Research On Fast Acquisiton Technoligies Of Low SNR Rdss Inbound Signals

Radio Determination Satellite Service (RDSS) is a positioning system based on spreadspectrum modulation, which can simultaneously provide navigation, communications andother services to mobile users. RDSS is integrated in Beidou satellite navigation system,and it is a civil or military application. Because the users of RDSS transmit inbound signalsin short frame burst-mode, the time of communication is so short that signalsynchronization and demodulation are difficult. The key to solve this problem lies in theperiod of acquisition, as a consequence, research of RDSS inbound signals’ fast acquisitionmethod, especially capturing signals with low signal to noise ratio (SNR) is important toour development of navigation.This paper mainly focus on fast acquisition methods of RDSS inbound signals withlow SNR. Combined with the principle of pseudo-code spread spectrum signal acquissition,a method of capturing RDSS inbound signals quickly at low carrier to noise ratio conditionsis designed and implemented.Firstly, this paper introduces the basic principles of RDSS systems and pseudo-codespread spectrum system. And the spread spectrum signal acquisition technologies aredetailed, including the two-dimensional search at time and frequency, the integrationmethods, detection and decision strategies, serial and parallel capture methods. In addition,combined with RDSS inbound signal frame format and fast acquisition technique data, thepaper presents a two-dimensional parallel acquisition algorithm based FFT that can makelow SNR signal get a higher coherent integration gain in short time and complete the rapidacquisition of RDSS inbound signal in20milliseconds. Secondly, the performance of thealgorithm is analysised by mathematical derivation, and the appropriate data preprocessingmethod, detection and decision strategies are selected by considering the simulation results.Finally, the implementation of algorithm on FPGA is proposed. The algorithm has beentested on FPGA platform, the test result shows that the algorithm can be implementedeffectively, and it has a good acquisition result. The performance of capture module couldachieve the desired targets.