Abstract
The next generation of mobile/wirelesscommunication systems is expected to includeheterogeneous broadband wireless networks that willcoexist and use a common IP core to offer a diverserange of high data rate multimedia services to endusers with contemporary mobile devices that areequipped with multiple network interfaces since thenetworks have characteristics that complement eachother. This requires the provision of seamless verticalhandoff. This paper provides components of anadaptive multiple attribute vertical handoff decisionalgorithm that enables access network selection at amobile node. A performance study using theintegration of wireless wide area networks (WWANs)and wireless local area networks (WLANs) as anexample shows that our proposed vertical handoffdecision algorithm is able to determine when a handoffis required, and selects the best access network that isoptimized to network conditions, quality of servicerequirements, user preferences, and service cost.
1. Introduction
The next generation of mobile/wirelesscommunication systems is expected to includeheterogeneous broadband wireless networks that willcoexist and use a common IP core to offer a diverserange of high data rate multimedia services to end userssince the networks have characteristics thatcomplement each other. For example, given thecomplementary characteristics of 802.11x WLAN(faster, high-bandwidth, lower-cost, short-distanceaccess) and third-generation (3G) cellular WWANsuch as Universal Mobile Telecommunications System(UMTS) (slower, higher-cost, long-range alwaysconnected access), it is compelling to combine them toprovide ubiquitous wireless access for users withcontemporary mobile devices that are equipped withmultiple network interfaces. The integration andinteroperation of these heterogeneous networksrequires the design of intelligent vertical handoffdecision algorithms (VHDAs) to enable seamlessterminal, personal and network mobility, and toprovide for continuity and transfer of existing sessions.A decision for vertical handoff may depend onseveral issues relating to the current network that themobile node is already connected to and to the networkthat it is going to handoff. Vertical handoff decisioninvolves a tradeoff among many handoff metrics, suchas network conditions, system performance, applicationtypes, power requirements, mobile node conditions,user preferences, security, and cost; that is, quality ofservice (QoS) parameters. Using these metrics involvesthe optimization of key parameters (attributes),including signal strength, network coverage area, datarate, service cost, reliability, security, battery power,and network latency. These parameters may be ofdifferent levels of importance to the vertical handoffdecision.In this paper, we present the design of a fuzzy logicbased vertical handoff initiation scheme involvingsome key parameters, and the solution of the wirelessnetwork selection problem using a fuzzy multipleattribute decision making (FMADM) algorithm. Inparticular, an optimum access network is selected usinga wireless network selection function defined onmultiple attributes. The remainder of the article isorganised as follows. In the next section we providerelated literature work. We introduce the componentsof the vertical handoff decision algorithm in section 3.Then the fuzzy logic handoff initiation algorithm ispresented in section 4. We explain the networkselection scheme using a wireless network selectionfunction in section 5. A numerical performanceevaluation of the vertical handoff decision scheme isgiven in section 6. Finally, we conclude the article

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