Multiuser interference mitigation in time-hopped ultra-wideband Receivers

Offering a large bandwidth under strict transmission power limits, UWB communications can overcome the spectral congestion and consequent performance impairment experienced by narrowband devices operating in common unlicensed frequency bands. The impulse radio (IR) class of UWB systems typically uses time-hopping (TH) and repetition codes. The TH scheme is intended to prevent catastrophic interference between TH-UWB transmissions. However, in applications where several UWB devices are located at close range, multiple-user interference (MUI) can impair uncoordinated transmissions. In particular, a conventional receiver does not properly exploit the TH code and performs poorly in the presence of strong MUI. In this paper, the properties of MUI in TH-UWB are reviewed, and two classes of techniques for mitigation of this MUI are presented. The first class uses statistical characterizations of the MUI-plus-AWGN disturbance as a basis for receiver design, leading to improved nonlinear receiver structures. The second class uses interference-sensing techniques specifically developed for TH-UWB radio, which control combining of pulse replicas at the receiver. Both methods lead to greatly improved bit error rate performance versus the conventional receiver. Different implementations are presented for each class, and the complexity and performance of each implementation is discussed. Both types of interference mitigation can be powerfully and efficiently used in a single receiver, and composite receiver designs are shown that provide superior performance.