Wireless Sensor Networks

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Nov 21, 2013 (3 years and 27 days ago)

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Wireless Sensor Networks

Mixalis Ombashis


ECE
-
654

Advanced Networks


Instructor
:
Dr. Christos
Panayiotou

Outline


Introduction



Design Factors


Fault Tolerance


Scalability


Production Cost


Hardware Constrains






Protocol Stack


Physical Layer


Data link Layer






Cross layer Protocols For WSN


XCP


XLM


What Is A Sensor ?


A sensor (
also called detector
) is a converter that
measures a physical quantity and converts it into a
signal
which can be read by an observer or by an
(
today mostly electronic
) instrument.

Applications


Area
Monitoring



Environmental
Sensing



Military
Applications



Health



Fire Detection



Home
Automation

Introduction


Sensor Node Components


Introduction


Sensor Position


Need to be engineered or predetermined


Random Deployment in inaccessible terrains


Disaster Relief Operations



Self organizing Capabilities


Protocols


Algorithms



Local Computation


Transmit Only Required Partially Processed Data


Centralized Approach where all sensors readings are gathered at a
sink
(Directed
Diffusion
)



Stationary Sink


Pre
determined
Position

Implementation of

Sensor

Field
-

Sink
-

User

Two
-
Tier Data
Dissemination Model
For Large Scale WSN


Locations are known through the
use of GPS and localization
algorithms



Homogeneous Sensor nodes



S
hort
R
ange Radio



Multiple Hops for long distances



Sinks query the network



Two level Flooding

Design Factors


Fault Tolerance


Nodes May Fail, Blocked or Physical Damaged



Ability to sustain functionalities without any
interruption due to sensor node failures





Source of Faults in WSN Applications


Node Faults


Network Faults


Sink Faults



Failure Classification


Crash or Omission


Timing


Value


Arbitrary

Design Factors


Fault detection techniques


Self
-
Diagnosis


Group Detection:
Only if a reference value is available


Hierarchical
Detection:
Trees


Fault recovery techniques


Active replication

1.
Multipath routing

2.
Sensor value aggregation

3.
Ignore values from faulty
nodes


Passive
replication

1.
Node
selection

a)
Self
-
election :
Probabilistic Algorithms

b)
Group
election:
Clusters With Cluster Heads

c)
Hierarchical
election

2.
Service
Distribution

a)
Pre
-
Copy:
Make The Code of All nodes available on all nodes before deployment

b)
Code
distribution

c)
Remote Execution

Design Factors


Scalability


Number of Deployed nodes vary from hundreds to thousands or
millions depending on the applications



Density has to be utilized
:



N

is the number of scattered nodes


R
is the ratio transmission range


μ(
R)
gives the number of nodes within the transmission radius of each node in
region
A



Production Cost


Obviously has to be
low

Design Factors


Hardware Constrains


May need to fit into a matchbox
-
sized module


Consume Extremely Low Power






Environment


Unattended in Remote geographic areas


Bottom of an ocean


Battlefield

Design Factors


Transmission Media


Wireless Medium:
Radio, Infrared


Power Consumption


Limited Power Source


May be Impossible to Replenish Power Source


The malfunctioning of few nodes can cause
significant topological changes and might require
rerouting of packets and reorganization of the
network

Protocol Stack

Management
Planes

Protocol Stack


Management Planes


Power Management Plane
:


Manage how a sensor node uses its power


Mobility Management Plane:


Detects and registers the movement of sensor nodes, so a
route back to the user is always maintained and the sensor
nodes can keep track of who their neighbour sensors are


Task Management Plane:


Sensor can work together in a power efficient way, route
data in a mobile sensor network, and share resources
between sensor nodes

Protocol Stack


The Physical Layer


Responsible for


F
requency selection


C
arrier frequency generation


S
ignal detection


Modulation


Data encryption


The Physical
Layer


Requirements


The radio must be containable in a small
device,
since
the sensor nodes are
small



The radios must be cheap, since the sensors
will
be
used in large numbers in redundant
fashion



The radio technology must work with
higher layers
in the protocol stack to consume very
low power
levels

The Physical Layer


Signal propagation effects


Power required to transmit a signal is
Proportional
to
d
n

,

(

2


𝒏

<
4

)



n

closer to
4

for low
-
lying antennas and near
ground channels, due to signal cancellation by a
ground
-
reflected ray.


