Voice over IP (VoIP) תיטוחלא תרושקת · 1 introduction Wireless Communication Spring...

Wireless Communicationintroduction1

Dr. Martin LandHadassah CollegeSpring 2010

תקש ו רת א ל חו ט י ת

Wireless Communication



Global Communication

Wireless personal area network

Wireless local area network

Wireless metropolitan area network

Wireless wide area network

Commercial radio

Two-way radio

Mobile telephone

Mobile multimedia

Wireless

Ethernet

Frame Relay

Modem

Point-to-point

ATM

DSL

TelephoneWired

DataVoice / Audio

Voice over IP (VoIP)



Syllabus

Wireless personal area network

Wireless local area network

Wireless metropolitan area network

Wireless wide area network

Commercial radio

Two-way radio

Mobile telephone

Mobile multimedia

Wireless

Ethernet

Frame Relay

Modem

Point-to-point

ATM

DSL

TelephoneWired

DataVoice / Audio

Voice over IP (VoIP)



Some Basic ObservationsWireless

Free-space electromagnetic transmissionRadio, optical, IR

Differs from wired at infrastructure layersPhysical transmission / receptionMedium access issues

Application programmer usually ignores infrastructureGenerally sees OS-provided network API (sockets)Special case — telephone / PDA applications

Special issues in wireless infrastructuresMobility managementBroadcast infrastructureChannel reliability

Infrastructure LayersMedium access / physical

Internet LayersTCP/IP

Application LayerUser programs



Types of Wireless InfrastructuresWireless Personal Area Networks (wPAN)Wireless Local Area Networks (wLAN)

Wireless LAN with WAN accessWireless Metropolitan Area Network (wMAN)Wireless Wide Area Network (wWAN)

Cellular TelephonyCellular Data Networks Wireless Application Protocol (WAP)3rd Generation Cellular Systems



Wireless Personal Area Network (wPAN)Short range broadcast transmission Standard technologies

BluetoothInfrared Data Association (IrDA)Wireless USB

Applications Wireless computer peripheralsBluetooth earpiece Transfer interface for laptops,

PDAs, cellphonesRemote control



Wireless Local Area NetworksWireless equivalent to local Ethernet

Wireless network cardDefines user authentication and encryptionNo external connection

Standard technologiesIEEE 802.11 (Wi-Fi)BluetoothIrDA

Basic Wireless LAN

station

station

station



Wireless LAN with WAN InfrastructureExtension of wireless LAN

Allows mobile access to external networksAllows roaming between wLAN groups

Standard technologiesIEEE 802.11 (Wi-Fi)

DistributionSystem

Wireless LAN

station

station

gateway

Wireless LAN

station

station

gateway

Internet

Wireless LAN Access to WAN



Cellular TelephonyMedium range broadcast with private channel assignmentStandard technologies

AMPS / TACS (1G)GSM / d-AMPS (2G)CDMA (2G)UMTS / CDMA2000 (3G)WCDMA (4G)

ApplicationWireless voice network

Cellular Telephone Networks

Public Switched Telephone Networks



Cellular Data Networks and Wireless IPWireless wide area data network (wWAN)

Data WAN over cellular telephone networkStandard technologies

CDPD (1.5G)GPRS (2G)EDGE (2.5G)UMTS (3G)

Cellular Telephone Network

Internet



Wireless Application Protocol (WAP)Protocol stack for mobile web interface

Adapts web for Phone screens PDA keypad

WML interactive scripting language

Protocol stack for mobile web interface

Adapts web forPhone screens PDA keypad

WML interactive scripting language



Wireless Metropolitan Area Network (wMAN)Cellular broadband data access

WAN access via wireless networkStandard technologies

IEEE 802.16 (WiMAX)

Wireless MANInternet

Wireless LANAccess Point



Layered Protocol

Layern + 1

PeerLayer

n

Layern + 1

PeerLayer

n

p

Layer n SDU = Layer n - 1 PDULayer nHeader

Layer n PDU

Layer n + 1 PDU

Layern - 1

Layern - 1 Layer n - 1 SDU = Layer n PDULayer n - 1

Header

Layer n - 1 PDU

interface

protocol

Provides service to layer n + 1 Receives service from layer n - 1

Layer n

Payload carried to provide service to higher layerService Data Unit (SDU)

Raw data and header exchanged by peers at layer nProtocol Data Unit (PDU)

Communication between layersInterface

Communication between peersProtocol



OSI Model

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

ApplicationPDU

ApplicationPDU

PresentationHeader

Presentation PDUSessionHeader

Transport SDU = Session PDUTransportHeader

Network SDU = Transport PDUNetworkHeader

Data Link SDU = Network PDUData LinkHeader

Data LinkTrailer

Physical SDU = Bits (Data Link PDU)

Open System Interconnection

Requesting Layer Protocol Data Unit (PDU) = Serving Layer Service Data Unit (SDU)



Layer Definitions in OSI Model

Physicalתמסורת פיסית של סיביות מנ קודה לנקודה בין פיסי1

ישויות חומרה סמוכות

Data Linkבקרה על העברת סיביות במסגרת בסיסית מנקודה קישור2

לנקודה בין ישויות חומרה סמוכות

Networkהכוונה מסגרות בין ישויות חומרה קצה לקצה דרך רשת3

רשת

Transportבקרה על סדרה של העברות מסגרות בסדר נכון העברה4

או חזרות, אבדות, ורצוף ללא שגיאות תמסורת

Sessionבקרה על סדרת העברות הדדיות בין שתי ישויות מושב5

תוכנה בהקשר משותף והפרדה בין שיחות שונות

Presentation, הצפנה, שפה, קידודים, המרות בין צורות ייצוג נתוניםהצגה6

וכדומה

Applicationתוכנית יישום מחליפה נתונים עם תוכנית יישום אחרת יישום7

שיכול לעבד אותו מבנה נתונים



Sublayers in Data Link LayerMedium access (MAC)

User access rights to network Control of physical access proceduresPhysical network addressesBandwidth allocation

Logical Link Control (LLC)Point-to-point transport servicesError detection and correctionFrame sequencingFlow control

ExampleEthernet defines 802.3 MAC protocolEthernet may use 802.2 LLC service

802.3 trailerUser data (payload)802.2 header802.3 header



Why is OSI Model Useful?Criticism of OSI

Relationships among layers not relevant to every systemNot every layer is active in every system

Definition of functional layers is most useful featureDistinguishes principal functions in any communication systemProvides useful names for atomic communication functions

Examples System defines a Transport Layer above Session Layer

Incoming packets segregated by conversation and then error checked

System has multiple copies of IP Layer Lower IP Layer tunnels upper IP Layer packet through private network

