A Measurement-Based Study of WLAN to Cellular Handover

Smadi, M.N.; Azhari, Vahid; Todd, T.D.

doi:10.1109/mobhoc.2006.278643

Cited by 5 publications

(6 citation statements)

References 5 publications

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“…The study in [2] reports on propagation measurements taken of handsets moving at pedestrian speed when exiting WLAN building hotspots. As noted in the study, these indoor-to-outdoor transitions can be very abrupt, resulting in a rapid loss of WLAN coverage.…”

Section: The Vertical Handover/wlan Bandwidth Dilemmamentioning

confidence: 99%

“…This occurs when a mobile station moves rapidly out of WLAN coverage (such as when leaving through a building exit [2]), causing the WLAN link to quickly rate-adjust itself to low bit rates. If the cellular call leg cannot be created in time (as is typical in loosely coupled VHO), then for a short period during the handover execution, the call may occupy a high fraction of the total WLAN bandwidth.…”

Section: Contributionsmentioning

confidence: 99%

“…Exiting the indoor region results in a VHO if a MS has an active voice call. The latency of a VHO is chosen to be 3 seconds [2]. In this study we focus exclusively on a WLAN carrying real-time voice calls.…”

Section: The Problem With Static Bandwidth Reservationmentioning

confidence: 99%

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The bandwidth deficit problem in loosely coupled WLAN-to-cellular vertical handover

Azhari

Smadi

Todd

2007

Proceedings of the 2007 International Conference on Wireless Communications and Mobile Computing

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Seamless WLAN-to-cellular handover is often difficult to achieve, since WLAN coverage can often be lost very quickly. Recent results have shown that successful handover may require that the WLAN link be allowed to rate-adjust itself to very low values (e.g., 1-2 Mbps) before the vertical handover is completed. When this occurs the call temporarily occupies a WLAN bandwidth far higher than the value for which it was originally provisioned. This effect is referred to as the vertical handover bandwidth deficit problem. In this paper we consider the effects of the bandwidth deficit problem on system performance, and how the problem can be mitigated. It is shown that this bandwidth demand can result in significant vertical handover dropping due to a lack of bandwidth on the WLAN access point. A static bandwidth reservation scheme motivated by the classical cellular guard channel approach is first considered and is found to result in an unacceptable increase in the WLAN new call blocking rate. A novel transient bandwidth reservation scheme accompanied by a momentary forced handover mechanism is proposed to overcome the shortcomings of the static approach in multiple AP WLANs. Our presented results show that almost two orders of magnitude reduction in the vertical handover dropping rate can be achieved while maintaining an acceptable new call blocking rate at the WLAN AP.

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Section: The Vertical Handover/wlan Bandwidth Dilemmamentioning

confidence: 99%

Section: Contributionsmentioning

confidence: 99%

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The bandwidth deficit problem in loosely coupled WLAN-to-cellular vertical handover

Azhari

Smadi

Todd

2007

Proceedings of the 2007 International Conference on Wireless Communications and Mobile Computing

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“…At the same time, the link with the cellular BS must be established for a seamless communication. Unfortunately, the measured data in [2] points out that the successful access probability for A to connect to the cellular BS is usually less than 92%, which means interruptions will be occur a lot during this insufficient handover time.…”

Section: B the Modelmentioning

confidence: 99%

“…But the communication interruptions, especially the long interruptions occurring during crossing the heterogeneous wireless environments, make learners feel frustrated and lose their interests, which in turn resulting in inefficient learning. From the measured values presented in [2], we can see that, in many cases however, seamless handover between heterogeneous wireless environments can be very difficult to achieve. WLAN link may be lost long before a cellular call leg can be triggered and established when learners walk from indoor building WLAN coverage to outdoors during discussing with tutor by a multimodal wireless devices.…”

Section: Introductionmentioning

confidence: 99%

Collaborative handover support in a heterogeneous wireless environment for real-time communication in mobile learning

Yan

Cheng

et al. 2007

TENCON 2007 - 2007 IEEE Region 10 Conference

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Due to the thriving of mobile network and portable device, distance learning is evolved from desktop computer to mobile device. Real-time handover is a very important capability for mobile learning devices since the interruptions caused by handover make learners feel frustrated and lose their interests, which in turn resulting in less engagement in mobile learning. In this paper, we propose a collaborative seamless handover approach, called LCSH, suitable for real-time communications between heterogeneous wireless environments. LCSH takes not only spatial factors into account but also the potential benefits of collaborative work given by adjacent mobile nodes which can be identified by the spatial location information. Simulations show that LCSH consistently outperforms existing handover policies and significantly extends mobile clients' uninterrupted communication.I.

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Dynamically anchored conferencing handoff for dual-mode cellular/WLAN handsets

et al. 2007

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In this paper we consider vertical handoff for enterprise-based dual-mode (DM) cellular/WLAN handsets. When the handset roams out of WLAN coverage, the DM's cellular interface is used to maintain the call by anchoring it through an enterprise PSTN gateway/PBX. Soft handoff can be achieved in this case if the gateway supports basic conference bridging, since a new leg of the call can be established to the conference bridge while the existing media stream path is active. Unfortunately this requires that all intra-enterprise calls be routed through the gateway when the call is established. In this paper we consider a SIP based architecture to perform conferenced dual-mode handoff and propose a much more scalable mechanism for short-delay environments, whereby active calls are handed off into the conference bridge prior to the initiation of the vertical handoff. Results are presented which are taken from a dual-mode handset testbed, from analytic models, and from simulations which characterize the scalability of the proposed mechanism.

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A Measurement-Based Study of WLAN to Cellular Handover

Cited by 5 publications

References 5 publications

The bandwidth deficit problem in loosely coupled WLAN-to-cellular vertical handover

The bandwidth deficit problem in loosely coupled WLAN-to-cellular vertical handover

Collaborative handover support in a heterogeneous wireless environment for real-time communication in mobile learning

Dynamically anchored conferencing handoff for dual-mode cellular/WLAN handsets

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