26-05-2012, 12:02 PM
Wireless communication lectureset
[attachment=23121]
Propagation Models
Large scale models predict behavior averaged over distances >>
Function of distance & significant environmental features, roughly frequency independent
Breaks down as distance decreases
Useful for modeling the range of a radio system and rough capacity planning,
Experimental rather than theoretical
Path loss models, Outdoor models, Indoor models
Small scale (fading) models describe signal variations on a scale of
Multipath effects (phase cancellation) dominate, path attenuation considered constant
Frequency (and bandwidth) dependent
Focused on modeling of “Fading”: rapid change in signal over a short distance or length of time.
Log-Normal Shadowing Model
Shadowing occurs when objects block LOS between transmitter and receiver
A simple statistical model can account for unpredictable “shadowing”
Models for analysis
Review
Propagation mechanism: too theoretical for practice use. concept
Reflection
Diffraction
Scattering
Log-distance path loss model and log-normal shadowing: too simple
Tradeoff between simplicity and accuracy
Outdoor propagation models
Indoor propagation models
Longley-Rice Model
Point-to-point from 40MHZ to 100GHz. irregular terrain model (ITS).
Predicts median transmission loss, Takes terrain into account, Uses path geometry, Calculates diffraction losses
Inputs:
Frequency
Path length
Polarization and antenna heights
Surface refractivity
Effective radius of earth
Ground conductivity
Ground dielectric constant
Climate
Disadvantages
Does not take into account details of terrain near the receiver
Does not consider Buildings, Foliage, Multipath
Original model modified by Okamura for urban terrain
Durkin’s Model
It is a computer simulator for predicting field strength contours over irregular terrain. Adopted in UK
Line of sight or non-LOS
Edge diffractions using Fresnel zone
The disadvantage are that it can not adequately predict propagation effects due to foliage, building, and it cannot account for multipath propagation.
Okumura Model
It is one of the most widely used models for signal prediction in urban areas, and it is applicable for frequencies in the range 150 MHz to 1920 MHz
Based totally on measurements (not analytical calculations)
Applicable in the range: 150MHz to ~ 2000MHz, 1km to 100km T-R separation, Antenna heights of 30m to 100m
[attachment=23121]
Propagation Models
Large scale models predict behavior averaged over distances >>
Function of distance & significant environmental features, roughly frequency independent
Breaks down as distance decreases
Useful for modeling the range of a radio system and rough capacity planning,
Experimental rather than theoretical
Path loss models, Outdoor models, Indoor models
Small scale (fading) models describe signal variations on a scale of
Multipath effects (phase cancellation) dominate, path attenuation considered constant
Frequency (and bandwidth) dependent
Focused on modeling of “Fading”: rapid change in signal over a short distance or length of time.
Log-Normal Shadowing Model
Shadowing occurs when objects block LOS between transmitter and receiver
A simple statistical model can account for unpredictable “shadowing”
Models for analysis
Review
Propagation mechanism: too theoretical for practice use. concept
Reflection
Diffraction
Scattering
Log-distance path loss model and log-normal shadowing: too simple
Tradeoff between simplicity and accuracy
Outdoor propagation models
Indoor propagation models
Longley-Rice Model
Point-to-point from 40MHZ to 100GHz. irregular terrain model (ITS).
Predicts median transmission loss, Takes terrain into account, Uses path geometry, Calculates diffraction losses
Inputs:
Frequency
Path length
Polarization and antenna heights
Surface refractivity
Effective radius of earth
Ground conductivity
Ground dielectric constant
Climate
Disadvantages
Does not take into account details of terrain near the receiver
Does not consider Buildings, Foliage, Multipath
Original model modified by Okamura for urban terrain
Durkin’s Model
It is a computer simulator for predicting field strength contours over irregular terrain. Adopted in UK
Line of sight or non-LOS
Edge diffractions using Fresnel zone
The disadvantage are that it can not adequately predict propagation effects due to foliage, building, and it cannot account for multipath propagation.
Okumura Model
It is one of the most widely used models for signal prediction in urban areas, and it is applicable for frequencies in the range 150 MHz to 1920 MHz
Based totally on measurements (not analytical calculations)
Applicable in the range: 150MHz to ~ 2000MHz, 1km to 100km T-R separation, Antenna heights of 30m to 100m