Computer prediction of service areas for VHF and UHF land mobile radio services

A computer program written to predict the effective service area of a transmitter in a VHF or UHF mobile radio network is described. The computed results enable field strength contours to be determined, and hence provide more useful information than is possible by reference to standard statistical curves. Present manual methods of calculating the attenuation to be expected over transmission paths rely on the laborious extraction of essential ground profile information along the path joining the transmitter to the receiver. This difficulty may be overcome by using a topographical data base in a computerized method of service area prediction. With this scheme each data base entry represents the effective terrain height above sea level within each 0.5-km square. A high-speed computer can access the necessary information from the data base to reconstruct a close approximation of the radio path profile. The reconstructed profile is then processed to calculate the transmission loss. These computations are repeated for numerous points throughout the area and enable field strength contours to be deduced. The propagation model described forms part of a fully automated frequency assignment procedure for the private land mobile radio services in operation in the Directorate of Radio Technology, Home Office, UK.