The Algorithm Research Of Navigation Satellite Weak Signal Acquisition With Coherent And Differential Coherent Integration

Due to its good practicability, Global Navigation Satellite System (GNNS) is changing the human lifestyle. With the rapid development of Location Based Service (LBS) and other personal positioning service, satellite positioning service has become an indispensable part of our daily life, which requires the GNSS receivers have good performance in the environment where satellite signal is weak. However, ordinary receivers are not able to provide accurately positioning service in such environment. Developing a high sensitivity receiver with high positioning availability and accuracy is particularly important.Signal acquisition is the first step for a receiver to accurately find its position. Hence, in this thesis, we study the algorithms for weak signal acquisition. There are three basic signal acquisition algorithms:coherent integration, differential coherent and non-coherent integration. In order to improve the signal to noise ratio, the coherent integration may be combined with other two, respectively. The coherent integration and differential coherent integration cannot avoid the SNR loss caused by bit transition. Therefore, the impact of data transitions on coherent integration and differential coherent integration is investigated. In addition, considering data length is limited, to maximize the total gain, the impact of bit transition on the optimum combination of coherent and differential coherent integration (the optimum coherence time and accumulation times of differential coherent integration) is studied as well.In this paper, the basic principle of GNSS system is introduced,. Taking the GPS signal model for example, the gain of coherent and differential coherent integration is analyzed, respectively, and the approximate gain in signal-to-noise ratio of coherent integration and differential coherent integration is derived. Then, the impact of bit transition on two types of integration is analyzed. Moreover, the impact of bit transition on coherent integration is tabulated in terms of equivalent coherent integration length and integration loss, and the gain of differential coherent integration with bit transition is derived. The result is compared with the existing theoretical results. Finally, with the constraint of data length, considering bit transition, this thesis analyzes the possibility of the optimum combination of coherent integration and differential coherent integration (in terms of the optimum coherent integration length) and the impact of the input SNR as well as data length on this optimum combination. It is concluded that with different input SNR, selecting appropriate length of data and determining the optimum combination of coherent integration and differential coherent integration will enable the SNR to meet the minimum threshold requirement, and then the performance of the receivers is improved.