Types of Propagation Models & Use

8/10/2019 Types of Propagation Models & Use

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Understanding propagation model types

This section describes the propagation model types that Mentum Planet supports.Slope-based models, such as the Okumura-Hata model, take clutter into account automatically when generating predictions. Deterministic models, such as the CRC-Predict model, depend on the model of the environment and the specification of clutter property assignments. Table 1 rates how each of the three main propagation models perform when used under certain conditions.

Table 1 Ratings for popular propagation models

Used...CRC-PredictPlanet General ModelUniversal ModelFor macro-cell planningGoodGoodExcellentFor mini-cell planning (urban)PoorFair

ExcellentFor micro-cell planning (urban)Very poorPoorExcellentOver large propagation distancesExcellentFairGoodWith no model tuning

FairPoorGoodWith cluster tuningFairFairExcellentOn a per sector basisGoodExcellentExcellent

With merged predictionsGoodFairGood

Free Space model

You can use the Free Space propagation model where line of sight situations exis


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t with no Fresnel zone obstructions. For example, this model is useful for highfrequency, short distance, and Local Multipoint Distribution Service (LMDS) applications.

The Free Space model is used for path loss estimation where there is an unobstructed line of sight between the transmitter and the receiver and there are no obstructions within the first Fresnel zone. This is often the case for satellite and microwave communications. The Free Space model is based on the Friis Free Space equation, which states that the received power drops off and is calculated asthe square of the distance between transmitter and receiver (i.e., 20 dB/decade).

Okumura-Hata model

You can use the Okumura-Hata model for urban or suburban areas if little is known about the terrain and clutter.

The Okumura-Hata algorithm is entirely empirical. It is based on a multitude ofmeasurements from selected urban centers in Japan. Okumura developed a set of curves giving the median attenuation relative to free space for an urban area of quasi-smooth terrain. Base station effective height varied from 30 meters to over800 meters, and mobile antenna height was 3 meters and 1.3 meters, both using omni-directional antennas. Sets of signal attenuation curves were plotted as a function of frequency and distance by which relevant gain factors were determined.

Okumura calculated that the base station antenna height gain factor varies at arate of 20 decibels per decade, and the mobile antenna height gain factor varies at a rate of 10 decibels per decade for heights less than three meters. Terrain corrections such as undulation height, isolated ridge height, and average slope can be applied to the Okumura model. The correction factors are published as plotted curves.

The Hata equation model is appropriate if you do not have detailed terrain information and are working in urban or suburban environments. The Planet Hata equation model includes the COST 231 extensions from 1 500 MHz to 2 000 MHz.

The Okumura model performs well for cellular systems in cluttered environments with common standard deviations between predicted and measured path loss values o

f approximately 10 to 14 decibels. Hata has reduced the main results of Okumuraet al. to a few equations, and an application of these equations is commonly known as the Okumura-Hata method.

Model versions

Two versions of the Okumura-Hata propagation model are shipped with Planet: 2.0and 2.5. If you are building a new project, you can use version 2.5 of the Okumura-Hata model.

The Hata method requires an average terrain elevation from the transmitter to the receiver. Averaging starts at 3 kilometers and goes to the receiver, or to 15kilometers, whichever is less. If the receiver is less than 3 kilometers away fr

om the transmitter, there is no average; the terrain height at the receiver is used. Version 2.0 of the Okumura-Hata propagation model calculates the average to15 kilometers in all cases. If you have sites in a valley and have been gettingexcessively small predicted signal strengths, you can reconfigure these sites using version 2.5 of the Okumura-Hata model.

Planet General Model

The Planet General Model is a flexible hybrid model that can be used to model many different kinds of propagation environments. It enables you to migrate data f


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rom Planet 2.8 to Planet and obtain the same coverage results as Planet 2.8.

