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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 sub-carriers, mobile station's velocity, and frequency offset. The results show that the effects of frequency offset become crucial as system loading increases. The precise error-rate analysis is extended to a system using multichannel reception with maximal ratio combining (MRC). It is demonstrated, through both analysis and numerical evaluation, that the error-rate performance over a frequency selective channel deteriorates by increasing frequency offset. In addition, it is clear from the results that using multichannel reception enhances system performance.
Date of Conference: 18-20 Nov. 2007