Study on characteristics of MC-CDMA communication system

OFDM is widely used in recent wireless communication systems. The advantages of this technique are robustness in frequency selective fading and high spectrum efficiency. OFDMA which is a multiple access system using this scheme is used for the 4th generation (4G) system. However, the number of OFDMA access users within an allocated frequency bandwidth is limited. It is thus required that a new multiple access system can accommodate much more users within a limited frequency bandwidth in the future. MC-CDMA combining OFDM and CDMA is recognized as the promising candidate modulation method. Various studies about this have been conducted. To realize a power-efficient MC-CDMA system, it is important to understand the damage to the property of the spreading sequence due to the nonlinearity of the high power amplifier (HPA). However, the effects are not well investigated. In this study, the authors investigated the degradation of communication quality due to nonlinear characteristics when performing Forward error correction (FEC) coding. From the results, it became clear that MC-CDMA outperforms OFDMA as a multiple access scheme, but is more sensitive to the nonlinearity, especially in higher mode modulation.