Performance of Frequency-Time MMSE Equalizer for MC-CDMA over Multipath Fading Channel

A cyclic prefix of sufficient length is inserted (longerthan the maximum delay spread of the channel) in Multi-Carrier CDMA (MC-CDMA) transmission over dispersive channels such that thechannel, as seen by subcarrier, is a simple multiplicativedistortion in the frequency domain, that can be compensated for by aone-tap Frequency Equalizer (FE). If, in addition to the spectralinefficiency caused by insertion of the cyclic prefix, the delayspread should exceed the designed prefix length, the FE will attempt tocompensate for the mismatched signal model and the system performancewill degrade significantly. In this paper, we derive a multi-input,multi-output (MIMO) model for received signal in synchronousMC-CDMA system over a multipath channel. Based on this model, aFrequency-Time MMSE Equalizer (FTE) is proposed. The performanceof the FTE is studied as a function of key system parameters, suchas prefix length and number of subcarriers, as well assensitivity to channel estimation errors. The numerical result showsthat system performance degradation due to insufficient guardtime can be recovered with the FTE; i.e., full spectralefficiency can be achieved at the price of additional receivercomplexity.