Energy ConservationinWireless Sensor Networks
Giuseppe Anastasi
Pervasive Computing & Networking Lab (PerLab)
Dept. of Information Engineering, University of Pisa
E-mail: giuseppe.anastasi@iet.unipi.it
Website: www.iet.unipi.it/~anastasi/
PerLabCOST Action IC0804 Training School – Palma de Mallorca, Spain, April 24-27, 2012

Overview
PerLabIntroduction
The Energy Problem in WSNs
Energy Conservation in static WSNs
Data-driven approaches
Topology Management
Power Management

Energy Conservation in WSNs with Mobile Nodes
Power Management & MN Discovery

WSNs for Energy Efficiency
Energy Efficiency in Buildings
Adaptive Lighting in Tunnels
21Introduction

Sensor Node Architecture
PerLabUsually Short
negligible
rangeLocal
wirelessdatacommunication
processing
Battery powered devices
powerRadio noris the most powerand data
hungrystoragecomponent
Batteries cannot be changed
consumption
recharged
42

Wireless Sensor Networks
PerLab5

WSNs with Mobile Nodes
PerLabMobile Collector Node63

Potential Application Areas
PerLabMilitary Applications
Environmental Monitoring
Precision Agriculture
Health Monitoring
Smart Home/OfficeIntelligent Transportation Systems
Industrial applications…

7

The Energy Problem

4

The energy problem
PerLabEnergy is the key issue in the WSN design
Applications may require a network lifetime in the order ofseveral months or even years
If always active, sensor nodes deplete their energy in lessthan a week

Possible approaches
Low-power sensor nodes
Energy harvesting
Energy conservation
Energy efficient protocols/applications
Cross-layering…
9

TmoteSky Mote
PerLab10

5

Breakdown of TmoteSky Energy Consumption
PerLabNakyoung Kim, Sukwon Choi, Hojung Cha,
Automated Sensor-specific Power Management
for Wireless Sensor Networks, Proc. IEEE MASS
2008, Atlanta, USA, Setp. 29 – Oct. 2, 200811

Power Consumption of CC2420
PerLabSupply Voltage: 1.8 V

Mode

Current

Power
Consumption

Reception

19.7 mA

35.46 mW

Transmission

17.4 mA

31.32 mW

Idle

0.426 mA

0.77 mW

Sleep

20 µA

36 µW

Source: Chipcon CC2420 Data sheet
2.4 GHz IEEE 802.15.4/ZigBee-ready RF Tranceiver
http://focus.ti.com/docs/prod/folders/print/cc2420.html
126

Energy Conservation in
Static WSNs

Energy conservation
PerLabGoal
Try to reduce as much as possible the radio activity,
possibly performing local computations
The radio should be in sleep/off mode as much as possible

Different approaches
Energyconservation

Duty-cycling

Data-driven

Mobility-based

G. Anastasi, M. Conti, M. Di Francesco, A. Passarella, Energy Conservation in Wireless Sensor
Networks: A Survey, Ad Hoc Networks, Vol. 7, N. 3, May 2009. Elsevier.

14

7

Mobility-based Energy Conservation
PerLabMobility-based
Approaches

Mobile Sink

Mobile Relay

Mobility-based schemes will be re-considered in theframework of WSNs with Mobile Nodes
15

Data-driven approaches
PerLabReduces the amount of data to be transmittedThis reduces the radio activity and, hence, the energy
consumption
Data-driven
Approaches

Data
Reduction

Data
Aggregation

Energy-EfficientAcquisition

Data
Compression

Data
Prediction
16

8

Data aggregation
PerLabData can be reduced as it flows through the network
E.g., which is the max/min temperature in sensing area?
Each intermediate nodes forwards just one value to the sinkAlso called in-network aggregation
Application-specific schemes
22
23
23
Sink

24

21
24
23
24

25

24
17

Model-driven Data Prediction
PerLabInstead of reporting all data to sink, only sends thetrend
only if and when it changes

Acquired data value

18

9Limitations of Data-driven approaches
PerLabJust reducing the amount of data does notnecessarily result in energy consumption
reduction
Transmitting a message requires approximately thesame energy, irrespective of the message size
Energy costs for maintaining the sensor network
cannot be avoided
Data reductions eliminates data redundancy
100% communication reliability is required
How much energy-consumption reduction in practice?
19

Limitations of data-driven approaches
PerLabUsman Raza, Alessandro Camerra, Amy L Murphy, Themis Palpanas, Gian Pietro Picco,
What Does Model-Driven Data Acquisition Really Achieve in Wireless Sensor
Networks?, Proc. IEEE PerCom 2012, Lugano, Switzerland, March 19-23, 2012.

