Logical Topology Design and Interface Assignment for Multi-

Channel Wireless Mesh Networks

A. Hamed Mohsenian Rad Vincent W.S. Wong

The University of British Columbia, Vancouver, Canada

Globecom 2006

Outline

IntroductionProposed algorithm (TiMesh)Performance comparisonConclusion

Introduction

Multi-channel wireless mesh network Each mesh router is equipped with multiple net

work interface cards (NICs) Each interface operates on a distinct frequency

channel in the 802.11 a/b/g bands

Introduction

Three important issues need to be addressed in MC-WMNs Logical Topology Design Interface Assignment Channel Allocation

TiMesh

Problem Formulation Bidirectional Constraint Channel Dependent Constraint Ripple Effect Constraint Total Flow on a Logical Link Flow Conservation at Each Node Hop Count Constraint Effective Capacity and Link Utilization Objective Function

Problem Formulation

Logical Topology

Physical Topology G(N,E)Each router has I network interface

m n

If I=3

Bidirectional Constraint

1 denote an I x 1 vector

Assume the logical links are bidirectional

The linear term is equal to 1 if node m assigns one interface to communicatewith node n, and is equal to 0 otherwise

There is a logical link between nodes m and n if both terms are equal to one

m n1

1Logical

Link

Channel Dependent Constraint

n

m

k

s

r

Upper bound

Determines the number of additional logicalLink share an interface with link (m,n)

The lager the value of the summation, the smaller the proportion of time thateach logical link can access the shared NIS

Ripple Effect Constraint

Ripple Effect Constraint

n m

s

r

Ch 6

Total Flow on a logical link

denote the average packet arrival rate

Flow Conservation at each nodeHop count constraint

Flow conservation at each node

Hop count constraint

Denote the minimum hop countbetween the source and destinationin the physical topology

Effective capacity and Link utilization

Capacity ofthe logicallink

Utilization ofthe logicallink

When the utilization is close to 1, the queuing delay tends to be lager

Objective Function

Performance Comparison

Using NS-2 simulator Network field is 1000m * 800m 30 wireless mesh router 4 of them also serve as gateways (locate at corn

er) Each router is equipped with 3 NICs Communication and sensing/interference range

are 250m and 450m 10 random physical topologies 40 data flows: half of them are internal flows and

the others are external flows

Performance Comparison

Compare with Hyacinth mechanism Aggregated goodput Average round-trip time Packet delivery ratio Average end-to-end delay

Aggregated goodput

Total number of correctly received packets at the destinations

Average round-trip time

Average time delay between sending a TCP segment and receiving its ack

Packet delivery ratio

Total number of packets received by all destination to the total number of Packets transmitted by all sources

Average end-to-end delay

The average time it takes for a packet to traverse the network from a sourceto a destination

Conclusions

TiMesh MC-WMN architecture The algorithm prevents ripple effect among cha

nnel dependent wireless logical links The algorithm guarantees network connectivity,

supports both internal traffic among the wireless routers and external to the Internet