Design of Optimal LDPC Code for the System of GMSK Concatenated with LDPC Codes
GMSK is continuous-phase signals, which pre-filters incoming data with Gaussion low-band filter. This paper mainly concerns on the continuous phase modulation system of GMSK concatenated with LDPC codes. Decomposing GMSK signal into differential coding and PAM modulating manner, the authors analyze the iterative demodulating and decoding principle and design optimal LDPC codes based on EXIT chart. Simulation result shows that the performance of designed optimal LDPC code is only 0.9dB away from the capacity of the channel when using iterative quasi-coherent demodulation and decoding algorithm.