An optimized algorithm for vertical handoff in heterogeneous wireless networks

In a heterogeneous network consisting of diverse wireless access standards, vertical handoff (VHO) plays a major role in handling seamless data transfer. Vertical Handoff decision is based upon Received Signal Strength (RSS) measurements, where handoff (HO) decision is made individually without considering other HO user equipments (UE). This results in higher block rate and power consumption at the mobile devices. User mobility is an important factor that is to be considered in VHO decision, i.e., VHO is required only at lower speeds, and since high speed user velocity may cause unnecessary handovers that can degrade system capacity and QoS level. By considering UE velocity also, in making a HO decision, we can reduce the transmission cost and transmission time. This paper adopts the mathematical model based VHO prediction approach comprising a well defined objective function considering RSS, UE velocity, load and cost per user bandwidth. The system performance can be enhanced according to the user preferences by adjusting the weights in the defined objective function. Due to the high bandwidth and ease of networking we consider the wireless access standards: Wi-Fi and Wimax. The propagation model considered in this paper is Jake´s model. The algorithm is simulated in MATLAB and the performance of the network is evaluated in terms of user velocity and handover numbers.