Research On Distributed Adaptive Channel Assignment In WLANs

Wireless Local Networks (WLANs) is the combination of the traditional computing networks and wireless communication technology. As the solution of the"last-hop"network connection, WLANS expand the application area of the LAN, and give a power support to the mobile portable communication, so became more and more popular.As all know, 802.11 protocol family is the authority of WLAN standard, for it's simple and reliable. And today, most enterprises and campuses offer near-ubiquitous wireless coverage. However, the 802.11 b/g, most common used protocols in 802.11 family, are all working in the 2.4GHz ISM band, with very limited channel count. So the explosive popularity of WLANs mean to a dramatic rise in the density of WiFi Access Points (APs) in wireless environments. Due to the broadcast nature of wireless, this density of APs would interfere and compete with each other, naturally lead to a decrease in the total network throughput. Growing densities of deployment together with increasing traffic volumes only exacerbate these problems.How to assign channels to the APs to resolve the above problems is the purpose of this article. First of all, from the 802.11 protocol, the cause of the problem is described in theory, and a set of tests are carried out to verify the worth of the channel assignment. Then, a model of interfere between APs is analyzed, help to represent the disadvantages and challenges in the channel assignment. Also, based on the current distributed channel assignment algorithm, a new one is proposed with following features: 1. it is distributed and adaptive; 2. Comprehensive network dynamic information is gathered. And a traffic factor is added to distinguish the detected interference better, which enables each AP to find the most suitable channel more accurately; 3. A back-off mechanism is designed to reduce the collision overhead during the algorithm running, and accelerates the algorithm convergence rate as well; 4. The scanning mechanism in protocol is replaced by sniffer scan, which not only expand the nodes'interference detecting region, but also improve the efficiency of the scanning. And the total time consumption of the scanning is reduced based on the co-channel influence.To evaluate the performance of the features in the new algorithm, a series of simulation experiment is carried out in the Network Simulate platform NS-2, which is extended with several function modules before emulating. Simulation results verified the high efficiency of the new algorithm. At last, on the Linux platform, some research and practice are done on the realization of the channel assignment function in NIC driver.