Adaptive TF-domain Spread MC-CDMA System in Frequency-Selective Rayleigh Fading Channels

In this paper, an adaptive time-frequency domain (TF-domain) spread multicarrier code-division multiple-access (MC-CDMA) system is considered for application in downlink of cellular radio network over frequency selective fading channels. In the proposed system, the overall system spreading factor (SF), defined as the product of the T-domain SF and F-domain SF, is fixed but can be dynamically allocated to F-domain and T-domain according to the number of active users. It is shown in this paper that one can achieve a tradeoff between the multiple access interference (MAI) level and frequency diversity gain by adaptively adjusting the T-and F-domain SFs, thus resulting optimum bit error rate (BER) performance.