In this paper we show that a one-hop repeater in an ultra-wideband (UWB) communication system for a wireless personal area network (WPAN) can be used to achieve diversity gain in a Rayleigh fading channel. We use maximal ratio combining (MRC) in the transmitter-repeater link and space-time coding (STC) in the repeater-receiver link, where the repeater has two antennas for transmission as well as reception. The repeater transmits at a higher rate than the transmitter so that the symbols are properly synchronized. We then derive the closed-form expression for the probability of bit error and show that there exists a trade-off between the bit error rate (BER) performance and the transmit powers of the transmitter and the repeater. Based on our BER curves, we then show that the performance of the proposed system is much better than a conventional repeater as well as the traditional communication system. © 2005 IEEE.