  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.
