Energy efficiency of outage constrained two-tier heterogeneous cellular networks

In this paper, the energy efficiency (EE) of a 2-tier cellular network subject to downlink transmission outage probability constraints is analyzed under a shared spectrum scenario. The heterogeneous network considered consists of randomly distributed microcell BSs overlaid with picocell BSs. Based on the analysis of the structure of the EE function, the sufficient condition that enables the EE of the 2-tier network to exceed that of a single tier network is determined. The operational bounds for the network in terms of the pico tier BS density is derived by analytically solving the optimization problem that maximizes the outage constrained 2-tier EE. The Lagrange multipliers attributed to the outage constraints, which quantify the marginal loss in the EE performance, are found to be strongly dependent on the power consumption parameters of both the micro and pico tier BSs. The implication of the findings is that, by carefully tuning the BS power consumption parameters, it is possible to realize significant improvement in the EE performance for different operational scenarios while satisfying the outage probability objectives.