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.