A Channel Assignment Algorithm for A Channel Assignment Algorithm for Multi-Radio Wireless Mesh NetworksMulti-Radio Wireless Mesh Networks

Stefano Avallone, Ian F. AkyildizStefano Avallone, Ian F. Akyildiz

Computer Communication, Jan. 2008

OutlineOutline

IntroductionIntroductionProblem DefinitionProblem DefinitionA Flow Rate Computation MethodA Flow Rate Computation MethodThe MCAR AlgorithmThe MCAR AlgorithmPerformance EvaluationPerformance EvaluationConclusionsConclusions

IntroductionIntroduction

Wireless mesh networks consist of a Wireless mesh networks consist of a backbone with mesh routersbackbone with mesh routers

Mesh RouterMesh RouterLow mobility Low mobility Multi-radioMulti-radioTransmission through wireless mediaTransmission through wireless media

IEEE standards define multiple channelsIEEE standards define multiple channels IEEE 802.11a have 12 non-overlapping IEEE 802.11a have 12 non-overlapping

channelschannels IEEE 802.11b/g have 3 non-overlapping IEEE 802.11b/g have 3 non-overlapping

channelschannels

Using multiple channels in multi-radio Using multiple channels in multi-radio WMN greatly improve the network WMN greatly improve the network throughputthroughput

IntroductionIntroduction

IntroductionIntroduction

The channel assignmentThe channel assignmentThe reuse of the same channel in a The reuse of the same channel in a

neighborhood neighborhood The bandwidth available on the network linkThe bandwidth available on the network link

The channel assignment has to preserve The channel assignment has to preserve the network connectivitythe network connectivity

IntroductionIntroduction

The static cannel assignment problemThe static cannel assignment problem Interference awareInterference aware

To minimize the interferenceTo minimize the interference

Traffic awareTraffic awareTo make a given set of flow rate schedulableTo make a given set of flow rate schedulable

IntroductionIntroduction

6

Each node has two radios

IntroductionIntroduction

Each node has two radio

MotivationMotivation

Existing channel assignment Existing channel assignment Only base on information related to node Only base on information related to node

within the interference rangewithin the interference rangeThis may break the radio constraint This may break the radio constraint

Depend on particular traffic profileDepend on particular traffic profile

Problem DefinitionProblem Definition

κ(R1) 1≧

|C| available channel

Problem DefinitionProblem Definition

Interference modelInterference model

u v

rI

rT

ch1

Xch1

ch1

Problem DefinitionProblem Definition

e0

flow rate f(e0)Capacity c(e0)

The conditions ensures that a set of flow rate are schedulable

Depend on channel

assignment

Problem DefinitionProblem Definition

GoalsGoals

Flow Rate ComputationFlow Rate Computation

To compute the flow rates having the To compute the flow rates having the objective to maximal the achievable rateobjective to maximal the achievable rate

At this timeAt this timeChannel assignment is not decideChannel assignment is not decideThe knowledge of the expected traffic demand The knowledge of the expected traffic demand

is unknown is unknown

Flow Rate ComputationFlow Rate Computation

To maximal the throughputTo maximal the throughput Using network throughput instead of the demand Using network throughput instead of the demand

traffic traffic To compute the maximal achievable throughputTo compute the maximal achievable throughput

Channel assignment is not decideChannel assignment is not decide The interference is also unknownThe interference is also unknown In this, the interference is absentedIn this, the interference is absented

The channel assignment is assume to handle the The channel assignment is assume to handle the interference probleminterference problem

Flow Rate ComputationFlow Rate Computation

Maximum the multi-commodity flow Maximum the multi-commodity flow problemproblemNP-completeNP-completeTranslate into single-commodity flow problemTranslate into single-commodity flow problem

Flow Rate ComputationFlow Rate Computation

Mesh aggregation devices

Mesh gateway

Virtual node Virtual node

capacity= ∞

capacity= ∞

Mesh Router

MCAR AlgorithmMCAR Algorithm

Two stagesTwo stagesLinks are grouped based on the flows they Links are grouped based on the flows they

carrycarryFirst stage assure that the number of different First stage assure that the number of different

groups assign to its link does not exceed the groups assign to its link does not exceed the number of radionumber of radio

Each group is assigned a channelEach group is assigned a channel

Link-group BindingLink-group Binding

MCAR AlgorithmMCAR Algorithm

rt

rt

rt

rt

rt

rt

eg1

g1

g2

g1g2

g3

g1

Link-group BindingLink-group Binding

Assume the node has three radio

1

2

3

4R(e) = 1.5 R(e) = 1.2

R(e) = 1.1

R(e) = 1.3 j’

J’’ 3R(e) = 2.3

R(e) = 2.0

Link-group BindingLink-group Binding

g1

g2 g1

g2

R(e) = 1.5

R(e) = 1.2

R(e) = 1.0

R(e) = 1.3

g1

Group-Channel AssignmentGroup-Channel Assignment

Group-Channel AssignmentGroup-Channel Assignment

Group-Channel AssignmentGroup-Channel Assignment

ri

ri

ri

rtrtrt

P(g) : the set of links potentially interference with the link assign to group g

Group-Channel AssignmentGroup-Channel Assignment

ri

ri

rtrtrt S(g,c) : all the link that are assigned

channel c and potentially interference with links of g

εc: all the link that are assigned channel c

Group-Channel AssignmentGroup-Channel Assignment

Performance EvaluationPerformance Evaluation

Compare withCompare withLACA (Load Aware)LACA (Load Aware)BSCA (Balanced Static)BSCA (Balanced Static)

MetricMetric

Performance EvaluationPerformance Evaluation

Transmission range 90m Interference range180m Transmission range 90m Interference range180m Scenario1Scenario1

25 nodes25 nodes300m* 300m300m* 300mTwo radio 60% Three Radio 40%Two radio 60% Three Radio 40%

Scenario2Scenario250 nodes50 nodes400m* 400m400m* 400mTwo radio 20% Three Radio 40% Four Radio 40%Two radio 20% Three Radio 40% Four Radio 40%

Performance Evaluation Performance Evaluation

25 nodes

Capacity fixed to 54Mbps

Performance Evaluation Performance Evaluation

50 nodes

Capacity fixed to 54Mbps

Performance EvaluationPerformance EvaluationCapacity from 6 to 54Mbps

25 nodes

Performance EvaluationPerformance EvaluationCapacity from 6 to 54Mbps

50 nodes

ThroughputThroughput

25 nodes

ThroughputThroughput

50 nodes

DelayDelay

25 nodes

DelayDelay

50 nodes

ConclusionsConclusions

This paper proposedThis paper proposedA Flow Rate ComputationA Flow Rate Computation

Independent from the traffic demandIndependent from the traffic demandMaximal the network throughMaximal the network through

A channel assignment schemeA channel assignment schemeAttempt to make a given set of flow rate Attempt to make a given set of flow rate

schedulable schedulable