Formulating and solving the femtocell deployment problem in two-tier heterogeneous networks

Recently, there has been an increasing interest in the deployment and management of femto base stations (BSs) to optimize the overall system performance in macro-femto heterogeneous networks. While deployment of femto BSs is typically not as planned as that of pico BSs, given a number of femto BSs to be distributed to candidate customer sites, questions regarding the optimal deployment locations and transmission configurations still need to be answered. In this paper, we formulate a joint optimization problem involving deployment location, cell selection, and power control to maximize the number of users that can be supported for a given number of femto BSs to be deployed in the macro cell. Since the formulated problem belongs to mixed-integer non-linear programming (MINLP), we propose an anytime algorithm that can yield a desirable solution within proper time limit. Specifically, based on the concept of coalition structure generation, the algorithm decouples the problem into the cluster formation sub-problem and power control sub-problem to find the optimal cluster head (femto BS location), cluster membership (cell selection), and transmission power in an iterative fashion. Evaluation results presented in this paper show that the proposed algorithm can effectively solve the problem with better complexity-optimality tradeoffs compared to baseline approaches.