Millimeter Wave Multiple-input Multiple-output Research Articles

A millimeter-wave MIMO antenna applied to the n260 frequency band

In order to effectively alleviate the current situation of low-frequency spectrum congestion and meet people's demand for high-speed communication, a four element multiple input multiple output (MIMO) millimeter wave antenna was designed for the n260 frequency band (37-40GHz), with an overall size of 10mm12mm 0.508mm. This antenna is based on a dipole broadband millimeter wave unit antenna and adopts a coplanar waveguide feeding method. The four element antenna is placed orthogonally to improve the isolation of the antenna. The operating bandwidth is 36.76-41.73GHz, fully covering the n260 frequency band of 5G, with a relative bandwidth of 12.7%. The simulation results show that the impedance bandwidth of each port of the antenna covers this frequency band, and the isolation degree between each antenna unit port is less than -15dB. The envelope correlation coefficient (ECC) is less than 0.05, and has good radiation characteristics, which meets the performance requirements of MIMO antenna and can ensure the normal operation of the antenna.

Location-Aware Beam Training and Multi-Dimensional ANM-Based Channel Estimation for RIS-Aided mmWave Systems

In this paper, we propose a location-aware channel estimation based on the atomic norm minimization (ANM) for the reconfigurable intelligent surface (RIS)-aided millimeter-wave multiple-input-multiple-output (MIMO) systems. The beam training overhead at the base station (BS) is reduced by the direct beam steering towards the RIS with the location of the BS and the RIS. The RIS beamwidth adaptation is proposed to reduce the beam training overhead at the RIS, and also it enables accurate channel estimation by ensuring the user equipment receives all the multipath components from the RIS. After the beam training, the cascaded effective channel of the RIS-aided MIMO systems is estimated by ANM. Depending on whether the beam training overhead at the BS or at the RIS is reduced or not, the channel is represented as a linear combination of either 1D atoms, 2D atoms, or 3D atoms, and the ANM is applied to estimate the channel. Simulation results show that the proposed location-aware channel estimation via 2D ANM and 3D ANM achieves superior estimation accuracy to benchmarks.

A High-Frequency Planar-Configured Millimeter-Wave MIMO Antenna for Fifth-Generation NR Operations

This article presents a simple planar millimeter-wave (mm-wave) multiple input multiple output (MIMO) antenna with four closely spaced radiating elements. The antenna is intended to enhance the bandwidth for 5G new radio (NR) applications and also cover the industrial Ka-band (26.5-40 GHz), Q-band (30-50 GHz), and U-band (40-60 GHz) frequency ranges. The antenna is designed using Rogers RT/duroid 5880 substrate with a size of 25 × 26 × 1.6 mm3. The proposed antenna consists of four identical radiating elements with two of them positioned in a linear configuration facing each other, while the other two elements are placed opposite to the first two, which improves isolation between the elements. Across the entire operating frequency range (26-60 GHz), the antenna demonstrated excellent performance, including 34 GHz wide bandwidth, high isolation of >25 dB, nearly omnidirectional radiation patterns, high gain of 11.1 dB with a high radiation efficiency of 94%, low envelope correlation coefficient (ECC) of 0.0068, and high diversity gain (DG) of 9.967 dB. The simulated findings exhibit a strong positive correlation with the experimental results. The proposed MIMO antenna design is a promising solution for 5G NR applications.

A Novel Multiperson Activity Recognition Algorithm Based on Point Clouds Measured by Millimeter-Wave MIMO Radar

Radar is widely used in human activity recognition (HAR). The radar-based HAR algorithms can be roughly categorized into the feature map-based and the point cloud-based. Between the two, the point cloud-based algorithms are more suitable for multi-person activity recognition (MPAR) tasks due to the spatial properties of point clouds, and are therefore increasingly attracting attentions. However, most existing point cloud-based algorithms make decisions by utilizing either Doppler or coordinate features of point clouds, which are not sufficient to characterize the activity; the remaining algorithms have a large randomness in extracting both features. Neither of these algorithms can fully exploit the advantage of feature fusion, which is the key to recognition performance. To address this shortcoming, this paper proposes a novel MPAR algorithm. First, a feature mapping approach is proposed and defined in equation form, the Doppler, range, azimuth, and elevation features of the point clouds are calculated and accumulated sequentially, so we can obtain the four time-domain feature maps. Second, with the four feature maps as inputs, a four-channel CNN classification model with channel attention is trained for MPAR tasks. Datasets of multi-person activities are collected respectively under the indoor circumstance and aquatic circumstance using the millimeter-wave multiple-input-multiple-output (MIMO) radar platform. The dataset-based evaluation performance shows that the proposed algorithm achieves accuracy results of 96.09% for the indoor-MPAR task and 93.97% for the aquatic-MPAR task, and outperforms three conventional point cloud-based algorithms in terms of the overall MPAR accuracy, the generalization ability to the aquatic activity recognition, and the robustness of distance and headcount.

