Dynamic Load Balancing Based on Sojourn Time in Multitier Cellular Systems

Efficient load balancing algorithm is indispensable to serve more mobile stations in the heterogeneous wireless networks. In this paper, we propose a dynamic load balancing algorithm based on sojourn time for heterogeneous multitier wireless networks consisting of macrocell cellular network and microcell cellular network. The sojourn time is calculated by the velocity, direction of motion and position of mobile station. This algorithm is able to balance load by transferring some ongoing calls with longer sojourn time from overloaded cells to overlapping under-loaded heterogeneous cells. The number of transferred ongoing calls per load balancing period is calculated by the new calls arrival rate of overloaded cells and the workload states of overlapping cells. In addition, high-speed mobile stations can hand off from macrocells to microcells and slow mobile stations can hand off from microcells to macrocells, which can decrease the call dropping probability. Simulation results show that call blocking probability, call dropping probability and overall system utilization using our proposed dynamic load balancing algorithm are improved significantly.