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To exploit multiuser spatial cooperative diversity, relay nodes can assist the transmission of signal from multiple sources to their corresponding destinations in order to combat the noise, the channel fading and the cross-interferences. In this work, we consider a network consisting of N source-destination pairs and a set of M relay nodes. We assume that a fixed total budget of transmit energy is available for allotment among all transmitters, i.e., the source and relay nodes. For such network, we consider the time division Amplify-and-Forward (AF) scheme in 2N time slots, and propose an algorithm to optimize the beamformers and the powers allocated to all transmit nodes. The proposed method maximizes the network sum capacity assuming that the channels state information (CSI) is known. Numerical simulations illustrate the significant improvement obtained under power constraint. This betterment is more pronounced for low power regimes.

The throughput of a multi-user broadcast opportunistic communications system is highly affected by the accuracy of the available channel state information (CSI) at the transmitter side. It is a questionable assumption to have almost perfect knowledge of the user SNRs at the transmitter due to the error in the channel measurement, or due to reporting feedback errors from users to the transmitter. As a result such errors, the system can not gain its maximum throughput. In this paper, we investigate the performance of opportunistic communications system considering imperfect SNR reports. We show that in order to maximize the throughput, the transmitter needs to estimate the channel state information. The imposition of a correlation constraint will prevent the estimate of channel from fluctuating too widely. Employ Kalman filter, we estimate the channel state information and show that the throughput is significantly improved.

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