Handover Management In Next Generation Heterogeneous Wireless Networks

The development of handheld mobile terminals (MT) capable of operating over both cellular networks and the Wireless Local Area Network (WLAN) is an important step towards the evolution of next-generation integrated networks. The MT is enabled with the choice of selecting between the better of the two networks depending on its preferences and the availability of the networks. In the presence of both networks, the MT chooses to connect over the one that either provides a better quality of service (QoS), or incurs a lower cost or battery power consumption. The WLAN, when available in full strength, is usually the network of choice since it provides a better bandwidth and costs less. But while connected to the WLAN, an MT may experience signal strength degradation due to its mobility that can result in deterioration of the QoS, or even in loss of service. Therefore, a vertical (i.e. inter-network) handover to the cellular network needs to be triggered in due time to maintain the service. When the WLAN link is up again, the MT should quickly switch back to the WLAN in order to exploit its superior features. A handover process can be split into three stages: neighboring cell discovery and measurement, handover decision and handover execution.VHD algorithms help mobile terminals to choose the best network to connect to among all the available candidates. The design of this vertical handover algorithm and the development of a performance evaluation framework is the focus of this dissertation.Vertical handover decision (VHD) algorithms are essential components of the architecture of the forthcoming Fourth Generation (4G) heterogeneous wireless networks. These algorithms need to be designed to provide the required Quality of Service (QoS) to a wide range of applications while allowing seamless roaming among a multitude of access network technologies.There are various ways to classify VHD algorithms. In this dissertation, VHD algorithms are divided into four groups based on the handover decision criteria used and the methods used to process them.RSS based algorithms:RSS is used as the main handover decision criterion in this group.Bandwidth based algorithms:Available bandwidth for a mobile terminal is the main criterion in this group. In some algorithms, both bandwidth and RSS information are used in the decision process Cost function based algorithms:This class of algorithms combines metrics such as monetary cost, security, bandwidth and power consumption in a cost function and the handover decision is made by comparing the result of this function for the candidate networksUser-Centric Approaches:Among the different criteria that a vertical handover decision takes into account, user preferences, in terms of cost and QoS, are the most interesting policy parameter for a user-centric strategy.In This dissertation we first explores the problem of handover failure, and unnecessary handover during handover process. A new vertical handoff decision algorithm, handover necessity estimation (HNE), is proposed to minimize the number of handover failure and unnecessary handover in heterogeneous wireless networks. HNE proposed multi criteria vertical handoff decision algorithm based on two parts:traveling time estimation and time threshold calculation. The proposed methods are compared against two other methods:(a) the fixed RSS threshold based method, in which handovers between the cellular network and the WLAN are initiated when the RSS from the WLAN reaches a fixed threshold, and (b) the hysteresis based method, in which a hysteresis is introduced to prevent the ping-pong effect.Next we investigate the problem of wastage of resource and connection breakdown during handover process. A handover should neither be triggered too late resulting in a connection breakdown, nor too early resulting in the wastage of available WLAN resource. Hence, a vertical handover triggering estimation (VHTE) method is introduced. This method attempts to estimate the optimal handover triggering point when a MT needs to initiate a handover back from a WLAN to a cellular network. VHTE provide the user with control over the tradeoff between connection breakdown probability and WLAN usage. In simulation results, the proposed methods are compared against two other methods; through simulation experiments with MATLAB, it is demonstrated that the VHTE algorithm is able to offer the flexibility of choosing either for increased WLAN usage or reduced probability of connection breakdown.Third, we develop an algorithm named User Preferences Handoff (UPHO). This method considers not only the traditional handover decision factor (RSS) but also user preferences, in terms of Cost, Quality, power consumption and user profiles. APBSW (Access Point Best Satisfied Weights) has been introduced for selecting access network; the proposed methods, UPHO (User Preference Handoff) use a fuzzy logic-based inference system to process all appropriate context information, which satisfy the best user preferences. The simulation result show that UPHO algorithm performs better than other handover decision algorithm in terms of user preferences satisfaction.Last, the limited available spectrum and the inefficiency in the spectrum usage necessitate a new communication paradigm to exploit the existing wireless spectrum opportunistically. This new networking paradigm is referred to as Dynamic Spectrum Access (DSA) or cognitive radio networks. We study the characteristics of cognitive radio, and proposed an algorithm to perform channel allocation among secondary users. The proposed schemes can load more power into SUs’band in order to achieve higher transmission capacity for a given interference threshold specified by the PUs’network...