Decode-and-forward cooperative diversity with power allocation in wireless networks

We study power allocation for the space-time-coded decode-and-forward cooperative diversity protocol in a wireless network under the assumption that only mean channel gains are available at the transmitters. In a Rayleigh fading channel with uniformly random node locations, a near-optimal power allocation that minimizes the outage probability is derived under a short-term power constraint, wherein the total power is fixed for each two-stage transmission. This near-optimal scheme allocates one half of the total power to the source node and splits the remaining half equally among selected relay nodes; a node is selected for relay if it is able to decode the signal from the source and its mean channel gain to the destination is above a threshold. Numerical results show that this scheme significantly outperforms the constant-power scheme, wherein all nodes use the same power at all times, and the best-select scheme, which employs one relay node with the largest mean relay-destination gain