CommSys1_Lecture1

CE-250 Communication System I

Lecture 1(Reference Ch#1 of text book)

Course Literature

Textbook:

• “Modern Digital and Analog Communication Systems”, (4th Edition) by B. P. Lathi, Zhi Ding

Reference Books:

• “Communication Systems”, (4th Edition) by Simon Haykin

Pre-requisites

• Signals and Systems

Lecture Material

• Will be emailed before/after lecture

• PPT slides

• Papers

• HWs, Assignments etc

• Background/review material

• Email me by 10:00 pm tonight on [email protected]

• Subject: COMMUNICATION SYSTEMS 1

• Body: “Name:……………………………..”

• NOTHING ELSE

Honesty

• Don’t LIE, Don’t CHEAT

– Tests, Assignments (prog /otherwise), anywhere

• In fairness to the honest majority, ALL incidents of academic

misconduct will be reported to the Office of the HoD. You are

expected to report to the instructor all incidents of academic

misconduct you observe in this class.

Exams

• The exams are cumulative. Test/exam grades become final one

week after they are returned in class. HWs/Assignments are

take‐home exam problems and students should NOT work

together on them.

• The exams (tests and final exam) will be closed book/notes or

cheat sheet allowed(will inform later) exams. In NO CASE

will a make‐up exam be given unless the student obtained

approval from the instructor PRIOR to the exam.

Grading (Tentative)

• Quizzes ‐ 15%

• Assignments/HWs ‐ 5%

• OHT (3) ‐ 30%

• Final Exam ‐ 50%

• Total ‐ 100%

Late Policy

No late assignments/HWs will be accepted for grading

Attendance Policy

At IST it is required by the students to have at least 80% of

attendance in the class

Important

• If you have questions/problems:

– ask questions before, during, or after the class

– email questions to the instructor

– make an appointment to see the instructor

• Do practice problems

• Any questions on course info ?

Communication

• Communications = Information transfer

• Communication is the process of conveying information at a

distance or it is the basic process of exchanging information.

OR

• Communication is the science of transmitting, receiving and

processing of information.

• Electrical Communication is a process in which the message

or information is transmitted from one point to another point

or from one person to another in the form of electrical signal,

through some communication link.

• A physical entity that operates on a set of primary signals (the

inputs) to produce a corresponding set of resultant signals (the

outputs).

• Operations, or processing, may take several forms:

modification, combination, decomposition, filtering, extraction

of parameters, etc.

System

Communication System

• The electrical equipments or devices which are used for the

purpose of communication are known as communication

equipments and integrating of different communication

equipments for the purpose of communication form a

communication system.

• This course is about communications

– Limited to information in electrical form

– We will primarily cover information transfer at systems

level (We will not deal too much with circuits, chips, signal

processing, microprocessors, protocols, and networks)

Purpose of communication systems (1)

• Exchange information, usually via a common protocol

• Telecommunication

– Use of technology to aid and enhance distance

communications

– Analog communications: telephone, radio, TV, etc

– Digital communications: telegraphy, cellular phone,

computer network

Purpose of communication systems (2)

• Information is a word that is too generic for our purposes

– We will use the word message which is a physical manifestation ofinformation

• What do communication systems have to do with messages?

– Communication systems are responsible for producing an “acceptable”replica of message at the destination

What exactly is information?

• Just like information, signal is also a generic word

– Derived directly from information

• Scientists and Engineers use signal to denote information inelectrical form

– We will use signal and message interchangeably

Is Signal = Message?

• Provide for electronic exchange of multimedia data

– Voice, data, video, music, email, web pages, etc.

• Communication Systems Today

– Radio and TV broadcasting (covered later in the course)

– Public Switched Telephone Network (voice, fax, modem)

– Cellular Phones

– Computer Networks (LANs, WANs, and the Internet)

– Satellite Systems (pagers, voice/data, movie broadcasts)

– Bluetooth

Communication Systems

A Simple Communication System

Source ofInformation

SourceEncoder

ChannelEncoder Modulator

Channel

DemodulatorChannelDecoder

SourceDecoder

User

A Digital Communication System

Baseband signalRecovered Baseband signal

Block Diagram of a Generic Communication System

Description of Communication Systems (1)

• Sources of Information

– Speech: 300~3300 Hz (0-4KHz)

– Music: 20 Hz ~ 15 kHz

– Picture and video: ~4.2 MHz

– Computer data: wideband

Description of Communication Systems (2)

• Channels

– Wireline: twisted-pair, coaxial cable, wave guide

– Fibers

– Wireless: broadcast, mobile communications, satellite communication

Description of Communication Systems (3)

• Channel Properties

– Channels can be modeled as a system (has input and

output), such as a filter

– Linear vs. Non-linear

– Time invariant vs. Time varying

Primary Communication Resources (1)

