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Lecture 1

Introduction & Background

Government College University Faisalabad 1

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1897:Marconi invented wireless concept

1960s & 1970s:Bell laboratories developed the cellularconcept

1970s:

Development of highly reliable, miniaturesolid state radio frequency hardware

Wireless communication era was born

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Figure 1.1 The growth of mobile telephony as compared with other popular inventions of the 20th century.

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Mobile Describes any radio terminal attached to a high

speed mobile platform (e.g., A cellular phone in a fast

moving vehicle).

Portable Describes a radio terminal that can be hand-held and used by someone at walking speed (e.g., cordless

telephone).

Subscriber Mobile or portable user.

Subscribers Unit each users communication device. Base stations Link mobiles through a backbone network.

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Simplex Communication is possible only in onedirection, (e.g., paging systems, CB radio etc).

Half Duplex Two way communication, but usesthe same radio channel for both transmission andreception.User can only transmit or receive information

(e.g., push-to-talk, release-to-listen etc)

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Full Duplex Allows simultaneous

two-way radio transmission and reception

between subscriber and base station. Two simultaneous but separate channels (FDD)

or

Two adjacent timeslots on a single radio channel(TDD)

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Provides simultaneous radio transmission channels for subscriber andbase station

Separate transmit and receive antennas at base station used toaccommodate two separate channels

Single antenna at subscriber unit with duplexeris used. Duplexer enables same antenna to be used for simultaneous

transmission and reception A pair of simplex channels with a fixed and known frequency

separation is used Forward channel: used to convey traffic to mobile user from base

station Reverse channel: used to carry traffic from mobile user to base

station

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Share a single radio channel in time i.e., some portion oftime for transmission and remaining time for reception

Can store information bursts and appear as full duplex ifusers transmission rate is slower than that of channel.

Only possible with digital transmission formats anddigital modulation and is very sensitive to timing.

Used only for indoors and small area wireless

applications

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Paging systems are communication systems that send briefmessages to a subscriber

Depending on the type of service the message may be: Numeric messages

Alpha-numeric message Voice message

News headlines

Stock quotes

Faxes

Coverage area of simple paging systems: 2 to 5 km or withinindividual buildings

Wide area paging systems can provide worldwide coverage

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Wide area paging systems consists of a

network of telephone lines, many base

station transmitters, and large radio towersthat simultaneously broadcast a page from

each base station - Simulcasting

Designed to provide reliable communication

to subscriber wherever they are.

This requires large transmitter powers & low

data rates for maximum coverage.

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Satellite linkSatellite linkSatellite linkSatellite link

Landline linkLandline linkLandline linkLandline link

Landline linkLandline linkLandline linkLandline link

City 1:City 1:PagingPagingterminalterminal

City 1:City 1:PagingPagingterminalterminal

City 2:City 2:

PagingPagingterminalterminal

City 2:City 2:

PagingPagingterminalterminal

City N:City N:PagingPaging

terminalterminal

City N:City N:PagingPaging

terminalterminal

PagingPagingcontrolcontrolcentercenterPagingPagingcontrolcontrolcentercenter

PSTNPSTNPSTNPSTN

Figure 1.3 A wide area paging system. The paging control center dispatches pages received from the PSTN throughout

several cities at the same time

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Full duplex communication

Uses radio to connect a portable handset to a

dedicated BS which is then connected to a dedicated

telephone line with a specific telephonenumber on PSTN

Limited range and mobility: few hundredmeters

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FixedFixedPortPort

(Base(BaseStation)Station)

FixedFixedPortPort

(Base(BaseStation)Station)

wirelesswireless

linklink

wirelesswireless

linklinkPublicPublicSwitchedSwitchedTelephoneTelephoneNetworkNetwork(PSTN)(PSTN)

PublicPublicSwitchedSwitchedTelephoneTelephoneNetworkNetwork(PSTN)(PSTN)

cordlesscordlesshandsethandsetcordlesscordlesshandsethandset

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Provides wireless connection to PSTN for any userlocation within the range of the system.

Accommodate large number of users over a large

geographic area within a limited frequency spectrum Coverage area divided into cells for same radio channels

to be reused by another base station located somedistance away

Handoff: enables a call to proceed uninterrupted whenthe user moves from one cell to another

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Mobile Switching Center (MSC): responsible

for connecting all mobiles to the PSTN

Mobile station: contains a transceiver, anantenna & control circuitry

Base station: consists of several transmittersand receivers. Serves as a bridge between

mobile users in a cell and connects mobilecalls to MSC

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Forward voice channels (FVC): for voice

transmission from the base station to the

mobiles Reverse voice channels (RVC): for voice

transmission from the mobiles to the basestation

Two channels responsible for initiatingmobile calls are forward control channel

(FCC) and reverse control channel (RCC)

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