Session 1
Introduction of Basic Communication System
Communication:
The imparting or exchanging of information by speaking, writing, or using some other medium.
Communication is the activity of conveying information through the exchange of ideas, feelings,
intentions, attitudes, expectations, perceptions or commands, as by speech, non-verbal gestures,
writings, behavior and possibly by other means such as electromagnetic, chemical or physical
Phenomena and smell. It is the meaningful exchange of information between two or more
participants (Machines, organisms or their parts).
Interchange of information from one place to other. Information can be different types such as
sound, Picture, music, computer data etc.
The importance of good communication
1.
Good communication is an essential tool in achieving productivity and maintaining
strong working relationships at all levels of an organization.
2.
Employers who invest time and energy into delivering clear lines of communication will
rapidly build up levels of trust amongst employees, leading to increases in productivity, output
and Morale in general.
3.
Poor communication in the workplace will inevitably lead to unmotivated staff that may
begin to question their own confidence in their abilities and inevitably in the organization.
The Elements of Communication System OR The Block Diagram of Communication
System:
Fig: Block diagram of the basic communication system.
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1.
Information or input signal: The information can be in the form of a sound signal like
speech or music or it can be in the form of pictures (TV signals) or it can be data information
coming from a computer.
2.
Input Transducer: Transducer convert any signal into a suitable electrical one.
Commonly used input transducer are microphone, TV camera etc.
3.
Transmitter: It’s function is to convert the electrical equivalent of the information to a
suitable form. It increases the power level (to cover a large range) of signal. It consist of
electronic circuits such as amplifier, Mixer, Oscillator & Power amplifier.
4.
Communication channel or Medium: It is the medium used for transmission of
electronic signal from one place to other. It can be conducting wire, cables, optical fiber or free
space.
Depending on type of communication medium two types of communication system will
exist they are
i.
Wired communication or line communication.
ii.
Wireless communication or Radio communication
5.
Noise: Noise is a random, undesirable electric energy that enters the communication
system via
the communication medium and interfere with the transmitted message.
It is an unwanted electrical signal which gets added to the transmitted signal. when it is
travelling towards the receiver.
It can be natural or man-made. Natural means lightening or radiation from sun & stars etc.
man-made means Automobile, welding machines, electric motors etc.
6.
Rceiver: It is exactly opposite process of transmission. The received signal is amplified,
Demodulated& converted into a suitable form.
It consists of electronic circuits like mixer, oscillator, detector or amplifier etc.
7.
Output Transducers: It converts the electrical signal at the output of the receiver back
to
the original form i.e.-sound or TV pictures etc.
eg- loudspeakers, Picture tubes, computer monitor etc.
Bandwidth Requirement:
The bandwidth is the frequency range over which an information signal is transmitted.
Bandwidth is the difference between the upper & lower frequency limits of the signals
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Type of signal
Range of frequency in HZ
Bandwidth in Hertz
Voice signal (speech) for
300-3400
3100
2
2
3
4
telephony.
Music signal
TV signals(picture)
Digital data
20-15000
0-5Mhz
300-3400
14980
5Mhz
3100
Actually the required bandwidth in the data transmission depends on the rate at which the data
is being transmitted. The BW increases with increase in the rate of data transmission.
IEEE Frequency Spectrum:
The information signal should be first converted into an electromagnetic signal before
transmission
because the wireless transmission takes place using electromagnetic waves.
The electromagnetic waves consist of both electric and magnetic fields. The electromagnetic
waves
can travel a long distance through space.
Fig: Complete Electromagnetic Spectrum.
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Session 2
Transmission Media
Transmission Media: A communication media is the medium over which information travel
from
sender to receiver.
Transmission Media
Wired media
Media)
Twisted
Pair
Wireless Media (Guided
(Unguided Media)
Coaxial
Cable
Optical
Fiber
Radio
Transmission
Infrared
Light
1.Twisted pair cable: It is cheaper than co-axial cable.
Unshielded Twisted pair (UTP):
These are very cheap and easy to install. But they are badly affected by noise interference.
