Digital Transmission Lecture o3 Advanced Computer Networks (ACN) 545

Mr. Thilak de Silva.BSc. Eng., MSc, CEng, FIE(SL), FIET(UK), CITP(UK), MBCS(UK), MIEEE (USA)

M.Sc. in IT - Year 1 Semester II - 2012

JitterDigital to Digital ConversionLine codingBlock codingScramblingAnalog to Digital Conversion


At the end of this session you will have a broad understanding of Digital to Digital conversion and Analog to Digital Conversion of signals.


All data packets may not follow the same route.

Due to delays (in routers, media etc) different data packets reach the destination at different times.

Then jitter occurs. Is vital in multimedia applications. M.Sc. in IT - Year 1 Semester II -

2012

Line coding – converting digital data into a digital signal that can be transmitted through a transmission media.

Data elements – what we need to send

Signal elements – what we can send

Signal elements are the carriers who carries data elements. M.Sc. in IT - Year 1 Semester II -

2012


Source - http://train-srv.manipalu.com/wpress/wp-content/uploads/2011/10/clip-image0044-thumb4.jpg

Ratio (r)= Data elements Signal elements

Unipolar - NRZPolar – NRZ,RZ and

biphase(Manchester and differential Manchester)

Bipolar-AMI and pesudoternaryMultilevel – 2B/1Q , 8B/6T and 4D-

PAM5Multitransition – MLT 3


8 binary values in 6 signals

Additional Combinations = 729 – 256 = 473


10110011 -0++0-

Data Signal2^8 =256 3^6 =729

256 number of combinations are already defined and if there are any undefined combinations, that means there is a error.

Having additional combinations leads to easy error detection at the receiving end


Every line coding schema should have, Error Detection and Self Synchronization (done by PLL)

PLL will not Operate if there are no state changes Eg: All 0 s in RZ



Source :http://www.google.lk/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/1/11/Transmission_line_element.svg/220px-Transmission_line_element.svg.png&imgrefurl=http://en.wikipedia.org/wiki/Characteristic_impedance&usg=__mIMtU47Cbk5Fjqt5yYJ1BPgoJYI=&h=134&w=220&sz=4&hl=en&start=1&zoom=1&tbnid=_6PLMVwREZh4GM:&tbnh=65&tbnw=107&ei=n6kmT_6EE87NrQf8lvyoCA&prev=/search%3Fq%3Dcharacteristic%2Bimpedance%26hl%3Den%26gbv%3D2%26tbm%3Disch&itbs=1

R - resistance per unit length,

L - inductance per unit length,

G - conductance of the dielectric per unit length,

C - capacitance per unit length,

j - imaginary unit, and

ω - angular frequency.

Because of capacitor signal gets charged,

In Manchester coding it gets charged to a some extent and remains.

We need to have a way of discharging DC component, (avg =0), Eg: AMI


Changes a block of m bits into a block of n bits. (n>m)

Eg: 4B/5B coding – 4 bits converted to 5

bits(32-16 = 16 number of redundant

combinations)

8B/10B – 8 bits are converted to 10 bits M.Sc. in IT - Year 1 Semester II - 2012


Block Coding

Line coding

Line coding

Block Coding

DATA

DATA

Convert data to signal

For Error detection

Sender

Receiver

Transmission media

Long sequence of zeros (0) are converted into a combination of bits.

000000 010110

Mainly for synchronization.Useful to achieve security.Eg:

B8ZS HDB3


Converting an Analog signal to a Digital signal.

Used in telephone systems to convert the voice signal to digital signal.

Eg: Pulse Code Modulation Delta Modulation Adaptive Delta Modulation


Data Communications and Networking, Forouzan, Chapter 04, 4th Edition


Digital Transmission Lecture o3 Advanced Computer Networks (ACN) 545

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