Analog Communication Systems

Lecture 1Instructor: Bakhtiar Ali, Room 201 Academic Block 1, bakhtiar_ali@comsats.edu.pk

Lab Instructor: Arooj Mubasharra

*EEE 352*Course LiteratureTextbook: Analog and Digital Communication, (4rth Edition) by B. P. Lathi, Oxford Printing PressDigital Communication, Fundamentals and Applications (2ndEdition) by B. Sklar, Pabitra Kumar Ray

Reference Books: Communication Systems, (4th Edition) by A. Bruce Carlson, Paul B. Crilly, Janet C. Rutledge.Communication Systems, (3rd Edition) by Simon Haykin, John Wiley & SonsAnalog and Digital Communication Systems, (6th Edition) by Leon W. Couch II, Prentice Hall, 2001

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*EEE 352*Pre-requisites

Signals and Systems

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*EEE 352*Marks DistributionTheory Assessment:

Sessional I10 MarksSessional II15 MarksQuizzes 10 MarksAssignments 10 MarksClass participation 5 MarksTerminal Exam50 MarksTotal 100 Marks

Lab Work Assessment:

Labs 70 MarksLabs Final30 MarksTotal 100 Marks

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*EEE 351*Attendance Policy

At CIIT it is required by the students to have at least 80% of attendance in the class.

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**EEE 352*Course Objectives

To introduce principles of analog communication systems and methods used in modulating and demodulating signals in order to carry information from a source to a destination

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Introduction

Chapter 1

**EEE 352*CommunicationMain purpose is to transfer information from a source to destination (sink) via a channel or a medium.

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**EEE 352*Communication System

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**EEE 352*A source originates a message, such as a human voice, a television picture, a teletype message.

The message is converted by an input transducer into an electrical waveform (baseband signal).

The transmitter modifies the baseband for efficient transmission.

The channel is a medium such as a coaxial cable, an optical fiber, a radio link.

The receiver processes the signal received to undo modifications made at the transmitter and the channel.

The output transducer convert the signal into the original form

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**EEE 352*Digital and Analog Sources and SystemsBasic Definitions:Analog Information Source: An analog information source produces messages which are defined on a continuum. (E.g. :Microphone)

Digital Information Source: A digital information source produces a finite set of possible messages. (E.g. :Typewriter)

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**EEE 352*Digital and Analog Sources and SystemsA digital communication system transfers information from a digital source to the intended receiver (also called the sink).

An analog communication system transfers information from an analog source to the sink.

A digital waveform is defined as a function of time that can have a discrete set of amplitude values.

An Analog waveform is a function that has a continuous range of values.

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**EEE 352*A/D and D/AAnalog to Digital conversion; Digital to Analog conversionGateway from the communication device to the channelCan be achieved by Sampling and Quantization

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**EEE 352*A/D and D/A (cont)Quantization

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**EEE 352*BandwidthBandwidth of a channel is the range of frequencies it can transmit with reasonable fidelity. e.g. if a channel can transmit a signal whose frequencies range from 0 to 5000 Hz then B = 5KHz

Increasing the transmission rate by compressing the signal will increase the requirement of the B.

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**EEE 352*Signal Power SIt is important in two waysFirst Increasing the Signal Power will reduces the effect of Noise on it. Larger SNR allows transmission over longer distance.

Second role of signal power is that S and B are exchangeable e.g using 16 different pulses for each level or a group of four binary pulses can be used to transmit each sample

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**EEE 352*Tradeoff Between S and BTelephone channels have limited Bandwidth but a lot of Power

Space vehicles have infinite bandwidth but power is limited.

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**EEE 352*Channel CapacityShannon Equation helps us in finding the capacity of the channel

C is also known as rate of information transmission per second

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**EEE 352*ModulationProcess of varying a carrier signal in order to use that signal to convey information Carrier signal can transmit far away, but information cannotModem: amplitude, phase, and frequencyAnalog: AM, amplitude, FM, frequency, Vestigial sideband modulationDigital: mapping digital information to different constellation: Frequency-shift key (FSK)

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**EEE 352*Modulation (cont)The basic idea here is to superimpose the message signal in analog form on a carrier which is a sinusoid of the form

Acos(wt + ) There are three quantities that can be varied in proportion to the modulating signal: the amplitude, the phase, and frequency.

The first scheme is called Amplitude Modulation and the second two are called Angle Modulation schemes

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**EEE 352*Why ModulateAntenna size is a major concernThe radiating antenna should be one tenth or more of the wavelengthFor a speech signal (100 to 3000 Hz) corresponding wavelength will be 100 to 3000 kmFor 1MHz signal you need antenna size of only 30 meter = c / fWhere c = 3x108 m/s

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**EEE 352*Why Modulate (Cont.)Simultaneous Transmission of several Signals

Frequency Division Multiplex (FDM)

Time Division Multiplex (TDM)

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**EEE 352*RandomnessNoise is a limiting factor in communication systems

Randomness is because of Noise, which is the essence of Communication System

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**EEE 352*RedundancyImportant for reliable communication

Helps to combat noise

Removing the redundant info will speed up the data transmission

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**EEE 352*CodingAdd one more pulse to each code word of such polarity as to make the number of positive pulses evenIt will help in detection of the errorMake 0001 to 00011 (even positive) by adding a positive pulse in itIf this parity (even) is violated then it means error has taken place

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**EEE 352*Questions?

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