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A Topology Control Approach for Utilizing Multiple Channels in Multi-Radio Wireless Mesh Networks (broadnet2005) Mahesh K. Marina, Samir R. Das. 2006/9/14 Kim Young Hoon. Contents. Introduction Problem Formulation Channel Assignment Algorithm Simulations Results Conclusions. Contents.

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2006 9 14 kim young hoon

A Topology Control Approach for Utilizing Multiple Channels in Multi-Radio Wireless Mesh Networks (broadnet2005)Mahesh K. Marina, Samir R. Das

2006/9/14

Kim Young Hoon

contents
Contents
  • Introduction
  • Problem Formulation
  • Channel Assignment Algorithm
  • Simulations Results
  • Conclusions
contents1
Contents
  • Introduction
  • Problem Formulation
  • Channel Assignment Algorithm
  • Simulations Results
  • Conclusions
introduction
Introduction
  • Wireless mesh networks
    • Wired router nodes/wireless nodes
    • No need of infrastructure
    • Wider coverage
  • Mesh networks with multi-hop extension of 802.11 standard
    • Different from 802.11 LANs: risk of disconnection
    • All nodes use same channel in mesh for connectivity
  • Inefficient Utilization of Available Channels
  • Need to use Multiples Channels
introduction1
Introduction
  • Single radio for multiple channels?

Possible. But need of ...

    • Dynamically switch between channels
    • Tight time synchronization among nodes
      • Slow switching

 reducing synchronization requirements and overhead,

 increasing end-to-end delay

    • Require MAC or hardware modification
  • Therefore, Multiple radios per node
    • Effective use of given channels
    • Overcoming the deficiencies of single radio
introduction2
Introduction
  • What happens in multi-radio mesh network?
    • Disconnection between nodes can happen
    • Node’s transmission is interfered by other nodes’
  • So, a key issue in multi-radio mesh network architecture is Channel Assignment Problem.
introduction3
Introduction
  • Channel Assignment Problem
    • has to balance between connectivity and interference
    • is viewed as topology control problem (adjustable links between nodes in wireless)

In this paper, authors proposed base channel assignment

to obtain an initial, well-connected topology.

contents2
Contents
  • Introduction
  • Problem Formulation
  • Channel Assignment Algorithm
  • Simulations Results
  • Conclusions
problem formulation
Problem Formulation
  • Channel Assignment Problem belongs to the class of NP-complete

Proof flow)

Channel Assignment Problem

Topology Control Problem

Topology Control’s Target

 Reducing Interference

Channel Assignment Problem

 Optimization Problem

Optimization Problem

 Decision Problem

Showing that decision problem is in NP-complete (using minimum edge coloring)

For more detail, see 2nd part of the paper

channel assignment algorithm
Channel assignment algorithm
  • CLICA (Connected Low Interference Channel Assignment)
    • Polynomial time heuristic
    • Order nodes by their degree of flexibility
      • degree of flexibility: amount of freedom when choosing channel
    • Greedily assign channel between nodes
channel assignment algorithm1

Coloring uncolored links with a common color to already assigned radios

Coloring nodes which have no available radios

Greedily coloring uncolored links

Channel assignment algorithm
channel assignment algorithm case 1
Channel assignment algorithm - case 1

Initial order: a-d-c-b

  • Starting from a, assign channel a-b, b’s priority bumps up
  • Assign channel b-c, and c-d in similar manner
  • Node a and d have a common channel, so assign that to a-d

<1>

<5>

b

a

c

<2>

<6>

<4>

d

<7>

<3>

channel assignment algorithm case 2
Channel assignment algorithm - case 2

Node a and d has two radios

  • Starting from a, assign channel a-b, b’s priority bumps up
  • Assign channel b-c, and c-d in similar manner
  • Node a and d have additional radios, so assign different channel to a-d

<1>

<5>

b

a

c

<2>

<6>

<4>

d

<7>

<3>

channel assignment algorithm2
Channel assignment algorithm
  • Each coloring decision is made in a greedy fashion
    • Locally optimal choice
  • Theorem 2: CLICA algorithm yields a connectivity preserving color assignment
contents3
Contents
  • Introduction
  • Problem Formulation
  • Channel Assignment Algorithm
  • Simulations Results
  • Conclusions
simulation results part 1
Simulation Results – part 1
  • Graph-based simulations
    • Interference and capacity properties of topologies generated by different channel assignment algorithms
      • Compared with CCA (Common Channel Assignment – assign same set of channelr to all nodes)
    • Measure:
      • Maximum link conflict weight – network wide interference
      • Maximum number of concurrent transmissions – total one-hop capacity
simulation results part 11
Simulation Results – part 1
  • CCA
    • CCA interference performance is unaffected by the number of channels
    • CCA capacity performance shows a linear growth
  • CLICA
    • As the number of radios increases, interference goes up and capacity shows marginal perfromance
    • Minimum interference doesn’t match maximum capacity

DUE TO HEURISTIC NATURE

simulation results part 2
Simulation Results – part 2
  • Ns-2 simulations
    • Evaluating the performance of CLICA
    • Aggregate throughput and average delay
    • 50 nodes with 250m TX range in 1000m x 1000m
    • 550m interference range
    • 802.11 physical layer model in ns-2
    • Fixed data rate of 2Mbps
conclusions
Conclusions
  • The authors
    • have formulated base channel assignment as a topology control optimization problem
    • solved the channel assignment (radio-channel mapping) problem in greedy way (called CLICA)
    • shows the interference-reducing results by simulations
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