Dynamic Channel Assignment in Wireless LANs
Bo Wang
1
, William Wu
2
, Yongqiang Liu
3
1
Institute of Computing Technology, Chinese Academy of Sciences
2
Electrical Engineering Dept. Stanford University
3
NEC Laboratories China
bwang@jdl.ac.cn, willywu@stanford.edu, liuyongqiang@research.nec.com.cn
Abstract
A traffic-aware and client-aware algorithm for dynamically
assigning channels to Access Points (APs) in Wireless Local
Access Networks (WLANs) is proposed. Traffic loads and
Received Signal Strength (RSS) values are used to
characterize interference. The problem of selecting channels
to minimize total interference then reduces to the Max k-Cut
problem, which we efficiently solve with semidefinite
programming (SDP) relaxation. Testbed experiments
demonstrate that our traffic-aware algorithm can significantly
improve the quality of a channel assignment in terms of total
network throughput and channel utilization. Under a
randomly generated continuous traffic distribution,
throughput gains of 40% on average over static channel
assignment are observed.
1. Introduction
The explosive popularity of Wireless Local Area Networks
(WLANs) in recent years has led to a dramatic rise in the
density of WiFi Access Points (APs) in wireless environments.
The wireless spectrum is divided into “channels” – bands over
which APs can operate. A natural problem that arises is how to
assign channels to the APs so as to increase the total network
throughput. A well-established heuristic approach is to
minimize the interference between APs using the same
channel. Due to the broadcast nature of wireless, as the AP
density of WLANs continues to increase, this problem of
interference is becoming more severe and important.
Currently, network administrators often manually decide on
a static channel assignment for APs based on RF profiles [1].
However, traffic loads in a network tend to vary with time,
and consequently, such assignments do not result in the best
performance.
In this work, we propose a centralized dynamic channel
assignment algorithm that efficiently adapts the channel
assignments alongside variations in traffic. Our approach
incorporates the observed traffic demands of wireless APs and
clients, as well as their power-inferred locations, in order to
increase network throughput as a whole. The key points and
advantages of our algorithm may be summarized as follows:
(1) We adopt the heuristic of minimizing sum network
interference to increase overall network throughput.
Experiments in our paper confirm the validity of this.
(2) Our algorithm is “traffic-aware”, constantly monitoring
the traffic patterns of both APs and stations. This allows
us more efficient channel usage by designing channel
assignments that accommodate to the traffic distribution.
(3) Our algorithm is “client-aware”. This means that in
addition to APs, clients also take part in measuring and
reporting received signal power and traffic, thereby
giving us a better picture of interference in the network.
(4) We use actual measurements of signal power and traffic
load to intuitively define and measure interference. This
measurement-based approach allows us to avoid making
simplistic modeling assumptions for the wireless channel
and MAC protocol, as such theoretical models are known
to be especially inaccurate indoors. It also allows us to
assess interference at a higher resolution than otherwise.
(5) Characterizing interference in terms of signal power has
the desirable property of additivity, which will more
easily allow us to address simultaneous interferers.
Namely, additivity allows us to reduce the minimization
problem to Max k-Cut, which can then be relaxed into a
semidefinite programming problem that can be
efficiently solved.
Due to all of these design characteristics, the techniques
proposed in this paper improve channel assignment for
WLANs, exploiting opportunities both to make use of idle
channels, and also to reuse active channels. Our experiments
show that our channel assignment algorithm substantially
improves network throughput by 40% on average when
compared to a static assignment scheme.
Our paper is structured as follows: In Section 2, we give
some background on WLANs. Section 3 presents an analysis
and model for interference. Section 4 describes the reduction
to Max k-Cut, and the SDP relaxation used to approximately
2008 Workshop on Power Electronics and Intelligent Transportation System
978-0-7695-3342-1/08 $25.00 © 2008 IEEE
DOI 10.1109/PEITS.2008.105
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