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Edition:Final Report; April 2002 - June 2004
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Abstract:Wireless communications plays an important role in KDOT operations. Currently, decisions pertaining to KDOT’s
800MHz radio system are made on the basis of coverage models that rely on antenna and terrain characteristics to model the
coverage. While this technique is well accepted, its effectiveness could be significantly improved if empirical data were
available to better calibrate and validate the models. The University of Kansas was asked to develop and execute a plan for
collecting the needed empirical data to better calibrate and validate coverage models. Eight towers were selected by KDOT
based on antenna and terrain characteristics to represent a cross section of KDOT’s tower array. A passenger car was
outfitted with an integrated system to record a received signal strength index (RSSI) value every time period. For each data
point, the computer would record the most recent position fix from the GPS receiver (updated about once per second) and
would poll the spectrum analyzer for an RSSI value. A route was planned for each tower to provide the best pattern of data
point locations. Once the data was collected, it was imported into a geographic information system (GIS). Thematic maps of
each tower were generated, showing the RSSI values in graduated colors indicating the strength of the signal. Linear
interpolation was used to generate an RSSI surface plot for each tower. Over 6,500 miles were driven, collecting more than
33,000 RSSI values for the 8 towers considered in this effort. The resulting data provides a wealth of drive test data, useful
for calibrating the ComStudy propagation model, and is sufficient to show the general size and shape of the coverage area for
each tower. Surface plots generated by linearly interpolating the data over a geographic area show the coverage area and
potential dead spots. By using this data to improve the existing propagation models, KDOT can obtain a more precise picture
of the coverage of their radio system across the entire state, and as a result be able to use these and associated resources more
efficiently and effectively.
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