Performance of Random Spreading MC-CDMA in the Presence of Multiple Interferences and Doppler Shift

The performance of multicarrier code division multiple access (MC-CDMA) systems that employ random spreading sequence in downlink slowly fading channels is analyzed. An expression of the probability density function (pdf) of multiple access interference (MAI) is derived for CDMA systems and the results are extended to MC-CDMA systems to determine the pdf of MAI, inter-carrier-interference (ICI) and noise in terms of the number of users, the spreading factor, the number of sub-carriers and frequency offset. The results show that the effects of frequency offset becomes crucial as system loading increases. In this paper the synchronous downlink of cellular MC-CDMA is considered where, a Gaussian approximation of the MAI and ICI is derived to reduce the computational complexity in calculating the system performance.