Multiple-Access Slightly Frequency-Shifted Reference Ultra-Wideband Communications for Dense Multipath Channels

The design of ultra-wideband (UWB) communication systems has proven to be challenging. Coherent systems require a rake receiver with many taps that is difficult to train, and transmitted-reference (TR) schemes require a wideband analog delay line whose implementation has proven extremely difficult. In response to this challenge, we have recently proposed the frequency-shifted reference (FSR-UWB) system, which leads to the replacement of the delay line in the receiver of the standard TR-UWB system with a mixer, and the resulting system is easily implemented. In this paper, the FSR-UWB idea is extended to provide multiple-access, and a performance analysis is presented. This analysis and the corresponding numerical results reveal that, due to the large bandwidth expansion of the UWB system, the FSR-UWB single-user receiver can still be successfully employed in lightly loaded systems; in other words, successful multiple- access can be achieved without the need for the wideband analog delay line of TR-UWB or the despreading circuitry generally associated with conventional multiple-access spread-spectrum systems. The result is an extremely simple architecture for wideband multiple-access communications in the wireless environment.