Network beamforming with channel means and covariances at relays

This paper is on beamforming in networks whose relays know the channel means and covariances. The question we answer is: To optimize the network performance. how much power should each relay use? Instead of the widely used aggregate relay power constraint, we use the more practical assumption that each relay has a separate power constraint. We generalize the distributed space-time coding scheme so that each relay can adapt its transmit power according to the channel information. For two-relay networks, we analytically solve the relay power control problem at high transmit powers using the pairwise error probability (PEP) minimization. Simulation shows that appropriate relay power control can largely improve the reliability, especially when the qualities of relay paths are far apart.