High-Data-Rate Communication Techniques for Small Satellites

Modulation and coding techniques that are both power and bandwidth-efficient are examined at the system level in this paper. Such techniques include convolutional encoding with QPSK modulation and the relatively new trellis-coded modulation. Power and bandwidth trade-offs are discussed, a sample link calculation is given, and hardware implementation is considered

Tone-Based Command of Deep Space Probes using Ground Antennas

A document discusses a technique for enabling the reception of spacecraft commands at received signal levels as much as three orders of magnitude below those of current deep space systems. Tone-based commanding deals with the reception of commands that are sent in the form of precise frequency offsets using an open-loop receiver. The key elements of this technique are an ultrastable oscillator and open-loop receiver onboard the spacecraft, both of which are part of the existing New Horizons (Pluto flyby) communications system design. This enables possible flight experimentation for tone-based commanding during the long cruise of the spacecraft to Pluto. In this technique, it is also necessary to accurately remove Doppler shift from the uplink signal presented to the spacecraft. A signal processor in the spacecraft performs a discrete Fourier transform on the received signal to determine the frequency of the received signal. Due to the long-term drift in the oscillators and orbit prediction model, the system is likely to be implemented differentially, where changes in the uplink frequency convey the command information

Tone based command system for reception of very weak signals

This disclosure presents a communication receiver system for spacecraft that includes an open loop receiver adapted to receive a communication signal. An ultrastable oscillator (USO) and a tone detector are connected to the open loop receiver. The open loop receiver translates the communication signal to an intermediate frequency signal using a highly stable reference frequency from the USO. The tone detector extracts commands from the communication signal by evaluating the difference between tones of the communication signal

SIGNAL-TO-NOISE RATIO PERFORMANCE OF THE SAWTOOTH PHASE DETECTOR WHEN DEMODULATING PM SUBCARRIERS

International Telemetering Conference Proceedings / October 13-16, 1986 / Riviera Hotel, Las Vegas, NevadaThe noise performance of the sawtooth phase detector when demodulating a sinusoidal subcarrier plus direct data modulation is studied. At predetection signal-to-noise ratio (SNR) levels of about 10 dB or more, significant improvements in the postdetection SNR of the subcarrier can be obtained using the sawtooth detector rather than a linear multiplier. Below predetection SNR levels of about 10 dB, significant improvements can still be obtained; however, a threshold occurs and the performance degrades until leveling off at 3.2 dB worse than that of a linear multiplier. The predetection SNR level where the sawtooth detector performance becomes worse than that of a linear multiplier depends upon the subcarrier and direct data modulation indices. Performance curves are given between predetection SNR levels of -20 dB and +20 dB for various values of subcarrier modulation index and direct data modulation index.International Foundation for TelemeteringProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit http://www.telemetry.org/index.php/contact-us if you have questions about items in this collection

A Highly Integrated S-Band Transceiver System with Two-Way Doppler Tracking Capability

The present-day emphasis on smaller, lower cost spacecraft missions has generated significant interest in higher levels of integration for spacecraft electronics. One of the more effective approaches is to integrate the core electronics, including the RF hardware, into a single card-based chassis commonly referred to as an Integrated Electronics Module (IEM). This approach has been adopted for the TIMED spacecraft, currently being built for NASA by the Johns Hopkins University Applied Physics Laboratory. Breaking from traditional approaches, TIMED incorporates the S-band transmitter and receiver functions into the IEM along with the spacecraft digital electronics. These RF functions are integrated with portions of the command and data handling system, thus blurring the traditional boundaries between subsystems and resulting in two plug-in cards (uplink and downlink) that perform high level functions for the spacecraft. Although designed for S-band operation, the architecture of the cards is scaleable, permitting them to be adapted to X-band for deep space or high data rate applications. In addition, the cards are capable of performing highly accurate two-way Doppler tracking. Using a noncoherent technique recently developed at APL, velocity accuracy has been demonstrated at the 0.1 mm/s level, thus meeting the stringent requirements of a deep space mission