You can use the Planet General Model to model many different kinds of propagation environments. The path loss equation incorporates losses due to a number of models (such as Okumura-Hata), contributors, and coefficients that can be pieced together to create a user-defined propagation model. Some of these are defined byalgorithms derived from statistical data. These algorithms are quite accurate under specific conditions, but become less appropriate as the terrain and cluttervaries from these conditions. Various correction factors exist to compensate for these varying conditions, and it is very important for these values to be assigned accurately in order to make models simulate the real situation.

The Planet General Model predicts the path loss for each element within the prediction area. This is achieved by constructing a terrain and clutter profile fromthe base station (transmitter) to each element and then computing the path lossfor that profile. In order to ensure that path loss at each element within theprediction region is computed, a profile can be constructed to each element on the perimeter of the prediction region. Thus the number of radials, , is given by

However, for most practical applications, a fraction of the above number of radials is sufficient. A corresponding signal strength at each element is also computed using the antenna pattern.

One of the most visible differences between the Planet General Model used with Planet 2.8/Planet DMS and the one used with Planet is the shape of the predictionarea; Planet 2.8/Planet DMS uses a square prediction area, whereas Planet defines a circular prediction area. Although the shape and the total area of the prediction areas are markedly different, this has no effect on the computed path loss or signal strength values. Using simple geometry, you can convert Planet 2.8 Prediction Size to Planet Propagation Distance using

The above equation overlaps the Planet circular prediction area with Planet 2.8square prediction region, thus assuring total coverage of the prediction zone.

For more information on the Planet General Model, see the Planet General Model T

echnical Note. Application Notes and Technical Notes are available from the Mentum web page.

ITU 370-Recommendation model

You can use the ITU 370-Recommendation 2.5 propagation model for modeling VHF and UHF broadcast services.

Planet includes both the ITU 370-Recommendation 2.0 model and the 2.5 model. Version 2.0, which lacks the model tuning capability of version 2.5, has been addedfor backward compatibility with existing projects. The ITU 370-Recommendation model is the implementation of ITU Recommendation ITU-R P.370-7 and is designed specifically for broadcast services in the VHF and UHF bands. The model is based

on propagation curves and correction factors that determine the dependency of signal strength on transmitting-antenna height and on the distance from a transmitter. Each propagation curve shows the effect of the frequency band, landscape type, and the percentage of time on the signal strength. In Planet, you can specify percentages of time and of locations, frequency mode, bandwidth, environmentalsettings, and terrain factors. The ITU 370-Recommendation model provides coefficients of correction for Rural, Suburban, and Urban clutter types, which are user selectable. You cannot make any numeric adjustments (e.g., dB) to the clutterattenuation.


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The ITU 370-Recommendation model is best suited to frequencies between 30 and 1000 MHz and distances up to 1000 kilometers.

Interpreting Recommendation 370 results

When you are interpreting Recommendation 370 results, keep in mind the followingpoints:

The signal strengths in the ITU 370-Recommendation models refer to one kilowattEffective Radiated Power (ERP) from a half-wave dipole. However, Planet adjuststhe results to the sectors parameters in the site table.

The basic calculation accommodates for any effective transmitter antenna height,while the receiving antenna height is fixed at 10 meters. However, a height gain function in the ITU 370-Recommendation models allows you to consider other receiving antenna heights.

The land path curves refer to the value of terrain irregularity at 50 meters, which generally applies to rolling terrain commonly found in Europe and North America. The ITU 370-Recommendation models also include a terrain-clearance-angle correction that depends on the terrain close to the receiver.

COST 231 Walfisch-Ikegami model

You can use the Walfisch-Ikegami model for urban or suburban areas with uniformbuilding heights and separation on flat ground.

COST 231 has proposed a combination of the Walfisch and Ikegami models that hasbeen accepted by the ITU-R and included in Report 567-4. This model is statistical and not deterministic, because terrain and clutter are not considered.

The parameters used by the model are shown in Figure 4.1. When you use the model, you need to input the height of the buildings (hRoof), the widths of roads (w), the building separation (b), and the road orientation. The parameters that youdefine in Planet include the transmitter height, the receiver height, and the frequency.

