CDMA-Based Onboard Adaptive Digital Beamforming System for Data Relay Satellite

Abstract

Code Division Multiple Access (CDMA) based onboard adaptive digital beamforming (DBF) system is proposed and implemented on hardware. It is essentially required for Tracking, Telemetry and Tele-command (TTC) operations of multiple moving users (LEO) simultaneously through GEO stationary Data Relay Satellite System (DRSS). CDMA based multiple access scheme is proposed on S-band to provide services to multiple users simultaneously on same frequency and to meet power spectral density requirements on the ground. CDMA based adaptive DBF hardware for S-band nine elements axial mode helix antenna array is developed and performance of system is demonstrated in radiation mode conditions. New signal acquisition scheme based on processing of signal received through wide-receive beam using single antenna element is proposed and implemented on hardware. New scheme to generate reference signal by tracking carrier phase and code phase of incoming signal independently from adaptive DBF module is also proposed and implemented on hardware. End-to-end system simulation results are shown for typical DRSS and human space flight mission (LEO). It shows that system provides 0.8° accuracy in adaptive beam steering which is better than 10% of 3 dB beam-width of nine elements array antenna and provides 9 dB adaptive array gain. CDMA-based adaptive DBF hardware provides array gain of 7 dB in radiation mode under lab environment.