c03 technology fundamentals

8/3/2019 C03 Technology Fundamentals

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EPL476 Mobile NetworksFall 2009

Wireless Technology Fundamentals

Instructor: Dr. Vasos Vassiliou

Slides adapted from Prof. Dr.-Ing. Jochen H. Schiller and W. Stallings


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Sensor networks are another form of infrastructurelessnetwork, with many similarities to ad-hock


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Fundamental concepts inwireless networks

Sharing Resources Cellular concepts (reuse resources)

WLAN (shared space)

Adhoc (shared resources) Sensor (shared resources, large space)


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What is a Cell?

Cell is the Basic Union in The System defined as the area where radio coverage is given by

one base station. A cell has one or several frequencies, depending

on traffic load. Fundamental idea: Frequencies are reused, but not inneighboring cells due to interference.


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Cell characteristics Implements space division multiplex: base station

covers a certain transmission area (cell) Mobile stations communicate only via the base

station Advantages of cell structures:

higher capacity, higher number of users less transmission power needed more robust, decentralized base station deals with interference, transmission area

etc. locally Problems:

fixed network needed for the base stations handover (changing from one cell to another) necessary interference with other cells

Cell sizes from some 100 m in cities to, e.g., 35 kmon the country side (GSM) - even less for higher

frequencies


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Different Types of Cells


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Cell Planning (1/3)

The K factor and Frequency Re-Use Distance

K = i2 + ij + j2

K= 22 + 2*1 + 12

K = 4 + 2 + 1

K = 7i

j

1

2

3

4

5

6

7

Frequency re-use distance is based on the cluster size K

The cluster size is specified in terms of the offset of the center of a cluster from the

center of the adjacent cluster

D = 3K * RD = 4.58R

1

2

35

6

7

D

R


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Cell Planning (2/3)

A3

A1

A2

G3G1

G2C3

C2

B3B1

B2

F3F1

F2

D3D1

D2

E3

E1

E2

G3

G1

G2

F3F1

F2

C3C1

C2

A3A1

A2B3

B1

B2

E3E1

E2

D3D1

D2

7-cell reusepattern

Frequencyreuse

C1


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Cell Planning (3/3)

Cell sectoring Directional antennas

subdivide cell into 3 or6 sectors

Might also increasecell capacity by factorof 3 or 6

Cell splitting Decrease transmission

power in base andmobile

Results in more andsmaller cells

Reuse frequencies innon-contiguous cellgroups

Example: cell radiusleads 4 fold capacityincrease


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Hierarchical Cell Structures(HCS) (1/2) HCS allows traffic to be directed to a preferred

cell Each cell is defined in a particular layer The lower the layer, the higher the priority

Mobiles will select a cell on the lowest layer as long asit has sufficient signal strength, even if higher layercell are stronger


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WLAN: Definition

A fast-growing market introducing theflexibility of wireless access into office,home, or production environments.

Typically restricted in their diameter tobuildings, a campus, single rooms etc.

The global goal of WLANs is to replaceoffice cabling and, additionally, tointroduce a higher flexibility for ad hoccommunication in, e.g., group meetings.


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WLAN: Characteristics

Advantages: very flexiblewithin radio coverage ad-hoc networks without previousplanningpossible wireless networks allow for the designof small, independent

devices more robustagainst disasters (e.g., earthquakes, fire)

Disadvantages: typically very low bandwidthcompared to wired networks (~11 54

Mbit/s) due to limitations in radio transmission, higher error ratesdue to interference, and higher delay/delay variationdue toextensive error correction and error detection mechanisms

offer lower QoS many proprietary solutions offered by companies, especially for

higher bit-rates, standards take their time (e.g., IEEE 802.11) slow standardization procedures standardized functionality plus many enhanced features these additional features only work in a homogeneous environment (i.e.,

when adapters from the same vendors are used for all wireless nodes) products have to follow many national restrictionsif working

wireless, it takes a very long time to establish global solutions


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WLAN: Design goals

global, seamless operation of WLAN products low power for battery use (special power saving modes

and power management functions) no special permissions or licenses needed (license-free

band)

robust transmission technology simplified spontaneous cooperation at meetings easy to use for everyone, simple management protection of investment in wired networks (support the

same data types and services)

security no one should be able to read others data,privacy no one should be able to collect user profiles,safety low radiation

transparency concerning applications and higher layerprotocols, but also location awareness if necessary


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WLAN: Technology Overview

Core technologies (IEEE 802.1x family)

