A novel terminal-controlled handover scheme in heterogeneous wireless networks

Abstract

In the next generation heterogeneous wireless networks, a mobile terminal (MT) with a multi-interface may have network access from different service providers using various technologies. In spite of this heterogeneity, seamless intersystem mobility is a mandatory requirement. One of the major challenges for seamless mobility is the creation of a vertical handover scheme, which is for users that move between different types of networks. In this article a seamless mobility handover scheme is presented. The novelty of the proposed scheme is that handover is fully controlled by the terminal. To improve the performance of the proposed handover scheme, a network discovery algorithm with fuzzy logic and a handover decision algorithm using multi criteria decision making (MCDM) based on vague sets are derived, which are both user-centric. With these algorithms, the handover scheme is power-saving, cost-aware, and performance-aware. Simulation results show that the novel handover scheme can perform network discovery in time to reduce handover dropping rate and present unnecessary activation of its interface to save the battery power, while effectively choose the optimum network through making trade-off among the user preference, network condition, and system performance.

Introduction

Continued advances wireless technology has led to the use of mobile terminals (MT) with multiple interfaces to access various services in heterogeneous wireless networks. Future mobile users will be always best connected anywhere and anytime via diverse access technologies. One of the challenges for the future mobile communication systems is the integration of existing and future wireless technologies and supporting seamless handover between these heterogeneous networks.

In 2G and 3G wireless networks mobile-assisted handovers are used, where MT sends the measurement report to the network and the network makes the handover decision [1]. Handovers are usually carried out considering only one technology, and work efficiently in circuit switched networks. However, in IP-based heterogeneous networks, mobile-assisted handovers have some disadvantages. For example, in order to find an optimal network for a user, user preferences have to be considered, such as service prices in different domains and personal preferences. User preferences need to be sent to the network by signaling over the air, which increases the signaling overhead in the air, and also induces latency. Moreover, a user may be unwilling to disclose such information to the network, and potentially distrust the current network to find a cheaper network from its competitors.

The evolution toward next generation networks will necessitate a user-centric approach where users have greater control of their terminal behavior [2], [3]. In this paper, we propose a terminal-controlled handover (TCHO) scheme for heterogeneous wireless networks. Users can access different networks and services using a single device equipped with multiple radio interfaces. This will allow users to select preferred wireless access systems to maximize their profitability and improve their perceived quality of service (QoS). Moreover, the multi-interfaced terminal is in a strong position to make handover decisions since it has access to information relating to its capacity, user preferences and, most important, knowledge of neighboring access networks. Accordingly, the terminal will be able to select the most efficient access network in terms of user satisfaction and perform the handover in a highly scalable and flexible manner.

The proposed TCHO scheme comprises three stages:

Handover initialization: Discover all the available Radio Access Networks (RANs) in advance, and communicate with these networks for fetching the additional information.

Handover decision: Select the appropriate network based on the network information, application requirements, signal quality, and user preference.

Handover execution: Handover the session seamlessly to the chosen network.

Many works [4], [5], [6], [7] have indicated that the handover initialization step significantly affects handover performance. For instance, when a user moves in a heterogeneous wireless network environment, an MT must know the impending handover in time because the MT must take additional time to perform related network discovery procedures. If insufficient time is available for the MT to execute these procedures, the connection is disrupted. However, the issue of power-saving also arises in network discovery because unnecessary interface activation can increase power consumption. Therefore, activating and terminating an MT’s interfaces at appropriate times are important in network discovery to eliminate unnecessary power consumption and minimize handover dropping rate. In our proposed TCHO scheme, we derive a network discovery algorithm based on fuzzy logic, FLND, in Section 3, for a MT with multimode support in a wireless heterogeneous network environment. The basic idea of FLND is as follows: if the grade of satisfaction (GoS) of a user, irrespective stationary or mobile, in the current network is below a predefine threshold, it indicates that the current network maybe not the best network for the MT, so the MT must perform related network discovery procedure in advance. Otherwise, the MT can terminate the unused interface to save battery power since it unnecessary to initiate a handover to other networks. In FLND, the GoS is decided based on a fuzzy logic system, which takes both received signal strength (RSS) and the acquirable bandwidth (aBW) in the current network as input parameters. With this algorithm, a MT can activate and terminate its interfaces in a good time to reduce the handover dropping rate and unnecessary power consumption.

Traditional handover decision are related only with the link quality, such as Signal to Noise Ratio (SNR), while in next generation heterogeneous wireless networks, handover between different technologies and administrative domains is possible, and handover decision will be based on more criteria, such as the price of the service, QoS supporting, battery consumption, etc. Facing multiple criteria during handover decision, we can no longer easily rank the candidate networks according to our preference on a single criterion. In such cases, different criteria have to be combined and scaled in a meaningful way. The problem mentioned above can be identified as a MCDM problem, which has been an active area of research. A simple policy-enabled handover system across heterogeneous wireless networks is presented in [8], which allows users to express policies on what is the best wireless system at any moment, and make trade-offs among network characteristics such as cost, performance, and power consumption. Ref. [9] has proposed the combined application of analytic hierarchy process (AHP) and Grey system theory in an algorithm for network selection between Universal Mobile Telecommunications System (UMTS) and wireless local area networks (WLANs). A unique decision process that uses non-compensatory and compensatory multi-attribute decision-making algorithms jointly on the network side to assist the terminal to select the top candidate network(s) is proposed in [10]. However, those ideas are only presented by general description without details on how various contextual settings and parameters work in the algorithm. In the proposed TCHO scheme, we present a handover decision algorithm using MCDM based on vague sets, in Section 4, which is an easy and indisputable method suitable in heterogeneous networks.

The rest of paper is organized as follows: The overall TCHO scheme is described in Section 2. In Section 3, the fuzzy logic based network discovery algorithm is derived. The handover decision algorithm using MCDM based on vague set is proposed in Section 4. We evaluate the performance of the TCHO in Section 5 and conclude the paper in Section 6.