Network Beamforming using Relays with Perfect Channel Information

This paper is on beamforming in wireless relay networks with perfect channel information at the receiver and relays. It is assumed that every node in the network has its own power constraint. An amplify-and-forward protocol is used. Relays use not only the channel direction information to form a beam at the receiver but also the channel strength information to adaptively adjust their transmit powers. Our results show that the optimal power used at a relay is not a binary function. It can take any value between zero and its maximal transmit power. Also, surprisingly, this value depends on the quality of all other channels in addition to the relay´s own channels.