Cell breathing in wireless LANs: Algorithms and evaluation

Wireless LAN administrators often have to deal with the problem of sporadic client congestion in popular locations within the network. Existing approaches that relieve congestion by balancing the traffic load are encumbered by the modifications that are required to both access points and clients. We propose Cell Breathing, a well-known concept in cellular telephony, as a load balancing mechanism to handle client congestion in a wireless LAN. We develop power management algorithms for controlling the coverage of access points to handle dynamic changes in client workloads. We further incorporate hand-off costs and manufacturer specified power level constraints into our algorithms. Our approach does not require modification to clients or to the standard. It only changes the transmission power of beacon packets and does not change the transmission power of data packets to avoid the interactions with autorating. We analyze the worst-case bounds of the algorithms and show that they are either optimal or close to optimal. In addition, we evaluate our algorithms empirically using synthetic and real wireless LAN traces. Our results show that cell breathing significantly outperforms the commonly used fixed power scheme and performs at par with sophisticated load balancing schemes that require changes to both the client and access points.