Differential Detection of Serially Concatenated Precoded GMSK with Iterative Decoding

Differential detection for a serially concatenated coding system consists of an outer convolutional encoder, an interleaver and an inner rate-1 precoded Gaussian minimum-shift keying (GMSK) modulation is addressed. Using differential phase detector (DPD) combined with an iterative MAP (maximum a posteriori) decoding scheme is devised to improve the system performance. It is shown that the combination of GMSK modulation and DPD results in a feedforward tapped delay line. Therefore, a rate-1 recursive precoder is employed in front of the GMSK to produce a combined inner MAP decoder with a trellis of four states only. Numerical results show that the proposed scheme outperforms previous work about 2 dB in the AWGN channel and about 9 dB in the flat Rayleigh fading channel at BER is equal to 10^-4 respectively.