Thermal Aware Routing in Implanted Sensor Networks

Masters thesis by

Naveen Tummala

Advising Committee:

Dr. Sandeep Gupta

Dr. Arunabha Sen Dr. Partha Dasgupta

Outline

IntroductionSystem model and AssumptionsProblem statementRelated workThermal Aware Routing AlgorithmSimulations and ImplementationConclusion and Future Work

Wireless Sensor Networks

Minute devices used for sensing. Low power, battery operated devices Typically transmit data in multi-hop Several routing techniques based on application Focus on energy efficiency, lifetime and latency.

Medical Biosensor Networks

A Medical biosensor is a device that detects, records and transmits information regarding a physiological change in biological environment.

How are they different from environment sensors? - Operating environment is sensitive - Invasive – alternative power, less maintenance - Continuous monitoring Applications: Prosthesis, Organ monitoring,

Cancer Detection, Glucose monitoring

Heating in biological bodies

Specific to biological bodies, Pennes bio heat equation [6]

gives rate of rise in temperature.

perfusion. blood ofeffect cooling theis B

,metabolism basal theis A

re, temperatuflow blood theisT

space and timeoffunction a as re temperatu theis T

ty,conductivi thermal theisK

heat, specific theis C

density, theis

)T-B(TA K T/

0

b

b02

sourcePTtC

System model

B

Sensor node

Gateway node

B Base station

Communication is done through radio frequency

Assumptions

The neighbor set of a node is constant Protocol is operated in a homogeneous tissue

environment Nodes are aware of their location Each node has a forwarding path to the gateway Heat does not have effect on sensor processor

speed

Problem Statement

Given a biosensor network, BSN=<V,E> |V|=k.

E = set of links; V = set of nodes;

for each k ε V, the problem is to route the data from k to the gateway node by

- keeping the temperature rise caused by communication

within a safe value

- Achieving the minimum possible delay caused by

tradeoff for thermal efficiency.

Related work- Dosimetry

Hirata et al. [1] calculated the temperature rise in human eye when exposed to ISM frequency radiation.

Lazzi et al. [2] simulated temperature increase in a head/eye model containing retinal prosthesis.

Related Work - Routing

On demand routing protocols like AODV, [3] ODMRP are not suitable due to large amount of control messages involved in finding route.

Energy efficiency protocols [4] doesn’t necessary reduce the radiation exposure of a tissue area.

Geographic routing protocols [5] are used in a similar scenario like a biosensor network – static, known location but doesn’t consider the radiation effects.

Thermal Aware Routing AlgorithmTARA

Salient features Routing is done based on

- temperature residue in tissue at forwarding node - forwarding node’s proximity to gateway

Use Finite Differential Time Domain (FDTD) to estimate the temperature at neighbors. Use cordoning to prevent communication in hotspots. Two phases: setup, operation.

TARA- Setup Phase

A D

C

B

EGateway

TARA- Setup Phase

A D

C

B

EGateway

TARA- Setup Phase

At the end of setup phase, each node has Hop number – number of hops to gateway Neighbor set {neighbor id, neighbor hop no}

A D

C

BE

Gateway1

2

2

3

TARA- operation phase

1 4

3

2

5Gateway

{2,2}{3,2}

{4,1}{1,3}

{4,1}{1,3}

{5,0}{3,2}{2,2}

Data

TARA- operation phase

1 4

3

2

5Gateway

{2,2}{3,2}

{4,1}{1,3}

{4,1}{1,3}

{5,0}{3,2}{2,2}

Data

?

?

TARA-FDTD

sourceb PTTBATKC )(02tT/

Pennes equation

we denote j)(i,nT as temperature at location i,j and at time n

=tjiji /)T (T tT/ ),(

n),(

1n

Similarly for xT/

xjiji /)T (T xT/ ),(n

),1(n , Similarly for y

xxxx jijijiji /)/)T (T - /)T ((T /T ),1(n

),(n

),(n

),1(n22

/T /T T 22222 yx

TARA-FDTD Substituting the discretized values in the bioheat

equation, the bioheat equation becomes

For all (i,j),

)

sourcebj)(i,n

0 P )T -B(T-A

xxx jijijiji /)/)T (T - /)T ((T ),1(n

),(n

),(n

),1(n

j)(i,n

j)(i,1n T T

(t/C

yyy jijijiji /)/)T (T - /)T ((T )1,(n

),(n

),(n

)1,(n

c.37 T oj)(i,

0

TARA-FDTD

1 4

3

2

5

Node 1 and 4 can calculate the temperature rise using FDTD.

