Research On Multiple Access Interference And Interference Suppression For Non-stationary Communication System

With the rapid development of mobile internet and mobile payment, security of wireless mobile communication attracts more and more attention. As the key access technology of the third generation(3G) mobile communication system, the code division multiple access(CDMA) technology, which is based on the direct spread spectrum method, has some merits of high communication quality, large system capacity, strong anti-interference and security etc. Frequency hopping(FH) is another kind of commonly used spread spectrum communication technology, which transmits signal by hopping its carrier frequency to prevent interception or interference. Although spread spectrum communication has a certain ability to hide signal’s spectrum into noise, its signal, is still a statistical stationary or cyclostationary signal due to its pseudo-random property. This means that the signal of spread spectrum communication system can still be detected by energy detection or spectrum correlation methods, and the communication parameters may be estimated by complex signal processing. Based on novel physical layer signal generation mechanism, a new non-stationary communication system was designed. The stationarity or cyclostationarity of designed signal was eliminated by novel symbol generation, spreading spectrum and modulation methods. With increased physical layer security, non-stationary communication system has a great potential in the highly secure mobile communication domain.Interference is another key problem in mobile communication system. In the CDMA system, the non-ideal orthogonality of pseudo-code may cause multiple access interference(MAI). The existence of MAI has significant effect on the performance and capacity of CDMA system seriously. The designed non-stationary communication system is based on CDMA technology, which means MAI affects it too. Due to parameter randomization, the MAI of non-stationary communication system has features of randomness and time variety, which is much more complicated than traditional CDMA system.This thesis focuses on the implementation of non-stationary communication system and the analysis of its MAI problem. Firstly, this thesis reviews the causes of MAI and multi-user detection technology in traditional CDMA system. Secondly, the generation of non-stationary signal is discussed and its simplified solution based on joint randomization is proposed in consideration of the implementation complexity. Based on the simplified solution, design and implementation of non-stationary communication system was proposed and VHDL implementation had been accomplished and verified on ML-605 FPGA platform. Then, the non-stationary communication system’s multiple access scheme based on CDMA and the features of MAI under this multiple access scheme was analyzed. Since the MAI of non-stationary communication system is too complicated to describe precisely by mathematical model, this thesis focuses on the simulation of the correlation of address code under random parameter, jam probability with different carrier frequency and SIR with different jam bandwidth, and tries to find out the pattern of non-stationary communication system’s MAI. At last, according to the features of MAI, the interference suppression method, including the design of address code and system parameter, was studied.