lecture23-1233854096875992-3

8/3/2019 lecture23-1233854096875992-3

http://slidepdf.com/reader/full/lecture23-1233854096875992-3 1/41

1

Simplified Reference Model

Application

Transport

Network

Data Link

Physical

Medium

Data Link

Physical

Application

Transport

Network

Data Link

Physical

Data Link

Physical

Network Network

Radio

8/3/2019 lecture23-1233854096875992-3


2

Reference Model

Physical Layer :

Bit Stream to signal conversion

Frequency selection Generation of carrier frequency

Data modulation over carrier frequency

Data encryption

8/3/2019 lecture23-1233854096875992-3


3

Reference Model

Data Link Layer :

Data Multiplexing

Error detection and correction

Medium Access

In essence :

Reliable point-to-point transfer of databetween sender and receiver.

8/3/2019 lecture23-1233854096875992-3


4

Reference Model

Network Layer :

Connection setup

Packet routing Handover between networks

Routing

Target device location Quality of service (QoS)

8/3/2019 lecture23-1233854096875992-3


5

Reference Model

Transport Layer :

Establish End-to-End Connection

Flow control Congestion control

TCP and UDP

Applications – Browser etc.

8/3/2019 lecture23-1233854096875992-3


6

Reference Model

Application Layer:

Multimedia applications

Applications that interface to variouskinds of data formats and transmissioncharacteristics

Applications that interface to variousportable devices

8/3/2019 lecture23-1233854096875992-3


7

Overlay Networks - the global goal

regional

metropolitan area

campus-based

in-house

verticalhandover

horizontalhandover

integration of heterogeneous fixed and

mobile networks with varyingtransmission characteristics

8/3/2019 lecture23-1233854096875992-3


8

Frequency Ranges

WIRELESS TRANSMISSION

1 Mm300 Hz

10 km30 kHz

100 m3 MHz

1 m300 MHz

10 mm30 GHz

100 m3 THz

1 m300 THz

visible lightVLF LF MF HF VHF UHF SHF EHF infrared UV

optical transmissioncoax cabletwistedpair

VLF = Very Low Frequency UHF = Ultra High FequencyLF = Low Frequency SHF = Super High Frequency

MF = Medium Frequency EHF = Extra High Frequency

HF = High Frequency UV = Ultraviolet Light

VHF = Very High Frequency

8/3/2019 lecture23-1233854096875992-3


9

Frequencies

kHz Range (Low and Very Lowfrequencies)

Used for short distances using twisted copper wires

Several KHz to MHZ (Medium and HighFrequencies)

For transmission of hundreds of radio stations in the

AM and FM mode Use co-axial cables

Transmission power is several kW.

8/3/2019 lecture23-1233854096875992-3


10

Frequencies

Several MHz to Terra Hz Range (VHF andUHF)

Typically 100 MHz to 800 MHz and

extending to terraHz)

Conventional Analog TV (174-230 MHzand 470-790 MHz)

DAB Range (220 – 1472 MHz) DTV (470 – 872 MHz)

Digital GSM (890-960MHz)

8/3/2019 lecture23-1233854096875992-3


11

Frequencies

3G Mobile Systems (1900-2200 MHz)

Super High(SH) and Extremely SuperHigh(ESH)

Hundreds of GHz

Fixed Satellite Services

Close to infra-red.

8/3/2019 lecture23-1233854096875992-3


12

Frequencies

For Several TerraHz : Optical Transmission

Why do we need very high transmissionfrequencies?

The information content in video, satellitedata etc is enormous.

If we need to accommodate many signalssimultaneously, we need a high bit ratewhich in turn demands high frequency.

8/3/2019 lecture23-1233854096875992-3


13

REGULATIONS

International Telecommunications Union(ITU), Geneva responsible for world-widecoordination of telecommunications

activity.

ITU – R (Radio Communications sector)handles standardization in Wireless

sector.

8/3/2019 lecture23-1233854096875992-3


14

REGULATIONS

ITU-R

Region-1

Europe, Middle East,

Former Russia, Africa

Region-2

Greenland, N & S

America

Region-3

Australia, New

Zealand

8/3/2019 lecture23-1233854096875992-3


15

Frequency AllocationEurope USA Japan

CellularPhones

GSM 450-457, 479-486/460-467,489-496, 890-915/935-960,1710-1785/1805-1880UMTS (FDD) 1920-1980, 2110-2190UMTS (TDD) 1900-1920, 2020-2025

AMPS, TDMA, CDMA 824-849,869-894TDMA, CDMA, GSM 1850-1910,1930-1990

PDC 810-826,940-956,1429-1465,1477-1513

CordlessPhones

CT1+ 885-887, 930-932CT2864-868DECT

1880-1900

PACS 1850-1910, 1930-1990PACS-UB 1910-1930

PHS 1895-1918JCT 254-380

WirelessLANs

IEEE 802.112400-2483HIPERLAN 25150-5350, 5470-5725

902-928IEEE 802.112400-24835150-5350, 5725-5825

IEEE 802.11 2471-24975150-5250

Others RF-Control27, 128, 418, 433,

868

RF-Control315, 915

RF-Control 426, 868

8/3/2019 lecture23-1233854096875992-3


16

REGULATIONS

PDC : Personal Digital Cellular

NMT : Nordic Mobile Telephone

DECT : Digital Enhanced CordlessTelephone

PACS : Personal Access CommunicationsSystem

8/3/2019 lecture23-1233854096875992-3


17

SIGNALS

A sine wave is represented as

g(t) = At sin (ω.t + ø)

Here, At : Maximum amplitudew : angular frequency = 2πf

ø : Phase Displacement

8/3/2019 lecture23-1233854096875992-3


18

SIGNALS

Different representations of signals amplitude (amplitude domain)

frequency spectrum (frequency domain)

phase state diagram (amplitude M and phase

in

polar coordinates)

A [V]

I= M cos

Q = M sin

A [V]

t[s]

8/3/2019 lecture23-1233854096875992-3


19

Signals

According to fourierseries, it is possible toreconstruct the original

signal using the sineand cosine functions.