Layer names still characterize layer function



Mapping TCP/IP Model to OSI Model

Example — Web BrowserApplication handles user data, language, encryption, HTTP sessionsTCP handles sockets for HTTP sessions and data reliabilityIP handles datagram addressing for end-to-end networkingInfrastructure is usually Ethernet or PPP over modem

בקרה על סדרת העברות הדדיות בין שתי ישויות

OSIFunctionTCP/IP

Infrastructure

Internet

Transport

Application

Physicalתמסורת פיסית

Data Linkבקרה על העברת סיביות במסגרת בסיסית

Networkהכוונה מסגרות דרך רשת

Transportבקרה על סדרה של העברות מסודרות

Sessionתוכנה בהקשר משותף והפרדה בין שיחות שונות

Presentationהמרות בין צורות ייצוג נתונים

Applicationהחלפת נתונים בין תוכנית יישום



Tunneling in the OSI Model

NetworkLayer

(translation)

Data LinkLayer

(translation)

PhysicalLayer

(translation)

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

Local PhysicalProtocol

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

End-to-End Application Protocol

End-to-End Presentation Protocol

End-to-End Session Protocol

End-to-End Transport Protocol

Local NetworkProtocol

Local Data LinkProtocol


End User Intermediate System

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

Local SessionProtocol

Local TransportProtocol



Host / Server

PhysicalLayer



PhysicalLayer

(translation)

Proxy / Gateway

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer


Local SessionProtocol

Local TransportProtocol





ADSL in Bezeq VPN

usermanagement

and IP datagramforwarding

IP datagramforwarding

Bezeq ISP

Internet routing

ADSL modem onpoint-to-point

channel

Server

IPnetwork

phonenetwork

Client

switchedATM

network



ADSL in Bezeq VPN

Client forms standard internet packetsIP packets to destination PPP packets for ISP authentication and billing

Virtual private network (VPN)PPP packet encapsulated in IP tunnel addressed to ISPVPN built on Bezeq ATM switching infrastructure

Client

PHY

Ethernet

ATM

IP

PPP

IP

TCP

App

PHY

ATM

ADSL Modem

PHY

Ethernet

ATM

Server

PHY

MAC

IP

TCP

App

PHY

MAC

IP

Bezeq

PHY

ATM

IP

PHY

MAC

IP

ISP

PHY

MAC

IP

PPP

IP



Energy and PowerEnergy

The ability to do workEnergy can be kinetic (movement) or potential (stored)

PowerEnergy transfer per secondTransfer can be kinetic (motion) or potential (moving stored energy)

UnitsPower is measured in WattsEnergy is measured in Joules = Watts × seconds 1 kW-hour = 1000 Watts × 3600 seconds/hour

= 3.6 × 106 Joules



Electricity and Magnetism

2 ,

0

Electric field

Magnetic field

Power

chargeat distance

RR

∝

= −

=

EB

E×B

E

B

A charged object may create

Radiation (transfer of power) from a charged object

Motionless charge does not radiate

Antenna accelerat0 0Accelerated charges induce fields and

Antenna radiates power as electromagnetic waves

=

≠ ≠E B

es charges electric current



Wave Motion

Wave height has peaks and troughsy = height of peak above center = depth of trough below center

At fixed distance from shore, wave rises and falls over timeT = time between two wave peaks (period) f = 1/T = number of wave peaks per second (frequency)

At fixed time, multiple wave peaks at various distancesλ = distance between two wave peaks (wavelength)

Surfer rides peak of wavePeak depends on distance and time ⇒ peak moves over timeSpeed of moving peak = f × λ

R

yy

λ

Ocean waves rolling onto a beach



Radio Communication

Moving electric charge is called electric currentCurrent depends on time ⇒ charges must accelerate

Electromagnetic radiation satisfies wave equation Radiated power depends on time t and distance R from antenna

Transmitteraccelerates

chargesup and downon antenna

Informationsignal

controlsmotion

of charges

Power needed to accelerate charges getsradiated away as electromagnetic power

Radiation spreads in every directionlike expanding sphere

Radiated poweraccelerates

chargesup and downon receiver

antenna

Motionof chargeprovides

informationsignal toreceiver



Charge Moving on AntennaCharge on antenna accelerated up and down

Oscillates top to bottom (distance L) every T seconds

t0

T/4 T/2 3T/4 T( )y t

2L

2L

−

( )

( ) ( )

1

cos 2 cos 22 2

Frequency oscillation cycles per second

position of charge on antenna at time y

y

f Tt t

L t Lt ftT

π π

=

=

⎛ ⎞= =⎜ ⎟⎝ ⎠

L

movingcharge

y (t)



Field is Solution to Maxwell Equations

( )( )

( )( )0 0

0 0

cos 2 cos 2, ,

1/,

distance from antenna to point of measurement

time (measured on some clock)

frequency

are physical constants

speed of light

R Rf t f tc cR t R tR R

Rtf T

c

π π⎡ ⎤ ⎡ ⎤− −⎣ ⎦ ⎣ ⎦= =

=== =

=

E BE B

E B

Radiation fields

R

R

P( )

( )

20 02

0 020

cos 2

1 12

T

Rf tcR

P P t dtT R

π× ⎡ ⎤= × = −

⎣ ⎦

×= =∫

E BP E B

E B

Radiated power

Average power Fading



Wavelength

( )( ) 0 00

cos 2 cos 2cos 2,

cos 2 1 0,1,2,...

ccT f cf

f R R tftRf t c TcR tR R R

R t R tT T

R tT

λ λ

π ππ λ

πλ λ

λ

= = ⇒ =

⎡ ⎤ ⎡ ⎤⎛ ⎞ ⎛ ⎞− −⎡ ⎤ ⎜ ⎟ ⎜ ⎟− ⎢ ⎥ ⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎣ ⎦ ⎣ ⎦= = =

⎡ ⎤⎛ ⎞ ⎛ ⎞− = ⇒ − =⎜ ⎟ ⎜ ⎟⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦⎛ ⎞−⎜⎝

E EEE

Define electromagnetic wavelength

Radiation field

Wave peaks

0 0 0

Wave peaks travel at speed of light

R R t t R tT T

Rv f ct T

λ λ

λ λ

+ Δ + Δ Δ Δ⎛ ⎞ ⎛ ⎞= → − = ⇒ − =⎟ ⎜ ⎟ ⎜ ⎟⎠ ⎝ ⎠ ⎝ ⎠

Δ= = = =Δ

Speed



Spherical Waves in Space and TimeAt fixed distance wave rises and falls over time

t

T/4 T/2 3T/4 T

( )

( )

0

1 2

, cos 2

cos 2

constconst

const

ttT

ft

RR

RC C

πλ

π

⎡ ⎤⎛ ⎞= −⎢ ⎜ ⎟⎥⎝ ⎠⎣ ⎦

= × −

EE

( )

