Browsing by Author "Chen, Hung-Hsi"

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Network selection with joint vertical and horizontal handoff in heterogeneous WLAN and mobile WiMax systems
(2007)
Wang, Li-Chun
;
Chen, Anderson
;
Chen, Hung-Hsi
;
電信工程研究所
;
Institute of Communications Engineering
As the IEEE 802.11 wireless local area networks (WLANs) have become very popular and the emerging IEEE 802.16e wireless metropolitan area networks (WMANs) also attract a great deal of attentions, in the future we can expect the appearance of the hybrid IEEE 802.11 WLANs and IEEE 802.16e WMANs systems. Clearly, seamless handoffs in this hybrid network will become an increasingly important issue. However, the system which has shortest handoff latency may not always have the highest throughput. In this paper, we develop a dynamic network selection scheme to determine the connecting system in a new "WLAN to hybrid WLAN/WiMax" handoff scenario, in which we consider both the vertical and horizontal handoffs. The proposed scheme requests the station to wait an additional network selection time "t(w)" before the selection to maximize the amount of delivered bits during a dwelling time. We also formulate an optimization problem to find the optimal network selection time t(w)(*) and show that the proposed scheme can improve the delivered information bits during handoff.
Optimal Channel Search Time for Handoff in the IEEE 802.11 WLANs
(2006)
Wang, Li-Chun
;
Chen, Hung-Hsi
;
Chen, Anderson
;
Chan, Chung-Ju
;
交大名義發表
In recent years, the IEEE 802.11 wireless local area networks (WLANs) have become a very popular access network technique. However, due to the large handoff latency, most application scenarios are limited to hot spot areas without handoff across different access points (APs). As the advance of many real-time or highly interactive applications such as voice over IP (VoIP), one of burning issues for the WLAN is to reduce the handoff latency. Current studies in the literature have indicated that the latency in searching available APs dominates the handoff latency. Thus, we propose a simple analytical model to calculate the search latency and success probability for the handoff in the IEEE 802.11 WLAN. A new performance metric, namely the "effective search time (EST)", is introduced to evaluate the latency that is required for a station to successfully search a channel from neighboring APs. Based on the developed model, the optimum numbers of the probe request and response transmission for minimizing the EST can be obtained. Our results demonstrate that, in the environment of 100 contending stations, the EST with optimum number of transmissions can be reduced by 30% compared to that in the legacy IEEE 802.11 WLAN.