A Low-Latency and Energy-Efficient Algorithm for

Convergecast in Wireless Sensor Networks

Authors

Sarma Upadhyayula, Valliappan Annamalai, Sandeep Gupta

Presented by

Bin Wang

Arizona State University

Presentation Flow

Introduction Problem Description System Model Algorithm Results Conclusions and Future Work References

Introduction

Wireless Sensor Networks (WSN) – long life expectancy

Power Anemic Communication consumes maximum energy Data aggregation (convergecast) is a frequent

operation in WSN – important to minimize its energy consumption

Prior Work: PEGASIS [Step02], LEACH[Wendi00], CCTCCA[Valli03]

Typically, convergecast follows broadcast – broadcast tree for convergecast. [Bhas02]

Introduction Contd...

Prior work concentrate on energy efficiency alone.

We have dual objective – Energy-Efficiency and Low-Latency

Conventional approach not necessarily the best approach

Problem Description

n nodes in the network Data from all the nodes to be collected at a

central node Single Hop or Multi-Hop communication Energy consumed for communication is

proportional to distance ( , between 2 and 4)[Wendi00]

Objective # 1: Find a route connecting all nodes to central node consuming minimum energy.

Objective # 2: Minimum latency

r

System Model

Assumptions Nodes are static and clocks are synchronized Every node has only one transceiver A node can transmit or receive at a time but

not both Intermediate nodes concatenate the data

they receive during upstream transmission Intermediate nodes wait until it receives data

from all the nodes in whose path it lies.

System Model

Energy Model [Wendi00] total i

i V

i Tx Rx

Tx elec amp

Rx elec

E E

E E E

E E k k r

E E k

elecE

amp is the electrical energy required on the circuit of transceiver is the amplification energy required to transmit a unit of data over unit distance k is the size of the data packet transmitted by a noder is the distance between communicating nodes

System Model

Latency Model [Valli03]

Let be time taken to transmit longest data packet Latency is the total time required to transmit data from all

the nodes to the central node

S

1C 2C nC

1 2max{ , ,..., }nD d d d

DT

System Model

Latency Model Balanced trees increases possibility of

multiple simultaneous transmissions : number of children per node

where is a positive integer If, due to the rule, a node will be left out of

the tree – overlook the rule.

rule 2

Algorithm (CCA)

Rationale for Tree Construction Broadcast trees may not be suitable for

convergecast

Broadcast ConvergecastSame data packet is transmitted to all nodes

Different data packets are collected

Latency depends on longest tree path

Latency depends on # of parallel transmissions

Tree Construction Algorithm

Constructs tree following greedy approach A set of nodes chooses closest neighbors as its

children – subject to This process is followed iteratively until all the

nodes in the network join the tree

rule

Tree Construction Algorithm

S

c d

e f

g

1

2 3

3

3

Network Tree

S

c d

e f

g

1

2 3

3

3

3

1.4

2.2

2

1

Channel Allocation Algorithm

A fixed number of CDMA codes are given Each node is assigned a triplet (Transmission

Code, Reception Code, Transmission Time Slot) Reception code of a node and Transmission

code of all its children are same A node uses a time slot and a code for

transmission if Its parent is receiving using same code Choosing the code and time slot will avoid any

collisions with all of its neighbors

Channel Allocation Algorithm

S

c d

e f

g

1

2 3

3

3

3

1.4

2.2

2

1

Network

S

c d

e f

g

1

2 3

3

3

(1, 1,1) (1, 1,2)

(2, 1,1)

(1,2,2)(1,1,3)

(Transmission Code, Reception Code, Transmission Time Slot)

Results

Energy for Convergecast ( = 3)

[Valli03] and [CCA] consumes almost same amount of energy for convergecast

[CCA] gains upto 8% over [Imrich87] for network of size >150 nodes

Results

Latency for Convergecast ( = 3)

[CCA] is almost 4 times faster than [Valli03] and 2 times faster than [Imrich87]

Conclusions and Future Work

Proposed a tree construction and channel allocation algorithm for convergecast satisfying two objectives

Showed that broadcast trees are not efficient for convergecast

The proposed work should be studied for distributed manner

Cluster based convergecast can be studied in future work

References

[Valli03] V. Annamalai., S.K.S. Gupta and L. Schwiebert “On Tree-Based Convergecasting in Wireless Sensor Networks”. IEEE Wireless Communications and Networking Conference 2003, New Orleans 2003.

[Imrich87] I. Chalmatac. and S. Kutten “Tree-Based Broadcasting in Multihop Radio Networks”. IEEE Transactions on Computers Vol. C-36, No. 10, Oct 1987.

[Wendi00] W. R. Heinzelman, A. Chandrakasan and H. Balakrishnan “Energy-Efficient Communication Protocol for Wireless Micro Sensor Networks”. Proceedingsof the Hawaii International Conference on System Science, Jan 2000.

Reference

[Step02] S. Lindsey, C. Raghavendra, K. M. Sivalingam “Data Gathering Algorithms in Sensor Networks Using Energy Metrics”. IEEE Transactions on Parallel and Distributed Systems, Vol. 13, No. 9, Sept 2002.

[Bhas02] B. Krishnamachari, D. Estrin and S. Wicker “Impact of Data Aggregation in Wireless Sensor Networks”. International Workshop on Distributed Event-Based Systems (DEBS, ‘02) Vienna, Austria, July 2002.