Performance of a new adaptive grouping and modulation procedure for multiuser group orthogonal MC-CDMA

Adaptive OFDM systems could achieve great results in terms of channel efficiency when the channel state information is perfectly estimated. In practice, in most cases the acquired channel information is not perfect neither complete, therefore some diversity or coding are more than suitable/necessary. In Multi-Carrier CDMA (MC-CDMA) systems, diversity is achieved by the frequency spreading. The spreading procedure is more effective whichever better sub-carrier conditions are experienced. The optimal approach should load the subcarriers adaptively according to every sub-carrier state. The general MC-CDMA spreads the symbols over the whole assigned bandwidth. However, in the Group Orthogonal MC-CDMA approach, only a part of this bandwidth is assigned to each user. In this paper we investigate the performance of the use of adaptive grouping and modulation procedures in a conventional MC-CDMA on the downlink transmission mode with the aim of increasing the system's user-capacity while maintaining a satisfactory bit error rate performance threshold.