Research On Acquisition Algorithms For Satellite Navigation Signal Of CPM Modulation

In recent years, with the development of the global satellite navigation technology, the design and implementation of a high-performance software receiver has become the main research direction. As one of the key technologies, the capture technology is a hot spot of research. In order to meet the needs of users, it is required that the GPS receiver should be able to work properly under the strong attenuation environment of multi path effect, multi obstacle occlusion and so on. It is more and more strict to the requirement of receiver sensitivity. In addition, for some special positioning requirements, such as the navigation and positioning of the aircraft, missile trajectory control, GPS receiver should have very high dynamic. So the weak signal detection, fast algorithms for high dynamic signal searching are problems must be solved in signal capture. At present, most of the research of the spread spectrum signal acquisition is based on the BPSK modulation in the domestic. This paper studies weak signal acquisition and high dynamic signal acquisition algorithm for the satellite navigation signal based on the direct sequence spread spectrum of CPM modulation system.First of all, this paper introduces the GPS signal structure and related characteristics of spread spectrum code in GPS signal and SOQPSK modulation mode. We construct the signal capture model of spread spectrum of CPM modulation system.Secondly, the basic principle of GPS signal acquisition is presented in this paper. As the key of capture lies in the estimation of the initial phase of the pseudorandom spread spectrum code and the doppler frequency shift of the carrier wave, we introduce the commonly used acquisition strategy and focus on parallel code phase acquisition of FFT based on frequency domain in this paper. In addition,Matlab simulation of this capture scheme is made. Here we analyzed the factors that affect the acquisition performance of GPS weak signal or high dynamic signal and the key parameters of the process. The factors that affect the acquisition performance of GPS weak signal or high dynamic signal and the setting method of the key parameters in the process of capturing are analyzed.Then, the efficiency of the weak signal acquisition algorithm is improved by using parallel code phase acquisition based on frequency domain of FFT. We studied three weak signalcapture algorithm of coherent accumulation, non-coherent accumulation and simple difference coherent accumulation. The algorithm based on phase compensation and simultaneous data block accumulation, or the algorithm of delayed stacked PMF can implement fast acquisition. The algorithm of delayed stacked PMF can also be applied to the high dynamic signal acquisition.At the same time, we use the rule of binary accumulation in the radar signal detection for reference to solve weak signal acquisition. In order to meet the detection performance of the system, we make correlation decisions for many times to reduce the requirement of detection probability and false alarm rate.All in all, this paper fully studies the GPS signal structure, spread spectrum and CPM modulation, and the basic principle of signal acquisition, and then designs different acquisition algorithms to different environment for capture, and then it can achieve higher acquisition performance with rule of binary accumulation.