Backhaul-aware adaptive TP selection for virtual cell in ultra-dense networks

Ultra-dense network (UDN) in 5G provides more potential transmission points (TPs) for users. To take advantage of dense TPs, 5G will shift the network paradigm from traditional cell-centric to user-centric. Virtual cell redefines the cell from the view of users to build user-centric networks. Virtual cell is a logical cell consisting of multi physical TPs. By data synchronization as a way of cooperation between TPs at different protocol layers, virtual cell can enhance spectral efficiency. Data synchronization will utilize backhaul resources. However, non-ideal backhaul will be extensively deployed, which will take a significant share of the energy consumption in future systems. Therefore, TP selection in a virtual cell should take spectral efficiency (SE) and energy efficiency (EE) into account. To trade off between the SE and EE, we present an analysis of the backhaul power consumption and put forward an adaptive algorithm for TP selection in a virtual cell. We define the normalized outage capacity as goodput to represent the SE. Then, we consider the power of backhaul link as the energy consumption. Thus, the objective of TP selection is maximizing the defined energy efficiency. A dynamic ergodic method is used to solve the problem. Our simulation shows the dynamic selection scheme has better performance than static scheme and random scheme. Besides, with the size of virtual cell increasing, the growth rate of energy efficiency is decreasing. Thus, the size of virtual cell and TP numbers should be controlled.