Collection of Empirical Data for Assessing 800 MHz Coverage Models

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.