Research On Vertical Handover For Multi-mode Intelligent Terminal In Heterogeneous Wireless Networks

Over the past decade, various wireless communication technologies and network systemsprovided mobile session and data transmission services users respectively, and mobile terminalgradually become diversification, intelligent, multi-mode and other trends. For fully utilize andintegrate various wireless access resources to optimize the user’s QoS, the next generationmobile communication systems will be a coexistence with different formats, and supportmoving of wireless terminal in heterogeneous wireless converged network.The vertical handoff technology is the basis of operator for heterogeneous wirelessnetwork, it is said that mobile users can maintain wireless session during handover phasebetween different wireless access technologies according to the wireless environment and thetype of business. Vertical handover technology is still in the phase of theoretical research, as itrelates to different operators, network architecture and bearer mode, the traditional handovermechanism used in heterogeneous wireless networks will cause higher rate of call drop andpacket loss, and longer handover delay. So, it is necessary to seek more flexible and efficientvertical handover mechanisms and performance optimization algorithm to meet the dual needsof mobile users’ high transmission rate and high QoS.The specific implementation of the vertical handover process involves protocol layersfrom the link layer to the application layer. In this paper, we mainly focus on the verticalhandover technique of multi-mode intelligent mobile terminals in heterogeneous wirelessnetworks. We use cross-layer design theory, cooperative diversity, mobility predictiontechnology, connection management mechanisms comprehens ively to enhance the verticalhandover performance, by means of reducing the packet loss rate and handover relay time, andimproving the wireless resource utilization during the handover process. The research topicsinclude network selection, link layer handover prediction mechanism, and handoveroptimization protocol in network layer and transport layer.Aiming at the imperfect computation of attribute weight and lower recognizableproblem, a network selection algorithm based on intuitionist fuzzy multiple attribute decisionmaking was proposed. The decision attribute values are given in the form of intuitionist fuzzynumbers, and according to the current business type of mobile terminal, two cases are proposedto solve attribute weighting factor. When the business type is single, we transform the probleminto fuzzy multiple attribute decision making with partly-known weights information accordingto the QoS requirement, and use λ fuzzy measure to represent attribute weight, combine withsubjective weight obtained from analytic hierarchy process, and finally sorted the candidatenetworks. When the business type non-single, it is converted to weight completely unknown fuzzy multi-attribute decision making problems, we describe attribute values usinginterval-valued intuitionist fuzzy numbers, and solve the objective weight vector bycomputing the total relative entropy between attributes, and finally sort the candidate networksbased on score function or precise function of interval-valued intuitionist fuzzy numbers.Aiming at how to determine the best link-layer handover trigger time to minimizepacket loss rate at all times, a gray prediction-based link layer switch trigger algorithm wasproposed. Firstly, we established gray prediction model for the state parameters of the link layer,then determine the prediction step by estimating the handover required time. Based on spacepropagation model of the wireless link, we analyze packet loss probability before and afterhandover, and solve the most appropriate handover trigger time using convex optimizationtheory. We also proposed a media independent handover optimization mechanism base onenhanced information services. For quickly receive the information of link layer, we extend thefunctionality of MIIS(media independent information services) entity refer to MIH(mediaindependent handover) architecture, which can provide real time state parameters of link layerto mobile terminal in the form of four-tuple. We also given the update mechanism of serviceinformation, and estimation algorithm of link state parameter, which can be used to reduce scantime of terminal in handover preparation phase.Aiming at the network layer handover delay time is too long for inter-domain handoverin hierarchical mobile IPv6protocol, a network layer handover mechanism based on timethreshold and cooperative diversity was proposed. We selected appropriate relay node (RN) byconsidering the possible connection time between mobile terminal and RN, and dwell time ofRN within new access network. RN can operate pre-handover instead of mobile terminal tocomplete the configuration and duplicate detection for LCoA(link Care-of address) and RCoA（Regional Care-of Address）; When start to link layer handover, RN can execution bindingupdate at the same time, and reducing network layer handover delay time; After completing thehandover, mobile terminal can build heterogeneous collaboration channel with new access pointby RN, and improve the quality of communication.Aiming at longer handover interruption time and binding update delay for T-PHMIPv6,a inter-domain handover mechanism based on dual direction cooperative node was proposed.When mobile terminal complete link layer handover according to T-PHMIPv6, it need to waitthe binding update operation at network layer, which may cause longer link down time. ByB-CDHO mechanism, mobile terminal firstly probe a forward-Relay node (fRN) within newaccess point, which can get LCoA and RCoA instead of mobile terminal before handovertrigger; When link is going down, mobile terminal can also probe a backward-Relay node (bRN)within current access point, by which to extend connection time with current access point, then mobile terminal can receive date on new link after completing binding update immediately, andreduce the packet loss during handover.Aiming at the problem of transport layer vertical handoff delay is too long, and datathroughput decrease suddenly during handover using SCTP protocol, a handover algorithmbased on MIH and bandwidth estimation was proposed. we use cross-layer design of MIH,inform the link going down information to transport layer by mean of MIIS, and triggerdynamic address configuration process, to stop sending data from correspondent node oncurrent path; in addition, by estimate available bandwidth of new path, we can avoid slow startof congestion window after handover, and reduce the unnecessary retransmission because ofout-of-order through delay delivery mechanism. Proposed a mSTCP handover optimizationmechanism based on packet loss prediction (LP-mSCTP). Aiming at the fact that real-timeapplication can tolerate partial lose but do not allow longer transmission delay, LP-mSCTP canestimate the possible packet loss during primary path handover by computing move speed ofterminal and the require time of handover. Mobile terminal can inform corresponding node thepossible packet loss range before adding new IP address, and then corresponding node cantransmit these packets immediately after finishing handover, to reduce the packet loss becauseof handover for real-time application.