Jonathan I. Tamir

Broadband Millimeter-Wave Propagation Measurements and Models Using Adaptive-Beam Antennas for Outdoor Urban Cellular Communications

The spectrum crunch currently experienced by mobile cellular carriers makes the underutilized millimeter-wave frequency spectrum a sensible choice for next-generation cellular communications, particularly when considering the recent advances in low cost sub-terahertz/millimeter-wave complementary metal–oxide semiconductor circuitry. To date, however, little is known on how to design or deploy practical millimeter-wave cellular systems. In this paper, measurements for outdoor cellular channels at 38 GHz were made in an urban environment with a broadband (800-MHz RF passband bandwidth) sliding correlator channel sounder. Extensive angle of arrival, path loss, and multipath time delay spread measurements were conducted for steerable beam antennas of differing gains and beamwidths for a wide variety of transmitter and receiver locations. Coverage outages and the likelihood of outage with steerable antennas were also measured to determine how random receiver locations with differing antenna gains and link budgets could perform in future cellular systems. This paper provides measurements and models that may be used to design future fifth-generation millimeter-wave cellular networks and gives insight into antenna beam steering algorithms for these systems.

A 38 GHz cellular outage study for an urban outdoor campus environment

Wireless systems require increasingly large system bandwidths that are only available at millimeter-wave frequencies. Such spectrum bands offer the potential for multi-gigabit-per-second data rates to low-cost massively broadband® devices. To enable mobile outdoor millimeter-wave cellular-type applications, it is necessary to determine the coverage potential of base stations in real-world environments. This paper presents the results of a measurement campaign of 38 GHz outdoor urban cellular channels using directional antennas at both the mobile and the base station, and assesses outage probabilities at two separate transmitter locations on the campus of The University of Texas at Austin. Our measurements demonstrate the viability of directional antennas and site-specific planning for future mm-wave cellular, and show that cell radii of ~200 M will provide a very high probability of coverage in an urban environment. As production costs for millimeter-wave technologies continue to fall [1], we envision millimeter-wave cellular systems with dense base station deployments as a cost effective means of delivering multi-Gbps data rates to mobile cell phone and internet users.

Cellular broadband millimeter wave propagation and angle of arrival for adaptive beam steering systems (invited paper)

The advent of inexpensive millimeter wave devices and steerable antennas will lead to future cellular networks that use carrier frequencies at 28 GHz, 38 GHz, 60 GHz, and above. At these frequencies, the available RF bandwidth is much greater than that of current 4G systems, and high gain millimeter wave steerable antennas can be made in much smaller form factor than current products. This paper presents an extensive measurement campaign and initial results for base-station - to - mobile propagation situations at 38 GHz carrier frequencies in an outdoor urban environment using directional, steerable antennas. This work provides angle of arrival (AOA) and RF multipath characteristics for highly directional antenna beams that may exploit non-line-of-sight propagation paths for futuristic channels at 38 GHz. This work yields data for a variety of antenna pointing and antenna beamwidth scenarios in line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios.

Comprehensive motion‐compensated highly accelerated 4D flow MRI with ferumoxytol enhancement for pediatric congenital heart disease

To develop and evaluate motion‐compensation and compressed‐sensing techniques in 4D flow MRI for anatomical assessment in a comprehensive ferumoxytol‐enhanced congenital heart disease (CHD) exam.

T2 shuffling: Sharp, multicontrast, volumetric fast spin-echo imaging.

A new acquisition and reconstruction method called T2 Shuffling is presented for volumetric fast spin‐echo (three‐dimensional [3D] FSE) imaging. T2 Shuffling reduces blurring and recovers many images at multiple T2 contrasts from a single acquisition at clinically feasible scan times (6–7 min).

Wireless index coding through rank minimization

Index coding, initially introduced within theoretical computer science to address a specialized class of problems, has gained significant interest within communications and networking communities in recent years. Index coding has been shown to be analogous to a large class of challenging wired network coding and wireless multi-terminal problems, the latter class being of primary interest in this paper. Here, a (relaxed) rank minimization based analytic framework is presented for wireless index coding, which represents a first step in a systematic algorithmic approach to index coding for practical use. Further, the paper demonstrates its applicability over a real-world wireless testbed. The scheme operates at the network layer, and can be understood as a (non-trivial) generalization of existing principles of random linear network coding. Experimental results demonstrate that, for a class of network topologies, the rank-minimized index coding system presents a throughput gain of 50 to 100 percent greater than random linear coding for this system.

