SRI I n t e r n a t i o n a l 1 6 1 1 N . Kent S t r e e t Arlington, VA 22209 SRI International (formerly Stanford Research Institute) has developed a VHF communication system performance model which p r e d i c t s t h e p r o b a b i l i t y of successful communications (es! i n i r r e g u l a r t e r r a i n for both analog voice and d i g l t a l systems. The Longley-Rice model i s used to predict the propagation eff e c t s . A new n o i s e model, based upon i n f o r m a t i o n i n C C I R Report 258, i s used to help estimate predetection s i g n a l -t o -n o i s e r a t i o s (R). A communication success i s achieved when R 2 Rr, where Rr is a v a l u e of R r equired for acceptable performance.The v a l u e of Rr f o r a given system i s e i t h e r e s t i m a t e d a n a l y t i c a l l y o r determined empirically for a given application. Theref o r e , t h e model p r e d i c t s t h e p r o b a b i l i t y t h a t R 2 Rr v e r s u s r a n g e ( o r o t h e r v a r i a b l e s of i n t e r e s t ) . A f t e r a user has established an operationally required prob a b i l i t y of successful communication (esr), the operat i o n a l r a n g e (OR) of a r a d i o s y s t e m i n i r r e g u l a r t e rrain can be defined as the range where ps = psr. The model was used t o compute OR f o r VHF-FM voice systems f o r s e v e r a l example c a s e s , and t h e r e s u l t s were compared with measured data. Reasonable agreement between t h e p r e d i c t i o n s and observations was obtained. I n t r o d u c t i o n Concept of Communications Operational Range One important measure of t h e u t i l i t y of a mobile radio communication system i s the range that can be achieved. The range of a radio communication system depends upon the radio system parameters (e.g., trans-1 .o 0.9 3 0.1 m i t t e r p o w e r ) , t h e loss of s i g n a l power due to propagat i o n from t h e t r a n s m i t t e r t o t h e r e c e i v e r , and t h e amb i e n t r a d i o n o i s e and interference environment in which t h e r e c e i v i n g a n t e n n a must o p e r a t e . The operational requirements and usage also influence the range. The loss a t t r i b u t a b l e t o p r o p a g a t i o n i s not a d e t e r m i n i s t i c q u a n t i t y , n o r i s the ambient radio noise level. Theref o r e , t h e r a n g e of a r a d i o i s b e s t t r e a t e d a s a random ~a r i a b l e . l -~ Also, the propagation, noise and system performance models each have uncertainties that are b e s t d e a l t w i t h a s random v a r i a b l e s . We must consider t h e odds of achieving a s u c c e s s i n a given noiseenvironm e n t . T h i s a p p r o a c h r e q u i r e s t h e s t a t i s t i c a l c o m b i n a t i o n o f t h e u n c e r t a i n t i e s of the many p a r a m e t e r s t h a t e n t e r i n t o p r e d i c t i o n of system performance, including the s t a t i s t i c a l u n c e r t a i n t y of t h e model i t s e l f . One can compute t h e p r o b a b i l i t y of successful communication, p s ...
