ara-anna-wireless.ppt

8/10/2019 ara-anna-wireless.ppt

1/123

Ad Hoc and Sensor

Networks

Dr.M.ARAMUDHAN

Associate ProfessorPKIET, Karaikal609 603


2/123

Introduction

Characteristics of Ad Hoc Networks

Applications

Routing Table-driven Routing Protocols

Source-initiated On-demand Routing

Hybrid Protocols

Wireless Sensor Networks Flat Routing in Sensor Networks

Fixed Wireless Sensor Networks


3/123

WLAN:- To solve four nagging problems

- Mobility- Mobility-to-Mobility networking- relocation

- alternative to locations that are difficult to wire.

Advantages: - Installation and simplicity- Installation flexibility- Scalability

- Improved productivity and services- Reduced cost of ownership.


4/123

Introduction An ad-hoc network is a local area network (LAN) that is built

spontaneously as devices connect. Instead of relying on a base stationto coordinate the flow of messages to each node in the network, theindividual network nodes forward packets to and from each other.

A wireless ad hoc network is a decentralized type of wireless network.The network is ad hoc because it does not rely on a preexistinginfrastructure, such as routers in wired networks or access points inmanaged (infrastructure) wireless networks. Instead, each nodeparticipates in routing by forwarding data for other nodes, and so thedetermination of which nodes forward data is made dynamically basedon the network connectivity.

A Mobile Ad hoc Network (MANET) is an autonomous system of nodes(MSs) connected by wireless links.

A MANET does not necessarily need support from any existing networkinfrastructure like an Internet gateway or other fixed stations.


5/123

The networks wireless topology may dynamically changein an unpredictable manner since nodes are free to move.

Information is transmitted in a store-and forward mannerusing multi hop routing.

Each node is equipped with a wireless transmitter and areceiver with an appropriate antenna.

We assume that it is not possible to have all nodes withineach others radio range.

When the nodes are close-by i.e., within radio range, thereare no routing issues to be addressed.

At a given point in time, wireless connectivity in the form ofa random multi-hop graph exists between the nodes.


6/123

A Mobile Ad Hoc Network

MS3

MS2

MS4

MS1

MS5

MS6

MS2

MS7Symmetric link

Asymmetric link


7/123

Technologies for Ad Hoc networks:

- IEEE 802.11 family of protocols

- High performance LAN ( HiperLAN)2 protocols

- Bluetooth specifications


8/123

802.11 Wireless LAN

Provides network connectivity over wireless media

An Access Point (AP) is installed to act as Bridgebetween Wireless and Wired Network

The AP is connected to wired network and is

equipped with antennae to provide wireless

connectivity

LAN Technologies

Network

connectivity

to thelegacy

wired LAN

Desktop

with PCI 802.11 LAN card

Laptop

with PCMCIA 802.11 LAN cardAccess Point


9/123

802.11 Wireless LANRange ( Distance between Access Point and WLAN

client) depends on structural hindrances and RF

gain of the antenna at the Access Point

To service larger areas, multiple APs may beinstalled with a 20-30% overlap

A client is always associated with one AP and when

the client moves closer to another AP, it associates

with the new AP (Hand-Off)

Three flavors:

802.11b

802.11a

802.11g

LAN Technologies


10/123


11/123

IEEE 802.11 operates either with infrastructure or without infrastructuresupport.

Infrastructure based network, there is a centralized controller for each cell,referred as access point. It is connected to the wired backbone.

Infrastructure free network, a group of stations communicate directly with

each other in an ad hoc fashion, independent of infrastructure or basestations.

When two or more stations come together to communicate with each otherthey form BSS ( Basic Service Set). BSS is not connected with base stationcalled as IBSS.

Creating large and complex networks using a number of BSSs leads us tothe next level of hierarchy called ESS.

Services supported are association, reassociation, disassociation,distribution and integration.


12/123

Frame Formats

MAC Header format differs per Type: Control Frames (several fields are omitted)

Management Frames

Data Frames

FrameControl

DurationID

Addr 1 Addr 2 Addr 3 Addr 4SequenceControl

CRCFrameBody

2 2 6 6 6 62 0-2312 4

802.11 MAC Header

Bytes:

Protocol

VersionType SubType

To

DSRetry

Pwr

Mgt

More

DataWEP Rsvd

Frame Control Field

Bits: 2 2 4 1 1 1 1 1 1 1 1

DS

From More

Frag


13/123

Address Field Description

Addr. 1 = All stations filter on this address.Addr. 2 = Transmitter Address (TA), Identifies transmitter to addressthe ACK frame to.

Addr. 3 = Dependent on Toand From DS bits.

Addr. 4 = Only needed to identify the original source of WDS

(Wireless Distribution System) frames

Protocol

VersionType SubType

To

DSRetry

Pwr

Mgt

More

DataWEP Rsvd

Frame Control Field

Bits: 2 2 4 1 1 1 1 1 1 1 1

DS

From More

Frag

To DS

0

0

1

1

From DS

0

1

0

1

Address 1

DA

DA

BSSID

RA

Address 2

SA

BSSID

SA

TA

Address 3

BSSID

SA

DA

DA

Address 4

N/A

N/A

N/A

SA


14/123

Type field descriptions

Type and subtype identify the function of the frame:

Type=00 Management Frame

Beacon (Re)Association

Probe (De)Authentication

Power Management

Type=01 Control Frame

RTS/CTS ACK

Type=10 Data Frame

Protocol

VersionType SubType

To

DSRetry

Pwr

Mgt

More

DataWEP Rsvd

Frame Control Field

Bits: 2 2 4 1 1 1 1 1 1 1 1

DS

From More

Frag


15/123

Multiple Access with Collision

Avoidance (MACA)

Before every data transmission

Sender sends a Request to Send (RTS) framecontaining the length of the transmission

Receiver respond with a Clear to Send (CTS) frameSender sends dataReceiver sends an ACK; now another sender cansend data

When sender doesnt get a CTS back, it assumescollision

LAN Technologies

sender receiverother node insenders range

RTS

CTS

ACK

data

other node inreceivers range


16/123

Characteristics of Ad Hoc Networks

Dynamic topologies: Network topology maychange dynamically as the nodes are free tomove.

