Most of users in heterogeneous networks (HetNets) associate to macro base stations (BSs) due to their high transmission power while small cell BSs are underutilized. Current research has addressed this load balancing problem based on biased user association where all small cell BSs that belong to the same tier, e.g femto or pico BSs are assigned a static biasing value in order to increase their coverage area. This work utilises particle swarm optimisation to assign each small cell BS a certain

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... iasing value with the objective of maximising the achievable throughput and controlling the load per-BS. Simulation results show that the proposed PSO approach achieves better performance in terms of the achievable throughput. In addition, the proposed approach is able to provide fairness among users by controlling the load per-BS.