Multihop

communication in a sensor network can
effectively overcome shadowing and path loss
effects, if the
node density
is high enough


Protocol Stack


The Data Link Layer


Responsible for


Multiplexing of data streams


Data frame detection


Medium Access Control


Error Control



Medium Access Control (MAC)


Two Goals:

1.
Creation of the network infrastructure

2.
Share communication resources between sensor nodes


Collision
avoidance


Energy
efficiency


Scalability in node density


Why existing MAC protocols can’t be used?


The primary goal of the existing MAC protocol is the provision of high
QoS

and bandwidth efficiency


Energy is not taken into account



MAC
protocols
for sensor network must
have


B
uilt
-
in
power
conservation


M
obility management


Failure
recovery

strategies


Medium Access Control (MAC)

Need To Turn Off The RADIO!!

Medium Access Control (MAC)


Major
sources
of energy
waste


Long
idle time when no sensing event happens


Collisions


Overhearing


Control overhead


MAC Protocols Proposed For Sensor
Networks


The SMACS protocol
-

Self
-
Organizing
Medium Access Control For Sensor Networks


Achieves network start
-
up and link
-
layer
organization



CSMA

-

Carrier
Sense Multiple
Access based
MAC



Hybrid TDMA/FDMA
based




Major
components of
SMAC


Periodic
listen and sleep


Collision
avoidance


Overhearing
avoidance



Neighboring nodes are synchronized
together


Periodic updating using a SYNC packet




Listen interval divided into two
parts



Each
part further divided into time slots




RTS/CTS Similar to IEEE 802.11


Interfering nodes go to sleep after they hear the RTS or CTS packet



Power conservation is achieved by using a
random wake
-
up schedule

during the connection phase and by turning the radio off during idle time
slots.


SMACS protocol

Sender Node ID

Next
-
Sleep Time

CSMA Based Mac Protocol


Two important components


T
he listening mechanism


T
he back off scheme.



As reported and based on simulations


Constant listen periods are energy efficient


The introduction of random delay provides
robustness against repeated collisions



CSMA Based Mac Protocol


Adaptive Transmission Rate Control Scheme
-

ARC


A
chieves medium access fairness by balancing the rates
of
originating

and
route
-
through

traffic



The ARC controls the data origination rate of a node in
order
to allow the route
-
through traffic to propagate
.



R
oute
-
through traffic is preferred over the originating
traffic


Since dropping route
-
through traffic is costlier ,the associated
penalty is lesser



Hybrid TDMA/FDMA
based Protocol


Centrally controlled MAC scheme



The system is made up of energy constrained sensor nodes that
communicate to a single, nearby, high powered
base station
(<10
m).



While a pure
TDMA

scheme dedicates the
full bandwidth
to a single
sensor node, a
pure FDMA
scheme allocates
minimum signal
bandwidth
per node.



Optimum number of channels found to depend on the ratio of
power consumption between transmitter and receiver


If transmitter consumes more power TDMA scheme is preferred


If receiver consumes more power FDMA scheme is preferred



The Data Link Layer


Power saving modes of operation


T
urn the transceiver off when it is not required.


Not exactly


Dominance of Start
-
up Energy


Power saving modes of operation


Dynamic Power Management Scheme


An
event occurs when a sensor node
picks up
a
signal with power above a
predetermined
threshold
.



Probability assumed to be
Exponential

<
e
-
λ
t
>

The Data Link
Layer


Error Control


Two important modes of error control


Forward
error correction (FEC
)


Higher Decoding Complexity


If the associated
processing power
is greater than
the coding gain, then the whole process in energy
inefficiency and the system is
better off without
coding
.


A
utomatic
repeat request (ARQ
)


Limited by the additional retransmission energy
cost and overhead.




Cross layer Protocols For
WSN


Performance
limitations in the layered
architecture


It
doesn’t consider dependencies
between different
layers
.



Two
kinds of
cross
-
layer architecture


P
acket
-
based
interaction
scheme


Each layer
puts all information that used for
cross
-
layer
approaches
into packet header and other layers
catch interesting
information by inspecting the each packet
.


