Handover delay in cellular wireless systems

Handover is the process by which a mobile terminal maintains a communication session as it crosses through the coverage area of the grid of base stations providing service in a cellular wireless system. Because of imperfect channel measurements, it is difficult to determine the correct point for a handover. Acting too soon may force a handover back to the original base station; delaying too long may make it impossible for the mobile to meet its quality of service objectives. It is important to quantify the handover delay in terms of various system parameters in order to efficiently design cellular wireless communication systems. This paper presents an exact expression for handover delay as a function of the base station separation, the standard deviation of log-normal shadowing, and the averaging distance. It also presents a simple closed form approximation that includes the hysteresis margin. These are the first such expressions available within the literature. The approximation is validated via simulation and is shown to work well over the range of interest.