Bandwidth-constrained, variable capacity links:

Realized throughput of wireless communicationis less than the radios maximum transmissionrate. Collision occurs frequently.

Energy-constrained operation: Some nodes in

the ad hoc network may rely on batteries orother exhaustible means for their energy. Limited physical security:More prone to physical

security threats than fixed cable networks.


17/123

High Performance LAN

To produce WLAN that would beindistinguishable in performancefrom wired LAN.

To carry multimedia data andprovide QoS as it basic data

transport functions. ETSI (European

Telecommunications StandardsInstitute)

Developing HiperLAN standardsas part of an effort called BRAN(Broadband Radio AccessNetwork)

HiperLANs have four types

DLC

PHY(5 GHz)

20 + Mb/sec

MAC

PHY(5 GHz)

20 + Mb/sec

HIPERLAN

Type 1Wireless LAN

HIPERLAN

Type 2Wireless ATMIndoor access

DLC

PHY(17 GHz)

150 + Mb/sec

HIPERLAN

Type 4Wireless ATMInterconnect

PHY(5 GHz)

20 + Mb/sec

DLC

HIPERLAN

Type 3Wireless ATM

Remote Access


18/123

HIPERLAN 1 HIPERLAN 2 HIPERLAN 3 HIPERLAN 4

Application wireless LAN access to ATMfixed networks

wireless localloop

point-to-pointwireless ATMconnections

Frequency 5.1-5.3GHz 17.2-17.3GHz

Topology decentralized ad-

hoc/infrastructure

cellular,

centralized

point-to-

multipoint

point-to-point

Antenna omni-directional directional

Range 50 m 50-100 m 5000 m 150 m

QoS statistical ATM traffic classes (VBR, CBR, ABR, UBR)

Mobility 20 Mbit/s 155 Mbit/s

Powerconservation

yes not necessary


19/123

Characteristics

Data transmission point-to-point, point-to-multipoint, connectionless

23.5 Mbit/s, 1 W power, 2383 byte max. packet size

Services

asynchronous and time-bounded services with hierarchicalpriorities

compatible with ISO MAC

Topology infrastructure or ad-hoc networks

transmission range can be larger then coverage of a single node(forwarding integrated in mobile terminals)

Further mechanisms power saving, encryption, checksums


20/123

HIPERLAN - reference model

Medium Access Control

(MAC) Sublayer

Channel Access Control

(CAC) Sublayer

Physical (PHY) Layer

Application Layer

Presentation Layer

Session Layer

Transport Layer

etwork Layer

Data Link Layer

Physical Layer

higher layer protocols

OSI

Reference Model

HIPERLAN

Reference Model


21/123

HIPERLAN 1 - Physical layer

Scope

modulation, demodulation, bit and frame synchronization

forward error correction mechanisms

measurements of signal strength

channel sensing

Channels 3 mandatory and 2 optional channels (with their carrier frequencies)

mandatory

channel 0: 5.1764680 GHz


channel 2: 5.2235268 GHz optional




22/123

HIPERLAN 1 - Physical layer frames Maintaining a high data-rate (23.5 Mbit/s) is power consuming - problematic

for mobile terminals

packet header with low bit-rate comprising receiver information only receiver(s) address by a packet continue receiving

Frame structure

LBR (Low Bit-Rate) header with 1.4 Mbit/s

450 bit synchronization

minimum 1, maximum 47 frames with 496 bit each for higher velocities of the mobile terminal (> 1.4 m/s) the maximum

number of frames has to be reduced

LBR synchronization data0 data1 datam-1. . .

HBR

ModulationGMSK for high bit-rate, FSK for LBR header

HIPERLAN 1 EY NPMA I


23/123

prioritization

HIPERLAN 1 - EY-NPMA I

EY-NPMA (Elimination Yield Non-preemptive Priority Multiple Access)

3 phases: priority resolution, contention resolution, transmission

finding the highest priority

every priority corresponds to a time-slot to send in the firstphase, the higher the priority the earlier the time-slot to send

higher priorities can not be preempted

if an earlier time-slot for a higher priority remains empty, stationswith the next lower priority might send

after this first phase the highest current priority has beendetermined

contention transmissiontransmission

synchronization

priorityd

etection

prioritya

ssertion

t

user

data

eliminationburst

eliminationsurvival

verificatio

n

yieldlistening

IYSIPS IPA IES IESV


24/123

HIPERLAN 1 - EY-NPMA II

Several terminals can now have the same priority and wish to send

contention phase

Elimination Burst: all remaining terminals send a burst to eliminatecontenders (11111010100010011100000110010110, high bit- rate)

Elimination Survival Verification: contenders now sense thechannel, if the channel is free they can continue, otherwise theyhave been eliminated

Yield Listening: contenders again listen in slots with a nonzeroprobability, if the terminal senses its slot idle it is free to transmit atthe end of the contention phase

the important part is now to set the parameters for burst durationand channel sensing (slot-based, exponentially distributed)

data transmission

the winner can now send its data (however, a small chance ofcollision remains)

if the channel was idle for a longer time (min. for a duration of 1700

bit) a terminal can send at once without using EY-NPMA synchronization using the last data transmission


25/123

HIPERLAN 1 - MAC layer

Compatible to ISO MAC

Supports time-bounded services via a priority scheme

Packet forwarding

support of directed (point-to-point) forwarding and broadcast forwarding(if no path information is available)

support of QoS while forwarding

Encryption mechanisms

mechanisms integrated, but without key management

Power conservation mechanisms

mobile terminals can agree upon awake patterns (e.g., periodic wake-ups to receive data)

additionally, some nodes in the networks must be able to buffer data forsleeping terminals and to forward them at the right time (so calledstores)


