TiremPropagationModel Class

To use the TIREM Signal Propagation Model, you must have a TIREM Library license and an additional DLL, which customers can request from AGI Support by emailing support@agi.com.

Note that this implementation uses native libraries to perform the calculation. As a result, this implementation only supports 64-bit Windows and Linux platforms. An older implementation, TiremPropagationModel3_18, is also available without these limitations.

TIREM contains its own versions of signal free-space path loss and atmospheric attenuation. DME Component Libraries also has versions of these loss models, and FreeSpacePathLossModel is added by default by WirelessLinkExtension, and CommunicationSystem. Note that WirelessLinkExtension will check to ensure that only one model computes free-space path loss, and throw an exception, to avoid incorrect results. When using TIREM, decide which free-space path loss model you want to use, and either disable the TIREM calculation by setting UseFreeSpaceLossModel, or remove the FreeSpacePathLossModel.

TIREM (Terrain Integrated Rough Earth Model) examines the terrain profile between the antennas, using the effective Earth radius geometry to determine whether the antennas are within line of sight (LOS) or beyond Line of Sight (BLS) and to find the number, location and extent of sea water bodies along the path. Note that you must ensure you have set the MeanSeaLevel property of the EarthCentralBody for TIREM to work properly. If it is not set, an exception will be thrown.

If LOS, the loss above free space is estimated as the smaller of the reflection region loss due to terrain intrusion into the first Fresnel zone or the spherical Earth loss for an assumed all land path. If there is sea water along the profile, the spherical Earth loss is calculated for an assumed all-sea path using sea water constants. The LOS loss above free space is then taken to be a combination of the all-land loss and all-sea loss weighted by the proportion of land and sea segments along the profile. The total path loss is found as the sum of the LOS loss, the loss due to atmospheric absorption, and the free space loss.

If BLS, the knife edge diffraction losses are found using the Epstein-Peterson method. If these average less than 7 dB, the terrain is regarded as smooth and the diffraction loss above free space is calculated using the spherical Earth model with ground constants for land. If there are bodies of sea water along the profile, the spherical Earth model is used again with sea water constants and the diffraction loss above free space is weighted by the proportion of land and sea segments along the profile. If the average knife edge diffraction loss exceeds 7 dB, the terrain is regarded as rough and the diffraction loss above free space is the sum of the knife edge losses, the reflection region losses that occur between the transmitter and its horizon and the receiver and its horizon (using a method similar to LOS), and (if diffraction occurs on sea water) spherical Earth losses for the sea water segments of the profile. In any case, the loss due to atmospheric absorption and the free space loss are added. Next, the tropospheric-scatter loss is calculated and combined with the atmospheric absorption for the troposcatter geometry. The total path loss is found by comparing the diffraction loss and troposcatter loss and selecting the dominant (noted by the smaller loss) mode.

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