Research On Fast Handoffs In WLAN

In public areas such as airports, hotels, universities and shopping centers, wireless networks, especially those based on the IEEE802.11 standard (Wi-Fi), have already been successfully deployed. When people are working in WLAN (Wireless Local-Area Network), the demands of mobility and multimedia applications are increasing. Therefore, fast handoffs play an important role in WLANs to guarantee QoS, but which are not specified in IEEE802.11WLAN. The latency caused by handoff can not satisfy the delay requirement of real-time multimedia applications. In this paper, we focus on the research on fast-handoffs algorithms and schemes.First, we study the mobility of IEEE802.11 WLAN in details. The latency caused by handoff consists of the following parts: probe latency, authentication latency and (re)association latency. This paper is devoted to the study and analysis the algorithms and schemes for reducing the last two latencies.In the part of reducing probe latency, precisely we introduce three fast probe algorithms, i.e, NG, NG_Pruning, and GPS_NG algorithms. NG_Pruning algorithm is an improved NG algorithm with the concept of non-overlap graphs, and GPS_NG algorithm is another improved one with GPS information. Finaly, we compared these three algorithms by simulations with OPNET10.0 software. The simulation results demonstrate that GPS_NG algorithm can remarkably reduce the probe latency.In terms of reducing the (re)association latency, we propose a new fast (re)association scheme that is suitable for multimedia applications. We introduce a concept of WD, that is the transmit periods of WN frame. Also, we modify the calculation of P_re, the probability of the additional retransmission time. We compare this new scheme with IEEE802.11 (re)association scheme through numerical calculations, and also provide some helpful discussions on the fast (re)association of multimedia applications.