1) Communication systems transmit and receive information through signals carried over various media like electrical, acoustic, optical or wireless channels. They involve a source that encodes a message, a transmission medium or channel, and a receiver that decodes the message. 2) Key aspects of communication systems include the signal, carrier, bandwidth, data transmission rate, noise level and signal-to-noise ratio. Common modulation techniques are amplitude modulation (AM), frequency modulation (FM) and digital encoding. 3) Communication media include electrical cables, optical fibers, radio waves and microwaves. Optical fibers use total internal reflection of light to transmit signals over long distances with high bandwidth. Wireless systems modulate properties of electromagnetic carriers like radio frequency

1. Communication systems

2. By
Professor AJAL A J
Head of Ekalavya
Academy
MOB: 8907305642
Communication
systems

3. Learning outcomes
• describe communication systems in terms of
– signal, carrier, noise, range, data transmission rate and bandwidth
– a source – journey – detector model, with transmitter and receiver
– modulation and demodulation (encoding and decoding)
• calculate the critical angle for total internal reflection using
Snell's law
• describe advantages and limitations of optical fibre systems
• describe amplitude modulation (AM), frequency modulation (FM)
and digital signals graphically and in words
• use a variety of appropriate experiments and simulations when
teaching about communications

4. Signal Examples
• Electrical signals --- voltages and currents in a circuit
• Acoustic signals --- audio or speech signals (analog or
digital)
• Video signals --- intensity variations in an image (e.g.
a CAT scan)
• Biological signals --- sequence of bases in a gene
• Noise: unwanted signal
:

5. Measuring Signals
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1 22 43 64 85 106 127 148 169 190 211 232 253 274 295 316 337 358 379 400 421 442 463 484 505 526 547 568 589 610 631 652 673 694 715
Period
Amplitude

6. Communication System
A B
Engineering System
Genetic System
Social System
History and fact of communication

7. What is a communications system?
• Communications Systems: Systems designed
to transmit and receive information
Info
Source
Info
Sink
Comm
System

8. Communication systems
system carrier signal carried as
hilltop beacons light on-off (fire or no fire)
telegraph electric current on-off (Morse code)
cable TV infrared in optical fibres ultra-fast (on-off) pulses
mob phone microwave ultra-fast (on-off) pulses
AM radio radio wave changing amplitude (AM)
FM radio radio wave changing frequency (FM)

9.  Signals are variables that carry information
 System is an assemblage of entities/objects, real or abstract,
comprising a whole with each every component/element
interacting or related to another one.
Systems process input signals to produce output signals
 Examples
i. Motion, sound, picture, video, traffic light…
ii. Natural system (ecosystem), human-made system
(machines, computer storage system), abstract system
(traffic, computer programs), descriptive system (plans)
Signal and System

10. Telecommunication
• Telegraph
• Fixed line telephone
• Cable
• Wired networks
• Internet
• Fiber communications
• Communication bus inside computers to
communicate between CPU and memory

11. Wireless Comm Evolution:
UMTS (3G)
http://www.3g-generation.com/
http://www.nttdocomo.com/reports/010902_ir_presentation_january.pdf

12. Communication s technologies
change

13. Communications: key terms
transmitter ……………........… receiver
encoding …………………….. decoding
modulation…………….... demodulation
All communication systems must contend with noise – unwanted
interference. Engineers consider signal-to-noise ratio.
Other parameters: data transmission rate, range, signal encoding.

14. Wireless Communications
• Satellite
• TV
• Cordless phone
• Cellular phone
• Wireless LAN, WIFI
• Wireless MAN, WIMAX
Bluetooth
Ultra Wide Band
Wireless Laser
Microwave
GPS
Ad hoc/Sensor Networks

15. Comm. Sys. Bock Diagram
)(~ tmTx
s(t)
Channel
r(t)
m(t)
Noise
Rx
Baseband
Signal
Baseband
Signal
Bandpass
Signal• “Low” Frequencies
• <20 kHz
• Original data rate
• “High” Frequencies
• >300 kHz
• Transmission data rate
Modulation
Demodulation
or
Detection

16. How transmissions flow over media
• Simplex – only in one direction
• Half-Duplex – Travels in either direction, but
not both directions at the same time
• Full-Duplex – can travel in either direction
simultaneously

