Dennis R. Morgan

Partially adaptive array techniques

The selection of auxiliary elements for partially adaptive antenna arrays for the purpose of optimizing performance in a multiple narrow-band jammer environment is studied. An explicit solution for the two-jammer problem is derived. This case is sufficient to illustrate the interaction of multiple jammers and at the same time affords a degree of understanding of more complex problems. Computer solutions are also presented and discussed for several line array and planar array configurations.

The Partial-Rank Algorithm for Adaptive Beamforming

This paper describes a new family of algorithms for adaptive weight computation for sensor arrays with arbitrary geometries. This family includes existing algorithms of the steepest-descent and matrix-factorization types, plus a range of new algorithms that are intermediate between these two classes, in terms of performance and computational complexity. This approach is particularly valuable for applications where steepest descent is too slow, but the standard matrix methods require too much computation.

An analysis of multiple correlation cancellation loops with a filter in the auxiliary path

A technique known as a multiple correlation cancellation loop and also as the LMS algorithm is widely used in adaptive arrays for radar, sonar, and communications, as well as in many other signal processing applications. In this paper, an analysis of this technique is extended to the case when a linear filter appears in the auxiliary signal path. A general solution to this problem is obtained and several examples for narrowband and broad-band signals are presented.

Adaptive Multipath Cancellation for Digital Data Communications

In this paper, an adaptive spectral equalization technique is developed for multipath cancellation, and more generally for any minimum-phase distortion, which is implemented by a constrained form of adaptive linear prediction. The technique does not use decisiondirected feedback, has guaranteed convergence and stability, and is simple to realize using conventional circuit technology. Binary amplitude-shift-keying (ASK) is considered as an example of the technique, and the theoretical performance characteristics are derived for a bandlimited pulse shape. Experimental results are also presented for an operational real-time processing system which has been developed for this application and are shown to conform favorably to theory. The analytic and experimental results presented in this paper clearly indicate the usefulness of this concept for a single multipath channel, yielding a performance advantage of between 5 and 20 dB. Particularly significant is the potential of this adaptive technique to acquire and track the multipath without any a priori knowledge of the specific parameters.

Discrete-time distortion analysis of quantized sinusoids

Results are presented for the harmonic distortion and intermodulation products associated with file quantization of two sinusoids, with and without noise present. For the case of one sinusoid strong and the other weak, it is demonstrated that the intermodulation distortion is not as large as the self-distortion of the quantized strong sinusoid alone.

A note on real-time linear prediction of speech waveforms

A well-known, real-time computational algorithm for use in adaptive linear prediction of speech waveforms is discussed and is related to known research in other fields.

Adaptive array cancellation of multipath interference

The steady-state performance of a narrowband adaptive array processor using a single auxiliary tapped delay line is analyzed for a simple two-path interference scenario, and computer solutions are presented for various combinations of signal and multipath parameters. It is shown that auxiliary delay taps are required for effective cancellation of multipath interference, even for fractional bandwidth-delay products. Good cancellation is generally achieved provided that (a) the delay line taps are spaced somewhat closer than the Nyquist sampling rate, and (b) the total length of the delay line considerably exceeds the longest multipath delay, depending on multipath component strengths. A simple impulse response model is also developed to provide an understanding of the behavior of cancellation performance and how it relates to the various parameters involved.

Response of a delay-constrained adaptive linear predictor filter to a sinusoid in white noise

An analysis is presented for the response of a delay-constrained adaptive linear predictor filter to a sinusoid in white noise. Expressions are derived for the steady-state adaptive weights, frequency response, and line suppression. A useful bound is also derived for the worst-case output signal-to-noise ratio as a function of normalized frequency and the order of the filter.

A/D Conversion Using Geometric Feedback AGC

A digital signal processing technique is described which utilizes a built-in automatic gain control (AGC) function. A particularly attractive algorithm called geometric feedback is developed which has certain desirable properties. A simple analytic solution of the response is derived for the special case of linear geometric feedback.