Radio system performance model for predicting communications operational ranges in irregular terrain

SRI International (formerly Stanford Research Institute) has developed a VHF communication system performance model which predicts the probability of successful communications (Ps) in irregular terrain for both analog voice 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 (R). A communication success is achieved when R ≥ Rr, where Rris a value of R required for 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 R ≥ Rrversus range (or other variables of interest). After a user has established an operationally required probability of successful communication (Psr), the operational range (OR) of a radio system in irregular terrain can be defined as the range where Ps= Psr. The model was used to compute OR for VHF-FM voice systems for several example cases, and the results were compared with measured data. Reasonable agreement between the predictions and observations was obtained.