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Communication
Theory-2
Assoc. Prof. Hakan DOĞAN
Department of Electrical and Electronics Engineering
Source
Destination
Telephone, Radio, Television, Radar, Sonar, Telemeter, ...
In electronics and telecommunications, modulation is the process of varying
one or more properties of a high-frequency periodic waveform, called the
carrier signal, with a modulating signal which typically contains information to
be transmitted.
In telecommunications, modulation is the process of conveying a message
signal, for example a digital bit stream or an analog audio signal, inside
another signal that can be physically transmitted. Modulation of a sine
waveform is used to transform a baseband message signal into a passband
signal, for example low-frequency audio signal into a radio-frequency signal
(RF signal).
Transmitting very low frequencies require antennas with miles in wavelength
When free space is the communication channel, antennas radiate and receiver
the signal. Theory shows that the antennas operate effective only when their
dimensions are of the order of the magnitude of wavelength of the signal being
transmitted.
The condition for resonance in a linear dipole antenna is usually that the
electrical length be equal to a multiple of a half-wavelength, λ/2, while for a
monopole antenna it is a multiple of a quarter-wavelength, λ/4.
Vertical Dipole: Monopole, Quarter-wavelength, Marconi
In simplest terms, the antenna current must be zero at both ends of a half wave
antenna, these are called the current nodes. But where the current nodes are
zero, the voltage anti-nodes are at maximum. So you have voltage maximums
at both ends of the half wave antenna causing the maximum possible antenna
current to flow and the maximum amount of electromagnetic radiation from the
antenna. For that reason the half wave antenna is considered to be the most
efficient.
In general, an antenna should not be shorter than a half wavelength long, but
you will find exceptions to this especially at very low frequencies and long
wavelengths where even a half wave antenna would be too long to be
physically practical. One solution is to use a quarter wave antenna and ground
one end, letting the ground act as the other quarter wave, so you still have a
half wave antenna. This is known as the Marconi antenna.
A monopole antenna is a class of radio antenna consisting of a straight
rod-shaped conductor, often mounted perpendicularly over some type of
conductive surface, called a ground plane.
Audio is in the range approx. 30 - 20 kHz.
If an electromagnetic signal with a frequency of 30 Hz is transmitted it will have a
wavelength of (speed of light /frequency) = 300,000/30 km = 10,000 km.
To pick up this signal an aerial of size approx. 2,500 km will be required –
impractical.
If this signal is used to modulate a carrier of 1 MHz the wavelength will be
300,000/1,000,000 km = 300 m, and an aerial of 75 m will suffice.
If the carrier is 100 MHz, the wavelength is 3 m and a 75 cm aerial is sufficient.
So, then the connection between the frequency and the size of the
antenna, the higher the frequency the lower the antenna size.
Therefore, modulation is necessary in order to shift frequency
components of the baseband signal around the frequency of the carrier
signal
The ability of different users sharing a medium (multiple access)
A large number of radio transmitters are trying to transmit at the same time. It is
necessary for the receiver to pick up only the wanted signal and to reject the
rest.
One way to do to this is to assign a carrier with a known frequency to each
transmitter, modulate this carrier with the signal, and then design the receiver
to pick up only that known carrier frequency and reject the rest, using
appropriate filtering methods. Then the original signal is removed from the
received carrier.
Frequency division multiplexing (To support multiple transmissions via a single
channel). To avoid interference
Amplitude modulation
Telemetre
A telemeter is a device used to remotely measure any
quantity. It consists of a sensor a transmission path and a
display, recording, or control device
Radar(Radio Detecting And Ranging)
Radar is an object detection system which uses radio waves
to determine the range, altitude, direction, or speed of objects.
Sonar (Sound Navigation And Ranging)
Sonar is a technique that uses sound propagation (usually
underwater, as in submarine navigation) to navigate,
communicate with or detect objects on or under the surface of
the water, such as other vessels.
