ECET422a Digital Communications Course

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Course information

� Scope of the course

� Digital Communication Systems

� Resources

� Lectures posted in Yahoo Group

<ecet422a_dlsu_2012_2@yahoogroups.com>

� Course Syllabus

� Reading Materials (for voluntary recitation)

� Introduction to digital communication systems

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Background

� Communication is a process by which information is exchanged between individuals through a common system of symbols, signs, or behavior

� Communication systems are reliable, economical and efficient means of communications� Public switched telephone network (PSTN), mobile

telephone communication (GSM, 3G, WiFi ...), broadcast radio or television, navigation systems, ...

� The course is aiming at introducing fundamental issues in digital communication systems

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Scope of the course ...

� Example of a (digital) communication systems:

Cellular wireless communication systems (e.g. 3GPP Terms)

Base Station (BS)

User Equipment (UE)

UE UE

UE

BS

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Scope of the course ...

General structure of a communication systems

FormatterSource

encoder

Channel

encoderModulator

FormatterSource

decoder

Channel

decoderDemodulator

Transmitter

Receiver

SOURCE

Info.Transmitter

Transmitted

signal

Received

signalReceiver

Received

info.

Noise

ChannelSource User

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Scope of the course …

� Learning fundamental issues in designing a digital

communication system (DCS):

� Utilized techniques

� Formatting and source coding (Prelims)

� Modulation (Baseband and bandpass signalling) – (MidTerms)

� Channel coding (MidTerms and Finals – Supplement)

� Equalization

� Synchronization

� ....

� Multiplexing (Finals)

� Trade-offs between various parameters

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Resources

� Course material� Course text books:

� “Electronic Communications System: Fundamentals Through Advanced”by W. Tomasi, 5th Edition Boston: McGraw-Hill

� Additional recommended books� “Digital communications: Fundamentals and Applications” by Bernard

Sklar,Prentice Hall, 2001, ISBN: 0-13-084788-7

� “Communication systems engineering”, by John G. Proakis and Masoud Salehi, Prentice Hall, 2002, 2nd edition, ISBN: 0-13-095007-6

(Personal Advice – Do not hesitate to use/borrow older versions – the lecturer will provide examples of newer applications not covered by such books)

� Material accessible from course yahoo group:� Message Posts

� Lecture slides (.ppt, pdf)

� Assignments, Exercises and formulae

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Staff

� Course responsible and lecturer and giving

tutorials:

� Joel C. Delos Angeles

� Office: CEAT

� Consultation Hours: Tuesday/Thursday

(1 PM to 2 PM)

� Email: joeldelosangeles@yahoo.com

ECET422a

Digital Communications Course

Lecture 1

Signals and Spectra

Primary Reference Book: Sklar chapter 1

Thanks to:

catharinacarlemalm@signal.uu.se

Lecture 1

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Today, we are going to talk about:

� What are the features of a digital communication system?� Why “digital” instead of “analog”?

� What do we need to know beforehand?� Classification of signals

� Random process

� Autocorrelation

� Power and energy spectral densities

� Noise in communication systems

� Signal transmission through linear systems

� Bandwidth of signal

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Digital communication system

� Important features of a DCS:� Transmitter sends a waveform from a finite set of

possible waveforms during a limited time

� Channel distorts, attenuates the transmitted signal and adds noise to it.

� Receiver decides which waveform was transmitted from the noisy received signal

� Probability of erroneous decision is an important measure for the system performance

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Digital versus analog

� Advantages of digital communications:

� Regenerator receiver

� Different kinds of digital signal are treated

identically.

Data

Voice

Media

Propagation distance

Original

pulse

Regenerated

pulse

A bit is a bit!

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Classification of signals

� Deterministic and random signals

� Deterministic signal: No uncertainty with respect to the signal value at any time.

� Modeled by explicit mathematical expressions

� Random signal: Some degree of uncertainty in signal values before it actually occurs.

� Non-explicit mathematical expressions instead over a long

period, may exhibit certain regularities described by probabilities

and statistical averages

� Thermal noise in electronic circuits due to the random movement

of electrons

� Reflection of radio waves from different layers of ionosphere

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Classification of signals …

� Periodic and non-periodic signals

� Analog and discrete signals

A discrete signal

Analog signals

A non-periodic signalA periodic signal

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Classification of signals ..

� Energy and power signals

� A signal is an energy signal if, and only if, it has nonzero but

finite energy for all time (Joules):

� A signal is a power signal if, and only if, it has finite but nonzero

power for all time (Joules/seconds – watts; T in the denominator

below):

� General rule: Periodic and random signals are power signals. Signals

that are both deterministic and non-periodic are energy signals.

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Sample Problems ..