introduction & wireless transmission
DESCRIPTION
TRANSCRIPT
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Simplified Reference Model
Application
Transport
Network
Data Link
Physical
Medium
Data Link
Physical
Application
Transport
Network
Data Link
Physical
Data Link
Physical
Network Network
Radio
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Reference Model
Physical Layer :Bit Stream to signal conversionFrequency selectionGeneration of carrier frequencyData modulation over carrier frequencyData encryption
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Reference Model
Data Link Layer :Data Multiplexing Error detection and correctionMedium Access
In essence :Reliable point-to-point transfer of data
between sender and receiver.
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Reference Model
Network Layer :Connection setupPacket routingHandover between networksRoutingTarget device locationQuality of service (QoS)
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Reference Model
Transport Layer :Establish End-to-End ConnectionFlow controlCongestion controlTCP and UDPApplications – Browser etc.
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Reference Model
Application Layer:Multimedia applicationsApplications that interface to various
kinds of data formats and transmission characteristics
Applications that interface to various portable devices
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Overlay Networks - the global goal
regional
metropolitan area
campus-based
in-house
verticalhandover
horizontalhandover
integration of heterogeneous fixed andmobile networks with varyingtransmission characteristics
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Frequency Ranges
WIRELESS TRANSMISSION
1 Mm300 Hz
10 km30 kHz
100 m3 MHz
1 m300 MHz
10 mm30 GHz
100 m3 THz
1 m300 THz
visible lightVLF LF MF HF VHF UHF SHF EHF infrared UV
optical transmissioncoax cabletwisted pair
VLF = Very Low Frequency UHF = Ultra High Fequency
LF = Low Frequency SHF = Super High Frequency
MF = Medium Frequency EHF = Extra High Frequency
HF = High Frequency UV = Ultraviolet Light
VHF = Very High Frequency
wave length , speed of light c 3x108m/s, frequency f
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Frequencies
kHz Range (Low and Very Low frequencies)
Used for short distances using twisted copper wires
Several KHz to MHZ (Medium and High Frequencies)
For transmission of hundreds of radio stations in the AM and FM mode
Use co-axial cables Transmission power is several kW.
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Frequencies
Several MHz to Terra Hz Range (VHF and UHF)Typically 100 MHz to 800 MHz and
extending to terraHz) Conventional Analog TV (174-230 MHz
and 470-790 MHz) DAB Range (220 – 1472 MHz) DTV (470 – 872 MHz)Digital GSM (890-960MHz)
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Frequencies
3G Mobile Systems (1900-2200 MHz)
Super High(SH) and Extremely Super High(ESH) Hundreds of GHz Fixed Satellite Services Close to infra-red.
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Frequencies
For Several TerraHz : Optical Transmission
Why do we need very high transmission frequencies?
The information content in video, satellite data etc is enormous.
If we need to accommodate many signals simultaneously, we need a high bit rate which in turn demands high frequency.
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REGULATIONS
International Telecommunications Union (ITU), Geneva responsible for world-wide coordination of telecommunications activity.
ITU – R (Radio Communications sector) handles standardization in Wireless sector.
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REGULATIONS
ITU-R
Region-1
Europe, Middle East, Former Russia, Africa
Region-2
Greenland, N & S America
Region-3
Australia, New Zealand
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Frequency Allocation
Europe USA Japan
Cellular Phones
GSM 450-457, 479-486/460-467,489-496, 890-915/935-960, 1710-1785/1805-1880 UMTS (FDD) 1920-1980, 2110-2190 UMTS (TDD) 1900-1920, 2020-2025
AMPS, TDMA, CDMA 824-849, 869-894 TDMA, CDMA, GSM 1850-1910, 1930-1990
PDC 810-826, 940-956, 1429-1465, 1477-1513
Cordless Phones
CT1+ 885-887, 930-932 CT2 864-868 DECT 1880-1900
PACS 1850-1910, 1930-1990 PACS-UB 1910-1930
PHS 1895-1918 JCT 254-380
Wireless LANs
IEEE 802.11 2400-2483 HIPERLAN 2 5150-5350, 5470-5725
902-928 IEEE 802.11 2400-2483 5150-5350, 5725-5825
IEEE 802.11 2471-2497 5150-5250
Others RF-Control 27, 128, 418, 433, 868
RF-Control 315, 915
RF-Control 426, 868
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REGULATIONS
PDC : Personal Digital Cellular
NMT : Nordic Mobile Telephone
DECT : Digital Enhanced Cordless Telephone
PACS : Personal Access Communications System
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SIGNALS
A sine wave is represented as
g(t) = At sin (ω.t + ø)
Here, At : Maximum amplitude
w : angular frequency = 2πf
ø : Phase Displacement
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SIGNALS
Different representations of signals amplitude (amplitude domain) frequency spectrum (frequency domain) phase state diagram (amplitude M and phase in
polar coordinates)
A [V]
I= M cos
Q = M sin
A [V]
t[s]
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Signals
According to fourier series, it is possible to reconstruct the original signal using the sine and cosine functions.
