Article Abstract

	Title:	Ad hoc assisted handoff for real-time voice in IEEE 802.11 infrastructure WLANs
	Author:	Ming He, Xiaofan Wang, Terence D. Todd, Dongmei Zhao, Vytas Kezys
	Address:	LCC International, Inc., 7900Westpark Drive, Suite A-315, McLean, Virginia 22102, USA. ' PacketHop, Inc., 333 Ravenswood Avenue, Menlo Park, CA, USA. ' Department of Electrical and Computer Engineering, ITB-A324, McMaster University, Hamilton, Ontario L8S 4K1, Canada. ' Department of Electrical and Computer Engineering, ITB-A324, McMaster University, Hamilton, Ontario L8S 4K1, Canada. ' Research in Motion Limited, 305 Phillip Street, Wateerloo, Ontario N2L 3W8, Canada
	Journal:	International Journal of Wireless and Mobile Computing 2007 - Vol. 2, No.4  pp. 324 - 336
	Abstract:	In this paper we propose and investigate the use of IEEE 802.11 Ad Hoc Assisted Handoff (AAHO), where a single additional ad hoc hop may be used by a Mobile Station (MS) to obtain range extension or channel quality needed to maintain its real-time voice connection. There are the 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 access point that the MS is using. In Forward Ad Hoc Assisted Handoff (FAAHO) the additional hop uses a relay station whose access point is different from the one that the MS is currently associated with. 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, in that they can be implemented as a transparent overlay across existing IEEE 802.11 infrastructure deployments. A relaying mechanism is introduced which permits stations to control the real-time relaying of voice packets between the channels. An analytical model is developed to study the performance of the proposed AAHO schemes based on a simplified system model. Detailed simulation results show that AAHO can greatly improve the handoff connection dropping probability for an IEEE 802.11-based WLAN with incomplete AP coverage and relatively fast moving MSs and HAAHO can achieve even better performance than BAAHO. Our results also show that the proposed AAHO schemes can maintain good real-time performance, in terms of packet transmission delay, for voice transmissions.
	Keywords:	ad hoc networks; IEEE 802.11; ad hoc assisted handoff; AAHO; real-time voice; WLANs; wireless LANs; local area networks; wireless networks; range extension; channel quality; simulation; transmission delay; voice transmission.
	DOI:	10.1504/IJWMC.2007.016725
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