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ECE 457Communication Systems

Selin AviyenteAssistant Professor

ECE

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Announcements• Class Web Page: http://www.egr.msu.edu/~aviyente/ECE

457-05.htm• Lectures: M, W, F 10:20-11:10 a.m. 221

Natural Resources Building• Office Hours: W 11:30- 1:00 pm, Th

9:30-11:00 am or by e-mail appointment (2210 EB)

• Textbook: Principles of Communications, Rodger E. Zimmer and William H. Tranter, John Wiley, 5th Edition, 2002.

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ECE 457 and ECE 458• ECE 458 is designed to complement

this course.• ECE 458 focuses on providing practical

experience.• You will learn material in ECE 457 that

is not covered in ECE 458 and vice versa.

• No labs this week.• There is no lab manual this year,

everything will be online.

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Course Requirements• 2 Midterm Exams (50%)

– February 25, April 8 in class

• Final Exam, May 3 (30%)• Weekly HW assignments (10%)

– Will include MATLAB assignments– HWs should be your own work (no copying!)– Assigned on Fridays due next Friday (except

during exam weeks)– No late HWs will be accepted.

• Quizzes (10%)– They will be unannounced.– Based on HW questions (10-15 minutes long)

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Policies• Cheating in any form will not be

tolerated. This includes copying HWs, cheating on exams and quizzes.

• You are allowed to discuss the HW questions with your friends, and me.

• However, you have to write up the homework on your own.

• There is no make-up for missed quizzes.• If you have an excuse for not being in

class, please e-mail me before class.

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Honors Option• Honor credit option is available• Typical projects have either a

software/hardware implementation component and an oral presentation.

• Past projects include:– Building a FM transmitter– MATLAB simulation of digital modulation

systems.

• Please feel free to come and talk to me about your ideas for a possible project.

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Tentative Syllabus• Overview of Communication Systems• Review of Signal Analysis (ECE 366)• Deterministic Modulation

– Linear (DSB,AM,SSB,VSB)– Angle Modulation (FM, PM)

• Review of Probability and Random Processes

• Noise in Modulation Systems• Digital Modulation (as time permits)

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Communication Systems• A communication system conveys

information from its source to a destination.

• Examples: – Telephone– TV– Radio– Cell phone– PDA– Satellite

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Communication Systems• A communication system is composed

of the following:

InputTransducer Transmitter Channel Receiver

Output

Transducer

Source

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Input Transducer• Source: Analog or digital • Example: Speech, music, written text• Input Transducer: Converts the

message produced by a source to a form suitable for the communication system.

• Example: Speech wavesMicrophoneVoltage

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Transmitter• Couple the message to the channel• Operations: Amplification, Modulation• Modulation encodes message into

amplitude, phase or frequency of carrier signal (AM, PM, FM)

• Advantages: – Reduce noise and interference– Multiplexing– Channel Assignment

• Examples: TV station, radio station, web server

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Channel• Physical medium that does the

transmission• Examples: Air, wires, coaxial cable,

radio wave, laser beam, fiber optic cable

• Every channel introduces some amount of distortion, noise and interference

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Receiver• Extracts message from the received

signal• Operations: Amplification,

Demodulation, Filtering• Goal: The receiver output is a scaled,

possibly delayed version of the message signal (ideal transmission)

• Examples: TV set, radio, web client

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Output Transducer• Converts electrical signal into the form

desired by the system• Examples: Loudspeakers, PC

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Capacity of a Channel• The most important question for a

communication channel is the maximum rate at which it can transfer information.

• There is a theoretical maximum rate at which information passes error free over the channel, called the channel capacity C.

• The famous Hartley-Shannon Law states that the channel capacity C is given by:

C=B*log(1+(S/N)) b/s where B is the bandwidth, S/N is the

signal-to-noise ratio.

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Fundamental Limitations• Therefore, there are two factors that

determine the capacity of a channel:– Bandwidth– Noise

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Frequency Spectrum• Most precious resource in

communications is “frequency spectrum”

• The “frequency spectrum” has to be shared by a large number of users and applications:

• AM Radio, FM Radio, TV, cellular telephony, wireless local-area-networks, satellite, air traffic control

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Frequency Spectrum• The frequency spectrum has to be

managed for a particular physical medium• The spectrum for “over-the-air”

communications is allocated by international communications organization

• International Telecommunications Union (ITU)

• Federal Communications Commission (FCC) designates and licenses frequency bands in the US.

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Frequency Spectrum Example

Application Frequency

Band

AM Radio 0.54-1.6 MHz

TV (Channels 2-6)

54-88 MHz

FM Radio 88-108 MHz

TV (Channels 7-13)

174-216 MHz

Cellular mobile radio

806-901 MHz

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Noise• Internal and External Noise• Internal Noise: Generated by

components within a communication system (thermal noise)

• External Noise: – Atmospheric noise (electrical discharges)– Man-made noise (ignition noise)– Interference (multiple transmission paths)

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History of Communications Year Event

1838 Telegraphy (Morse)

1876 Telephone (Bell)

1902 Radio transmission (Marconi)

1933 FM radio

1936 TV broadcasting

1953 Color TV

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History of Communications

Year Event

1962 Satellite communication

1972 Cellular phone

1985 Fax machines

1990s GPS, HDTV, handheld computers