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PART 2: PHYSICAL LAYER & MEDIA

CHAPTER 4

DIGITAL TRANSMISSION

Department of Electrical Engineering.

COMSATS Institute of Information Technology, Islamabad.

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Digital to Digital Conversion

Digital data by using digital signals. The

conversion involves three techniques: line

coding, block coding, and scrambling. Line

coding is always needed; block coding and

scrambling may or may not be needed.

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Line Coding & Decoding

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Signal Element vs Data Element

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Effect of lack of synchronization

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Line Coding Schemes

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Unipolar NRZ Scheme

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Polar NRZ-L and NRZ-I Schemes

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In NRZ-L the level of the voltage determines

the value of the bit.

In NRZ-I the inversion

or the lack of inversion

determines the value of the bit.

Note

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Return to Zero Scheme

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Polar Biphase: Manchester and

Differential Manchester Schemes

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In Manchester and differentialManchester encoding, the transition

at the middle of the bit is used for

synchronization.

Note

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The minimum bandwidth of Manchesterand differential Manchester is 2 times

that of NRZ.

Note

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Bipolar Schemes: AMI and Pseudo

ternary

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Analog to Digital Conversion

Two techniques used for analog to digital

conversion.

pulse code modulation and delta modulation.

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Components of PCM Encoder

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According to the Nyquist theorem, thesampling rate must be

at least 2 times the highest frequency

contained in the signal.

Note

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Delta Modulation

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Delta Modulation Components

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Transmission Mode

The transmission of binary data across a link

can be accomplished in either parallel or serial

mode. In parallel mode, multiple bits are sent

with each clock tick. In serial mode, 1 bit is

sent with each clock tick. While there is only

one way to send parallel data, there are three

subclasses of serial transmission:asynchronous, synchronous, and isochronous.

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Data Transmission and mode

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Parallel Transmission

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Serial Transmission

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In asynchronous transmission, we send 1 startbit (0) at the beginning and 1 or more stop bits

(1s) at the end of each byte. There may be a

gap between

each byte.

Note

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Asynchronous Transmission

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In synchronous transmission, we send bits one

after another without start or stop bits or

gaps. It is the responsibility of the receiver to

group the bits.

Note

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Synchronous Transmission

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THANK YOU

HAVE A NICE WEEKEND!

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