Exploring the Energy-Latency Trade-off for Broadcasts in

Energy-Saving Sensor Networks

Matthew J. Miller, Cigdem Sengul, Indranil Gupta

Department of Computer Science University of Illinois Urbana-Champaign

IEEE ICDCS 2005.6

outlines

Introduction Energy-efficient Communication in Wireless

Sensor Networks Probability-Based Broadcast Forwarding

(PBBF) Analytical Results Simulation Results Conclusion Future Work

Introduction

Sensor nodes are inherently resource constrained.

Offer better reliability and performance to a sensor network application

Provide enough flexibility for a designer to choose the appropriate operation point on the resource-performance spectrum.

Introduction

Broadcast is useful to applications for disseminating sensor data, instructions, and code updates.

The goal is to design a broadcast protocol that allows a range of operating points from which an application designer can choose.

PBBF (Probability-Based Broadcast Forwarding), which is a MAC-layer approach and can be integrated into any sleep scheduling protocol

Related Work

Gossip-Based Ad Hoc Routing [5],• site percolation model

• Achieving a given level of reliability requires the probability of forwarding to be beyond a threshold.

• The approach does not allow an energy-latency trade-off.

PBBF protocol• bond percolation model

• Two knobs, p and q, can be tuned to explore the energy-latency trade-off.

Energy-efficient Communication in Wireless Sensor Networks

Efficient Broadcast Protocols Sleep Scheduling Mechanisms

Efficient Broadcast Protocls SPIN protocols [6,MobileCom 1999]

• Incorporate negotiation in order to avoid deficiencies of the class flooding approach.

[15][16]• Virtual infrastructure

[5,Infocom 2002][13]• To forward a message with some probability

(i.e., gossip)

Sleep Scheduling Mechanisms

reduce energy consumption in WSNs• Active-sleep cycle

• IEEE 802.11 PSM, S-MAC, T-MAC

• Additional low-power wake-up radio

problem• Increasing latency

• redundant packets

Probability-Based Broadcast Forwarding (PBBF)

PBBF exploits the redundancy in broadcast communication and forwards packets using a probability-based approach

The goal is to ensure that, with high probability, a node receives at least one copy of each broadcast packet, while reducing the latency due to sleeping.

p=0.5 q=0.5

N1

N2

N3

The two Knobs

p• It is the probability that a node rebroadcasts a packet

immediately without ensuring that any of its neighbors are active

q• It is the probability that for a given node and a given

time instant when it is supposed to be asleep due to its active-sleep schedule, the node instead stays awake in the expectation that it might be a receiver of an immediate broadcast

Probability-Based Broadcast Forwarding (PBBF)

PBBF exploits the redundancy in broadcast communication and forwards packets using a probability-based approach

The goal is to ensure that, with high probability, a node receives at least one copy of each broadcast packet, while reducing the latency due to sleeping.

p=0.5 q=0.5

N1 O O

N2 ♦ X

N3 X O

Probability-Based Broadcast Forwarding (PBBF)

PBBF exploits the redundancy in broadcast communication and forwards packets using a probability-based approach

The goal is to ensure that, with high probability, a node receives at least one copy of each broadcast packet, while reducing the latency due to sleeping.

p=0.5 q=0.5

N1 ♦ O

N2 O O

N3 ♦ ♦

Probability-Based Broadcast Forwarding (PBBF)

PBBF exploits the redundancy in broadcast communication and forwards packets using a probability-based approach

The goal is to ensure that, with high probability, a node receives at least one copy of each broadcast packet, while reducing the latency due to sleeping.

p=0.5 q=0.5

N1 ♦ O

N2 O O

N3 ♦ ♦

Pseudo-code for PBBFSleep-Decision-Handler()1 /* Called at the end of active time */2 /* If stayOn is true, remain on; otherwise sleep*/3 stayOn false4 5 If DataToSend=ture or DataToRecv=true6 then7 stayOn ture8 else if Uniform-Rand(0,1) < q9 then stayOn true---------------------------------------------------------------------------------------Receive-Broadcast(pkt) 1. /* Called when broadcast packet pkt is received */2. If Uniform-Rand(0,1) < p3. then Send(pkt)4. else Enqueue(nextPktQueue,pkt)

