Load balancing with cell breathing to maximize the system reward in mobile WiMAX

Worldwide Interoperability for Microwave Access (WiMAX) supports high bandwidth, broadband access, mobility, and Quality of Service (QoS) guarantee. Load balancing is required due to uneven distribution of traffic among different WiMAX base stations (BS) as well as mobility of WiMAX Subscriber Station (SS). Cell breathing is a well-known load balancing technique adopted in wireless networks. By changing transmission power of base stations, the technique is able to adjust traffic load of base stations. However, overloaded traffic cannot be alleviated by cell breathing without proper Call Admission Control (CAC). In this paper, we propose a directional cell breathing (DCB) mechanism combined with a Markov Decision Process based (MDP-based) CAC for achieving both load balancing and system reward maximization. In our approach, the call admission control problem is formulated as a Markov decision process such that the long-term reward loss rate can be calculated efficiently. Each BS then can adaptively select a proper power level for each of its directional antennas to minimize the long-term reward loss rate. We demonstrate the performance of our approach via simulations. The simulation results show that our approach provides an effective solution to achieve load balancing and reward maximization.