Reeder N. Ward

Laser/rf personnel identification system

This paper documents the design of a Laser/RF Personnel Identification System developed for the US Army Communications and Electronics Command (CECOM) for soldier identification. The system has dual use applications, including law enforcement officer protection, and includes a laser interrogation unit with a programmable activation code. The interrogation unit is very directive for low probability of intercept (LPI), which is of interest during covert operations. A responder unit, worn by the law enforcement personnel or soldier, transmits an LPI radio frequency (RF) response only after receiving the proper interrogation code. The basic subsystems for the identification system are a laser interrogation unit, an RF responder unit, and a programming/synchronization unit. In this paper, the operating principles for the subsystems are reviewed and design issues are discussed. In addition to the design performed for CECOM, a breadboard system was developed to validate the concept. Hardware implementation is reviewed and field testing of the breadboard is presented.

Signal distortion in an adaptive excision system

A narrowband signal excision system uses spatial light modulators in the spatial frequency domain to notch energy caused by narrowband interferers. We review the signal excision process and discuss the optical system developed to monitor the noise spectrum. A postdetection system searches for narrowband interferers in wideband spectra and provides control signals to implement the required notch; experimental results of the distortion imposed on short pulse signals are given.

Soldier identification system for dismounted soldier application: prototype development and testing

This paper documents the design and testing of a prototype laser/radio frequency (RF) Soldier Identification (ID) System developed by Dynetics, Inc., Harris, Corp., and the U.S. Army Communications and Electronics Command (CECOM). The Soldier ID system consists of an Interrogation Unit, a Responder Unit, and a Programming Unit. The Interrogation Unit consists of a directive, eyesafe laser and a spread-spectrum RF transceiver. This allows for a low probability of intercept (LPI) interrogation, which is of interest during covert operations. A Responder Unit is worn, for example, by a soldier and transmits an LPI spread-spectrum RF response, only after receiving the proper interrogation codes. The operating principles for the subsystem are reviewed, and key design issues are presented. In addition, both breadboard and prototype test results are presented.

Multifunctional receiver using an acousto-optic spectrum analyzer: an example application and results

Low probability of intercept (LPI), spread-spectrum signals are becoming commonplace in both communication and radar systems. Cooperative receivers process these signals to provide large gains in the output signal-to-noise ratios (SNRs). Given the low signal power expected during reception and the lack of a priori signal knowledge, intercept receivers have difficulties in providing adequate detection of LPI signals. This detection problem is compounded when high power, narrow-band interference is simultaneously present with the LPI signal. A 512-channel acousto-optic spectrum analyzer is used in conjunction with digital processing to implement an autocorrelation-type receiver with interference rejection. Although difficult to implement in radio frequency (rf) or digital electronics, acousto- optic spectrum analyzers may provide a practical solution with sufficient dynamic range for the intercept application. Implementation and algorithm considerations are provided as well as simulated results. Initial experiments confirm LPI signal detection when the signal is minus 5 dB relative to noise and minus 40 dB relative to multiple narrowband interference sources.

Multifunctional receiver using an acousto-optic spectrum analyzer

Acousto-optic spectrum analyzers (AOSAs) provide a convenient means of separating wide bandwidth signals into their frequency components. The two commonly implemented AOSA receivers are fast frequency channelizers and integrating spectral radiometers. By modifying the input signal and by providing additional digital post-processing, the AOSA can also perform radiometry, signal autocorrelation, and cross-correlation. The latter function allows a matched filter receiver to be implemented for signals that have time durations much longer than the signal processor. The resulting signal-to-noise (SNR) improvements from the receiver are consistent with the time-bandwidth product of the waveform, rather than the time-bandwidth product of the acousto-optic device. A mathematical foundation of the processor is presented along with specific receiver implementations.

Coding development for an optical associative memory

An optical associative memory provides rapid content addressing of freeform alphanumeric text stored on an optical disk. A highly parallel, space-integrating intensity correlator has been breadboarded using off-the-shelf components for proof of concept and identification of component characteristics. Performance is found to be sensitive to light source coherence, optics modulation transfer function, media bit placement and contrast uniformity. Simplified processing algorithms extendable to on-chip implementation are evaluated with simulated and experimental results. Conventional codes cannot be optimized to provide a unique coding for a given work, nor do they have a constant optical return from large-area illumination; these are essential to facilitate the correlation readout. A custom code has been developed for correlation readout optimization.