitting the integral accumulation time length into coherent accumulation time and incoherent accumulation time includes: setting the coherent accumulation time of strong signals and weak signals to 1 millisecond, setting the incoherent accumulation time of strong signals to 20 milliseconds, and setting the incoherent accumulation time of weak signals to 200 milliseconds.

5. A high-speed code GNSS tracking start method according to claim 1, characterized in that: The process of adjusting the startup boundary information at one time according to 2N+1 integration results includes: obtaining the maximum value position in the 2N+1 integration results, and calculating the delay time according to the maximum value position; selecting the channel corresponding to the maximum value position as the optimal tracking channel, and resetting the remaining channels; sending the delay time to the tracking channel to adjust the startup boundary information at one time.

6. A high-speed code GNSS tracking start method according to claim 1, characterized in that: The process of making algorithmic decisions on the 2N+1 integral results includes: Select the maximum value of the integral result from 2N+1 integral results; Calculate the average value of all integral results whose distance from the maximum integral result position is greater than 3; Calculate the ratio of the maximum value to the average value. If the ratio is greater than the preset threshold, the tracking startup is successful; otherwise, the tracking startup fails and waits for the next startup.

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