Urban and Terrestrial Models

Urban Propagation Wireless InSite Model

The Urban Propagation Wireless InSite model offers a selection of a deterministic model and some empirical models for calculating path loss between two locations in an urban environment. The deterministic model, Triple Path Geodesic, was developed by Remcom as a derivative of their Wireless InSite 3D propagation loss module, Wireless InSite.

The Triple Path Geodesic model is a rapid urban propagation model that uses the buildings' 3D geometry data to define an urban environment. The 3D geometry data is used to compute wedge diffractions. The Triple Path Geodesic model produces higher-fidelity results than empirical models, but this comes with greatly increased computation time as a full physics-based model.

For more information on the fidelity of Remcom's Wireless InSite module, see Fidelity at High Speed: Wireless Insite Real Time Module (PDF).

The Urban Propagation Wireless InSite model accounts for the directional gains of complex transmitter and complex receiver antennas for computing propagation field strengths.

Wireless InSite uses mean sea level (MSL) as its internal altitude reference. The submodels, such as Hata, COST-Hata, and Walfisch-Ikegami, apply minimum and maximum limits on the transmitter and receiver object altitudes as well as on the link range on the shapefile tile. AGI recommends using terrain as the altitude reference in the scenario. An option is to have AGI World Terrain in the scenario as the base terrain. The reference you use for urban building geometry should be the same as for your STK objects. Here are some guidelines for ensuring compatibility:

Using terrain: When you select Terrain as the reference for the building geometry, then any STK objects (facilities, aircraft, etc.) must use terrain as the altitude reference. Therefore, you must have terrain available for your STK scenario.
Terrain is not available: You can use MSL for your building geometry reference. STK will default to using WGS-84 as the scenario altitude reference. Therefore, you must either switch your STK scenario to using MSL as the altitude reference, or you should adjust the altitudes of your STK objects so that the resulting altitudes of the objects are correct with respect to MSL.

The following frequency and STK object settings are recommended or required for analysis with the Triple Path Geodesic model:

Frequency: Frequency cannot go below 100 MHz. There is no upper limit restriction; however, above 7 GHz, predictions can become more sensitive to the finer resolution building details that may not be present in the shapefile or in the model's internal, simplified geometry.
Height Above Ground: Provided that both transmitter and receiver are above ground, there is no height restriction. However, prediction fidelity declines if both the transmitter and receiver are on or close to the ground (less than one meter). This is because ground conditions that are important to the analysis (e.g., ground cancellation) are not included.
Line of Sight and Az-El Mask constraints: AGI recommends that you not enable STK Line-of-Sight and Az-El Mask constraints. The Triple Path Geodesic model of the Urban Propagation Extension employs a higher-fidelity algorithm to simulate RF propagation in an urban environment than a simple line-of-sight prediction. In particular, the model has the capability to make signal attenuation predictions in situations with an obscured line-of-sight transmission. It does so by considering three of the most significant paths of diffracted energy around buildings and over terrain. Thus, the use of Line-of-Sight and Az-El/terrain mask constraints is not appropriate when using the Triple Path Geodesic model.

For information on the recommended shapefile types, see Shapefile Requirements for the Urban Propagation Extension.

Click here for step-by-step instructions on modeling propagation loss in an urban environment.

In STK 10.0.1, access sampling was increased for the Urban Propagation model to help capture small and sudden variations in visibility and the constraint figures of merit computations. However, AGI advises that you review your scenario objects' dynamics and adjust the sampling step size on the Access Advanced properties page, if needed.

You can set the following parameters for the Urban Propagation Wireless InSite model:

