Minimum variance multiuser detection for impulse radio UWB systems

The minimum variance (MV) technique minimizes output variance of a receiver subject to a constraint, which guarantees no cancellation of the desired signal while interference is mitigated. It has been successfully applied to multiuser detection for a direct sequence code-division multiple access (CDMA) system even when multipath channel is unknown. Its applicability in multiple access ultra-wideband (UWB) systems is investigated in this paper. First, similarities between a time-hopping (TH) UWB system using pulse position modulation (PPM) and a multirate CDMA system are explored where a code matrix for each user can be defined based on its unique TH sequence, similar to a spreading code matrix in a CDMA system. Meanwhile, modulation delays are transformed to amplitudes of pulses, yielding a virtually linear model. After following MV optimization procedures, the desired signal can be detected from outputs of a bank of receivers. Performance of the proposed detection criterion is analyzed and verified.