Efficient Evaluation of Incident Power Density by Millimeter-Wave MIMO User Equipment Using Vectorized Field Superposition and Stochastic Population Optimizers

In this work, stochastic population optimizers are applied with vectorized field values to determine the peak exposure of user equipment (UE) installed with a multiple-input multiple-output (MIMO) antenna operating at 28 GHz. This problem presents a significant challenge due to the difficulty in evaluating all possible configurations of the input values. By aids of optimization on initial population size as well as the sampling spacing, two optimizers incorporating variable population size exhibit good robustness and efficiency, i.e., an error of 1% compared to the results by Monte Carlo (MC) simulation of 1 000 000 times. A reduction in the simulation time of 90% compared to MC simulation of 10 000 times. The proposed method demonstrates its performance in evaluating exposure at both planar and nonplanar surface according to the standards. Besides, the method can be applied in postprocessing of the numerical simulation and the measured data for maximized spatial-average power density. The study provides a new and easy to implement method for efficiently characterizing the maximum exposure from millimeter wave MIMO UE.

Hybrid Beamforming Design for Self-Interference Cancellation in Full-Duplex Millimeter-Wave MIMO Systems with Dynamic Subarrays.

Full-duplex (FD) millimeter-wave (mmWave) multiple-input multiple-output (MIMO) communication is a promising solution for the extremely high-throughput requirements in future cellular systems. The hybrid beamforming structure is preferable for its low hardware complexity and low power consumption with acceptable performance. In this paper, we introduce the hardware efficient dynamic subarrays to the FD mmWave MIMO systems and propose an effective hybrid beamforming design to cancel the self-interference (SI) in the considered system. First, assuming no SI, we obtain the optimal fully digital beamformers and combiners via the singular value decomposition of the uplink and downlink channels and the water-filling power allocation. Then, based on the obtained fully digital solutions, we get the dynamic analog solutions and digital solutions using the Kuhn-Munkres algorithm-aided dynamic hybrid beamforming design. Finally, we resort to the null space projection method to cancel the SI by projecting the obtained digital beamformer at the base station onto the null space of the equivalent SI channel. We further analyze the computational complexity of the proposed method. Numerical results demonstrate the superiority of the FD mmWave MIMO systems with the dynamic subarrays using the proposed method compared to the systems with the fixed subarrays and the half-duplex mmWave communications. When the number of RF chains is 6 and the signal-to-noise ratio is 10 dB, the proposed design outperforms the FD mmWave MIMO systems with fixed subarrays and the half-duplex mmWave communications, respectively, by 22.4% and 47.9% in spectral efficiency and 19.9% and 101% in energy efficiency.

Target Classification Using Frontal Images Measured by 77 GHz FMCW Radar through DCNN

This paper proposes a target classification method using radar frontal imaging measured by millimeter-wave multiple-input multiple-output (MW-MIMO) radar through deep convolutional neural networks. Autonomous vehicles must classify targets in front of the vehicle to attain better situational awareness. We use 2D sparse array radar to capture the frontal images of objects on the road, such as sedans, vans, trucks, humans, poles, and trees. The frontal image includes information regarding not only the shape of a target but also the reflection characteristics of each part of the target. The measured frontal images are classified by deep convolutional neural networks, and the classification rate yielded 87.1% for six classes and 92.6% for three classes.