WSN for adaptive lighting in road tunnels
Model-driven data acquisition approach
Derivative-Based Prediction (DBP)

The proposed technique suppresses 99.1% of reports
However, lifetime “only” triples
Idle listening
Overhead introduced by the routing protocol
Routing tree management

Need for reliable communication protocols

20

10

Duty-cycling
PerLabDuty-cycling

Topology
controlPowermanagement

Node’s components are
switched off when notneededTopology Control
Exploits network redundancy
Selects the minimum set of nodes that guarantees connectivity
All the other nodes are kept in sleep mode to save energy
Increases the network lifetime by a factor depending on the
degree of redundancy
typically in the order of 2-3
21

Duty-cycling
PerLabDuty-cycling

Topology
controlPowermanagement

Node’s components are
switched off when notneededPower Management
Exploits idle periods in the communication subsystem
Switches off the radio during inactive periods
Extends the network lifetime significantly
Duty cycles of some percents are quite common in WSNs

22

11

Topology Control

Topology Control
PerLab

How many nodes to activate?
Few active nodes:
Distance between neighboring nodes high -> increase packet
loss and higher transmit power and reduced spatial reuse;reuse;

Too many active nodes:
At best, expending unnecessary energy;
energy;At worst nodes may interfere with one another by congesting
the channel.

2412Topology control protocols
PerLab

Goal:
Find out the minimum subset of nodes that is able toensure network connectivity
Approaches
Location driven
needs to know the exact location of nodes
GAF
Topology
Connectivity driven
control
more flexibility
ASCENT, SPAN
Location
Connectivity
drivendriven25

Geographic Adaptive Fidelity (GAF)
PerLabEach node knows its location (GPS)A virtual grid of size r issuperimposed to nodes
Each node in a grid is equivalentfrom a traffic forwarding perspective
Keep 1 node awake in each grid ateach timeABCR ≥ r 2 + (2r )

2

1

2

4

r
3
r

5

r≤

R
5

Y. Xu, J. Heidemann, D. Estrin, Geography-informed Energy Conservation for Ad Hoc, Proc. ACM
MobiCom 2001, pp. 70 – 84. Rome, 2001.
26

13

Geographic Adaptive Fidelity (GAF)
PerLabTopology Management + Routing
Clustering
Cluster-head election
Cluster-head rotation for uniform energy consumption
All nodes inside a cluster, but the cluster-head, are sleeping

Routing
As soon as the cluster-head detects an event, it wakes up all theother nodes in the cluster
The cluster-head receives packets from cluster nodes, andforwards them to the sink node (no data aggregation)

27

ASCENT
PerLab

Adaptive Self-Configuring sEnsor Networks Topologies
Does not depend on the routing protocol
Decision about joining the network based on local

measurements
Each node measures the number of neighbors and packet loss
locally.
locally
Each node then makes an informed decision to join the network
topology or to sleep by turning its radio off.

A. Cerpa, D. Estrin, Ascent: Adaptive Self-Configuring Sensor Network Topologies, Proc. IEEE
INFOCOM 2002.
28

14

ASCENTPerLab• Nodes can be in active or passive state– Active nodes are part of the topology (or stay awake) and forward data
packets– Nodes in passive state can be sleeping or collecting network
measurements. They do not forward any packets.
– An active node may send help messages to solicit passive neighbors
to become active if it is experiencing a low message loss
– A node that joins the network (test state) sends an announcement
message.
– This process continues until the number of active nodes is such thatthe experienced message loss is below a pre-defined applicationdependent threshold.
– The process will re-start when some future network event (e.g. a node
failure) or a change in the environmental conditions causes anincrease in the message loss.
A. Cerpa, D. Estrin, Ascent: Adaptive Self-Configuring Sensor Network Topologies, Proc. IEEE
INFOCOM 2002.
29

