Improved Cochannel Interference Cancellation Algorithms For The MFSK/FH-SSMA System

Frequency hopping technology is an effective spread-spectrum technology with distinguished anti-interference and anti-interception capability. Frequency hopping spread spectrum multiple access (FH-SSMA) communication system has been widely studied because of its inherent frequency diversity and resistance to the near-far problem. It has been widely used in both the military and civilian communications. Frequency hopping spread spectrum multiple access (FH-SSMA) communication system is able to enable multiple users share the same frequency resources by designating each user with an user-specific FH code for spread spectrum processing. However, since it is not possible to devise the ideal FH codes with perfect cross correlationcan, there will always exist the cochannel interference (CCI) at the shared temporal-frequency slot. In FH-SSMA communication system, the CCI will be the main reason for the degradation in both the detection reliability and the system capacity. This thesis firstly reviews briefly the application and the development of frequency-hopping communication systems. The characteristics of frequency-hopping communication system, the parameters together with the key technologies of frequency hopping communication system are presented to highlight the background and significance of the work in this thesis.In this thesis, we investigate the cochannel interference cancellation technology for the fast frequency hopping MFSK/FH-SSMA communication system. After a survey and comparision of some of the most known CCI cancellation algorithms for MFSK/FH-SSMA system, such as the MKI algorithm and the iterative interference cancellation (IIC) algorithm, it is shown that the ambiguities detection will be the critical factor which dominates the achieved performance and the realization complexity for different CCI cancellation algorithms. And some effective methods, such as the multiple level temporal-frequency received matrix via a preprocessing step, and the serial detection mechanism for ambiguities resolution one by one, are presented. Based on the analysis, it is shown that both tricks could be utilized to derive the serial IIC (S-IIC) scheme. Simulations are performed to validate that the S-IIC scheme is able to outperform the MKI scheme based on the temporal-frequency received matrix with binary entry. Meanwhile, a sub-group method is proposed for the MKI scheme to reduce the calculation complexity. It is shown that the sub-group based Maximum Likelihood is able to improve the detection complexity significantly with little performance degradation. And the same idea was extended to derive the sub-group based IIC algorithm. Here we consider the temporal-frequency received matrix with multiple level entry. Simulation results are presented to unveil that the proposed sub-group based IIC algorithm can significantly improve the IIC algorithm with some increase in the computation complexity. It is concluded that the sub-group based processing is also an effective scheme for the ambiguities resolution for MFSK/FH-SSMA system.The work in this thesis provides some preliminary but helpful exploration on the improved CCI cancellation in MFSK/FH-SSMA system. The related analysis and method could be used as a reference for the related investigations.