Optimal Power Allocation for Downlink Cooperative Cellular Networks

In cellular networks, base stations can cooperate in order to bring spatial diversity. Cooperative diversity enables to increase link capacity and signal to noise ratio. This paper presents source and relay base station's optimal power allocation in order to maximize the sum capacity over all relayed links. Average power allocation is solved by an iterative method which allocates relay and source powers separately, by convex optimization. Then source symbol powers are set with simple water-filling, in order to maximize the capacity. Simulation results show that sum capacity is highly increased by relaying under optimal power values. Relaying is especially efficient for user terminals who would have poor radio conditions without relaying. The paper also presents a simple method, based on path loss characterization, to determine the need for relaying. It can be used independently in the source base stations, which is particularly adapted for flat architectures.