WLAN-WiMAX Vertical Handover Hybrid Satisfaction Mechanism Mohammed Shakil University of Jordan Amman, Jordan m.shakil@ju.edu.jo Nizar Zorba Iquadrat Barcelona, Spain projects@iquadrat.com Cosmas Adam MTN Nicosia, Cyprus cadam@mtn.com.cy Christos Verikoukis CTTC Barcelona, Spain cveri@cttc.es Abstract— Handover is the key enabling option to guarantee seamless mobility within any wireless communication system, where the inter-systems handover option has recently acquired large importance, both in the research and commercial fields. The motivation behind the vertical handover can be either based on the user demands to achieve larger data rates or lower service delays, but also it can be operator-based to balance the system load or to increase the system coverage. This paper presents a hybrid technique for vertical handover where both the operator satisfaction and the user satisfaction are concerned whenever a vertical handover is to be accomplished. Results are presented for the system behaviour with and without the proposed handover mechanism. I. I NTRODUCTION The capability of switching between the different access technologies will provide a service added feature, as the user will select the most suitable technology in each location and for each application [1]. Such capability is widely known as the handover mechanism that has been a long time ago implemented in cellular systems, to allow the user to move over a large geographical area without any drop in the voice connection, and always within its network. The heterogeneity of different wireless access systems has motivated the search for a modified version of the handover mechanism, where the user can handover to different net- works based on the coverage, data rate, price per Megabyte, scheduling delay-jitter, etc. Such a kind of handover is named the Vertical Handover (VHO) approach [2] [3] that can be considered within the main wireless technologies as IEEE 802.11 WLAN, IEEE 802.16e WiMAX, 3G and 4G, among others. The motivation behind any vertical handover technique must stand on the benefits from 2 main points of views: Customer interests and Operator interests. Several algorithms appear in literature to present the proposals to deal with either one of the two approaches, where the customer benefit-based techniques may collide with the operator benefit-based strategies, and vice versa. Therefore, for any handover proposal to succeed in realistic systems, a joint consideration of the interests of both parties should be tackled. From the user part, the benefit from handover is presented in an improvement of the obtained Quality of Service (QoS) and data rate, and as long as the user is satisfied with its QoS, it is not interested in searching for another access technology through a handover mechanism, that can lead to a connection failure (remind that handover success probability is not 100%). The user satisfaction is shown to be based on thresholds [4] [5]. Regarding the minimum rate requirement per user, several studies have shown that the user satisfaction is insignificantly increased by a performance higher than its demands, while on the other hand, if the provided resources fail to guarantee its requirements, the satisfaction drastically decreases [6]. Therefore, the best scheduling approach is to deliver each user with its exact requirements, and do not allow for vertical handover unless its demands are not satisfied. There are some predefined properties for each access tech- nology and its usage/load. While WLAN is known to offer very large data rates, it lacks the control on the delay and its coverage is smaller than WiMAX. On the other hand, the latter shows wider coverage at lower data rate than WLAN, but a stricter control on the delay is accomplished [7]. As an example, if a user wants to run an online game, then the delay- jitter is its main requirement that motivates the user to move to WiMAX, while in the case of an FTP application, WLAN seems to be the most useful option. Not only the user benefits from the VHO mechanism, but also the operator does. The benefits for the operator from the handover procedure can be presented in terms of a load balancing among the different cells and/or access technology, so that if some cell is saturated with users/rate, the system can redistribute some of the users to other access networks [8]. This paper tackles the two above benefits at the same time, and a joint metric is proposed to include both the user and operator satisfactions. Such a metric will indicate VHO mechanism to start or not, providing the system designer with the ability to offer both advantages at the same time, where the metric can be even modified to account for one single objective. The rest of the paper is organized as follows: while Section II presents the system model employed along the paper, Section III introduces the VHO proposed mechanism with the presentation of the joint metric. Section IV tackles the simulations to show the system performance with the proposed technique to end with the paper conclusions in section V.