Date of Award

Spring 2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering - (Ph.D.)

Department

Electrical and Computer Engineering

First Advisor

Alexander Haimovich

Second Advisor

Yeheskel Bar-Ness

Third Advisor

Osvaldo Simeone

Fourth Advisor

Ali Abdi

Fifth Advisor

Mark A. Govoni

Abstract

The dissertation discusses compressive sensing and its applications to localization in multiple-input multiple-output (MIMO) radars. Compressive sensing is a paradigm at the intersection between signal processing and optimization. It advocates the sensing of “sparse” signals (i.e., represented using just a few terms from a basis expansion) by using a sampling rate much lower than that required by the Nyquist-Shannon sampling theorem (i.e., twice the highest frequency present in the signal of interest). Low-rate sampling reduces implementation’s constraints and translates into cost savings due to fewer measurements required. This is particularly true in localization applications when the number of measurements is commensurate to antenna elements. The theory of compressive sensing provides precise guidance on how the measurements should be acquired, and which optimization algorithm should be used for signal recovery.

The first part of the dissertation addresses the application of compressive sensing for localization in the spatial domain, specifically direction of arrival (DOA), using MIMO radar. A sparse localization framework is proposed for a MIMO array in which transmit and receive elements are placed at random. This allows for a dramatic reduction in the number of elements needed, while still attaining performance comparable to that of a filled (Nyquist) array. By leveraging properties of structured random matrices, a bound on the coherence of the resulting measurement matrix is obtained, and conditions under which the measurement matrix satisfies the so-called isotropy property are detailed. The coherence and isotropy concepts are used to establish uniform and non-uniform recovery guarantees within the proposed spatial compressive sensing framework. In particular, it is shown that non-uniform recovery is guaranteed if the product of the number of transmit and receive elements, MN (which is also the number of degrees of freedom), scales with K (log G)2, where K is the number of targets and G is proportional to the array aperture and determines the angle resolution. In contrast with a filled virtual MIMO array where the product MN scales linearly with G, the logarithmic dependence on G in the proposed framework supports the high-resolution provided by the virtual array aperture while using a small number of MIMO radar elements.

The second part of the dissertation focuses on the sparse recovery problem at the heart of compressive sensing. An algorithm, dubbed Multi-Branch Matching Pursuit (MBMP), is presented which combines three different paradigms: being a greedy method, it performs iterative signal support estimation; as a rank-aware method, it is able to exploit signal subspace information when multiple snapshots are available; and, as its name foretells, it possesses a multi-branch structure which allows it to trade-off performance (e.g., measurements) for computational complexity. A sufficient condition under which MBMP can recover a sparse signal is obtained. This condition, named MB-coherence, is met when the columns of the measurement matrix are sufficiently “incoherent” and when the signal-to-noise ratio is sufficiently high. The condition shows that successful recovery with MBMP is guaranteed for dictionaries which do not satisfy previously known conditions (e.g., coherence, cumulative coherence, or the Hanman relaxed coherence).

Finally, by leveraging the MBMP algorithm, a framework for target detection from a set of compressive sensing radar measurements is established. The proposed framework does not require any prior information about the targets’ scene, and it is competitive with respect to state-of-the-art detection compressive sensing algorithms.

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