This document discusses various concepts related to communication systems, including:
- The basic elements of a communication system are a transmitter that converts a signal, a channel or medium for transmission, and a receiver that converts the signal back. Noise can interfere with the transmitted information.
- Types of communication include one-way or two-way, analog or digital signals, and baseband or modulated signals. Serial and parallel transmission methods are also covered.
- Key concepts discussed include bandwidth, data rate, baud rate, Nyquist theorem, signal-to-noise ratio, error handling codes, Shannon's theorem, and the electromagnetic spectrum. Noise sources and types are also defined.
2. Importance of communication.
Elements of Communication System.
Types of Communication System.
Concept of Communication System-
◦ Signal bandwidth.
◦ Channel bandwidth.
◦ Data rate.
◦ Baud rate.
◦ Nyquist theorem
◦ Signal to noise ratio.
◦ Channel capacity.
◦ Error handling code-Hamming Code.
◦ Shannon theorem.
◦ Concept of Companding.
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3. Communication is the process of exchanging
information
Methods of communication:
1.Face to face
2.Written word (letters)
3.Electrical innovations:
Telegraph
Telephone
Radio
Television
Internet (computer)
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4. Basic Elements of Communication:
◦ Transmitter
◦ Channel or medium
◦ Receiver
Noise degrades or interferes with transmitted
information.
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5. Transmitter
◦ The transmitter is a collection of electronic components and
circuits that converts the electrical signal into a signal suitable
for transmission over a given medium.
◦ Transmitters are made up of oscillators, amplifiers, tuned circuits
and filters, modulators, frequency mixers, frequency
synthesizers.
Communication Channel
◦ The communication channel is the medium by which the
electronic signal is sent from one place to another.
◦ Types of media include
Electrical conductors
Optical media
Free space
System-specific media (e.g., water is the medium for sonar).
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6. Receivers
◦ A receiver is a collection of electronic components and circuits
that accepts the transmitted message from the channel and
converts it back into a form understandable by humans.
◦ Receivers contain amplifiers, oscillators, mixers, tuned circuits
and filters, and a demodulator or detector that recovers the
original intelligence signal from the modulated carrier.
Transceivers
◦ A transceiver is an electronic unit that incorporates circuits that
both send and receive signals.
◦ Examples are:
• Telephones
• Fax machines
• Handheld CB radios
• Cell phones
• Computer modems
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7. Noise
◦ Noise is random, undesirable electronic energy that enters the
communication system via the communicating medium and
interferes with the transmitted message.
◦ Noise is basically unwanted, undesired electrical signal along
with desire signal.
◦ Noise is actually a random character.
◦ Sometimes Noise also produced in receiver.
◦ Generally noise comes from atmosphere.
◦ Natural phenomenon that gives rise to noise includes electric
storms, solar flares and various kinds of radiation In space.
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8. Types of Noise-
1. External Noise-Noise created outside of receiver. Difficult to
remove(prefer to move system location). That is main reason radio
telescope always located away from industrial area.
2. Atmospheric Noise- it is a natural noise.
3. Industrial Noise
4. Man made Noise
5. Internal Noise
i. Shot noise
6. Low Frequency/Flicker Noise
7. Extraterrestrial Noise
i. Space noise
ii. Cosmic noise
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9. Electromagnetic Spectrum-
The range of electromagnetic signals encompassing all frequencies
is referred to as the electromagnetic spectrum.
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10. Extremely Low Frequencies (ELF) 30–300 Hz.
Voice Frequencies (VF) 300–3000 Hz.
Very Low Frequencies (VLF) 3K-30K
Low Frequencies (LF) 30–300 kHz.
Medium Frequencies (MF) 300–3000 kHz
High Frequencies (HF) 3–30 MHz
Very High Frequencies (VHF) 30–300 MHz
Ultra High Frequencies (UHF) 300–3000 MHz
Super High Frequencies (SHF) 3-30 GHz
Extremely High Frequencies (EHF) 30-300 GHz
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11. Frequency and Wavelength:
Frequency
◦ Frequency is the number of cycles of a repetitive wave that
occur in a given period of time.
◦ Frequency is measured in cycles per second (cps).
◦ The unit of frequency is the hertz (Hz).
Wavelength
◦ Wavelength is also the distance traveled by an electromagnetic
wave during the time of one cycle.
◦ The wavelength of a signal is represented by the Greek letter
lambda (λ).
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12. Wavelength (λ) = speed of light ÷ frequency
Speed of light = 3 × 108 meters/second
Therefore:
λ = 3 × 108 / f
Example:
◦ What is the wavelength if the frequency is 4MHz?
λ = 3 × 108 / 4 MHz
= 75 meters (m)
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13. Types of Electronic Communication
Electronic communications are classified according to whether they
are
1. One-way (simplex) or two-way (full duplex or half duplex)
transmissions
2. Analog or digital signals.
3. Base band/ Modulated signal Communication.
1. Simplex-
◦ The simplest method of electronic communication is referred to
as simplex.
◦ This type of communication is one-way. Examples are:
Radio
TV broadcasting
Beeper (personal receiver)
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14. 2. Half Duplex
◦ The form of two-way communication in which only one party
transmits at a time is known as half duplex. Examples are:
Police, military, etc. radio transmissions
Citizen band (CB)
Family radio
Amateur radio
3.Full Duplex
◦ Most electronic communication is two-way and is referred to as
duplex.
◦ When people can talk and listen simultaneously, it is called full
duplex. The telephone is an example of this type of
communication.
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15. 4.Base band/ Modulated signal Communication.
o The original information signal is known as baseband signal.
o It may analog or digital.
o If original voice, video or digital signal is transmitted through medium then it
is referred as base band signal.
o In telephone line and intercom communication system, voice itself is placed
on wire and transmitted over some distance.
o In PC-PC communication, direct digital signal is transmitted through coaxial
cable.
o In many cases we can not transmit original signal as it is, we need to
process it first, known as Modulation.
o Technique using modulation are called as Broad band.
