Effect of Frequency Offset and Multiple Interferences on the Performance of Random Spreading Downlink MC-CDMA

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The performance of Multi-Carrier Code Division Multiple Access (MC-CDMA) systems that employ random spreading sequence in downlink frequency selective fading channels is analyzed. An expression of the Probability Density Function (PDF) of multiple access interference (MAI), Inter-Carrier-Interference (ICI) and noise is derived for MC-CDMA systems in terms of the number of users, the spreading factor, the number of subcarriers, mobile station's velocity, and frequency offset. The results show that the effects of frequency offset become crucial as system loading increases. In this paper the synchronous downlink of MC-CDMA in a time variant channel is considered where, a Gaussian approximation of the MAI and ICI is derived to reduce the computational complexity in calculating the system performance.