Design, implementation and testing of a flexible fully-digital transponder for low-earth orbit satellite communications

This paper presents a flexible Telemetry, Tracking & Command (TT&C) transponder for Earth Observation (EO) small satellites. The proposed device adds to the state-of-the-art EO TT&C transponders the possibility of scientific data transfer thanks to the high downlink datarate (up to 40 Mbps) and in-flight reconfigurability via Telecomand (TC). The integration of these features in one single device represents a considerable optimization in terms of mass budget, which is important for EO small satellites. Furthermore, in-flight reconfigurability of communication parameters via TC is important for in-orbit link optimization, which is especially useful for Low-Earth Orbit (LEO) satellites where visibility can be as short as few hundreds of seconds. The proposed transponder is a digital radio unit working at 70MHz intermediate frequency (IF). A new custom and configurable hardware accelerator was developed to cover intensive radio DSP functions at IF. The custom hardware is integrated in a single FPGA with a space-compliant processor core, for control, conFIguration and interface with the other satellite subsystems. All the quantization parameters were FIne-tailored to reach a trade-off between hardware complexity and implementation loss (IL). The IF RX/TX ports require eight bits and seven bits, respectively. The IL is 0.5 dB at BER = 10(-5) for the RX chain. A system proof-of-concept was implemented on the Xilinx Virtex 6 VLX75T-FF484 FPGA. The total device occupation is 82%. The power consumption of the design fitted in FPGA is less than 2W. The power consumption of the whole demonstrator board is less than 9W.