Orbiter Interface Unit and Early Communication System

This report describes the Orbiter Interface Unit (OIU) and the Early Communication System (ECOMM), which are systems of electronic hardware and software that serve as the primary communication links for the International Space Station (ISS). When a space shuttle is at or near the ISS during assembly and resupply missions, the OIU sends groundor crew-initiated commands from the space shuttle to the ISS and relays telemetry from the ISS to the space shuttle s payload data systems. The shuttle then forwards the telemetry to the ground. In the absence of a space shuttle, the ECOMM handles communications between the ISS and Johnson Space Center via the Tracking and Data Relay Satellite System (TDRSS). Innovative features described in the report include (1) a "smart data-buffering algorithm that helps to preserve synchronization (and thereby minimize loss) of telemetric data between the OIU and the space-shuttle payload data interleaver; (2) an ECOMM antenna-autotracking algorithm that selects whichever of two phased-array antennas gives the best TDRSS signal and electronically steers that antenna to track the TDRSS source; and (3) an ECOMM radiation-latchup controller, which detects an abrupt increase in current indicative of radiation-induced latchup and temporarily turns off power to clear the latchup, restoring power after the charge dissipates

Design of globally optimal multiple description scalar quantizers

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references.This thesis investigates the design of globally optimal multiple description scalar quantizers. The design of multiple description scalar quantizers is formulated as a combinatorial optimization problem due to the index assignment issue. The first approach uses the simulated annealing technique coupled with the generalized Lloyd algorithm developed for multiple description scalar quantizers. The second approach utilizes deterministic annealing, where a sequence of smooth energy functions, parameterized by a temperature coefficient is generated. The design of the multiple description scalar quantizer with the simulated annealing algorithm resulted in good index assignments. For Gaussian and Laplacian sources, a significant improvement in the overall distortion of the quantizer was achieved. For the Uniform source, no improvement was observed. The deterministic annealing algorithm used for the design of the multiple description scalar quantizer, performed poorly and was worse than the conventional design method at high rates