Sensor Network - Rabie Ramadan

decisioncrunchNetworking and Communications

Nov 20, 2013 (3 years and 9 months ago)

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Sensor Network

教育部資通訊科技人才培育先導型計畫

1.Introduction

Goal



Wireless Sensor Network


Ubiquitous Computing


Ubiquitous Network Society


Human
-
centric



1.Introduction

Ubiquitous


Ubiquitous


7A


Anytime


Anyone


Anywhere


Any Device


Affordable


All Security


Any Information/Service


1.Introduction

General Purpose


A
wireless sensor network

(WSN) is a
wireless network using sensors to
cooperatively monitor physical or
environmental conditions


The development of wireless sensor
networks was originally motivated by
military applications.


Wireless sensor networks are now used in
many wide
-
range application areas.

1.Introduction

Sensors

Image Sensor Modules (8
×
8
×
5.7mm)

Ultrasonic Magnetic Sensor (22.5
×
22.5
×
39mm)

WII sensor (240
×
35
×
15mm)

1.Introduction

Typical Sensor Network

sensor

sensor

sensor

sensor

sensor

sensor

Center

Relay

node

Relay

node

Data
gathering

Data
transmitting

processing

1.Introduction

sensor characteristics



Wireless sensors are small devices that
gather information.


Pressure, Humidity, Temperature


Speed, Location



Wireless sensors have some
characteristics:


Low power


Small size


Low cost

1.Introduction

sensor network characteristics


Primary Function


Sample the environment for sensory
information


Propagate data back to the infrastructure



Traffic pattern in sensor network


Low activity in a long period


Bursting data in short time


Highly correlated traffic


1.Introduction

sensors categories


Sensors can be classified into two
categories:


Ordinary Sensors


Data gathering


Ordinary Sensors require external circuitry to
perform some dedicated tasks like data analyzing.


Smart Sensors


Data gathering and processing


Smart Sensors have internal circuitry to perform
dedicated tasks.

1.Introduction

Related Work


Related work



CSMA


To improve the energy consumption by avoiding
overhearing among neighboring nodes


TDMA


No contention
-
introduced overhead and collisions


Not easy to manage the inter
-
cluster
communication and interference


Not easy to dynamically change its frame length
and time slot assignment


1.Introduction

Related Work


PAMAS


Power off radio when not actively transmitting
and receiving packet.


Zigbee


Combined with IEEE 802.15.4 (Low
-
Rate
Wireless Personal Area Network, LR
-
WPAN)


Low rate: 250kbps


Short distance: 50
-
300m


Low power consumption


frequency band:


Global: 2.4GHz ,16 channels


America: 915MHz, 10 channels


Europe: 868MHz, 1 channel.

1.Introduction

Zigbee stack


Zigbee Platform Stack and IEEE802.15.4

PHY Layer

MAC Layer

Network / Security

Layers

Application Framework

Application/Profiles

IEEE

802.15.4

ZigBee or OEM

ZigBee

Alliance

Platform

1.Introduction

Zigbee Application

Reference: NTP
無線感測網路與
ZigBee
協定簡介

2.MAC for Sensor Network

Sensor Network MAC Protocol


Carrier Sensing


Only during low traffic load.


Backoff


Backoff in application layer is desired other
than in MAC layer.


Contention


RTS
-
CTS only during high traffic load.

2.MAC for Sensor Network

Sources of Energy Wastage


The major sources of energy wastage are:


Collisions


Overhearing


Control packet overhead


Idle listening



Achieving good scalability and collision
avoidance capability is necessary.

2.MAC for Sensor Network

S
-
MAC


Sensor
-
MAC (S
-
MAC): Medium Access Control
for Wireless Sensor Networks



S
-
MAC is a medium
-
access control (MAC)
protocol designed for wireless sensor networks.



Sensor networks are deployed in an ad hoc
fashion, with individual nodes remaining largely
inactive for long periods of time, but then
becoming suddenly active when something is
detected.


2.MAC for Sensor Network

S
-
MAC


These characteristics of sensor networks
and applications motivate a MAC that is
different from traditional wireless MACs
such as IEEE 802.11 in almost every way


Energy conservation and self
-
configuration
are primary goals.


Per
-
node fairness and latency are less
important.

2.MAC for Sensor Network

Three techniques in S
-
MAC


S
-
MAC uses three techniques to reduce
energy consumption.



Nodes go to sleep periodically.


Nearby nodes form virtual clusters to
synchronize their wake
-
up and sleep periods
to keep the control packet overhead of the
network low.


Message passing is used to reduce the
contention latency and control overhead.

