Receiver architectures for DS-CDMA ultrawideband communication systems

Classical rake receivers generally ignore the effect of intersymbol interference (ISI) as the bit period is expected to be much longer than the channel delay spread. When DS-CDMA is considered for ultra-wideband communication to achieve high data rates, the effect of ISI can no longer be ignored. In this paper, we investigate receiver architectures for DS-CDMA ultra-wideband systems which take the effect of ISI into account. Specifically, the receiver is composed of an rake detector, whose coefficients are found using a MMSE criterion, followed by a maximum likelihood sequence estimator (MLSE) implemented via the Viterbi algorithm. To lower the computational complexity of the proposed structure, we also investigate reduced complexity detectors in which a feedback filter removes some of the ISI terms, thereby allowing the Viterbi detector to be employed with a corresponding reduction in its number of states. We present simulation results to compare the performance of these receivers with other methods proposed for ultra-wideband communication.