Accurate Ultra-Wideband Array Radar Imaging Using Four-Dimensional Unitary ESPRIT

Abstract

Adaptive signal processing techniques can estimate the directions of arrival (DOAs), ranges, and radial velocities of radar targets with high resolution when applied in the space, frequency, and time domains, respectively. However, the performance of these techniques is limited when they are applied separately in each domain. Recently, adaptive signal processing algorithms based on high-dimensional signal subspaces have been studied extensively. We apply a four-dimensional unitary estimation of signal parameters via rotational invariant techniques (ESPRIT) algorithm for the simultaneous estimation of the DOAs, ranges, and Doppler velocities of multiple targets in an ultra-wideband radar imaging setting and show the effectiveness of the high-dimensional ESPRIT for the near-field imaging of distributed moving targets. The four-dimensional ESPRIT algorithm is demonstrated to be able to separate targets moving in close proximity, whereas the two-and three-dimensional ESPRIT algorithms fail to separate these targets accurately because of their limited resolutions. The application of the high-dimensional ESPRIT to near-field radar imaging covers a wide range of applications that require the measurement of multiple moving targets in close proximity. An example of such an application is radar-based human monitoring. Therefore, the superior resolution of the high-dimensional ESPRIT has the potential to improve the performance of various real-world security and healthcare systems. INDEX TERMS Adaptive signal processing, direction-of-arrival, multidimensional signal processing, radar imaging, ultra wideband radar.

Ultra-Wideband Radar and Wireless Human Sensing

“…Therefore, the importance of radar-based human body imaging technology has increased, and millimeter-wave radar-based body scanners are already in operation at security checkpoints in airports and railway stations in Japan and overseas [8]. ProVision 2 (L3 Technologies, New York, NY, USA) is a widely used body scanner that realizes high-resolution radar imaging using an array radar that employes ultra-wideband signals (24)(25)(26)(27)(28)(29)(30) in the quasi-millimeter wave band, and it can detect the shape of objects hidden on a person. Clothing is highly permeable at this frequency band, and the waves reflected from the skin surface and concealed objects are dominant.…”

“…In addition, we expanded the frequency domain interferometry method that separates multiple echoes in the frequency domain using the difference in the Doppler velocities, and realized high-resolution radar imaging in conjunction with adaptive array signal processing [24]. In addition, for human body imaging, we applied the 4D ESPRIT (estimation of signal parameters via rotational invariance techniques) algorithm in the four-dimensional space (x, y, t, ω) using an ultra-wideband array radar to realize high resolution radar imaging [25]. We believe that these high-dimensional signal processing approaches are the key to breakthroughs in the radar measurement of human movements in future.…”

Three-Dimensional High-Resolution MIMO Radar Imaging via OFDM Modulation and Unitary ESPRIT

“…Moreover, with an orthogonal transmit set, the equivalent virtual array could be formed in a single snapshot illumination with fewer elements than a conventional array radar. MIMO radar 3D imaging techniques [12,14,[30][31][32][33][34][35][36][37][38] have been proposed in recent years. In [12,14,30,31,38], with wideband transmission for range resolution, the two-dimensional (2D) cross ranges were resolved with two mutually perpendicular uniform linear arrays (ULAs).…”

“…MIMO radar 3D imaging techniques [12,14,[30][31][32][33][34][35][36][37][38] have been proposed in recent years. In [12,14,30,31,38], with wideband transmission for range resolution, the two-dimensional (2D) cross ranges were resolved with two mutually perpendicular uniform linear arrays (ULAs). Additional range unit alignment and compensation steps were still necessary before cross-range imaging.…”

“…It exploits the rotational invariance among the signal subspace and has no searching process as in the MUltiple SIgnal Classification (MUSIC) techniques. e high-resolution imaging method based on the ESPRIT algorithm was reported in [33,36,38,[42][43][44][45][46]. However, three problems have to be taken into account for the ESPRIT algorithm applied in OFDM-MIMO radar imaging.…”