2

0

1

, cos 2

cos 2

constconst

RRR T

C

t

R CR

t πλ

πλ

⎡ ⎤⎛ ⎞= −⎢ ⎜ ⎟⎥⎝ ⎠⎣ ⎦

⎡ ⎤⎛ ⎞= −⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

EE

R

-1/R

4λ

2λ 3

4λ λ

1/R

At fixed time, multiple wave peaks at various distancesWave peaks decrease at larger distances from source



Electromagnetic Spectrum

Radio antennas are effective in the frequency rangefrom ~ 30 kHz (λ = 10 km)to ~ 300 GHz (λ = 1 mm)

Chemical reactions generate higher frequencies:Infra-Red (IR) Visible LightUltra-Violet (UV) X-rays (Roentgen)

Nuclear reactions generate gamma rays (γ)



Electromagnetic Spectrum

ExampleLine antenna most efficient when L = λ / 2GSM cellphones operate at f ~ 1 GHzλ = (3×1010 cm/sec)/(109 Hz) = 30 cm ⇒ L ~ 15 cm = phone size

Wavelength (m) 104 102 100 10-2 10-4 10-6 10-8 10-10 10-12 10-14 10-16

Frequency (Hz) 104 106 108 1010 1012 1014 1016 1018 1020 1022 1024

radio microwave IR visible UV X-ray gamma

1 MHz ~ 300 m 100 MHz ~ 3 m 10 GHz ~ 3 cm

VLF < 30 kHz LF 30 - 300 kHz MF 300 kHz - 3 MHz HF 3 - 30 MHz VHF 30 - 300 MHz UHF 300 MHz - 3 GHz SHF 3 - 30 GHz EHF > 30 GHz

103 10 cm/s f cλ = = ×



Frequency and Harmonic Content

( ) ( )

( ) ( ) ( )

( ) ( ) ( )2 2 1

0 1

0 0 0

1 11

! 2 ! (2 1)!

1

cos 2 sin 2

cos sin

st

fundamental frequency

Fourier series

(n 1) harmonic

k kn k k

n nn n

i

n k ki

n k k

y t T y t f T

y t b nft a nft

n f

e i iθ θ θ θ

π π

θ θ+

∞ ∞

= =

∞ ∞ ∞

= = =

− −

+

−

+ = = =

= +

=

= = + = +

∑ ∑

∑ ∑ ∑

For any periodic function

Using

Fourie

( )

( ) ( )*1 12 2

22

stgives relative weight of (n 1) harmonic

,

n

n

i tn n

n

n n n n n n

n

ny t e nfT

b ia b ia

ω πα ω π

α α α

α

∞

=−∞

−

−

= = =

= − = = +

∑

r series with complex coefficients



Fourier Coefficients

/2

/2

/2 /2

/2 /2

0

1,10,

1 1( )

( ) 1 , 0 22

1( ) sin( )

for

for

n m

m m n

T i t i tnmT

T Ti t i t i tn mT T

n

n m

n n

n me e dt

n mT

e y t dt e e dtT T

iy t t t

y t t

ω ω

ω ω ω

δ

α α

α

π

−

−

∞− −

− −=−∞

≠

=⎧= = ⎨ ≠⎩

⎡ ⎤= =⎢ ⎥⎣ ⎦

−= − ≤ ≤ ⇒ =

≈ +

∫

∑∫ ∫144424443

From

It follows that

Example

2

3 4

1sin(2 ) sin(3 )2 2

1 1sin(4 ) sin(5 )2 2

t t

t t

π π

π π

+

+ +

-1.5

-0.5

0.5

1.5

0 1 2 3 4



Fourier Transform

( )

( )

/ 2

/2

2 2

( ) ( )

lim lim2

1 ( )2

Fourier transform (spectrum)

n

T in t i tn n T

in t in t in tnn nT Tn n n

i t

n nT T

T

F T e y t dt F e y t dt

Fy t e e F e

T

F e d

ω ω

ω ω ω

ω

π πω ω ω ω

α ω

ωαπ

ω ωπ

∞− Δ −

− −∞

∞ ∞ ∞Δ Δ Δ

→∞ →∞=−∞ =−∞ =−∞

∞

−∞

Δ = ⇒ = → = Δ

→∞

= = → =

Δ= → =

=

∫ ∫

∑ ∑ ∑

∫

Define

Take limit

Fourier integral (spectral representation)



Waves in MediumEffect of medium on waves is frequency dependent

( ) ( )1 1( ) ( )2 2

i t i tout out int e d H e dω ωω ω ω ω ω

π π

∞ ∞

−∞ −∞

= =∫ ∫E F F

( )H ω( )in ωF ( )out ωF

( )( ) ( )out inHω ω ω=F F

( )in tE medium ( )out tE

( )( ) i tin in t e dωω ω

∞−

−∞

= ∫F E

( )H ω

Resolve incoming wave into frequency components

Medium acts as linear filter on each frequency component

Outgoing wave is transform of filtered incoming wave



Radio Wave PropagationTransmitter generates radio wavesWaves propagate (spread out) through space

Part of radiated power may be obstructedPart of radiated power is detected by receiver

ionotropic wave

line of sight wave

ground wave

tropospheric wave

Transmitter Receiver



Interference and FadingObstacles reflect, absorb, or refract (bend) radio waves

Similar to effect of material on visible lightTransparent objects do not reflect, absorb, or refractDepends on material and frequency

Signals pass through unchangedClear Transparent

Radio wavesVisible light

Signals change directionGlass lens or water poolRefractive

Signals absorbed in materialBlack or opaqueAbsorbent

Signals bounce back White and shinyReflective

As radio frequency f increasesReflection increasesAbsorption increasesRefraction decreases



Interference with Radio Signals

absorption

reflection

refraction

medium



Four Main Propagation PathsLine of sight wave

Dominant received signalAffected by obstacles in path

Ground wave Dominant signal after line of sight Affected by obstacles on ground (low buildings, trees)Absorbed by earth above UHF frequencies

Tropospheric waveEffective in VHF bandInterferes with UHF cellular systems

Ionospheric (sky) waveCauses DXing (long distance transmission up to thousands of km)Effective below VHF band

ionotropic wave

line of sight wave

ground wave

tropospheric wave



Multipath FadingObstacles reflect radio waves

Receiver gets signals from multiple pathsTime-to-arrive depends on path taken by signalReceiver gets signals transmitted at different times

ExampleThree signals sent at times t1 < t2 < t3

Antenna receives all three signals at time tSignal 1 ⎯ sent first and followed longest path d1

Signal 2 ⎯ sent second and followed second longest path d2 < d1

Signal 3 ⎯ sent last and followed shortest path d3 < d2

Sum of waves can cancel out signals

d3

d1

d2



Cancellation of Signals in Wave MotionWave amplitudes

combine by adding

pulse

pulse

String receives two pulses at t = 0

String at t = 1

String at t = 2

String at t = 3

String at t = 4



Wave Interference

( ) ( )

