Ultraviolet (UV) communications has been proposed as a promising modality for short-range military communications, as it is often presumed to have low-probability-of-detection characteristics, has desirable non-line-of-sight properties, and resides within an underutilized frequency band. Recent research efforts have sought to formalize the first presumption of the detection of UV communications. This effort seeks to begin the study of the localization of UV communication sources after they are detected. We focus here exclusively on the range estimation problem. Using a phenomenon relating UV received power and range over short-to-medium distances (≪ 1 km), we develop a range estimator using only the received signal strength. The approach does not require information about other system or environmental parameters. We also theoretically study the performance of the estimator using the Cramér-Rao bound, via simulations, and using previously collected data.

Challenging Army-relevant communications and networking environments require novel methods and systems with sufficient robustness and resilience to enable operation in a covert fashion, especially in the presence of sophisticated adversaries. Recent studies suggest that regions of electromagnetic spectrum, such as deep ultraviolet (UV) spectrum, that are not being utilized in existing systems can provide unique advantages, particularly for more-covert short- range operations. However, the UV channel is not well understood, and techniques for the effective and efficient use of this channel for networking, such as spatial multiplexing, are still being investigated. In this paper, we report on experiments that validate previously hypothesized channel modeling behaviors, where we isolate and accurately measure the line-of-sight (LOS), single-scattering, and multiple-scattering components of measured returns and compare the measurements with theory. These experimental measurements exhibit good agreement with theoretical predictions, and demonstrate, in particular, predicted variations from ideal behavior in the multiple-scattering case. The validated behaviors play a key role in a previously proposed UV networking optimization framework. As such, we conclude this paper with additional development and examples of that framework in order to demonstrate the utility of the validated channel modeling.

The predicted ubiquity of light-emitting diodes (LEDs) suggests great potential for dual-use systems with visible light communications (VLC) capabilities. One class of LEDs employs multiple emitters at different wavelengths, making them appropriate for applications requiring colored output and providing multiple channels for communication. We present a design framework for optimizing the signaling constellation of VLC systems employing an arbitrary number of such LEDs, each with an arbitrary number of emitters. In particular, by considering the design of constellation-symbol locations jointly across LED emitters, the framework provides for the precompensation of linear channel distortions arising from, for example, cross-channel leakage, noise correlation, or wavelength-dependent received-signal and/or noise power, as well as the incorporation of design constraints for color-shift keying, dimming, and/or perceived color. Simulation results demonstrate the design approach and the potential performance enhancement that can be achieved for particular system scenarios. Experimental measurements using a prototype VLC system confirm such performance enhancements, providing real-world evidence of the benefit of applying the proposed framework to VLC channel precompensation.

We describe a novel way to implement high-radix crossbar switches. Our work is enabled by a new chip interconnect technology called proximity communication (PxC) that offers unparalleled chip IO density. First, we show how a crossbar architecture is topologically mapped onto a PxC-enabled multi-chip module (MCM). Then, we describe a first prototype implementation of a small-scale switch based on a PxC MCM. Finally, we present a performance analysis of two large-scale switch configurations with 288 ports and 1,728 ports, respectively, contrasting a 1-stage PxC-enabled switch and a multi-stage switch using conventional technology. Our simulation results show that (a) arbitration delays in a large 1-stage switch can be considerable, (b) multi-stage switches are extremely susceptible to saturation under non-uniform traffic, a problem that becomes worse for higher radices (1-stage switches, in contrast, are not affected by this problem).

This paper apply the factor graph framework to the techniques of linear equalization and decision feedback equalization to obtain a new class of low complexity equalization algorithms. The estimation of Gaussian processes has been studied in previous work, and the application of factor graphs to this problem is a recent extension. Here it uses a factor graph model for the specific estimation problem of equalization and use the sum-product algorithm to obtain the desired estimate. The reduced complexity message passing update equations are derived and detail the complexity of the resulting algorithms.