Prototype Design of a Software-Defined Radio Based SATCOM Modem

Beyond line-of-sight communication is important from a tactical point of view, as it yields network-centric capability and data link between multi-generation machines. Satellite communication (SATCOM) is the only technology that provides this capability. The SATCOM modem is an important communication component that provides the capability to convert baseband data to radio frequency (RF) band and vice versa. The commercial off-the-shelf (COTS) modems for SATCOM have well-known packet and communication standards resulting in non-confidentiality and limited user control for customized usage. Considering recent trends in modern digital communication systems, namely 4G/5G networks, satellite constellations and tactical communication, it is evident that reliable and low latency communication between multi-generation machines is inevitable. Keeping in view the limitations of COTS modems, in this paper, we present a prototype design of a software-defined radio based SATCOM modem for geostationary satellites with a bent-pipe satellite transponder. The proposed design accommodates multiple provisions such as selection of variable-length message signal, formation of packet structure, inclusion of cyclic redundancy check, implementation of Reed-Solomon codes for short block-lengths at various rates, direct sequence spread spectrum with various modulation schemes including binary phase shift-keying (BPSK), quadrature phase shift-keying (QPSK) and 8PSK at various transmission rates and reliability requirements. In addition, the proposed design incorporates anti-jamming capability and user anonymity along with self-reliance. The prototype provides a testing platform for communication in both static and dynamic environments in different orbits such as geostationary Earth orbit (GEO), medium Earth orbit (MEO), and low Earth orbit (LEO).