Study On OFDM-CDM System In Wireless Fading Channels

In this paper, combining orthogonal frequency-division multiplexing with code-division multiplexing (i.e. OFDM-CDM) system in wireless fading channels is presented. Exploiting CDM, Each data symbol is spread over several sub-carriers and an additional frequency diversity gain can be obtained. Although the additional frequency diversity gain can be attained, by using efficient detection techniques, the performance of OFDM-CDM system is better than that of conventional OFDM. In OFDM-CDM receiver, single-symbol detection (SD) or multi-symbol detection (MD) techniques are applied. Several schemes which correspond to single-symbol or multi-symbo are proposed in this paper. The algorithms to obtained the optimum reliability information (i.e. LLR) for the Viterbi decoder which derived of OFDM-CDM system is presented .The results of simulation is shown that the performance of multi-symbol is better than that of single-symbol and the performance of soft decision decoding is better than that of hard decision decoding. According to the simulation results presented in this paper, it can be shown that OFDM-CDM outperforms conventional OFDM with respect to bit error rate (BER) performance.