Wireless communication lectureset: 8

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. 2

Free Space Path Loss Path Loss is a measure of attenuation based only on the distance to the transmitter : P(L)=Pt / Pr Free space model valid only in far-field; Path loss models typically define a “close-in” point d0 and reference other points from there: eq 4.8 Log-distance generalizes path loss to account for other environmental factors Choose a d0 in the far field. Measure PL(d0) or calculate Free Space Path Loss. Take measurements and derive  empirically. 3

Typical large-scale path loss 4

Log-Normal Shadowing Model Shadowing occurs when objects block LOS between transmitter and receiver A simple statistical model can account for unpredictable “shadowing” PL(d)(dB)=PL(d)+ X , eq 4.69 Add a 0-mean Gaussian RV (with standard deviation  ) to Log-Distance PL Variance  is usually 3 to 12. Reason for Gaussian 5

Measured large-scale path loss Determine n and  by mean and variance Read Q and erf functions Equ. 4.70 Equ. 4.72 Read basic of Gaussian distribution 6

Area versus Distance coverage model with shadowing model Percentage for SNR larger than a threshold Equ. 4.79 Example 4.9 7

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 9

Longley-Rice Model, OPNET implementation 10

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. 11

2-D Propagation Raster data Digital elevation models (DEM) United States Geological Survey (USGS) 12

Algorithm for line of sight (LOS) Line of sight (LOS) or not 13

Multiple diffraction computation 14

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 15

Okumura Model The major disadvantage with the model is its low response to rapid changes in terrain, therefore the model is fairly good in urban areas, but not as good in rural areas. Common standard deviations between predicted and measured path loss values are around 10 to 14 dB. G(hre)： 16

Okumura and Hata’s model Example 4.10 17

Hata Model Empirical formulation of the graphical data in the Okamura model. Valid 150MHz to 1500MHz, Used for cellular systems The following classification was used by Hata: ■Urban area ■Suburban area ■Open area 18

PCS Extension of Hata Model COST-231 Hata Model, European standard Higher frequencies: up to 2GHz Smaller cell sizes Lower antenna heights f >1500MHz Metropolitan centers Medium sized city and suburban areas 19

Walfisch and Bertoni Model Path loss (1) (2) (3) (1) Free space path loss : (2) Roof-top-to-street diffraction and scatter loss term : (3) Multiscreen diffraction loss : 20

Walfisch and Bertoni’s model 21

Wideband PCS Microcell Model A 2-ray ground reflection model is a good estimate for path loss in LOS microcells, Low antenna heights A simple log-distance path loss model holds well for obstructed microcells, Urban clutter df represents the distance at which the first Fresnel zone just becomes obstructed by the ground 22

Measured data from San Francisco 23

Indoor Propagation Models The distances covered are much smaller The variability of the environment is much greater Key variables: layout of the building, construction materials, building type, where the antenna mounted, …etc. In general, indoor channels may be classified either as LOS or OBS with varying degree of clutter The losses between floors of a building are determined by the external dimensions and materials of the building, as well as the type of construction used to create the floors and the external surroundings. Floor attenuation factor (FAF) Partition losses 24

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Partition losses 26

Partition losses between floors 27

Partition losses between floors 28

Log-distance Path Loss Model Equation 4.93 The exponent n depends on the surroundings and building type X is the variable in dB having a standard deviation . 29

Ericsson Multiple Breakpoint Model 30

Attenuation Factor Model FAF represents a floor attenuation factor for a specified number of building floors. PAF represents the partition attenuation factor for a specific obstruction encountered by a ray drawn between the transmitter and receiver in 3-D  is the attenuation constant for the channel with units of dB per meter. 31

Measured indoor path loss 32

Measured indoor path loss 33

Measured indoor path loss 34

Devasirvatham’s model Eq 4.96 35

Signal Penetration into Buildings RF penetration has been found to be a function of frequency as well as height within the building. Signal strength received inside a building increases with height, and penetration loss decreases with increasing frequency. Walker’s work shows that building penetration loss decrease at a rate of 1.9 dB per floor from the ground level up to the 15th floor and then began increasing above the 15th floor. The increase in penetration loss at higher floors was attributed to shadowing effects of adjacent buildings. Some devices to conduct the signals into the buildings 36

Ray Tracing and Site Specific Modeling Site specific propagation model and graphical information system. Ray tracing. Deterministic model. Data base for buildings, trees, etc. SitePlanner 37

Assignments 4.9 4.15 4.16 4.19 4.25 4.30 4.34 38