Multiple-access performance of slightly frequency-shifted reference UWB communications

Transmitted reference (TR) ultra-wideband (UWB) systems have been proposed to alleviate the implementation issues of UWB Rake receivers due to channel estimation and the need for a large number of Rake fingers. However, the wideband analog delay line used in TR receivers is difficult to implement in practice as well. A slightly frequency-shifted reference (FSR) UWB system has been introduced to retain the benefits of TR UWB systems while avoiding the analog delay line of TR systems. The single-link performance of FSR systems has been investigated in the literature. In this paper, the multiple-access (MA) performance of FSR UWB systems is derived under both AWGN and multipath channel conditions. The power delay profile (PDP) of the multipath channel is incorporated in the analysis of the MA interference power. A theoretical comparison between FSR and TR UWB systems in a multiuser environment is given. We show that FSR UWB systems support fewer users than TR UWB systems given the same data rate and E_b/N₀.