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It can be used for either analog to digital transmission. The bandwidth supported by the wire
depends on the thickness of the wire and distance travelled. It supports several megabits/sec for
a few kilometers and have less cost.
Shielded Twisted Pair (STP):
It has a metal foil or braided mesh to cover each pair of insulating conductors.
This is known as metal shield. It reduces the interference of the noise, but makes the cable bulky
& expensive.
So practically UTP is more used than STP.
Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted
together for the purposes of canceling out electromagnetic interference (EMI) from external
sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and
crosstalk between neighboring pairs.
It was invented by Alexander Graham Bell.
Why to twist the wire?
A type of cable that consists of two independently insulated wires twisted around one another.
The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction.
While twisted-pair cable is used by older telephone networks and is the least expensive type of
local-area network (LAN) cable, most networks contain some twisted-pair cabling at some point
along the network. Other types of cables used for LANs include coaxial cables and fiber optic
cables.
Advantages

It is a thin, flexible cable that is easy to string between walls.

More lines can be run through the same wiring ducts.

Electrical noise going into or coming from the cable can be prevented.

Cross-talk is minimized.
Disadvantages

Twisted pair's susceptibility to electromagnetic interference greatly depends on the pair
twisting schemes (usually patented by the manufacturers) staying intact during the installation.
As a result,

Twisted pair cables usually have stringent requirements for maximum pulling tension as
well as minimum bend radius. This relative fragility of twisted pair cables makes the installation
practices an important part of ensuring the cable's performance.

In video applications that send information across multiple parallel signal wires, twisted
pair cabling can introduce signaling delays known as skew which cause subtle color defects and
ghosting due to the image components not aligning correctly when recombined in the display
device. The skew occurs because twisted pairs within the same cable often use a different
number of twists per meter in order to prevent crosstalk between pairs with identical numbers of
twists. The skew can be compensated by varying the length of pairs in the termination box, in
order to introduce delay lines that take up the slack between shorter and longer pairs, though the
precise lengths required are difficult to calculate and vary depending on the overall cable length.
Coaxial Cable:
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It consist of two concentric conductor separated by a dielectric material. The external conductor
is metallic braid and used for the purpose of shielding.
The wire mesh protects the wire from electromagnetic interference (EMI). A tough plastic jacket
forms the cover of the cable providing insulation and protection.
The co-axial cable was initially developed as the backbone of analog telephone networks where a
single telephone cable would be used to carry more than 10,000 voice channel at a time.
Coaxial cable or coax is a type of cable that has an inner conductor surrounded by a tubular
insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an
insulating outer sheath or jacket.
The term coaxial comes from the inner conductor and the outer shield sharing a geometric axis.
Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, who
patented the design in 1880. Coaxial cable differs from other shielded cable used for carrying
lower-frequency signals,
such as audio signals, in that the dimensions of the cable are controlled to give a precise,
constant conductor spacing, which is needed for it to function efficiently as a radio frequency
transmission line.
Application:
1. Analog Telephone Network.
2. Digital Telephone Network.
3. cable TV
4. Traditional LANs.
5. Digital Transmission.
6. Fast LANs
Optical Fiber Cable:
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It consist of an glass core surrounded by a glass core surrounded by a glass cladding which as a
lower refractive index.
Digital signals are transmitted in the form of intensity modulated light signal which is trapped in
the glass core. Light is launched into the fiber using a light source such as light emitting diode
(LED) or LASER.
It is detected on the other side using a photo detector such as a phototransistor.
Principle of light propagation in a fiber:
The light enters into a glass core fiber from one end, and get reflected within the fiber. It follows
a zigzag path along the length of the fiber.
