Performance of DS–CDMA with chip interleaving and frequency domain equalisation in a fading channel

Conventional time domain rake combining can be replaced by minimum mean square error frequency domain equalisation (MMSE–FDE) with much better performance in a frequencyselective fading channel, since the frequency selectivity of the channel is thoroughly exploited. Chip interleaving is a form of channel interleaving that improves the DS–CDMA performance by taking advantage of the time selectivity of the channel. The combined effect of chip interleaving and MMSE–FDE is evaluated. The theoretical analysis of uncoded BER performance in a frequencyselective Rayleigh fading channel is presented and confirmed by computer simulations. It is found that chip interleaving improves the performance for all channel conditions and that the chip interleaving gain increases with the increase in spreading factor SF. In addition, it is shown by computer simulations that chip interleaving is beneficial in the presence of turbo coding and antenna diversity as well.