Analysis of load dependent energy efficiency of two-tier heterogeneous cellular networks

In this paper, a tractable analytical framework for investigating the energy efficiency (EE) of a 2-tier heterogeneous cellular network consisting of macro and picocell base stations (BS) is developed. The BSs, which are randomly distributed, serve a number of users in the downlink under shared spectrum operation. By incorporating a tunable downlink power control mechanism, the successful transmission probability and the average throughput achievable in both tiers are analytically derived. Since varying load conditions has an important implication on the network performance, the EE is investigated as a function of the load level, considering the ability to transfer the load between the 2 tiers. An optimization problem that maximizes the throughput constrained 2-tier EE is formulated and solved to determine the optimal network operational parameters. In addition to providing valuable design insights, the findings reveal that, for different load conditions, it is feasible to significantly enhance the EE performance by optimally adapting the network configuration.