Radiation Mode Simulation for Simultaneous Operation of Spread Spectrum and Phase Modulated Telemetry Downlinks of Co-located GEO Spacecrafts

Abstract

Transmission of telemetry data to the ground station is critical for all spacecraft missions. The allocated spectrum for Telemetry downlinks of GEO spacecraft has been overcrowded in recent years due to a steady increase in the number of GEO missions. Implementation of Code Division Multiple Access (CDMA) systems in the same bandwidth is proposed as a solution to overcome this problem. To prove the compatibility of the proposed scheme with existing telemetry downlinks in the same bandwidth, a real-time data acquisition-based experiment has been carried out with hardware in radiated mode to simulate in-orbit conditions in an anechoic chamber. This paper explains the estimation of interference, test methodology & results and recommends the optimal configuration of the ground receiver for demodulation of the CDMA signal in the presence of interference from multiple narrow-band phase modulated signals. The proposed configuration has been proved successful in a recent GEO spacecraft mission.