Figure 4.1 COST 231 Walfisch and Ikegami model parameters

The model distinguishes between line-of-sight (LOS) and non-line-of-sight (NLOS)situations. The LOS case describes a street canyon situation, such as when thetransmitter is located at a street corner and LOS is achieved in the direction of the streets. The NLOS case uses the building and street properties to estimatethe path loss at a given location.

COST 231 has defined the following restrictions on the model:

Frequency: 800-2000 MHz

hBase: 4-50 m

hMobile: 1-3 m

Distance: 0.02-5 km

Planet does not restrict the range of these parameters; therefore, predictions must be considered with care outside of these ranges.


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The estimation of path loss agrees rather well with measurements for base station antenna heights above roof-top levels. The error becomes larger when hBase isapproximately equal to hRoof. The performance of the model is quite poor when hBase is much less than hRoof.

The parameters b, w, and f are not considered in a meaningful way for microcells. Therefore, the prediction error in microcells might be quite large.

The model does not consider multipath propagation, and the reliability of the prediction decreases if the terrain is not flat or the clutter is not homogeneous.

Longley-Rice model

You can use the Longley-Rice area calculation for rural (non-urban) areas if little is known about the terrain and clutter.

The Longley-Rice model is applicable to point-to-point communication systems inthe 20 MHz to 10 GHz range over different types of terrain (Rappaport, 1996). The Longley-Rice model operates in two modes. The point-to-point mode uses terraininformation if it is available, while the point-to-area mode uses techniques that estimate the path-specific parameters when little terrain information is available.

In point-to-point mode, median path loss is predicted by using tropospheric refractivity and terrain geometry. However, only some features of the terrain are used. The terrain profile is used to find effective antenna heights, horizon distances and elevation angles as seen from the antennas, the angular distance for atrans-horizon path, and the terrain irregularity of the path. The prediction isperformed in terms of these parameters. A ray optic technique using primarily atwo-ray ground reflection model is used within the radio horizon. The two or three isolated obstacles causing the greatest obstruction are modeled as knife edges using the Fresnel Kirchoff theory. Forward scatter theory is used to make troposcatter predictions for long paths and far field diffraction losses are predicted using a modified Van der Pol-Bremmer method (Rappaport, 1996). The Longley-Rice point-to-point model is also referred to as the Irregular Terrain Model (ITM)(Hufford, et al. 1982).

Although the point-to-area mode is an old method, it is still perhaps the best method of estimating path loss in open country if the only parameters known aboutthe ground are its irregularity and (less importantly at UHF) its electrical constants.

The Longley-Rice model is best suited to the following parameters:

Frequency: 20 MHz to 10 GHz

Distance: 1 km to 2000 km

Antenna Heights: 0.5 m to 3000 m

Polarization: Vertical or Horizontal

References

For more information about the Longley-Rice model, see the following references:

Rappaport, T.S. Wireless Communications: Principles and Practice. Prentice Hall,1996.


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Hufford, Longley, and Kissick. A Guide to the Use of the ITS Irregular Terrain Model in the Area Prediction Mode, U.S. Department of Commerce. April 1982.

Lee model

You can use the Lee propagation model when you have survey results that show thenature of signal decay for local propagation conditions. The Lee model combinesboth an analytical and experimental approach to the estimation of both signal strength and path loss.

The standard equation for the Lee propagation model is described below.

Where:

is the mean received signal level at distance R from the transmit antenna.

is the expected signal strength in dBm for the reference conditions defined by, , , and .

is the slope or rate of signal strength decay as a function of distance from the transmitter in dB/decade.

is the distance from the transmitter in kilometers.

is the reference distance from the transmitter in kilometers.

is the effective antenna height of the transmitter in meters.

is the antenna height of the reference transmitter in meters.

is the effective antenna height of the receiver in meters.

is the antenna height of the reference receiver in meters.

is the effective radiated power of the transmitter in watts.

is the effective radiated power of the reference transmitter in watts.

is the knife-edge diffraction losses or additional loss due to terrain obstruction.

is the antenna pattern gain or additional loss or gain as a result of the actual antenna pattern used in the prediction.

