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Cross-layer Design & Optimization for Wireless Sensor Networks

Weilian Su and Tat L. LimDepartment of Electrical and Computer Engineering

Naval Postgraduate School

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Outline

Objectives Framework Approach Results & Findings Conclusions

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Objectives

Develop a framework for the cross-layer design and optimization study

Investigate & explore the various areas where performance gains can be achieved in the context of WSNs

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Cross-layer Design Framework

Physical

Network

Transport

Session

Presentation

ApplicationOp

timiz

atio

n A

gen

t (O

A)

OA

Top-downfeedback

Bottom-up feedback

Intra-layer interactionsInter-layer interactions

OSI Stack

Data Link (MAC/Link)

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Approach

-> Approach: Study the effects of the wireless channel and performance at PHY to develop insights that can be used to design the optimization agent (OA)

Tapped delay line implementation for wireless channel modeling

Performance measurements using the micaz motes from Crossbow, Inc.

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Tap Delay Line (TDL) Implementation

2-TDL channel model 12-taps TDL channel model from

GSM REC.05-05 model to validate the results

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TDL implementation

2-TDL Modelx(t)

Transmitted

signal

AWGN

Doppler

Filter(Jakes)

Doppler

Filter(Jakes)

τ1 τ1- τ2

y(t) : Received signal

Delay

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Results & Findings (1): TDL implementation

(a) BER of 2-TDL model (b) BER of 12-TDL model (GSM REC.05-05)

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Performance measurements of WSN using Micaz Motes

Interference / Co-existence problems

Transmission range & power transmit levels

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Interference Measurements:Frequency Spectrum

IEEE 802.11b channels

Overlap

Overlap

Overlap

IEEE 802.15.4 channels

Overlapping of frequency bands between IEEE802.15.4 and IEEE802.11b channels within 2.4

GHz ISM band

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Experimental Setup for Interference Measurements

Setup 2 networks: IEEE802.15.4 network (using 4 micaz motes) IEEE802.11b (via 2 laptops) – interference source

IEEE802.11b Ad-hoc Network channel 1

Micaz moteNode 1

MIB600

Micaz moteNode 2

Micaz moteNode 3

10 m

3 m5 m

IEEE802.15.4 Channel 11

Laptop 2

Laptop 1

Laptop 3

Micaz moteNode 0 (Base)

5 m

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Results & Findings (2): Interference Measurements

(a)Interference turned on (b) Interference turned off

73% 100%

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Results & Findings (2): Interference Measurements

Packets Received Rate for Micaz Motes

0

20

40

60

80

100

120

0 20 40 60Duration (mins)

Per

cent

age

Yie

ld

Node 3

Node 2

Node 1

Interference Period

Packets received rate

Node 3 (@ 10 m) more affected by interference

Node 1 & 2 (@ <5 m) unaffected

by interference

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Results & Findings (3): Transmission range and power levels

Maximum transmission range of 55-60m

Transmission Range of Micaz Motes (at 0dBm)

0

20

40

60

80

100

120

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

Distance (meters)

Lin

k Q

ualit

y (%

)

Transmission range for micaz motes set at max power of 0

dBm

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Conclusions Increasing BER under mobility conditions Possible interference within ISM bands and can

affect the performance of WSN (especially for long links/hops)

Max range for micaz motes is around 60m and recommended operating range < 30m

Many factors need to be considered in the design of WSN

Insights gained can be used to design and develop the optimization agent, to enhance the performance of wireless sensor networks

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Q & A

Thank You