Gerald L. Fudge

A Nyquist folding analog-to-information receiver

Many radar and communications applications require detection and estimation of signal information across an extremely wide radio frequency (RF) bandwidth. In practice, however, direct digitization of this broadband RF environment is problematic. Physical limitations in analog-to-digital converter (ADC) technology restrict the total bandwidth that can be digitized, as well as the ability to digitize high RF signals directly. This paper describes a novel ldquoanalog-to-informationrdquo receiver, motivated by recent developments in compressed sensing (CS), which overcomes both of these challenges in certain settings. The proposed receiver performs frequency modulated pulsed sampling at sub-Nyquist/Shannon rates to compress a broadband RF environment into an analog interpolation filter. The RF sample clock modulation induces a Nyquist-zone dependent frequency modulation on the received signals, allowing separation and recovery of the signal information from a sparse broadband RF environment.

Detecting Signal Structure from Randomly-Sampled Data

Recent theoretical results in Compressive Sensing (CS) show that sparse (or compressible) signals can be accurately reconstructed from a reduced set of linear measurements in the form of projections onto random vectors. The associated reconstruction consists of a nonlinear optimization that requires knowledge of the actual projection vectors. This work demonstrates that random time samples of a data stream could be used to identify certain signal features, even when no time reference is available. since random sampling suppresses aliasing a small (sub-Nyquist) set of samples can represent high-bandwidth signals. Simulations were carried out to explore the utility of such a procedure for detecting and classifying signals of interest.

Nyquist folding analog-to-information receiver: Autonomous information recovery using quadrature mirror filtering

A broadband Nyquist-folding analog-to-information receiver, allows multiple Nyquist zones to be directly undersampled and subsequently folded into a continuous time analog interpolation filter. This paper presents a new algorithm that autonomously extracts the intercepted pulse parameters on the time-frequency plane using a quadrature mirror filter bank at the output of the interpolation filter. Parameters include a running calculation of the exact bandwidth, frequency, pulse duration and slope. By the examination of the signals slope we show that a direct computation of the actual Nyquist zone is possible. Monte Carlo simulation runs are presented to demonstrate the robustness of the algorithm for −20≤SNR≤10 dB.

A reconfigurable direct RF receiver architecture

This paper describes a bandpass sampling architecture for direct RF conversion that is reconfigurable and efficient. The receiver architecture avoids the requirement for high clock speeds and fast quantizers by using a two-stage sampling process. In the first stage, the RF signal is bandpass filtered and sampled using an impulse-like sampling device without quantizing the signal. After continuous time low-pass or bandpass filtering, the resulting analog signal is then sampled and quantized by a traditional analog-to-digital converter. This architecture also provides a high degree of reconfigurability in tuning range and bandwidth by using a tunable or selectable anti-aliasing filter before the first stage of sampling and by using a tunable sample clock in the first stage of sampling.