Research On Efficient Encoding And Modulation Technology

Frequency hopping communication system has a strong anti-jamming and anti-interception ability in the complex electromagnetic environment. Moreover, it also has the advantage of good concealment, so it is the focus of the military field. Efficient modulation and coding technology can be utilized in the frequency hopping system. Because of the low radiation power and the narrow spectral density of CPM signal, the advantages of high efficiency and high frequency spectrum utilization, especially the combination of CPM modulation and encoding, can be used in this paper. In the way of encoding and decoding, the Turbo code and LDPC code with near Shannon limit are currently used.Firstly, the working principle and application of Turbo codes and LDPC codes are introduced in detail. For Turbo codes, the method of iterative decoding is proposed, which includes MAP algorithm and Max-Log-MAP algorithm, and the two algorithms are deduced and described in detail. For the MAP algorithm, we can get the addition SISO algorithm for the generalized Turbo codes iterative decoding, and the derivation of the algorithm is given in detail.Secondly, the working principle of CPM system is deeply studied and analyzed, and several kinds of CPM signals are listed. And two kinds of methods for CPM demodulator, the maximum likelihood criterion and Viterbi detection algorithm, are given, respectively. The maximum likelihood sequence estimation based on maximum likelihood criterion is used.Finally, Matlab performance simulation is carried out for the following two algorithms used in the project, and the performance simulation results of different parameters are compared and analyzed. One is MSK modulation combined with Turbo codes of the transmitter, and the receiver uses demodulation decoding of Max-Log-MAP combined with Turbo, which the Turbo decoder is based on the Max-Log-MAP algorithm; the other is that the transmitter uses GMSK modulation combined with LDPC codes, and the receiver uses demodulation decoding of LDPC combined with Max-Log-MAP, which the LDPC decoder is based on the Log-BP algorithm. According to the project requirements, we get the data from FPGA by using a DSP chip whose model is TMS320C6416,and then obtain the results of demodulation and decoding from the the DSP chip. The obtained decoding output results are transmitted to the FPGA. The internal structure and function of the DSP chip in this model are described in detail in this paper. And the development platform of CCS3.3 based on DSP are also presented. This paper still introduces how to write a suitable CMD file, and the method of DSP demodulation and decoding process of FPGA is described in detail.