Biased User Association in 5G Heterogeneous Networks

The deployment of heterogeneous networks (HetNets) is one of the promising approaches to meet the 5G requirements. The traditional user association approach is inefficient for HetNets due to the high transmission power of macro base stations (BSs) and the low transmission power of small cell BSs, i.e., pico and femto BSs. This approach causes macro BSs to be overloaded whereas small cell BSs are lightly loaded. To address this load imbalance in 5G HetNets, 3GPP introduced the concept of cell range expansion (CRE) where the coverage area of small cell BSs is artificially increased by adding a bias value to the power received from small cells. Although the biasing approach can better balance the load among tiers, users at the expansion area suffer from severe interference coming from neighbouring macro BSs. This work utilizes coordinated multi-point transmission (CoMP) to reduce interference. User-centric clustering where a user can be served by a number of BSs is implemented. The results have sown that user-centric CoMP can significantly improve the SINR levels of all users and cell-edge users as well.