Multicarrier CDMA

Abstract

Abstract Multi‐Carrier Code Division Multiple Access (MC‐CDMA) is a multiple access scheme which combines Multi‐Carrier Modulation (MCM) and Direct Sequence CDMA (DS‐CDMA). MC‐CDMA aims at combining the bandwidth efficiency and long symbol duration inherent in MCM and the interference rejection capabilities inherent in DS‐CDMA. The use of MCM introduces frequency domain spreading in the signal design and the use of Direct Sequence Spread Spectrum (DS‐SS) time domain spreading, thus giving MC‐CDMA systems the unique possibility to spread signals in both the time and frequency domains. In fact, MC‐CDMA schemes have been proposed that cover the entire range in the frequency vs. time domain spreading trade‐off, from performing all spreading in the time‐domain (similarly to DS‐CDMA) to performing all spreading in the frequency domain (a system often referred to as OFDM‐CDMA). Among all MC‐CDMA schemes, OFDM‐CDMA has attracted the most research interest because it offers a large degree of flexibility in system design, high bandwidth efficiency and good performance with acceptable complexity. Under certain conditions OFDM‐CDMA systems can outperform DS‐CDMA, other MC‐CDMA schemes and Multiuser OFDM (M‐OFDM) at the expense of increased complexity. However, implementation issues and the operational environment can affect the performance of each system significantly and in a different way, making different schemes more appropriate in specific conditions. Therefore, no scheme is universally superior and the trade‐offs have to be considered carefully before a system design is selected.