On Access Point Selection in IEEE 802.11 Wireless Local Area Networks

In wireless local area networks often a station can poten- tially associate with more than one access point. Therefore, a relevant question is which access point to select "best" from a list of candidate ones. In IEEE 802.11, the user simply associates to the access point with the strongest re- ceived signal strength. However, this may result in a signifi- cant load imbalance between several access points, as some accommodate a large number of stations while others are lightly loaded or even idle. Moreover, the multi-rate flexi- bility provided by several IEEE 802.11 variants can cause low bit rate stations to negatively affect high bit rate ones and consequently degrade the overall network throughput. This paper investigates the various aspects of "best" access point selection for IEEE 802.11 systems. In detail, we first derive a decision metric the selection can be based on. Us- ing this metric we propose two new selection mechanisms which are decentralized in the sense that the decision is performed by each station, given appropriate status infor- mation of each access point. In fact, only few bytes of status information have to be added to the beacon and probe re- sponse frames which does not impose significant overhead. In addition, we show that our mechanism improves station quality of service and better utilizes network resources com- pared to the conventional one implemented today in IEEE 802.11 devices.