Composite Study Maps
Q: How can I use a Composite Study map to show areas where the problem is low signal level from all the server sites?
A: With HDMapper™ in TAP 6 systems with TAP version 6.0.2100 or higher with a Maintenance Subscription date of August 31, 2006, or later, you can use two different Composite functions together on a map.
The Best Server function in the TAP Composite study enables you to use studies computed for two or more individual sites. The resulting map shows areas where each individual server provides the best signal, and where the “capture margin” requirement is met. The capture margin is the required difference between the maximum signal and any other signals. Adequate capture margin is normally required to enable receiving equipment to discriminate between signals.
For example, consider a study involving four sites as shown below:
The map shows the areas where each site (named “530” through “533”) provides the highest signal level and meets the capture margin requirement (specified as 12dB when the Composite study was set up for this example).
The two other areas shown indicate the locations where the signal level is below 44.56dBu (the minimum required field specified when the study was set up), and where the capture margin specification was not met.
You can adjust the legend settings to display the information that best suits your needs. For example, you can make the “Below 44.56dBu” and “Spec Not Met” symbols transparent. Then the map will display only the areas of service for each site:
You can also reverse the settings to show only the areas that are not served:
It is important to understand the meaning of the two unserved categories.
The Composite study Best Server function first tests for the capture margin requirement. Any locations where the capture margin is not met are ignored, regardless of the field strength levels. Therefore, the “Below…” category means that although the capture margin requirement was met (at least 12dB between the highest signal and all others), the highest signal level was below the minimum required field.
On the other hand, the “Spec not met” category means that the capture margin specification was not met, so the location is unusable, whether or not the field strength level is adequate.
That means that some of the “Spec not met” locations may have adequate field strength and others do not. You may want to distinguish between these unusable areas for the purpose of determining site locations, power levels, etc., to mitigate unserved areas.
The “Maximum” function in the Composite study (in contrast to the “Best Server” function) looks only at the maximum signal level without considering capture margin requirements. Combining a Best Server study along with a Maximum Signal study in HDMapper enables you to see which areas are unusable due to insufficient signal, and which areas have sufficient signal but are unusable because the capture margin specification is not met.
In this example, you can run a Composite study and select Maximum as the Composite Operation when you set up the study. The results are shown below:
Note that the service areas from the four sites are contiguous in several areas, in contrast to the Best Server study. The Maximum study shows only the maximum signal. The Best Server study usually shows areas of non-service between service areas, indicating locations where both sites may provide a high signal level, but the levels are too close to each other in magnitude to meet the capture margin. The Maximum study, with no capture margin specification, does not show this buffer area.
As before, the legend settings can be change to show only the areas of the Maximum Signal study where no site provides the minimum signal level. (All the other settings are made transparent.)
Now, to show both results together, start with the Best Server study in HDMapper:
To add the Maximum Signal study results, click the “Add Coverage Shapefile Layer” button (adding a Composite study with this function requires TAP 6.0.2100 or later and a Maintenance Subscription date of August 31, 2006, or later):
Select the Maximum Signal Composite study for the same sites:
The Maximum layer will completely cover the Best Server Layer:
Double-click the Maximum Signal layer in the legend:
When the Layer property form is displayed, set all symbols as transparent except the “Below …” level:
With the Maximum Signal layer above the Best Server layer, and only the “Below…” layer visible, the Maximum layer shows the areas with inadequate field strength from all sites, and the underlying Best Server layer shows the areas where the signal level is adequate from at least one site, but the capture margin specification is not met.
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Copyright 2006 by SoftWright LLC