The Lee model relies on a set of path loss curves that apply to a reference transmitter. These curves are straight lines on a logarithmic scale of distance, andare defined by a slope (a) and an intercept at 1.0 or 1.6 kilometers. These parameters are usually obtained from survey measurements that show the speed of signal decay as a function of distance under local propagation conditions. The Lee

model formula calculates the signal strength at any given point by modifying thereference signal strength to take into account the distance, the antenna heights, and so on actually encountered.

If the terrain is flat, nothing more is done. With hilly terrain, the terrain data is used to calculate an effective antenna height for the transmitting antenna, and also to estimate the additional path loss due to terrain obstructions modeled as knife edges. The changes in signal strength due to a modified effective antenna height and due to the knife-edge obstructions are added to the signal strength calculated for flat terrain.


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IEEE 802.16 model

You can use the IEEE 802.16 model when designing Multipoint Distribution System(MDS) and LMDS networks with frequencies in the 10 to 66 GHz range. This frequency range is characterized by very high data rates and short range due to rain and foliage attenuation.

The IEEE 802.16 model is recommended for use with broadband wireless access technologies.

Terrain types

The following types of terrain are recommended for use with the IEEE 802.16 model:

Type Acharacterized by hilly, moderate-to-heavy tree density (for light to moderate urban areas)

Type Bcharacterized by hilly, light tree density or flat, moderate-to-heavy density

Type Ccharacterized by flat, light tree density

Path loss equation

The standard path loss equation for the IEEE 802.16 model is described below.

The path loss calculation only accounts for the following parameters:

transmitter height

receiver height

frequency

the ground type as defined in the IEEE.802.16 dialog box

The clutter grid, the elevation file, the rain attenuation, and clutter absorption losses have no effect on the path loss calculation.

Where:

is equal to .

is the wavelength in meters.

is the path loss exponent equal to .

is the height of the base station in meters.

is equal to 100 m.

, , and are constants dependent on the terrain type.

is a statistical term for random shadow fading (zero mean).


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References

For more information about the IEEE 802.16 model, see the following references:

Erceg, Vinko, et al. An Empirically Based Path Loss Model for Wireless Channels in Suburban Environments. IEEE Journal on Selected Areas in Communications. Vol. 17, No 7, July 1999.

The IEEE 802.16 Working Group on Broadband Wireless Access Standards web site athttp://ieee802.org/16.

Chang, D.K. IEEE 802.16 Technical Backgrounder. IEEE 802.16 Broadband Wireless Access Working Group. May 2002.

CRC-Predict model

You can obtain information about CRC-Predict model properties by pressing the F1key from the Predict Parameters or the Predict Properties dialog box. For moredetailed information, see the CRC-Predict Propagation Model Technical Note. Planet Application Notes and Technical Notes are available from the Mentum web page.

CRC-Predict is a general-purpose model intended for macrocell planning. It is not a ray-tracing model and, as such, should not be used with high-resolution data. Instead, it is best used with geodata with a resolution between 20 to 30 meter

s. You can use it in most circumstances, regardless of the kind of terrain, if detailed terrain or clutter information or both are available. The following cases are exceptions:

for very short paths, for example micro-cellular paths, in which the locations of individual buildings are important

when a very rapid calculation is wanted, because the CRC-Predict model is more computationally intensive than most models

The path loss calculation in the CRC-Predict model is designed for the VHF to UHF (30 MHz to 3 GHz) frequency range. The physical principles used by the CRC-Predict model are also applicable up to 30 GHz. However, accurate predictions for t

hat range depend on very detailed and accurate terrain data, and currently thereare no supporting test measurements. Also, above 10 GHz, rain attenuation becomes significant. The principal algorithm is a diffraction calculation, based on the Fresnel-Kirchoff theory that takes terrain into account in a detailed way. Anestimate of the additional loss for obstructions such as trees, buildings, or other objects is included when data on clutter classes are available. Tropospheric scatter is included for long paths. Estimates of time and location variabilitycan be made.

