Stephen Riter

An Optimum Phase Reference Detector for Fully Modulated Phase-Shift Keyed Signals

Many modern telemetry systems which use phase-shift keying (PSK) have receivers which derive a coherent reference from the fully modulated PSK signal itself and thus conserve the energy which otherwise would be allocated to a discrete reference signal. In this paper, an optimum receiver structure for estimating a phase reference from the PSK signal itself is derived and its realization discussed. It is shown that at low signal-to-noise ratios, the optimum detector can be realized with a Costas loop. Since a Costas loop and squaring loop exhibit identical performance, it follows that either of these simple devices gives optimum performance for low-input signal-to-noise ratios.

Pulse position modulation acoustic communications

Pulse position modulation (PPM) is a simple and effective technique for transmitting information via the underwater acoustic channel. In this paper engineering design considerations for an underwater acoustic PPM system, including the location of threshold and the effects of multipath, attenuation, and time dispersion, are discussed. Techniques for calculating the required transmitter power, pulse repetition rate, and pulse width to communicate over some specified geometry are given.

Receiver Bandwidth for Optical Fiber PPM Communications

The mean squared error (MSE) in the estimate of the threshold-crossing instant for the received pulse of an optical fiber PPM communications system is calculated for the case of a Gaussian shaped

Dereverberation by Linear Systems Techniques

A linear system approach is presented for the modeling of a stationary layered medium assuming representation by a finite number of thin layers and wave propagation normal to these layers. A linear recursive mathematical model is developed and a method for the identification of parameters is discussed. The results, although specifically derived for the processing of marine seismic data, are applicable to similar type problems in communications and remote sensing.

Comparison Of Three Motion Detection Techniques

The accuracy of motion detection in an image by three proposed techniques is explored using synthetic images with varying contrasts and noise levels. The maximum likelihood test consistently results in a higher probability of detection of true motion than either mean or median tests. However, the maximum likelihood test also consistently has a higher probability of false alarms, that is, the detection of stationary objects as moving objects, than either mean or median tests. For applications in which execution efficiency is at least as important as a high probability of detection, the mean or median tests may be used to advantage.

Telecommunications in Urban Public Services

This paper surveys present municipal communications, the potential for interactive modes in municipal communication systems, and some illustrative applications of the new cable systems for governmental and public service communications. Constraints which will inhibit some applications in the near future are summarized. Many diverse and competing interests will interact in the evolution of the new cable systems and the development of plans for controlling their operation. It is not assured that the public interest will be adequately represented or well served in this process.

Security Applications Of Computer Motion Detection

An important area of application of computer vision is the detection of human motion in security systems. This paper describes the development of a computer vision system which can detect and track human movement across the international border between the United States and Mexico. Because of the wide range of environmental conditions, this application represents a stringent test of computer vision algorithms for motion detection and object identification. The desired output of this vision system is accurate, real-time locations for individual aliens and accurate statistical data as to the frequency of illegal border crossings. Because most detection and tracking routines assume rigid body motion, which is not characteristic of humans, new algorithms capable of reliable operation in our application are required. Furthermore, most current detection and tracking algorithms assume a uniform background against which motion is viewed - the urban environment along the US-Mexican border is anything but uniform. The system works in three stages: motion detection, object tracking and object identi-fication. We have implemented motion detection using simple frame differencing, maximum likelihood estimation, mean and median tests and are evaluating them for accuracy and computational efficiency. Due to the complex nature of the urban environment (background and foreground objects consisting of buildings, vegetation, vehicles, wind-blown debris, animals, etc.), motion detection alone is not sufficiently accurate. Object tracking and identification are handled by an expert system which takes shape, location and trajectory information as input and determines if the moving object is indeed representative of an illegal border crossing.

Threshold Performance of Suboptimum PPM Receivers

The threshold performance of a pulse position modulation (PPM) telemetry system which uses a slicer for a detector, suboptimum technique, is investigated, and curves for predicting the occurrence of threshold are developed.

An algorithm for machine detection and tracking of moving objects in television images

An important area of application of computer vision is the detection of object motion. We are currently developing a computer vision system to automatically detect and track human motion across the international border between the United States and Mexico. Because of the wide range of environmental conditions, this application represents a stringent test of computer vision algorithms for motion detection and object identification. The desired output of this vision system is both accurate statistical data as to the frequency of illegal border crossings and accurate, real-time locations for individuals. Fundamental requirements are that the system work in real time under varying environmental conditions with minimally expensive hardware. Such a system would have applications to a wide range of multiple object tracking problems.

Computer Detection and Tracking of Moving People in Television Images/sup 1/

An important area of computer vision is the detection and tracking of moving people in television images. This paper descr ibes the development of a computer vision system which can detect and track human motion across the international border between the United States and Mexico. The system consists of 16 parallel microprocessors which each operate on a segment of the total video image to determine if there has been motion in that segment of the image. Motion is detected based upon a novel scheme for calculating the median pixel value in the segment and comparing it with the median value from an earlier frame. Motion is detected if the median varies by more than a predetermined amount. When this happens a bit is sent to a controlling CPU. Also, each segment exchanges information with its neighbors thereby improving its ability to track the motion of a person. The paper also describes a practical realization of the design and problems associated with its use in a practical security system.