Joint optimization of 2-tier dual-homing for NodeBs and RNCs in UMTS networks using meta-heuristic techniques

Conventional design of UMTS networks usually involves single-homing (i.e., many-to-one mapping) of NodeBs to Radio Network Controllers (RNCs) in tier-1 (i.e., a group of NodeBs is connected to a single RNC) and that of RNCs to Mobile Switching Centres (MSCs) as well as to Serving GPRS Support Nodes (SGSNs) in tier-2 (i.e., a group of RNCs is connected to a single MSC/SGSN). Thus, any NodeB is connected to only one RNC and any RNC is connected to only one MSC/SGSN. However, as subscriber distribution changes over time and new mobility patterns of subscribers begin to evolve, single homing solution sometimes becomes inefficient in terms of handoff cost minimization. One solution to this brown-field operational problem is dual-homing extension of some selected NodeBs and RNCs (i.e., some NodeBs are connected to two RNCs in tier-1 and some RNCs to two MSCs/SGSNs in tier-2) in order to reduce the handoff cost. Traditionally, this optimization problem has been formulated separately for each tier and solved independently, thereby missing the global optimal solution. In this paper, we have first shown how to combine the optimization problems across the two tiers and then mapped the joint dual homing optimization problem into a classical search problem. Next, we have used two common meta-heuristic techniques, namely Simulated Annealing and Tabu Search, to solve the above problem. Comparison of the results obtained from joint dual homing with the published results for individual dual homing reveals that the joint dual homing performs considerably better than individual dual homing that attacks NodeB level and RNC level separately and independently.