26/123

Piconet

Collection of devices connected in anad hoc fashion

One unit acts as master and the othersas slaves for the lifetime of the piconet

Master determines hopping pattern,slaves have to synchronize

Each piconet has a unique hoppingpattern

Participation in a piconet =synchronization to hopping sequence

Each piconet has one masterand up to7 simultaneous slaves (> 200 could beparked)

M=MasterS=Slave P=ParkedSB=Standby

M

S

P

SB

S

S

P

P

SB


27/123

Characteristics

2.4 GHz ISM band, 79 (23) RF channels, 1 MHz carrier spacing

Channel 0: 2402 MHz channel 78: 2480 MHz

G-FSK modulation, 1-100 mW transmit power

FHSS and TDD

Frequency hopping with 1600 hops/s

Hopping sequence in a pseudo random fashion, determined by a master Time division duplex for send/receive separation

Voice linkSCO (Synchronous Connection Oriented)

FEC (forward error correction), no retransmission, 64 kbit/s duplex, point-to-point, circuit switched

Data linkACL (Asynchronous ConnectionLess)

Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9 kbit/ssymmetric or 723.2/57.6 kbit/s asymmetric, packet switched

Topology

Overlapping piconets (stars) forming a scatternet

Forming a piconet


28/123

Forming a piconet

All devices in a piconet hop together

Master gives slaves its clock and device ID

Hopping pattern: determined by device ID (48 bit, unique worldwide) Phase in hopping pattern determined by clock

Addressing

Active Member Address (AMA, 3 bit)

Parked Member Address (PMA, 8 bit)

SB

SB

SB

SB

SB

SB

SB

SB

SB

M

S

P

SB

S

S

P

P

SB


29/123

Scatternet Linking of multiple co-located piconets through the sharing of common master or

slave devices

Devices can be slave in one piconet and master of another

Communication between piconets

Devices jumping back and forth between the piconets

M=MasterS=SlaveP=ParkedSB=Standby

M

S

P

SB

S

S

P

P

SB

M

S

S

P

SB

Piconets(each with acapacity of

< 1 Mbit/s)


30/123

Bluetooth protocol stack

Radio

Baseband

Link Manager

Control

HostControllerInterface

Logical Link Control and Adaptation Protocol (L2CAP)Audio

TCS BIN SDP

OBEX

vCal/vCard

IP

NW apps.

TCP/UDP

BNEP

RFCOMM (serial line interface)

AT modemcommands

telephony apps.audio apps. mgmnt. apps.

AT: attention sequenceOBEX: object exchangeTCS BIN: telephony control protocol specificationbinaryBNEP: Bluetooth network encapsulation protocol

SDP: service discovery protocolRFCOMM: radio frequency comm.

PPP


31/123

Five main protocols : Bluetooth radio, base band, Link manager protocol,Logical link control and adaptation protocol and service discovery protocol.

Bluetooth radio is responsible for the electrical interference to thecommunication media, coding/decoding and modulation/demodulation ofdata transmission.

Base band layer and link controller control physical links via radio layer byassembling packets, controlling frequency hopping and performing errorchecking and correction.

LMP is responsible for connection setup and maintenance.

L2CAP performs management and data flow control. Connection oriented

and connection less links , QoS, protocol multiplexing, segmentation andreassembly and group management.

Identity the device, establish connection and data transmission.


32/123

Routing in MANETS - Goals

Provide the maximum possible reliability - use alternative routes ifan intermediate node fails.

Choose a route with the least cost metric. Give the nodes the best possible response time and throughput. Route computation must be distributed. Centralized routing in a

dynamic network is usually very expensive. Routing computation should not involve the maintenance of globalstate.

Every node must have quick access to routes on demand. Each node must be only concerned about the routes to its

destination.

Broadcasts should be avoided (highly unreliable) It is desirable to have a backup route when the primary route has

become stale.


33/123

Routing Classification

The existing routing protocols can be classified as,

Proactive: when a packet needs to be forwarded,the route is already known.

Reactive: Determine a route only when there is datato send.

Routing protocols may also be categorized as ,

Table Driven protocols

Source Initiated (on demand) protocols


34/123

Table Driven Routing Protocols

Each node maintains routing informationto all other nodes in the network

When the topology changes, updates arepropagated throughout the network.

Examples are: Destination Sequenced Distance Vector

routing (DSDV)

Cluster-head Gateway Switch routing (CGSR) Wireless Routing Protocol (WRP)


35/123

Destination Sequenced DistanceVector Routing (DSDV)

Each mobile node maintains a routing table in terms of number ofhops to each destination.

Routing table updates are periodically transmitted.

Each entry in the table is marked by a sequence number which helpsto distinguish stale routes from new ones, and thereby avoiding loops.

To minimize the routing updates, variable sized update packets areused depending on the number of topological changes.

Nodes periodically transmit routing tables throughout the network to

maintain table consistency. Updates contain destination, number of hops to reach destination,

destination sequence number, sequence number that identifies theupdates


36/123

Route Update done based on recent sequence number. Node A, sequence number is increased for destination

when A detects that the route to D has broken. If so A

advertised the route to D with infinite hop count and asequence number that is larger than the present one.


37/123

Cluster-head Gateway Switch Routing(CGSR)

CGSR is a clustered multi-hop mobile wireless network with severalheuristic routing schemes.

A distributed cluster-head (CH) selection algorithm is used to elect anode as the cluster head.

It modifies DSDV by using a hierarchical CH to route traffic.

Gateway nodes serve as bridge nodesbetween two or moreclusters. A packet sent by a node is first routed to its CH and then the packet

is routed from the CH to a gateway of another cluster and then tothe CH and so on, until the destination cluster head is reached.

Frequent changes in the CH may affect the performance of therouting protocol.


38/123

1

3

2

4 710

5

6

8

9

11

12

Cluster Head

Internal Node

Gateway Node

Routing in CGSR from node 1 to node 8

CGSR (Contd)

The Wireless Routing Protocol


39/123

The Wireless Routing Protocol(WRP)

It is a path finding algorithm that calculate shortest pathusing length and second-to-last hop of the path to eachdestination.