ASCENT
PerLabNetwork Self-Configuration - Example(a) A communication hole is detected(b) Transition from passive to active state(c) Final State
A. Cerpa, D. Estrin, Ascent: Adaptive Self-Configuring Sensor Network Topologies, Proc. IEEE
INFOCOM 2002.
30

15

ASCENTPerLabA. Cerpa, D. Estrin, Ascent: Adaptive Self-Configuring Sensor Network Topologies, Proc. IEEE
INFOCOM 2002.
31

ASCENT Performance
PerLabEnd-2-end Delivery Ratio

Energy Savings

ASCENT

Adaptive
ACTIVE (always ON)

Fixed

A. Cerpa, D. Estrin, Ascent: Adaptive Self-Configuring Sensor Network Topologies, Proc. IEEE
INFOCOM 2002.
32

16

Power Management

Power Management
PerLabDuty-cycling

Topology
Control

PowerManagement

Generalsleep/wakeup
schemes

Low duty-cycle
MAC protocols

34

17

General sleep/wakeup schemes
PerLabWhen should a node wake up for communicatingwith its neighbors?

35

General sleep/wakeup schemes
PerLabWhen should a node wake up for communicatingwith its neighbors?
When another node wants to communicate with it (ondemand)At the same time as its neighbors (scheduled rendez-vous)
Clock synchronization required

Whenever it wants (Asynchronous)
Generalwake-upschemesOn-demand

Scheduled
rendez-vous

Asynchronous

STEM, PTW

Fully Sync, (Adaptive) Staggered

AWP, RAW36

18

On-demand Schemes
PerLabSparse Topology and Energy Management (STEM)
Wake up the nodes along the path
Sensor-triggered node wakeup
user
event
Zzz

Zzz

Zzz

Zzz

sensor network
Path nodes need to be woken up

C. Schurgers, V. Tsiatsis, M. B. Srivastava, STEM: Topology Management for Energy Efficient Sensor
Networks, IEEE Aerospace Conference '02, Big Sky, MT, March 10-15, 2002.
37

On-demand Schemes
PerLabSparse Topology and Energy Management (STEM)
Can be used in combination with topology control
GAF + STEM can provide a duty cycle of about 1%

STEM trades energy saving for path setup latency
Two different radios
data transmissions
wakeupsWakeup radio
Data radio

C. Schurgers, V. Tsiatsis, M. B. Srivastava, STEM: Topology Management for Energy Efficient Sensor
Networks, IEEE Aerospace Conference '02, Big Sky, MT, March 10-15, 2002.
38

19

On-demand Schemes
PerLabSparse Topology and Energy Management (STEM)
Wakeup Radio
Ideally, a low-power radio should be used
It would result in a wakeup range shorter than the data transmission
range

In practice, two similar radios are used for data and wakeup
Similar power consumption, similar transmission range

Duty cycle on the wakeup radio, using an asynchronous
approach
A potential target node wakes up periodically
The initiator node transmits a stream of periodic beacons (STEM-B) or acontinuous wakeup tone (STEM-T)

C. Schurgers, V. Tsiatsis, M. B. Srivastava, STEM: Topology Management for Energy Efficient Sensor
Networks, IEEE Aerospace Conference '02, Big Sky, MT, March 10-15, 2002.
39

Power Management on Wakeup RadioPerLabAsynchronous Initiator
Periodic beacon transmission
Busy tone

Potential Target Nodes periodically listening
S
Ton~

~

~Tidle~Trx = Ton + Tidle + Ton

R~Trx~
C. Schurgers, V. Tsiatsis, M. B. Srivastava, STEM: Topology Management for Energy Efficient Sensor
Networks, IEEE Aerospace Conference '02, Big Sky, MT, March 10-15, 2002.
40

20

On-demand Schemes
PerLabAntenna

Radio-triggered Power Management

Radio

ON/OFFCPU

Wakeup Message
Radio-triggered circuit
interrupt

L. Gu, J. Stankovic, Radio-Triggered Wake-up for Wireless Sensor Networks, Real-Time Systems
Journal, Vol. 29, pp. 157-182, 2005.
41

General sleep/wakeup schemes
PerLabWhen should a node wake up for communicatingwith its neighbors?
When another node wants to communicate with it (ondemand)At the same time as its neighbors (scheduled rendez-vous)
Clock synchronization required

Whenever it wants (Asynchronous)
Generalwake-upschemesOn-demand

Scheduled
rendez-vous

Asynchronous

STEM, PTW

Fully Sync, Staggered, FPS

AWP, RAW

42

21

Scheduled Rendez-Vous
PerLabFully Synchronized Scheme (TinyDB)
1
...

