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Difference between first and second generationcellular systems

Digital traffic channels – 

first-generation systems are almost purely analog;

second-generation systems are digital

Encryption–

  all second generation systems provide encryption

Error detection and correction – 

second-generation digital traffic allows for detection and

correction, giving clear voice reception Channel access

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Paging Systems and

Cordless Telephone Systems

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 What are Paging Systems?

 What are Paging Systems? Broad coverage for short messages. That

message is called a page.

These systems are used to notify asubscriber of the need to call a particulartelephone number or travel to a known

location to receive further instructions. Numeric pager: incorporating a small

display panel which is able to display telephone numbers or other numeric data.

  Alphanumeric pager: which is able todisplay both textual and numeric data and

so may be used to pass a message to theuser.

One-way communication.

Simple terminals. : low complexity, very low-power pager.

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Block diagram

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INTRODUCTION TO CORDLESSSYSTEMS

 What is it?? Came in 1970s.

  Wireless link between handset andtelephone base .

Both the mobile handset and the basestation are radio transceivers.

cordless telephone or portabletelephone is a telephone with a wireless handset that communicates via

radio waves with base station connectedto a fixed telephone line, usually within alimited range of its base station (whichhas the handset cradle).

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Block diagram

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Difference between cellular and cordless

Range

In a cellular system, the operator provides aservice that you can be anywhere where you

 want In cordless    what the operator provides is simply a wire-line

telephone link to your house. And there you have a small

personal "base station" so you can walk around yourhouse with a direct link to your own base station. Butthere is no provision for taking your cordless phone toanother city and placing a call there. ... ."

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CT-1 standard

 Analog.

The two frequencies are spaced well apart in the direction base to handset the frequency is 1.7 MHz

in the direction handset to base the frequency is 47 MHz.

The CT1 system has a number of disadvantages:

The quality of the received speech is not very good.

Transmissions can be received by a sound broadcast radio receiver.

Only eight r.f. channels are allocated.

Blocking probability was more.

The range is limited to about 50 m.

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CT-2 standard

Digital: Gaussian Frequency shift keying. The cordless phones had better speech quality, were more resistant to interference, noise and fading as compared to the

earlier generation. The digital signals were also very hard to intercept and decode, and thus

provided a high level of security. The user needed to enter a PIN number in the cordless phone to gain

access to it. Thus it provided safety against misuse if the handset fell into the hands of a stranger.

Bandwidth: 864.10 MHz to 868.10 MHz. 40 channels each having a bandwidth of 100 KHz.

CAI Full duplex operation is obtained by the use of a digital

technique known as time division duplex (TDD). TDD CT2 frame consisted of 2 ms.Forward:1ms and reverse :1ms.

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HOW AN INCOMING CALL IS DETECTEDBY BASE STATION

 When an incoming call is detected by the base station, it scansthe 40 r. f. channels to find a free one that has an adequatesignal-to-noise Ratio.

The base station then transmits a call signal over the selectedchannel.

Periodically the handset moves out of its SLEEP state into itsSCAN state, in which it scans the r.f. channels.

 When the call signal is detected on one of the r.f. channels, thehandset remains on that frequency and achieves bitsynchronization with the base station. The handset then

checks that the call is for it (not for someother handset) ; if so , burst synchronization is obtained toestablish a link to the base station. Theringer of the handset then rings until the call is answered,

 when speech can commence.

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HOW HANDSET ORIGINATES THE CALL

  When a handset wishes to make a call, the CALL button ispressed

IT will scan the 40 r.f. channels to find a free one withadequate signal-to-noise ratio.

The handset then signals the base station over the selectedchannel.

The base station is continually scanning all the 40 r.f.channels, and so it rapidly detects the call from thehandset.

Synchronization between handset and base station isestablished .

Then the base station seizes a line to the local telephoneexchange or PABX. Dialling tone is then returned to the caller.

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