In this paper we emphasis the effect of the variation of major parameters on Orthogonal Frequency Division Multiple Access (OFDMA) systems and the evaluation of channel estimation and equalization are made, in which the bit/symbol error rate of a time varying channel has to be estimated in order to correct the channel interference prior to the decoding of information symbols. We evaluated the channel capacity to quantify the potential of OFDMA and Code Division Multiple Access (CDMA) to improve the performance of the overall system. With the advantages of CDMA and OFDMA, a new multiple access technique has been developed called Coded-OFDMA(C-OFDMA) Multiple Access, which provides more dominant and robust, superiority and greatly improves the performance. Reuse partitioning of Hybrid Multiple Access(HMA) increases the system capacity. Simulation results show that the proposal is more effective, feasible and yields improved results.