lec 1 intro wireless communication

8/8/2019 Lec 1 Intro Wireless Communication

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Wireless Communications

By

Dr. Mustafa Shakir


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Course Material

Text: Wireless Communications: Principles andPractice by T. Rappaport

References

Wireless Communications and Networks by W.Stallings

Wireless Communications by Andrea Goldsmith

Wireless Communications by Roy Blake.

Wireless & Mobile Networks Architecture by Yi Bing

and Imrich Chlamtac

Other Books & Internet.


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What is wireless

communication?

Any f ormof communication that does not require the transmitter

and receiver tobe in physical contact

Electr omagnetic wave propagated through free-space

Radar, RF, Microwave, Optical (infrared, Laser).


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Early History of Wireless

Communicati

on

. Many people in history used light for communication.

1. 150 BC smoke signals ( Greece)

2. 1794, optical telegraph,

Disadvantages of these forms of communication Limited alphabets

Noisy

Br oadcast (no privacy or security)

Limited distance (or require relay which is unreliable)

Require line-of-sight between transmitter and receiver


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Lateron Electromagnetic waves

becam

e im

po

rtant1. 1831 Faraday demonstrates

electromagnetic induction.

2. J. Maxwell (1831- 79): Theory ofelectromagnetic fields, wave equations

(1864)

3. H. Hertz (1857-94): demonstrated thewave characterof electrical transmission

through space.


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Evolution of Voice Oriented

Wireless Networks The origin of wireless communication dates back to

the era of Marconi ---- 1897, when he demonstratedthe radios communication ability to provide continuous

contact with the ships sailing the English channel. Mobile telephone service was first offered by AT&T in

1946. This service was mobile, but not cellular. Thebase station had a coverage of about 100 km.

Early systems, based on FM, required 120 KHz ofspectrum for an information bandwidth of 3 kHz. Largeequipment (mounted in cars). Low capacity: 50 usersormore cause overloading, 65% blocking probability.Multiple Access method used was FDMA.


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Evolution of Voice Oriented

Wireless Networks Next step was the introduction of trunking - relaxing theconstraint of using a channel for each user.

Cellular concept emerges in early 1970s. Cellular is not a newtechnology but rather a new organization.

Replication of the wide-area network concept. Cellularconcept leads to frequency-reuse concept. By late 60's therewere 70,000 users throughout US.

Invention of the microprocessor facilitated the implementationof the complex control algorithms required mainly for switching

between base stations.


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Todays Wireless Communication

System

sFollowing are some famous wireless

communication systems.

Cellular Teleph

one Syste

ms/P

CS

Cordless Telephone Systems

Paging Systems

WLAN/PAN/Ad-Hoc NetworkingBlue Tooth


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Personal Communication

Systems

PCS

Cell l r obile

Com ti

Cor less Pagi g


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CELLULAR CONCEPTS


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Single Cell Network


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History ofCellular Networks

Why cellular networks?

greater capacity

efficient use of frequency

To increase coverage of non cellular system

replaces a large transmitter with smallerones

smaller transmitting power

each cell is assigned a portion of the total frequency


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Replacement of huge single cell by a

number of small cells


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Types of Mobile Communication

CellsThe size of a cell is dictated by capacity demand

Macro-cell

Micr o-cell

Pico-cell

Mega-cell


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Capacity Computations

Assume there are N cells, each allocated k

different frequency channels. These N cells

are said to form a cluster. Total number of

channels per cluster is given by S = k N

Total capacity associated with Mclusters:

C=

M k N=

MS


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Means of Increasing System Capacity

There are several approaches for increasing cellular

system capacity including:

Cell clustering

Sectoring of cells

Cell splitting

Frequency reuse

Reduction of adjacent cell interference and co-channel

interference


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Cell Clusters

ServiceService areasareas areare normallynormally divideddivided intointo clustersclusters ofof

cellscells toto facilitatefacilitate systemsystem designdesign andand increasedincreased

capacitycapacity

DefinitionDefinition::

AA gr oupgroup ofof cellscells inin whichwhich eacheach cellcell isis assignedassigned aa

differentdifferent frequencyfrequency


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Cell Clusters

A clusterof 7 cells

1

2

5

6

7

4

3


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Cell Clusters (1)

A network of cell clusters in a densely populated Town

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Frequency Plan

Intelligent allocation of frequencies used

Each base station is allocated a group of channels

Adjacent cell base stations are assigned

completely different channel groups

Adjacent channels are not assigned to same

or even adjacent cells.


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Frequency Reuse Factor

Definition:

When each cell in a clusterof N cells uses one

of N frequencies, the frequency reuse factor

is 1/N


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Excitation of Cells

centre-excited, base station is at the centre of the cell

or

edge-excited, base station at 3 of the 6 cell vertices


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Finding the Nearest Co-Channel

After selecting smallest possible value of N we should see

that N should follow the f ollowing eg. N= i2+j2+ij

(1) Move i cells along any chain of hexagons

(2) Turn 600 counter-clockwise and move j cells, to reach the

next cell using same frequency sets


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Freq Reuse ( N=7 , i=2 j=1)

A

B

EDF

CG

A

B

E

DF

CGA

B

E

DF

CGi

j


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MULTIPLE ACCESS TECHNIQUES


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Multiple Access Techniques

FDMA

TDMA

CDMA


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FDMA-Frequency Division Multiple

Access

Time

Fr

e

q

u

en

c

y

-Requires no synchronization or central timing,

channels independent.


