This document provides an overview of a communication systems course. It introduces the instructor, textbook, learning outcomes, and assessment criteria. The contents will cover communication systems fundamentals including analog and digital messages, modulation and detection techniques, source and error coding, and a brief history of telecommunications. Students will learn about signals, channels, modulation schemes like AM and FM, and analyze different transmission methods.

1. 30820-Communication Systems
Week 1 – Lecture 1-3
(Ref: Chapter 1 of text book)
INTRODUCTION

2. Course Information
• Instructor: Dr. Adnan Zafar (Assistant Professor)
– Office: Room 15, EE Department, Block VI
– Email: adnan.zafar@ist.edu.pk
• Text Book: “Modern Digital and Analog Communication Systems”, 4th Edition,
By B. P. Lathi, Zhi Ding
• Program Learning Outcome: The course is designed so that students will
achieve
– Problem Analysis: PLO-02
– Design/Development of Solution: PLO-03
• Course Learning Outcome: Upon successful completion of the course, the
students will be able to
– Apply the concepts of signals and systems to different communication systems
– Analyze different analog and digital transmission schemes
– Design amplitude modulation (AM) and frequency modulation (FM) transmitter
308201- Communication Systems 2

3. Assessment
Quizzes (surprise, announced) 20%
Assignments (week 5-7 & week 8-10) 10%
OHT Exams (7th week & 13th Week) 25%
Final Exam (Scheduled Week) 45%
Total 100%
308201- Communication Systems 3

