by g.padmavathi 06-530

8/14/2019 By g.padmavathi 06-530

1/19

BY

G.PADMAVATHI

06-530


2/19

Off-the-shelf radio Representative of spread-

spectrum radios (frequencyhopping)

Free 2.4 GHz band Promise to be cheap

The Bluetooth stack iscomplex Stripped down version of

Bluetooth adapted toconstraints of sensor nodes?

A Bluetooth moduleembeds front-end radio,

baseband and MAC layer Are standard Bluetooth

physical layer and MAC layeradapted to the sensornetwork regime?

Multihop capabilities Scatternet support has been

announced for years but wasnot supported at the time ofour study

How to build multihopBluetooth-based networks?

Bluetooth is connection-based How to define network self-

assembly based on Bluetoothdevice discovery. What is theimpact on performance?

Bluetooth implements TimeDivision Multiplexing (TDM)at the radio level Can applications leverage

radio-driven TDM?


3/19

Pragmatic ApproachBTNodes from ETH Zurich

Atmega 128 7.32 MHz

128 KiB flash

Dual-radio Ericssons Bluetoothmodule ROK 101 007

Port of TinyOS to BTNodes Development of

TinyBluetooth

Self-Assembly Procedure Application using Radio-

level TDM UC Berkeleys TinyDB on top

of TinyBluetooth

Performance Evaluation Intrinsic properties

Prototype properties


4/19

1.Physical bus driver

2.Hcl driver


5/19

Physical bus driver:This layer abstractsthe characteristics of the physical bus

HCL driver:This layer maps the interface

of the underlaying HCL layer into theprogramming model used forimplementing the higher layers


6/19

RF

Baseband

HCI

L2Cap

Profiles

Applications

Physical Bus Hardware


7/19

RF

Baseband

HCI

Physical Bus Hardware

TinyBluetooth

TinyOS Application


8/19

AsynchronousProgramming Model HCI mapped onto tinyOS

events and commands UART events decoupled

from HCI events

Buffer Trading Buffers swapped betweenmodules

Generic Packet type castedinto specific packetdepending onevent/command

Interesting informationencapsulated insideBluetooth module


9/19

Each node is equippedwith 2 radios

For each node

To which node toconnect?

Connect as master orslave?

3 node configurations: S-SM-M

M-S, S-M


10/19

Building a connection tree asa baseline (BlueTree [Petrioli,Basagni 2002]) Each node has a radio set up as

a master, the other as a slave

Recursive connectionestablishment First slave radio is turned on. One node is chosen as the root of

the connection tree. Master radio turned on once a

connection is established on slaveradio.

Rely on Bluetooth devicediscovery and connectionestablishment

M

M

M

M

M

M

M

M

M

S

S

S

S

S

S

S

S

S


11/19

Connection treesupports hierarchicalrouting tree.

Radio drives TDM Bluetooth radio in Sniff

mode: Master andSlaves agree onsynchronization points(ideally once perepoch). Rest of timesensor node sleeps orsenses. Microcontrollerwaken up on radio

signal. Pipelined aggregationalong the routing tree.

Separated Channels No unplanned collisions

M M

MS

S

S

S

M

M


12/19

Problem # 1: The sniffperiod is not longer than 40secs.

Problem # 2: When aconnection is in sniff mode,the microcontroller sleepsin idle mode (which is lessefficient than thepower

save mode according to theAtmel specs).

M M

MS

S

S

S

M

M


13/19

- Point-to-pointthroughput is

high!- The performance weachieve is far from the

theoretical max UART limit is 45Kib/sec

Junk sent byBluetooth module

- Slave-to-master andmaster-to-slave

throughput

are similar- Throughput degrades

forMultipoint connections

73,2 59,73 90,4

0

5

10

15

20

25

30

35

40

45

50

DM1 DH1 DM3 DH3 DM5 DH5Bluetooth Encoding

Throughput(kb/sec)

20 bytes payload

668 bytes payload (max)

Theoretical max

DM and DH are two encoding schemes.

DM offers a lower error rate. 1, 3 and 5 corresponds to the number of

consecutive slots during which slaves and masters

communicate.

1 2 3

Aggregate 38.1 25.4 19.3

Per Slave 38.1 12.7 6.4


14/19

50mW when idle and250 mW whencommunicating

Berkeleys mica

motes: 10 mW whenidle and 160 mW

when communicating

Maintaining connections is very expensive

Different sleep modes!


15/19

a. Node is turned on.b. Connection on slave radioc. 1st Connection on master

radiod.

2nd Connection on masterradioe. Master radio is

discoverablef. Data packets are

transmittted

g. Disconnections on masterradio

h. Disconnection on slaveradio


16/19

Throughput is high Best suited for applications that transmit

lots of data

Energy consumption is high (inparticular connections) Life time of applicatoin must be short

(days)

Short periods of connections Suited for Asynchronous In-Network

Processing with radio driven TDM.Bluetooth-Based Sensor Network well suited for short lived deployments

With unplanned burst of data with high throughput (images, video).


17/19

Intrinsic Bluetooth Properties It is feasible to develop a Bluetooth stack for TinyOS

devices Encapsulation within Bluetooth module hurts

Frequency hopping hurts (40 sec period for sniff mode) Inquiry, connection establishment is slow

Better engineering might improve Scatternet support Cost of connection maintenance

Throughput max

decrease on point-to-multipoint


18/19

Code available in TinyOS contribdirectory

More info on our project home page:

http://www.distlab.dk/manatee This study is a baseline for:

Intel motes 802.15.4 radios Tailored radios relying on Bluetooth front-end

(Pico Radio)


19/19

QUESTIONS

by g.padmavathi 06-530

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