in Wireless Sensor Networks

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21 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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1

Energy Efficient Communication
in Wireless Sensor Networks


Yingyue Xu

11/21/2013


2

Characteristics of Sensor Devices


Ability to monitor a wide variety of
ambient conditions:


temperature,


pressure,


mechanical stress level on attached
objects…


Will be equipped with significant
processing, memory, and wireless
communication capabilities.

3

Sensor Node Architecture

Power

Unit


Power
Generator


Location Finding
System


Mobilizer


Sensor


ADC


Processor


Storage


Transceiver


4

Sensor Networks


Large number of

heterogeneous sensor
devices



Scalable


Energy constrained


Dynamic, adaptive to changeing


Data centric: data is requested based on
certain attributes, SPIN and Direct
diffusion


Application specific


Unattended operation, configuration done
automatically and repeatedly

5

Sensor Networks Architecture

6


Fault Tolerance (sustain functionalities)


Scalability (hundreds or thousands)


Production Cost (now $10, near future $1)


Hardware Constraints(small, environment,
unattended)


Network Topology (pre
-
, post
-
, and re
-
deployment)


Transmission Media (RF (WINS), Infrared
(Bluetooth), and Optical (Smart Dust))


Power Consumption (with < 0.5 Ah, 1.2 V)

Design Factors
(
Akyildiz et al, IEEE
Comm. Mag. Aug. 2002)

7

Energy Save Ideas

Task Level

Algorithm Level

Protocols Level

Physical Level

Acceptable Functionality

with Reduced Computations

Collaborative Signal Processing

and

Coordinated Communications

Power Aware Routing

and

Selective Multicasting

Radio Power Control

and

Dynamic Bandwidth Management

Application

and

QoS Driven

Energy,

Delay, and

Bandwidth

Management

8

Energy Save Methods

Power Save Protocols

Network layer

MAC layer

Topology
based

Synchronous

Asynchronous

Application
layer

Power Control
Techniques

Topology control [Tang01]

Maximum lifetime
routing

Shutdown

Scaling

Mobile
-
agent
-
based

Put a node into sleep state

Span,
LEACH

IEEE 802.11

BECA/AFECA

[Srinivasan01]

Energy aware application, localization, tracking

Assign per
-
node transmit
powers

Maximum PA route

Minimum energy route

Minimum hop route

Maximum minimum PA node route

9

Sensor node energy model

Micro Sensor Node

Power Model

(Energy Consumers and Providers)

Battery

Model

Radio Model

CPU Model

Sensor #1 Model

Sensor #2 Model



10

1.
linear model

2.
discharge rate dependent model

3.
relaxation model


Battery model

11

Radio model

r
E
r
d
E
rx
n
tx
*
*
)
(
12
2
11






Rx
elec
RF
Tx
elec
E
E
E
W



12

Computation model

t
leak
dd
dd
tot
tot
I
V
V
C
E



2
13

Sensing model

12
3
3
sin
*





r
E
g
sen
14


Turning the transceiver off may not
always be efficient. Operation in a
power
-
saving mode is energy
-
efficient only if the time spent in that
mode is greater than a certain
threshold

Power saving mode

15


Using several short hops may be
more energy efficient than using one
large hop.

Multiple hops

16


Sending>Receiving>Idle>Sleep


Small packets (such as “hello”
message) are a relatively expensive
mechanism


Broadcast is expensive in a dense
network

Some notes

17


Good for distributed environment, such as
sensor networks


Low delay


Energy efficient


Migrate the nodes near the
phenomenon
, other nodes can
keep in sleep state


Reduce network traffic


Itinerary design can further improve the lifetime of
sensor network


Fault tolerant



Mobile agent paradigm