Performance of turbo coded partial response quaternary CPM over correlated fading channels

Abstract

This paper investigates the performance of a turbo coded system transmitted over correlated flat fading channels using quaternary partial response continuous phase modulation (CPM). The system provides an attractive option for spectral efficient communications systems. We consider both Rayleigh and Rician fading and compare the performances of a maximum a posteriori (MAP) algorithm and a soft output Viterbi algorithm (SOVA). The paper considers the hybrid concatenation of a parallel designed turbo encoder and a partial response quaternary CPM modulator. Based on the decomposition theory of CPM, the quaternary CPM modulator is decomposed into a quaternary ring continuous phase encoder (CPE) and a memoryless modulator (MM). This allows a quaternary convolutional encoder to be combined with the CPE without the need of a mapper. The hybrid design combined with iterative decoding yield very good performances. The results show the considerable superiority of the MAP algorithm to that of the SOVA.