( )0 0

0 0

, ,

cos 2 cos 2

cos 2 c1

where and

R t R R t tR R t t

R R Rft f t tR R R

R ftRR R

R

π πλ λ

πλ

= + + Δ + Δ

Δ << Δ <<

⎡ ⎤ ⎡ ⎤+ Δ⎛ ⎞ ⎛ ⎞= − + − + Δ⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎢ ⎥+ Δ⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎣ ⎦⎡ ⎤⎛ ⎞= − +⎜ ⎟⎢ ⎥ Δ⎛ ⎞⎝ ⎠⎣ ⎦ +⎜ ⎟

⎝ ⎠

E E E

E EE

E EE

Two waves arrive at antenna by slightly different paths

0

os 2

1

cos 2 cos 2 2

R R ft f t

RR

R R Rft ft f tR

πλ λ

π π πλ λ λ

⎡ ⎤Δ⎛ ⎞+ − − Δ⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Δ<<

⎧ ⎫⎡ ⎤ ⎡ ⎤Δ⎛ ⎞ ⎛ ⎞ ⎛ ⎞≈ − + − + − Δ⎨ ⎬⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎢ ⎥⎝ ⎠ ⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎣ ⎦⎩ ⎭

EE

Ignoring



Wave Interference

( ) ( ) ( ) ( )

0

1 12 2

0

cos 2 cos 2 2

cos cos 2cos cos

2co c2 ss o

R R Rft ft f tR

A B A B A B

R ftR

R c

R f t

t

π π πλ λ λ

πλ

πλ

⎧ ⎫⎡ ⎤ ⎡ ⎤Δ⎛ ⎞ ⎛ ⎞ ⎛ ⎞≈ − + − + − Δ⎨ ⎬⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎢ ⎥ ⎢ ⎥⎝ ⎠ ⎝ ⎠ ⎝ ⎠⎣ ⎦ ⎣ ⎦⎩ ⎭

+ = + × −

⎧ ⎫⎡ ⎤⎛ ⎡⎞= − ×⎨ ⎬⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦⎩

⎤Δ⎛ ⎞− Δ⎭

Δ = Δ ⇒

⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

EE

EE

Using identity

Transparent medium

( ) 0

1c

1 cos 02

os

co2

s

R c tf t t f c f

R f

R

t

Rf t f t

λλ λ λ

π

λ

λ

π

πλ

⎡ ⎤Δ⎛ ⎞− Δ⎜ ⎟⎢ ⎥

Δ Δ⎛ ⎞− Δ = Δ − = − =⎜ ⎟⎝ ⎠

=

Δ ⎛ ⎞− Δ

⎝ ⎠⎣ ⎦

⎡ ⎤Δ⎛ ⎞− Δ⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦= ⇒ = =⎜ ⎟

⎝ ⎠

Total cancellation



Carrier SignalTransmitter accelerates charge on antenna

Position of charge described by

Transmitter

Antenna

y

-y

t

( ) ( )0

0

cos 2 cos 2

1

2

fA At -

y t πi i

fT

Tt

tT

π t

A

φ

φπ

⎡ ⎤⎛ ⎞ ⎡ ⎤= = +⎢ ⎜ ⎟⎥ ⎣ ⎦⎝ ⎠⎣ ⎦

=

= −

Amplitude (maximum height)

Frequency

Phase



ModulationCarrier signal

Simple cosine waveFrequency f assigned to transmitterAmplitude A determines transmitted power

Carrier signal carries no informationFrequency and amplitude are set by lawReceiver already knows what to expect

Modulation

( ) ( )cos 2y t A πft φ= +

( )

( )

, ,

Data signal varies continuously

Data signal takes discrete levels

Vary carrier parameters according to data signalAnalog data

Digital data

d t

d t

A f φ



Amplitude ModulationSource information signal

Signal from source device Voice, video, digital data

Carrier signal amplitude becomes function of source

-2

-1

0

1

2

0 0.5 1.0 1.5 2.0

( ) ( )( ) ( )cos 2AM d ty t A a m πft φ= + × +



Pulse Amplitude Modulation (PAM)AM technique for digital dataSymbol

Amplitude takes one of N = 2n possible levels00…00 , 00…01 , 00…10 , 00…11 , … , 11…11

Each level called a transmission symbol Symbol transmits n bits in parallel

Example4-level PAM4 = 22 possible levels (symbols)

00 , 01 , 10 , 11

Each symbol transmits 2 bits

0001

1011

level 0 level 1 level 2 level 3

transmission amplitude



Frequency Modulation Source information signal

Signal from source device Voice, video, digital data

Carrier signal frequency becomes function of source

-0.5

0.5

0 0.1 0.2 0.3

( ) ( )( )( )cos 2FMy t A π d ta m ft φ= + × +



Frequency Shift Keying (FSK)FM system for digital data

Used in 1960s and 1970s for 300 bps telephone modemsVery inefficient

Binary 1

Transmit at frequency f0 + ΔfBinary 0

Transmit at frequency f0 – Δf

1 0 0 1 1 0 1



Phase Modulation Source information signal

Signal from source device Usually digital data

Carrier signal phase becomes function of source

Phase Shift Keying (PSK)N = 2n different symbols (phases) transmit n bits per cycleExample — 2-bit PSK

φ (t) = 0 ⇒ 00 φ (t) = π/2 ⇒ 01 φ (t) = π ⇒ 10 φ (t) = 3π/2 ⇒ 11

-1.0

-0.5

0

0.5

1.0

0 1 2 3 4

( ) ( )( )( )cos 2PMy t A πft a d tm φ= + + ×

( ) ( )sin 22PMy t A πft d tπ⎛ ⎞= + ×⎜ ⎟

⎝ ⎠



Quadrature Amplitude Modulation (QAM)Source information signal

Signal from source device Usually digital data

Carrier signal amplitude and phase becomes function of sourceN = 2n amplitude-phase combinations transmit n bits per cycleExample

N = 1024 = 210 transmits 10 bits per cycleUsed for standard home modems at 33.6 kbps and 56 kbps

A φ

( ) ( ) ( )( ) ( ) ( ),

cos 2

determined by data QAMy t fA tt t

A t t d t

φ

φ

π⎡ ⎤= +⎣ ⎦



Advantages and Disadvantages

BestBetterWorstNoise Immunity

NarrowestWidestNarrowBandwidth

More ComplexComplexSimplestImplementation

PM/QAMFMAM



Spread Spectrum ModulationDirect Sequence Spread Spectrum (DSSS)

User generates data at m bits per secondSends n-chip sequence for every user bit

1-sequence for data 10-sequence for data 0

Operates at n × m chips per second (chip rate)Receiver easily distinguishes 1-sequence from 0-sequence Works well in noisy environment

