Outage Probability and Average Rate Analysis of User-Centric Ultra-Dense Networks

User-centric ultra-dense network (UUDN) is a promising research direction for 5G, which organizes a dynamic transmission point group (TPG) consisting of potential transmission points (TPs) for each user. This paper is the first to give a general result of UUDN performance to characterize the gain obtained from the increased TP diversity within TPG, without considering cell coordination. Specifically, the outage probability and average achievable rate under general assumptions are analyzed and simple closed-form expressions for Rayleigh fading are derived, which gives a theoretical performance bound as the TPG's member is adjusted adaptively with the change of the instantaneous channel conditions. The numerical results show that the outage performance can be improved by 75% with low signal-to-interference-plus-noise ratio (SINR) threshold and the average achievable rate can be improved by 16% in comparison with ultra-dense network (UDN). In addition, the optimal TPG radius can be decided according to the requirements of users, which can provide guidance for TPG forming/reforming in UUDN.