OFDM systems with differential modulation schemes and turbo decoding techniques

Orthogonal frequency division multiplexing (OFDM) has some technical advantages compared with single carrier transmission in high data rate applications and multipath fading channels. Differential modulation techniques are used in combination with OFDM to avoid any effort for channel estimation and equalization in the receiver. In this paper, the combination of differential modulation and convolutional channel coding is re-interpreted as a concatenated code in which the differential modulation scheme is the rate R=1 inner code and the convolutional code the outer code. Turbo decoding is applied in this case 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.