Advantages:
1. Small size & light Weight.
2. Easy availability and low cost.
3. No electrical or electromagnetic interference.
4. Large Bandwidth.
5. No cross-talk inside the optical fiber cable.
6. Signal can sent upto 100 times faster.
7. Intermediate amplifier are not required as the transmission losses in the optical fiber are low.
8. Ground loops are absent.
9. Installations is easy as the fiber optic cable are flexible.
10. These cables are not affected by drastic environment conditions.
Disadvantages:
1. Sophisticated plants are required for manufacturing optical fiber.
2. The initial cost incurred is high.
3. Joining the optical fiber cable is a difficult job.
Applications:
1. The installation cost of optical fiber is higher than that for coaxial or twisted wire cable.
2. Optical fiber is now used in telephone system.
3. In the local area networks (LANs).
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Twisted Pair Cable
Co-axial cable
Affected due to external Less affected due to
magnetic field
external
magnetic
field
Short circuit between Short
circuit
two
conductor
is between
two
possible.
conductor
is
possible.
Cheapest
Moderately
Expensive
Can support low data Moderately
high
rates.
data rates.
Installation is easy
Installation is fairly
easy
EMI can take place
EMI is reduced due
to shielding
Noise immunity is low Higher
noise
therefore more distortion immunity
Transmission of the Transmission
of
signals take place in the signals take place
electrical form over the electrical form over
metallic
conducting the inner conductor
wires.
of the cable.
Optical fiber
Not affected due to
external magnetic field.
Short circuit between
two conductor is not
possible.
Expensive
Very high data rates.
Installation is difficult.
Emi is not present.
Highest
noise
immunity.
Signal transmission take
place in an optical form
over a glass fiber.
Infrared Transmission
1. Infrared transmission uses low frequency light waves (below the visible spectrum)
2. In order to carry the data through the air it should be a direct line-of-sight path between two
points
3. It is prone to interference, particularly from heavy rain, smoke, and fog that obscure the light
transmission
4. Unlike satellite and microwave systems, infrared is not bound by many government
regulations.
5. Transmitters are also quite small, it is easier to install and use.
6. It is used to transmit data between adjacent buildings.
Broadcast Radio
1. AM (AMPLITUDE MODULATION)
2. FM (FREQUENCY MODULATION)
3. Shortwave
4. CB (Citizens Band )
5. UHF (Ultra-High Frequency)
6. VHF (Very High Frequency)
7. Broadcast Radio Is Omnidirection
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8. AM Station Broadcast Its Signal A Longer Distance than FM.
9. Each Station Transmits Its Signal On A Different Frequency As Assigned by the FCC.
10 Television Station Transmit At Higher Frequencies Than Radio Stations. The Higher
Frequency is
Needed to Transmit the Picture plus sound.
11. The VHF Television Stations Transmit On Channels 2 Through
12. UHF Television Stations Transmit and Thing Above Channel 13.
13. VHF Travel Longer Distances and Produce A Stronger Signal
Microwave
1. Microwave transmission is unidirectional
2. It should be direct line-of-sight transmission
3. Because microwave signals approach the frequency of visible light waves, they show the same
characteristic as light waves, reflection, focusing, and refraction.
4. Microwave signals can be affected by rain and snow and by obstacles between the microwave
station
and by obstacles between the microwave stations.
5. Microwave is an extremely high frequency radio communication beam.
6. A microwave can carries hundreds of different simultaneous messages (data, video, voice, and
images)
7. It is most used for long distance data or voice transmission.
8. The most common type of microwave antenna is the parabolic "dish"
9. A typical size is about 10 feet in diameter.
10. Common frequencies used for transmission are in the range 2 to 40 Ghz.
11. Higher-frequency microwave is being used for short point-to-point links between buildings;
typically, the 22 Ghz band is used
12. At higher frequencies the antennas are smaller and cheaper.
13 microwave station are place approximately 25 to 30 miles apart.
14. Large cities are becoming microwave congested, and they do interfere with each other, and
the air
wave are saturated.
Satellite Microwave
1. A communication satellite is, in effect, a microwave relay station.
2. It is used to link two or more ground-based microwave transmitter/receivers, known as earth
stations or
ground stations
3. The satellite receives transmissions on one frequency band (uplink), amplifies or repeats the
signal, and
transmits it on another frequency (downlink)
4. In general two common configurations for satellite communication exist.
A. Point-to-point link between two distant ground-based antennas.
B. Communications between one ground-based transmitter and a number of ground-based
receivers.
