Signal Processing Hardware Research Articles

Ultranarrowband searches for extraterrestrial intelligence with dedicated signal-processing hardware

Multichannel spectroscopy with millihertz resolution constitutes an attractive strategy for a microwave search for extraterrestrial intelligence (SETI), assuming the transmission of a narrowband radiofrequency beacon. Such resolution matches the properties of the interstellar medium, and the necessary receiver Doppler corrections provide a high degree of interference rejection. We have constructed a frequency-agile swept receiver with an 8,388,608-channel spectrum analyzer, on-line signal recognition, and multithreshold archiving. A search of 250 Sun-like stars at 1.4 and 2.8 GHz has been carried out with the Arecibo 305-m antenna, and a meridian transit search of the northern sky is in progress at the Harvard-Smithsonian 26-m antenna. Successive spectra of 400 kHz at 0.05 Hz resolution are searched for features characteristics of an intentional narrowband beacon transmission. These spectra are centered on guessable (“magic”) frequencies (such as the 21-cm hydrogen hyperfine line), referenced successively to the local standard of rest, the galactic barycenter, and the cosmic blackbody rest frame.

SoundDroid: A New System for Electronic Post-Production of Sound

Sound Droid is a system with sophisticated sound editing capabilities, which provides eight channels of mixing in its minimal configuration. Sounds are stored on magnetic disk, and can be played back at any time and in any sequence. The fluidity of “soft” cuts encourages creative experimentation, and all sound manipulations are automatically memorized. Being all-digital, Sound Droid eliminates distortion and generation loss in audio processing while providing a significant increase in productivity. Sound Droid incorporates a large variety of special processing – including reverberation, pitch-changing, and Doppler shift. In addition, custom signal-processing software modules can be provided to suit the particular needs of the user. A sophisticated data-base management system facilitates tracking the flow of sound through a production. Sound Droid is based on the audio signal processor, a programmable digital signal processor. A modular architecture makes it possible to adjust the system configuration to suit the needs of the user. Later developments will be based on the same signal-processing hardware, changing only the software and user interface. For example, systems could be provided with additional sliders in a mixing system, multiple operator consoles for a large-scale post-production, and even a keyboard for sound synthesis.

The Devevolpment of a New High Speed 3-Terminal Line Protection Scheme

A new high speed Current Differential protection scheme for application to three-terminal transmission lines is described. The scheme utilises a wide-band Fibre Optic Link and the results show that the special filtering and signal processing techniques developed provide a performance which satisfies the requirements for reliable and secure protection of Teed feeders. The protection was developed using CAD techniques and the methods proposed are readily implemented using present generation signal processing hardware.

Real time signal processing applications of a distributed array processor

A compact and highly programmable processor based on the architecture of the ICL Distributed Array Processor (DAP) is under current development for real time signal processing applications. The architecture is described and the applicability of this highly concurrent machine is demonstrated with specific reference to algorithms in speech recognition, radar, signal classification and image processing. The results indicate that the performance compares well with existing dedicated digital signal processing hardware.

Signal processing and engineering analysis on personal computers

Initially, the ability of personal computers to perform signal processing or multivariate analysis was severely limited by small memory address space and lack of scientific language support. Recently, however, this situation has changed, with large memory sizes common and with the availability of mainframe languages such as FORTRAN-77 to support complex and double-precision expressions. Today, personal computers can be applied to data collection, multivariate analysis, pattern classification, simulation of signal processing hardware, and other engineering applications. We discuss the conversion of mainframe data analysis software for personal computers, and the use of high-resolution personal computer graphics for data displays. The process is illustrated with the conversion of part of the IEEE signal processing library and of the ARTHUR81 multivariate analysis routines to run on a personal computer. Timing and accuracy results are given for two personal computers--the TI Professional and the IBM PC AT. The use of a personal computer to validate data, obtain measurement statistics, perform classification and cluster analysis, and perform modern spectral analysis is illustrated with run information and typical output displays.

A modern hardware setup for real-time turbulence measurements in two-phase flows

A modern concept of cost-effective digital signal processing hardware for measuring and analysing data from experiments investigating turbulent two-phase flows is presented. Using an array processor together with an appropriate analog-to-digital converter, conventional turbulence characteristics such as turbulence spectra, correlation functions, turbulence intensities and — scales can be evaluated in real time.

VLSI and VHSIC in Signal Processing

Digital technology with its clear advantages over its analogue counterpart has in the last decade further extended its horizons with the advent of Very Large Scale Integration (VLSI) coupled with high operating speed, thus incorporating several functions in a single chip. This functional block design aspect of VLSI coupled with Very Large Scale Integrated Circuits (VHSIC) that promises to revolutionize signal processing hardware is reviewed along with other relevant aspects in this paper. A typical signal processor design example incorporating such devices is presented in detail.

Acoustic signatures of railroad wheels

When a railroad wheel is impacted with a hammer blow it emits a characteristic sound. By comparing sounds from the two members of a wheelset a measure of the difference of their mechanical properties is obtained. Both frequency and time domain processing is found to be useful. Reference will be made to both laboratory and field tests and results will be summarized. Considerations in the design of automatic hammers, wheel sensors, and all weather microphones will be discussed. The influence of train speed on the required performance of hardware will be discussed, and parameters in the selection of signal processing hardware will be defined. The principal objective of the work is to recognize the presence of cracks. The main difficulty with meeting this objective is avoiding false alarms due to differential wheel wear, etc. Progress in developing algorithms to reduce this false alarm rate will be described. [Work supported by the Association of American Railroads.]

Receivers for the NAVSTAR global positioning system

The NAVSTAR global positioning system (g.p.s.) is being actively developed by the USA and is likely to become operational for both civilian and military users in the mid-1980s. Accuracy of position in three dimensions of afew metres and velocity within 0.1 m/s is predicted. The user equipment, essentially a receiver and an antenna, will employ a considerable volume of signal-processing hardware and software. This paper aims to provide for the signal-processing community some basic understanding of the system outline and its operation as a navigation aid; a typical receiver outline is broken into a number of units whose operation is described with some emphasis on the signal-processing aspects. Areas in which improved signal-processing methods could contribute to improved performance, particularly in interference conditions, are examined. The potential of the antenna in improving user equipment performance by providing angular selectivity against interference is examined briefly; results from the literature indicate improvement of up to 30dB. New signal-processing technologies, surface-accoustic-wave devices and c.c.d.s are likely to contribute to g.p.s receiver development in both frequency-generation and signal-processing areas.

On decoding techniques for residue number system realizations of digital signal processing hardware

In a recent issue of this journal, a hardware implementation of the Chinese Remainder Theorem was proposed for the translation of residue coded outputs into natural integer for an FIR filter realization. The method requires a modulo <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> adder-shifter network which is not commercially available and has to be constructed from more basic logic elements. This letter presents a more successful technique based on a mixed-radix conversion process. The residue to binary decoder can be built using commercially available elements and requires shorter word lengths in the ROM which stores the output function.

Delay Generated Offset: A Direction Sensitive Pulse-Coherent Doppler Detection Technique

An offset-frequency (heterodyne) direction sensitive coherentpulsed Doppler detection method requiring a single digitally synthesized phase-shiftable oscillator and a single mixer is described. Less stringent demands are imposed on hardware in obtaining offset-frequency stability and rejection of internally generated electrical clutter, as compared with the conventional offset method employing two oscillators. Simplification of hardware and postdetector signal processing as compared with the quadrature method (two parallel homodyne detectors) is anticipated. This technique has direct application in medical ultrasonics and is generally applicable to sonar and radar systems.