Performance of frequency-time MMSE equalizer for MC-CDMA over multipath fading channel

A cyclic prefix of sufficient length is inserted (longer than the maximum delay spread of the channel) in Multi-Carrier CDMA (MC-CDMA) transmission over dispersive channels such that the channel, as seen by subcarrier, is a simple multiplicative distortion in the frequency domain, that can be compensated for by a one-tap Frequency Equalizer (FE). If, in addition to the spectral inefficiency caused by insertion of the cyclic prefix, the delay spread should exceed the designed prefix length, the FE will attempt to compensate for the mismatched signal model and the system performance will degrade significantly. Ln this paper, we derive a multi-input, multioutput (MIMO) model for received signal in synchronous MC-CDMA system over a multipath channel. Based on this model, a Frequency-Time MMSE Equalizer (FTE) is proposed. The performance of the FTE is studied as a function of key system parameters, such as prefix length and number of subcarriers, as well as sensitivity to channel estimation errors. The numerical result shows that system performance degradation due to insufficient guard time can be recovered with the FTE; i.e., full spectral efficiency can be achieved at the price of additional receiver complexity.