Frequency Hopping Spread Spectrum (FHSS)Transmitter changes carrier frequency every N bitsH carrier frequencies of bandwidth B

Total required frequency band = H × B

Works well with noise in one frequency bandDifficult to follow ⇒ improves security

data 1 chip sequence

data 0 chip sequence

chip — transmitted pulse



Broadcast ChannelsRadio Frequency (RF) carrier wave

Allocate frequency f0 to transmitterModulate carrier wave with data/voice signal

Data signal contains a band of frequencies

Bandwidth Δf depends on Bandwidth of data signalModulation scheme

Broadcast channel

Dedicated use of all frequencies from f0 – Δf / 2 to f0 + Δf / 2

f

fΔ

fΔ

f

0f



Bandwidth in AM

( )

( ) ( )( )( ) ( )

( ) ( )( )

( )

0

0 0

0 0 0

2

2

1 ( )2

( ) 0, 2 2

1 cos

cos cos

1cos exp exp2

1 ( )2

for

i t

AM

Bi t

B

d t F e d

F f B

y t A m d t t

A t Am d t t

t i t i t

d t F e d

ω

πω

π

ω ωπ

ω ω π π

ω

ω φ ω

ω ω ω

ω ωπ

∞

−∞

−

=

= = >

= + ×

= + + ×

= + −

=

∫

∫

Data signal

Bandwidth

Modulation

Replace

( )F ω

02 fω π=

2 Bπ2 Bπ−



Bandwidth in AM

( ) ( )

( ) ( )

0 0

0 0

0 02

10 2

2

2 2

02 2

2 2

02 2

1cos ( )2

cos ( ) ( )4

cos ( ) ( )4

Bi t

AMB

B Bi t i ti t i t

B B

B Bi t i t

B B

i t i ty t A t Am F e d e e

AmA t F e e d F e e d

AmA t F e d F e d

πω

π

π πω ωω ω

π π

π πω ω ω ω

π π

ω ωω ω ωπ

ω ω ω ω ωπ

ω ω ω ω ωπ

−

−

− −

+ −

− −

−⎡ ⎤ ⎡ ⎤= + × +⎢ ⎥ ⎣ ⎦⎣ ⎦⎡ ⎤

= + +⎢ ⎥⎣ ⎦⎡ ⎤

= + +⎢ ⎥⎣ ⎦

∫

∫ ∫

∫ ∫

0 0

0 0

0 0

2 2' "

0 0 02 2

' "

cos ( ' ) ' ( " ) "4

B B

i t i t

B B

AmA t F e d F e dω π ω π

ω ω

ω π ω π

ω ω ω ω ω ω

ω ω ω ω ω ω ωπ

+ − +

− − −

= + = −

⎡ ⎤= + − + +⎢ ⎥

⎢ ⎥⎣ ⎦∫ ∫

Change variables

0

2 fω π=

0 2 Bω π+0 2 Bω π− 0ω0 2 Bω π− +0 2 Bω π− − 0ω−



ChannelizationData/voice channel

Require bandwidth Δf to transmit one data streamFrequency Division Multiplexing (FDM)

Total allocated bandwidth BDivide total bandwidth into channels of bandwidth ΔfAllows N = B / Δf independent channels transmitting at same time

Channel carrier frequencies

Channels i = 1, ... , NChannel i has bandwidth Δf around carrier frequency fi



Channelization

...f1 f2 f3 fN

1f f− Δ 1f f+ Δ

2f f− Δ 2f f+ Δ

3f f− Δ 3f f+ Δ

2 1B N f b b= ×Δ = −

( )11 2Channel carrier frequency if b i f= + − Δ

fΔfΔfΔfΔfΔ

2b1b



Commercial FM RadioTotal Bandwidth: B = 20 MHz

Low end of band: b1 = 87.5 MHzHigh end of band: b2 = 107.5 MHz

Δf = 0.2 MHz / channel

N = B / Δf = 20 MHz / (0.2 MHz/channel) = 100 channelsCarrier frequencies: 87.6, 87.8, 88.0, … , 107.4 MHz

FDM permits up to 100 FM radio stations to broadcastIndependently and simultaneouslyOn same mediumUsing same techniqueListeners regard channels as completely separate



Sampling (Analog to Digital)

Sequence of sample valuesdata signal

t

sampling signal

tsampled signal ( ) ( )d t S t×

( )d t

( )S t

2

Filter data signal to bandwidth

Sample data signal at sample rate

Can reproduce data signal from samples without distortion

sample max

max

f f

f≥

Nyquist Theorem



Convert Samples to Digital FormRounding-off

Allocate n-bit integer describing 2n possible levels

Round-off each sample to fit into n-bit integer

Distorts data — equivalent to added noise

Bigger n ⇒ more levels ⇒ better resolution ⇒ less noise

ExampleSampled values — 158.276, 158.879, 159.724, 159.821, 159.312, 158.791Digitized values — 158, 159, 160, 160, 159, 159

158159

160 160159 159

157

158

159

160

161t



Sampling for Standard TelephonyTelephone line

Filtered to carry audio frequencies from 300 Hz to 3300 HzSample voice channel

fsample = 8000 samples / second > 2 × 3300 HzRound-off samples

Scale is 28 = 256 levels (0 to 255)Each sample encoded as 8-bit byte

DS-0 voice channel 8000 samples/second × 8 bits/sample = 64 kbps

10011110 10011111 10100000 10100000 10011111 10011111 158 159 160 160 159 159

158159

160 160159 159

157

158

159

160

161



Sampling for Standard CD AudioCD audio

Filter audio frequencies from 20 Hz to 22,000 HzSample voice channel

fsample = 44,100 samples / second > 2 × 22,000 HzRound-off samples

Scale is 216 = 65,536 levels (0 to 65,535)Each sample encoded as 16-bit word

CD audio channel44,100 samples/second × 16 bits/sample = 705,600 bps

MP3 encoding → 5 times compression rate705,600 bps / 5 ~ 140 kbps ~ 17,508 bytes / sec ~ 1 MB / minute

158159

160 160159 159

157

158

159

160

161



Modeling InformationInformation

Set of possible answers (outcomes) to questions (tests)Finite set (yes/no, day of week, 232 pixel colors, etc)Infinite set ("you won’t believe what happened today!")

