Communication system introductory lecture

1. AAMRA ARSHAD
Lecture 1: Introduction to
Communication Systems
Course Code: EET321
Course Title: Communication Systems
Fall-2020

2. Communication Systems
 System: is an arrangement or combination of different physical
components connected in such a manner to attain a certain objective
 Communication: Transfer of information from one place to another
place
“Communication System is a system which serves to transfer
the information from one place to another place”

3. Examples of Communication Systems

5. Satellite Communication

6. Radar Communication

7. Mobile Communication (GSM)

8. Basic Blocks of a Communication System
Source Destination

9. Information Types
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 Major classification of data: analog vs. digital
 Analog signals
 speech (words are sometimes discrete in time)
 music (closer to a continuous signal)
 temperature readings, barometric pressure, wind speed
 images stored on film
 Analog signals can be represented (approximately) using bits
 digitized images (can be compressed using JPEG)
 digitized video (can be compressed to MPEG)
 Bits: text, computer data
 Analog signals can be converted into bits by quantizing/digitizing
 The word bit (binary digit) was coined in the late 1940s by John Tukey.
Today a byte is 8 bits. Originally it depended on the computer-6, 9, or 10 bits were also used.

10. Analog Messages
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 Early analog communication
 Telephone (1876, Alexander Graham Bell)
 Phonograph (1877, Thomas Alva Edison)
 Film soundtrack (1923, Lee DeForest, Joseph Tykoci´nski-Tykociner)
 Magnetic Recording (1899, Valdemar Poulsen & 1939, Marvin Camras)
 Key to early analog communication is the amplifier
(1908, Lee DeForest, triode vacuum tube)
 Broadcast radio (AM, FM) is analog – HD radio is digital
 Broadcast television (1927, Philo Farnsworth) was analog
until 2009 – now digital

11. Digital Messages
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 Early long-distance communication was digital
 semaphores, white flag, smoke signals, drums, bugle calls,
telegraph (1844, Samuel Morse)
 Teletypewriters (stock quotations)
 Emile 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)
 In 1990s the accounted for majority of transPacific telephone use. Sadly, fax machines are still
in use.
 First fax machine was Alexander Bains 1843 device required conductive ink
 Pantelegraph (Giovanni Caselli, 1865) set up telefax between Paris and Lyon
 Ethernet, WiFi, Internet

12. Analog vs. Digital Systems
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 Analog signals
 Values 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

13. Communication System Block Diagram (Basic)
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 Source Message is generated (Example: Speaker generates an audio signal)
 Transducer: It will convert message to electrical signal (at the source) and vice versa at the destination
 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
Sourc
e
Destinatio
n

14. Parts of Communication System

15. Parts of Communication System

16. Parts of Communication System

17. Parts of Communication System

18. Parts of Communication System

19. Examples of Communication Channels
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 Communication systems convert information into a format appropriate
for the transmission medium
 Some channels convey electromagnetic waves (modulated signals).
 Radio (20 KHz to 20+ GHz)
 Optical fiber (200 THz or 1550 nm)
 Laser line-of-sight (e.g., from Mars)
 Other channels use sound, smell, pressure, chemical reactions (baseband signals)
 sound
 smell: ants
 chemical reactions: neuron dendrites
 dance: bees
 Analog communication systems convert (modulate) analog signals into
modulated (analog) signals – amplification to extend distance – noise grows linearly
 Digital communication systems convert information in the form of bits
into binary/digital signals – bit regeneration to extend distance – BER grows, but
slowly

20. Physical Channels
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 Physical channels have constraints on what kinds of signals can be
transmitted
 Radio uses E&M waves at various frequencies
 Submarine communication at about 20 KHz
 Cordless telephones: 45 MHz, 900 MHz, 2.4 GHz, 5.8 GHz, 1.9 GHz
 Wired links may require DC balanced codes to prevent voltage build up
 Fiber optic channels use 4B5B (data redundancy) modulation to
accommodate time-varying attenuation
 CD and DVD media require minimum spot size but position can be
more
precise
 The process of creating a signal suitable for transmission is called
modulation (modulate from Latin to regulate)

21. Channel Utilization
 Multiplexing
- Also known as MUX
- Resource distributor method
 Multiplexing techniques
- TDM (Time Division Multiplexing)
- FDM (Frequency Division Multiplexing)

22. Channel Utilization
 Radio Electromagnetic Spectrum
- Designated Frequency

23. Channel Errors
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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.

