A subspace approach to blind estimation of ultra-wideband channels

In impulse radio based ultra-wideband (UWB) multiuser communication systems, each user´s transmitted symbols are modulated by pulse position modulation (PPM), and corrupted by both intersymbol interference and multiple access interference at the receiver end. To construct low-complexity linear receivers for efficient symbol detection, channel information is needed. In this paper, following a particular input/output model that transforms a PPM system model into a sum of seemingly pulse amplitude modulation signals, a structure similar to a code-division multiple access system, we show that subspace technique can be applied to blindly estimate multipath channels. Performance of the proposed channel estimator is studied. To detect desired symbols, MMSE receivers are constructed. Simulation results demonstrate superiority of the proposed method to the existing maximum likelihood channel estimator.