Massive MIMO is a Reality -- What is Next? Five Promising Research Directions for Antenna Arrays

Massive MIMO (multiple-input multiple-output) is no longer a "wild" or "promising" concept for future cellular networks - in 2018 it became a reality. Base stations (BSs) with 64 fully digital transceiver chains were commercially deployed in several countries, the key ingredients of Massive MIMO have made it into the 5G standard, the signal processing methods required to achieve unprecedented spectral efficiency have been developed, and the limitation due to pilot contamination has been resolved. Even the development of fully digital Massive MIMO arrays for mmWave frequencies - once viewed prohibitively complicated and costly - is well underway. In a few years, Massive MIMO with fully digital transceivers will be a mainstream feature at both sub-6 GHz and mmWave frequencies. In this paper, we explain how the first chapter of the Massive MIMO research saga has come to an end, while the story has just begun. The coming wide-scale deployment of BSs with massive antenna arrays opens the door to a brand new world where spatial processing capabilities are omnipresent. In addition to mobile broadband services, the antennas can be used for other communication applications, such as low-power machine-type or ultra-reliable communications, as well as non-communication applications such as radar, sensing and positioning. We outline five new Massive MIMO related research directions: Extremely large aperture arrays, Holographic Massive MIMO, Six-dimensional positioning, Large-scale MIMO radar, and Intelligent Massive MIMO.Comment: 20 pages, 9 figures, submitted to Digital Signal Processin

Design and Implementation of a FPGA and DSP Based MIMO Radar Imaging System

The work presented in this paper is aimed at the implementation of a real-time multiple-input multiple-output (MIMO) imaging radar used for area surveillance. In this radar, the equivalent virtual array method and time-division technique are applied to make 16 virtual elements synthesized from the MIMO antenna array. The chirp signal generater is based on a combination of direct digital synthesizer (DDS) and phase locked loop (PLL). A signal conditioning circuit is used to deal with the coupling effect within the array. The signal processing platform is based on an efficient field programmable gates array (FPGA) and digital signal processor (DSP) pipeline where a robust beamforming imaging algorithm is running on. The radar system was evaluated through a real field experiment. Imaging capability and real-time performance shown in the results demonstrate the practical feasibility of the implementation

The 32-GHz performance of the DSS-14 70-meter antenna: 1989 configuration

The results of preliminary 32 GHz calibrations of the 70 meter antenna at Goldstone are presented. Measurements were done between March and July 1989 using Virgo A and Venus as the primary efficiency calibrators. The flux densites of theses radio sources at 32 GHz are not known with high accuracy, but were extrapolated from calibrated data at lower frequencies. The measured value of efficiency (0.35) agreed closely with the predicted value (0.32), and the results are very repeatable. Flux densities of secondary sources used in the observations were subsequently derived. These measurements were performed using a beamswitching radiometer that employed an uncooled high-electron mobility transistor (HEMT) low-noise amplifier. This system was installed primarily to determine the performance of the antenna in its 1989 configuration, but the experience will also aid in successful future calibration of the Deep Space Network (DSN) at this frequency

Subsurface sounders

Airborne or spaceborne electromagnetic systems used to detect subsurface features are discussed. Data are given as a function of resistivity of ground material, magnetic permeability of free space, and angular frequency. It was noted that resistivities vary with the water content and temperature

Design and Measurement of a Millimeter-wave 2D Beam Switching Planar Antenna Array

A millimeter-wave 2-D beam switching microstrip patch antenna array excited by a 4x4 substrate integrated waveguide (SIW) Modified Butler Matrix is designed and experimentally evaluated in this thesis. A novel architecture is introduced for the Butler Matrix feed network to give designers a choice for phase shifter location to pursue a smaller circuit area. In addition, it enables the designer to control the BM phased outputs for achieving a set of desired 2-D beam directions, e.g., ϕ0=45°, 135°, 225°, and 315° at θ0=45°, with a passive beam switching network for a given array geometry. Full-wave simulation results show when the so designed 4x4 Butler Matrix feeds a 2x2 planar patch antenna array, 4-quadrant beam switching is achieved. To meet the goal of providing a low cost small footprint solution, the presented Modified Butler Matrix features straight SIW phase shifter using periodic apertures. The Modified Butler Matrix is fabricated on a single layer Rogers RO4350B substrate, achieving a circuit area of 222.5 mm2, which is a 54% improvement over previously published 60 GHz results. The fully-integrated antenna array system is created by development of a new SIW to planar patch antenna transition structure which maintains a total antenna frontend area of 333 mm2, just 42% of the area of the next closest SIW 2-D beam switching publication at 60 GHz. For verification of beam switching via over the air (OTA) measurements at 60 GHz, a benchtop anechoic chamber with proper transmitter and receiver antenna positioners is designed and fabricated using in-house maker laboratory resources. 2-D beam steering is proved in the intended 4 quadrants of radiation space at ϕ0=50°, 140°, 220°, and 300° and θ0=30±5° demonstrating meeting the design specifications with a very good margin. As well, for each switched beam the gain of antenna array was measured to be between 4.8 to 6 dBi at 60 GHz which is within 1dB deviation from the simulated results