The diffraction algorithm samples the propagation path from the transmitter to the receiver and determines the signal strength at many points in space. First, the wave field is determined as a function of height (a vertical column of many values) above a terrain point close to the transmitter by an elementary calculati

on. Then, using the Huygens principle of physical optics, each of these field points is regarded as a source of radiation, and from them, the signal strength iscalculated a little farther away. In this way, a marching algorithm simulates the progress of the radio wave from the transmitter to the end of the path. Eventhough the signal strength is calculated at many points, an efficient integration algorithm and a choice of only the most important signal strength points permit the integration calculation to be fast enough for practical use.

The CRC-Predict model also uses surface-type or clutter data in its calculations. See Appendix C: Clutter Propertieson page 443. Because CRC-Predict is a determi


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nistic model, the more precise and physically realistic terrain and clutter information you use, the more accurate the output tuned model will be.

Clutter interacts with the algorithm in two ways:

As the wave propagates over the ground toward a distant receiver, the effectiveheight of the ground is assumed to be the real height of the ground plus the assumed clutter height.

Clutter close to the receiver is assumed to terminate close to the receiver, e.g., 50 meters. That is, the receiving antenna is not assumed to be on the doorstep of a building, or in the middle of a forest, but rather on a street or in a road allowance in the forest. Part of the calculation is an estimate of the attenuation from the clutter down to street level.

In addition to the height and distance of solid (opaque) clutter, there is an additional attenuation, entirely empirical, which takes into account trees and other absorbing material adjacent to the receiving antenna. This attenuation factor(expressed in decibels) is the parameter most easily used to make median predictions agree with measurements in a particular area (model tuning).

CRC Predict-Air

Only masked path loss is calculated and saved in the prediction files. As a resu

lt, if you change any site setting (other than transmitted power), all of the prediction files are regenerated.

CRC-Predict Air is a unique model designed for high-altitude communication (e.g., aircraft to ground) where the signal is being broadcast upwards (between 0 and+90/-90 degrees). It is based on the CRC-Predict 4.0 propagation model. You canuse the CRC-Predict Air model in two modes:

AMSL (Above Mean Sea Level) modein this mode, you can define the antenna height.For the purpose of propagation calculation, the receive height remains at a constant height above sea level.

AGL (Above Ground Level) modein this mode, the receiver antenna height will be relative to the ground level as defined by the input Digital Elevation Model (DEM).

Unlike the CRC-Predict model, this new model will not generate path loss predictions (grid files) which can be re-masked. It is also important to note that youcannot tune CRC-Predict Air models.

The Point-to-Point tool does not support the CRC-Predict Air propagation model;however, the CRC-Predict 4 model provides results similar to the CRC-Predict Airmodel when used in AGL mode.

Universal model

The Universal model is only available if you have purchased a license. You can obtain detailed information about the Universal model by pressing the F1 key fromthe Universal Model Parameters dialog box. The online Help for this model contains context-sensitive help, as well as the Universal Model User Guide.

The Universal model is a high-performance deterministic propagation model that has been integrated into Planet. Unlike other propagation models, the Universal model automatically adapts to all engineering technologies (i.e., micro, mini, sm


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all, and macro cells), to all environments (i.e., dense urban, urban, suburban,mountainous, maritime, and open), and to all systems (i.e., GSM, GPRS, EDGE, UMTS, WIFI, and WIMAX) in a frequency range that spans from 400MHz to 5GHz.

In addition, the Universal Model:

uses a new AGL layer and a new polygon layer where modifications to the layers can be done directly in the Map window.

outperforms other models in terms of the speed and accuracy of predictions.

