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Transcript
REVIEW TO
COMMUNICATION SYSTEM
COMMUNICATION:
Transfer of Information from one place to
another.
Should be efficient, reliable, and secured.
COMMUNICATION SYSTEM:
components/subsystems act together to
accomplish information transfer/exchange

Need For Communication
2 main BARRIERS: Language & Distances

Importance of communication:
exchange of information between two parties
separated in distances in a more faster and
reliable way.
Brief History in Communication
Year
1844
1876
1904
1923
1936
1962
1966
1972
Events
Telegraph
Telephone
AM Radio
Television
FM Radio
Satellite
Optical links using laser and fiber optics
Cellular Telephone
Analog vs Digital
Analog
-Continuous Variation
-Assume the total range of frequencies/time
-All information is transmitted
 Digital
-Takes samples:-non continuous stream of
on/off pulses
-Translates to 1’s and 0’s

Analog vs Digital
(Advantages& Disadvantages)

Digital CS
Advantages:
-Inexpensive
-Privacy preserved(data encrypted)
-Can merge different data
-error correction

Analog Cs
Disadvantages:
-expensive
-No privacy preserved
-Cannot merge different data
-No error correction capability
Disadvantages:
-Larger bandwidth
-synchronization problem is
relatively difficult
Advantages:
-smaller bandwidth
-synchronization problem is
relatively easier.
Basic Requirements of
Communication System




Rate of information transfer:
-how fast the information can be transferred
Purity of signal received:
-whether the signal received is the same as the signal
being transmit
Simplicity of the system
-The simpler the system, the better
reliability
Elements of Communication
System(CS)
Elements of CS(cont’d)


Information source:
any source of information; i.e human voice,
music, etc
Input transducer:
convert message to a form suitable for the
particular type of communication system. Eg:
speech waves are converted to voltage
variation by a microphone
Elements of CS(cont’d)


Transmitter:
Processes input signal to produce a transmitted
signal that suited the characteristic of
transmission channel. Eg: modulation, coding,
mixing, translate
Other functions performed: Amplification,
filtering, antenna
Elements of CS(cont’d)

Channel(transmission media):
a medium that bridges the distance from
source to destination. Eg:Atmosphere (free
space), coaxial cable, fiber optics, waveguide
signals undergoes degradation from noise ,
interference and distortion
Elements of CS(cont’d)


Receiver: to recover the message signal
contained in the received signal from the
output of the channel, and convert it to a form
suitable for the output transducer. Eg:
superhetrodyne, mixing, demodulation,
decoding
Other functions performed: Amplification,
filtering.
Elements of CS(cont’d)


Output transducer:
converts the electrical signal at its input into a
form desired by the system used.
Eg:Loudspeaker, PC, and tape recorders, cd
burners
Simplex and Duplex



Simplex: a one way communication. Info
travels in one way directions. Eg: TV
broadcasting and radio.
Half duplex: two ways comm but only one
party can transmit in one time. eg:radio for
military, police, etc.
Full duplex: two ways, can transmit and
receive simultaneously. Eg:mobile phone.
Baseband Signals



Any original signals, regardless of whether it is
analog/digital, referred as base band signals.
In Comm Sys, some info signals may be
transmitted directly by themselves over the
medium or using modulation.
Putting the original signal directly to the
medium is called base band transmission.
Modulation Process
What is modulation?
-a process of changing one or more properties of
the analog carrier in proportion to the
information signal.In other word : Modulation
is the process of shifting a message signal to a
higher frequency.
 Techniques using modulation is called
broadband.

Modulation Process(cont’d)
Why modulation is needed?
-it is impractical to propagate information signals
over standard transmission media.Thus, the
signal need to be modulate with a higher
frequency, called the carrier. This carrier
signals will carry the information through the
system.

Noise, interference and distortion






Noise:unwanted signals that coincide with the desired
signals. Noise is random, undesirable electric energy.
Two type of noise:internal and external noise.
Internal noise: Caused by internal
devices/components in the circuits.
External noise:noise that is generated outside the
circuit. Eg: atmospheric noise,solar noise, cosmic
noise, man made noise.
Interference-one type of external noise
Distortion: signal being distorted
Limitations in communication
system
Physical constraint
-Delay, attenuation, bandwidth limitation, etc
 Technological constraint
- hardware.
- Expertise
- economy, law

EM Frequency Spectrum
electromagnetic spectrum: The range of frequencies of
electromagnetic radiation from zero to infinity.
EM Frequency
Spectrum(cont’d)
Various types of communication
system




Broadcast: radio and television
Mobile communications
Fixed communication system- land line
Data communication-internet
Frequency Spectrum &Bandwidth


The frequency spectrum of a waveform
consists of all frequencies contained in the
waveform and their amplitudes plotted in the
frequency domain.
The bandwidth of a frequency spectrum is the
range of of frequencies contained in the
spectrum.It is calculated by subtracting the
lowest frequency from the highest.
Frequency Spectrum &Bandwidth
(cont’d)


Bandwidth of the information signal equals to
the difference between the highest and lowest
frequency contained in the signal.
Similarly, bandwidth of communication
channel is the difference between the highest
and lowest frequency that the channel allow to
pass through it