Mobile MIMO Research Articles

Simulation and Design of Three 5G Antennas

In the context of 5G networks, this paper investigates microstrip array antennas and mobile terminal MIMO array antennas. It introduces two innovative designs and, based on these, develops and fabricates a mobile terminal antenna. The first of these designs, a 4 × 4 microstrip array antenna operating in the LTE band 42 (3.4–3.6 GHz), is researched and fabricated and an innovative approach, combining embedded and coaxial feeding methods, is proposed and employed. Measurement results indicate a bandwidth of 373 MHz (3.321–3.694 GHz), achieving a relative bandwidth of 10.7%. The antenna exhibits a high gain of 12.7 dBi, with an undistorted radiation pattern, demonstrating excellent directional characteristics. The second of these designs, a “loop-slot” MIMO antenna designed for 5G mobile devices with metal frames, is investigated. By opening slots in the metal frame and integrating them into the antenna’s feeding structure, the decoupling principle is analyzed from the perspective of characteristic mode theory. This design shares resonant modes between the loop and slot antennas, allowing for the overlapping placement of the two antenna units. Experimental results confirm an isolation level exceeding 21 dB, with significantly reduced dimensions. Finally, an eight-unit MIMO antenna is designed and fabricated for 5G mobile devices with metal frames. Continuous optimization of the “loop-slot” module layout and unit spacing leads to a compact and miniaturized antenna structure. Measurement results show an isolation level exceeding 17 dB, radiation efficiency ranging from 65.8% to 73.7%, and an envelope correlation coefficient (ECC) below 0.03. Finally, an analysis of specific absorption rate (SAR) demonstrates excellent MIMO performance in terms of human body radiation exposure.

From Data-Driven Learning to Physics-Inspired Inferring: A Novel Mobile MIMO Channel Prediction Scheme Based on Neural ODE

From Data-Driven Learning to Physics-Inspired Inferring: A Novel Mobile MIMO Channel Prediction Scheme Based on Neural ODE

Mobile Cell-Free Massive MIMO: Challenges, Solutions, and Future Directions

Mobile Cell-Free Massive MIMO: Challenges, Solutions, and Future Directions

Continuous Beam Alignment for Mobile MIMO

Continuous Beam Alignment for Mobile MIMO

A MIMO-Based Dual Polarized Antenna Applicable for Mobile Terminal

At present, numerous small-size mobile terminal devices, such as mobile phones, have embedded the antenna in the cases, which will lead to considerable restrictions on the space for installing multiple antennas. Aiming at the requirements of rational design and layout of multi-antennas for MIMO mobile terminals and combining with the broadband and miniaturization technologies, a dual polarized antenna suitable for mobile terminals was designed in this paper through an adoption of polarization diversity. For a dual polarized multilayered micro-strip antenna with a ground plate, it is easy to be conformal to the carrier. In this paper, the design and the process of simulation optimization of the antenna unit were analyzed in detail. The bandwidth of the antenna unit was 1890 to 2200 MHz, the return loss was superior to -33dB, and both of the horizontal polarization gain and the vertical polarization gain were 8.2 dB. Accordingly, the characteristics of a high gain and dual polarization were achieved.

Channel prediction based on non-uniform pilot pattern for mobile massive MIMO scenarios

Channel prediction based on non-uniform pilot pattern for mobile massive MIMO scenarios

Wideband Low-Profile Eight-Port Eight-Wave Annular-Ring Patch Antenna Based on Using Eight Dual-Shorted Dual-Resonant Ring Sectors for 8 × 8 MIMO Mobile Devices