5. Satellites are located at a fixed spot above the earth.
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6. The satellites are put into what is called a geosynchronous orbit, which is located at 22,300
miles above
the earth's surface.
7. At that height, the earth's gravity keeps the satellite in orbit at the same rate as earth.
8. Two satellites using the same frequency band, if close enough together will interfere with each
other.
9. To avoid this, current standards require a 4 degree spacing.
10. The signal from a satellite can only reach a certain part of earth, which is called footprint on
the earth.
11. Only earth station within the footprint on the satellite can recieve the transmission that
satellite.
12. One disadvantage of satellite transmission is the delay that occurs because the signal has to
travel out into space and back to earth (propagation delay)
13. The optimum frequency range for satellite transmission is in the range 1 to 10 Ghz.
Application
A. Television distribution
B. Long-distance telephone transmission
C. Private business networks
Session 3
Modulation& Its Different Scheme
Baseband Signal & Baseband Transmission:
The information or the input signal to a communication system can be analog i.e.- sound, picture
or it can be
Digital eg.- the computer data.
The electrical equivalent of this original information signal is known as the baseband signal.
It is the transmission of the original information signal as it is. However it is not possible
to use the
baseband transmission for the radio transmission. Thus it cannot be used for long distance
communication.
We have to use modulation for sending signal over long distances.
Modulation:
Modulating
Modulator
Modulator
Signal
Modulated
Signal
Carrier
Signal
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The modulating signal is nothing but the baseband signal for or Information signal while carrier
is a high
frequency sinusoidal signal.
Ex.- A person travels in his car or on his bike from once place to other. The person can be
viewed as the
modulating signal & the car or bike as the carrier.
Need of Modulation:The baseband transmission has many limitations which can be overcome using modulation.
In the process of modulation, the baseband signal is translated i.e. shifted from low frequency to
high
frequency. This frequency shift is proportional to the frequency of carrier.
Reasons for Using Modulation:1.
To reduce the height of antenna.
2.
To avoid the mixing of signals
3.
To increase the range of communication
4.
To make multiplexing possible
5.
To improve quality of reception
1.
To reduce the height of antenna.
For the transmission of radio signals, the antenna height must be a multiple of (λ/4). Here λ is the
wavelength,
λ = C/f
where, C is the velocity of light and
f is the frequency of the signal to be transmitted.
Therefore, the minimum height required to transmit a baseband signal of f = 10 KHz is
calculated.
Minimum Antenna = λ = C/4f = 3 X 108 /4 X 106 = 7500 meter = 7.5 km
The antenna of this height is practically impossible to install. Now consider a modulated signal
of f = 1 MHZ.
The minimum height is given by
Minimum Antenna = λ = C/4f = 3 X 108 / 4 X1 X 106 = 75 meter.
This antenna can be easily installed. Practically thus modulation is necessary to reduce the height
of antenna.
2.
To avoid the mixing of signals
If the baseband sound signals are transmitted without using the modulation by more than one
transmitter, then all the signals will be the same frequency range i.e. 0 to 20 KHz.
Therefore all the signals get mixed together & a receiver cannot separate them from each other.
So if each baseband sound signal is used to modulate a different corner then they will occupy
different slots in frequency domains (different channels).
Thus modulation is necessary to avoid mixing of signals.
3.
To increase the range of communication
The modulation process increases the frequency of the signal to be transmitted. Hence
modulation increases the range of communication.
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4.
To make multiplexing possible
Multiplexing is a process in which two or more signal can be transmitted over the same
communication channel. Simultaneously, this is possible only with the modulation. The
multiplexing allows the same channel to be used by many signals.
Therefore many TV channels can use the same frequency range without getting mixed with each
other.
5.
To improve quality of reception
With frequency modulation (FM) & the digital communication techniques like PCM, the effect
of noise is reduced to a great extent. This improves quality of reception.
