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 (p
s
) 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 (
R
). A communication success is achieved when
R \geq R_{r}
where R
r
is a value of
R
required for user-determined acceptable performance. The value of R
r
for a given system is either estimated analytically or determined empirically for a given application. Therefore, the model predicts the probability that
R \geq R_{r}
versus range (or other variables of interest). After a user has established an operationally required probability of successful communication
(p'_{sr})
, the operational range (OR) of a radio system in irregular terrain can be defined as the range at which
p_{s} = p_{sr}
. The model was used to compute p
s
versos range for VHF-FM voice systems for several cases involving helicopters, and the results were compared with measured p
s
data. Reasonable agreement between the predictions and observations wan obtained, but the sample size of the measured p
s
value was too small to consider the comparison to be a validation of the model.