Research On Multiuser Detection Algorithm For Multistage Fast-FH/MFSK System Based On Frequency Hopping Sequence With No-Hit-Zone

Frequency hopping communication is one of the spread spectrum communication technologies, which is a multiple access technology. Frequency hopping coded division multiple access (FH-CDMA) communication can allow multiuser to transfer information in the same bandwidth at the same time. FH-CDMA technology has some important advantages, first, the frequency usage does not have to contiguous, frequency bands interfered by another system can be avoided; second, FH-CDMA systems are less susceptible in general to the near-far problem and do not request power control. So FH-CDMA technology has been widely used in many fields, such as military, commerce and so on. Whereas, as the same as DS-CDMA, FH-CDMA systems have been confronted with multiple access interference (MAI). There are two important methods to overcome interference, one is to design frequency hopping sequence with a hamming correlation as low as possible; the other is to improve the system performance by using the multiuser detection (MUD) technology of eliminate or reduce MAI.The thesis combines both methods to improve the performance of anti-MAI. First of all, a class of FH sequence with no hit in a certain correlation zone (NHZ) is chose, and according to the characteristic of NHZ hopping code, we exploit quasi-synchronous multistage fast FH/multiple level shift keying (FFH/MFSK) system. The active users are divided into a number of groups here, a unique NHZ FH sequence is assigned to each group, and the optimum address codes are assigned to the users in the same group. The MAI among users of different groups can be eliminated as long as their relative delays do not exceed NHZ. Then, to obtain better bit error rate (BER) performance, MUD algorithm is exploited in the receiver, such as a based-MMSE multiple access interference cancellation algorithm of asynchronous fast FH communication system. At last, the multistage iterative interference cancellation (MS-IIC) algorithm is studied.The main studying results of this thesis are provided as follows:First, a class of NHZ FH sequences are introduced and constructed based on finite field GF(p) and GF(p'"). Some properties of NHZ FH sequence are also analyzed.Second, the multistage FFH/MFSK system model based on NHZ frequency sequence is established, including the models of transmitter and receiver. The construction and coding scheme of the optimum address is introduced particularly. Then the MAI among users belonging to the same group is analyzed, and symbol interference formula is derived. Finally, the function models simulation of FFH/MFSK system are carried out on MATLAB simulation platform.Third, a MMSE multiuser detection algorithm of asynchronous FFH/MFSK system is studied deeply, according to the detection performance and complication of the MMSE algorithm, the algorithm is improved. In the AWGN channel and Rayleigh fading channel, the author does a simulation study on these two detectors. Simulation results show that the improved detector improves the integral BER performance of system, even if the signal-to-noise ratio (SNR) is low. The author proves that the improved detector has higher detection efficiency and lower complication by illustration. And the effect of the threshold on system capacity is also studied. Simulation results show that the influence of the threshold on the improved algorithm is small. Otherwise, there exist the parameters combination can obtain the best BER performance.Forth, MS-IIC algorithm is studied and improved. Simulation analysis and illustration comparison show that the improved MS-IIC algorithm has higher detection efficiency, better performance and lower complication.Fifth, the deficiencies of MUD algorithm are pointed out. The improved methods and the vision for the future are given at last.