• System Resources

1) Transmitted Power

• Average power of the transmitted signal, affect SNR

2) Channel Bandwidth

• Band of frequencies allocated for the transmission of message signal,

affect transmission speed

Example:

– Dial-up modem: limited bandwidth (~4 kHz), power not very important

(can be tens of watts, SNR is high)

– Satellite: extremely power limited (low SNR), bandwidth not very

critical (can be several GHz)

Bandwidth for certain Channels

• For cable transmission, the usable spectrum is determined by the cable, and

can be reused by using more cables

– Unlimited spectrum (e.g., fiber optics)

• For wireless transmission, the spectrum is shared by all applications (TV,

radio broadcasting, satellite, wireless LAN, cellular, etc)

– Spectrum becomes a scarce resource

– Only spectrum of 3MHz – 30 GHz range is especially suitable for

general purpose wireless communications

This is why we look for optimal

bandwidth efficiency

Primary Communication Resources (2)

• Concept of SNR

1 ) Signal-to-noise ratio• Ratio of the average signal power to the average noise power

2) Transmission power is quantified by SNR• If noise is small (such as in telephone channel), transmitted power need not

be large for a high SNR

• If noise is large (such as in wireless channel), transmitted power has to belarge in order to guarantee certain SNR

• Objective of communication system design

– Efficiency: use transmission power and bandwidth as effectively aspossible and a achieve certain transmission speed with minimumbandwidth, and guarantee certain SNR with minimum transmittedpower

Basic Types of Communication System

Multiplex Systems

Multiplexing

• To combine multiple signals (analog or digital) for transmission over asingle line or media.

• A common type of multiplexing combines several low-speed signals fortransmission over a single high-speed connection.

• Multiplexing Methods

• Space Division Multiplexing (SDM): Each signal is assigned a differentphysical link

• Frequency Division Multiplexing (FDM): Each signal is assigned adifferent frequency

• Time Division Multiplexing (TDM): Each signal is assigned a fixed timeslot in a fixed rotation

• Statistical Time Division Multiplexing (STDM): Time slots are assigned tosignals dynamically to make better use of bandwidth

• Wavelength Division Multiplexing (WDM): Each signal is assigned aparticular wavelength; used on optical fiber

Space Division Multiplexing (SDM)

Frequency Division Multiplexing (FDM)

• It is a form of signal multiplexing where multiple baseband signals are

modulated on different frequency carrier waves and added together to

create a composite signal

Time Division Multiplexing (TDM)

• Short for Time Division Multiplexing, a type of multiplexing that

combines data streams by assigning each stream a different time slot in a

set.

• TDM repeatedly transmits a fixed sequence of time slots over a single

transmission channel.

• TDM combines Pulse Code Modulated (PCM) streams created for each

conversation or data stream

Wavelength Division Multiplexing (WDM)

• The term Wavelength Division Multiplexing is commonly applied to an

optical carrier (which is typically described by its wavelength), whereas

Frequency Division Multiplexing typically applies to a radio carrier (which

is more often described by frequency).

• However, since wavelength and frequency are inversely proportional, and

since radio and light are both forms of electromagnetic radiation, the two

terms are closely analogous.

Modulation

• Modulation is the process of varying a carrier signal, typically a sinusoidalsignal, in order to use that signal to convey information.

• The three key parameters of a sinusoid are its amplitude, its phase and itsfrequency, all of which can be modified in accordance with an informationsignal to obtain the modulated signal.

• In analog modulation, the change is applied continuously in response to thedata signal. The modulation may be applied to various aspects of the signalas the lists below indicate.

• In digital modulation, the changes in the signal are chosen from a fixed list(the modulation alphabet) each entry of which conveys a different possiblepiece of information (a symbol). The alphabet is often convenientlyrepresented on a constellation diagram.

Table of Modulation Methods

AM/FM/PM: Amplitude / Frequency / Phase Modulation

ASK/FSK/PSK: Amplitude / Frequency / Phase shift-keying

Modulating Signal Modulation performed on

Analog Modulation Methods AM FM PM

Digital Modulation Methods ASK FSK PSK

( ) sin(2 )s t A ft

Modulation

Carrier Wave

Message or “Baseband” Signal, m(t)

AM – m(t) used to vary carrier Amplitude

FM – m(t) used to vary carrier Frequency

Advantages of Modulation

• Ease of Radiation

• Simultaneous Transmission of Several Signals

• Exchanging the SNR with Bandwidth

A Brief History of Communications

• 1837: Telegraph, Morse code

• 1864: Electromagnetic theory, Maxwell equations

• 1875: Telephone (Bell)

• 1918: Super-heterodyne radio receiver (Armstrong)

• 1928: TV (Farnsworth), Signal transmission theory (Nyquist)

• 1937: PCM system (Reeves)

• 1947: Geometric representation of signal (Kotel’nikov)

• 1948: Digital communication theory (Shannon)

• 1955: Satellite communications (Pierce)

• 1966: Fiber optic communications