  To achieve the available performance gains in half-duplex wireless relay
networks, several cooperative schemes have been earlier proposed using either
distributed space-time coding or distributed beamforming for the transmitter
without and with channel state information (CSI), respectively. However, these
schemes typically have rather high implementation and/or decoding complexities,
especially when the number of relays is high. In this paper, we propose a
simple low-rate feedback-based approach to achieve maximum diversity with a low
decoding and implementation complexity. To further improve the performance of
the proposed scheme, the knowledge of the second-order channel statistics is
exploited to design long-term power loading through maximizing the receiver
signal-to-noise ratio (SNR) with appropriate constraints. This maximization
problem is approximated by a convex feasibility problem whose solution is shown
to be close to the optimal one in terms of the error probability. Subsequently,
to provide robustness against feedback errors and further decrease the feedback
rate, an extended version of the distributed Alamouti code is proposed. It is
also shown that our scheme can be generalized to the differential transmission
case, where it can be applied to wireless relay networks with no CSI available
at the receiver.
