Multi Rate Adaptive Cluster Spreading OFDMA System

The multi-carrier code division multiple access (MC-CDMA) and orthogonal frequency division multiple access (OFDMA) are the main systems for engineers to mitigate the demands of 4G networks. In this paper, the proposed system utilizes the entire system bandwidth by using several orthogonal sub-carrier blocks. Users´ data are multiplexed through the use of spreading code into the orthogonal frequency sub-carrier blocks, and multiple-user access is accomplished through the OFDMA technique. The proposed system combines all the facilities of OFDM and CDMA, which ensures better performance than using MC-CDMA and OFDMA individually. By combining the multiple MC-CDMA system among orthogonal frequency sub-carrier blocks, the system provides multi-rate multiple access among the verities of services according to the demand of users at a given time. In this paper, we evaluate the performance of the proposed system over multi-path Rayleigh fading channels. We also compare the BER performance and throughput of the proposed system with that of the conventional MC-CDMA system, under the assumptions of identical conditions and channel estimation for both system.