Page 2 Lecture Notes in Computer Science 2865 Edited by G. Goos ...

Towards Adaptive WLAN Frequency Management Using Intelligent Agents 117popular in many countries. Many reasons can be mentioned for such a success: lowprice, software support and a very successful interoperability under the WiFi logo.WLAN products continue to raise new expectations since they can demonstrate efficientLAN access at rates above 2 Mbps (IEEE 802.11), at 11 Mbps for the IEEE802.11b specifications, or even several tens of Mbps in the near future (IEEE 802.11aand HIPERLAN) 1 .In this paper, we propose a novel approach to address the dynamic frequency allocationof WLAN Access Point (AP) in a multi-provider Hot-Spots environment, inorder to maintain high level of Quality of Service (QoS) taking into account users'traffic. In Section 2, a description of the WLAN channel allocation problem and managementissues are outlined. Our intelligent agent based approach to tackle the channelallocation problem of the WLAN access points is described in Section 3. Section 4briefly presents the fundaments of frequency optimization. Section 5 shows somepreliminary results in our test environment, and Section 6 concludes this paper.2 Channel Allocation in WLAN NetworksCorporate users and, as price decreased, campus communities [4], have been the firstto exploit the benefits of WLAN based on the IEEE802.11x family of standards. Privateusers are also using the technology to avoid new wires in their homes and sometimesto share Internet access with other users. An increasing number of telecommunicationoperators and visionary companies have identified new business models forthe deployment of public WLAN access at popular locations (Hot-Spots) or in theirbusiness premises [5]. As a single example close to the authors, the Swiss operatorSwisscom Mobile has launched commercial services based on public WLAN Hot-Spot access based on GSM subscriptions or special value cards since the end of2002 2 .In this rapidly evolving environment, the deployment of WLAN has to face typicalissues regarding optimal utilization of radio resources that can be provided within theallocated radio spectrum. The complexity of the optimization problem is amplified bythe fact that all WLAN stakeholders, from private to business entities, share the samespectrum allocation without any cooperation unless proprietary bi-lateral agreementscould be arranged. For example, a public WLAN Hot-Spot operator might find difficultiesto offer its service at the bus stop near a popular restaurant, which has installedits own WLAN coverage. Adding private WLAN users in the flats above the restaurantfurther illustrates the need for an autonomous management of the WLAN accesspoints. A manual and static configuration of each access points, besides being tedious,could only provide an acceptable solution for the conditions found during the measurementssurvey. A better solution would be to centralize some information about allthe access points potentially interfering. Based upon a centralized database, the bestfrequency allocation could be computed. However, this solution is not possible inpractice because it does not scale to a very large number of access points. Furthermore,the conditions can be quite complex since the access points are deployed inplanned or ad-hoc manners depending on operators and service providers.1http://www.alcatel.com/atr2http://www.swisscom-mobile.ch/sp/4EGAAAAA-fr.html, visited March, 2, 2003.