Adaptive Rain Fade Compensation

Abstract

Any satellite communications system operating near 20 GHz will occassionally experience deep fades due to rain attenuation. To maintain a high grade of service in spite of these fades such a system must have a large available margin. An approach to providing this margin in a high capacity FDMA communications satellite without requiring exorbitant spacecraft power or ground station antenna diversity is to dynamically provide a large margin to those links experiencing deep fades while maintaining only a small fade margin on all other links. This paper presents a brief description of FDMA systems; single beam SCPC operation, multiple beam satellite switched FDMA (SS-FDMA),and investigates the optimization of the dynamic FDMA links in a severely fading environment. A solution taking into consideration transponder intermodulation distortion, cochannel and cross polarization antenna interference (in multiple beam antenna systems) and rain fade statistics is derived. The system is optimized with respect to minimum required thermal signal to noise ratio under peak interference conditions. A sample system configuration is presented which shows that such systems can achieve availability approaching 0.9999 at Ka-Band.