Distributed channel management in uncoordinated wireless environments

Abstract

Wireless 802.11 hotspots have grown in an uncoordinated fashion with highly variable deployment densities. Such uncoordinated deployments, coupled with the difficulty of implementing coordination protocols, has often led to conflicting configurations (e.g., in choice of transmission power and channel of operation) among the corresponding Access Points (APs). Overall, such conflicts cause both unpredictable network performance and unfairness among clients of neighboring hotspots. In this paper, we focus on the fairness problem for uncoordinated deployments. We study this problem from the channel assignment perspective. Our solution is based on the notion of channel-hopping, and meets all the important design considerations for control methods in uncoordinated deployments -distributed in nature, minimal to zero coordination among APs belonging to different hotspots, simple to implement, and interoperable with existing standards. In particular, we propose a specific algorithm called MAXchop, which works efficiently when using only non-overlapping wireless channels, but is particularly effective in exploiting partially-overlapped channels that have been proposed in recent literature. We also evaluate how our channel assignment approach complements previously proposed carrier sensing techniques in providing further performance improvements. Through extensive simulations on real hotspot topologies and evaluation of a full implementation of this technique, we demonstrate the efficacy of these techniques for not only fairness, but also the aggregate throughput, metrics.We believe that this is the first work that brings into focus the fairness properties of channel hopping techniques and we hope that the insights from this research will be applied to other domains where a fair division of a system's resources is an important consideration.

QoS provisioning for large-scale multi-ap WLANs

“…There have also been numerous efforts to mitigate the inter-cell interference problem, including channel assignment [17,28,34], power control (or carrier sense control) [8,26,36], and association control [9,10].…”

“…Mishra et al in [27] formulated the channel assignment as a weighted vertex coloring problem. The authors of [28] addressed the problem of distributed channel assignment in uncoordinated wireless environments, and proposed a dynamic channel hopping protocol that distributively assig the channel of an AP. It provides good fairness and can also take full advantage of partially-overlapped channels for a throughput gain in densely-deployed networks.…”

“…The performance imbalance problem is mainly due to the fundamental limitation of CSMA-based random access mechanism, which gives preference in media access to some links over others depending on their spatial locations [23,16]. Although the inter-cell channel contention and interference can be reduced by allocating orthogonal channels to neighbor cells [19,28,22,17,34], only 3 orthogonal channels are available in the 2.4 GHz band, which is not enough to eliminate the co-channel interference. Consequently, the inter-cell channel contention and interface are inevitable in such the multi-cell environment with high AP densities.…”

A topology control-based self-organisation in wireless mesh networks

“…The channel assignment problem was initially addressed in the work of Kaufmann, Baccelli, Chaintreau, Papagiannaki, and Diot (2005) and more recently by Leith and Clifford (2006) and Mishra, Shrivastava, Agarwal, Banerjee and Ganguly (2006). These references consider the problem of interference in an 802.11 based infrastructure networks when collocated networks are owned by different entities and there is no wireless connectivity present between them.…”

“…Since this research does not consider WMN it is not directly related to our work. However, it is still important because it proposes a fully distributed self-organisation algorithms for the collocated networks and the use of partially overlapping channels for traffic transfer as in Mishra, Shrivastava, Agarwal, Banerjee and Ganguly (2006) The algorithm proposed by Kaufman is based on a Gibbs's sampler and does not require an explicit coordination among network devices such as access points (APs). Gibbs sampling is an algorithm that uses the joint probability distribution of two or more random variables to generate a sequence of samples.…”