A Review of Cross-Layer Scheduling and Resource Allocation for Wireless

Mesh Networks

Jason Ernst and Mieso Denko

IEEE TIC-STH 2009 SESMETSeptember 26-27 2009

Department of Computing & Information Science University of Guelph, ON, Canada 1

Pervasive Computing and Wireless Networking Research Group (PerWin)

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Introduction

• Wireless Mesh Networks

• OSI VS Cross-Layer Design

• Cross Layer Design Architectures

• Cross-Layer Design Techniques

• Our scheme

• Conclusions & Future Work

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Wireless Mesh Networks

• Multi-hop wireless ad hoc network• Mesh Routers MR• Gateways GW• Mesh Clients MC

• Majority of traffic between MC and GW• Not MC to MC

• MR often assumed static, more resources• CPU, Memory, Power (battery life)

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Wireless Mesh Networks

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Wireless Mesh Networks

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• Applications• Commercial internet access• Also applications in Military communication• Search and Rescue• Sensor applications where Mesh provides backbone

• Advantages• Cheap and easy to deploy compared with wired• Autonomous: self-configuration, self-optimization, self-healing network• Good for rural applications and sparsely populated areas

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OSI VS Cross-Layer Design

• Cross-Layer• Provides feedback from multiple layers• More intelligent decisions made at routing, MAC layers• Must be designed carefully to allow for extensions

• OSI• Good design from software engineering point of view• Provides good separation and abstraction compared with a “flat” model

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Cross-Layer Design

• Cross-Layer Design an Emerging Technology?• It has been around for about 5 years now

• Last major survey covered only the beginning of cross-layer design• Many developments in the last 5 years

• Somewhat controversial technique •Many different ideas are being applied to cross-layering

• Cognitive radio techniques• Adaptive control• Network coding

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Cross-Layer Design Architectures

Application

Presentation

Session

Transport

Network

Link / MAC

Physical

OSI 7 Layer Stack

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Cross-Layer Design Architectures

Application

Presentation

Session

Transport

Network

Link / MAC

Physical

OSI 7 Layer Stack

Direct Communication:• Layers which do not normally interact exchange information• Difficult to maintain• Poor extensibility

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Cross-Layer Design Architectures

Application

Presentation

Session

Transport

Network

Link / MAC

Physical

OSI 7 Layer Stack

Status

Status:• Link quality• Queue sizes• Application requirements• Distance between nodes

• Easily enable cross-layer interactions by querying thestatus stack

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Cross-Layer Design Techniques

• Power Control

• Rate Control

• Route Control

• Network Coding

• Mixed-Bias

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Power Control

• Power levels of competing nodes are adapted to ensure less contention and interference

• Often combined with Rate Control, Route Control

• Makes use of Physical, MAC and Network layers

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Power Control

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No Interference between MCs

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Power Control

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Interference between MCs

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Rate Control

• Allows MRs to control the transfer rates of associated MCs

• Rates are raised for a given link when the quality is higher• Thresholds to ensure other MCs are not affected

• Solutions make use a wide range of layers• Some take parameters from application layer (multimedia applications)• Generally Physical, MAC, Network layers are used

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Rate Control

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Obstruction between devices

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Rate Control

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No Obstruction between devices

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Route Control

• Avoid congested links, links with poor quality• Use SINR, queue sizes to determine which links to avoid

• Existing solutions make use of Network, Transport and Link (MAC) layers

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Route Control

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Obstruction or Congestion on one link

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Network Coding

• Allow multiple unicast transmissions simultaneously• Assign a unique code for each link• The correct information is decoded and separated from other simultaneous transmissions• SINR measure taken from physical layer to determine which links may cause conflict

• Often combined with other previous techniques

• Usually uses the MAC / Physical layer

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Summary of Techniques

Reference Technique Layers

[12] J. Tang et. al Power Control MAC, Physical

[15] J. Thomas Power Control Network, MAC, Physical

[28] X. Wang et. al Rate Control Transport, MAC

[13] J. Tang et. al Rate Control Transport, Network, Link

[16] K. Karakayali et. al Power / Rate MAC, Physical

[1] C.E. Huang et. al Power / Rate Application, MAC, Physical

[7] H-Y. Wei Route Control Physical, Link, Network

[22] M.J. Neely et. al Route Control Transport, Network

[21] M.S. Kuran et. al Route Control Network, Link

[17] K. Li et. Al Network Coding MAC, Physical

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Cross-Layer Mixed Biasing

• Mixed bias technique [Singh et al]

• Studied using different levels of bias• A comparison against proportionally fair and max-min algorithms• Strong bias, weak bias• Mixed bias combines a strong and a weak bias together

• Only bias against one characteristics• Distance between GW and MR

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Our Scheme

• Our Mixed-Bias technique

• Additional characteristics• Distance between GW and MR• Queue Size• Link Quality

• Combined Technique• Biases against multiple characteristics at once

21

1

ccR

332211 RRRR (1) (2)

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Our Scheme

• Scheduling / Resource assigned according to a cost function at the gateways

• Multiple gateways are supported• Each GW is responsible for scheduling / allocation for MRs associated with it

• At each schedule a measure of the parameters is taken and applied to the cost function

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Initial Results

Parameter Value

MRs 10 to 30

GWs 1 to 5

MCs 250

Flows 2 to 5

Environment Dimensions 1000 x 1000 m

Node Range 150 m

Simulation Parameters

NS3 Simulation Tool

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Initial Results

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

10 15 20 25 30Number of MRs

Avera

ge E

nd

-To

-En

d D

ela

y

M-B Distance

Combined M-B

M-B Queue Size

802.11

5 Flows – Effect of Varying MRs on End-to-End Delay

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Initial Results

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

2 2.5 3 3.5 4 4.5 5

Number of Flows

Pa

ck

et

De

live

ry R

ati

o

M-B Distance

Combined M-B

M-B Queue Size

802.11

5 GWs - Effect of Varying Flows on Packet Delivery Ratio

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Conclusions and Future Work

• Conclusions• Cross-Layering should be viewed as intimidating• Many existing approaches can apply cross-layer design• The results show that our cross-layered mixed bias approach is promising

• Future work• Experiment with tuning the weightings and bias factors in the mixed bias approaches• Implement the scheme in real equipment to compare• Many existing schemes make assumptions that limit the application (single GW, no mobility of MCs or MRs)

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Contact: Jason Ernst – jernst@uoguelph.ca

Thank you for listening!

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Questions?

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