In the EDX program software within the propagation dialogue the two statistical mechanisms known as “Time“Time/Location Variability” and “Reliability” Variability” and “Reliability” are completely independent of one another.
“Time/Location Variability” are propagation parameters that adjust the path loss calculation and are used to gain confidence that you have an accurate mean path loss prediction.
Whereas, “reliability” is determine by a signal level analysis (a study) and is used to understand receiver performance in the presence of a received signal that is variable. Also, even though these two approaches to signal fading are statistical in nature they don’t necessarily use the same methods. The Time/Location calculations are from Longley-Rice, the Reliability study is a regular Log Normal distribution.
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You can see that these two statistical mechanisms are independent of one another. “Time/Location Variability” is used to gain confidence that you have an accurate mean path loss prediction and “reliability” is used to understand receiver performance in the presence of received signal that is variable.
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To keep things straightforward, A default EDX recommends the Time and Location be set to 50% when doing reliability studies. If you need additional path loss margin to account for propagation loss mechanisms for which the propagation model doesn’t accommodate (unknown clutter effects, wall penetration loss, multipath, etc.), add those in the “dB Margin” entry. Ultimately the best way to determine this value (as well as the dB loss values of your clutter database clutter categories) is to perform drive test measurements. |