Each node maintains 4 tables:

-- Distance table

-- Routing table

-- Link cost table

-- Message Retransmission List table (MRL)

MRL contains the sequence number of the updatemessage, a retransmission counter and a list ofupdates sent in the update message


40/123

Wireless Routing Protocol (Contd)

Nodes inform each other of link changes using

update messages. Nodes send update messages after processing

updates from their neighbors or after detecting achange in the link.

If a node is not sending messages, it must send aHELLO message within a specified time to ensureconnectivity.

If the node receives a HELLO message from a new

node, that node is added to the table. It avoids the count to infinity problem.


41/123

Source-Initiated On-Demand Routing

Ad hoc On-Demand Distance Vector(AODV).

Dynamic Source Routing (DSR)

Temporary Ordered Routing Algorithm(TORA)

Associativity Based Routing (ABR)

Signal Stability Routing (SSR)


42/123

Ad hoc On-Demand Distance vector

AODV is an improvement over DSDV, based on the concept of

next-hop routing model, which minimizes the number of requiredbroadcasts by creating routes on demand.

.Host keeps routing table that indicates the next host to be used as

the immediate relay to reach destination.

Each node receives the data, checks the routing table and if avalid route for the destination of the data exists, it forwards the

packet to the next node

.Route discovery-route selection: A source node initiates a path

discovery process to locate the other intermediate nodes (and thedestination), by broadcasting a Route Request (RREQ) packet to

its neighbors


43/123

Node waits for a route reply. If the reply is not received withincertain time, the node rebroadcast RREQ.

Ensure that all routes are loop-free and up-to-date. Each nodemaintains its own sequence number as well as broadcast ID.

Node received RREQ, it checks already available by notingsource and broad cast ID pair. If so, it discards the message.

ROUTE MAINTAINCE: Each node peridically transmit abroadcast message called HELLO and updates the informationassociated with neighbour.


44/123

Route Discovery in AODV Protocol

SourceDestination

13

2

5

7

46

8

(a) Propagation of Route Request (RREQ) Packet

SourceDestination

(b) Path Taken by the Route Reply (RREP) Packet

1

3

2

5

7

46

8

Hop1 Hop2 Hop3


45/123

Dynamic Source Routing

The protocol consists of two major phases: RouteDiscovery, Route Maintenance.

When a mobile node has a packet to send to some

destination, it first consults its route cache to check

whether it has a route to that destination.

If it is an un-expired route, it will use this route.

If the node does not have a route, it initiates route

discovery by broadcasting a Route Request packet.

This Route Request contains the address of the

destination, along with the source address.


46/123

Dynamic Source Request (Contd)

Each node receiving the packet checks to see whether it

has a route to the destination. If it does not, it adds its own

address to the route record of the packet and forwards it.

A route reply is generated when the request reaches either

the destination itself or an intermediate node that contains

in its route cache an un-expired route to that destination.

If the node generating the route reply is the destination, it

places the the route record contained in the route request

into the route reply.


47/123

Hop1 Hop2 Hop4Hop3

1

4

7

5

3

SourceDestination

(a) Building Record Route During Route Discovery

4

1

46

8

7

2

3

Source

Destination

(b) Propagation of Route Reply with the Route Record

1

2

3

5

6

7

8

Creation of Route Record in DSR

Temporarily Ordered Routing


48/123

Temporarily Ordered RoutingAlgorithm (TORA)

. TORA is a highly adaptive loop-free distributedrouting algorithm based on the concept of linkreversal.

TORA decouples the generation of potentially far-

reaching control messages from the rate oftopological changes.

The height metric is used to model the routing stateof the network.

The protocol performs three basic functions: routecreation, route maintenance, route erasure.


49/123

Source

Destination

H = 0

H = 1

H = 2

H = 3

Illustration of Tora height metric

TORA (Contd)


50/123

TORA (Contd)

During the route creation and maintenance phasesnodes use a height metric to establish a Directed

Acyclic Graph (DAG) rooted at the destination.

Thereafter links are assigned a direction based onthe relative heights


51/123

1

2

3

4

5

6

7

8

(-,-)

(-,-)

(-,-)

(-,-)

(-,-)

(-,-)

(-,-)

(0,0)

1

2

3

4

5

6

7

8

(0,3)

(0,1)

(0,1)

(0,2)

(0,2)

(0,3)

(0,3)

(0,0)

Source Destination

DestinationSource

Figure 13.6(a)Propagation of the query message

Nodes height updated as a result of the update message

TORA (Contd)



52/123


The three phases of ABR are: route discovery, routereconstruction, route deletion.

In ABR a route is selected based on the degree of stabilityassociated with mobile nodes.

Association stability is defined by connection stability of onenode with respect to another node over time and space.

Each node generates a beacon to signify its existence.

When received by neighboring nodes, the beacon causes theirassociatively tables to be updated.

The route discovery is accomplished by a Broadcast Query-Reply (BQ-REPLY) cycle.

When a discovered route is no longer desired, the source nodeinitiates a Route Delete broadcast so that all the nodes along theroute update their routing tables.

Si l St bilit R ti (SSR)


53/123

Signal Stability Routing (SSR)

SSR selects a route based on the signal strength

between nodes and a nodes location stability. This route selection criteria has the effect of choosing

routes that have a better link connectivity.

Node maintains two tables signal stability table and

routing table. Two phases route discovery and route maintenance.


54/123

Hybrid protocols

Zone Routing Protocol(ZRP): a node proactivelymaintains routes to destinations within a localneighborhood. The construction of a routing zonerequires a node to first know who its neighbor,which is implemented through a MAC layerNeighbor Discovery Protocol.

Fisheye State Routing(FSR): There are multi-

level fisheye scopes to reduce routing updateoverhead in large networks. It helps to make arouting protocol scalable by gathering data on thetopology, which may be needed soon.

