Distributed Channel Management System

Wireless hotspots are typically implemented using 802.11 APs. Each AP typically operates on a single, administrator-configured wireless channel. Each client associates with a single AP and subsequently interacts with this AP alone, on the AP’s configured channel. As a basic design rule, APs within radio frequency (RF) range of each other are set to different ‘non-overlapping’ channels. Proper assignment of channels to APs is important so that the network can take full advantage of the total wireless bandwidth offered by the multiple channels. Channel Assignment Approaches. Most APs are initialized for their channel of operation through manual input. This is inefficient as it is based on human judgment of which channel is the best. Apart from this, some AP vendors implement a simple distributed method commonly called the least congested channel search (LCCS) algorithm [9]. In LCCS, upon initialization, the AP scans and selects the channel that offers the least amount of congestion, for example, the channel on which there was least amount of traffic belonging to other APs and clients. Since in LCCS, APs perform a scan without involving client feedback, it is possible that two APs might not detect each other and utilize the same channel. As a result, it is possible for clients to be positioned unfavorably so as to suffer considerable interference as a hidden terminal. Figure 2(a) shows this problem. It is possible to mitigate such interference through client feedback, as shown by the (centralized) CFAssign algorithm [4] shows that client feedback in finding interfering APs can mitigate this problem. In Section 6.3, we explore a variant of our channel-hopping technique that is uses such client feedback to detect and mitigate effects of such ‘hidden Aps.

CHAPTER ONE

CHAPTER TWO

CHAPTER THREE

CHAPTER FOUR

CHAPTER FIVE