24. Transmitting Methodology
 Antenna required for transmission
- Antenna are designed for required frequency/various input parameters
- Devices which are capable to generate signal of required frequency set
- Static/Variable Oscillator
 Types of Oscillators
- Colpitts Oscillator
- Hartleys Oscillator
- Crystal Oscillator
- Voltage Controlled Oscillator (VCO)

25. Modulation
- Varying a property of a periodic waveform
- Basic types of Modulation (AM,FM,PM)

26. Modulation and Demodulation
 Usually modulators are installed at the transmitting end (Tx) and
demodulator at the receiving (Rx) end.
 Types of Filters (BS/BP/LF/HF)
 Designing of Filters using active and passive
components

27. Modulation
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 Modulation is the process of conveying a message signal, for example
a digital bit stream, inside another signal that can be physically
transmitted.
 Types of modulation:
1. Amplitude Modulation
2. Frequency Modulation
3. Phase Modulation
Amplitude of a carrier is varied to represent the data being
added to the signal.
frequency of the carrier waveform is varied to reflect the
frequency of the data.
Phase of the carrier waveform is varied to reflect the
frequency of the data.

28. Signal Type: Analog and Digital
- Difference
- Practical Noise Effect (Noise Immunity)
- Repetitive Generators

29. Analog and Digital Signal
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 A signal is any kind of physical quantity that conveys information
 An analog signal is a kind of signal that is continuously variable (The Signal Intensity
varies in a smooth fashion)
 A digital signal is a physical signal that is a representation of a sequence of discrete values
(The Signal Intensity maintains a constant level for some period and the abruptly changes
to another constant level).

30. Analog to Digital Conversion
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Analog
Signal
Sampling
Quantization
Encoding
Digital
Signal
• The Most Common technique for Analog to Digital Conversation is Pulse Code
Modulation (PCM)
• PCM is an analog signal is sampled to derive a data stream that is used to
modulate a digital carrier signal.
• PCM follows the three step process
1. Sampling of analog signal
2. Quantization of sampled signal
3. Encoding of Quantized Signal

31. Sampling
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 Sampling is the reduction of a continuous signal to
a discrete signal.
 Analog signals are sampled at a specific interval (i.e. Ts)
 Inverse of Sampling Interval is Sampling rate or sampling
Frequency. (i.e. fs= 1/Ts)
 There are three sampling methods:
1. Ideal sampling
2. Natural sampling
3. Flat-Top sampling

32. Sampling
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1. Ideal sampling
 Also Known as Impulse sampling.
 Practically not possible as the impulse width cannot be zero and generation of
impulse train cannot be easily implemented.
2. Natural sampling
 High speed switch is turned on for a short period when sampling occurs.
3. Flat-Top sampling
 Most commonly used
 Also known as sampling and Hold

33. Sampling
33
 Sampling Rate:
 What are the restrictions for sampling rate?
 Nyquist Theorem: The Sampling rate must be at least 2 times the
highest frequency contained in the signal.
 The Signal should be band limited.

34. Quantization
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 Quantization is the procedure of constraining
something from a continuous set of values (such as
the real numbers) to a relatively small discrete set (such
as the integers).

35. Quantization
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 Step for Quantization Process:
1. We assume that the signal has instantaneous amplitude b/w Vmin and Vmax.
2. We divide the range into L zones, with each height of Delta.
3. We assign quantized values of 0 to L-1 to the mid point of each zone.
4. We approximate the sample amplitude to quantized values.

36. Quantization and Encoding
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37. Analog to Digital Conversion
- Sampling
- Quantization

38. Pulse Code Modulation – A Digital Representation

39. Digital Transmission and Regeneration
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Simplest digital communication is binary amplitude-shift keying (ASK)
(a) binary signal input to channel; (b) signal altered by channel;
(c) signal + noise; (d) signal after detection by receiver

40. Characteristics and Resources of a Communication
System
 Signal Bandwidth
 Signal Power
 Channel Capacity
 Data Rate

41. Bandwidth
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 Bandwidth of a medium:
• The maximum capacity of the medium (e.g.: water pipe or data
communication cable) is it's bandwidth
• Every medium has a limited bandwidth.
• The limit on the bandwidth of the medium is due to its nature (physical
characteristics).
 Bandwidth of a signal:
• Difference between the highest and the lowest frequencies is called the
bandwidth of a signal
• A signal can be carried by a medium only if the bandwidth of the signal is
less than that of medium. That is why telephone/voice signal can be
transmitted over twisted wire pair but TV/video signals require co-axial
cable or an optical fiber

42. Trade off between Communication
Resources and System Performance

43. Signal to Noise Ratio / Capacity / Data Rate
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 Maximum data rate R is limited by signal power, noise power, distortion
 Without distortion or noise, we could transmit at R = ∞ and error
probably Pe = 0
 The channel capacity (1948, Claude Shannon) is the maximum possible data rate for a
system with noise and distortion
 This maximum rate can be approached with bit probability close to 0
 For additive white Gaussian noise (AWGN) channels (no distortion),
notes: B = bandwidth, SNR = voltage ratio
 This theoretical result does not tell how to design real systems and assumes that you have forever to decide
what bit was received. Engineers have spent the last 70 years trying to achieve speed approaching the
channel capacity.
 Shannon obtained C = 32 Kbps for telephone channels (B=3kHz, SNR~30dB)
 Get higher rates with video modems/DSL (They use much more bandwidth)

44. Telecommunication- Is the Future

45. Telecommunication- Is the Future

46. Telecommunication- Is the Future