2.MAC for Sensor Network

Three techniques in S
-
MAC


Periodic Listen and Sleep:



Nodes do not waste energy by listening to an
empty channel or when a neighboring node is
transmitting to another node.


Nodes use RTS and CTS to talk to each other
and contend for the medium.

2.MAC for Sensor Network

Three techniques in S
-
MAC


Collision and Overhearing Avoidance:


S
-
MAC adopts a contention
-
based scheme to
avoid collisions.


A duration field is introduced in each
transmitted packet which indicates how much
longer the transmission will last.


When a node receives a packet, it will not transmit
any packets for at least the time that is specified in
the duration field.

2.MAC for Sensor Network

Three techniques in S
-
MAC


Collision and Overhearing Avoidance:


Overhearing is avoided by letting the nodes,
which get RTS and CTS packets which are
not meant for them, go to sleep.


All immediate neighbors also go to sleep till
the current transmission is completed after a
sender or receiver receives the RTS or CTS
packet.

2.MAC for Sensor Network

Three techniques in S
-
MAC


Message Passing:


Long messages are fragmented into smaller
messages and transmitted in a burst.


To avoid the high overhead and delay encountered
for retransmitting when message is lost.


ACK messages are used to indicate if a
fragment is lost at any time.


The sender can resend the fragment again.


The ACK message also have the duration field to
reduce overhearing and collisions.

3. Challenges


Challenges:


1.
Energy Efficiency:


Power consumptions are crucial to wireless sensor
network applications because sensor nodes are
not connected to any energy source.


Energy efficiency is a dominant consideration no
matter what the problem is.


Sensor nodes only have a small and finite source
of energy. Many solutions, both hardware and
software related, have been proposed to optimize
energy usage.

3. Challenges


2. Ad hoc deployment:



Most sensor nodes are deployed in regions which
have no infrastructure.


We must cope with the changes of connectivity
and distribution.



3. Unattended operation:



Generally, once sensors are deployed, there is no
human intervention for a long time.


Sensor network must reconfigure by itself when
certain errors occur.

3. Challenges



4. Dynamic changes:


As changes of connectivity due to addition of more
nodes or failure of nodes, Sensor network must be
able to adapt itself to changing connectivity.

4.Coverage


Coverage can be classified into three
types:


Area coverage


deployment of sensors to cover a given area


Point coverage


deployment of sensors to cover a set of points


Barrier coverage


The goal is to minimize the probability of
undetected penetration through the barrier.


To find a path in a region


For any point on the path, the distance to the
closest sensor is minimized.

4.Coverage


Area coverage


Area
coverage


deployment
of sensors
to cover a
given area

4.Coverage


Point coverage


Point
coverage


deployment of
sensors to
cover a set of
points

4.Coverage


Point coverage


Barrier
coverage


To find a path
from A to B


For any point
on the path, the
distance to the
closest sensor
is minimized.


A

B

5.Localization


In sensor networks, nodes are deployed
without priori knowledge about their
locations.



Estimating spatial
-
coordinates of the node
is referred to as localization.


5.Localization

GPS


Global Positioning System (GPS) is an
immediate solution.


There some factors against the usage of
GPS:


GPS can work only outdoors.


GPS receivers are too expensive to
unsuitable for wide
-
range deployment.


It cannot work in the presence of obstructions.

5.Localization

Categories


Localization can be classified into two
categories:


Fine
-
grained


Based on timing / signal strength


Coarse
-
grained


Based on proximity

5.Localization

Proximity base localization


Trilateration / Multilateration technique


Proximity based localization:


Some nodes which can know their position through
some technique (ex. GPS) broadcast their position
information.


Other nodes listen to these broadcast messages
and calculate their own position.


A simple method would be to calculate its position
as the centroid of all the positions it has obtained.


This method leads to accumulation of localization
error.



5.Localization

Trilateration Example


Trilateration


A is 5m from B


A is 10m from C


A is 8m from D

B

C

D

A

5.Localization

Trilateration


Trilateration is a geometric principle which
allows us to find a location if its distance
from other nodes are known.


The same principle can be extended to
three
-
dimensional space.


Four spheres would be needed to locate
certain point in 3D space.

5.Localization


Fine
-
grained method


Signal strength method


Attenuation happens when signals are
propagated. We can use the degree of
attenuation to calculate the distance.



Timing method


The distance between two nodes is
determined by the time of flight of the signal.



6.Routing


Categories


Routing protocols can be divided into two
types.


Proactive routing protocol


Proactive routing protocol maintain consistent
updated routing information between all nodes.


To update routing table periodically.


Reactive routing protocol


Routes are created only when they are needed.