TARA - Cordoning

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13{9,temp residue}

Gateway-ve

Simulations

Model a human body in a small region and calculate the effect of temperature using MATLAB

Goal is to demonstrate the significance of thermal aware routing.

Compare our protocol with a shortest hop routing protocol.

Simulation

3D plot of temperature rise across the network using TARA

6X6 grid topology with source at 1,1 and gateway at 6,6.

Simulation

3D plot for temperature rise across the network using shortest-hop

Simulation100X100 mm

Placement is predetermined

Average rise in temperature

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

Seconds 1000 2000 3000 4000 5000 6000

tem

pe

ratu

re r

ise

in C

TARA

Shortest-hop

Simulation

Highest rise in temperature

0

0.05

0.1

0.15

0.2

0.25

Seconds 1000 2000 3000 4000 5000 6000

Te

mp

era

ture

ris

e in

C

TARA

Shortest-Hop

Implementation

Goal of implementation is to demonstrate the tradeoffs the protocol makes with delay.

mica2 motes and tinyos. Issues with using motes

- motes have limited memory capability.

- motes are difficult to debug.

- motes transmission is unpredictable and

wide ranged.

Implementation

0

20

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Deadline 350 360 370 380 390 400 410 420 430 440 450 460 470

Deadline in msec

% o

f p

ac

ke

ts m

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tin

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ea

dlin

e

Shortest-hop

TARA

Implementation

performance of Tara and shortest hop for low traffic

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10

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Deadline 100 200 300 400 500 600

Deadline in msec

% o

f p

ac

ke

ts m

ee

tin

g d

ea

dlin

es

Tara

Shortest-hop

Implementation

Performance of TARA and shortest-hop for high traffic

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Deadline 100 200 300 400 500 600

Deadline in msec

% o

f p

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ts m

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tin

g d

ea

dlin

e

Tara

Shortest-hop

Implementation

Average delay at each node in a scenario

0

50

100

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200

250

300

350

400

450

Node 1 2 3 4 5 6 7 8 9 10 11

Nodes

Av

era

ge

De

lay

Shortest-Hop

TARA

Conclusion

Thermal effects of wireless sensors should be considered during the design of communication protocols for medical biosensor network.

Proposed a protocol, TARA for routing in wireless biosensor network.

TARA is compared with shortest-hop

- causes less exposure of radiation to the tissue.

- Performs better at higher traffic.

Future Work

Extend the protocol to route in real-time considering soft and hard real time deadlines.

Enhance the protocol to work in restrictive scenarios.

References

[1] A.Hirata, G.Ushio and T.Sciozawa. “Calculation of temperature rises in the human eye for exposure to EM waves in the ISM frequency bands.” IEICE Transactions on Communications, vol.E83-B, no.3, pp.541-548,2000.

[2] G.Lazzi, S.C. Demarco, W.Liu and M.Humayun. “Simulated Temperature Increase in a Head/Eye Model Containing an Intraocular Retinal Prosthesis.”

IEEE Int'l Symp. Antennas and Propagation Society, vol.2,pp.72-75,July 2001. [3] http://moment.cs.ucsb.edu/AODV/aodv.html[4] W.R.Heinzelmann, A.Chandrakasan and H.Balakrishnan. “Energy-efficient

Communication for Wireless Microsensor Networks”, In Hawaii Int'l Conf. System Sciences, 2000.

[5] B.Karp and H.T.Kung. “Greedy Perimeter Stateless Routing for Wireless Networks”, Mobicom 2000.

[6] H.H.Pennes. “Analysis of tissue and arterial blood temperaturein the resting human forearm”, J. Appl. Physiol. Vol 1, 1948.

Demonstration Scenario

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Problem statementGiven a biosensor network, BSN=<V,E> |V|=k.E = set of links; V = set of nodes;

tempij is the temperature residue across link ijT- temperature rise due to communication of 1 data unit.

xij is the total data units to be forwarded across link

Tcutoff is the maximum safe temperature at tissue

Hf -number of hops the node f is away from destinationWe introduce a cost function, fnij which determine the selection of forwarding node.

fnij((xij*T) + tempij, hij).With reference to the cost function which determines the selection of forwarding node, the

problem can be written as

for all ij ε E, minimize the fnij(..) subject to the following constraints

(xij*T) + tempij < Tcutoff

Appendix -1

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713 Gateway