Telecommunications, also known as telecom, is the exchange of information over significant distances by electronic means and refers to all types of voice, data and video transmission. This is a broad term that includes a wide range of information-transmitting technologies and communications infrastructures, such as wired phones; mobile devices, such as cellphones; microwave communications; fiber optics; satellites; radio and television broadcasting; the internet; and telegraphs.
A complete, single telecommunications circuit consists of two stations, each equipped with a transmitter and a receiver. The transmitter and receiver at any station may be combined into a single device called a transceiver. The medium of signal transmission can be via electrical wire or cable -- also known as copper -- optical fiber, electromagnetic fields or light. The free space transmission and reception of data by means of electromagnetic fields is called wireless communications.
Types of telecommunications networks
The simplest form of telecommunications takes place between two stations, but it is common for multiple transmitting and receiving stations to exchange data among themselves. Such an arrangement is called a telecom network. The internet is the largest example of a telecommunications network. On a smaller scale, examples include the following:
corporate and academic wide area networks (WANs);
telephone networks;
cellular networks;
police and fire communications systems;
taxi dispatch networks;
groups of amateur (ham) radio operators; and
broadcast networks.
Data is transmitted in a telecommunications circuit by means of an electrical signal called the carrier or the carrier wave. In order for a carrier to convey information, some form of modulation is required. The mode of modulation can be categorized broadly as analog or digital.
In analog modulation, some aspect of the carrier is varied in a continuous fashion. The oldest form of analog modulation is amplitude modulation (AM), which is still used in radio broadcasting at some frequencies. Digital modulation actually predates AM; the earliest form was Morse code. Modern telecommunications use internet protocols to carry data across underlying physical transmissions.
Telecommunications industry and service providers
Telecommunications systems are generally run by telecommunications service providers, also known as communications service providers. These providers historically offered telephone and related services and now offer a variety of internet and WAN services, as well as metropolitan area network (MAN) and global services.
In many countries, telecom service providers were primarily government-owned and -operated. That is no longer the case, and many have been privatized. The International Telecommunication Union (ITU) is the United Nations (UN) agency that administers telecommunications and broadcasting regulations, although most countries also have their own government agencies to set and enf
Working Principle of Echo Sounder and Doppler Effect.pdf
chapter 2-part 2.pdf
1. Principles of Communicartion System by N Hasan
For updated version, please click on
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Principles of Communication
Systems
Chapter 2 (part 2): AM Variations
by
Nurulfadzilah Hasan
Faculty of Electrical & Electronics Engineering
nurulfadzilah@ump.edu.my
For updated version, please click on
http://ocw.ump.edu.my
2. Principles of Communicartion System by N Hasan
Chapter 2
2.4 Double side band, single side band and
vestigial side band
2.5 Suppressed carrier AM
3. Principles of Communicartion System by N Hasan
Learning Outcomes
• By the end of this chapter, you should be able
to:
• Solve problems involving AM: SSB, DSB and VSB
• Compare SSB transmission to conventional DSB
4. Principles of Communicartion System by N Hasan
Full carrier AM: Frequency Domain
carrier Lower side bands Upper side bands
5. Principles of Communicartion System by N Hasan
Power Relationship
LSB
USB
c
T P
P
P
P
%
100
T
SB
P
P
Transmission efficiency, η for AM:
%
100
2
%
100
2
1
2
2
2
2
2
m
m
m
P
P
m
c
c
c
c
c
LSB
USB
SB P
m
P
m
P
m
P
P
P
2
4
4
2
2
2
6. Principles of Communicartion System by N Hasan
If m = 1 (100% modulation),
• the average power,PSB = 50% Pc= Pc/2
• Transmission efficiency becomes:
%
33
.
33
%
100
1
2
1
%
100
2 2
2
m
m
Power Relationship
7. Principles of Communicartion System by N Hasan
AM power efficiency Problems:
• Information are contained in the sidebands, not in the
carrier
• But carrier signal occupies 67% of total power: most of
the power is wasted in the carrier signal
• Also, the upper and lower sidebands are mirror images
of each other: carries exactly the same information.
• SOLUTION?