Landmark Routing (LANMAR): Uses a landmark

(C )


55/123

Hybrid protocols (Contd)

Distance Routing Effect Algorithm for

Mobility(DREAM): It is based on the distanceeffect and a nodes mobility rate. Each node can

optimize the frequency at which it sends updatesto the networks and correspondingly reduce thebandwidth and energy used.

Relative Distance Micro-discovery Ad Hoc

Routing(RDMAR): This is based on thecalculated relative distance between twoterminals. The query flood is localized to alimited region centered at the source node.

Power Aware Routin : ower-aware metrics


56/123

Protocol Characteristics (1/2)

RoutingProtocol

RouteAcquisition

Flood for RouteDiscovery

Delay for RouteDiscovery

MultipathCapability

Effect of Route Failure

DSDV Computed apriori

No No No Updates the routing tables of allnodes

WRP Computed apriori

No No No Ultimately, updates the routingtables of all nodes by

exchanging MRL betweenneighbors

DSR On-demand,only whenneeded

Yes. Aggressiveuse of cachingmay reduce flood

Yes Not explicitly.The techniqueof salvagingmay quicklyrestore a route

Route error propagated up tothe source to erase invalid path


57/123

Protocol Characteristics (2/2)

RoutingProtocol

RouteAcquisition

Flood for RouteDiscovery

Delay for RouteDiscovery

MultipathCapability

Effect of Route Failure

AODV On-demand,only whenneeded

Yes. Controlleduse of cache toreduce flood

Yes No, althoughrecent researchindicate viability

Route error propagated upto the source to eraseinvalid path

TORA On-demand,only when

needed

Basically one forinitial route

discovery

Yes. Once the DAG isconstructed, multiple

paths are found

Yes Error is recovered locally

LAR On-demand,only whenneeded

Reduced byusing locationinformation

Yes No Route error propagated upto the source

ZRP Hybrid Only outside asource's zone

Only if the destinationis outside thesource's zone

No Hybrid of updating nodes'tables within a zone andpropagating route error tothe source


58/123

Sensor Networks

Sensor networks are highly distributed networks of small, lightweightwireless node, deployed in large numbers to monitor theenvironment or system.

Each node of the sensor networks consist of three subsystem: Sensor subsystem: senses the environment Processing subsystem: performs local computations on the

sensed data Communication subsystem: responsible for message exchange

with neighboring sensor nodes

The features of sensor nodes Limited sensing region, processing power, energy


59/123

The advantage of sensor networks Robust : a large number of sensors

Reliable :

Accurate : sensor networks covering a wider region

Fault-tolerant : many nodes are sensing the same event

Two important operations in a sensor networks Data dissemination : the propagation of data/queries throughout

the network

Data gathering : the collection of observed data from the

individual sensor nodes to a sink The different types of sensors

Seismic, thermal, visual, infrared


60/123


61/123

Real-time communication over sensor networks must besupported through provision of guarantees on maximum delay,minimum bandwidth, or other QoS parameters.

Provision must be made for secure communication over sensornetworks, especially for military applications which carrysensitive data.


62/123

Sensor networks - Node architecture 62

Sensor node architecture

Main components of a WSN node

Controller

Communication device(s)

Sensors/actuators

Memory Power supply Memory

ControllerSensor(s)/actuator(s)

Communicationdevice

Power supply


63/123


Controller Main options:

Microcontrollergeneral purpose processor, optimized for embeddedapplications, low power consumption

DSPsoptimized for signal processing tasks, not suitable here

FPGAsmay be good for testing

ASICsonly when peak performance is needed, no flexibility

Example microcontrollers

Texas Instruments MSP430

16-bit RISC core, up to 4 MHz, versions with 2-10 kbytes RAM,

several DACs, RT clock, prices start at 0.49 US$ Atmel ATMega

8-bit controller, larger memory than MSP430, slower


64/123


Communication device Which transmission medium?

Electromagnetic at radio frequencies?

Electromagnetic, light?

Ultrasound?

Radio transceivers transmit a bit- or byte stream as radio wave

Receive it, convert it back into bit-/byte stream


65/123


Transceiver characteristics Capabilities

Interface: bit, byte, packet level?

Supported frequency range?

Typically, somewhere in 433MHz2.4 GHz, ISM band

Multiple channels?

Data rates? Range?

Energy characteristics

Power consumption tosend/receive data?

Time and energy consumption tochange between different states?

Transmission power control?

Power efficiency (whichpercentage of consumed power isradiated?)

Radio performance Modulation? (ASK, FSK, ?)

Noise figure? NF = SNRI/SNRO

Gain? (signal amplification)

Receiver sensitivity? (minimum S toachieve a given Eb/N0)

Blocking performance (achieved BERin presence of frequency-offsetinterferer)

Out of band emissions

Carrier sensing & RSSI characteristics

Frequency stability (e.g., towardstemperature changes)

Voltage range


66/123


Transceiver states Transceivers can be put into different operational states, typically:

Transmit

Receive

Idleready to receive, but not doing so

Some functions in hardware can be switched off, reducing energy

consumption a little Sleepsignificant parts of the transceiver are switched off

Not able to immediately receive something

Recovery t ime and star tup energyto leave sleep state can besignificant

Research issue: Wakeup receiverscan be woken via radio when in sleepstate (seeming contradiction!)


67/123


Example radio transceivers Almost boundless variety available Some examples

RFM TR1000 family

916 or 868 MHz

400 kHz bandwidth

Up to 115,2 kbps On/off keying or ASK

Dynamically tuneable outputpower

Maximum power about 1.4 mW

Low power consumption

Chipcon CC1000 Range 300 to 1000 MHz,

programmable in 250 Hz steps

FSK modulation

Provides RSSI

Chipcon CC 2400 Implements 802.15.4

2.4 GHz, DSSS modem

250 kbps

Higher powerconsumption than abovetransceivers

Infineon TDA 525x family

E.g., 5250: 868 MHz

ASK or FSK modulation

RSSI, highly efficient

power amplifier Intelligent power down,

self-polling mechanism

Excellent blockingperformance


68/123


Wakeup receivers Major energy problem: RECEIVING

Idling and being ready to receive consumes considerable amounts ofpower

When to switch on a receiver is not clear

Contention-based MAC protocols: Receiver is always on TDMA-based MAC protocols: Synchronization overhead, inflexible

Desirable: Receiver that can (only) check for incoming messages

When signal detected, wake up main receiver for actual reception

Ideally: Wakeup receiver can already process simple addresses

Not clear whether they can be actually built, however


69/123


Sensors as such Main categories

Any energy radiated? Passive vs. active sensors

Sense of direction? Omidirectional?

