Study On Acquisition Algorithm Of BeiDou’s QPSK Signal And BOC Signal

Satellite navigation systems can protect national security, promote social development and brought great convenience to people’s life. With the construction and test run of the Bei Dou satellite navigation system, it will become one of the GNSS system which can be comparable to the GPS system. In the future, the Bei Dou satellite navigation system will provide users with all-day, all-weather, high-precision positioning and timing services. Currently, many agencies are developing high-performance Bei Dou navigation receivers. However, acquisition algorithm is one of the key links in the Bei Dou navigation receiver design. This article will study the acquisition algorithm of Bei Dou receivers. The work I have done is following:1.At first, the signal structure of Bei Dou’s QPSK signal is described. And after that, the IF signal of Bei Dou has been simulated. This paper studies the spectrum and autocorrelation function of Bei Dou’s signal, providing a simulated signal source to the acquisition algorithm’s simulation.2.The next generation of satellite navigation signal systems will use the BOC modulation. BOC signal has different characteristics with traditional BPSK signal. This paper will discuss the principle, the spectrum and the autocorrelation function of BOC, MBOC and Alt BOC signals. Autocorrelation function of the BOC signals has multiple peaks, which bring some new problems. This paper will introduce some BOC signal’s acquisition algorithms, such as double sideband signal acquisition algorithm, SSB acquisition algorithm and BPSK-like acquisition algorithms.3.The acquisition probability and algorithm complexity can be used as a measure of acquisition algorithm‘s performance. In this paper, Bei Dou signal’s acquisition process is modeled, and the expression composed of the false alarm rate, noise power and threshold is derivate. This paper also will analyze the relationship between acquisition probability and the integration time. The basic acquisition algorithm(serial search acquisition algorithms, parallel frequency algorithms and parallel code phase algorithm) will be analyzed and simulated, and Tong algorithms will be introduced.4.In forests, urban canyons and tunnels, the satellite signal is weakened by obstacles,which makes it relies on high-sensitivity acquisition algorithms to acquisition the signal. Extend the integration time is one of the common methods to improve acquisition sensitivity. The impact of extending the integration time is analyzed in the later. This paper introduces differential coherent integration algorithm, semi-bit / full bit algorithm, and the circumferential algorithm based on estimated navigation data bits. Through simulation, under the same conditions, the third one has the highest probability of acquisition, but it needs a large amount of calculation. To simplify the computational complexity, we have 3 ways: the idea of "accumulated first and correlation after", using FFT operations to replace Correlators, and using the parallel program structure. After optimization, the efficiency of this algorithm has been improved.