Research On Optimum Receiver Of Differential Frequency Hopping Communication System Based On The MAP Detection

Digital communication system receiver is one of the central fields of research on communication theory, and algorithms for signal processing of digital communication are enriched stage by stage along with the development of science and technology. Depending on the sufficient mathematical theory, the MAP algorithm has been focused on all along among the great family of algorithms for communication system. The performance of Turbo codes can be regarded as the most powerful evidence supporting the superiority of MAP algorithm. After the emergence of Turbo codes, researchers in other countries have investigated the application of MAP algorithm to the channel with ISI or DPSK system. Wireless channels with ISI primarily caused by Multipath transmission and limited bandwidth can be classified as channels with memory, and the received signal can accordingly be modeled as the output of a Markov source. In this way, this problem essentially is detection of Markov source, which becomes a great opportunity of the application of MAP algorithm. Having refered lots of relevant data, we found that research in this field is still in its incipience. Considering the above, we choose the application of MAP algorithm to digital communication receiver as the kernel of our research. The other integral part of our research is differential frequency hopping (DFH) communication system. One of the important characteristics of this system is the frequency sequence of the transmitted signals is a Markov stochastic process, which means great improvement in performance can be achieved by applying MAP algorithm to this system. Based on the facts mentioned above, we propose a brand-new design scheme for the receiver of DFH system——DFH optimum receiver based on MAP detection. This is the first time to employ MAP algorithm in this system. The simulation result shows that comparing with the traditional receiver with 64 frequency points the new one can achieve 3dB at least. Moreover, the new receiver can make up for an obvious disadvantage of the traditional one, which suffers performance degradation from the increase in the number of frequency point. In the end, we modified the algorithm without any loss in performance so as to lower the complexity. Through the discussion and result of this thesis, the scheme of the new receiver is practicable, and it is its great theoretical significance that characterizes the research.