Ad Hoc Assisted Handoff in IEEE 802.11 Infrastructure WLAN s

Abstract

<p>IEEE 802.11 wireless local area networks (WLANs) are increasingly used to support real-time services such as voice and video. Reliable and portable operation, however, is often difficult due to factors such as imperfect customer access point (AP) installation, unpredictable WLAN coverage, and unexpected co-channel interference.</p> <p>There has been much recent activity that considers the combination of ad hoc relaying and infrastructure wireless networks as alternative solutions to coverage extension. In this thesis, we propose and further investigate the use of IEEE 802.11 Ad Hoc Assisted Handoff (AAHO). In AAHO, an additional ad hoc hop may be used by a mobile station (MS) to obtain the range extension or channel quality needed to maintain its real-time voice connection. An MS that is currently not carrying active traffic may offer itself as a potential relay station (RS). Three versions of IEEE 802.11 AAHO are discussed in this thesis. In the case of Backward Ad Hoc Assisted Handoff (BAAHO), the additional hop uses a relay station which already has an IEEE 802.11 association with the AP that the MS is using. In the case of Forward Ad Hoc Assisted Handoff (FAAHO), however, the additional hop uses a relay station whose AP is different from the one that the MS is currently using. Hybrid Ad Hoc Assisted Handoff (HAAHO) is a combination of these two concepts that allows an MS to perform in either BAAHO or FAAHO mode. The proposed AAHO schemes are backward compatible to existing IEEE 802.11 infrastructure. They can be implemented as a transparent overlay across existing IEEE 802.11 deployments. Two implementation options for achieving this compatibility are proposed. A criterion in selecting relay station is introduced, which permits mobile stations to control real-time relaying of voice packets. Our simulation results show that AAHO can greatly improve performance in many realistic situations.</p>