Reduction of handoff search phase time in IEEE 802.11 WLAN to fulfill real time services requirements

The performance of passive and active scanning is analyzed for wireless LAN, during handoff search phase based on the IEEE 802.11b standard. The performance analysis indicates that the active scanning method is faster and works well if the number of mobile stations is less than 15. Active scanning can reduce the search phase time to 55% compared to that of passive scanning, for 10 mobile stations in a cell. The timer MinChannelTime of active scanning is set to 1 ms and the MaxChannelTime timer is set according to the number of mobile stations allowed in the WLAN cell. We propose a technique in which a WLAN cell is aware of the number of mobile stations in the surrounding WLAN cells and their associated used channels. In this way, the number of scanned channels can be reduced dramatically and a mobile station can switch to passive or active scanning and modify the active scanning MaxChannelTime parameter accordingly. Using this technique the search phase time can be reduced to below 50 ms for a WLAN cell with 10 mobile stations.