Electronic Communication Systems
Analog
Communication Systems
AM
FM
Digital
Communication Systems
PM
PCM
(Pulse Code Modulation)
DM
(Delta Modulation)
Depending on which characteristics of which carrier is being changed the modulation systems
are classified as –
Modulation Systems
Amplitude Modulation
DSB-FC DSB- SC
SSB-SC
Angle Modulation Systems
VSB
FM
DSB-FC  Double Side Band Full Carrier
DSB-SC  Double Side band Suppressed Carrier
SSB –SC  Single Side Band Suppressed Carrier
FM  Frequency Modulation
PM  Phase Modulation
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PM
Amplitude Modulation (AM) :Amplitude modulation is the process of changing the amplitude of a high frequency carrier signal
in
Proportion with the instantaneous value of the modulating signal (Information).
In AM the instantaneous amplitude of the sinusoidal high frequency carrier is changed in
proportion to
the instantaneous amplitude of modulating signal.
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Note that frequency & phase of carrier remain constant.
Applications:
Radio Transmission
TV Transmission
Session 4
Amplitude Modulation
Mathematical Representation of an AM wave:It can be divided into two parts
1) Time Domain Description
2) Frequency Domain Description
Modulation Index or Modulation Factor:It is defined as the ratio of amplitude of the modulating wave to carrier wave.
Modulation Index = m =Em/Ec
when Em≤Ec , then Modulation Index ‘m’ has values between 0 & 1 and no distortion is
introduced in AM wave.
But if, Em≥Ec, then m>1, this will distort the shape of AM signal. This distortion is called “Over
Modulation”,
Modulation Index = Modulation Factor = Modulation Coefficient = Degree of Modulation
%Modulation = Em/Em*100
m is the dimensionless quantity.
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Time-Domain Description:Let modulating signal is represented as
em=EmCoswmt
where em = instantaneous amplitude of mod signal
ωm=2πfm
fm=frequency of the modulating signals
ee=EcCoswct
The AM wave is expressed as
eAM=ACos(2πfct)
where, A = instantaneous Amplitude of envelope
A = Ec + em = Ec + EmCos2πfmt
eAM = ACos2πfct
= (Ec + EmCos2πfmt) (Cos2πfct)
= Ec Cos2πfct + EmCos2πfmt Cos2πfct
= Ec [ 1 + Em/EcCos2πfmt ] Cos2πfct
Let m = Em/Ec
eAM = Ec
[ 1 + mCos2πfmt ]Cos2πfct
This expression represent the amplitude modulated (AM) signal in time domain.
Frequency Domain [Frequency Spectrum] of AM Wave:eAM = (Ec + EmCoswmt) (Coswct)
= Ec [ 1 + Em/EcCoswmt ] Coswct
m = Em/Ec
eAM = Ec [ 1 + mCoswmt ] Coswct
eAM = EcCoswct + m EcCoswmtCoswct
CosACosB = Cos (A+B) + Cos (A-B)
eAM = EcCoswct + mEc/2(Coswc + Coswm)t + mEc/2(Coswc - Coswm)t
(Carrier)
(USB)
(LSB)
The first term is nothing else but unmodulated carrier signal. The second term is a sinusoidal
signal at a frequency (Ec + Em). This is called UEB.
Its amplitude is mEc/2.
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Amplitude
Ec
(Carrier)
LSB USB
mEc/2
mEc/2
Frequency
0
fLSB fc
fUSB
(fc – fm) (fc + fm)
Bw= 2fm
Bandwidth Requirement
Bw= fLSB - fLSB = (fc + fm) - (fc – fm)
Bw= 2fm
Effect of Modulation Index on Modulated Wave
1. Linear Modulation or Under Modulation:
If m≤1 or if % modulation is less than 100% then type of modulation is linear.
2. Over Modulation:
If m<1,
It can introduce envelope distortion.
Ex. A modulating signal 10sin(2πx103t) is used to modulate a carrier signal 20sin(2πx104t). Find
modulation
index, percent modulation, frequencies of sideband components & their amplitudes. What is
bandwidth of the
modulated signal? Also draw spectrum of AM wave.