– remove the carrier and/or one of its sidebands
• Suppressed Carrier AM System
– Remove one of the sidebands
• Single sideband AM system
10. Principles of Communicartion System by N Hasan
DSB Suppressed Carrier (DSBSC)
Generated by circuit called balanced modulator where it produces
sum (fusb) and difference (flsb) freq but cancel or balance out the
carrier (fc).
10
DSBSC helps in reducing power but bandwidth still the same as DSBFC.
fusb)
flsb fc
No carrier
Power (W)
Frequency (Hz)
11. Principles of Communicartion System by N Hasan
Suppressing the carrier
Double-sideband suppressed carrier (DSSC or
DSB) envelope:
Suppressed carrier AM signal
Full carrier AM signal
12. Principles of Communicartion System by N Hasan
AM DSBSC Equation:
t
mE
t
mEc
t
v m
c
c
m
c
DSBSC
cos
2
cos
2
)
(
t
mE
t
mEc
t
Ec
t
v m
c
c
m
c
c
DSBSC
cos
2
cos
2
sin
)
(
From full AM equation:
Remove the carrier signal, the equation becomes:
13. Principles of Communicartion System by N Hasan
AM DSBSC Power distribution
R
E
R
E
R
E
R
E
R
E
R
V
R
V
P
P
P
m
m
m
m
m
USB
LSB
USB
LSB
T
rms
rms
4
8
8
2
2
2
2
2
2
2
2
2
2
2
In DSBSC, all the power
transmitted is sidebands
power.
If R = 1 ohm.
4
2
m
T
E
P
SB
T P
P
Therefore the efficiency, η = 100%
15. Principles of Communicartion System by N Hasan
AM SSBSC Equation:
t
mEc
t
v m
c
LSB
cos
2
)
(
t
mE
t
mEc
t
Ec
t
v m
c
c
m
c
c
DSBSC
cos
2
cos
2
sin
)
(
From full AM equation:
Remove the carrier signal, and one of the sideband, the
equation becomes:
t
mE
t
v m
c
c
USB
cos
2
)
(
LSB:
USB:
17. Principles of Communicartion System by N Hasan
c
m
c
)
(V
Amplitud
)
( 1
rads
0
2
m
A
m
m
A
USB
Modulating Band
c
)
(V
Amplitud
)
( 1
rads
m
c
0
2
m
A
m
m
A
LSB
Modulating Band
Frequency domain
SSB signals
18. Principles of Communicartion System by N Hasan
SSB: Signal Power Considerations
R
E
R
E
P
P
m
m
LSB
T
8
2
2
2
2
R
E
R
E
P
P
m
m
USB
T
8
2
2
2
2
OR
Therefore the efficiency, η = 100%
Theoretically,
19. Principles of Communicartion System by N Hasan
SSB: Signal Power Considerations
• In SSB, the transmitter output is better expressed in
terms of peak envelope power (PEP), the maximum
power produced on voice amplitude peaks.
• Carrier power is useless as a measure of the power in a
DSBSC or SSBSC signal
• Why? Because it carrier power is theoretically zero.
• Instead, the peak envelope power (PEP) is used
20. Principles of Communicartion System by N Hasan
Peak Envelope Power
• It is simply the power at
modulation peaks, calculated
using RMS formula:
=
PEP = peak envelope power in Watts
Vp = peak signal voltage in volts
RL = load resistance in ohms
21. Principles of Communicartion System by N Hasan
Vestigial sideband (VSB) transmission
• Vestigial sideband (VSB) transmission : Modified AM
transmission in which one sideband, the carrier, and only a
portion of the other sideband are transmitted
• This kind of signal is used in TV transmission.
• The BW is typically 25% greater than that of SSBSC.
R
V
Pc
2
Amplitude
Modulating
signal, fm usb
lsb P
P
4
2
m
P
P c
usb
lsb
c
c
t P
P
m
P
P
4
2
f
VSB
22. Principles of Communicartion System by N Hasan
For updated version, please click on
http://ocw.ump.edu.my
Collaborative authors:
Nurulfadzilah Binti Hasan
Noor Zirwatul Ahlam Binti Naharuddin
Norhadzfizah Binti Mohd Radi
Mohd Hisyam Bin Mohd Ariff
Faculty of Electrical & Electronics Engineering,
UMP