Some factors for Wireless Communication
The total number of sources
The total number of users
Distance
Mobility
Security
Input Signal
Input
Transducer
Input Message
Source
Transmitter
Transmitted Signal
Transmission
Medium
Unwanted
effects
Received Signal
Output Signal
Receiver
Output
Transducer
Ouput Message
Destination
Representation of Modulation Signals
Bandpass signals (signals with small bandwidth compared to carrier
frequency) can be represented in any of three standard formats:
Converts a nonelectrical “input message” into an “electrical”
input signal (microphone, video camera, photocell, thermocouple, displacement
gauge, etc.) The input signal can also be referred as the “baseband signal”
Microfon
Output Transducer: Converts the electrical signals into its Original form as needed by
the user. A loudspeaker and a picture tupe are the most familiar examples of the
output transducer.
Modifies the the baseband signal for efficient transmission
Analog Modulation : AM, FM, PM
Digital Modulations: BPSK, QPSK, 16-QAM, 64 QAM
The medium through which transmitter
output is sent.
Responces the signal from the channel
modifications made at the transmiter and the channel.
by undoing the signal
Twisted pair
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.
Coaxial cable, or coax, has an inner conductor surrounded by a flexible,
tubular insulating layer, surrounded by a tubular conducting shield. The
term coaxial comes from the inner conductor and the outer shield sharing a
geometric axis.
Coaxial Cable
Waveguide : A waveguide is a structure which guides waves, such as
electromagnetic waves. The original and most common meaning is a hollow
conductive metal pipe used to carry high frequency radio waves, particularly
microwaves.
An Optical Fiber
Fiber-optic communication is a method of transmitting information from one
place to another by sending pulses of light through an optical fiber. The light
forms an electromagnetic carrier wave that is modulated to carry information
Wireless communication is the transfer of information between two or more
points that are not connected by an electrical conductor.
The most common wireless technologies use electromagnetic wireless
telecommunications, such as radio. With radio waves distances can be short,
such as a few metres for television remote control, or as far as thousands or
even millions of kilometres for deep-space radio communications.
IEEE.802.11
IEEE.802.16
IEEE 802.11 is a set of standards for implementing wireless local area network
(WLAN) computer communication in the 2.4 and 5 GHz frequency bands. They
are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE
802).
802.11g
2.4-2.5 GHz
19 Mbit/s
35 meter
54 Mbit/s
110 meter
The Institute of Electrical and Electronics Engineers (IEEE, read
I-Triple-E) is a professional association headquartered in New York
City that is dedicated to advancing technological innovation and
excellence
IEEE 802.16 is a series of Wireless Broadband standards authored by the
Institute of Electrical and Electronics Engineers (IEEE). The IEEE Standards
Board established a working group in 1999 to develop standards for broadband
for Wireless Metropolitan Area Networks.
Wireline
Wireless
LIMITS
1- Noise
2- Distortion
3- Signal to Noise Ratio-SNR
4- Attenuation
5- Channel
6- Interference
A distortion is the alteration of the original shape (or other characteristic) of
waveform.
Attenuation is an important consideration in the modern world of wireless
telecommunication. Attenuation limits the range of radio signals and is
affected by the materials a signal must travel through (e.g., air, wood,
concrete, rain).
Path loss (or path attenuation) is the reduction in power density
(attenuation) of an electromagnetic wave as it propagates through space.
Path loss is a major component in the analysis and design of the link
budget of a telecommunication system.This term is commonly used in
wireless communications and signal propagation.
In physics, interference is a phenomenon in which two waves superimpose
to form a resultant wave of greater or lower amplitude.
Co-channel interference or CCI is crosstalk from two different
radio transmitters using the same frequency. There can be
several causes of co-channel radio interference;
Adjacent-channel interference (ACI) is interference caused by
extraneous power from a signal in an adjacent channel. ACI may
be caused by inadequate filtering (such as incomplete filtering of
unwanted modulation products in FM systems), improper tuning
or poor frequency control (in the reference channel, the
interfering channel or both).
Noise : AWGN (Additive White Gaussian Noise)
“internal noise sourses”
Signal to Noise Ratio (SNR)
*Thermal noise
*Shot noise
“external noise”
* Solar intergalactic radiation
*Thunderbolts and lightninings
*Fluorescent lamps
*Running electrical motor