Space-time coded user cooperation for ultra-wideband systems

In this paper, we consider the user cooperation in ultra-wideband (UWB) systems characterized by severe frequency selective channels. To circumvent this problem we present a space-time coded UWB system employing the multiband orthogonal frequency division multiplexing (MB-OFDM). Space-time coded cooperation is subject to error floors due to hard-decision detection errors in between users. For this reason we propose a soft-information aided iterative cooperation mechanism which lower the error floor significantly. The simulation results and comparisons with the single user case indicate that the proposed user cooperative UWB transceiver architecture has significantly improved error floor and bit-error rate (BER) performance. The simulation results also show that additional gains are attained when turbo processing is employed at the receiver side as well.