Passive, omnidirectional

Examples: light, thermometer, microphones, hygrometer,

Passive, narrow-beam

Example: Camera

Active sensors

Example: Radar

Important parameter: Area of coverage

Which region is adequately covered by a given sensor?

Energy supply of mobile/sensor nodes


70/123


Goal: provide as much energy as possible at smallestcost/volume/weight/recharge time/longevity

In WSN, recharging may or may not be an option Options

Primary batteriesnot rechargeable

Secondary batteriesrechargeable, only makes sense in combinationwith some form of energy harvesting

Requirements include Low self-discharge

Long shelf live

Capacity under load

Efficient recharging at low current

Good relaxation properties (seeming self-recharging) Voltage stability (to avoid DC-DC conversion)


71/123


Energy scavenging How to recharge a battery?

A laptop: easy, plug into wall socket in the evening

A sensor node?Try to scavengeenergy from environment

Ambient energy sources

Light ! solar cellsbetween 10 W/cm2and 15 mW/cm2

Temperature gradients80 W/cm2@ 1 V from 5K difference

Vibrationsbetween 0.1 and 10000 W/cm3

Pressure variation (piezo-electric)330 W/cm2from the heel of ashoe

Air/liquid flow

(MEMS gas turbines)


72/123


Energy consumption A back of the envelope estimation

Number of instructions

Energy per instruction: 1 nJ

Small battery (smart dust): 1 J = 1 Ws

Corresponds: 109instructions!

Lifetime

Or: Require a single day operational lifetime = 246060 =86400 s

1 Ws / 86400s 11.5 Was max. sustained power consumption!

Not feasible!

Multiple power consumption


73/123


p p pmodes

Way out: Do not run sensor node at full operation all the time If nothing to do, switch to pow er safe mode

Question: When to throttle down? How to wake up again?

Typical modes

Controller: Active, idle, sleep

Radio mode: Turn on/off transmitter/receiver, both

Multiple modes possible, deeper sleep modes

Strongly depends on hardware

TI MSP 430, e.g.: four different sleep modes

Atmel ATMega: six different modes

Operating system challenges in


74/123


p g y gWSN

Usual operating system goals Make access to device resources abstract (virtualization)

Protect resources from concurrent access

Usual means

Protected operation modes of the CPUhardware access onlyin these modes

Process with separate address spaces

Support by a memory management unit

Problem: These are not available in microcontrollers

No separate protection modes, no memory management unit

Would make devices more expensive, more power-hungry

! ???

Operating system challenges in


75/123


p g y gWSN

Possible options Try to implement as close to an operating system on WSN nodes

In particular, try to provide a known programming interface

Namely: support for processes!

Sacrifice protection of different processes from each other

! Possible, but relatively high overhead

Do (more or less) away with operating system

After all, there is only a single application running on a WSN node

No need to protect malicious software parts from each other

Direct hardware control by application might improve efficiency

Currently popular verdict: no OS, just a simple run-time environment

Enough to abstract away hardware access details

Biggest impact: Unusual programming model

Main issue: How to support


76/123


ppconcurrency

Simplest option: No concurrency, sequentialprocessing of tasks

Not satisfactory: Risk of missing data (e.g.,from transceiver) when processing data, etc.

! Interrupts/asynchronous operation has to be

supported

Why concurrency is needed

Sensor nodes CPU has to service the radio

modem, the actual sensors, performcomputation for application, executecommunication protocol software, etc.

Poll sensor

Processsensor

data

Poll transceiver

Process

receivedpacket

Traditional concurrency:


77/123


yProcesses

Traditional OS: processes/threads Based on interrupts, context

switching

But: not availablememoryoverhead, execution overhead

But: concurrency mismatch One process per protocol

entails too many contextswitches

Many tasks in WSN small withrespect to context switchingoverhead

And: protection between processesnot needed in WSN

Only one application anyway

Handle sensorprocess

Handle packetprocess

OS-mediatedprocess switching

Event-based concurrencyAlt ti S it h t


78/123


Alternative: Switch to event-based p rogramm ing model

Perform regular processing or be idle

React to events when they happen immediately

Basically: interrupt handler

Problem: must not remain in interrupt handler too long

Danger of loosing events

Only save data, post information that event has happened, then

return! Run-to-complet ionprinciple

Two contexts: one for handlers, one for regular execution

Idle / Regularprocessing

Radioevent

Radio event handler

Sensorevent

Sensor eventhandler

Components instead of


79/123


pprocesses

Need an abstraction to group functionality Replacing processes for this purpose

E.g.: individual functions of a networking protocol

One option: Components Here: In the sense of TinyOS

Typically fulfill only a single, well-defined function

Main difference to processes:

Component does not have an execution

Components access same address space, no protectionagainst each other

NOT to be confused with component-based programming!

API to an event-based protocol


80/123


pstack

Usual networking API: sockets Issue: blocking calls to receive data

Ill-matched to event-based OS

Also: networking semantics in WSNs not necessarily well matched to/bysocket semantics

API is therefore also event-based

E.g.: Tell some component that some other component wants to beinformed if and when data has arrived

Component will be posted an event once this condition is met

Details: see TinyOS example discussion below


81/123

12.1.2 Comparison with Ad Hoc Wireless Networks

Different from Ad Hoc wireless networks

The number of nodes in sensor network can be several orders ofmagnitude large than the number of nodes in an ad hoc network.