Analog compressed sensing for RF propagation channel sounding

Massively broadband® RF channel sounding is severely constrained by the sampling rates required for analog to digital conversion. Analog compressed sensing (CS) techniques based on Xampling have demonstrated the ability to lower sampling rates far below the Nyquist rate. Here, we show attributes of the multipath channel sounding problem appear to be well suited to CS approaches for reducing measurement acquisition time while simultaneously estimating time delays, multipath amplitudes, and angles of arrival. This paper presents results of the fusion of CS with modern channel sounding. We show measured propagation data from 60 GHz field trials and note the channel sparsity in time and space. We then propose an architecture for the first massively broadband CS channel sounder based on the Xampling framework (which we call the Channel Sounding Xampler) to exploit the sparsity, and we use field measurements to explore tradeoffs between analog and digital signal processing to perform channel impulse response (CIR) parameter estimation in real time. We also offer conceptual approaches for the Channel Sounding Xampler designed to trade off analog and digital components with the goal of improving CIR acquisition at sub-THz frequencies.

Fast comprehensive single‐sequence four‐dimensional pediatric knee MRI with T2 shuffling

To develop and clinically evaluate a pediatric knee magnetic resonance imaging (MRI) technique based on volumetric fast spin‐echo (3DFSE) and compare its diagnostic performance, image quality, and imaging time to that of a conventional 2D protocol.

Object Signature Acquisition through Compressive Scanning

In this paper we explore the utility of compressive sensing for object signature generation in the optical domain. We use laser scanning in the data acquisition stage to obtain a small (sub-Nyquist) number of points of an object’s boundary. This can be used to construct the signature, thereby enabling object identification, reconstruction, and, image data compression. We refer to this framework as compressive scanning of objects’ signatures. The main contributions of the paper are the following: 1) we use this framework to replace parts of the digital processing with optical processing, 2) the use of compressive scanning reduces laser data obtained and maintains high reconstruction accuracy, and 3) we show that using compressive sensing can lead to a reduction in the amount of stored data without significantly affecting the utility of this data for image recognition and image compression.

Variable-Density Single-Shot Fast Spin-Echo MRI with Deep Learning Reconstruction by Using Variational Networks

Purpose To develop a deep learning reconstruction approach to improve the reconstruction speed and quality of highly undersampled variable-density single-shot fast spin-echo imaging by using a variational network (VN), and to clinically evaluate the feasibility of this approach. Materials and Methods Imaging was performed with a 3.0-T imager with a coronal variable-density single-shot fast spin-echo sequence at 3.25 times acceleration in 157 patients referred for abdominal imaging (mean age, 11 years; range, 1-34 years; 72 males [mean age, 10 years; range, 1-26 years] and 85 females [mean age, 12 years; range, 1-34 years]) between March 2016 and April 2017. A VN was trained based on the parallel imaging and compressed sensing (PICS) reconstruction of 130 patients. The remaining 27 patients were used for evaluation. Image quality was evaluated in an independent blinded fashion by three radiologists in terms of overall image quality, perceived signal-to-noise ratio, image contrast, sharpness, and residual artifacts with scores ranging from 1 (nondiagnostic) to 5 (excellent). Wilcoxon tests were performed to test the hypothesis that there was no significant difference between VN and PICS. Results VN achieved improved perceived signal-to-noise ratio (P = .01) and improved sharpness (P < .001), with no difference in image contrast (P = .24) and residual artifacts (P = .07). In terms of overall image quality, VN performed better than did PICS (P = .02). Average reconstruction time ± standard deviation was 5.60 seconds ± 1.30 per section for PICS and 0.19 second ± 0.04 per section for VN. Conclusion Compared with the conventional parallel imaging and compressed sensing reconstruction (PICS), the variational network (VN) approach accelerates the reconstruction of variable-density single-shot fast spin-echo sequences and achieves improved overall image quality with higher perceived signal-to-noise ratio and sharpness.