6.Routing

Three types in sensor network


Because of the energy constrained nature
of sensor networks, conventional routing
protocols have many limitations when
being applied to sensor networks.


Three types of routing protocol in sensor
network:


Data
-
centric


Hierarchical


Location
-
based


6.Routing

Data
-
centric


Data
-
centric:


Managers broadcast a Query message to the network.


If a sensor observes some events related to the
Query message, it sends the data to the data center.


Data aggregation:

sensor1

sensor2

Relay

node1

Data

Center

Data A

Data A

Data A

6.Routing


Data
-
centric


Data centric: Flooding


Flooding is one of basic data transmitting
methods.


If any sensor receives or generates some
packets, it will broadcast these packets to
all its neighbors.


Nodes may receive duplicate data.


More power consumption.


6.Routing


Data
-
centric


Data centric:
S
ensor
P
rotocols for
I
nformation via
N
egotiation (SPIN)



There are three messages in SPIN:


Advertisement (ADV): When a node has some
data to send, it sends an ADV message to its
neighbors containing data descriptor (meta
-
data).


Request (REQ): When a node wants to receive
some data. It sends an REQ message first.


DATA: Actual data message with a meta
-
data
header.

6.Routing


Data
-
centric

Node1

Node6

Node3

Node2

Node4

Node5

Node7

ADV

(meta data A)

ADV

(meta data A)

ADV

(meta data A)

REQ

(meta data A)

DATA

(meta data A)

ADV

(meta data A)

ADV

(meta data A)

ADV

(meta data A)

REQ

(meta data A)

DATA

(meta data A)

SPIN:

6.Routing


Data centric


Data centric: Directed Diffusion


This is a destination
-
initiated reactive routing
technique.


Routes are established when requested.


A interest is propagated throughout the network
for named data by a node and data which
matches this interest is then sent toward this
nodes.


Interests are described by a list of attribute
-
value
pairs.


Example: type=birds & response=20 ms

6.Routing


Data centric


Directed Diffusion


The propagation of data and its aggregation
at intermediate nodes on the way to the
request originating node are determined by
the messages which are exchanged between
neighboring nodes within some distance.


6.Routing


Data centric

Node5

Node4

Node3

Node2

Node1

Node7

interest

interest

interest

interest

interest

interest

Node6

interest

interest

interest

interest

Gradient

Gradient

Gradient


Gradient


Gradient


Gradient

Gradient

Gradient


Gradient

Gradient

Node5

Node4

Node3

Node2

Node1

Node7

Node6

return path (Gradient)

Forward interest

Directed Diffusion:

6.Routing


Data centric



Directed Diffusion:


Sender can choose the best return path.


EX: minimum response time, least hops


Node5

Node4

Node3

Node2

Node1

Node7

Node6

6.Routing


Hierarchical


Hierarchical:
L
ow
E
nergy
A
daptive
C
lustering
H
ierarchy (LEACH)


LEACH is a two
-
tier protocol.


Cluster head


Cluster member


Every node runs a random algorithm
periodically to decide its identity. (cluster head
or not)



6.Routing


Hierarchical


LEACH


All cluster heads broadcast Advertisement
(ADV) message and other nodes decide
which cluster they belong to according the
strength of ADV message.


Cluster members only send data to their
cluster head. Then, cluster heads reply data
to Sinks.

6.Routing


Hierarchical

Node1

Node4

Node2

Node3

Sink

Node5

Cluster

Head1

Cluster

Head2

Cluster

Head3

Node7

Node6

Node9

Node10

Node8

Node12

Node13

Node11

Cluster 1

Cluster 2

Cluster 3

LEACH
Example

6.Routing


Location
-
based


Location
-
based:
G
eographic
A
daptive
F
idelity (GAF)


GAF divides the network into several
virtual grids.


For adjacent virtual grids A and B, every node
in A can directly connect with every node in B.


In GAF, every node has three types of
status:


Active


Discovery


Sleep


6.Routing


Location
-
based


GAF:


Initially, every node is in discovery status and
tries to find out nodes belong to the same grid
with itself.


Every node in discovery status sets a timer
“Td”. Once the Td timer ends, Nodes
broadcast discovery message and get into
active status.



6.Routing


Location
-
based


GAF:


When a node is in active status, it will start a
timer “Ta”.


Data transmission is allowed until Ta timer ends.


In active status, nodes will periodically broadcast
discovery message at Td intervals.


Once Ta timer ends, nodes return to discovery
status.


6.Routing


Location
-
based


GAF:


If a node in discovery status receives a
discovery message sent from the node which
is in the same grid and has higher ranking, it
will get into sleep status.


After a Ts timer, it will return to discovery status.


Ranking can be done by remaining power or ID
sequence.