Calibrating TAP Propagation Models
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Q: How can I use measured field strength data to improve the accuracy of predicted values in TAP?
A: While there is not an automated calibration function in TAP to use measured data, the measurements can be quite useful to help you manually adjust the Propagation Model template to find the settings that best model your environment and applications.
Note that all values in this example are for demonstration purposes only. You should determine appropriate settings for your application.
The article Importing Measured Field Strength Values describes how you can import a file of measured values into TAP. These imported data values then can be used in plotting the coverage just as with predicted values computed in TAP.
Comparing predicted results from TAP with actual measured field data is a good way to determine how to adjust the parameters in TAP to improve future predictions. If you have measured field strength data there are a few things you can do.
Naturally you can compare measured values at certain locations with the computed values from TAP at those locations on an Area Coverage study. If you have an Area Coverage study where the measurements were taken, you can use the mouse tips function to find the computed field strength at or near the measured location.
You can compute a new study at the measurement locations (a “Target Point” study) so you will have computed values at the measured locations.
To “calibrate” your field strength calculations with measured values, compute several studies in TAP with different parameter settings, then compare each study with the measured results to find which parameter settings best match the measured data. Those "best match" parameter settings would be the best place to start when conducting a new study for an unfamiliar area or a new rf system. For example, computing Longley-Rice field strength values with different settings for the Longley-Rice Variability values would be a good way to see the effects of the different variability values and which settings best match the measured data.
With the locations where you have the measured data values you can run area coverage studies using the Target Point coverage area approach) or you can run individual paths profiles in HDPath and compute the field strength values at the RX site in that program one path at a time.
By setting up multiple Longley-Rice Propagation Templates and using different combinations of parameters (primarily changing the Time and Situation variability percentage values) you can run a number of studies or paths and from the results determine which Template settings provide you the best correlation with your measured values.
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