Mobility and Routing based Channel Estimation for Hybrid Millimeter-Wave MIMO WSNs

Recently, technological developments have enhanced, the use of Millimeter-wave (mm-Wave) Multiple Input Multiple Output (MIMO) system in various communication applications and wireless sensor networks as channel estimation efficiency can be immensely improved with the help of this technological developments in Millimeter-wave MIMO system and wireless sensor network as well. Moreover, they can improve quality of communication services to a great extent. However, cell interference in Millimeter-wave (mm-Wave) MIMO system can produce a massive impact on spectral efficiency. Therefore, a Routing Enabled Channel Estimation (RECE) technique is presented in this article to minimize interference between cells. The proposed Channel Estimation technique improves channel capacity as well as spectral efficiency. Moreover, Normalized Mean Square Error (NMSE) is minimized heavily using proposed RECE technique. Here, main aim of this article is to reduce cell interference and channel estimation inside a cell by using route selection, beam selection, and spatial frequency estimation. Here, different scenarios and parameters are considered to evaluate performance efficiency of proposed RECE technique in terms of spectral efficiency, NMSE and SNR and compared against varied traditional channel estimation techniques. Moreover, it is clearly evident from performance results that the proposed channel estimation technique performs better than the other two methods.

Anti-Jamming Beam Alignment in Millimeter-Wave MIMO Systems

In millimeter-wave (MMW) multiple-input multiple-output (MIMO) communications, users and their corresponding base station (BS) have to align their beam during both initial access and data transmissions to compensate for the high propagation loss. The beam alignment (BA) procedure specified for 5th Generation (5G) New Radio (NR) has been designed to be fast and precise in the presence of non-malicious interference and noise. A smart jammer might exploit this weakness and may launch an attack during the BA phase in order to degrade the accuracy of beam selection and, thus, adversely impacting the end-to-end performance and quality-of-service experienced by the users. In this paper, we study the effects of a jamming attack at MMW frequencies during the BA procedure used to perform initial access for idle users and adaptation/recovery for connected users. We show that the BA procedure adopted in 5G NR is extremely vulnerable to a smart jamming attack and, consequently, we propose a countermeasure based on the idea of randomized probing, which consists of randomly corrupting the probing sequence transmitted by the BS in order to reject the jamming signal at the UE via a subspace-based technique based on orthogonal projections and jamming cancellation. Numerical results corroborate our theoretical findings and show the very satisfactory accuracy of the proposed anti-jamming approach.

GAMP-SBL-based channel estimation for millimeter-wave MIMO systems

Based on the finite scattering characters of the millimeter-wave multiple-input multiple-output (MIMO) channel, the mmWave channel estimation problem can be considered as a sparse signal recovery problem. However, most traditional channel estimation methods depend on grid search, which may lead to considerable precision loss. To improve the channel estimation accuracy, we propose a high-precision two-stage millimeter-wave MIMO system channel estimation algorithm. Since the traditional expectation–maximization-based sparse Bayesian learning algorithm can be applied to handle this problem, it spends lots of time to calculate the E-step which needs to compute the inversion of a high-dimensional matrix. To avoid the high computation of matrix inversion, we combine damp generalized approximate message passing with the E-step in SBL. We then improve a refined algorithm to handle the dictionary matrix mismatching problem in sparse representation. Numerical simulations show that the estimation time of the proposed algorithm is greatly reduced compared with the traditional SBL algorithm and better estimation performance is obtained at the same time.

Two-Step Codebook-Assisted Alternating Minimization (CA-AltMin) for Low-Complexity Hybrid Beamforming Design

Hybrid beamforming can effectively reduce the cost of millimeter wave multiple-input-multiple-output (MIMO) system. However, the analog beamformer realized by the unit-norm phase shifters makes the design of the hybrid beamformers a complicated non-convex optimization problem, and prior works suffer from high computational complexity. In this letter, we focus on the single-user scenario and propose a two-step procedure for the low-complexity hybrid beamforming design. The first step employs a codebook-based algorithm to provide an initial setting of the hybrid beamformers. The second step employs the AltMin-based algorithm to refine the hybrid beamformers. In particular, we also modify the loss function used in the AltMin algorithm for complexity reduction. Simulation results show that the proposed codebook-assisted AltMin (CA-AltMin) reduces the complexity by 96% and achieves better performance than the state-of-the-art algorithms from different technical aspects.

Wideband 22–44-GHz Phased-Array Beamformers for 5G and Beyond

For supporting communication links with increased date rate between the base station and the user, millimeter-wave multiple-input–multiple-output (MIMO) will be adopted globally, the 24–29- and 37–43-GHz bands are now approved worldwide as the standard 5G communication bands, and several 5G systems have been presented in the 28- and 39-GHz bands [item 1) in the Appendix]. The key challenge now is how to reduce the entire MIMO systems’ sizes and weights, particularly the costs.