Communication — transmission of symbol to receiverBefore transmission receiver has limited knowledge of symbol

Permitted range of symbols (universe of outcomes)Statistical distribution of symbols within range

After transmission receiver has better knowledge of outcomeReceiver tests message to decides on most likely symbol (outcome)Decision accuracy limited by noise

NoiseInterference, rounding-off errors, resolution of detector, etc.Communication does not determine unique outcome



Modeling NoiseReceiver detects

Signal from transmitterNoise sources

Other transmittersResolution errorsElectrical cables and devicesLightening

Input Electrical current or voltageSum of Signal and Noise

Transmitter Receiver

Signal

Noise

Input = Isignal + Inoise



Quantifying InformationSet of possible outcomes

K = 2k different symbolsLabel symbols

k-bit binary integersCommunication content

One symbol out of K possible symbolsOne label: k = log2 K bits

Information RatesSystem transmits one symbol in τ seconds

b

W

= (W symbols / second) × (k bits / symbol)= W × k bits / second= W log2 K bps

Bit rate

= (1/τ) symbols / secondBaud rate



Example Symbol SetsSimple binary

2 = 21 possible levels (symbols) with k = 1 0 , 11 bit per symbol

4-level PAM4 = 22 possible levels (symbols)

00 , 01 , 10 , 11

Each symbol transmits 2 bitsQuadrature Amplitude Modulation

2k symbols — combinations of amplitude and phaseV.34 modems

Frequency is fixed at f = 3300 HzK = 210 symbols transmits

k =10 bits per symbols Bit Rate = 10 bits/symbol × 3300 symbols/second = 33,000 bps

0001

1011

level 0 level 1 level 2 level 3

transmission amplitude



Signal and Noise Inputs in 2-Level Transmission

1 1 0 0 1 0 1 0 1 0 0 0

time0 2 3 4 5 6 7 8 9 10 11 12τ τ τ τ τ τ τ τ τ τ τ τ

AT

time

0 time

AA/2

Binary 2 level transmission

22 2 20noise noise noise noiseI I I I σ= − = =

2 21 12 2T signal signalA A I A I A< = =

Gaussian additive noise

DecisionSignal < A / 2 ⇒ binary 0

Signal > A / 2 ⇒ binary 1

Received signal = faded transmission + added noise

Signal to Noise Ratio

2 2

22 2signal

noise

I ASNRI σ

= =



Shannon’s TheoremTransmission Capacity

Bit Rate = W log2 K bps

W = system bandwidth (symbols / second)Maximum rate of symbol-to-symbol transitions in systemDetermined by physical characteristics of system

K = system resolution (symbols)Maximum number of symbols that can be resolved (distinguished)Determined by physical characteristics of system and noisek = log2 K is number of bits / symbol

Shannon Theorem[ ]21 log 1Maximum CapacityK SNR W SNR= + ⇒ = × +

Carrier to interference ratio (CIR or C/I)SNR in frequency division multiplex (FDM) systemsIncludes external noise and interference from multiplexed channels



Examples of Shannon’s TheoremAverage signal power = average noise power

V.34 modemCapacity (Bit Rate) = 33,000 bps Symbol rate W = 3,300 Hz

[ ] [ ]2 2log 1 log 1 1Capacity W SNR W W= × + = × + =

[ ][ ]

2

102

log 1

log 1 10 2 1

33,000 3,300

Required 1023

SNR

SNR SNR

= × +

+ = ⇒ = − =



Probability of Error in 2 Level Transmission( ) ( ) ( ) ( ) ( )

( ) ( )

( ) ( )

2 22 2

22 2

2 22

| 0 0 |1 11 1| 0 |12 2

1 | 0 |1212 2 2

1 1 12 2 2

1 11 erf 12 22 2

error error error

error error

error error

noise noise

AI I

A

P P P P P

P P

P P

A AP I P I

e dI e dI

A

σ σ

πσ πσ

σ

−∞ − −

−∞

= ⋅ + ⋅

= ⋅ + ⋅

⎡ ⎤= +⎣ ⎦

⎡ ⎤⎛ ⎞ ⎛ ⎞= > + < −⎜ ⎟ ⎜ ⎟⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦⎡ ⎤⎢ ⎥= +⎢ ⎥⎣ ⎦

⎡ ⎤⎛ ⎞= − = −⎢ ⎥⎜ ⎟

⎝ ⎠⎣ ⎦

∫ ∫

( ) 2

2 2

2 2

0

1 1 12erf 1 erf2 2 2

1 1 21 erf erf2 2

,

signal

noise

xy

A I

I

SNR x e dy

σ

π−

⎡ ⎤⎛ ⎞ ⎡ ⎤⎛ ⎞⎢ ⎥⎜ ⎟ ⎢ ⎥⎜ ⎟= −⎢ ⎥⎜ ⎟ ⎢ ⎥⎜ ⎟⎜ ⎟⎢ ⎥ ⎢ ⎥⎝ ⎠⎣ ⎦⎝ ⎠⎣ ⎦

⎡ ⎤⎛ ⎞= − =⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦∫

( )( )

( )

4

113

1 0.24

25 2.1 10

1023 1.2 10

error

error

error

SNR P

SNR P

SNR P

−

−

= → =

= → = ×

= → = ×



Probability of Error in DSSSDirect Sequence Spread Spectrum (DSSS)

Encode 1 data bit as an m-bit chip sequence 1 data bit error requires m/2 bit errors in a chip

bit = 8 Chips

Bit 1

Bit 0



DSSS Lowers Probability of Error

( ) ( )( ) ( )

( ) ( )

( )

2

2

/ 2

/ 2 / 2 1

1

/ 2

bit error at least chip errors

chip errors chip errors

chip error chip error

chip error

m k m k

mk

m

P P m

P m P m

mP P

k

mP

m

−

=

=

= + + +

⎛ ⎞⎡ ⎤ ⎡ ⎤= −⎜ ⎟ ⎣ ⎦ ⎣ ⎦

⎝ ⎠

⎛ ⎞= +⎜ ⎟⎝ ⎠

∑

K

L

( )

( ) ( ) ( )

2

4 42 2 6

810

810 1 10 ... 10

4

bits per chip

chip error

chip error

mP

P

−

− − −

=

=

⎛ ⎞= − + ≈⎜ ⎟⎝ ⎠

Example



Inter-Symbol Interference

Transmitted signal undergoes multipath delayReceived signal is sum of delayed contributions

Inter-Symbol Interference (ISI)Interference caused by overlap between sequential bitsCauses bit errors

Jitter Delay varies from bit to bitDifficult to determine proper sampling clock

T1

T3 > T2 > T1

T2 > T10 1 0



Orthogonal Frequency Division Multiplexing1-bit Phase Shift Keying (PSK) on carrier frequency f0

Bandwidth = Δf

Orthogonal Frequency Division Multiplexing (OFDM)Buffer n-bit data frameTransmit n bits on n parallel PSK channelsn carrier frequencies

Bandwidth/channel = Δf / n

PSK1 1 0 1

1 1 0 1

PSK

1

1

0

1

n = 4 OFDM

1 1 0 1

Δf

ff1 f2 f3 f4

fΔ

f

0f



Advantage of OFDMStandard 1-bit PSK

Transmit pulse of width T/2 every T secondsMultipath interference creates pulses delayed by time ΔTInter-Symbol Interference (ISI)

