arXiv subjects

David A. Hague

Publications and source records attributed to David A. Hague.

21 records · Page 2Linked to original sources

arXiv2019

Waveform Design using Multi-Tone Feedback Frequency Modulation

This paper introduces a waveform design method using Multi-Tone Feedback Frequency Modulation (MT-FFM), a generalization of the single oscillator feedback FM method developed by [Tomisawa, 1981]. The MT-FFM utilizes a collection of $K$ harmonically related oscillators each governed by a design parameter $z_k$ which are utilized as a discrete set of parameters that may be modified to generate a richer set of modulation functions than in the single oscillator case. The resulting modulation function is represented using a form of Kapteyn series composed of Generalized Bessel Functions. This paper describes the structure of the MT-FFM waveform, derives the Kapteyn series representation of the waveform's modulation function, and demonstrates the design method with a waveform design example.

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arXiv2018

An Experimental Evaluation of the Generalized Sinusoidal Frequency Modulated Waveform for Active Sonar Systems

This paper experimentally evaluates the Generalized Sinusoidal Frequency Modulated (GSFM) waveform, a generalization of the Sinusoidal Frequency Modulated (SFM) waveform. The Instantaneous Frequency (IF) of the GSFM resembles the time/voltage characteristic of a Linear FM (LFM) chirp waveform. Consequently, the GSFM possesses an Ambiguity Function (AF) that resembles a thumbtack shape. Practical sonar system design must consider two factors beyond the AF. The spectral efficiency (SE), defined as the ratio of energy in an operational frequency band to the total waveform energy, is another important metric for waveform design. The Peak-to-Average-Power Ratio (PAPR) quantifies how close the waveform is to constant amplitude. These measures predict a waveform's energy efficiency and ability to be accurately replicated on practical piezoelectric transducers, which have limits on both their bandwidth and maximum transmit power. This paper explores these design considerations for the GSFM waveform and evaluates its performance against a host of other well established waveforms using simulated and experimental acoustic data. The GSFM possesses superior SE, PAPR, and overall energy efficiency when compared to thumbtack waveforms.

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arXiv2018

The Generalized Sinusoidal Frequency Modulated Waveform for Active Sonar Systems

Pulse Compression (PC) active sonar waveforms provide a significant improvement in range resolution over single frequency sinusoidal waveforms also known as Continuous Wave (CW) waveforms. Since their inception in the 1940's, a wide variety of PC waveforms have been designed using either Frequency Modulation (FM), phase coding, or frequency hopping to suite particular sonar applications. The Sinusoidal FM (SFM) waveform modulates its Instantaneous Frequency (IF) by a single frequency sinusoid to achieve high Doppler sensitivity which also aids in suppressing reverberation. This allows the SFM waveform to resolve target velocities. While the SFM's resolution in range is inversely proportional to its bandwidth, the SFM's Auto-Correlation Function (ACF) contains many large sidelobes. The periodicity of the SFM's IF creates these sidelobes and impairs the SFM's ability to clearly distinguish multiple targets in range. This dissertation describes a generalization of the SFM waveform, referred to as the Generalized SFM (GSFM) waveform, that modifies the IF to resemble the time/voltage characteristic of a FM chirp waveform. As a result of this modification, the Doppler sensitivity of the SFM is preserved while substantially reducing the high range sidelobes producing a waveform whose Ambiguity Function (AF) approaches a thumbtack shape. This dissertation describes the properties of the GSFM's thumbtack AF shape, compares it to other well known waveforms with a similar AF shape, and additionally considers some of the practical considerations of active sonar systems including transmitting the GSFM on piezoelectric transducers and the GSFM's ability to suppress reverberation. Lastly, this dissertation also describes designing a family of in-band nearly orthogonal waveforms with potential applications to Continuous Active Sonar (CAS).

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