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The IEEE 802.16e standard provides quality of service (QoS) for real-time traffic; however, packet transmission disrupted by the handover (HO) process is still a big concern, particularly when frequent HO is performed by mobile stations (MSs) with high mobility. Therefore, an HO scheme that supports frequent HO and provides short service disruption time (SDT) is necessary for providing QoS to real-time traffic. In this paper, we present a novel network architecture, which complies with the IEEE 802.16e standard, to support seamless frequent HO, particularly for MSs with high mobility. Based on this architecture, a network-assisted fast HO (NFHO) scheme is proposed to shorten SDT during the HO process. By resolving connection identifier (CID) assignment and uplink (UL) timing adjustment issues, the proposed NFHO scheme can restart both the UL and downlink (DL) packet transmissions before the MS proceeds to the HO ranging, which is a unique feature of our scheme. In addition, based on the NFHO scheme, an analytic model has been developed to investigate the expected number of buffered packets, packet loss probability, and SDT during HO. Performance evaluation results show that the NFHO scheme reduces the DL SDT by 75%, compared with the IEEE 802.16e hard HO scheme, and it also reduces the UL SDT by 55.6% and 75% compared with the work of Jiao and the IEEE 802.16e hard HO scheme (also the work of Choi ), respectively. In addition, the proposed NFHO scheme has the best performance in terms of expected number of buffered packets and packet loss probability among existing hard HO schemes for the IEEE 802.16e. Furthermore, our analytic model can be integrated into an admission-control policy to guarantee proper QoS for ongoing HO MSs.
Date of Publication: Feb. 2010