At high data rates ΔT ~ T/2 Delayed pulses interfere with

new pulses

OFDMTransmit pulse of width nT/2 every nT secondsPulses are farther apart since nT >> ΔTLess ISILess power required for good Signal/Noise ratioOrthogonal frequencies

fk ≠ k × f0Simpler demodulation

PSK

1 1 0 1

T

T+ΔT

PSK1

n = 4

T

T T+ Δ



Datagrams and Virtual Circuits Datagram Service

Network of store and forward routers Every packet

Has source and destination address in headerRouted individually through network

Packets of one message may follow separate routes

Switched Virtual Circuit (SVC)Network of store and forward switchesVirtual circuit

Set up and assigned VC ID before message transmissionClosed down after message transmission

Packet routing by VD ID in headerOnly set-up / close messages have source and destination addressesEvery packet follows same VC route



Virtual Circuits Circuit Mode (Circuit Switching)

Similar to standard telephone callSet up point-to-point call over SVCSVC is dedicated to one call until circuit is closedPackets flow from one source to one destination by VC ID

Packet Mode (Packet Switching)Similar to conference call with holdSet up several calls (multiple SVCs) on one physical systemSVC shared by many callsPackets arrive at destination by VC ID number



Telephone — World’s Largest Network

Frame Relay,ATM, X.25



Circuit Mode Packet Mode

Serial Dataon Analog Modem

Analog Local Loop300 - 3300 Hz

Voice on AnalogTelephone

Voice on DigitalTelephone

Digital Local Loop (ISDN)64 kbps (DS-0)

Serial Dataon ISDN

PSTN provides dedicated point-to-pointSVC connections and charges for timeand distance of connection

PSTN provides packet forwarding overone-to-many SVC connections and chargesfor packet volume

ESSHierarchy

PSTN

PDHSDH



POTS vs ISDNPOTS — Plain Old Telephone Service

Analog phone transmits 300 Hz to 3300 Hz on phone line Phone line (local loop) connects phone to Telco local officeAnalog converted to digital (DS-0) in telephone local officeDS-0 bit-stream routed to destination by digital switch (ESS/ATM)

ISDN — Integrated System Digital NetworkAnalog to digital conversion in telephoneTwo (or more) phones + control information as bits to local officeDS-0 bit-stream routed to destination by digital switch (ESS/ATM)Elaborate protocol and control structureControl information allows advanced services

Mix voice, video, data, etc.Call waiting, call forwarding, conference calling, caller ID, etc.



ISDN Protocol StructureD-channel (control plane) carries control information at 16 kbps

Handles call set-up and configurationQ.921 (LAP-D) — L2 protocol provides LLC servicesQ.931 — L3 protocol for call control and end-to-end signalingRequires specific protocols

2 or 30 B-channels (bearer) carry voice/data/video at 64 kbpsAny protocol structure (or none) permitted

Control plane

User plane



Call Set-up in ISDN

calling party network called partysetup

setup ACKinformation

call proceeding setupcall proceeding

alertingalerting

connectconnect

connect ACKconnect ACK

user datauser data

D-Channel

B-Channel



ESS vs ATMESS — Electronic Switching System (Signaling System 7)

Only handles DS-0 traffic (64 kbps bit streams)Circuit Mode SVC

Switch maps physical input i to output j at call set-up timeEvery bit from source i forwarded to destination j on dedicated pathSwitch does not read bit stream after call set-up

SS7 switches organized in tree ATM — Asynchronous Transfer Mode

Bandwidth and Quality of Service (QoS) parametersHandles traffic at requested bit rate (by pre-arranged contract)

Circuit Mode or Packet Mode SVC Checks each packet for SVC ID numberCan emulate ESS single source to single destination mappingCan perform packet mode forwarding by SVC ID

ATM switches organized in a general mesh



Quality of Service (QoS) ParametersSpeed

Delay Time andDelay Variation

ErrorControl Transmission

SpeedAccessDelay

CongestionControl

PriorityControl

ConnectionType

Variations in Delay Time parametersJitter

End to end transmission time for one bitHigher speed ⇒ less delayCongestion, priority ⇒ internal network delayError correction retransmission ⇒ more delayAccess protocols, security, conversion ⇒ more delayConnection ⇒ connectionless adds routing delay

Delay Time

Errors repaired or ignored by host protocolsShannon: Higher speed ⇒ higher bit error rate (BER)Congestion control policy (data discard) ⇒ higher BER

Error Control

Bit transmission rate at physical layerSpeed



QoS RequirementsTiming characteristics

SynchronousData transfer determined by external clock signalExample — DS-0 line is controlled by a 64 kHz clock

Asynchronous Data transfer has no relationship to any timing clockPackets arrive at internet router when software sends them

IsochronousData transfer at regular periodic clock intervalsDigital phone generates 1-byte voice sample every 125 μs

Requirements

GoodHighGoodHighReal Time Control

OKHighGoodHighMultimedia

Maximum—GoodHighNFS and Database

Maximum—OKOKFile Transfer

Error Controlσ2(Delay)<Delay>Speed



T1 Time Division Multiplexing (TDM)

24 inputsat

8000bytes/sec

Multiplexor (MUX) accepts and buffers1 byte from each line 8000 times per secondCombines bytes into frame

byte from line 0

byte from line 1

byte from line 2

byte from line 23

0 1 2 ... 23

1=125 sec /byte

8000 bytes / secondμ

125 sec / frame=5.21 sec /byte

24 bytes / frameμ μ

T1 transmits 24 samplesin the time required to

store 1 sample

125 secμ

125 secμ

bit stream at 24 8000 bytes/sec plus 1 frame bit×

(24 8 + 1) bits/frame 8000 frames/sec = 1.544 Mbps× ×



E1 Time Division Multiplexing (TDM)E1 frame contains 32 bytes

1 byte from each of 30 DS-0 digital voice streams2 bytes for controlE1 transmits 32 bytes in the time required to store a single byte

E1 bit rate = 32 × 64 kbps = 2.048 Mbps

byte from line 1

byte from line 2

byte from line 3

125 μs

byte from line 32

125 μs

1 2 3 ... 3218000

125 bytes / second

s /byte= μ

125 μsec/frame=3.9 μsec/byte

32 bytes/frame



PDH and SDHDigital Multiplexing

Combine many DS-0 voice streams into high speed data streamBuild data frame containing bytes from each DS-0 stream

Multiplex HierarchiesUS PDH rates

T2 ⎯ 4 T1 channels at 6.312 MbpsT3 ⎯ 6 T2 channels at 44.736 MbpsT4 ⎯ 7 T3 channels at 274.176 Mbps

