Cost-Efficient Optimization of Base Station Densities for Multitier Heterogeneous Cellular Networks

Heterogeneous cellular networks have emerged as the primary solution for overwhelming traffic demands. This study addresses the architecture optimization of multitier open-access downlink heterogeneous cellular networks. A distinguishing feature of this work is that the transmission requirements of mobile users and the profit requirements of operators are all considered. Spatial throughput is maximized under practical constrains on the network deployment cost and traffic loads of individual tiers. By using stochastic geometry, the problems of optimizing the densities of base stations (BSs) in different tiers are shown to be linear-fractional programming that can be further transformed into linear programming by employing Charnes-Cooper transformation. The linear-fractional programming can then be solved efficiently. For a two-tier network, the optimal BS densities are derived in closed form by using the graphical method. Our results indicate that enlarging the densities of BSs may not always improve network throughput and that the optimal densities of each tier exist to satisfy the communication demands of mobile users and the profit requirements of operators. Numerical results demonstrate the significant throughput gain from the optimal deployment of multitier heterogeneous cellular networks.