The Research Of Multi-user Detection In Spread Spectrum Navigation Recievers

The radio navigation system completed the extraction of position data through receiving and detecting the spread spectrum navigation signal. But in the system the working performance of the receiver is badly influenced by the multi-address interference and the sky-wave reflecting interference, so this paper presents a multi-user detection solution to eliminate the impact to the performance of the receiver.In this paper, the working principle of the radio navigation system is discussed firstly, it is detailed introduced of the spread spectrum communication theory, CDMA basic principle. The propagation characteristic of the sky-wave is analyzed. For sky-wave interference, multi-path channel model is established and the multi-user detection solution is proposed.Then for multi-user detection technology, a variety of multi-user detection technology principles are emphasis introduced and analyzed, mostly including the traditional multi-user detection technology, the optimal multi-user detection technology, the linear and nonlinear multi-user detection technology; For three technical standards of multi-users detection different multi-users detection methods are paid attention to the analysis by the comparison of simulations.The structure and simulation of a hybrid interference canceller that combine successive interference canceller (SIC) and parallel interference canceller (PIC) are given by studying and analyzing the interference cancellation method. The results show that hybrid interference canceller is a good method to solve the sky-wave. Then the structure design of the hybrid interference canceller is given in the paper, including the range estimation modules, phase estimation module and interference cancellation module, and the estimated error on the impact of interference cancellation was in the detailed mathematical analysis.Finally the FPGA hardware implementation of the hybrid interference canceller is completed, including the signal rebuilding circuit, interference cancellation circuit, sky-wave interference cancellation circuit of stage 1 and ground-wave parallel interference cancellation of stage 2. The results that have been tested actually in the environment of the laboratory show the interference cancellation module can exactly estimate and rebuild the interference signal to decrease the infection of the strong sky-wave signal, and improve the SNR of the weak signal.