European PDH ratesE2 ⎯ 4 E1 channels at 8.848 MbpsE3 ⎯ 4 E2 channels at 34.304 MbpsE4 ⎯ 4 E3 channels at 139.264 MbpsES ⎯ 4 E4 channels at 565.148 Mbps

SDH / SONETUp to 2.4 Gbps on optical fibers



0G (1970) Mobile Phone System (MPS) One central transceiver (transmitter/receiver)

Mobile telephones communicate via central transceiverTransmit at high power for maximum distanceSystem covers 65 to 80 km

Modulation is standard analog FM Supports 12 simultaneous mobile phone calls If 12 channels busy, other calls are blocked

Requires 24 carrier frequencies2 frequencies per phone:

Dedicated transmit frequency Dedicated receive frequency



Cellular ConceptDivide coverage area into cells In each cell

Central cell transceiver serves all clients in cellMobile Stations communicate via cell transceiver

Transmit at low power (just enough to cover a cell)Use same frequencies in many cellsNo interference between cells

Handoff Telephone can move from cell to cell during a callRequires cell-to-cell infrastructure and coordination



Cell ImplementationDivide region into clustersDivide cluster into seven cells

A, B, ... , GIn each cell

One central transceiverMany mobile stations (telephones)A frequency group (set of dedicated frequencies)

Each telephone has a private link with central transceiverDedicated transmit frequencyDedicated receive frequency

7 cell reuseFrequency group A assigned to every A cellFrequency group B to every B cell, …At least two cells separate every pair of A cells, etc.

B

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

D

E

F

G

A



Transmission Directions

DownlinkBase Station (BS) transmit frequencyMobile Station receive frequencyForward Channel

UplinkMobile Station (MS) transmit frequencyBase Station receive frequencyReverse Channel

UplinkReverse Channel

DownlinkForward Channel

MS

BS



HandoffUser moves between cellsHard Handoff

Old cell transfers control to new cell Break-Before-Make sequence

Transceiver in old cell stops transmitting to userTransceiver in new cell begins transmitting to user

Transceiver in new cell assigns user a transmit frequency from its frequency group

Soft HandoffCentral transceiver coordinates with nearest cellsDetermines which transmitter is receiving strongest signal from userMake-Before-Break sequence

Transceiver in old cell transmitting to userTransceiver in new cell begins transmitting to user Transceiver in old cell stops transmitting to user



Cell Splitting EconomicsEconomics of cellular telephony:

Number of Clients = Channels/cell × Number of CellsInvestment ~ Cost/cell-site × Number of Cells

Start smallSmall Number of Clients ⇒ small Number of CellsSmall Number of Cells ⇒ small initial investmentSmall Number of Cells ⇒ large cells (to cover clients)Large cells ⇒ transmit at high power (to cover cells)

To growRedefine 1 cell as clusterSplit new cluster into 7 new cells ⇒ more clientsInstall transceivers in new cells ⇒ more investmentLower power of new transceivers (cover smaller cells)



Reuse Patterns

B

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

A

C

C

B

A

B

A

B

A

C

B

7 cell reuse

3 cell reuse

4 cell reuse

B

D

A

C

B

C

D

D

C

A

B

A

A



Reuse Patterns

R

D

i

j

R2

R

32

R

60o

( )

( ) ( )

2

2 2

2 2

2 2

32 32

3 ,

3 2 , ,

3 2 cos 60

3

RD R

D R i j

R i j i j i j

R i j ij

R i j ij

= × =

= ×

= × + + ⋅

= × + +

= × + +

Distance between adjacent cell centers

Distance between two cell centers

D/RReuse

3

4

7

2 23 1 1 1 1 3× + + × =

3 2 3.46× =2 23 2 1 2 1 4.58× + + × =



Mobile Network Switching HierarchyMobile Service Provider

Service Areas or Registration AreasClusters

Cells

Mobile ServiceProvider

Mobile ServiceProvider

ServiceArea

ServiceArea

ServiceArea

ServiceArea

BC

DE

F

GA

BC

DE

F

GA

BC

DE

F

GA

B

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

D

E

F

G

AB

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

D

E

F

G

A

B

C

D

E

F

G

A

Cluster

Cell



Elements of GSM Mobile Network HierarchyMobile Station (MS)

The telephone/terminal Base Transceiver Site (BTS)

Fixed radio transmitter/receiverManages channels for with MSs in one cell

Base Station Controller (BSC)Coordinates cluster of cells

Base Station Subsystem (BSS)One BCS and all BTSs it controls

Mobile Switching Center (MSC)Telephone Central Office for one Service AreaHandles local calls and Routes calls out of Service Area

Public Land Mobile Network (PLMN)The wired portion of one Service Area (BTSs, BCSs, and MCS)



The Cellular and Wired Telephone Network

Mobile Station(MS)

Base System(BS)

Public SwitchedTelephoneNetwork(PSTN)

Base TransceiverSite (BTS)

BTSBase

StationController

(BSC)

Mobile SwitchingCenter (MSC)

PLMN

BSS

Base System(BS)

Mobile Station(MS)

Base Station Subsystem

Public Land Mobile Network

HLRVLR



Mobility Service AreasHome Service Area

Service Area in which MS subscribes to cellular serviceHome Subscriber

MS operating in its Home Service AreaRoamer

MS operating outside its Home Service AreaHandoff

Call control transfer when MS moves between cells in Service AreaRoaming

Call control transfer when MS moves between Service Areas



Problems of MobilityMS must locate service provider access point

User must authenticate to service providerService provider must locate the MS

Provider must verify user's access rightsHome Location Register (HLR)

Located in MSC of Home Service AreaMaintains user's account informationMaintains location information for active MSs

Visitor Location Register (VLR)Located in MSC for each Service AreaCache of HLR data on active roamers



Registration ProcessMS enters Service Area

Establishes low bit-rate control channel with service providerMS requests service

BS allocates a frequency pair MS reports to Mobile Switching Center (MSC)

Location, Status, and IdentityDedicated hardware ID code in phoneSubscriber Identity Module (SIM) card identifies customer in GSMMobile Station generates access code to network

Transmits code by public key encryption (PKE) algorithmMobile Switching Center (MSC)

Authenticates customer identity with HLRFor roaming subscriber, creates VLR entry Updates Home Location Register (HLR) and billing database



Mobility Elements in the Cellular Network

Base System(BS)

BTSBSC MSC

PLMN

BSS

HomeSubscribers

BTSBSC MSC

PLMN

BSS

Base System(BS)

Service Area

Service Area

Roamer

HLRVLR

HLRHome

Subscribers

Home SubscriberRegistration

Roaming SubscriberRegistration

Query to HomeMSC HLR

for VLR Entry

Voice over IP (VoIP) תיטוחלא תרושקת · 1 introduction Wireless Communication Spring...

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