Method for capturing weak signals of Big Dipper D1 satellite navigation system

Abstract

The invention discloses a method for capturing weak signals of a Big Dipper D1 satellite navigation system. The method comprises the steps of: a. estimating a signal-to-noise ratio of a signal; b. utilizing the signal-to-noise ratio to set a signal detection threshold value and judging the weakness; c. selecting an NH secondary coding sequence and carrying out two-dimensional capturing processing of a CA code phase and a Doppler frequency; d. utilizing lms coherent integration and collecting twenty integration results; e. selecting a first type of the NH secondary coding sequence and gradually multiplying with the twenty integration results; f. carrying out non-coherent integration and storing the result; g. repeating the steps c-d until the twenty types of NH secondary codes are traversed; h. selecting the maximum value of the twenty types of integration and comparing the maximum value with a set signal detection threshold value to obtain whether a positioning satellite signal exists in a received signal or not; i. if so, positioning; when the signal is not found, replacing Doppler frequency sections until all the Doppler frequency sections are traversed; and j. replacing a satellite and repeating the steps c-i. According to the method disclosed by the invention, the NH secondary codes can be stripped to obtain a high-integration gain, so that the weak signals of the Big Dipper D1 satellite navigation system are captured.

Description

technical field [0001] The invention relates to a method for capturing a weak signal of a D1 message in a Beidou satellite navigation system, in particular to a method for capturing a weak signal of a Beidou D1 satellite navigation system. Background technique [0002] Spread spectrum communication technology is widely used in modern communication systems, especially in the field of satellite navigation. The Beidou satellite navigation system independently developed by China (hereinafter referred to as Beidou) has a signal system similar to the GPS system of the United States and the Galileo system of the European Union. For the Beidou system, in occasions with high signal-to-noise ratio (such as outdoor open environments), it is relatively easy to capture successful satellite signals and obtain information such as code phase and carrier frequency. However, in places with weak signals, such as indoors and urban streets under dense tree shade, the carrier-to-noise ratio of s...

AI Technical Summary

Problems solved by technology

[0012] 1) For coherent integration: Due to the influence of crystal oscillator stability, satellite signal frequency and receiver recurrence frequency mismatch, the coherent integration time is not easy to be too long. The most important thing is that in the Beidou D1 message, due to the NH secondary code In the existence of the signal, the NH secondary coding symbols modulated on the current millisecond signal and the next millisecond signal may be reversed, which makes the traditional method of lengthening the coherent integration time invalid;

[0013] 2) The non-coherent integration method takes the absolute value of the correlation results every 1ms before summing, which can alleviate the problem caused by the change of data bits, but, with the reduction of signal-to-noise ratio, it will cause excessive square loss

[0015] However, the above two methods 2) and 3) are to avoid the loss of signal-to-noise ratio caused by data bit jumps during the integration period. Although they have achieved certain results, they are still smaller than the coherent integration signal-to-noise ratio.

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