Development of a compact and flexible software-defined radio transmitter for small satellite applications

The volume of data generated by Earth observation satellites has drastically increased in the last years. Consequently, more RF bandwidth is required to download data to ground, and migration to higher frequency is an option. However, the limited resources on small satellite platforms regarding volume, mass and DC power limit the enhancement of bandwidth. The research reported here focusses on the enhancement of integrity, re-configurability and miniaturization. Furthermore, cost-efficient solutions are studied for implementation of high bandwidth downlinks on small satellites. Clearly, a bandwidth-efficient implementation and a migration from the ham radio S-band to the corresponding X-band will increase the download capacity. Low-cost ground receivers, which support the telecommunication standard DVB-S2, are available. DVB-S2 can be adapted for small satellite applications by implementing the Consultative Committee for Space Data System (CCSDS) standard above DVB-S2 in the protocol stack. DVB-S2 supports constant, variable as well as adaptive coding and modulation. Thus, the modulation and coding scheme can change on a frame-by-frame basis depending on channel conditions. In this paper, we describe the development of an own-developed low-cost flexible radio platform by using commercial-off-the-shelf components. An FPGA-based architecture for implementing CCSDS above DVB-S2 protocol stack is presented. This design is capable to compensate for changes in the link conditions, increasing download capacity by 66% for variable and by 130% for adaptive coding and modulation. This increase is crucial for ground terminals located in regions with high rain loss such as South-Asia, or for satellite constellations in low-earth orbit where each satellite has a limited ground station contact window.