Capacity maximization for distributed beamforming in one- and bi-directional relay networks

In cooperative networks, users share their resources to establish reliable connections between each other. If two users want to communicate through a cooperative network, different transmission schemes are possible in which other users serve as relays. In this work, we compare different relaying schemes on the basis of their maximal capacity. We assume that the channel state information is available and the relays use the amplify-and-forward protocol. An optimal technique for one-directional transmissions forms the basis for capacity maximization of the bi-directional four-phase scheme. The analysis for the asymptotic behavior of the one-directional scheme also provides simple relations for the maximal sum-capacity of the bidirectional two-phase scheme. For the third bi-directional scheme with three-phases, upper bounds on the maximal capacity are obtained.