Space programs summary no. 37-64, volume 2 for the period 1 June to 31 July 1970. The Deep Space Network

Mariner Mars 1971 mission support, engineering, and design of Deep Space Networ

Synchronization with permutation codes and Reed-Solomon codes

D.Ing. (Electrical And Electronic Engineering)We address the issue of synchronization, using sync-words (or markers), for encoded data. We focus on data that is encoded using permutation codes or Reed-Solomon codes. For each type of code (permutation code and Reed-Solomon code) we give a synchronization procedure or algorithm such that synchronization is improved compared to when the procedure is not employed. The gure of merit for judging the performance is probability of synchronization (acquisition). The word acquisition is used to indicate that a sync-word is acquired or found in the right place in a frame. A new synchronization procedure for permutation codes is presented. This procedure is about nding sync-words that can be used speci cally with permutation codes, such that acceptable synchronization performance is possible even under channels with frequency selective fading/jamming, such as the power line communication channel. Our new procedure is tested with permutation codes known as distance-preserving mappings (DPMs). DPMs were chosen because they have de ned encoding and decoding procedures. Another new procedure for avoiding symbols in Reed-Solomon codes is presented. We call the procedure symbol avoidance. The symbol avoidance procedure is then used to improve the synchronization performance of Reed-Solomon codes, where known binary sync-words are used for synchronization. We give performance comparison results, in terms of probability of synchronization, where we compare Reed-Solomon with and without symbol avoidance applied

Codes for protection from synchronization loss and additive errors

Codes for protection from synchronization loss and additive error

Optical Communication with Semiconductor Laser Diode

Theoretical and experimental performance limits of a free-space direct detection optical communication system were studied using a semiconductor laser diode as the optical transmitter and a silicon avalanche photodiode (APD) as the receiver photodetector. Optical systems using these components are under consideration as replacements for microwave satellite communication links. Optical pulse position modulation (PPM) was chosen as the signal format. An experimental system was constructed that used an aluminum gallium arsenide semiconductor laser diode as the transmitter and a silicon avalanche photodiode photodetector. The system used Q=4 PPM signaling at a source data rate of 25 megabits per second. The PPM signal format requires regeneration of PPM slot clock and word clock waveforms in the receiver. A nearly exact computational procedure was developed to compute receiver bit error rate without using the Gaussion approximation. A transition detector slot clock recovery system using a phase lock loop was developed and implemented. A novel word clock recovery system was also developed. It was found that the results of the nearly exact computational procedure agreed well with actual measurements of receiver performance. The receiver sensitivity achieved was the closest to the quantum limit yet reported for an optical communication system of this type

Space programs summary no. 37-32, volume iv, for the period 1 february - 31 march 1965. supporting research and advanced development

Space programs on telecommunications, space science, propulsion, engineer mechanics, guidance and control, systems, and project engineerin

The Ionospheric Continuous-wave E-region Bistatic Experimental Auroral Radar (ICEBEAR)

The Sun drives many atmospheric processes on Earth through solar electromagnetic radiation, the solar wind, and the solar magnetic field. These solar phenomena interact with a region around the Earth where plasma can be formed, the ionosphere. This region is located 60–1000 km above the surface of the Earth, and is of interest to many scientists and engineers due to the interaction between radio waves and plasma. Variations in the ionospheric plasma density can cause disruptions to GPS signals and radio communications. Attempts have been made to measure the ionospheric plasma properties through the use of rockets, satellites, and remote sensing instrumentation. One of the issues with measuring the ionosphere, specifically the lower altitudes of the ionosphere, is that it is expensive to do in situ. Rockets are required for in situ measurements at altitudes of 90–150 km (the E-region of the ionosphere). Rocket launches are expensive, so more efficient remote methods of measuring the E-region are typically used. This includes radars utilizing radio waves to scatter from the ionospheric plasma. From the scattered signal, plasma properties can be derived to provide insight into the physical processes occurring. The Ionospheric Continuous-wave E-region Bistatic Experimental Auroral Radar (ICEBEAR) was developed to probe the E-region of the ionosphere using this mechanism. Through the use of modern radar hardware and techniques, it was possible to obtain simultaneously high temporal (down to 0.1 s) and spatial (≈ 1.5 km) resolution images of ionospheric plasma density perturbations over a 600 km × 600 km field of view. The radar operates at 49.5 MHz and transmits a continuous-wave, pseudo random noise, phase modulated code to obtain these images. The radar is bistatic, with both transmitter and receiver being located in Saskatchewan, Canada, and operated by the University of Saskatchewan. The radar was designed with future improvements in mind, where each transmitter and receiver antenna are individually controlled/sampled. This Ph.D. dissertation describes the dynamics of the ionosphere, the design and construction of ICEBEAR, and presents some preliminary results, exhibiting the exciting modern capabilities of the system

1995 BRAC Commission

Naval Research Lab: Special Facilities and Equipment Capability Data Call. Tabular data, memos, documents. Box 178, L-110

NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 06)

For abstract, see N75-20149

NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 05)

For abstract, see N75-13677