Transcript EEE440 Lecture Slide Part 1ver2011

Wireless and Mobile
Communication Systems
Lecture Slide Part 1 Version 2011-2012
Mohd Nazri Mahmud
Introduction, OBE
• This course reviews the topics on
optical fibre, wireless & mobile and
satellite communication systems.
• It covers the topics of system
components, channels, operations and
performance.
• Important concepts are introduced and
necessary analytical techniques are
applied to solve system problems.
Introduction OBE
Reference books
(for wireless and mobile)
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Schwartz, M., “ Mobile Wireless Communications”,
Cambridge University Press, 2005
Gary S. Rogers, John Edwards, “An Introduction to
Wireless Technology “, Prentice Hall, 2003
Tse, D.and Viswanath, P.,”Fundamentals of Wireless
Communication”, Cambridge University Press, 2005.
Simon Haykin, Micheal Moher, “Modern Wireless
Communication”, Pearson Prentice Hall, 2005
Introduction
• What is a wireless communication system?
• What is a mobile communication system?
• Different types of wireless and mobile systems
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Cellular
Wireless LAN
Wireless WAN
Wireless PAN
Wireless Sensor Network
Wireless BAN
Mobile Ad-hoc network (MANET)
Cooperative wireless network
Cognitive Radio Network
Group assignment – facts finding
• Divide into 7 groups (3 students per group)
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Group 1: Cellular
Group 2: WiFi and WiMAX
Group 3: WPAN and WSN
Group 4: WBAN
Group 5: MANET
Group 6: Cooperative Wireless Network
Group 7: Cognitive Radio Network
• Find and read general information regarding these
communication systems
• Develop a 5 minutes presentation to share your
understanding on these systems. Just share what you
understand from your reading and avoid complicated
analytical contents. Make sure you record all your
references
• Present in the next class (next week)
Characteristics of Mobile Wireless
radio propagation
6 common effects
• Propagation loss
– Fresnel effect
• Fading
– Large Scale (Shadow fading)
– Small scale (multipath fading)
• Flat fading: Rayleigh or Rician
• Frequency Selective Fading
– Small scale fading due to movements:Doppler effects
• Fast or Slow fading
• Time-selective fading
Characteristics of Mobile Wireless
radio propagation
• In free space propagation, the power incident on
a receiving antenna is given by the free space
received power equation
  
PR  PT GT GR 

 4d 
2
• In wireless environment where obstacles exist,
the average power decrease with distance at a
rate greater than d2 (usually to the power of 3 or 4)
• This is commonly known as the propagation loss
Characteristics of Mobile Wireless
radio propagation
• The actual power received over a relatively long
distance will vary randomly about the average
power
– A good approximation reveals that the power
measured in decibel follows a gaussian or normal
distribution centred about its average value with some
standard deviation ranging typically from 6 to 10dB.
– The power probability distribution is commonly called
a log-normal distribution
– This is commonly referred to as the shadow fading
Characteristics of Mobile Wireless
radio propagation
• The actual power received over a much
smaller distance also vary considerably
due to the destructive/constructive
interference of multiple signals that follow
multiple paths
– This is commonly referred to as multipath
fading
Characteristics of Mobile Wireless
radio propagation
• The three effects can be modelled by the
following equation
PR
Multipath
fading
x
  21010 g
Shadow
fading
d PT GT GR
Propagation loss
Characteristics of Mobile Wireless
radio propagation
• The effect of multipath fading depends of the
signal bandwidth
• For a relatively large bandwidth, different
frequency components of the signal being
handled differently over the propagation path
leading to signal distortion called frequency
selective fading
• This is manifested in inter-symbol interference
(ISI) due to successive digital symbols overlap
into adjacent symbol intervals
• For narrower signal bandwidth, non-selective or
flat fading occur
Characteristics of Mobile Wireless
radio propagation
• Terminal mobility with respective to the
incoming wave introduces a frequency
shift called Doppler shift
• Signal fades due to the movement of the
terminal
Characteristics of Mobile Wireless
radio propagation
• Time selective fading occurs when the
channel changes its characteristics during
the transmission of the signal
• The change in the channel characteristics
is proportional to the receiver mobility
Propagation loss
• The average power measured at the
receiver at a distance d from the
transmitter is given by
PR  g d PT GT GR
• g(d) represents the path loss with the
general expression
g d   kd n
Propagation loss
• There are many models for the path loss
• A common two-ray model is most often used
g d   kd 4
g d   kd 4
Propagation loss: Two-ray model
• The two-ray model is the simplest representation
that models the effect on the average received
power of multiple rays due to reflection,
diffraction and scattering
• It treats the case of a single reflected ray
• Provides reasonably accurate results in
macrocellular environment with relatively high
BS antenna and/or L.O.S conditions
• Assumes that the signal arrives directly through
a L.O.S path and indirectly through perfect
relfection from a flat ground surface
Propagation loss: Two-ray model
Propagation loss: Two-ray model
• The reflected signal shows up with a delay relative to the direct path
signal and as a consequence, may add constructively (in phase) or
destructively (out of phase)
• Propagation starts out with an R2 falloff rate and then transitions to a
R4 falloff rate at greater ranges.
• The "point" where this transition occurs is often called the Fresnel
breakpoint.
• The nulls are representative of points where direct and reflected
signals cancel while the humps show points where signals add
• In practice, ground reflections are usually somewhat diffuse (rough
mirror instead of polished) and so the sharp nulls get filled in.
• In macrocellular communications systems, operating distances are
usually large enough so that signal strength can be thought of as
falling off at an R4 rate.
Fresnel Effects
• Propagation loss due to obstruction in the LOS path
• If there are obstacles near the LOS path between the
transmitter and the receiver, the radio waves reflecting
off these objects may arrive out of phase with the direct
LOS signal
• The power of the received signal might be reduced
• There is a zone called Fresnel zone that must be clear of
any obstacle
• There are multiple Fresnel zones; 1st , 2nd, 3rd and so on
• Signal within one set of a Fresnel zone have similar
strength
• The Fresnel zones are half-wavelength apart from one
another
Fresnel Effects
• The radius of the 1st Fresnel zone depends on the
frequency and the antenna height
• It is often useful to know the maximum radius of the first
Fresnel zone in which the primary signal energy resides
• The first Fresnel zone must be kept largely free from
obstructions
• General equation for calculating the Fresnel zone radius
at any point P
Fn 
n d 1 d 2
d1  d 2
Fn = The nth Fresnel zone radius (in metres)
d1 = The distance of P from one end (in metres)
d2 = The distance of P from the other end (in metres)
Λ = the wavelength of the transmitted signal (in metres)
Fresnel effects
Propagation loss: Other models
• Hata model or aka Okumura-Hata model
• A journal paper on Hata model is provided
online (in my staff webpage)
• Please print the paper and bring to our next
class
• Group reading in class: Read and understand
Hata’s paper within your group
• Base your understanding from group
discussions only (without referring to your
lecturer). This is to encourage group
members to assist one another in learning
• A quiz will be held in the next class