G(t) = ½ C + )2cos()2sin(11
nftbnftann
nn
In the above eqn, C represents the DC component.
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Signals
As n varies, increasing number of harmonics are added to the signal representation.
As n approaches infinity, the original signal is truly represented.
The given signal has to be modulated over a career frequency.
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Antenas
An Antenna aids in transforming a wired medium to a wireless medium
Antennas couple electromagnetic energy to the space and from the space TO and FROM a wire/coaxial cable.
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ISOTROPIC RADIATOR ANTENNA
Theoretical reference antenna is the isotropic radiator.
It emits equal power in all directions.
zy
x
z
y x
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Antennas
Practical Antennas Exhibit Directional properties.
Thin Centre-fed Dipole:
λ/2
• Dipole consists of two collinear conductors separated by a small feeding gap.
• Generally, the length of the Dipole is half the wavelength of the signal to be transmitted/received.(λ = C/f where is is the speed of light {3*10 8 m/s)
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Wavelength
Forms of electromagnetic radiation like radio waves, light waves or infrared (heat) waves make characteristic patterns as they travel through space. Each wave has a certain shape and length. The distance between peaks (high points) is called wavelength.
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Dipole Antenna
•When the signal is obstructed by mountains, buildings etc, the power of the sinal gets weak.
• It can be boosted by additional devices.
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Directional Antenna
Several directional antennas can be combined to form a sectored antenna.
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Signal Propagation Range
distance
sender
transmission
detection
interference
Transmission range communication possible low error rate
Detection range detection of the signal
possible no communication
possible Interference range
signal may not be detected
signal adds to the background noise
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Path Loss during Transmission
Propagation in free space is always in a straight line like that of light. Receiving power proportional to 1/d² in vacuum – much more in
real environments (d = distance between sender and receiver)
Receiving power additionally influenced by Fading (frequency dependent) shadowing reflection at large obstacles refraction depending on the density of a medium scattering at small obstacles diffraction at edges
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Path Loss Effects
reflection scattering diffractionshadowing refraction
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Signal Propagation effects
Signal Penetration through objects : At lower frequency, the penetration is higher. At very high frequencies, the transmission
behavior of the wave is close to that of light,
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Propagation behavior of waves
Ground Wave (<2 MHz): Can follow earth’s surface and can propagate long distances
[Submarine communication, AM Radio etc] Sky Wave (2-30 MHz) : Waves are reflected.
They can bounce back and forth between ionosphere and earth’s surface and can travel around the world.
Line of Sight [>30 MHz) : The waves are bent by refraction.
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Multipath Propagation
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Multipath Propagation
Radio waves sent from the sender to the receiver can travel in a straight line as well as may reach the destination after being reflected by several obstacles.
The signal arrives at different times at the receiver. THIS EFFECT IS CALLED DELAY SPREAD
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Multipath Propagation
The original signal gets a spread signalThe order of delays is 2 to 12 micro
secs.
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Effects of delay spread
Short-pulse signals will be spread into a broader impulse or several weaker pulses.
In the fig, the impulse at the sender is received as three smaller pulses at the receiver.
Also, the power level of the received pulses will be low. So, they will be perceived as noise.
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Effects-2 of delay spread
Inter Symbol Interference :The second symbol is separated from
the first in the transmitted signal.At the receiver, they overlap because of
delays.If the pulses represent symbols, they will
interfere with each other and there will be INTER SYMBOL INTERFERENCE.
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One possible solution
Receiver should know the delay characteristics of different paths.
Receiver can compensate for the distortion
Receiver can equalize the signals based on the channel characteristics.
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Effects of mobility
Channel characteristics change over time and location signal paths changedifferent delay variations of different signal
partsdifferent phases of signal parts
quick changes in the power received (short term fading) short term fading
long termfading
t
power
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Solution for Long Term Fading
Senders can increase/decrease power on a regular basis so that the received power is within certain bounds.
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Long Term Fading
Additional changes indistance to senderobstacles further away
slow changes in the average power received (long term fading)