G(t) = ½ C + )2cos()2sin(11

nft bnft ann

nn

In the above eqn, C represents the DC component.

8/3/2019 lecture23-1233854096875992-3


20

Signals

As n varies, increasing number ofharmonics are added to the signalrepresentation.

As n approaches infinity, the originalsignal is truly represented.

The given signal has to be modulatedover a career frequency.

8/3/2019 lecture23-1233854096875992-3


21

Antenas

An Antenna aids in transforming a wiredmedium to a wireless medium

Antennas couple electromagnetic energyto the space and from the space TO andFROM a wire/coaxial cable.

8/3/2019 lecture23-1233854096875992-3


22

ISOTROPIC RADIATOR ANTENNA

Theoretical reference antenna is theisotropic radiator.

It emits equal power in all directions.

zy

x

z

y x

8/3/2019 lecture23-1233854096875992-3


23

Antennas

Practical Antennas Exhibit Directional properties.

Thin Centre-fed Dipole:

λ /2

• Dipole consists of two collinear conductors separated by a small feedinggap.

• Generally, the length of the Dipole is half the wavelength of the signal tobe transmitted/received.(λ = C/f where is is the speed of light {3*10 8 m/s)

8/3/2019 lecture23-1233854096875992-3


24

Wavelength

Forms of electromagnetic radiation like radio waves, lightwaves or infrared (heat) waves make characteristicpatterns as they travel through space. Each wave has acertain shape and length. The distance between peaks

(high points) is called wavelength.

8/3/2019 lecture23-1233854096875992-3


25

Dipole Antenna

•When the signal is obstructed by mountains, buildings etc, the powerof the sinal gets weak.

• It can be boosted by additional devices.

8/3/2019 lecture23-1233854096875992-3


26

Directional Antenna

Several directional antennas can be combined to forma sectored antenna.

8/3/2019 lecture23-1233854096875992-3


27

Signal Propagation Range

distance

sender

transmission

detection

interference

Transmission range communication possible

low error rate

Detection range

detection of the signal

possible

no communicationpossible

Interference range

signal may not bedetected

signal adds to thebackground noise

8/3/2019 lecture23-1233854096875992-3


28

Path Loss during Transmission

Propagation in free space is always in a straight line like that of light.

Receiving power proportional to 1/d² in vacuum – much more inreal environments

(d = distance between sender and receiver)

Receiving power additionally influenced by Fading (frequency dependent)

shadowing

reflection at large obstacles

refraction depending on the density of a medium

scattering at small obstacles

diffraction at edges

8/3/2019 lecture23-1233854096875992-3


29

Path Loss Effects

reflection scattering diffractionshadowing refraction

8/3/2019 lecture23-1233854096875992-3


30

Signal Propagation effects

Signal Penetration through objects :

At lower frequency, the penetration is higher.

At very high frequencies, the transmission

behavior of the wave is close to that of light,

8/3/2019 lecture23-1233854096875992-3


31

Propagation behavior of waves

Ground Wave (<2 MHz): Can follow earth’s

surface and can propagate long distances

[Submarine communication, AM Radio etc]

Sky Wave (2-30 MHz) : Waves are reflected.They can bounce back and forth betweenionosphere and earth’s surface and can travel

around the world.

Line of Sight [>30 MHz) : The waves are bent

by refraction.

8/3/2019 lecture23-1233854096875992-3


32

Multipath Propagation

8/3/2019 lecture23-1233854096875992-3


33

8/3/2019 lecture23-1233854096875992-3


34


Radio waves sent from the sender to thereceiver can travel in a straight line aswell as may reach the destination after

being reflected by several obstacles.

The signal arrives at different times atthe receiver. THIS EFFECT IS CALLED

DELAY SPREAD

8/3/2019 lecture23-1233854096875992-3


35


The original signal gets a spread signal

The order of delays is 2 to 12 microsecs.

8/3/2019 lecture23-1233854096875992-3


36

Effects of delay spread

Short-pulse signals will be spread into abroader impulse or several weakerpulses.

In the fig, the impulse at the sender isreceived as three smaller pulses at thereceiver.

Also, the power level of the receivedpulses will be low. So, they will beperceived as noise.

8/3/2019 lecture23-1233854096875992-3


37

Effects-2 of delay spread

Inter Symbol Interference :

The second symbol is separated fromthe first in the transmitted signal.

At the receiver, they overlap because ofdelays.

If the pulses represent symbols, they willinterfere with each other and there willbe INTER SYMBOL INTERFERENCE.

8/3/2019 lecture23-1233854096875992-3


38

One possible solution

Receiver should know the delaycharacteristics of different paths.

Receiver can compensate for thedistortion

Receiver can equalize the signals basedon the channel characteristics.

8/3/2019 lecture23-1233854096875992-3


39

Effects of mobility

Channel characteristics change over timeand location

signal paths change

different delay variations of different signalparts

different phases of signal parts

quick changes in the power received(short term fading) short term fading

long termfading

t

power

8/3/2019 lecture23-1233854096875992-3


40

Solution for Long Term Fading

Senders can increase/decrease poweron a regular basis so that the receivedpower is within certain bounds.

8/3/2019 lecture23-1233854096875992-3


Long Term Fading

Additional changes in

distance to sender

obstacles further away

slow changes in the average powerreceived (long term fading)

Documents

lecture23-1233854096875992-3