2
3

4

...
...

Cons
Global duty-cycle

Pros
Simplicity

low energy efficiency

StaticSam Madden, Michael J. Franklin, Joseph M. Hellerstein and Wei Hong. TinyDB: An Acqusitional Query
Processing System for Sensor Networks. ACM TODS, 2005

43

Scheduled Rendez-Vous
PerLabFixed Staggered Scheme (TAG, TASK)
1
...

2
3

4

...
...

Parent-child talk intervals
Adjacent to reduce sleep-awake commutations
Cons
Pros
Staggered scheme
Suitable to data aggregation

Fixed activity times
Global parameters

Samuel R. Madden, Michael J. Franklin, Joseph M. Hellerstein, and Wei Hong. TAG: a Tiny AGgregation
Service for Ad-Hoc Sensor Networks. OSDI, December 2002
44

22

Scheduled Rendez-Vous
PerLab

Adaptive Staggered Scheme (ASLEEP)

Adaptive talk interval

Components

number of children
network traffic
channel conditions
nodes join/leaves, etc.

Talk Interval Prediction
Sleep Coordination

G. Anastasi, M. Conti, M. Di Francesco, Extending the Lifetime of Wireless Sensor Networks throughAdaptive Sleep, IEEE Transactions on Industrial Informatics, Vol. 59, N.2, February 2010.
45

ASLEEP Components
PerLabTalk Interval Prediction Algorithm
Sleep Coordination Algorithm
Direct Beacons
Reverse Beacons

Beacon Protection
Beacon Loss Compensation

46

23

ASLEEP: Analysis in Dynamic Conditions
PerLab2500

measured TI
q = 50 msecs
q = 100 msecs
q = 150 msecs

T a lk in te rva l (m s e c s )

2000
1500
1000
500
0
0

200

400
600
Communication period #

800

1000
47

Performance Comparison
PerLab
Latency (30 nodes)
100% loss
10% loss
20% loss

94

0

ASLEEP

Fixed
TAG
Sleep scheduling algorithm

50
40

0.07880.0721

0.06940.4132160

0.40603
270

Always-on

Delivery ratio (30 nodes)
100

30

90

ASLEEP

1.96

2.06

1.48

80

Fixed
TAG
Sleep scheduling algorithm

Always-on

Average delivery ratio (%)

0

5.83

10

2.96

20
1.37

Average duty-cycle (%)

80

50.330090

60.73220% loss
10% loss
20% loss

7

0.4093Duty-cycle (30 nodes)
100

0.2819Average latency (secs)

8

70
60
50
40
30
20
10
0

0% loss
10% loss
20% loss

ASLEEP

Fixed
TAG
Sleep scheduling algorithm

Always-on

48

24

General sleep/wakeup schemes
PerLabWhen should a node wake up for communicatingwith its neighbors?
When another node wants to communicate with it (ondemand)At the same time as its neighbors (scheduled rendez-vous)
Clock synchronization required

Whenever it wants (Asynchronous)
Generalwake-upschemesOn-demand

Scheduled
rendez-vous

Asynchronous

STEM, PTW

Fully Sync, (Adaptive) Staggered

RAW, AWP, …

49

Random Asynchronous Wakeup (RAW)
PerLabRouting Protocol + Random Wakeup Scheme
Several Paths towards the destination
Especially if the network is dense

Forwarding Candidate Set (FCS)
set of active neighbors that are closest to the destination
In terms of number of hops (h-FCS)
In terms of distance (d-FCS)

V. Paruchuri, S. Basavaraju, R. Kannan, S. Iyengar, Random Asynchronous Wakeup Protocol for
Sensor Networks, Proc. IEEE Int’l Conf. On Broadband Networks (BROADNETS 2004), 2004.
50

