Efficiency Analysis of Decoupled Downlink and Uplink Access in   Heterogeneous Networks
  This paper analyzes two-tier heterogeneous cellular network with decoupled downlink and uplink access. The basic performance benefits of uplink/downlink decoupling have been recently introduced. Here we provide a more elaborate treatment of the decoupling mechanism by analyzing spectral and energy efficiency of the system, as the joint improvement of these two features is crucial for the upcoming 5G systems. Contrary to the common assumption of a homogeneous user domain, we analyze two-tier user domain, whose transmit powers depend purely on the association process. The derived joint association probabilities and the distributions of the distance to the serving base station give deeper insight into the fundamentals of a system with decoupled access. The rigorous theoretical analysis shows that decoupling of downlink and uplink with two-level uplink power adaptation improves both, spectral and energy efficiency of the system. 
Katerina Smiljkovikj, Liljana Gavrilovska and Petar Popovski
cs.IT math.IT