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Sensor Array and Multichannel Technical Committee
Machine Learning for Signal Processing
Signal Processing for Communications and Networking
In recent years, the National Institute of Standards and Technology (NIST) and other institutions have pioneered the use of synthetic apertures for measuring the characteristics of propagating electromagnetic radiation in wireless communication environments. These synthetic apertures are created by using a precise mechanical positioner, such as a robot arm, to move a receive antenna along predetermined points on a spatial sampling lattice. The signal amplitude and phase measured at each spatial location can be used to reconstruct the power, directions of arrival, delays, and polarization of scattered electromagnetic waves that propagate across the observation plane of the synthetic aperture.
Synthetic apertures are capable of measuring signals over a very wide frequency bandwidth and with an almost arbitrarily large aperture size which in turn enables high angular and delay resolution to resolve closely spaced scatterers. Equally important is that synthetic apertures are affordable systems that can be constructed for a fraction of the cost of digital multichannel phased arrays and are capable of comparable estimation performance. While wireless channel sounding with synthetic apertures is a new and emerging research frontier, historically there have been other successful applications of synthetic apertures across a wide range of signal frequencies. For example, sonar, synthetic aperture radar, inverse synthetic aperture radar, radio astronomy, computational tomography, and other imaging techniques all rely on the use of a virtual aperture constructed by collecting discrete samples across a region of space for the purpose of estimating the parameters of propagating waves. In addition to these traditional applications, this TWG will also explore innovative new uses of synthetic apertures for solving problems not previously considered, such as in acoustics for human speaker localization.
Today there is a compelling need and a clear synergy to be gained by bringing together researchers working independently in these disparate fields to share ideas, methods and algorithms in a common venue for the mutual benefit of each participant and for the benefit of the broader technical community. Besides sharing a theoretical and mathematical framework, synthetic aperture measurement practitioners also find common ground in the best practices and lessons learned through the hardware implementations of synthetic apertures across the range of frequencies that spans acoustic to millimeter wave.
The overarching goal of the proposed TWG is to support the maturation of the theoretical framework and the associated empirical techniques that underpin the estimation of parameters of propagating waves through various media using synthetic apertures. The empirical component of the proposed TWG’s activities will involve designing experiments and performing data analyses to validate the performance of parameter estimation algorithms. Equally important is the theoretical component of the TWG’s work focused on deriving original and computationally efficient techniques. A third desired output of the TWG is to identify potential new applications for synthetic apertures that are enabled by the precise measurement and estimation of environmental parameters. For example, the output of a synthetic aperture could be used as an intermediate step in more complex systems that test wireless device performance, such as channel emulators.
The tangible products of the TWG’s empirical, theoretical, and new application focus areas will include:
The outputs of the TWG will accumulate the collective expertise of the group and document new state-of-the-art metrology practices and methods derived and tested by group members. These validated products could then be shared with the wireless communications industry, defense contractors, universities, and the medical imaging community to support their product development and internal research. The lessons learned by the TWG will help other institutions optimize their budget allocation strategies when procuring metrology equipment or device testbeds and this insight is especially important for small or medium-size companies that lack the resources to sustain risky research paths in the pursuit of new technologies.
The highest priority objective of the TWG is to establish the shared repository for data and algorithms. Accessibility to a variety of data sets is one of the largest obstacles facing synthetic aperture researchers today. Collecting quality data is an expensive and time-consuming exercise that strains the resources of many institutions. By providing a single repository for sharing data sets accumulated by different organizations, each TWG member has the opportunity to more robustly validate their particular synthetic aperture algorithms.
It is important to note that NIST has particularly deep and unrivaled expertise in conducting uncertainty analyses to quantify the impact of hardware errors on the accuracy of synthetic aperture measurements. This capability is unique to NIST and a valuable resource that other TWG members would be able to leverage. For further inquiries, please contact Peter Vouras, National Institute of Standards and Technology (NIST), Gaithersburg, MD, USA.
TWG Approval Date: 15 April 2020.