Analytical Results

Reliability Energy Latency Energy-Latency Trade-off

Reliability The reliability of PBBF protocol can be

analyzed using percolation model. Percolation model, [3]

• Bond percolation

• Site percolation

Site Percolation Theory

Site Percolation Theory

Bond Percolation Theory

Bond Percolation Theory

Percolation Theory [3]

G(V,E) : an infinite connected graph Co : the set of nodes, which can be reached by

a specific node no

Θbond(Pedge) : the probability of the component Co being of infinite size

so that Θbond(Pedge)=0 if Pedge<Pcbond(G)

xnVxC oo :

0:sup edgebond

edgebondc PPGP

Reliability (PBBF)

The probability of AB is p·q+(1-p)• p·q : A broadcasting the message immediatel

y after reception and that B being awake at the time

• (1-P) : a rebroadcast when B is awake• Each edge in the network is open with this probabili

ty.

Remark 1 (p and q for high reliability):• If Pedge=1-p·(1-q) P≧ c

bond(G), the broadcast is received at infinitely many node.

Reliability (PBBF) - simulator

Fig.4. Threshold behavior for 90% reliability

Fig.5. Threshold behavior for 99% reliability

Reliability (PBBF) - simulator

Fig.6. Pcbond for various grid sizes Fig.7. Relationship between p and q

for a given reliability level in a 30*30 grid network

Energy

sleepactiveframe

frame

activeoriginal

TTT

T

TE

frame

sleepactive

frame

PBBFactivePBBF

sleepPBBFsleep

sleepactivePBBFactive

T

TqT

T

TE

TqT

TqTT

:

:

:

1

active

sleep

active

sleepactive

original

PBBF

T

Tq

T

TqT

E

E

1

Fig.8. Average energy consumption.

Latency

L: the expected time between A sending the broadcast and B receiving it from A

BSlenLL BS ,,

qpp

pLL

pqp

pLLqpLL

1

1

1

121

211

145

,

o

BS dLL ,[4][10]

Latency - simulator

Fig.9. Average hops traveled by an update to reach a node 20 hops from the source

Fig.10. Average hops traveled by an update to reach a node 60 hops from the souce

Latency - simulator

Fig.11. Average per-hop update latency.

Energy-Latency Trade-off

originalactive

sleepPBBF E

T

T

p

pLL

LLLE

11 1

12

Fig.12. Energy-Latency trade-off for 99% reliability.

Simulation Results

Environment parameter• assume perfect

synchronization in the network

• Ns-2

• The values of our parameters are based on Mica2 Mote hardware

• Run time:500 sec

• Each data point is averaged over ten runs

Parameter Value

N 5625(75*75)

PTX 81mW

PI 30mW

PS 3μW

λ 0.01 pakcets/s

L1 ≈1.5s

Tframe 10s

Tactive 1s

q 0.25

∆ (node density) 10.0

Total Packet Size 64bytes

Data Packet Payload 30bytes

The impact of the q parameter

Fig.13. Average energy consumption

The impact of the q,p parameter

Fig.14. 2-hop average update latency Fig.15. 5-hop average update latency

The impact of the q,p parameter

Fig.16. Average updates received

The impact of △ A

NR2

Fig.17. Average update latency Fig.18. Average updates received

Conclusion

PBBF is an efficient broadcast mechanism

PBBF provides an application designer the opportunity to tune the system to an appropriate operating point along the reliability-resource-performance spectrum.

Future Work

Explore how PBBF can be augmented to improve performance

The p and q parameters could be adjusted dynamically by nodes

Compare its performance with other adaptive sleep protocols.

Thank you