Real-Time and Reliable Wireless Sensor Networks for Smart Wireless Automation Applications

Real-Time and Reliable WSNsfor Smart Wireless

Automation Applications

Maurizio Bocca, M.Sc.Department of Automation and Systems

TechnologyAalto University School of Electrical Engineering

www.wsn.tkk.fi

2

WSNs Applications

Maurizio Bocca - Automaatio XIX, Helsinki, 16.3.2011

3

Wireless Automation Challenges

• Energy efficiency: Guarantee an extended lifetime of the system

• Scalability: Cope with a large and varying number of nodes

• Reliability: Packets must arrive at destination

• Timeliness: Fulfill the deadlines of the monitored industrial

processes


4

Outline

-7 -6 -5 -4 -3 -2 -1 0 1-1

0

1

2

3

4

5

6

7

x-coordinate [m]

y-co

ordi

nate

[m

]

Node position Real path Tracked path

TSMP-Lite Initialization

RNP Protocol

Device-Free Tracking


5

TSMP-Lite Initialization

• TSMP-Lite: Time Synchronized Mesh Protocol for WSNs applications

• Network initialization procedure: Neighbors discovery and connectivity graph

Useful to adjust the routes in case of nodes failures Link quality evaluation and topology definition High-accuracy time synchronization

For energy-efficient multi-channel time-slotted communications


6

Case Study: Industrial Environment


7

Case Study: Greenhouse


8

Real-Time Networking Protocol

• Mesh networking based on nodes cooperation: Transmission in broadcast mode based on network

status Packet forwarding over multiple hops by

pyggybacking Redundant paths to be utilized when required Base for reliable wireless data transfer

Network status related information


9

RNP MAC and PHY Layers

• TDMA and CSMA hybrid channel access: TDMA to control delays and introduce determinism CSMA for avoiding collisions and improving

coexistance with other systems

• Antenna diversity: Additional redundancy at the physical layer Reduces link failures and need for retransmissions Improves reliability and decreases latency

GW 2 3

CSMA

Frame 1 Frame 2 Frame 3 Frame 1

GW 2 3 ALL GW 2 3 ALL GW 2

TDMA

ALL

CSMATDMA CSMATDMA TDMA

Superframe 1

GW 2 ...

CSMA

Frame 1 Frame 2 Frame 3 Frame 1

GW 2 ... ALL GW 2 ... ALL GW 2

TDMA

ALL

CSMATDMA CSMATDMA TDMA

Superframe 1

n n n


10

Case Study: Industrial Environment

Time (ms) Node 2 Node 3 Node 4 Node 5

0 < 100 99,9367 99,91009 99,98159 99,96224

100 < 500 0,038032 0,049052 0,016261 0,036419

> 500 (lost) 0,025265 0,040854 0,00215 0,001344

Received 99,97473 99,95915 99,99785 99,99866

Lost 0,025265 0,040854 0,00215 0,001344

Time (ms) Node 2 Node 3 Node 4 Node 5

0 < 100 99,99094 99,96132 99,99849 99,99472

100 < 500 0,009057 0,038676 0,001509 0,005283

> 500 (lost) 0 0 0 0

Received 100 100 100 100

Lost 0 0 0 0

NO antenna diversity

WITH antenna diversity


11

Device-Free Tracking

• A person crossing a LoS link between two nodes causes shadowing of the radio signal

• Movement in the close proximity of the nodes causes multipath fading

• Distributed processing of the RSSI: RSSI signals are processed locally in the nodes to

detect significant changes The nodes transmit to the sink only information

concerning significant events

• High-accuracy time synchronizationMaurizio Bocca - Automaatio XIX, Helsinki, 16.3.2011

12

DF Tracking Performance (1/2)

• Alarm notifications received from the network processed at the sink

• Tracking performance improved by applying a Kalman filter

• Experimental setup: 12 nodes covering 36 m2

• Average error: 0.17 m

-7 -6 -5 -4 -3 -2 -1 0 1-1

0

1

2

3

4

5

6

7

x-coordinate [m]

y-co

ordi

nate

[m

]

Node position Real path Tracked path


13

DF Tracking Performance (2/2)

• Distributed RSSI processing reduces the communication overhead Alarm notifications account only for 7.18 % of the

total number of broadcasts

• Through time synchronization, the radio is enabled for: TX slot: 2.30 ms RX slot: 4.05 ms

• Extended system lifetime

10 20 30 40 500

1

2

3

4

5

6

7

8

9

Transmission interval [ms]

Exp

ecte

d S

yste

m L

ifet

ime

[day

s]

Radio ON-OFFRadio always ON


14

Conclusions

• The use of WSNs in industrial environment brings several advantages: Possibility to deploy a high number of

sensors/actuators at a reduced cost Improved screening capability Reduction of installation time and costs Ease of maintenance

• Industrial applications are expected to increase significantly in number over the next years


15

A Look at the Future

“The Economist”December 2010


16

Thank You!

[email protected]://autsys.tkk.fi/MaurizioBocca

Questions?

mailto:[email protected]