Optimization of vertical handover decision processes for Fourth Generation heterogeneous wireless networks

Abstract

This thesis presents a vertical handover decision (VHD) scheme for optimizing the efficiency of vertical handover processes in the Fourth Generation (4G) heterogeneous wireless networks. The scheme consists of three closely integrated modules: Handover necessity estimation, handover target selection, and handover triggering condition estimation. Handover necessity estimation module determines whether a handover is necessary to an available network. Handover target selection module chooses the "best" network among the available candidates based on a set of criteria. Finally, handover triggering condition estimation module determines the right moment to initiate a handover out of the currently connected network.4G wireless networks are expected to support mechanisms for tight integration and cooperation of divergent access network technologies. In such networks of heterogeneous nature, roaming users will experience frequent handovers across network boundaries. Thus, to ensure seamless roaming and efficient resource usage over dissimilar networks, intelligent VHD algorithms need to be used extensively. The research project presented in this thesis report focuses on this problem and provides an optimized VHD scheme, which minimizes the handover failures, unnecessary handovers and connection breakdowns whilst maintaining users' satisfaction at high levels. In addition, the scheme also provides mechanisms for mobile applications to control the tradeoff between the usage of the preferred access network and number of handovers or connection breakdowns.Simulation based performance evaluations demonstrate that the scheme reduces the number of handover failures, unnecessary handovers and connection breakdowns by up to 80%, 70% and 70%, respectively. They also show an increase of up to 50% in the satisfaction level of users.

A novel travelling time estimation mechanism for minimizing unnecessary handovers from cellular networks to WLANs

“…The tolerable unnecessary handover probability ( uh ) has been preset at 0.04, WLAN cell exposure radius at 150m [7], 1 In [11 -13], the mathematical expression illustrated for PDF of is: ( ) = 1 1 2 , 0 2 wherein, absolute interior difference angle is erroneously assumed in [0, 2 ], as can never be greater than 2 PDF of traversal time (in a WLAN coverage area) obtained in [13] was ( ) = 2 4 2 2 2 , 0 2 and the handover latency and at 1s.…”

“…Moreover, if handover process is not accomplished before MT moves out of the WLAN boundary, the connection failure becomes unavoidable [9 -10]. In [13], a geometrical framework for the handover necessity estimation for MT traversing from a 3G network into a WLAN cell has been illustrated for reducing probabilities of handover failures and unnecessary handovers. The framework is based on the angle of arrival and departure, however, the absolute interior difference between angles is erroneously considered between [0, 2 ], which led to the mathematical imperfections in the estimation of distance (threshold) parameters.…”

A new method for handover triggering condition estimation

“…Owing to [4], we assume that angles of arrival (Φ i ) and departure (Φ o ) for an MT in a WLAN coverage area are uniformly distributed. We have 0 …”

Improving Vertical Handoffs Using Mobility Prediction

“…When a MT starts moving away from its connection-providing device, another device that covers the new location of the MT is needed. The process of moving a MT's communication session from an access technology device to another in order to ensure the continuity of the connection without affecting the ongoing session is called handoff [18], [21]. Two types of handoff are commonly discussed in the literature: (i) horizontal handoff, which occurs when the MT moves from one access point to another within the same wireless technology, and (ii) vertical handoff, which occurs when the MT moves from one access point to another access point that belongs to different wireless technology.…”