Tech Briefs

Traditional command uplink receivers are very limited in performance capability, take a long time to acquire, cannot operate on both uplink bands (NASA & AFSCN), and only support low-rate communications. As a result, transceivers end up on many programs’ critical paths, even though they should be a standard purchased spacecraft subsystem. Also, many missions are impacted by the low effective uplink throughput. In order to tackle these challenges, a transceiver was developed that will provide on-site frequency agility, support of high uplink rates, and operation on both NASA and AFSCN frequency bands.

The device is a low-power, high-reliability, and high-performance digital signal processing (DSP) demodulator for an on-orbit programmable command receiver. There are several drivers available for the modulation technique. Those drivers include receiver complexity, power consumption, spectral efficiency, and CCSDS (Consultative Committee for Space Data Systems) framework recommendations. Previous research suggests that GMSK (Gaussian Minimum Shift Keying) and BPSK (Binary Phase Shift Keying) are good choices for the uplink modulation format. This approach is supported by CCSDS and helps reduce receiver complexity.

Analysis and derived simulations were performed for power, bandwidth, clock generator, bit synchronizer, and carrier loop. At the time of this reporting, the code was not yet written, and will evolve from the existing analysis and simulation.

The demodulator operates on the two selected modes, BPSK and GMSK. The bit rate covers multiple octaves and includes a bit synchronizer function. The modulator is unique in that it operates with high Doppler, over a large bit rate range, and in a space environment. In addition, this demodulator attempts to maximize low power, small size, and ease of modification to new applications.

Novel features of the innovation include DSP logic for multiple modulation types in a low-power and rad-tolerant platform. Advantages include on-the-fly programmable low-power receive communications for spacecraft.

This work was done by Jeffrey Janicik and Assi Friedman of Innoflight, Inc. for Goddard Space Flight Center. GSC-16030-1

This Brief includes a Technical Support Package (TSP).

DSP/FPGA Design for a High-Speed Programmable S-Band Space Transceiver (reference GSC-16030-1) is currently available for download from the TSP library.

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