A functional description of the buffered telemetry demodulator for the Galileo mission to Jupiter

Abstract

The paper functionally describes a novel buffered telemetry demodulator (BTD) for the Galileo spacecraft's upcoming encounter with Jupiter. Due to an inoperative high gain antenna the Galileo signal is characterized by low data rates and an extremely weak space-to-ground communication link. The extremely weak downlink is expected to result in an unusually long acquisition time and frequent cycle slips. In this case, the BTD is most useful as it operates on recorded (or buffered) digital samples to extract symbols from the received signal. The key features of the BTD are (1) its ability to reprocess the signal to reduce acquisition time and enable resynchronization, (2) its ability to use future information about the signal and perform smoothing in the past to recover symbols lost during acquisition and resynchronization, (3) its minimized recording bandwidth as each harmonic of a square-wave subcarrier is recorded individually, and (4) its parallel architecture that enables a multi-processor implementation. The paper discusses baseband recording and demodulation schemes, as well as, the computational speed required to implement the BTD in software. Several general purpose computers that can be used for implementation are identified.<>