A Survey on Sensor Networks

Ian F. Akyildiz, Weillian Su, Yogesh Sankarasubramaniam, Erdal Cayirci

Presented by Alexandra Czarlinska

IEEE Communications Magazine, August 2002

Goals and Structure of this Paper

Survey Communication

Protocols for the 5 Layers

Special

constraints of

Sensor NetworksCommunication

Topology

Communication in Sensor Networks

Do these protocols work for Sensors? Encourage

new research

Analysis and

Conclusions

Introduction

Communication Topology

Sink / Base Station

Task Manager Node

Internet or Satellite

Self-organizing, non-homogenous Sensor Network

End User

Multi-hop wireless

Cluster-Head or Aggregator

Density of nodes μ(R) = N πR2/A

N = # of nodes in area AR is radio range

area A

Tiny sensor node with 7 sensing devices ; Photoresistor, Temperature, Barometric pressure, Barometric Pressure and Temperature, Humidity, Thermopile and Thermistor

UC- Berkeley mote

Inside a Sensor Node

Location Finder Mobilizer

Power Unit

Sensor ADCProcessor

StorageTX/RX

Actuator

Power Generator

Special Constraints for Communication in Sensor Networks

Fault Tolerance

Handle loss of nodes

ScalabilityHandle high density of nodes

CostsNodes die, make them low cost

Hardware LimitationsNodes are tiny

Changing Topology

Nodes moving, new nodes, loss of nodes

Hostile Environment

Survive and maintain communication

Transmission Media

wireless: RF, optical, infrared

PowerLimited Tx, computation, and lifetime

Security ?Security ?Confidentiality, Authentication

etc

Protocol Stack and Sensor Network Management

5. Application Layer5. Application Layer

4. Transport Layer 4. Transport Layer

3. Network Layer3. Network Layer

2. Data Link Layer 2. Data Link Layer

1. Layer Physical1. Layer Physical

Po

wer

Po

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Mo

ving

Mo

ving

Co

llabo

ration

C

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Sensor Network Manage-ment

1. Physical Layer

Responsible for frequency selection, modulation and dataEncryption. The big issue here is Power!

encryption

???modulation

freq 915 MHz?

0 1 1 0 1 0 1 . . .

source

Transmit

Sink

d distance

Low-lying antenna

Power to transmit

≈ dn where 2 ≤ n ≤ 4

High antenna

1. Physical Layer

• More research on smaller hardware that uses less power (battery!)

• Protocols that exploit node density and multi-hop redundancy

Have/Know

Need

• Binary Modulation needs less energy than M-ary modulation

• Direct Sequence Spread Spectrum is low power (transmission and security)

•Ultra wideband (UWB) uses low power, does well under multi-path and has simple Tx/Rx

2. Data Link Layer

Responsible for multiplexing of data streams, MediumAccess control (MAC) and Error Control

Problem: MAC ensures QoS and Bandwidth, not Power conservation, central base

Cellular MAC

Base Basewired

wireless

Problem: MAC ensures QoS under mobility. Not enough nodes, Tx power needed is too much, central base

Bluetooth and MANET

Master

slave

2. Data Link Layer

MAC Protocol

Method

SMACS and EAR

Fixed allocation of duplex time slots at fixed freq.

Hybrid TDMA/ FDMA

Sensors

Centralized freq. and time division

CSMA-based for Sensors

Contention-based random access

Power Conservation

Random wake up during setup and turning radio off while idle. Exploits large bandwidth available compared to sensor data rate.

Min energy use in Hardware. Picks the mix of TDMA/FDMA to min energy use

Uses constant “listening time” to min energy.

What we still need to improve

Not great for very mobile networks (good for mostly stationary nodes).

Should use more computation over handshaking. Use more Power-saving modes (sleeping). Need to derive bounds on energy needed by sensors.

3. Network Layer

Scheme Description

Flooding Broadcasts data to all neighbor nodes

Gossiping Sends data to one randomly selected neighbor

LEACH Forms a clusters to minimize energy loss

SPINSends data to sensor nodes only if they are “interested”, has 3 types of messages (ADV, REQ, DATA)

Directed Diffusion

Sets up gradients for data to flow from source to sink during interest dissemination

Have/Know

Also have: Pegasis, GEAR

Routes data supplied by the Transport Layer

3. Network Layer

Scheme Description

Power Efficiency Routing

Pick a route based on: max Power Available (PA) or, min Energy (ME), or Min Hop (MH) or Max Min PA.