Sensor nodes are more easy to failure and energy drain, and theirbattery sources are usually not replaceable or rechargeable.

Sensor nodes may not have unique global identifiers (ID), so uniqueaddressing is not always feasible in sensor networks.

Sensor networks are data-centric, the queries in sensor networks areaddressed to nodes which have data satisfying some conditions. AdHoc networks are address-centric, with queries addressed to particularnodes specified by their unique address.

Data fusion/aggregation: the sensor nodes aggregate the localinformation before relaying. The goals are reduce bandwidthconsumption, media access delay, and power consumption forcommunication.

S


82/123

12.2 Sensor Network Architecture

The two basic kinds of sensor network architecture

Layered Architecture

Clustered Architecture


83/123

12.2.1 Layered Architecture

A layered architecture has a single powerful base station, and thelayers of sensor nodes around it correspond to the nodes that havethe same hop-count to the BS.

In the in-building scenario, the BS acts an access point to a wired

network, and small nodes form a wireless backbone to providewireless connectivity.

The advantage of a layered architecture is that each node isinvolved only in short-distance, low-power transmissions to nodes ofthe neighboring layers.


84/123

Figure 12.2 Layered architecture

"Ad Hoc Wireless Networks", by C. Siva Ram Murthy and B. S. Manoj, published by Prentice Hall, 2004


85/123

Unified Network Protocol Framework (UNPF)

UNPF is a set of protocols for complete implementation of a layeredarchitecture for sensor networks

UNPF integrates three operations in its protocol structure:

Network initialization and maintenance

MAC protocol

Routing protocol


86/123

Network initialization and maintenance

The BS broadcasts its ID using a known CDMA code on thecommon control channel.

All node which hear this broadcast then record the BS ID. They senda beacon signal with their own IDs at their low default power levels.

Those nodes which the BS can hear form layer one

BS broadcasts a control packet with all layer one node IDs. Allnodes send a beacon signal again.

The layer one nodes record the IDs which they hear (form layer two)and inform the BS of the layer two nodes IDs.

Periodic beaconing updates neighbor information and change thelayer structure if nodes die out or move out of range.

MAC t l


87/123

MAC protocol

During the data transmission phase, the distributed TDMA receiveroriented channel (DTROC) assignment MAC protocol is used.

Two steps of DTROC :

Channel allocation : Each node is assigned a reception channel by theBS, and channel reuse is such that collisions are avoided.

Channel scheduling : The node schedules transmission slots for all itsneighbors and broadcasts the schedule. This enables collision-free

transmission and saves energy, as nodes can turn off when they are notinvolved on a send/receive operation.


88/123

12 2 2 Cl t d A hit t


89/123

12.2.2 Clustered Architecture

A clustered architecture organizes the sensor nodes into clusters,each governed by a cluster-head. The nodes in each cluster areinvolved in message exchanges with their cluster-heads, and theseheads send message to a BS.

Clustered architecture is useful for sensor networks because of itsinherent suitability for data fusion. The data gathered by all memberof the cluster can be fused at the cluster-head, and only the resultinginformation needs to be communicated to the BS.

The cluster formation and election of cluster-heads must be anautonomous, distributed process.

12 3 C


90/123

Figure 12.3 Clustered architecture

"Ad Hoc Wireless Networks", by C. Siva Ram Murthy and B. S. Manoj, published by Prentice Hall, 2004

L E Ad ti Cl t i Hi h (LEACH)


91/123

Low-Energy Adaptive Clustering Hierarchy (LEACH)

LEACH is a clustering-based protocol that minimizes energy dissipation insensor networks. The operation of LEACH is spilt into two phases : setupand steady.

Setup phase : each sensor node chooses a random number between 0 and 1. Ifthis is lower than the threshold for node n, T(n), the sensor node becomes acluster-head. The threshold T(n) is calculated as

P : the percentage of nodes which are cluster-heads

r : the current round

G : the set of nodes that has not been cluster-heads in the past 1/P rounds

After selection, the cluster-heads advertise their selection to all nodes. All nodeschoose their nearest cluster-head by signal strength (RSSI). The cluster-headsthen assign a TDMA schedule for their cluster members.


92/123

Steady phase : data transmission takes place based on the TDMAschedule, and the cluster-heads perform data aggregation/fusion.

After a certain period of time in the steady phase, cluster-heads areselected again through the setup phase.

Classification of SensorN t k


93/123

Networks

Proactive Networks

The nodes in the network periodically switch on theirsensors and transmitters, sense the environment andtransmit the data of interest.

Reactive Networks

In this scheme the nodes react immediately to suddenand drastic changes in the value of the sensed attribute.

Fundamentals of MAC Protocol forWi l S N t k


94/123

Wireless Sensor Networks

Static Channel Allocation In this category of protocols, if there are N nodes, the

bandwidth is divided into N equal portions either infrequency (FDMA), in time (TDMA), in code (CDMA),

in space (SDMA: Space Division Multiple Access) orOFDM (Orthogonal Frequency Division Multiplexing)

Dynamic Channel Allocation

In this category of protocols, there is no fixedassignment of bandwidth.

Routing Issues in Sensor


95/123

Routing Issues in SensorNetworks

In traditional wired networks each node is identified by a uniqueaddress, which is used for routing. Sensor networks, being datacentric do not, in general, require routing between specific nodes.

Adjacent nodes may have similar data. So it is desirable toaggregate this data and send it.

The requirements of the network change with application, hence itis application specific.

Routing in Sensor NetworksFlatRouting


96/123

Routing Directed Diffusion

The query is flooded throughout the network.

Events start from some specific points and move outwards toreach the requesting node

This type of data collection does not fully exploit the featureof sensor networks that adjacent nodes have similar data.

Sensor Protocols for Information via Negotiation(SPIN)

Disseminates the information at each node to every node inthe network.

Cougar

This is a warehousing approach. The data is extracted in apre-defined manner and stored in a central database (BS).Query processing takes place on the BS. Cougar is a uniquemodel for query representation in sensor networks.