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TDMA-Time Division Multiple

Access: Fixed Slots

Time

F

r

e

qu

e

n

c

y


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CDMA-Code Division Multiple

Access: Frequency Hopping

Time

F

r

e

qu

e

n

c

y


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Terminology

Base Station Fixed station used f or radio communication with

mobiles. Located at the centeror edge of coverageregion. Consists of radio channels, transmit/receiveantennas.

Control Channels Radio channels used for transmission of call setup,

request, initiation and other control purposes

Full Duplex

Communication system that allows simultaneoustwo-way communication, transmission receptionusually on two different frequencies (FDD)


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Forward Channel

Radio channel for transmission from base station to mobile

Reverse channel

Radio channel for transmission from mobile to base station

Handoff

Pr ocess of transferring a mobile fr om one channel orbase

station to another

Mobile Switching Center

Switching center that coordinates call r outing in a large

service area. MSC connects cellularbase stations and themobiles to the PSTN (also called Mobile Telephone switching

office (MTSO)

Terminology


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Wireless System Basics

Forward Link

Reverse Link

Mobile UnitBase Station

Control or

Setup Channels


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Major Division OfCellular Technologies

1 G ( AMPS ,NAMPS,TACS,NMT)

2G ( IS-54A, IS-136 ,GSM, IS95 CDMA )

2.5G ( IS-95B , HSCSD , GPRS , EDGE )

3G (CDMA2000, WCDMA)

4G (MIMO, WiMAX)


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1G Technologies


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1G Cellular System


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First Generation

Advanced Mobile Phone Service (AMPS)

US trials 1978; deployed in Japan (79) & US (83)

800 MHz band two 20 MHz bands

TIA-553

Still widely used in US and many parts of the worldNordic Mobile Telephony (NMT)

Sweden, Norway, Demark & Finland

Launched 1981; now largely retired

450 MHz; later at 900 MHz (NMT900)

Total

Access Communications System (

TACS)

British design; similar to AMPS; deployed 1985

Some TACS-900 systems still in use in Europe


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Characteristics Of 1G

Analog Systems

Digital Signaling

Low Capacity Limited Roaming

Less Secure

Only voice service


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2G Technologies


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Issues regarding 2G Deployment

Digital

Capacity

Spectrum Utilization Infrastructure changes

Subscriber unit upgrade


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GSM Network Architecture


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Evolution of wireless in Europe and the US can be

summarized in the following diagrams:

F M T e c h n o lo g y

T D M A C D M A

M a n y S ta n d a r d s

U n t il 1 9 8 8

G S M

1 9 8 9

D C S 1 8 0 0

1 9 9 1

A M P S

( A n a lo g )1 9 7 9

D ig i t a l T e c h n o lo g y

L a t e 1 9 8 0

U S E u ro p e


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Modern cellular standards

1979: NTT (Japan), FDMA, FM, 25 kHz channels, 870-940 MHz

1983: AMPS (US), FDMA, FM, 30 kHz channels, 824-894 MHz

1985: TACS (Europe), FDMA, FM, 25 kHz channels, 900 MHz

1990: GSM (Europe), TDMA, GMSK, 200 kHz channels, 890-960 MHz

1991: USDC/IS-54 (US), TDMA, T/4 DQPSK, 30 kHz channels, 824-894MHz

1993: IS-95 (US), CDMA, BPSK/QPSK, 1.25 MHz channels, 824-894 MHand 1.8-2.0 GHz

1993: CDPD (US), FHSS, GMSK, 30 kHz channels, 824-894 Mhz

2001: UMTS/IMT-2000 (3rd generation European cellular standard),supports data and voice (up to 2 Mbps), 1885-2025 MHz and 2110-2200Mhz


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Evolution OfCellular Mobile

Engineering Research To full fill the necessity : As the requirement of wireless connections and required data rate

increased engineers tried to full fill the requirement.

Simple Analog Mobile To Analog Cellular Mobile :

First simple mobile system was upgraded to cellular in the formofAMPS in 1983.

Analog Cellular Mobile to Digital Cellular Mobile : Then GSM was introduced with TDMA approach having more capacity

and data rate.

Digital Cellular Mobile ToCDMA:

After that to full fill the requirements ofmore data and more subscriberCDMA was introduced by Qualcomm.

CDMA supports a variable numberof users in 1.25MHz wide channelsusing direct sequence spread spectrum.

Interference Affordability:

CDMA system can operate at much larger interference levelsbecause of their inherent interference resistance properties.


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Evolution OfCellular Mobile

Just an overview Contd.

Large Capacity ofCDMA : The ability ofCDMA tooperate with a much smaller S/N ratio

than FM techniques allows CDMA systems to use the same

setof frequencies in every cell which pr

ovides a largeimprovement in capacity.

lec 1 intro wireless communication

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