Solution:- The modulating signal em= 10sin(2πx103t)
Compare em= Emsin(2π x fmt)
We get Em= 10V, fm= 103Hz = 1KHz
Carrier signal ec= 20sin(2πx104t)
ec= Ec sin(2πfct)
We get Em= 20V, fc= 104Hz = 10KHz
Modulation Index m = Em/Ec=10/20 = 0.5 = 50%
Frequencies of side band components
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Upper Side Band, fUSB = fc + fm = 10+1 = 11KHz
Lower Side Band, fLSB = fc –fm = 10-1 = 9KHz
Amplitude of each side band = mEc/2 = 0.5*20/2 = 5V
Bandwidth = 2fm = 2x1 = 2KHz
Spectrum:
Carrier
LSB
5V
9
20V
USB
5V
10
Bw = 2KHz
Session 5
Frequency Modulation
Frequency Modulation:The modulating signal x(t) = EmCos(2πfmt)
The carrier signal c(t) = sine wave at much higher frequency
FM is a system of modulation in which the instantaneous frequency of the carrier is varied in
proportion with the amplitude of the modulating signal. The amplitude of the carrier signal
remain constant.
Thus information is conveyed via frequency.
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Time-Domain Display of FM wave
X(t) = EmCos(2πfmt) – Modulated Signal
ec = Asin(wct + φ) – Unmodulated Carrier
Frequency Deviation (ɗ):- It represent the maximum departure of the instantaneous frequency
fi(t) of the FM wave from the corner frequency fc
ɗ = kfEm
EFM = Ecsin[wct + mfsinwmt]
Modulation Index = Frequency Deviation/Modulating Frequrncy
mf = ɗ/fm
Equation of FM wave
eFM = Ecsin[wct + mfsinwmt]
Where, Ec = Peak amplitude of FM wave
Deviation Ratio = Maximum Deviation/Maximum Modulating Frequency
%Modulation = Actual Frequency Deviation/Maximum Allowed Deviation
Frequency spectrum of EM wave:eFM= J0(mf)Ecsinwct + J1(mf)Ec[sin(wc±wm)t + --Carrier
Pair of First Side Bands
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J0(mf)Ec
fc - fm
fc
fc + fm
Ideal frequency spectrum of FM
Band width
Bw = 2fm x Number of Significant Sidebands
= 2 [ɗ + fm(max)]
ɗ = frequency deviation
Session 6
Mobile Communication System
Mobile Communication System:(Cellular Concept):Cellular phone is wireless communication just like a cordless phone. In the cellular system, city
is divided into small areas called ‘cells’. Each cell is around 10 square kilometer (depend upon
the power of base station).
The cells are normally thought of hexagons. Because cell phones and base station use low power
transmitters, the same frequencies can be reused in non-adjacent cells.
Each cell is linked to central locations called the Mobile Telephone Switching Office (MTSO).
MTSO co-ordinates all mobile calls between an area comprised of several cell sites and the
central office.
Telephone
Central Office
MTSO
Cellular Network
MTSO  Mobile Telephone Switching Office
TCP  Telephone Central Office
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Landline
Phone
Cell – Basic Geographic Unit of a communication system is called as a cell
Cluster – A group of cells is called as cluster
Time & billing information for each mobile is accounted for by MTSO.
At the cell site base station is equipped to transmit, receive and switch calls to & from any
mobile unit within the cell to the MTSO.
Session 7
GSM
Sample Block-Diagram of GSM System:GSM – Global System for Mobile
OSS
MS
BSS
NSS
MSMobile Station
BSS  Base Station Subsystem
NSS  Network & Switching Subsystem
OSS  Operating Subsystem
Mobile Station (MS):It is used to support the connections of the external terminals such as PC or FAX.
Base Station Subsystem (BSS):It gets connected to MS through a radio interface. It also gets connected to NSS.
GSM use Open System Interconnection (OSS) model.
Network & Switching Subsystem (NSS):It used Intelligent Network (IN). A signaling NSS is one of the main switching functions of
GSM.
OSS
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BSS
NSS
PSTN
BSS
It is designed to manage the communication between GSM users & other communication user.
OSS  Operating Subsystem
PSTN  Public Switched Telephone Network
Operating Support Subsystem
BSS
NSS
Base Station Subsystem Network Switching Subsystem
GSM System Architecture
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PN
Public Network
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