Research On Acquisition Algorithm Of Weak GPS Signal And Its Realization On Software Receiver Platform

In recent years, with the widely application of satellite navigation technology, high performance navigation receiver is becoming the main research directions. As one of the key technologies of the high performance navigation receiver, acquisition technology of weak navigation signal is the currently research focus. This paper aims at acquisition of the GPS signal under weak signal conditions. From two aspects, theoretical analysis and algorithm realization, the research work is carried out, and some significant achievements are obtained. These research achievements have strong portability, and can be used in other navigation systems after modification.Firstly, the structure and characteristics of GPS L1 signal is analysed and the mathematical model of the simulation signal is given. Acquisition principle of GPS signal is researched as well as two basic acquisition method respectively on time domain and frequency domain. It shows that while the FFT technique is used in acquisition, the speed of correlation operation will be greatly improved and the acquisition time will be reduced. And it makes the preparation for the following research and simulation.Secondly, acquisition techniques of GPS signal under weak signal conditions are researched in this paper. Theoretical and simulation analysis are done for coherent integration method, non-coherent integration method and differential coherent integration method. It illustrates that acquiring weak signal needs to improve the processing gain and accumulation must be carried out. Based on comparison of the three weak signal processing methods, half-bits algorithm, full-bits algorithm and circle algorithm, an improved differential coherent integration algorithm based on optimum path estimation is investigated. It could find the path of maximum sum of differential blocks by estimating every possible combination of product sign of the adjacent navigation data bit. The long time coherent integration can be used in this algorithm, and the loss of sqare is reduced. Simulation results show that the detection performance of this algorithm under weak signal conditions is superior to the traditional algorithm. The computation of the algorithm increases, but it is acceptable because of the optimum path estimation. A new coherent integration idea is also researched by simulation in this paper which could reduce the computation. In this new idea the first step of coherent integration is making accumulation of every 1ms received data, and the second step is making a 1ms integration, which makes a reverse of the common coherent integration.Then, combined acquisition technique of GPS L1 C/A signal and L2C signal is researched. Impact of new civil signal for the weak signal acquisition is analysed. Five combined acquisition algorithms of L1 C/A signal and L2 CM signal are investigated. Simulation results illustrate that the detection performance of the combined acquisition algorithms are better than the legacy non-coherent integration procssing of single channel. And the combined methods show the advantages in weak signal acquisition aspect.Finally, based on existing software receiver platform, the realization flow of non-coherent integration algorithm is designed, and is achieved by C program. The C program is then transplanted into the software receiver platform and positioning test is made. The results show that the new software receiver platform could acquire weak GPS signal at a power of -142dBm. This work has some significance of engineering practice.