Option	Description
Calculation Method	Select a propagation model to calculate path loss between two locations in an urban environment. All models except for TPGEODESIC perform submillisecond calculations. TPGEODESIC performs in the 1.5 millisecond range. All calculation models need building geometry data. Deterministic Model The deterministic model, which is the default, is the preferred model. It produces higher-fidelity results than empirical models. TPGEODESIC. Triple Path Geodesic is a Remcom deterministic, ray-based model designed to enhance vertical plane urban propagation calculations. It includes the additional energy that diffracts around the sides of building that obscure the line of sight between the transmitter and the receiver. The model determines side paths by constructing a convex hull in the plane perpendicular to the vertical plane that contains the transmitter and receiver. Triple Path Geodesic returns the no-data value unless it meets this restriction: the transmitter and receiver must be outside of buildings and above ground. The TPGEODESIC model provides good general coverage of cityscapes between any pair of antennas not located underground or indoors. Here is a summary of the capabilities of the TPGEODESIC model: Frequency range: 100 MHz - 100 GHz Range: Computation limited to paths over the urban geometry tile Antenna heights: all Antenna types: all Polarization: all Electric field summation: Power sum Empirical Models Select an empirical model if you want ultrafast characterization of urban performance. HATA. This is a purely statistical, nondeterministic model that uses simple equations to account for frequency, transmitting antenna height, receiving antenna height, and the distance from the transmitting to the receiving antenna. It uses these parameters to predict field strength using an equation derived from measurements. The Hata model constructs a single direct ray from the transmitter to the receiver and treats this as the ray path. Hata evaluates the patterns of the transmitting and receiving antennas using the direction of this ray. Therefore, this model will not capture multipath effects, so AGI recommends against using it to model urban areas. The Hata model will compute for a wide range of data, but validity of results is only assured when meeting the following criteria: Frequency: 150 - 1500 MHz Distance from transmitter to receiver: 1 - 20 km Transmitting antenna height: 30 - 200 m Receiving antenna height: 1 - 10 m Antenna type can be any; recommend using isotropic or omnidirectional for receiving antennas COST_HATA. This is also a purely statistical model that is an extension to the Hata model for higher frequencies. The model is intended for urban and suburban areas. The COST-Hata model constructs a single direct ray from the transmitter to the receiver and treats this as the ray path. COST-Hata evaluates the patterns of the transmitting and receiving antennas using the direction of this ray. Therefore, this model will not capture multipath effects, but it is available if you need very fast rough approximations. COST-Hata will compute for a wide range of data, but validity of results is only assured when meeting these criteria: Frequency: 1500 - 2000 MHz Distance from transmitter to receiver: 1 - 20 km Transmitting antenna height: 30 - 200 m Receiving antenna height: 1 - 10 m Antenna type can be any; recommend using isotropic or omnidirectional for receiving antennas WALFISCH_IKEGAMI. Walfisch-Ikegami is a semideterministic model with empirically derived coefficients that is useful in predictions where over-the-rooftop diffractions contribute the dominant energy. It is a hybrid model that needs the urban geometry of the tile, which drives the requirement for stringent limits on object altitudes and ranges. Buildings in the vertical plane between the transmitting and receiving antennas are used to seed the equations. If the transmitting and receiving objects are outside the shapefile boundary, STK will compute the link boundary crossings and will compute loss from boundary line to boundary line. STK will strictly enforce the limits; if you exceed them, STK will set the loss to 0 dB. These are the limits for Walfisch-Ikegami: Frequency range: 800 - 2000 MHz Distance from transmitter to receiver: 20 m - 5 km Transmitting antenna height: 4 - 50 m Receiving antenna height: 1- 3 m In some situations, a model may return a no-data value rather than a path loss value, such as when a receiver is underground. (for Hata and COST-Hata) Parsons, J.D., The Mobile Radio Propagation Channel Second Edition, 2000 John Wiley & Sons, Ltd. ISBN 0 471 98857 X.
Enable Ground Reflection	Select this option if you want the Urban Propagation Wireless InSite model to consider ground reflection when computing the direct line of sight (LOS) path. When there is no direct line of sight, such as when the path is obstructed by a building, ground reflection is not applicable.
Urban Geometry Data File	Browse to and select the shapefile (.shp) to use in calculating path loss. AGI recommends that the shapefile be limited to a maximum range of three square kilometers. The shapefile may contain holes in its building polygons (e.g., courtyards, shafts, and plazas), but those holes are not recognized either analytically or graphically by the Urban Propagation Extension. For additional guidelines on selecting shapefiles and using urban data, refer to Obtaining Urban Terrain Data and Shapefile Requirements. Sometimes one of the assets is outside of the shapefile geographic extents. When this occurs, STK uses the urban propagation model specified in the Calculation Method field to model the propagation loss along the portion of the signal path that is within the shapefile geographic extents. Also, STK uses the latest ITU-R P676 model from the border of the shapefile to the asset. The STK Urban Propagation Model does not support UTM coordinate-based geometry shapefiles STK does not process the shapefile until you compute an Access > Link Budget for the first time. The size and area of the shapefile determines the time it takes to process the shapefile. Large shapefiles can take several hours to process. The STK Message Viewer will show the start and completion of processing for both terrain facets and urban geometry. See Shapefile Requirements for the Urban Propagation Capability for more information about editing shapefiles and supported formats. STK will save the shapefile geometry computation whenever you save the scenario.
Projection/Horizontal Datum	Select the horizontal coordinate reference.
Building Height Data Attribute	Select the data attribute in the Urban Geometry Data file that provides the building height.
Building Height Reference Method	Specify the method for determining the height of buildings: HeightAboveSeaLevel: Use this if the z value is an absolute height that should not be moved. The terrain is placed under the z value of the building without affecting the building height. It is an error to have a roof underground. HeightAboveTerrain: Use this if the z value specifies the building height relative to the terrain. When you select HeightAboveTerrain, the calculation determines a building height relative to terrain. Buildings on irregular terrain may have corners at different terrain elevations. The Urban Propagation Extension adjusts building elevations until the first vertex touches the terrain. Then it extrudes the building walls until the building is in contact with the terrain at every point along the base of the building. The calculated building height becomes the minimum height of the building above irregular terrain.
Override Geometry Tile Origin	The origin of the urban geometry data coordinates appears in the Latitude and Longitude fields. You have the option to relocate the geometry data reference origin to a different location by overriding the data read from the file.
Use Terrain Data	If you loaded terrain into your scenario, select this check box to incorporate the effect of terrain in your urban propagation analysis. If not selected, the analysis instead uses mean sea level as its ground surface. Thirty-meter resolution terrain is a good representation of terrain. Having terrain with a high resolution requires a very large number of samples and a large amount of memory to process that terrain. For example, moving from thirty-meter resolution terrain to one-meter resolution terrain will create 900 times more samples, and will use more processing time and memory.
Min Required Terrain Extents	These latitude and longitude values show the extent of the loaded shapefile and are for informational purposes only. You can use these values to select an appropriate terrain source to cover the minimum extents for an urban propagation loss computation using terrain.