What is SDR?
Software-Defined Radio (SDR) is an architecture where the core radio processing functions — modulation, demodulation, filtering, channel coding, and signal processing — are implemented in software on reconfigurable digital processors (FPGAs, DSPs, or general-purpose CPUs) rather than fixed dedicated hardware. The hardware front-end (antenna, RF amplifiers, analog-to-digital converters) handles only the physical signal conversion; everything else is computed in software.
Benefits for satellite systems
SDR enables a satellite payload or ground terminal to support multiple waveforms from a single hardware platform. A ground terminal using SDR can be reconfigured via firmware update to support DVB-S2X, DVB-RCS2, proprietary VSAT waveforms, or military waveforms — adapting to new standards without hardware replacement. On-board SDR payloads allow operators to change the satellite's air interface, modulation scheme, or frequency plan in orbit, extending the operational relevance of the spacecraft over its 15-year lifetime. SpaceX's Starlink uses SDR principles in its phased-array ground terminals and Gen2 satellite payloads.
Ground terminal SDR evolution
The COTS SDR market — led by companies like Ettus Research (USRP), Analog Devices (ADALM-PLUTO), and Lime Microsystems — has dramatically lowered the cost of SDR hardware, enabling software-defined satellite ground stations for CubeSat operators at prices below $1,000. This has been transformative for the smallsat market, where operators can use SDR-based ground stations to support multiple satellite missions simultaneously, changing radio configurations between passes. Major VSAT modem suppliers (iDirect, Hughes, Comtech) have all moved to software-defined modem architectures.