Handover decision for small cells: Algorithms, lessons learned and simulation study

More and more cellular network operators enable the unplanned deployment of small-sized cellular stations by the end users into the predominant macrocellular network layout. This increases the spatial capacity of the cellular system and reduces the costs for installing, managing, and operating the radio access network. However, the impact of such an unplanned network densification on the robustness of cell handover (HO) still remains unclear and needs to be studied. For this purpose, in this paper we highlight the key aspects of the cell HO process in the presence of small cells and identify the main issues that affect its robustness. We summarize lessons learned from the rich literature on HO decision algorithms for small cells, and present an algorithm for alleviating interference in the cellular uplink while prolonging the battery lifetime of the user terminal. Based on the evaluation methodology of the Small Cell Forum, we conduct a comprehensive system-level simulation study to validate the accuracy of our findings and provide valuable insights on the key performance trade-offs inherent to the HO decision for small cells.