Ad Hoc Assisted Handoff for Real-time Voice in IEEE 802.11 Infrastructure WLANs

IEEE 802.11 WLANs are increasingly used to support Realtime services such as voice and video. Reliable portable operation however, is often difficult due to factors such as imperfect customer access point (AP) installation, unpredictable WLAN coverage, and unexpected cochannel interferers. In this paper we propose and investigate the use of IEEE 802.11 Ad Hoc Assisted Handoff (AAHO). In AAHO, a single additional ad hoc hop may be used by a mobile station (MS) to obtain the range extension or channel quality needed to maintain its Realtime voice connection. There are three versions of IEEE 802.11 AAHO. In 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 Forward Ad Hoc Assisted handoff (FAAHO) 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 the two and allows an MS to perform either BAAHO or FAAHO. The proposed AAHO designs are backward compatible, and thus can be implemented as a transparent overlay across existing IEEE 802.11 infrastructure deployments. Performance results show that AAHO can greatly improve performance in many practical situations.