IEEE 802.11 (Wireless LAN)

IEEE 802.15 (Wireless PAN Bluetooth)

IEEE 802.16 (Wireless M(etropolitan) AN) Underdevelopment

Facilitating technologies

RF-Id

IrDA Home-RF

PAN

LAN

MAN


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WLAN: Technology

Can be categorized according to the

transmission technique being used

Infrared (IR) LANs: Very limited coverage area

(IR cant penetrate walls!) Spread Spectrum LANs: Operate in industrial,

scientific, and medical (ISM) bands

Narrowband Microwave LANS: Operate at

microwave frequencies but not using spread

spectrum (in licensing or ISM bands)


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WLAN: infrared vs. radio transmission Infrared

uses IR diodes, diffuse light,multiple reflections (walls,furniture etc.)

Advantages simple, cheap, available in

many mobile devices no licenses needed simple shielding possible

Disadvantages interference by sunlight, heat

sources etc. many things shield or absorb

IR light low bandwidth

Example IrDA (Infrared Data

Association) interfaceavailable everywhere

Radio typically using the license free

ISM band at 2.4 GHz Advantages

experience from wireless WANand mobile phones can be used

coverage of larger areas

possible (radio can penetratewalls, furniture etc.)

Disadvantages very limited license free

frequency bands

shielding more difficult,interference with otherelectrical devices

Example: WaveLAN, HIPERLAN,

Bluetooth


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WLAN: Spread Spectrum

Most popular category!

Spread Spectrum Communications

Developed initially for military and intelligence

requirements

Essential idea: Spread the information signal

over a wider bandwidth to make jamming and

interception more difficult Frequency hopping

Direct sequence spread spectrum


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WLAN: infrastructure vs. ad-hocnetworks

infrastructurenetwork

ad-hoc network

APAP

AP

wired network

AP: Access Point


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WLAN: Infrastructure-based networks

Infrastructure networks provide access to other networks.

Communication typically takes place only between the wireless nodesand the access point, but not directly between the wireless nodes. The access point does not just control medium access, but also acts

as a bridge to other wireless or wired networks. Several wireless networks may form one logical wireless network:

The access points together with the fixed network in between canconnect several wireless networks to form a larger network beyondactual radio coverage.

Network functionality lies within the access point (controls networkflow), whereas the wireless clients can remain quite simple.

Use different access schemes with or without collision. Collisions may occur if medium access of the wireless nodes and the

access point is not coordinated.

If only the access point controls medium access, no collisions are possible. Useful for quality of service guarantees (e.g., minimum bandwidth for certain nodes)

The access point may poll the single wireless nodes to ensure the data rate.

Infrastructure-based wireless networks lose some of the flexibilitywireless networks can offer in general: They cannot be used for disaster relief in cases where no infrastructure

is left.


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WLAN: ad-hoc networks No need of any infrastructure to work

greatest possible flexibility Each node communicate with other nodes, so no access point

controlling medium access is necessary. The complexity of each node is higher

implement medium access mechanisms, forwarding data Nodes within an ad-hoc network can only communicate if they

can reach each other physically if they are within each others radio range if other nodes can forward the message


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WLAN: StandardsWireles

sLAN

2.4 GHz 5 GHz

802.11(2 Mbps)

802.11b(11 Mbps)

802.11g(22-54Mbps)

HiSWANa

(54 Mbps)

802.11a(54 Mbps)

HiperLAN2

(54 Mbps)

HomeRF

2.0(10 Mbps)

Bluetooth(1 Mbps)

HomeRF

1.0(2 Mbps)

802.11e(QoS)

802.11i(Security)

802.11f(IAPP)

802.11h(TPC-DFS)


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WLAN: Standards (ii) IEEE 802.11 and HiperLAN2 are typically infrastructure-

based networks, which additionally support ad-hoc networking

Bluetooth is a typical wireless ad-hoc network

IEEE 802.11b offering 11 Mbit/s at 2.4 GHz The same radio spectrum is used by Bluetooth

A short-range technology to set-up wireless personal area

networks with gross data rates less than 1 Mbit/s IEEE released a new WLAN standard, 802.11a, operating at 5GHz and offering gross data rates of 54 Mbit/s Shading is much more severe compared to 2.4 GHz Depending on the SNR, propagation conditions and the distance between

sender and receiver, data rates may drop fast

uses the same physical layer as HiperLAN2 does HiperLAN2 tries to give QoS guarantees IEEE 802.11goffering up to 54 Mbit/s at 2.4 GHz.

