Influence of code orthogonality on downlink throughput comparison between MC-CDMA and OFDMA in multi-cellular environments

Fourth generation (4G) mobile access is drawing particular attention as it promises to deliver high data rates and reliable coverage for broadband wireless access. In this paper, Orthogonal Frequency Division Multiplexing Access (OFDMA) and Multi-Carrier Code Division Multiplexing Access (MC-CDMA) are investigated to highlight their strengths and weaknesses as candidates for 4G wireless access. Using a multi-cell environment, MC-CDMA and OFDMA coverage is dimensioned based on the value of the Signal to Interference plus Noise Ratio (SINR). The results show that OFDMA system offers cell coverage of 92.5% and a maximum actual throughput of 24.2 Mbps/cell (fade margin 10 dB). Using the same assumptions for MC-CDMA, the results show better coverage only with complete orthogonal spreading codes which can guarantee 97% of user coverage and actual throughput of 28.8 Mbps. These measurements decrease as the orthogonality between the spreading codes is reduced. In the case of 94% orthogonality the MC-CDMA system achieved 89.3% coverage and 21.9 Mbps throughput while with a 60% orthogonality 47% coverage and 5.8 Mbps throughput was achieved.