25

Random Asynchronous Wakeup (RAW)
PerLabAlgorithm
Each node wakes up randomly once in every time interval of
fixed duration T
Remains active for a predefined time Ta (Ta < T), and thensleeps again.
Once awake, a node looks for possible active neighbors byrunning a neighbor discovery procedure.
If S has to transmit a packet to D and in the FCS of S there are m neighbors,then the probability that at least one of these neighbors is awake along with
S is given by 2 ⋅ Ta 
P = 1 − 1 −

T 


m

V. Paruchuri, S. Basavaraju, R. Kannan, S. Iyengar, Random Asynchronous Wakeup Protocol for Sensor
Networks, Proc. IEEE Int’l Conf. On Broadband Networks (BROADNETS 2004), 2004.
51

Random Asynchronous Wakeup (RAW)
PerLab

Performance 2 ⋅ Ta 
P = 1 − 1 −

T 


m

V. Paruchuri, S. Basavaraju, R. Kannan, S. Iyengar, Random Asynchronous Wakeup Protocol for Sensor
Networks, Proc. IEEE Int’l Conf. On Broadband Networks (BROADNETS 2004), 2004.
52

26

Asynchronous Wakeup Protocol (AWP)
PerLab

124
235
346
547
561
672
713
slot

1

2

3

4

5

6

7

An example of asynchronous schedule based on a symmetric (7,3,1)-design of the
wakeup schedule function.
R. Zheng, J. Hou, L. Sha, Asynchronous Wakeup for Ad Hoc Networks, Proc. ACM MobiHoc 2003, pp 3545, Annapolis (USA), June 1-3, 2003.
53

Asynchronous Sender and Periodic Listening
PerLabS~

Ton~~Tidle~Trx = Ton + Tidle + Ton

R
~Trx~

54

27

Asynchronous Sender and Periodic Listening
PerLabS~Ttx~
Ttx ≥ Trx

R
~Trx~

55

Power Management
Low-duty Cycle MAC Protocols

28Power Management
PerLabDuty-cycling

Topology
Control

PowerManagement

Generalsleep/wakeup
schemes

Low duty-cycle
MAC protocols

57

Low duty-cycle MAC protocols
PerLab

Embed a duty-cycle within channel access
TDMA-based (Bluetooth, LEACH, TRAMA)
effective reduction of power consumption
need precise synchronization, lack flexibility

Contention-based ([B,S,T,D]-MAC, IEEE 802.15.4)
good robustness and scalability
high energy expenditure (collisions, multiple access)Hybrid schemes (Z-MAC)
switch between TDMA and CSMA based on contention
Low duty-cycle
MAC protocols

TDMA-based

Contentionbased

Hybrid58

29

TDMA-based MAC Protocols
PerLab

TDMA: Time Division Multiple Access
access to channel in "rounds"
each station gets fixed length slot (length = pkt transtime) in each round - Guaranteed Bandwidtheach station is active only during its own slot, and cansleep during the other slots
unused slots go idle
example: 6-station WSN, 1,3,4 have pkt, slots 2,5,6
idle
6-slot
frame
1

3

4

1

3

4

59

LEACH
PerLabLow Energy Adaptive Clustering Hierarchy
Nodes are organized in clusters
A Cluster-Head (CH) for each cluster
Coordinates all the activities within the cluster

Nodes report data to their CH through TDMA
Each nodes has a predefined slot
Nodes wakeup only during their sleep

The CH has the highest energy consumption

W. R. Heinzelman, A. Chandrakasan, and H. Balakrishnan, Energy-Efficient Communication Protocol
for Wireless Microsensor Networks, Proc. Hawaii International Conference on System Sciences,
January, 2000.
60

30

LEACH Phases
PerLab

1. Subscription (Cluster Formation)
2. Synchronization
3. TDMA Table update notification
4. Data communication
5. Remote transmission

Node 3CH

Base
StationNode 1
Node 261

LEACH-PoliMI
PerLabNode-to-nodetransmission unit

RemoteCommunication
Radio Link

Sensorial
control
Energy harvestingboard
C. Alippi, R. Camplani, G. Boracchi, M. Roveri, Wireless Sensor Networks for Monitoring Vineyard,
Chapter in “Methodologies and Technologies for Networked Enterprises” (G. Anastasi, E. Bellini, E. Di
Nitto, C. Ghezzi, L. Tanca, E. Zimeo Editors), in preparation.

