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Sep 2004 QofIS 04 1

QoS Constraints in Bluetooth-based Wireless Sensor Networks

Veselin Rakocevic, Muttukrishnan Rajarajan,Kerry-Ann McCalla, Charbel Boumitri

City University, London

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Sep 2004 QofIS 04 2

Motivation

QoS in sensor networks

a change to the way we look at QoS

Need for satisfying human users much smaller

Independent, low-power nodes communicating

They require:

Connectivity

Reliability (Connection robustness)

Low-power operation FRESHNESS OF INFORMATION

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Sep 2004 QofIS 04 3

Bluetooth

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Sep 2004 QofIS 04 4

QoS Constraints in Bluetoothnetworks

Interference

Error Correction

Transport Control

Service Discovery, Connection Establishment,and Scatternet formation

Power Consumption

Scheduling

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Sep 2004 QofIS 04 5

Scheduling

Master is responsible for scheduling

Bluetooth specification does not specify ascheduling scheme round-robin scheduling isassumed

Lot of research being done on using differentscheduling paradigms

This paper presents a comparison betweenseveral scheduling schemes in sensor networkenvironment

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Simulation Model

7 slaves and one master

Slaves producing traffic Uniform file size we assume each slave produces a fixed

amount of fixed-size packets (bursts)

Master applying the scheduling schemes

Three schemes: Exhaustive: master serves a slave until there are any

packets in slaves buffer

Limited Exhaustive: master serves a slave until there are

any packets belonging to a single burst in the slavesbuffer

Maximum Burst Delay First: master serves a slave that hasa burst which had waited for the longest time

id id

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Sep 2004 QofIS 04 7

==

7

1

11

ii

ii

dN

df

==

7

1

11

ii

ii

dN

df

Simulation Model

Symmetric and asymmetric load

Measurements:

Percentage of flushed bursts

Average burst delay Fairness index (for asymmetric load)

=

=7

1

11

i

i

ii

d

N

df

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Results 1 symmetric load

2

3

4

5

6

7

8

9

10

1112

1.00E-02 1.00E-03 1.00E-04 1.00E-05

error probability

percen

tage

offlushe

dd

ata

bursts

exhaustive

BURSTMinimal burst delay

In terms of flushprobability, MBDF

is the best

In terms of average

delay, exhaustiveis the best

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Sep 2004 QofIS 04 9

Results 2 asymmetric load

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

1.E-02 1.E-03 1.E-04 1.E-05

bit error probability

delay

fairnessi

ndex

MBDF LimExh ExhMBDF is better for thehigh-load node

But how much?

More results neededand also implementation

details need to besolved

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Sep 2004 QofIS 04 10

Results 3 asymmetric load

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

1.00E-02 1.00E-03 1.00E-04 1.00E-05

bit error probability

flushp

robability

fairness

index

MBDF LimExh Exh

Interesting exhaustive schedulinggives more protectionto the asymmetric node

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Conclusions?

QoS requirements in pervasive/ad-hoc/sensorsystems not the same as QoS requirementsfor web and voice applications

Polling scheduling schemes very interesting toanalyse

Our preliminary results do not agree withexpectations

we need to work more

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Low power service discovery andscatternet formation

Using Bluetooth in a smart home environment

Connectivity, connection robustness, and lowpower operation essential

We are working on a Low Power Discovery

Scheme Objectives: to guarantee connectivity to all nodes

Nodes are in low-power SNIFF mode

If a master disappears, nodes have to find eachother and establish new piconets

Difficult to do if they are in low power mode, sincethey have to continuously listen to service discoverymessages

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