Abstract
Handoff is a momentous process when a mobile station (MS) moves from one cell to another, the channel in the old base station (BS) is released, and a channel is required in the new BS. This process is called handoff. With the increasing demand of high mobility users in heterogeneous network, handoff is confronted with more and more challenges since user's mobility will affect the quality of link and interference levels in cellular systems. This paper analyzes the performance of two type handoffs soft handoff (SHO) and hard handoff (HHO) of wideband code-division multiple-access cellular system (WCDMA). The benefits and shortages of these two schemes are discussed. However, in practical systems, soft handoff provides robust communication away from call disconnection although it come from the expense of additional network resources and implemented cost. By way of contrast, hard handoff provides a efficient spectrum utilization, however the blocking probability is worse than soft handoff. Thus, there is a tradeoff between hard and soft handoff. We compare the performance of hard and soft handoff schemes. Based on this, we further propose a hybrid handoff scheme which combining two handoff schemes. Moreover, we apply symmetric designs (SD) and quasi-semisymmetric designs (QSSD) to arrange radio resource or frequency bands in difference base stations (BSs). In order to choose the optimum design parameters, we take mobile users' speed and the cost between hard and soft handoffs into account. Moreover, we transform this problem to an optimization problem and using genetic algorithm to solve it.