Distributed transmit power management for small cell networks

Small cell networks (SCN) concept has been widely accepted as the most efficient method to increase cellular network capacity. As the cell size and networks become smaller and denser, respectively, inter-cell interference (ICI) at a user terminal equipment (UE), coming from the adjacent base station (BS) transmissions to their respective UEs, grows considerably and becomes more complex to manage. In this paper, we developed a distributed cooperative downlink power allocation algorithm for SCN that maximises the number of BSs transmissions to UEs such that the received signal-to-interference-plus-noise ratio (SINR) at the UEs is greater than a minimum SINR threshold for wireless transmissions. We first formulate the BS power allocation problem with BS transmit power as binary variables to indicate whether the BS is on or off. A factor graph representation and Belief Propagation (BP) method based on a sum-product approach for power allocation optimisation are developed. This optimisation representation allows each BS to cooperate by exchanging messages about the probability distribution of the number of BS transmissions. BS then uses this information to optimise its own transmit power allocation. To reduce the overhead information that needs to be exchanged by the BSs, we allow only a subset of randomly chosen BSs in the network to exchange messages. The simulation results show that the number of BSs transmissions obtained by the proposed algorithm is on average 5% less than the one obtained by using a global optimal exhaustive search method.