Rician Intersymbol Interference in Frequency Shift Keying

Abstract

Many communications links involve a reflected signal which is Rician in nature. In troposcatter systems, this reflection constitutes the entire received signal while in communications between satellites or aircraft, such a reflection from the surface corrupts the direct signal. Other such situations involve low elevation tracking or intentional coherent jamming. This paper derives the bit error probability for a non-coherent binary FSK link in this environment for any order of diversity and any ratio of specular to diffuse reflection assuming orthogonal signalling frequencies, matched filter detection and perfect bit synchronization. The interfering signal may represent the same datum as the direct signal (Mark-Mark interference) or, for delays longer than a bit period, the interference may appear in the opposite receiver channel from the direct signal (Mark-Space interference). Results are stated in terms of the direct signal energy to noise density ratio and factors determined by the geometry of the situation; the ratio of direct signal to interfering power, the ratio of specular to diffuse reflected power and the relative carrier phases of the direct signal and the specular reflection in the Mark-Mark case. These geometric parameters are most conveniently treated separately from the modulation and detection problem.