SISO Decoding Algorithm Based Study And Development Of CPM System

Continuous Phase Modulation is a kind of constant-envelope digital modulation schemes with continuous phase which provides good spectral-and-power efficiency, so it is widely used in the field of mobile communications, satellite communications and remote sensing etc. As a way of modulation and coding, CPM can be used as the inner code of the serially concatenated codes to construct Serial Concatenate Continuous Phase Modulation (SCCPM). When decoding with the iterative soft input and soft output algorithm, SCCPM can got BER performance close to Shannon limit.In this paper, CPM system based on SISO algorithm was studied and developed. Firstly, the decomposition model of the CPM and the SISO decoding based on BCJR algorithm was analyzed, and then modules in the receiver of CPM system was designed in detail including frame synchronization, sampling rate conversion and match, and SISO decoding. Continuous short training sequences were selected as the training sequence in the frame synchronization, which not only ensures the synchronization but also reduces the realization complexity. A way of realizing fast sampling rate conversion with matrix calculation combined with matching filter was adopted in order to realize the sampling conversion and matching only with one time vector multiply. Max-Log-MAP algorithm was used to approximate the SISO algorithm, which makes the complex decoding algorithm become operation with simple adding, comparing and selecting. Finally, by analyzing different modules based on FPGA, the receiver of MSK System was realized on the Quartus II platform.