Hierarchical Routing in SensorNetworks


97/123

Networks

Hierarchical clustering schemes are the most suitable for wirelesssensor networks.

The network consists of a Base Station (BS), away from the nodes,through which the end user can access data from the sensor

network.

BS can transmit with high power.

Nodes cannot reply directly to the BS due to their low powerconstraints, resulting in asymmetric communication.

Hierarchical Routing (Contd)


98/123

Base Station

3

3.1 3.2

3.32

2.12.2

2.3

11.0.11.0.2

1.0.3

1.2

1.2.5 1.2.4

1.2.3

1.2.2

1.2.11.11.1.3

1.1.4

1.1.51.1.1

1.1.2

Simple sensor nodeFirst Level Cluster Head

Second Level Cluster Head

g ( )

Cluster Based Routing Protocol


99/123

g

Cluster Based Routing Protocol (CBRP)

Here the cluster members just send the data to thecluster head (CH).

The CH routes the data to the destination.

Not suitable for a highly mobile environment, as a lotof HELLO messages are sent to maintain the cluster.

Reactive Network Protocol:TEEN


100/123

TEEN(Threshold-sensitive Energy Efficient sensor Networkprotocol)

It is targeted at reactive networks and is the first protocoldeveloped for such networks.

In this scheme at every cluster change time, the CH broadcaststhe following to its members:

Hard Threshold (HT):This is a threshold value for the sensedattribute.

Soft Threshold (ST):This is a small change in the value ofthe sensed attribute which triggers the node to switch on itstransmitter and transmit.



101/123

Cluster Formation

Cluster Change Time

Parameters

Cluster Head Receives Message

Attribute > Threshold

Time Line for TEEN


TEEN (Contd)


102/123

The nodes sense their environment continuously.

The first time a parameter from the attribute set reaches its hardthreshold value, the node switches on its transmitter and sendsthe sensed data.

The sensed value is stored in an internal variable, called SensedValue (SV).

The nodes will transmit data in the current cluster period onlywhen the following conditions are true:

-- The current value of the sensed attribute is greater than thehard threshold.

-- The current value of the sensed attribute differs from SV by anamount equal to or greater than the soft threshold.

TEEN


103/123

Important features: Suited for time critical sensing applications.

Message transmission consumes more energy thandata sensing. So the energy consumption in this

scheme is less than the proactive networks. The soft threshold can be varied.

At every cluster change time, the parameters arebroadcast afresh and so, the user can change them as

required. The main drawback is that if the thresholds are not

reached, then the nodes will never communicate.

Adaptive Periodic Threshold-sensitiveE Effi i t N t k t l


104/123

Energy Efficient sensor Network protocol(APTEEN)

Functioning:The cluster heads broadcasts the following parameters:

Attributes (A):This is a set of physical parameters whichthe user is interested in obtaining data about.

Thresholds: This parameter consists of a HardThreshold (HT) and a Soft Threshold (ST).

Schedule:This is a TDMA schedule, assigning a slot toeach node.

Count Time (CT):It is the maximum time period betweentwo successive reports sent by a node.

Adaptive Periodic Threshold-sensitive Energy Efficient

sensor Network protocol (APTEEN)


105/123

Frame TimeCluster Formation

Cluster Change Time

TDMA Schedule andParametersSlot for Node i

Time line for APTEEN

APTEEN (Contd)


106/123

The node senses the environment continuously.

Only those nodes which sense a data value at or beyondthe hard threshold transmit.

Once a node senses a value beyond HT, it nexttransmits data only when the value of that attribute

changes by an amount equal to or greater than the ST.

If a node does not send data for a time period equal tothe count time, it is forced to sense and retransmit thedata.

A TDMA schedule is used and each node in the clusteris assigned a transmission slot.

APTEEN (Contd)


107/123

( )

Main features of the scheme: It combines both proactive and reactive policies.

It offers a lot of flexibility by allowing the user to set thecount-time interval (CT) and the threshold values for

the attributes. Energy consumption can be controlled by changing

the count time as well as the threshold values.

The main drawback of the scheme is the additional

complexity required to implement the thresholdfunctions and the count time.

Hi hi l V Fl t t l i


108/123

Hierarchical Vs Flat topologiesHierarchical Flat

Reservation-based scheduling Contention-based scheduling

Collisions avoided Collision overhead present

Reduced duty cycle due to periodic sleeping Variable duty cycle by controlling sleep time of nodes

Data aggregation by cluster headNode on multi-hop path aggregates incoming data fromneighbors

Simple but non-optimal routing Routing is complex but optimal

Requires global and local synchronization Links formed on the fly, without synchronization

Overhead of cluster formation throughout thenetwork

Routes formed only in regions that have data fortransmission

Lower latency as multi-hop network formed bycluster-heads is always available

Latency in waking up intermediate nodes and setting upthe multi-hop path

Energy dissipation is uniform Energy dissipation depends on traffic patterns

Energy dissipation can not be controlled Energy dissipation adapts to traffic pattern

Fair channel allocation Fairness not guaranteed

Adapting to the Inherent DynamicNature of Wireless Sensor Networks


109/123

Nature of Wireless Sensor Networks

Certain objectives that need to be achieved are:

Exploit spatial diversity and density of sensors.

Build an adaptive node sleep schedule.

Explore the tradeoff between data redundancy and bandwidthconsumption.

The nodes on deployment should create and assemble a network, adapt

to device failure and degradation, manage mobility of sensor nodes andreact to changes in task and sensor requirements.

Adaptability to traffic changes. Certain nodes may detect an event thatcould trigger a number of updates and at other times very little trafficmay be present.

Allowing finer control over an algorithm rather than simply turning it onand off.


110/123


111/123


112/123


113/123


114/123


115/123


116/123


117/123


118/123


119/123


120/123


121/123


122/123


123/123

Date post:	02-Jun-2018
Category:	Documents
Upload:	jesse-vincent
View:	217 times
Download:	0 times

ara-anna-wireless.ppt

Documents