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In order to coexist with existing legacy wireless systems, the transmit power spectral density (PSD) of ultra-wideband (UWB) impulse radio systems is limited. The coverage range of the UWB systems is then confined within a few meters. One possible way to achieve a greater coverage is a short-range multihop relaying strategy. A one-hop relay node can be either an amplify-and-forward (AF) or decode-and-forward (DF) relay. This paper analyzes the bit error rate (BER) performance of a selective-Rake system using an uncoded DF relay under imperfect channel estimation in UWB multipath fading channels. A multiple-antenna relay system is proposed to further enhance the overall system performance. The influence of the number of selective-Rake fingers, the number of relay antennas, and channel estimation errors on the performance of the single- and multiple-antenna relay systems is investigated. Analytical and simulation results verify the performance improvement of the relay systems over the direct transmission system.