Integrated LTE and Millimeter-Wave 5G MIMO Antenna System for 4G/5G Wireless Terminals.

This work demonstrates an integrated multiple-input multiple-output (MIMO) antenna solution for Long Term Evolution (LTE) and Millimeter-Wave (mm-wave) 5G wireless communication services. The proposed structure is comprised of a two-element LTE MIMO antenna, and a four-element 5G MIMO configuration with rectangular and circular defects in the ground plane. For experimental validation, the proposed structure is fabricated on a Rogers RO4350B substrate with 0.76 mm thickness. The overall substrate dimensions are 75 mm × 110 mm. The proposed structure is capable of operating at 5.29–6.12 GHz (LTE 46 and 47 bands) and 26–29.5 GHz (5G mm-wave) frequency bands. Additionally, the measured peak gain of 5.13 and 9.53 dB is attained respectively for the microwave and mm-wave antennas. Furthermore, the analysis of the MIMO performance metrics demonstrates good characteristics, and excellent field correlation performance across the operating bands. Furthermore, the analysis of the Specific Absorption Rate (SAR) and Power Density (PD) at the lower frequency band (5.9 GHz) and PD only at mm-Wave frequency band (28 GHz) verifies that the proposed antenna system satisfies the international human safety standards. Therefore, the proposed integrated MIMO antenna configuration ascertains to be a potential contender for the forthcoming communication applications.

3-D Printed Wideband Cassegrain Antenna With a Concave Subreflector for 5G Millimeter-Wave 2-D Multibeam Applications

A novel wideband planar Cassegrain beam-former with a three-layered folded parallel plate waveguide geometry is investigated. By replacing the convex subreflector of the conventional design with a concave one, a 20% reduction in the size in boresight direction of the planar Cassegrain beam-former can be achieved, while its operating characteristics are not degraded. The direction of the radiation beam can be adjusted independently in the H- or E-plane by laterally offsetting the feed waveguide or bending the waveguide linking with the metallic flare that operates as a radiating structure. By this means, five Cassegrain subarrays with multiple waveguide inputs and different bending angles are stacked to build a high-gain wideband 2-D multibeam antenna array in the Ka -band, whose 3 dB beams cover angular ranges of ±60° in the E-plane and ±18° in the H-plane. A bandwidth of more than 40%, stable multibeam radiation with cross polarization of less than −25 dB, a gain of higher than 20 dBi, and a radiation efficiency of more than 90% are confirmed experimentally by a metallic 3-D printed subarray. With the compact printable geometry and the good operating performance, the presented 2-D multibeam antenna fed by the planar Cassegrain beam-formers is an attractive candidate for millimeter-wave multiple-input multiple-output (MIMO) applications in the fifth-generation (5G) mobile communications.

Rate-Loss Mitigation for a Millimeter-Wave Beamspace MIMO Lens Antenna Array System Using a Hybrid Beam Selection Scheme

The rate loss is an important issue in multiuser beamspace multiple-input–multiple-output (MIMO) millimeter-wave systems. In such systems, multicluster channel propagation results in quantization error (QE), and consequently, each active user suffers a significant rate loss. A conventional single beam selection (SBS) scheme is used in an equivalent beamspace MIMO channel to reduce the number of radio frequency (RF) chains required. However, this scheme does not properly mitigate the QE due to the limited number of channel propagation clusters per user. In addition, optimally selected RF chains are operated at the same number of precoded data streams. As a result, each active user inherently loses a huge number of data streams when utilizing the conventional SBS scheme. Therefore, we propose a novel hybrid beam selection scheme in an equivalent beamspace MIMO channel to enable multiple beam group selection and to achieve a reliable channel cluster for every active user, which directly aids in the mitigation of the QE. The numerical result is verified using computer simulations in a millimeter-wave MIMO downlink channel environment.

Millimeter-Wave Phased-Array Antenna-in-Package (AiP) Using Stamped Metal Process for Enhanced Heat Dissipation

This letter presents an unprecedented stamped metal antenna-in-package (AiP) concept for millimeter-wave multiple-input–multiple-output (MIMO) and phased array applications. The stamped metal antenna containing an aperture dually functions as an efficient heat sink. Moreover, the presented antenna topology can be mass-produced using a stamping technology, which is widely used for conventional heat sinks. The ground wall of the proposed antenna encompassed by the dielectric substrate, which is thermodynamically equivalent to a cooling medium, is connected to the shield structures to guide the convection heat emitted by the radio frequency integrated circuits (RFICs) and discharges this heat into free space. Details of the proposed AiP topology are discussed, and the parametric effects of the key design factors are quantitatively analyzed. To verify the proposed AiP, the optimized design is fabricated using standard printed circuit board (PCB) and press technology. The fabricated 1 × 8 subarray features an impedance bandwidth of 700 MHz with a center frequency of 28.5 GHz and a measured gain of 13.78 dBi. Computational fluid dynamics results ascertain that the proposed stamped metal AiP effectively discharges the heat emission generated from the RFICs.

