Defense Notices

The Doppler tolerance of a waveform refers to its behavior when subjected to a fast-time Doppler shift imposed by scattering that involves nonnegligible radial velocity. While previous efforts have established decision-based criteria that lead to a binary judgment of Doppler tolerant or intolerant, it is also useful to establish a measure of the degree of Doppler tolerance. The purpose in doing so is to introduce a Doppler "quasi-tolerant" trade-space that can ultimately inform automated/cognitive waveform design in increasingly complex and dynamic radio frequency (RF) environments. This idea of Doppler quasi-tolerance leads to the development of random FM (RFM) waveforms that retain a degree of Doppler tolerance while still providing the diversity of a nonrepeating waveform structure. The ensuing ambiguity functions split the delay/Doppler ridge into a variety of different patterns. Since these patterns are known at transmission, a strategy for appropriate coherent slow time combining is demonstrated in simulation. Separately, the application of slow-time coding (STC) to the Doppler-tolerant linear FM (LFM) waveform has been examined for disambiguation of multiple range ambiguities. However, using STC with non-adaptive Doppler processing often results in high Doppler "cross-ambiguity" side lobes that can hinder range disambiguation despite the degree of separability imparted by STC. To enhance this separability, a gradient-based optimization of STC sequences is developed, and a "multi-range" (MR) modification to the reiterative super-resolution (RISR) approach that accounts for the distinct range interval structures from STC is examined. The efficacy of these approaches is demonstrated using open-air measurements. Pulse agility is an alternative range disambiguation technique that relies on pulse-to-pulse waveform separability. Although pulse-agile waveforms are often uncorrelated and therefore amenable to range disambiguation, they may exhibit poor Doppler tolerance. To preserve Doppler tolerance and achieve separability, a class of hybrid waveforms is developed whereby a phase code is embedded on an LFM base waveform. A gradient-based optimization is developed for this waveform structure to achieve enhanced suppression of range-folded scattering in desired delay/Doppler regions. The Doppler tolerance and separability of the optimized waveforms are examined in simulation, and open-air measurements are used to demonstrate the range disambiguation capability.

Modern security relies heavily on public key cryptography, and private keys and secrets in general must be protected from attackers. Against a highly-capable adversary it is ideal to store secrets outside of main memory, which is easy on general purpose systems with the now widely-available Trusted Platform Module (TPM) 2.0. However, the lack of integration between the TPM and the OS makes protecting secrets with automated availability needs difficult. We develop a strategy to authenticate OS entities and protect TPM-stored secrets without restricting access to the TPM, using standard features available on Linux---SELinux, Integrity Measurement Architecture (IMA), Extended Verification Module (EVM), and Linux Unified Key Setup (LUKS).