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16. Signals used in Communication-
2. Analog Signals
◦ An analog signal is a smoothly and continuously varying
voltage or current. Examples are:
Sine wave
Voice
Video (TV)
Digital Signals
◦ Digital signals change in steps or in discrete increments.
◦ Most digital signals use binary or two-state codes. Examples
are:
Telegraph (Morse code)
Continuous wave (CW) code
Serial binary code (used in computers)
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17. Serial Transmission
o Bits are transmitted serially one after the other.
o In serial transmission one bit follows another, only one bit of data
is transmitted on each clock.
o We need only one channel rather than n transmission lines to
transmit data between two communicating devices.
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18. Advantages:
o one communication line reduces the cost of transmission over
parallel by roughly a factor of n.
Disadvantages:
o It is slow method as one bit at a time is transmitted.
o As communication within devices is parallel, we require
conversion devices at the interfaces.
o A. We required parallel to serial converter at the interface
between the sender
o B. and the channel, and parallel-to-serial converter between the
channel and the receiver
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19. Types of serial communication:
1. Synchronous serial communication-
Single clock pulse is shared between transmitter and receiver.
Data is sent in the form of Frames.
Data transfer rate is high.
Cost effective.
Easy and simple circuit design.
No gap in data.
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20. Types of serial communication:
2. Asynchronous serial communication-
Separate clock pulse is shared between transmitter and receiver.
Data is sent in the form of characters/bytes.
Data transfer rate is lower than synchronous transmission.
Costly.
Complex circuit design.
Gap in data.
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21. Parallel Transmission-
o One can send data as n bits at a time instead of single bit
o The processes of sending and receiving data in group of bits is called
parallel transmission.
o The mechanism for parallel transmission use n wires to send n bits at one
time.
o All n bits are transmitted with each clock pulse. Parallel transmission is used
for small distances.
o Figure below shows how parallel transmission works for n =8. Typically, the
eight wires are bundled in a cable.
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Advantages of parallel transmission:
o The advantage of parallel transmission is speed.
o n bits are transmitted simultaneously with a single clock.
Disadvantages of Parallel transmission:
o Not a cost effective method for long distance
communications as it requires n communication lines to
transmit the data stream.
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Concept of communication system-
1. Bandwidth (BW) -
o It is that portion of the electromagnetic spectrum occupied by a
signal.
o Also referred as Signal bandwidth.
o The bandwidth of a signal is defined as the difference between
the upper and lower frequencies of a signal generated.
o BW= F2-F1
25. 2. Channel bandwidth-
o The range of frequencies required to transmit desired information
is called as Channel capacity.
o The channel bandwidth of a wireless signal determines that
signal’s data rate. The higher the channel bandwidth, the faster
the connection.
3. Channel capacity-
o it is the upper bound on the rate at which information can be
reliably transmitted over a communication channel.
o It is expressed in bits per second is twice the channel bandwidth in
Hertz.
o Maximum channel capacity--- C=2B.
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26. 4. Data rate and Baud Rate-
Data Rate-
o The speed of data transfer is usually indicated by number of bits
per second (bit/s).
o Data rate is reciprocal of time duration of one bit (Tb).
o Data rate= 1/ Tb.
Baud Rate-
o Number of signaling elements or symbols that occer in the time
interval of 1 second.
o In the serial port context, "9600 baud" means that the serial port is
capable of transferring a maximum of 9600 bits per second.
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27. 6. Signal to noise ratio- The unwanted signal that associate with
the desired signal is called as noise.
o The relative strength of signal and noise is given by the term
signal to noise ratio.
o If the signal and noise power are known, S/N ratio can be
calculated.
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28. 5. Nyquist Theorem-
o Signal can be exactly reproduced if it is sampled at the rate fs which is
greater than twice the maximum frequency W.
o 20kfS=2W(input freq10k)
o Minimum sampling frequency of twice the heighest modulating signal
frequency known as Nyquist rate.
o Sampling is defined as, The process of measuring the instantaneous values
of continuous-time signal in a discrete form.
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29. It is usually expressed in decibels(dB).
If receiver has an input signal power of 1.5uW and noise power is 0.2uW
then S/N ratio is-
S/N=10 log 1.5/0.2
=10 log (2)
=0.3010dB.
7. Noise Figure: Also called as “Noise Factor”. Used to express noise in
receiver.
Ideally receiver contributes zero noise,so ideal receiver has noise figure of 1 or
0 dB, but practically it is not possible, so lower the noise figure, better the
receiver.
Noise figure is given by formula:
F=
𝑺
𝑵
𝑰𝒏𝒑𝒖𝒕
𝑺
𝑵
𝑶𝒖𝒕𝒑𝒖𝒕
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30. Shannon theorem- It is related to random noise.
It gives relation between bandwidth, channel capacity, noise.
Maximum capacity of an ideal channel is given by-
C=B Log2 (1+S/N)
C= Channel capacity
B=Bandwidth
S/N= Signal to noise ratio
E.g- Telephone line have bandwidth 3100Hz S/N ratio-30dB.
Max channel capacity is C=2B
i.e C=2*3100
=6200bps. (When there is no noise present.)
Convert S/N ration which is in dB into power as-
dB=10log P
P=ln(dB/10)
P=ln(30/10)
P=ln(3)
P=1000
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31. Channel capacity-
C=B Log2 (1+S/N)
C=3100 Log2(1+1000)
C=3100*9.97
C=30907bps
C=31000bps.
This is the channel capacity when there is noise which is present in
communication channel.
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