Design of LDPC coded recursive MSK systems

This paper investigates a low-density parity-check (LDPC) coded recursive minimum shift keying (MSK) scheme when the receiver employs iterative decoding and demodulation. Since the recursive continuous phase encoder (RCPE) of MSK can be expressed by a bipartite graph, the overall system can be viewed as a concatenation of two Tanner graphs. By analyzing the error correlation in the MSK demodulator and the overall loop in the joint Tanner graph, we show that the error correlation has a great impact on the performance of the iterative system when the LDPC codes are not well designed and interleavers are not employed. We develop a new design rule of LDPC codes to reduce the impact of the error correlation on the system performance while without interleavers. Simulation results show that the proposed design rule can reduce the impact of the error correlation in a simple and effective way.