Benefits from the better propagation characteristics at 2.4 GHz compared to 5GHz

Backward compatible to 802.11b

IEEE 802.11e: MAC enhancements for providing some QoS


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Ad Hoc Networks: Definition

A network made up exclusively of wirelessnodes without any access points operatingin peer-to-peer configuration, grouped

together in a temporary manner.


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Ad Hoc Networks: SomeFeatures Lack of a centralized entity

All the communication is carried over thewireless medium

Rapid mobile host movements Limited wireless bandwidth

Limited battery power

Multi-hop routing


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Ad Hoc Networks: Operation

Assumption Unidirectional link

Adjustable power level

Directional antenna GPS

Operation Broadcasting

Routing

Multicasting


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Ad Hoc Networks: Challenges(i)Hidden terminal problem

A transmits to B C wants transmits to B C does not hear As transmission Collision

Exposed terminal problem B transmits to A

C wants to transmit to D C hear Bs transmission Unnecessarily deferred

A B C

A B C D


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Ad Hoc Networks: Challenges(ii) Challenges

Mobility

Scalability

Power Minimizing power consumption during the idle time

Minimizing power consumption during communication

QoS

End to End delay Bandwidth management

Probability of packet loss


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Ad Hoc Networks: Broadcast (i)

Objective: paging a particular host

sending an alarm signal

finding a route to a particular host Two types:

Be notified -> topology change

Be shortest -> finding route

A simple mechanism: Flooding Suffer from broadcast storm


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Ad Hoc Networks: Broadcast(ii)

source

Be notified Be shortest

5 forwarding nodes4 hop time

source

6 forwarding nodes3 hop time


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Ad Hoc Networks: Routing

Table Driven vs. On Demand DSDV, TORA, DSR, AODV

Hierarchical and Hybrid ZONE

Specific assumption Unidirectional link, Directional antenna, GPS

QoS-aware Power, Delay, Bandwidth


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Ad Hoc Networks: Multicast

Parameter: The delay to send a packet to each destination

The number of nodes that is concerned in

multicast The number of forwarding nodes

s

D

D

D

s

D

D

D

s

D

D

D


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Sensor Networks: Definition

A sensor network is a collection ofcollaborating sensor nodes (ad hoc tinynodes with sensor capabilities) forming a

temporary network without the aid of anycentral administration or support services. Sensor nodes can collect, process, analyze and

disseminate data in order to provide access to

information anytime and anywhere.


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Sensor Networks: SomeFeatures Large number of sensors

Low energy use

Efficient use of the small memory

Data aggregationNetwork self-organization

Collaborative signal processing

Querying ability


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Sensor Networks: Operation

Sensors work in clusters Each cluster assigns a cluster head to manage

its sensors Three layers

Services layer Data layer Physical Layer

To compensate for hardware limitations (e.g.memory, battery, computational power): Applications deploy a large number of sensor nodes

in the targeted region.


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Sensor Networks: Challenges (i)

Hardware design

Communication protocols

Applications design

Extending the lifetime of a sensor network Building an intelligent data collecting

system

Topology changes very frequentlySensors are very limited in power

Sensors are very prone to failures

N k Ch ll


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Sensor Networks: Challenges(ii)Sensors use a broadcast paradigm

Most networks are based on point to pointcommunication

Sensors may not have a globalidentification (ID) Very large overhead

Dynamic environmental conditions require

the system to adapt over time to changingconnectivity and system stimuli


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Sensor Networks: Aggregation

Some sensor nodes are designed toaggregate data received from theirneighbors.

Aggregator nodes cache, process and filterdata to more meaningful information.

Aggregation is useful because: Increased circle of knowledge

Increased accuracy level

Data redundancy To compensate for sensor nodes failing

S N k


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Sensor Networks:Dissemination Two ways for data dissemination:

Query driven: sink broadcasts one query and sensornodes send back a report in response

Continuous update: sink node broadcasts one query

and receives continuous updates in response (moreenergy consuming but more accurate)

Problems: Intermediate nodes failing to forward a message

Finding the shortest path (a routing protocol) Redundancy: a sensor may receive the same data

packet more than once.


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Sensor Networks: Advantages

Coverage of a very large area through thescattering of thousands of sensors.

Failure of individual sensors has no major

impact on the overall network. Minimize human intervention and management.

Work in hostile and unattended environments.

Dynamically react to changing network

conditions. E.g. Maintain connectivity in case of unexpected

movement of the sensor nodes.

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