1. Introduction to Wireless Technologies
Dr. Farid Farahmand

2. Wired Vs. Wireless Communication
CS 625, IITK CSE
Jan3, 2002
Wired Vs. Wireless Communication
Wired
Wireless
Each cable is a different channel
One media (cable) shared by all
Signal attenuation is low
High signal attenuation
High interference
noise; co-channel interference; adjacent channel interference
No interference
Introduction to wireless communication

3. Why go wireless ? Limitations Bandwidth Fidelity Power (In)security
CS 625, IITK CSE
Jan3, 2002
Why go wireless ?
Limitations
Bandwidth
Fidelity
Power
(In)security
Advantages
Sometimes it is impractical to lay cables
User mobility
Cost
Introduction to wireless communication

4. Wireless Systems: Examples
CS 698T
Wireless Systems: Examples
Broadcast (analog)
AM, FM Radio
TV Broadcast
Satellite Broadcast
2-way Radios
Cordless Phones
Satellite Links
Mobile Telephony Systems
Wireless Local Loop (WLL)
Microwave Links
Wireless LANs
Infrared LANs
2-way communication
(analog)
2-way communication
(digital)
Q1. Can you think of any wireless system not already listed here?
Q2. These systems are not randomly listed. Can you spot any trend here?
OB1. It is interesting that operating frequency of these systems increases as we go down the list.
Q3. Discuss difference between analog and digital systems.
P. Bhagwat

5. Wireless Systems: Range Comparison
CS 698T
Wireless Systems: Range Comparison
1 m
10 m
100 m
1 Km
10 Km
100 Km
1,000 Km
Satellite
Links SW
Radio MW
Radio FM
Radio
Mobile
Telephony,
WLL
WLANs
Q1. Can you think of a system whose range of communication is more than satellite links?
Q2. Give an example of a system whose range of communication is shorter than IR links.
Point to ponder: Why does range of communication increase on logarithm scale?
Blueooth IR
P. Bhagwat

6. EM Spectrum
902 – 928 Mhz
2.4 – Ghz
5.725 – Ghz
ISM band
AM radio
S/W radio
FM radio TV TV
cellular LF HF
VHF
UHF
SHF
EHF MF  
30kHz
300kHz
3MHz
30MHz
300MHz
30GHz
300GHz
10km
1km
100m
10m 1m
10cm
1cm
100mm
3GHz
X rays
Gamma rays 
infrared
visible UV
1 kHz
1 MHz
1 GHz
1 THz
1 PHz
1 EHz
Propagation characteristics are different in each frequency band

7. Frequency Band Allocations
RADIO IR
VISIBLE UV
X-RAYS
GAMMA RAYS
RADIO
VLF LF MF HF
VHF
UHF
SHF
EHF 3k
30k
300k 3M
30M
300M 3G
30G
300GHz
VLF: Very Low Frequency LF: Low Frequency
MF: Medium Frequency HF: High Frequency
VHF: Very High Frequency UHF: Ultra High Frequency
SHF: Super High Frequency EHF: Extremely High Frequency

8. Wavelengths of Frequency Bands
VLF, LF  long waves
MF  medium waves
HF, VHF  short waves
UHF, SHF  microwaves 
EHF  millimeter waves
Above microwave region, only certain windows of frequencies propagate freely through air, rain, etc.
Infrared and visible light will not penetrate walls
X-rays and gamma rays interact with matter
Propagate well beyond line of sight
The distance the signal travels decreases
as the frequency increases

9. Electromagnetic Signals
Electromagnetic Signals are emitted and received in wireless systems
Requires a transmitting and receiving antenna
The EM signal goes through the unguided medium
Free space (vacuum)
Earth’s atmosphere
EM propagation is also referred to radio frequency propagation
Wireless communications examples
Terrestrial radio
Microwave radio
Broadband radio
Mobile radio
Cellular phone

10. What is EM?
EM involves both a varying electric field (E) and a varying magnetic field (H)
E and H appear at right angles to each other and to the direction of travel of the wave (Z-axis)
The power passing a given signal is called the power density (P)
P (Watt/m2)= H.E

11. EM Propagation Electromagnetic waves are invisible
We use the concept of rays to describe them
When radiating uniformly over a spherically we refer to it as isotropic radiation
Power Density (W/m2) = P_radiated / Area of sphere
As we get further from the source the radiation (received power) becomes smaller

12. Example of Power Density
Assume the isotropic radiated power from an antenna is 100 W. Assuming the receiving antenna is 100 m away, calculate the received power density (assume vacuum).
P(density) = 100W / 4p(100)2
=0.796 mW/m2 TX RX
R=100 m

13. Free Space Loss The signal disperses with distance
Free space loss, ideal isotropic antenna
Pt = signal power at transmitting antenna (watt)
Pr = signal power at receiving antenna (Watt)
 = carrier wavelength
d = propagation distance between antennas
c = speed of light (» 3 ´ 10 8 m/s)
where d and  are in the same units (e.g., meters)

14. Example of Power Radiation
Assume the isotropic radiated power from an antenna is 100 W. Assuming the receiving antenna is 100 m away, calculate the received power (assume vacuum and frequency of radiation is 100 MHz).
P(received) =Pr
=100W / (100x106x4p(100)/3x108)2
=0.057 mW  very little power received! TX RX
R=100 m

15. Attenuation
Strength of signal falls off with distance over transmission medium
Attenuation factors for unguided media:
Received signal must have sufficient strength so that circuitry in the receiver can interpret the signal
Signal must maintain a level sufficiently higher than noise to be received without error
Note: Attenuation in dB can be calculated by

16. Signal Loss and Attenuation
Pulse spreading in free space
Attenuation in non-vacuum
Attenuation due to particles absorbing the EM energy
Called “wave absorption”
Remember: Attenuation = 10 log (Pout/Pin)

17. Other Impairments
Multipath – obstacles reflect signals so that multiple copies with varying delays are received
Refraction – bending of radio waves as they propagate through the atmosphere
Atmospheric absorption – water vapor and oxygen contribute to attenuation

18. The Effects of Multipath Propagation
Multiple copies of a signal may arrive at different phases
If phases add destructively, the signal level relative to noise declines, making detection more difficult
Intersymbol interference (ISI)
One or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit

19. Multipath Propagation & Fading
Reflection – occurs when signal encounters a surface that is large relative to the wavelength of the signal
Diffraction - occurs at the knife-edge of an impenetrable body that is almost the same compared to wavelength of radio wave
Scattering – occurs when incoming signal hits an object whose size in the order of the wavelength of the signal or less

20. Multipath Propagation & Fading
Three basic propagation mechanisms (D is the size of the material)
Reflection
λ << D
Diffraction
λ  D
Scattering
λ >> D

21. Refraction Refraction – bending of microwaves by the atmosphere
Thin
Air
Dense
Refraction – bending of microwaves by the atmosphere
Velocity of electromagnetic wave is a function of the density of the medium
When wave changes medium, speed changes
Wave bends at the boundary between mediums

22. References
Narayan Mandayam,
Tomasi