4. Contents
• Communication Systems
• Analog and Digital Messages
• Channel Effect, Signal to Noise Ratio and Capacity
• Modulation and Detection
• Digital Source Coding and Error Correction Coding
• A Brief Historical Review of Modern Telecommunication
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5. What’s Communication?
• Communication involves the transfer of information from one point to
another.
• Three basic elements
– Transmitter: converts message into a form suitable for transmission
– Channel: the physical medium, introduces distortion, noise, interference
– Receiver: reconstruct a recognizable form of the message
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6. Analog Messages
• Early analog communication
– telephone (1876)
– phonograph (1877)
– film soundtrack (1923, Lee De Forest, Joseph Tykocinski-Tykociner)
• Key to analog communication is the amplifier (1908, Lee De Forest, triode
vacuum tube)
• Broadcast radio (AM, FM) is still analog
• Broadcast television was analog until 2009
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7. Digital Messages
• Early long-distance communication was digital
– semaphores, signal flags, smoke signals, bugle calls, telegraph
• Teletypewriters
– Baudot (1874) created 5-unit code for alphabet
– Today baud is a unit meaning one symbol per second
– Working teleprinters were in service by 1924 at 65 words per minute
• Fax machines: Group 3 (voice lines) and Group 4 (ISDN)
– First fax machine was invented by Alexander Bains in 1843
– Pantelegraph (Caselli, 1865) set up telefax between Paris and Lyon
• Ethernet, Internet
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8. Communication System Block Diagram
(Basic)
• Source encoder converts message into message signal (bits)
• Transmitter converts message signal into format appropriate for channel
transmission (analog/digital signal)
• Channel conveys signal but may introduce attenuation, distortion, noise,
interference
• Receiver decodes received signal back to message signal
• Source decoder decodes message signal back into original message
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9. Communication System Block Diagram
(Advanced)
• Source encoder compresses message to remove redundancy
• Encryption protects against eavesdroppers and false messages
• Channel encoder adds redundancy for error protection
• Modulator converts digital inputs to signals suitable for physical channel
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10. Communication Channels
• Communication systems convert information into a format appropriate for
the transmission medium
• The channel is central to operation of a communication system
– Linear (e.g., mobile radio) or nonlinear (e.g., satellite)
– Time invariant (e.g., fiber) or time varying (e.g., mobile radio)
• The information-carrying capacity of a communication system is
proportional to the channel bandwidth
• Pursuit for wider bandwidth
– Copper wire: 1 MHz
– Coaxial cable: 100 MHz
– Microwave: GHz
– Optical fiber: THz
• The process of creating a signal suitable for transmission is called
‘modulation’
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11. AM and FM Modulation
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12. Multiplexing
• To combine multiple signals (analog or digital) for transmission over a
single line or media.
• A common type of multiplexing combines several low-speed signals for
transmission over a single high-speed connection.
• The following are several examples of different multiplexing methods:
– Space Division Multiplexing (SDM): each signal is assigned a different physical link
– Frequency Division Multiplexing (FDM) : each signal is assigned a different frequency
– Time Division Multiplexing (TDM) : each signal is assigned a fixed time slot in a fixed
rotation . A variant of it is the Statistical Time Division Multiplexing (STDM) where time
slots are assigned to signals dynamically to make better use of bandwidth
– Wavelength Division Multiplexing (WDM) : each signal is assigned a particular
wavelength; used on optical fiber.
– Code Division Multiplexing (CDM) :The signals can be transmitted at the same time and
frequency band , but they can be made orthogonal by using special coding.
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13. Noise in Communications
• Unavoidable presence of noise in the channel
– Noise refers to unwanted waves that disturb communications
– Signal is contaminated by noise along the path
• External noise: interference from nearby channels, human-made noise,
natural noise
• Internal noise: thermal noise, random emission in electronic devices
• Noise is one of the basic factors that set limits on communications
• A widely used metric is the signal-to-noise (power) ratio (SNR)
𝑆𝑁𝑅 =
𝑆𝑖𝑔𝑛𝑎𝑙 𝑝𝑜𝑤𝑒𝑟 (𝑃𝑠)
𝑁𝑜𝑖𝑠𝑒 𝑃𝑜𝑤𝑒𝑟 (𝑃𝑛)
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14. Signal to Noise Ratio
• Signal-to-noise ratio is an engineering term for the power ratio between a
signal (meaningful information) and the background noise
𝑆𝑁𝑅 =
𝑃𝑠
𝑃𝑛
• Because many signals have a very wide dynamic range, SNRs are usually
expressed in terms of the logarithmic decibel scale.
• In decibels, the SNR is 20 times the base-10 logarithm of the amplitude
ratio, or 10 times the logarithm of the power ratio
𝑆𝑁𝑅 𝑑𝐵 = 10 log10
𝑃
𝑠
𝑃
𝑛
= 20 log10
𝐴𝑠
𝐴𝑛
• where 𝑃 is average power and 𝐴 is RMS amplitude.
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15. Analog vs. Digital Signals
• Analog signal value varies
continuously
• Digital signals value limited to a finite
set
– Digital systems are more robust
• Binary signals
– Have 2 possible values
– Used to represent bit values
– Bit time 𝑇 needed to send 1 bit
– Data rate 𝑅 =
1
𝑇
bits per second
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16. Sampling and Quantization, I
• To transmit analog signals over a digital communication link, we must
discretize both time and values.
• Quantization spacing is
2𝑚𝑝
𝐿
; sampling interval is 𝑇, not shown in figure.
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17. Sampling and Quantization, I
• The information in an analog waveform, with maximum frequency
𝑓𝑚 = 3𝐾𝐻𝑧 and peak voltage 𝑉
𝑝 = 2𝑉, is to be sample and
quantized with 𝐿 = 16 quantization levels.
– What is the quantization spacing?
2𝑚𝑝
𝐿
=
4
16
=
1
4
= 0.25
– What is the sampling interval?
𝑇𝑠 =
1
𝑓𝑠
=
1
2𝑓𝑚
=
1
6000
= 166.67𝜇𝑠
– What is the bit transmission rate?
𝑅 = 𝑙𝑓𝑠 = log2 𝐿 × 2 × 𝑓𝑚 = log2 16 × 2 × 3000 = 24𝑘𝑏𝑝𝑠
– What is the bandwidth efficiency if transmission bandwidth is 12KHz?
(Hint: BW efficiency unit is bits/sec/Hz)
η𝐵𝑊 =
𝑅
𝑊
=
24000
12000
= 2 bits/sec/Hz
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18. Sampling and Quantization, II
• Usually sample times are uniformly spaced (although, this is not always
true). Higher frequency content requires faster sampling. (Soprano must
be sampled twice as fast as a tenor.)
• Quantization levels can be uniformly spaced, but non-uniform
(logarithmic) spacing is often used for voice.
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19. Digital Transmission and Regeneration
• Simplest digital communication is binary amplitude-shift keying (ASK)
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20. Channel Errors
• If there is too much channel distortion or noise, receiver may make a
mistake, and the regenerated signal will be incorrect.
• Channel coding is needed to detect and correct the message.
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21. Pulse Code Modulation (PCM)
• To communicate sampled values,
we send a sequence of bits that
represent the quantized value.
• For 16 quantization levels, 4 bits
suffice.
• PCM can use binary representation
of value.
• The PSTN uses companded PCM
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22. Performance Metrics
• Analog communication systems
– Metric is fidelity, closeness to original signal
– We want 𝑚(𝑡) ≈ 𝑚(𝑡)
– A common measure of infidelity is energy of difference signal:
0
𝑇
𝑚 𝑡 − 𝑚(𝑡) 2 𝑑𝑡
• Digital communication systems
– Metrics are data rate 𝑅 in bits/sec and probability of bit error
𝑃𝑒 = 𝑃 𝑏 ≠ 𝑏
– Without noise, never make bit errors
– With noise, 𝑃𝑒 depends on signal and noise power, data rate, and channel
characteristics.
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23. Channel Capacity and Data Rate
• Channel bandwidth limits the signal bandwidth.
– Higher BW → More pulses over the channel
• Signal SNR at the receiver determines the recoverability of the transmitted
signal.
– High SNR → Signal pulse can use more signal levels → More bits with each pulse
transmission
• Both Bandwidth and SNR can affect the channel throughput.
• The Shannon capacity is the maximum possible data rate for a system with
noise and distortion
– This maximum rate can be approached with bit error probability close to 0
– For additive white Gaussian noise (AWGN) channels,
𝐶 = 𝐵 log2(1 + 𝑆𝑁𝑅)
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24. Example
A communication system has an available bandwidth of 4KHz. If
the noise power is 100 times less than signal power.
• What is the capacity in bits/s if signal power is 1W?
C = 4000 log2(1 + 100) = 26.63 kbit/s
• How can the capacity in bits/s be equal to the bandwidth in
hertz?
Signal power = Noise power
or
At a SNR of 0 dB
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25. Milestones in Communications
• 1837, Morse code used in telegraph
• 1864, Maxwell formulated the electromagnetic (EM) theory
• 1887, Hertz demonstrated physical evidence of EM waves
• 1890’s-1900’s, Marconi & Popov, long-distance radio telegraph
– Across Atlantic Ocean
– From Cornwall to Canada
• 1875, Bell invented the telephone
• 1906, radio broadcast
• 1918, Armstrong invented super heterodyne radio receiver (and FM in
1933)
• 1921, land-mobile communication
• 1928, Nyquist proposed the sampling theorem
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26. Milestones in Communications
• 1947, microwave relay system
• 1948, information theory
• 1957, era of satellite communication began
• 1966, Kuen Kao pioneered fiber-optical communications (Nobel Prize
Winner)
• 1970’s, era of computer networks began
• 1981, analog cellular system
• 1988, digital cellular system debuted in Europe
• 2000, 3G network
• 2010, 4G LTE
• 2020, 5G (expected)
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