Edward R. Beadle

New alternatives for interference tolerant waveforms hosted on a software programmable multi-mission platform

We present a dynamically reconfigurable (~ seconds) combined FPGA/DSP-based system-on-chip platform to address the need for an agile multi-function/multi-mission capability in size and weight constrained applications. The highly integrated system-in-a-package (SiP) format occupies <; 2 cu inch and has been demonstrated as a key element in both MODEM and RADAR platforms. Dynamic reconfiguration is achieved via software, thus implementing a software defined payload (SDP). MODEM operation is illustrated with two novel interference resistant communication waveforms, one digital chaotic-based and the other an enhanced OFDM (eOFDM). In trials, chaotic spreading achieved interference resistance of ~ 2.5 dB over comparable direct-sequence spread spectrum approaches with an uncoded BER of 8.5 × 10-6 when received at -13 dB SNR (100 kbps). Results indicate that this waveform holds promise as a concurrent secondary user (SU) in cognitive radio or shared spectrum schemes. The eOFDM provides > 36 Mbps and > 30 dB of additional pilot tone interference margin over typical OFDM, so it is suitable as a primary user (PU) format tolerant to both interference and wireless channel distortions. Lastly, to show the mission diversity, the FPGA platform is extended to a stretch mode inverse synthetic aperture RADAR (ISAR) experimentally achieving 0.25 m slant range resolution and multiplicative noise ratio (MNR) of -23 dB using a 40 MHz/us chirp on an actual target.

Blind separation of weak signals in non-isotropic spatio-temporal colored noise with possibly critically loaded uncalibrated arrays

A blind source separation (BSS) algorithm optimal in output signal-to-interference (SIR) for critically loaded arrays operating at possibly negative SNIR is proposed. The proposed technique uses generalized eigen-decomposition (i.e. spectral estimation) of a first-order matrix pencil of spatial fourth-order cumulant matrices of novel definition. The algorithm has demonstrated insensitivity to non-isotropic spatially and/or temporally correlated noise without the need for whitening processes. To illustrate the potential effectiveness of the proposed approach examples are provided involving narrowband statistically independent co-channel signal mixtures of analog and digital modulations with received SNIR < 0 dB, with noise environment and sensing array manifold completely unknown.