HANDOVER SCHEMES IN HETEROGENEOUS LTE NETWORKS: CHALLENGES AND OPPORTUNITIES

For satisfying rapidly increasing data rates at hotspots and enhancing coverage in buildings, small cells, such as femtocells, picocells, and microcells, are deployed in LTE-A. Femtocells are typically installed at hotspots and overlay with the macrocell to improve energy efficiency and data rates. In macro-femto HetNets, the handover issue is more important than that in macrocell networks. On one hand, more frequent handovers are triggered because the coverage range of a femtocell is small, and multiple femtocells are overlaid. On the other hand, some schemes, such as load balancing, aimed at improving network performance, will also cause frequent handover in macro-femto HetNets. Therefore, handover has a significant impact on the performance of macro-femto HetNets. In this article, we first survey the state-of-the-art handover techniques that are aimed at keeping ongoing connections uninterrupted or ensuring the quality of service of mobile users. Then we introduce load-balance-related handover schemes. Moreover, an energy-efficient handover scheme is presented. At last, we point out interesting research issues on handover schemes in macro-femto HetNets.