Design of Efficient LDPC Coded Non Recursive CPE Based GMSK System for Space Communications
We consider a low density parity check (LDPC) coded non recursive Gaussian minimum shift keying (GMSK) scheme for space communications subject to low signal to noise ratio (SNR) limited power, and spectrum resources. First, we design a non recursive continuous phase encoder (NRCPE) based GMSK modulator to alleviate the impact of the error propagation existed in a recursive CPE (RCPE) based one. Then, a corresponding pilot aided quasi coherent demodulation algorithm (PA QCDA) is developed for improving the performance of the non coherent demodulation and the impact of the Doppler shift in the coherent demodulation, whose basic principle is that a modified Bahl, Cocke, Jelinek, and Raviv (BCJR) algorithm based detection performs on the received signals with initial and ending trellis states being determined using the very small pilot overhead. Finally, we choose proper modulation parameters for the NRCPE based GMSK signaling according to the tradeoffs between power and spectral efficiency. The simulation results show that the proposed system using the PA QCDA can achieve excellent performance and can also work well in the presence of the large Doppler shifts and some burst errors.
IEEE Access