Turbo decoding of convolutional codes in differentially modulated OFDM transmission systems

Abstract

Orthogonal frequency division multiplexing (OFDM) is applied in systems which transmit a high data rate over multipath fading channels in order to avoid the effort of a channel estimation and equalization required in a single carrier system. If differential modulation is applied no channel equalization is necessary at all. In this paper, the combination of differential modulation and convolutional channel coding is re-interpreted as a concatenated code in which the differential modulation is the inner code and the convolutional code the outer code. Turbo decoding is applied at the receiver resulting in a signal-to-noise ratio (SNR) gain of more than 3.5 dB compared with classical soft decision Viterbi decoding.