VHF Radio System Performance Model for Predicting Communications Operational Ranges in Irregular Terrain

This paper describes a VHF communication system performance model which can predict the probability of successful communications (ps) in irregular terrain for both analog and digital systems. The Longley-Rice model is used to predict the propagation effects. A new noise model, based upon information in CCIR Report 258, is used to help estimate predetection signal-to-noise ratios ( ). A communication success is achieved when where Rris a value of required for user-determined acceptable performance. The value of Rrfor a given system is either estimated analytically or determined empirically for a given application. Therefore, the model predicts the probability that versus range (or other variables of interest). After a user has established an operationally required probability of successful communication , the operational range (OR) of a radio system in irregular terrain can be defined as the range at which . The model was used to compute psversos range for VHF-FM voice systems for several cases involving helicopters, and the results were compared with measured psdata. Reasonable agreement between the predictions and observations wan obtained, but the sample size of the measured psvalue was too small to consider the comparison to be a validation of the model.