Increasing interest in using wireless mesh networks (WMNs) as backbone networks recently

1. A-B B-C D-E C-D A B C D E Minimum Interference Channel Assignment in Multi-Radio Wireless Mesh Networks Anand Prabhu Subramanian, Rupa Krishnan, Samir R. Das, Himanshu Gupta, Computer Science Department SUNY at Stony Brook http://www.wings.cs.sunysb.edu Motivation • When (v,w) in E is assigned i , then nodesv and w have atleast one radio assigned to i Generate a random partition s; bestCol = f(s); sol = s; While <end condition>{ Generate η neighbors with moves not in tabu list; choose the neighbor (s’) with minimum cost; s = s’; Add the move from s to s’ to tabu list; If(f(s) < bestCol){ bestCol = f(s); sol = s; } } Conflict Graph • Increasing interest in using wireless mesh networks (WMNs) as backbone networks recently • Multihop nature of such wireless networks have a serious capacity problem [gupta & kumar] • Main cause - INTERFERENCE • Two interfering links can operate simultaneously in orthogonal channels - 3 channels in 802.11b and 12 channels in 802.11a • Mesh routers can be equipped with multiple radios and operate on orthogonal channels to reduce interference • Interference in the network is modeled using a conflict graph • In the conflict graph Gc = (Vc,Ec), Vc = E • There is an edge between two node u,v in Vc if the edges represented by them in G interfere • We can represent a variety of interference models • The number of colors γ(i) assigned to a node i in G by the first phase is the number of distinct colors assigned to its edges • We define a violation metric as α (i) = γ(i) - Ri • We take the edge-colored communication graph as input for phase II Communication Graph Conflict Graph Problem Definition • Given K orthogonal channels and Ri radios in each node i in the network, design an efficient channel assignment algorithm that preserves - Connectivity as in the single channel case - Minimizes interference as much as possible Sort the nodes in G in non-increasing order of violation For each node i in V do while α (i) > 0 do Merge two edge-connected components of node i which will give least increase in conflict α (i) = α (i) - 1 • Channel assignment problem – NP HARD • Our aim is to come up with an efficient heuristic Channel Assignment Algorithm Simulation Problem Formulation • 50 node network in a 300x300m area • Transmission range 150m • 95% confidence interval shown • We consider a wireless mesh network with stationary wireless routers equipped with multiple radios • Network modeled as an undirected graph G=(V,E) • V is the vertex set and e =(v,w) is in E if u, v in V are within each others’ transmission range • K available channels numbered from 1 to K • Each node i has Ri radios where 1 < Ri <= K • Problem modeled as a constrained edge-coloring problem where each edge in E is assigned one of the K channels • Two phase algorithm • First Phase – K partition the conflict graph • This phase does not consider that each node has limited number of radios (interface constraint) • A feasible solution is any K partition of Vc • Let I(Si) be the edges in Ec that have both end points in Si • The cost f(s)of the solution s is • We need to find a solution s with minimum f(s) S={S1,…,Sk} Future Work • Design Centralized Approximation Algorithm • Design Distributed Algorithm • Implement in real test bed ICNP 2005 Anand Prabhu Subramanian { anandps@cs.sunysb.edu }