Inter-Cell Interference Coordination for Expanded Region Picocells in Heterogeneous Networks

Because following current cell selection procedures, User Equipments (UEs) connect to the cell that provides the strongest DownLink (DL) Received Signal Strength (RSS), in a Heterogeneous Network (HetNet) comprised of macrocells and picocells, the large difference in DL transmit powers among macro Base Stations (BSs) and pico BSs may significantly reduce the DL service coverage area of picocells. In order to expand the DL coverage of picocells in the presence of macrocells, the concept of range expansion has been recently proposed, in which a positive offset is added to the DL RSSs of picocell pilot signals to increase their DL footprints. Although range expansion may increase the DL coverage of picocells, it may also create significant DL inter-cell interference in the Expanded Region (ER) of picocells, since pico ER UEs do not connect to the cells that provide the strongest DL RSSs. In this paper, we propose a novel cooperative macrocell-picocell scheduling approach to mitigate macrocell DL inter-cell interference towards pico ER UEs. Simulation results show that expanded region picocells supported by the proposed cooperative macrocell-picocell scheduling approach are able to mitigate UE outages and significantly improve spatial reuse of spectrum.