SMECNCreates a sub-graph of the sensor network that contains the minimum energy path

SARCreates multiple trees where the root of each tree is one hop neighbor from the sink

Have/Know

• allow higher topology changes• Allow higher scalability

Need

3. Network LayerPower Efficiency Routing

1- Max Power Available (PA) route, 2- Min Energy (ME) route, 3- Min Hop (MH) route and 4 - Max Min PA route

A1- Max Power Available route

P = 2

P = 2

P = 2B

P = 3

P = 1

P = 4

Total P = 6

4 -Max Min

Route along which the min PA is larger than the min PA of other routes

4. Transport Layer

Helps to maintain the flow of data if the Application Layerrequires it. Needed if End-User accesses the SensorNetwork through the Internet

Have/Know

Current TCP:

• has a window mechanism that may not suit Sensor Networks

• uses end-to-end Global Addressing (nodes may have Attribute-based or Location-based addressing)

• TCP and UDP not based on power conservation and scalability

4. Transport Layer

More research is needed to see if we need new protocols and what they might be. Suggestion by authors:

Need

TCP Splitting: TCP on one side, modified UDP on the other

UDPSink

Task Manager Node

Internet

TCP

UDP

End User

5. Application Layer

Task Manager Node

Internet Sink

End User

Makes the hardware and software of the lower layerstransparent to the Task Manager Node (and End-User)

5. Application Layer

SMPSMP TADAPTADAP SQDDPSQDDP

Sensor Management Protocol

Rules for Data Aggregation, Time sync.

Moving, turning nodes on/off

Task Assignment and Data Advertisement

Protocols

Sensor Query and Data Dissemination Protocol

Interest Dissemination from:

- user to nodes- nodes to user

Issue queries, collect replies

Allows for Attribute-based and Location-

based addressing

5. Application Layer

Attribute-Based Addressing:

The locations of nodes that sense temperature higher than 70 degrees

Location-Based Addressing:

What are the temperatures read by sensors in region A

In general, more research is needed in all the areas mentioned

Need

Data Centric Routing (not Address Based Routing):

Strengths and Contributions

Great overview of what exists, why it’s good or not good for Sensor Networks

Identifies and motivates new areas of research that are needed

Identifies certain general “design principles”

Gives a table of on-going Sensor Network research projects

“A Survey on Sensor Networks”

Analysis: Weaker side

• Does not mention security enough (should be designed right into the system, not after)

• Does not mention Asymmetric Links

• Does not mention Distributed Protocols sufficiently (could have no Base Station)

Keep in Mind

• Paper assumes that nodes do not have much energy but there is new research in:

– solar cells, temperature gradients, vibrations, RF Transfer, Micro Heat Engines (using MEMS)

• Assumes high density of cheap nodes vs. a few high quality nodes (keep in mind NASA)

• Does not always assume the most General Topology (ie: there could be no Base Station, there could be multiple sensing devices on one node etc)

References

• I. F. Akyildiz, W. Su, Y. Sankarasubramaniam, E. Cyirci, “ A survey on Sensor Networks”, Computer Networks, 38(4):393-422, March 2002

• http://www.greatduckisland.net

• Chee-Yong Chong, S. P. Kumar, “Sensor networks: evolution, opportunities, and challenges”, Proceedings of IEEE, pp 1247-1256, August 2003

Appendix

Additional slides with more detail

Sensor Network Communication Architecture

area A

Fault Tolerance rk(t) = e – λk t

λ k is failure rate of node k

t is time period

Density of nodes μ(R) = N πR2/A

N = number of nodes in area A

R is radio range

Ian F. Akyildiz

Yogesh

Sankarasu-

bramaniam

Weilian Su

Erdal

Cayirci

Authors of this Survey

Georgia Institute of Technology

Prof: wireless and satellite networks, next-gen Internet

Phd: Timing recovery, ad hoc routing and Sensor Networks

Phd: Sensor Networks and next-generation wireless

Sensor Networks, mobile comm., tactical and military

School of Electrical and Computer Engineering