Wireless Communications
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S.Swedan
Wireless Communications
Wireless Communications
Text Book:
1- Wireless Communications: Principles and practice
RAPPAPORT,
2nd Edition
2- Modern wireless Communications:
Simon Haykin
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Wireless Communications
Wireless Communications
Chapter - 1
Introduction to
Wireless Communications
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Wireless Communications
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Wireless Communications
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Radio wave propagation
Path : The direction from signal arrives.
Radio wave propagation consists of two main attributes
Simple path
-Direct path bet. Tx & Rx
-Only one path
-No objects bet. Tx & Rx
- Called Line of sight (LOS)
Multipath
-Many paths
-Many objects
- Called non-line of sight
NLOS
Radio wave propagation
 LOS Propagation
LOS wireless transmission can be categorized into 3 broad groups
A- Radio waves
EMW ranging in frequencies (3 kHz – 1 GHz)
- Omni-direction ( waves are propagated in all directions)
- Useful for multicasting (AM , FM , and TV )
- Susceptible to interference by another (if same frequency)
B- Micro waves
EMW ranging in frequencies (1 – 300 GHz)
- Uni-direction (propagation is Line-Of-Sight LOS)
(sending and receiving antennas need to be aligned)
Radio wave propagation
- A pair of antennas can be placed aligned without interfering with
another pair using the same frequency.
- Two types of antenna are used for -wave
- Parabolic dish antenna - Horn antenna
- High frequency microwave cannot penetrate walls
(receive antenna cannot placed inside building)
C- Infrared
EMW ranging in frequencies (300 GHz – 400 THz)
- Cannot penetrate walls
- They are used for short range communications
( TV remote control)
- Cannot used outside a building
( sun’s ray contain infrared waves that can interfere)
Radio wave propagation
LOS propagation modes
3 modes of propagation
1- Ground Wave propagation
▪ In this mode, the signal travels very close to the earth’s surface
following its curvature.
▪ Frequency range : 30 KHz to 3 MHz.
Radio wave propagation
2- Sky Wave propagation
▪ In this mode, the signals travel from transmitting antenna get
reflected from the F-layer of Ionosphere ( 50 – 200 Km from the
earth) back to the receiving antenna.
▪ Frequency range : 3 MHz to 30 MHz.
Radio wave propagation
▪ Need of space communications
▪ The ground wave, and sky wave `are dependent on earth’s
curvature and layers of ionosphere
for their operation. The maximum
hoop distance is limited to 1500 kms.
Radio wave propagation
3- Space Wave propagation
▪ the signal waves travel from Tx to Rx directly in straight path.
▪ Frequency range : >30 MHz.
Satellite Communications
• For satellite communications, a signal above 30 MHz is not
reflected by the ionosphere.
Difference between
RadioPrinciple
waves and Microwaves
Working
• The network consists of several earth stations on ground
which are linked with a satellite in space.
• The end users are connected to these earth stations through a
terrestrial communication network.
• The earth station modulate the signal and sends it to the satellite
on the uplink frequency spectrum.
• The satellite amplifies and processes
the signal and retransmits it back
on the downlink frequency spectrum.
•
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Satellite Communications
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Difference between
RadioPrinciple
waves and Microwaves
Working
• At the receiving earth station, the transmitted signal is received,
demodulated and amplified to get back the original signal.
• The signal is then sent to the user through terrestrial
communication network.
Satellite Communication Fundamental
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Satellite Communications
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Satellite Services
Fixed Satellite Services (FSS)
– P-P communications
– Provide links for existing Telephone Networks
– Link bet. ES’s could be (2 or more) satellites interconnected.
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Satellite Communications
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Satellite Services
Broadcasting Satellite Services
– Signal transmitted by satellites are intended for direct
reception by general public
(using small Rx antennas).
– Called “ Direct Broadcast satellite DBS”
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Satellite Communications
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Satellite Services
Mobile satellite Services
- R. com. services bet. Mobile ES’s & (1 or more) space stations.
- ES may consists (very small i.e. hand-held terminal, thuraia)
interconnected.
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Satellite Communications
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Frequency allocation for satellite services
• Allocation of frequencies to satellite services is a complicated
process which requires international coordination and planning.
This is done using ITU.
• To implement this planning the world is divided into 3 regions:
- Region 1: Europe, Africa, and Mongolia
- Region 2: North and south America and Greenland
- Region 3: Asia (excluding region 1 area), Australia, and southwest Pacific.
• Within these regions, the frequency bands are allocated to
various satellite services.
Performance Measurements
Common bands for satellite communication are
L , C , Ku , Ka &V bands.
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Radio wave propagation
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Radio wave propagation
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Multipath Propagation
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Effect of Multipath Propagation
Tx
A1 cos 2fct
Rx
A2 cos 2fc( t -  )

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Effect of Multipath Propagation
Must cellular radio systems operate in urban area where there is
no LOS path only between Tx and Rx, and where the presence of
high rise buildings and other objects causes severe diffraction loss
and reflections
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Effect of Multipath Propagation
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Wireless Communications modeling
The W. communications modeling is divided into 2 terms
Small-scale propagation
Large-scale propagation
models
models
Propagation
models
that - Propagation models are usually
characterize rapid fluctuations of the required to predict the average
received signal strength over very received signal strength over large
short
travel
distance
(vew T-R separation distances and
estimating the coverage area.
wavelength) or short time duration.
• The reference is the wavelength  of the propagated signal
- Large-scale means distance larger than 20 
- Small-scale means distance fraction of 
• (e.g. 4G mobile system,   14 cm)
So moving around 2 cm, the received power will changed rapidly
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Wireless Communications modeling
Importance of Large-scale fading study
• 4 parameters for the coverage planning
- Number of antennas
- Locations
- Height of antennas
- Power
• Cellular communications: (percentage of coverage inside a cell)
• Microwave communications : (Fresenel zone)
• Wireless LAN: (Access points locations)
• Who should study large-scale fading?
- Academia (research)
Only needs the concept
of large-scale
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- Industry
Most important: design the net.,
configuration the system
Wireless Communications
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Wireless Communications modeling
Importance of Small-scale fading study
- Transmission parameters
- Modulation type
- Coding
- Rate
( 4G ; frame length = 10 m sec)
• Who should study Small-scale fading ?
- Academia (research)
Most important
- Channel modeling
- Channel C/S
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- Industry
The concept of small-scale
Wireless Communications
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