62

31

Hierarchical LEACH
PerLabCluster Heads also use a TDMA approach for sending data
received from Cluster Nodes to the Base Station

63

TDMA-based MAC Protocols: Summary
PerLabHigh energy efficiency
Nodes are active only during their slots
Minimum energy consumption without extra overhead

Limited Flexibility
A topology change may require a different slot allocation
pattern

Limited Scalability
Finding a scalable slot allocation function is not trivial,
especially in multi-hop (i.e., hierarchical) networks

Interference prone
Finding an interference-free schedule may be hard
The interference range is larger than the transmission range

Tight Synchronization Required
Clock synch introduces overhead
64

32

CSMA-based MAC Protocols
PerLabNo synchronization required
Robustness
Synch may be needed for power management

Large Flexibility
A topology change do not require any re-configurationor schedule update notification

Limited Scalability
A large number of nodes can cause a large number ofcollisions and retransmissions

Low Energy Efficiency
Nodes may conflict
Energy consumed for overhearing
65

IEEE 802.15.4/ZigBee standard
PerLabIEEE 802.15.4
Standard for low-rate and low-power PANs
PHY and MAC layers
transceiver management, channel access, PAN management

ZigBee Specifications
Network/security layer
Application framework

66

33

IEEE 802.15.4: MAC protocol
PerLabTwo different channel access methods
Beacon-Enabled duty-cycled mode
Non-Beacon Enabled mode (aka Beacon Disabled mode)

67

IEEE 802.15.4: Beacon Enabled mode
PerLab

ActiveBeaconBeacon

GTS

CAP

GTS

Inactive

CFP

SD = aBaseSuperFrameDuration*2SO sym
BI = aBaseSuperFrameDuration*2BO sym

68

34

CSMA/CA: Beacon-enabled mode
PerLab

Wait for a random
backoff time
Check channel status
(CCA)

No

Idle?

At each trial the backoffwindow size is doubled
Only a limited number ofattempts is permitted(macMaxCSMABackoffs)

Yes
Check channel status
(CCA)

Idle?

No

Yes

Transmission
69

Acknowledgement Mechanism
PerLab

Optional mechanism
Destination SideACK sent upon successful reception of a data frame

Sender side
Retransmission if ACK not (correctly) received within thetimeout
At each retransmission attempt the backoff window size
is re-initialized
Only a maximum number of retransmissions allowed(macMaxFrameRetries)

70

35

IEEE 802.15.4: MAC protocol
PerLabTwo different channel access methods
Beacon-Enabled duty-cycled mode
Non-Beacon Enabled mode (aka Beacon Disabled mode)

71

Comparison between BE and BD
PerLab72

36

Comparison between BE and BD
PerLab

MAC Unreliability Problem in IEEE
802.15.4 Beacon-Enabled MAC Protocol

G. Anastasi, M. Conti, M. Di Francesco, A Comprehensive Analysis of the MAC Unreliability Problem
in IEEE 802.15.4 Wireless Sensor Networks, IEEE Transactions in Industrial Informatics, Vol. 7, N. 1,
Feb 2011.
73

MAC with asynchronous PM
PerLab802.15.4 Non-Beacon Enabled
Asynchronous: nodes can wake up and transmit at
any time
Possible conflicts are regulated by CSMA/CA

It assumes that the destination is always ON
The destination may be either the sink or a ZigBee routerThis is a strong limitation

74

37

B-MAC with Low-power Listening
PerLab

Availability
Designed before IEEE 802.15 MAC (at UCB)
Shipped with the TinyOS operating system

B-MAC design considerations
simplicity
configurable options
minimize idle listening (to save energy)

B-MAC components
CSMA (without RTS/CTS)
optional low-power listening (LPL)
optional acknowledgements
75

B-MAC Low-power Listening mode
PerLabNodes periodically sleep and perform LPL
Nodes do not synchronized on listen time
Sender uses a long preamble before each packet
to wake up the receiver

