A mathematical optimization approach for cellular radio network planning with co-siting

Wireless network operators are continuously enhancing their networks by deploying newly developed wireless technologies. In order to reduce the deployment costs, the operators try to reuse as many components of the existing networks as possible. This includes the possibility of reusing base station sites in order to reduce costs such as site rental, site acquisition, and backhaul connectivity. In this paper, we model the problem of base station co-siting as a nested mixed integer optimization problem in order to optimize target objectives that are a function of performance and cost. The formulated problem takes as input an area of interest with existing fixed sites and obtains as output the optimal number and locations of required sites including newly deployed and co-sited with the fixed sites. The goal is to minimize the deployment cost of the new network by reusing as many existing sites of the existing network as possible while guaranteeing that the outage probability is below a target threshold. We propose and implement an algorithm to solve the formulated optimization problem as a function of the mobile station distribution and the existing fixed site locations. A UMTS/GSM co-siting scenario is used as a case study in order to evaluate the performance of the proposed algorithm. Results show that the optimal solution depends on the mobile station distribution and the existing sites in addition to a threshold parameter that provides a tradeoff between the deployment cost and the outage probability.