The stratospheric platform or High Altitude Platform (HAP) is currently new proposal of wireless infrastructure in the near future. To provide high quality services, investigation of stratospheric platform channel is essential. This paper proposes the definition and the analysis of the narrowband wireless channel for the link between stratospheric platform and terrestrial users based on experiment in "semi-urban" environment. Narrowband channel characteristics are presented in terms of Ricean factor (K factor) and local mean received power over a wide range of elevation angles ranging from 10 0 to 900. Finally in this paper, we performed average bit error probability evaluations based on the proposed channels model. For a given environment where the measurements were conducted, we found a better performance for elevation angles greater than 400.