Constraint: check interval ≤ preamble duration

Shift most burden to the sender
Every transmission wakes up all neighborspresence of chatty neighbor leads to energy drain in dense
networks
Preambles can be really long!
76

38

Conclusions&
Research Key Questions

Summary
PerLabEnergyconservation

Duty-cycling
Duty-cycling

Topology
Control

Data-driven

Mobility-based

PowerManagement

Generalsleep/wakeup
schemes

Low duty-cycle
MAC protocols
78

39

Key Research Questions
PerLabData-driven approaches can significantly reduce
the amount of data to be transmitted
Up to 99% and beyond

However, this does not necessarily result inenergy consumption reduction, due toEnergy costs introduced by transmission overhead,
network management
Additional costs due to communication reliability

Are they really useful in practice?
79

Key Research Questions
PerLabTopology Management exploits node redundancy
The increase in the network lifetime depends on the actual
redundancy, and is limited in practice (some %)It allows a longer lifetime at the cost of increased
redundancy (i.e., larger economic costs)

80

40

Key Research Questions
PerLabPower Management eliminates idle times
May provide very large energy reductions, with limited
costs (in terms of additional complexity)
Energy Efficiency vs. Robustness
Simple approaches
high robustness/limited energy efficiency
Complex approaches
higher energy efficiency but lessrobustness
Very complex solutions cannot work in practice81

Key Research Questions
PerLabGeneral (i.e., application-layer) sleep/wakeup
schemes or MAC-layer schemes?

And which MAC protocol?
TDMA or contention-based (802.15.4, B-MAC)?
IEEE 802.15.4: BE or BD?
…

82

41

Key Research Questions
PerLabIs the radio the most consuming component?
SensorProducer

Sensing

Power
Cons.

STCN75

STM

Temperature

0.4 mW

QST108KT6

STM

Touch

7 mW

iMEMS

ADI

Accelerometer(3 axis)30 mW

2200 Series, 2600
SeriesGEMS

Pressure

50 mW

T150

GEFRAN

Humidity

90 mW

LUC-M10PEPPERL+F
UCHS

Level Sensor

300 mW

CP18, VL18,
GM60, GLV30

VISOLUX

Proximity

350 mW

TDA0161

STM

Proximity

420 mW

FCS-GL1/2A4AP8X-H1141

TURCK

Flow Control

1250 mW

Power Consumption
Radio

ProducerTransm.

JN-DSJN513x(Jennic)

Jennic

CC2420(Telos)

Texas
Instruments

Reception

111 mW(1 dBm)

111 mW

31 mW(0 dBm)

35 mW

CC1000(Mica2/Mica2
dot)

Texas
Instruments

42 mW(0 dBm)

29 mW

TR1000(Mica)RF
Monolithics

36 mW(0 dBm)9 mW

C. Alippi, G. Anastasi, M. Di Francesco, M. Roveri, Energy Management in Sensor Networks with Energy-hungry Sensors, IEEE
Instrumentation and Measurement Magazine, Vol. 12, N. 2, April 2009
83

Key Research Questions
PerLabPower Management or Energy Harvesting?
Power management reduces energy consumption, whileenergy harvesting captures energy

Are they really alternative approaches?

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Key Research Questions
PerLabWhen using energy harvesting the WSN protocols
and applications can take advantage of theavailable energy
How to maximize the WSN performance while
guaranteeing perpetual operations (i.e., infinite
lifetime)?

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References
PerLab

G. Anastasi, M. Conti, M. Di Francesco, A. Passarella, Energy
Conservation in Wireless Sensor Networks: a Survey,
Survey Ad Hoc
Networks, Vol. 7, N. 3, pp. 537-568, May 2009. Elsevier.
C. Alippi, G. Anastasi, M. Di Francesco, M. Roveri, Energy
Management in Sensor Networks with EnergyEnergy-hungry
Sensors, IEEE Instrumentation and Measurement Magazine,
Vol. 12, N. 2, pp. 16-23, April 2009.
M. Di Francesco, S. Das, G. Anastasi, Data Collection in
Wireless Sensor Networks with Mobile Elements: A Survey,
SurveyACM Transactions on Sensor Networks, Vol. 8, N.1, August
2011.
Available at
http://www.iet.unipi.it/~anastasi/
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