Energy-Spectral-Efficient Heterogeneous Cellular Networks: Joint Optimization of Cross-Tier Inter-BS Cooperation and BS Deployment

This paper enhances the energy/spectral utilization of a large-scale coordinated multi-point (CoMP) enabled two-tier heterogeneous cellular network (HCN) by the joint optimization of the associated cross-tier inter-BS cooperation and BS deployment, where a pair of BSs in different tiers can cooperate to transmit desired signals to the user equipment (UE) supported. We derive the energy-spectral efficiency (ESE) for the large-scale CoMP-enhanced two-tier HCN. Our ESE modeling distinctively includes: 1) The ESE's dependence on the activation degree of cross-tier inter-BS cooperation is quantified, which can be flexibly harnessed for transforming the grave interference-limited situation of the tier-edge UEs into harmonious CoMP-support. 2) Both the BS densities in these two tiers and the large-scale user-behaviors (LSUBs) are explicitly integrated into our ESE modeling. Under this tractable ESE model, we first optimize the network's ESE by choosing a suitable cooperation activation degree based on a specific cellular scenario, whilst satisfying the UE's outage constraint. We continue by formulating the joint optimization problem of the cooperation activation degree and of the BS density for maximizing the ESE, while varying the LSUBs. Our simulation results confirm the accuracy of our ESE modeling and quantify the impact of network parameters on the achievable ESE. We demonstrate that the proposed joint optimization strategy has a significantly higher ESE than its optimization counterpart only considering the cooperation activation degree. Our solution may be expected to pave the way for improving the resource efficiency of large-scale dense HCNs.