17. Source–journey–detector
A useful model when describing communication systems
based on:
– visible light
– infrared
– microwaves
– radio waves

18. Coaxial Cable
•First type of networking
media used
•Available in different
types (RG-6 – Cable TV,
RG58/U – Thin Ethernet,
RG8 – Thick Ethernet
•Largely replaced by
twisted pair for networks

19. Unshielded Twisted Pair
 Advantages
Inexpensive
Easy to terminate
Widely used, tested
Supports many network
types
 Disadvantages
Susceptible to interference
Prone to damage during
installation
Distance limitations not
understood or followed

20. Glass Media
• Core of silica, extruded glass or plastic
• Single-mode is 0.06 of a micron in diameter
• Multimode = 0.5 microns
• Cladding can be Kevlar, fibreglass or even steel
• Outer coating made from fire-proof plastic
 Advantages
 Can be installed over long distances
 Provides large amounts of bandwidth
 Not susceptible to EMI RFI
 Can not be easily tapped (secure)
 Disadvantages
 Most expensive media to
purchase and install
 Rigorous guidelines for
installation

21. Wireless

22. Fibre optic systems use light
Infrared light is used more commonly than visible light - less
attenuation and dispersion.
A simple transmitter:
button cell & LED
A simple detector:
phototransistor + multimeter

23. Constructing optical fibres
Two kinds of fibre are used.
within a
building
long
distances

24. schematic diagram
SEP Optical transmission set

25. Total internal reflection
In general, when passing from one medium (refractive index n1) to
another medium (refractive index n2),
(Snell’s law)
At the critical angle,
In optical fibres, the cladding material typically has a refractive
index ~1% lower than that of the core, so critical angle is ~82o
2211
sinsin  nn 
1
2
2
o
21
o
21
sin
90sinsin
so,90and
n
n
nnn
c
c
c







26. Wireless communication
… use microwaves and radio waves
Demonstration: Creating a radio wave

27. A radio frequency (r.f.) carrier wave of fixed amplitude is generated.
Its amplitude varies once an audio frequency (a.f.) signal is added.
Amplitude modulation

28. Making a simple radio receiver
A: AM modulated radio wave
B: After diode rectification
C: The r.f. wave is filtered out, leaving a.f. signal

29. Modulating the amplitude of a carrier wave
Amplitude modulation

30. A radio frequency (r.f.) carrier wave of fixed amplitude is generated.
Its frequency varies once an a.f. signal is added.
Frequency modulation

31. Modulating the frequency of a carrier wave
Frequency modulation
SKE Physics 17

32. (pulse code modulation, PCM)
Digital encoding of a carrier wave
Digital encoding

33. close-up of part of the previous image
Digital encoding

34. Analogue to digital encoding
analogue signal sampling and encoding the
analogue signal.
Digitised values are in binary form, so the resolution is expressed
in bits. 8 bits encode an analogue value as one of 256 different
levels (28 = 256).

35. Resolution too lowSampling rate too low
Encoding requires a sufficiently high sampling rate & resolution.
Digital to analogue decoding

36. Any waveform can be accurately represented as a sum of sine
waves, each with its own frequency.
If some of the frequencies are lost, then so is some of the
information in the signal.
Spectrum analysis

37. Bandwidth
Each kind of signal contains a range of frequencies.
The higher the data rate, the larger the bandwidth and the higher
the frequency band needed.
Bandwidth costs money: e.g. monthly charges for your mobile
phone and Internet services
system spectrum width bandwidth
phone 900 - 1800 MHz 900 MHz
FM radio station 88.8 - 108.8 MHz 20 MHz

39. The Bands
VLF LF MF HF VHF UHF SHF EHF
Submillimeter
Range
ELF
3MHz 30MHz 300MHz 3GHz 30GHz 300GHz
Far
Infra-
Red
300KHz30KHz 3THz
300mm
Radio Optical
3KHz
Near
Infra-
Red
700nm
1PetaHz
R
e
d
O
r
a
n
g
e
Y
e
l
l
o
w
G
r
e
e
n
B
l
u
e
I
n
d
i
g
o
V
i
o
l
e
t
600nm 400nm500nm
Ultraviolet
1ExaHz
X-Ray
1500nm