A wideband eight-port eight-wave annular-ring (AR) patch antenna for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> 8 MIMO mobile devices is presented. The AR patch antenna is formed into eight dual-resonant 45o-ring sectors to radiate eight very-low-correlated or generally uncorrelated waves for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> 8 MIMO application. Each ring sector is loaded with two shorting pins and excited by a simple probe feed to generate its half- and quarter-wavelength resonant modes at close frequencies to form a dual-resonant wide operating band. Additionally, all 16 shorting pins of the eight ring sectors have a same distance to the patch center, thereby forming a shorting circle to function like a circular metal wall in the AR patch. This makes the surface currents coupled from the excited ring sector to adjacent sectors to be mainly confined inside the shorting circle. Therefore, with the eight probe feeds located outside the shorting circle in the AR patch, enhanced port isolation is obtained. With the proposed design, the eight-port AR patch antenna having a low profile of 1.4 mm (about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.028\lambda $ </tex-math></inline-formula> at 5.9 GHz) and an outer diameter of 46 mm (about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.91\lambda $ </tex-math></inline-formula> at 5.9 GHz) can generate eight very-low-correlated waves over a wide band of about 5.9-7.2 GHz (fractional bandwidth 20% based on 3:1 VSWR for mobile device application). Also, the proposed antenna has a back ground plane and is especially suitable for on-metal surface application. The use of a single proposed antenna can be conveniently applied for the mobile device or Internet-of-Things (IoT) device to cover such as 5.925-7.125 GHz for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> 8 MIMO operation in the possible new mobile communication spectrum.

Low-Profile Six-Port Circular Patch Antenna With Six Triple-Shorted Dual-Resonant 60°-Disk Sectors to Generate Six Uncorrelated Waves for Wideband Mobile MIMO Antennas

A low-profile six-port circular patch antenna generating six uncorrelated waves in a wide band of about 5.8-7.5 GHz (based on 3:1 VSWR, fractional bandwidth about 25%) is presented. The antenna thickness is 1.4 mm (about 0.027&#x03BB; at 5.8 GHz), which includes a 0.4 mm thick FR4 substrate with the circular patch printed thereon and an additional 1.0 mm thick air layer to achieve a low-permittivity antenna substrate. The circular patch with a diameter of 40 mm (about 0.77&#x03BB; at 5.8 GHz) is separated into six 60&#x00B0;-disk sectors by using three linear slots across the patch center and sequentially rotated by 60&#x00B0;. Each disk sector is short-circuited to the ground plane through three properly located shorting pins. It thus makes the 0.5-wavelngth and 0.25-wavelength resonant modes excited at nearby frequencies to form a dual-resonant wide band for each port. Additionally, the six ports in the proposed antenna have their port isolation larger than 10 dB and the corresponding six radiating waves have very low envelope correlation coefficients (less than about 0.02) over the wide band. That is, six uncorrelated waves suitable for MIMO (multi-input-multi-output) operation are obtained. The proposed antenna can find applications for wideband mobile MIMO antennas to cover 6.425-7.125 GHz of the possible new mobile communication band or 5.925-7.125 GHz for the new unlicensed WiFi-6E band.

Allied Power Constraint Optimization and Optimal Beam Tracking Schemes for Mobile mmWave Massive MIMO Communications

The fifth generation (5G) networks and internet of things (IoT) promise to transform our lives by enabling various new applications from driver-less cars to smart cities. These applications will introduce enormous amount of data traffic and number of connected devices in addition to the current wireless networks. Thus 5G networks require many researches to develop novel telecommunication technologies to accommodate these increase in data traffic and connected devices. In this paper, novel power constraint optimization and optimal beam tracking schemes are proposed for mobile mmWave massive MIMO communications. A recently published novel channel model that is different from other widely used ones is considered. The channel model considers the number of clusters and number of rays within each cluster as varying due to user mobility. The proposed power constraint optimization scheme harmonizes conventional total power constraint (TPC) and uniform power constraint (UPC) schemes into a new one called allied power constraint (APC) that can significantly improve the system performance in 5G networks while achieving fairness among users. TPC and UPC have major drawbacks with respect to fairness and achieving quality-of-service (QoS) for users in dense networks. Thus APC aims to harmonize TPC and UPC by adjusting each antenna element’s constraint to adapt for some power resilience to a specific antenna element, hence proposing an intermediate solution between the two extreme case power constraint optimization schemes. Three optimal beam tracking schemes: (i) conventional exhaustive search (CES), (ii) multiobjective joint optimization codebook (MJOC), and (iii) linear hybrid combiner (LHS) scheme, have been provided for the mobile mmWave massive MIMO system with the proposed APC scheme. For the proposed APC scheme a comprehensive performance analysis is provided and compared with TPC and UPC. Spectral efficiency (SE), bit-error-rate (BER), Jain’s fairness index, channel occupancy ratio (COR) and instantaneous interfering power metrics are investigated. It has been shown that the proposed scheme can significantly outperform conventional schemes.