Object detection with radar : present and future automotive technology

Radar-based object detection in cars is an integral part of autonomous driving systems. Radar sensors benefit from their excellent robustness in adverse weather conditions such as snow, fog or heavy rain. Although machine learning-based object detection is traditionally a camera-based domain, great progress has been made in lidar sensors, and radar is also catching up. Radar has been a key element of advanced automotive driver assistance systems for more than two decades. As an inexpensive, all-weather, long-range sensor that simultaneously provides speed measurements, radar is expected to be indispensable for the future of autonomous driving. Traditional radar signal processing techniques are often unable to distinguish reflections from objects of interest and are generally limited to detecting the peaks of the received signal. These peak detection methods convert the radar signal as an image into a sparse point cloud. Fully autonomous vehicles and the need to improve road safety have increased the reliability requirements of various advanced driver assistance systems (ADAS). Automotive radar is a key component of ADAS, as it adds safety and comfort features to vehicles. One of the main challenges in developing automotive radar is to demonstrate its reliability, especially in the most difficult cases. Building and testing radar systems for specific cases is time- consuming, costly and impractical. Simulation is the only practical way to investigate the countless practical cases of automotive radar. One interesting case is the reduction of radar returns due to sharp road curves. In particular, crucial targets with low radar cross sections (RCS), such as pedestrians, can become invisible to radar when driving on sharp curves. This paper will implement a radar system for the simulation of object detection of a vehicle, and aims to show and analyse how reliable such systems can be, as well as their problems and more.Outgoin

Radar Imaging in Challenging Scenarios from Smart and Flexible Platforms

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The Goldstone solar system radar: A science instrument for planetary research

The Goldstone Solar System Radar (GSSR) station at NASA's Deep Space Communications Complex in California's Mojave Desert is described. A short chronological account of the GSSR's technical development and scientific discoveries is given. This is followed by a basic discussion of how information is derived from the radar echo and how the raw information can be used to increase understanding of the solar system. A moderately detailed description of the radar system is given, and the engineering performance of the radar is discussed. The operating characteristics of the Arcibo Observatory in Puerto Rico are briefly described and compared with those of the GSSR. Planned and in-process improvements to the existing radar, as well as the performance of a hypothetical 128-m diameter antenna radar station, are described. A comprehensive bibliography of referred scientific and engineering articles presenting results that depended on data gathered by the instrument is provided

FMCW Signals for Radar Imaging and Channel Sounding

A linear / stepped frequency modulated continuous wave (FMCW) signal has for a long time been used in radar and channel sounding. A novel FMCW waveform known as “Gated FMCW” signal is proposed in this thesis for the suppression of strong undesired signals in microwave radar applications, such as: through-the-wall, ground penetrating, and medical imaging radar. In these applications the crosstalk signal between antennas and the reflections form the early interface (wall, ground surface, or skin respectively) are much stronger in magnitude compared to the backscattered signal from the target. Consequently, if not suppressed they overshadow the target’s return making detection a difficult task. Moreover, these strong unwanted reflections limit the radar’s dynamic range and might saturate or block the receiver causing the reflection from actual targets (especially targets with low radar cross section) to appear as noise. The effectiveness of the proposed waveform as a suppression technique was investigated in various radar scenarios, through numerical simulations and experiments. Comparisons of the radar images obtained for the radar system operating with the standard linear FMCW signal and with the proposed Gated FMCW waveform are also made. In addition to the radar work the application of FMCW signals to radio propagation measurements and channel characterisation in the 60 GHz and 2-6 GHz frequency bands in indoor and outdoor environments is described. The data are used to predict the bit error rate performance of the in-house built measurement based channel simulator and the results are compared with the theoretical multipath channel simulator available in Matlab