User-Centric Joint Transmission in Virtual-Cell-Based Ultra-Dense Networks

摘要

In ultra-dense networks (UDNs), distributed radio access points (RAPs) areconfigured into small virtual cells around mobile users for fair andhigh-throughput services. In this correspondence, we evaluate the performanceof user-centric joint transmission (JT) in a UDN with a number of virtualcells. In contrast to existing cooperation schemes, which assume constant RAPtransmit power, we consider a total transmit power constraint for each user,and assume that the total power is optimally allocated to the RAPs in eachvirtual cell using maximum ratio transmission (MRT). Based on stochasticgeometry models of the RAP and user locations, we resolve the correlation oftransmit powers introduced by MRT and derive the average user throughput.Numerical results show that user-centric JT with MRT provides a highsignal-to-noise ratio (SNR) without generating severe interference to otherco-channel users. Moreover, we show that MRT precoding, while requiringchannel-state-information (CSI), is essential for the success of JT.