Joint Source Power Scheduling and Distributed Relay Beamforming in Multiuser Cooperative Wireless Networks

This paper considers the maximization of the sum capacity of a multiuser cooperative wireless network through the joint optimization of power allocation among source nodes and distributed beamforming weights across the relay nodes. The distributed beamforming techniques offer the capability of enhancing the sum network capacity by achieving spatial multiplexing to support concurrent communications of multiple source-destination pairs. In this paper, we consider a two-hop cooperative wireless network consisting of single-antenna nodes in which multiple concurrent links are relayed by a number of cooperative nodes. When a large number of relay nodes are available, the channels of the different source-destination pairs can be orthogonalized, yielding enhanced sum network capacity. Such an advantage is particularly significant in high signal-to-noise ratio (SNR) regime, in which the capacity follows a logarithm law with the SNR, whereas exploiting spatial multiplexing of multiple links yields capacity increment linear to the number of users. However, the capacity performance is compromised when the input SNR is low and/or when the number of relay nodes is limited. Joint optimization of source power allocation and distributed relay beamforming is important when the input SNR and/or the number of relay nodes are moderate or wireless channels experience different channel variances. In these cases, the joint optimization of source power and distributed beamforming weights achieves significant capacity increment over both source selection and equal source power spatial multiplexing schemes.