Pilot-assisted channel estimation based on MMSE criterion for DS-CDMA with frequency-domain equalization

The bit error rate (BER) performance of DS-CDMA in a frequency-selective fading channel can be significantly improved by the use of frequency-domain equalization (FDE). Accurate estimation of the channel transfer function is necessary for FDE. Direct application of pilot-assisted channel estimation (CE) degrades the BER performance, since the frequency spectrum of the pilot chip sequence is not constant over the spreading bandwidth. We propose a pilot-assisted frequency-domain CE based on a minimum mean square error (MMSE) criterion. The BER performance with MMSE-CE in a frequency-selective Rayleigh fading channel is evaluated by computer simulation. It is found that MMSE-CE always provides a good BER performance, irrespective of the choice of pilot chip sequence. For a spreading factor, SF, of 16, the E_b/N₀ degradation with MMSE-CE from the ideal CE case is as small as 0.4 dB at BER=10^-4 (a 0.28 dB loss due to the pilot insertion is included).