Abstract: An adaptive cooperative wireless communication system based on quadrature signaling is proposed, in which each user can transmit its own and the partner’s information simultaneously in the in-phase and quadrature components of a two-dimension modulated signal. The virtual multiple-antenna transmitter generated in this way allows each user to achieve transmit diversity in a distributed fashion, without expanding the bandwidth and boosting the transmit power. With the decode-and-forward(DF) relay channel model, a closed-form bit error rate(BER) performance expression is derived, and then the effect of different power allocation algorithms together with various inter-user and uplink channel qualities on the system performance is investigated. Simulation results show that the proposed system, with an equal power allocation algorithm, provides diversity gains and can achieve a full diversity order at high inter-user channel signal-to-noise ratios(SNRs). Furthermore, additional performance benefits can be obtained by employing an optimum power allocation algorithm.

Key words: cooperative communication, virtual multiple-antenna, diversity, resource allocation