Q9 model

The Q9 propagation model is based on the Okumura-Hata model. Using the variablesshown in Figure 4.2, it calculates the expected pathloss between the transmitter and the receiver using the terrain profile. In other words, it considers a cross-section of the earth along a straight line between the transmitter and the receiver. This propagation model is most useful for frequency bands in the 150-2000 MHz range and works best within a radius of 0.2-100 km. The Q9 model is intended for use with high-resolution elevation and clutter data.

Pathloss depends on frequency as well as the antenna heights of the transmitterand the receiver. The Q9 model allows for both uptilt and downtilt of antennas and takes into account the vertical antenna pattern.

There are three input values that the Q9 model considers:

Okumura-Hatas wave propagation equations with modifying parameters A0 to A3. SeeEquation 4.2 on page 155. For more information on the A0 to A3 parameters, pressthe F1 key in the Q9 Parameters dialog box.

Extra losses that occur when wave propagation is disturbed by obstacles such asmountain peaks. When the distance between the transmitter and receiver becomes sufficiently large, a correction due to earths curvature is necessary.

Land use code loss.

The Figure below illustrates the variables that are taken into account to calculate pathloss.

Equation 4.1 details the formula used to calculate pathloss.

Equation 4.1 Pathloss calculation

Where:

Lb is the pathloss

HOA (Hata Open Area) is a variant of Okumura-Hatas equation in dB as shown in equation Equation 4.2

mk[mobile] is the land use code at the mobile in dB

is a parameter related to the knife-edge diffraction

KDFR is the contribution from knife-edge diffraction in dB


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JDFR is the diffraction loss due to the spherical earth in dB

Equation 4.2 Hata Open Area equation

Where:

A11 is equal to A1 x log d

g(F) is equal to 44.49 x logF - 4.78 x (logF)2

HEBK is the effective antenna height in meters as defined in the Q9 propagationmodel.

d is the distance from the base antenna to the mobile in kilometers

A0, A1, A2, A3 are Q9 model tuning parameters

WaveSight model

The WaveSightmodel is only available if you have purchased a license. You can obtain detailed information about the WaveSight model by pressing the F1 key fromthe WaveSight Model Properties dialog box. The online Help for these models contains context-sensitive help, as well as the WaveSight User Guide.

The WaveSight model is based on the uniform theory of diffraction. To predict the signal power, the WaveSight model takes individual buildings and vegetation, as well as terrain and clutter, into account.

The WaveSight model is not restricted to specific environments. It can be applied in urban, suburban, rural, and open areas. However, most of the tests on the m

odel were conducted in urban and suburban areas. No tests were conducted for a radius greater than 20 km.

Because of the physical nature of the model, which uses the uniform theory of diffraction, frequency is a parameter of the model. Extensive tests were performedin the 800, 900, 1800, and 2000 MHz bands.

The WaveSight model enables computations with no limitation on transmitter or receiver heights; however, no drive test data was available for receiver heights greater than 2 m above ground.

The WaveSight model uses raster data, e.g., terrain and clutter, in a format similar to that used with Planet DMS. In certain cases, the raster data is availabl

e in several resolutionstypically a resolution of 20 m or more for a large area such as an entire state or nation, and 5 m for small built-up areas. In such cases, the WaveSight model uses the highest available resolution associated with thearea under consideration.

The required accuracy is 2 m on the wall position. All buildings with a footprint larger than 16 m2 must be represented in the building database. The WaveSightUser Guide lists the consistency rules required from the vector database, i.e.,no open polygons or building overlap.


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One of the input parameters used by the WaveSight model is the attenuation lossincurred going from outdoor to indoor. The WaveSight model uses this value to compute the signal strengths inside the building.

Wavecall is constantly improving WaveSight performance on an increasing pool ofmeasurements. Whenever a divergence between model and data is observed, the model is updated and retested on all available routes to ensure that the modified model is consistent with experimental data. Therefore the overall performance of the model is constantly increased. Thus, in general, there is no need for the model to be tuned.

Because of the subjective nature of the clutter, tuning is advisable in open andrural areas where clutter significantly influences propagation. Tuning must beapplied with care and only when there are sufficient measurement samples available that are representative of the environment.

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