| Summary: | 碩士 === 國立中興大學 === 電機工程學系所 === 96 === In the infrastructure mode of IEEE 802.11 wireless local area network, an access point (AP) is used to connect a wireless network to a wired network. A wireless station needs to associate with an AP before it can connect to a wired network. In 802.11 standard, when the signal strength of the registered AP falls below a threshold, the station begins to scan for signals from other AP’s. If the signal strength from one of the other AP’s is above a threshold, the station then switches to the new AP by re-associating with the new AP and de-associating with the old AP. However, an AP with large signal strength may have a high collision rate within its reception area. In other words, associating with this AP may not yield good connection quality because of the high collision rate. Therefore, our group has proposed a new roaming mechanism called “collision-rate-based roaming mechanism”. This mechanism used collision rate to decide when to switch from one AP to another AP. In this mechanism, an AP collects collision rate from all the stations associated with it and distributed the collision rate information back to stations. The stations can then use the information to decide whether to switch or not.
Based on collision-rate-based roaming mechanism, this thesis investigated in two new directions. The first direction is to speed up the roaming time. Our approach is to reduce the collision rate threshold and make the AP search start earlier. The second direction is that instead of collecting and distributing collision rate by AP, a station uses its own collision rate to decide whether to switch or not. This approach can greatly simplify the whole roaming process. Finally, we did simulation to verify the above two new methods.
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