Load balancing and control with interference mitigation in 5G heterogeneous networks

Biased user association is a promising load balancing approach in 5G heterogeneous networks due to its effectiveness in offloading users from macro base stations (BSs) to small cell BSs. However, users that are offloaded from macro BSs to small cell BSs suffer from severe interference as they are not served by the BS that provides the strongest received power. To mitigate this interference problem, this work utilises joint transmission coordinated multipoint (JT-CoMP) to enable users that are located in the cell expansion area (CRE) to be jointly served by multiple BSs thereby increasing their signal-to-interference noise ratio (SINR) and throughput. Unlike the traditional per-tier biasing approach, this paper utilises particle swarm optimisation (PSO) to assign each small cell BS a specific biasing value with the aim of balancing and control the load among BSs while the overall throughput of the system is still maximised. Simulation results demonstrate that per-tier biasing with no JT-CoMP achieves poor performance in terms of coverage probability, average user throughput and the throughput of offloaded users since offloaded users are not served by the best downlink BS. By implementing JT-CoMP with per-tier biasing, a 5 dB JT-CoMP biasing value can improve the throughput of offloaded users and it slightly improves the average user throughput. Comparing PSO with 5 dB CoMP, results show that per-BS biasing using PSO with CoMP improves the average user throughput from 0.59 to 0.72 Mbps (22%) and the throughput of an offloaded user from 0.04 to 0.1 Mbps (+ 150%).