A Decoupling Network for Resonant and Non-Resonant Sub-1 GHz MIMO Mobile Terminal Antennas With Improved Compactness and Efficiency

In this work, the design procedure of a new decoupling network for different antennas is presented for mobile terminals operating in the Sub-1 GHz band (from 0.698 to 0.96 GHz). To evaluate its applicability for different resonant and non-resonant antenna types, two antenna elements have been chosen to be decoupled using the proposed decoupling network: a printed inverted-F antenna and a capacitive coupling element antenna. Simulation and measurement results showed that the decoupling network offer promising improvements in terms of impedance matching, port isolation, envelope correlation coefficient (ECC), and total efficiency. In addition, the antennas are also investigated with the ergodic capacity, multiplexing efficiency, gain, and diversity gain (both calculated using maximal ratio combining technique). Due to the contribution of the decoupling network, the ECC of both types of multiple antennas are less than 0.3, with a 30 % improvement in total efficiency and an inter-element spacing miniaturization of 34 %.

Non-Linear Base-Station Processing Within a 3GPP Compliant Framework

MIMO mobile systems, with a large number of antennas at the base-station side, enable the concurrent transmission of multiple, spatially separated information streams, and therefore, enable improved network throughput and connectivity both in uplink and downlink transmissions. Traditionally, such MIMO transmissions adopt linear base-station processing, that translates the MIMO channel into several single-antenna channels. While such approaches are relatively easy to implement, they can leave on the table a significant amount of unexploited MIMO capacity and connectivity capabilities. Recently-proposed non-linear base-station processing methods claim this unexplored capacity and promise substantially increased network throughput and connectivity capabilities. Still, to the best of the authors’ knowledge, non-linear base-station processing methods not only have not yet been adopted by actual systems, but have not even been evaluated in a standard-compliant framework, involving all the necessary algorithmic modules required by a practical system. In this work, for the first time, we incorporate and evaluate non-linear base-station processing in a 3GPP standard environment. We outline the required research platform modifications and we verify that significant throughput gains can be achieved, both in indoor and outdoor settings, even when the number of base-station antennas is much larger than the number of transmitted information streams. Then, we identify missing algorithmic components that need to be developed to make non-linear base-station practical, and discuss future research directions towards potentially transformative next-generation mobile systems and base-stations (i.e., 6G) that explore currently unexploited non-linear processing gains.

Toward Mobile Integrated Electronic Systems at THz Frequencies

This paper discusses advances related to the integration of future mobile electronic THz systems. Without claiming to provide a comprehensive review of this surging research area, the authors gathered research on selected topics that are expected to be of relevance for the future exploration of components for practical mobile THz imaging and sensing applications. First, a brief technology review of integrated mobile THz components is given. Advances in III-V technology, silicon technology, and resonant-tunneling diodes (RTD) are discussed. Based on an RTD source and a SiGe-HBT direct detector, low-cost and compact computed tomography is presented for volumetric continuous-wave imaging at around 300 GHz. Moreover, aspects of system integration of mobile THz MIMO radars are discussed. Thereby, a novel phase-locked loop concept utilizing a high-stability yttrium-iron-garnet-tuned oscillator to synthesize ultra-stable reference mmWave signals is shown, and an adaptive self-interference cancellation algorithm for THz MIMO in the digital domain based on Kalman filter theory is proposed.

Dynamic Physical-Layer Secured Link in a Mobile MIMO VLC System

This paper proposes a novel approach to provide a privately secured multiple-input and multiple-output visible light communication (VLC) in the mobility conditions. In the proposed system, a private secured VLC link is adaptively allocated to a mobile user all the time thanks to the movement tracking assistance by a camera-based detection system. The generation of the dynamic location-based scrambling matrix will be introduced providing a secured communication zone within a full normal coverage illumination area. An extensive range of numerical evaluation and practical experiments is carried out to demonstrate and evaluate the proposed system performance in different environment configurations including the mobility, camera resolutions, link range, and environment light intensity. We demonstrate that the proposed system is fully capable of securely steering the information with respect to a receiver location with a high level of reliability.