D
irect interaction scheme


Allows
any two layers to communicate directly with
one another
via new
APIs



B
oth
schemes
,
existing system
software may need to
be modified to
support new
packet structures or APIs

XCP
(
eXtensible

Cross
-
layer design

Platform)


E
nables
the exchange of
information between
different layers for performance optimization

CPL (Communication Protocol Layer),

MRL (Mutual Reference across Layer)

PO (Performance
Optimization
)
component

XCP (
eXtensible

Cross
-
layer design

Platform)


Procedures of process of the XCP

1.
In initialization, each cross
-
layer module in the
PO component
requests the interesting information to
the MRL
component
using
REQUEST_INFORMATION
()

2.
If a cross
-
layer module
need not
more any information, it can
release the
requested information using
RELEASE_INFORMATION()

3.
T
he
bus arbiter
thread
pops a data
from information
queues
and informs it to requested
cross layer modules

4.
When
the requested information
is stored
at information base
in the each
cross
-
layer module
, it performs
optimization

5.
Then the results of optimization by each
cross
-
layer module
are applied to information set
using
APPLY_INFORMATION
()

Cross
-
layer
module (XLM)


Complete
unified cross
-
layering



Incorporates


I
nitiative determination


R
eceived
based
contention


L
ocal
congestion
control


Distributed duty
cycle operation

Cross
-
layer module (XLM)


Communication
in XLM is built on
initiative
concept


P
rovides
freedom for each node
to decide
on
participating in
communication


The next
-
hop
in each communication is not
determined in advance

Cross
-
layer module (XLM)


Initiative determination
procedure


A
node initiates transmission by broadcasting an RTS
packet to
indicate its neighbors that it has a packet to
send


Upon receiving
an RTS packet, each neighbor of node
i

decides
to
participate
in the communication or
not


This decision is
given through
initiative
determination


The
initiative
determination is
a binary operation where a node
decides to participate
in communication
if its initiative is 1.


Denoting
the initiative
as
I
,
it is determined as follows:

a)
RTS signals
requires that
the received signal to noise ratio (SNR) of an
RTS packet
,,
is above some
threshold

b)
P
revents congestion by
limiting the traffic a node can
relay

c)
Ensures
that the node does not experience any buffer overflow

d)
Ensures that
the remaining energy of a node
stays
above a
minimum
value

Cross
-
layer module (XLM)


Distributed duty cycle operation


Each node is implemented with
a
sleep
frame
with length T
S

sec. As a result, a
node is
active for δ
×

T
S

sec and sleeps for (1 − δ)
×

T
S

sec
.



Transmission
Initiation


Listens to the
channel for a specific period of
time


C
hecks
if
its information
is correlated with the transmitting source
nodes


I
f the
channel is occupied, the node
performs back off
based on
its contention
window


When the channel is idle,
the node
broadcasts an RTS packet, which contains
the
location of
the sensor node
i

and the location of the
sink


When a node receives an RTS packet, it
first checks
the source and destination
locations



Receiver
Contention


After an RTS
packet is
received, if a node has initiative to participate in
the
communication
, it performs receiver contention to forward
the packet

References


G.Hoblos
, M.
Staroswiecki
, and A.
Aitouche
, “
Optimal Design of Fault
Tolerantt

Sensor Networks
”,
IEEE Int’l. Conf. Cont. Apps.,
Anchorage, AK, Sept. 2000, pp. 467
-
72



Bulusu

et al., “
Scalable Coordination for Wireless Sensor Networks: Self
-
Configuring Localization
Systems
”,
ISCTA 2001
, Ambleside, U.K., July 2001



E.Shih

et al., “
Physical Layer Driven Protocol
aand

Algorithm Design for Energy
-
Efficient Wireless
Sensor Networks
”,
Proc. ACM
MobiCom

’01
, Rome, Italy, July 2001,
pp

272
-
86



A.Sinha

and A.
Chandrakasan
, “
Dynamic Power Management in Wireless Sensor Networks
”,
IEEE
Design Test Comp
., Mar./April. 2001



M.
-
S. Pan, C.
-
H. Tsai, and Y.
-
C. Tseng,
Implementation of an Emergency Guiding and Monitoring
System in Indoor 3D Environments by Wireless Sensor Networks
, Technical Report of CS/NCTU
2006
.



T.
Melodia
, M. C.
Vuran
, D.
Pompili
, “
The State of the Art in
Cross layer Design
for Wireless Sensor
Networks
,”
to appear in
Springer
Lecture
Notes in Computer Science (LNCS)
, 2006
.



Byounghoon

Kim and
Sungwoo

Tak
, “
A
Communication Framework Supporting Cross
-
Layer Design
for Wireless
Networks”,
IEEE Int’l Symposium On Ubiquitous Multimedia Computing,
Hobart,
Australia, Oct. 2008