Synchronization-Phase Alignment of All-Digital Phase-Locked Loop Chips for a 60-GHz MIMO Transmitter and Evaluation of Phase Noise Effects

A phase-coherent technique for multiple all-digital phase-locked loops (ADPLLs) is presented and developed in this paper to target a 57-63-GHz multiple-input multiple-output (MIMO) transmitter (TX) with a digital beam-steering capability. The ADPLL TX chains are first fabricated in nanoscale CMOS and then time-synchronized and frequency- phase locked by a field-programmable gate array (FPGA) evaluation board. The calibration approach for phase alignment is carried out using a cancellation method to acquire the out-of-phase state within two ADPLLs. The accuracy of beam steering and phase alignment is investigated and analyzed based on a time-domain model for ADPLL to consider the impact of phase noise. The analysis results offer the required values of the ADPLL parameters to allow a millimeter-wave (mm-wave) MIMO TX with a highly accurate digital beam-steering capability.

THE PERFORMANCE OF A HYBRID BEAMFORMING mmWAVE MIMO SYSTEM WITH NON-IDEAL HARDWARE

With the increasing wireless data traffic and data rate demands, milimeter-wave band corresponding to the frequency range 30-300 GHz has much attention of the researchers. Using multiple antennas at the transmitter and the receiver with beamforming helps overcome high transmission loss. Therefore, millimeter-wave Multiple-Input Multiple-Output (mmWave MIMO) is a key technology for the next generation wireless communication system. However, due to hardware constrains when operating in the high frequency range, the performance of a mmWave MIMO system will decrease. In this paper, we analysis system performance of a hybrid beamforming mmWave MIMO system with non-ideal hardware (phase noise and quantization noise).

A Simple Decoupling Method for 5G Millimeter-Wave MIMO Dielectric Resonator Antennas

A simple decoupling method of using metallic vias to improve the isolation of millimeter-wave multiple-input-multiple-output (MIMO) dielectric resonator antenna (DRA) elements is investigated. The vias are vertically added to the DRA elements, at appropriate positions. By means of the interaction with the electromagnetic fields, the vias can potentially affect the filed distributions and further reduce the coupled fields effectively. The isolation between the MIMO DRA elements can, therefore, be enhanced substantially. As the vias are placed inside the DRA elements, no extra footprint is needed, making the entire antenna system very simple and compact. Two typical examples, including an H-plane and an E-plane, coupled $1\times2$ MIMO DRA arrays, have been designed, fabricated, and measured to demonstrate the feasibility and universality of this method. The results show that by using the vias appropriately, the isolation of the H-plane coupled MIMO DRA array can be enhanced from ~15.2 to 34.2 dB, while that of the E-plane array can be improved from ~13.1 to 43 dB at 26 GHz.

A High-Precision Hybrid Analog and Digital Beamforming Transceiver System for 5G Millimeter-Wave Communication

In this paper, the development of a millimeter-wave hybrid beamforming (HBF) transceiver system for 5G millimeter-wave multiple-input-multiple-output (MIMO) communication is presented. The developed transceiver system is operated at 28-GHz band in the time division duplex (TDD) mode, with 500-MHz signal bandwidth. To implement high beamforming accuracy, a phased-array-based HBF transceiver with high-precision phase shifting network (PSN) at intermediate-frequency (IF)-paths is proposed. The designed PSN has 8-bit phase resolution within 360° range and 0.13-dB amplitude variation. With the use of such low-cost 8-bit PSN, this HBF transceiver system achieves 0.6° beam resolution and a good RF transceiver performance. In addition, under the over-the-air MIMO communication test with two data streams, the error vector magnitude (EVM) of the received signals at two user equipment (UE) is 2.58% and 2.34%. The high-data rate millimeter-wave communication and MIMO performance of this HBF are verified.