EKF-Based Beam Tracking for mmWave MIMO Systems

Beam tracking is an effective way to maintain high-quality links in mobile millimeter wave MIMO systems, which is achieved by accurately estimating angle-of-departure (AoD) and angle-of-arrival (AoA) of the desired path. Considering the slow variations of angular velocity for time-varying AoD and AoA, a second-order AoD/AoA variation model is proposed for extended Kalman filter (EKF) based beam tracking. By utilizing two well configured tracking beam pairs, the unknown path gain is removed from EKF’s measurement model and the optimal estimation of AoD/AoA is derived. Simulation results demonstrate that the proposed EKF-based beam tracking method achieves higher AoD estimation accuracy than previous methods.

A Lumped-Element Decoupling and Matching Network for a Four-Element Mobile Handset MIMO Antenna

This paper presents the first realization of a lumped-element decoupling and matching network (DMN) for more than two-element mobile MIMO arrays. The realization of the DMN is based on an existing method, which is improved in terms of bandwidth and the number of network elements. The array is designed to operate in the 2.6–2.7 GHz LTE band. The DMN is applied to a four-element MIMO antenna array located on one side of the mobile phone chassis. The array initially has a strong coupling of −3 dB, which is improved to −7 dB with the DMN. In other words, this denotes a reduction of 30 percentage points in coupled power. The DMN also improves the total efficiency by 21 percentage points at best.

Dual polarized antennas with reduced user effects for LTE-U MIMO mobile terminals

A concept of using dual-polarized, three dimensional antenna elements with minimized current distribution on ground plane to reduce the effects of user’s hand on a mobile terminal operating in LTE-U 5G band is proposed. This method which also minimizes mutual coupling (MC) is studied using a structure consisting of two non-identical antenna elements based on folded monopole topology, fed using distinct feeding mechanisms and consequently resulting in dual-polarization. For validation, the performance of this proposed MIMO antenna (MA1) is compared with a pair of dual-polarized conventional PIFA (MA2) placed orthogonally on an identical mobile terminal chassis. Both structures are assessed in terms of radiation efficiency (ƞrad), envelop correlation coefficient (ECC) and multiplexing efficiency (ME). Moreover, due to large radiation coverage, a multitude of hand phantoms and types of grips are used in simulations and experimental evaluations to validate users’ effect. Despite the presence of human hand in various modes and grips, the proposed antenna indicated decreased ƞrad and ME of about 27% and 25%, respectively. This is due to the near negligible difference in current distributions on ground plane. In comparison, conventional PIFA which exhibited ƞrad and ME decrease of up to 71% and 70%, respectively.

Compact 5G MIMO Mobile Phone Antennas With Tightly Arranged Orthogonal-Mode Pairs

In this communication, the novel compact tightly arranged pairs are employed to form a $4 \times 4$ multiple-input-multiple-output (MIMO) system and an $8 \times 8$ MIMO system operating at 3.4–3.6 GHz for fifth-generation (5G) mobile phones. Each tightly arranged pair is composed of a bent monopole and an edge-fed dipole with a compact size of $7 \times 12$ mm2. The orthogonal-mode method is presented to mitigate the mutual coupling of the tightly arranged pairs without any external decoupling structure. With the help of the orthogonal mode, isolation performances across the desired band of the $4 \times 4$ MIMO system and the $8 \times 8$ MIMO system are better than 20 and 17 dB, respectively, with the elements closely spaced. The measured efficiencies are 51.7%–84.5%/49%–72.9%, and the measured envelope correlation coefficients are less than 0.06/0.07 for the $4 \times 4/ 8 \times 8$ MIMO system. The proposed MIMO systems provide a promising solution to compact 5G MIMO mobile phone antennas with good isolation and diversity performance.

Fast Block LMS and RLS-Based Parameter Estimation and Two-Dimensional Imaging in Monostatic MIMO RADAR Systems With Multiple Mobile Targets

This paper presents novel adaptive schemes and the pertinent analysis for estimation of the number of targets, their associated radar cross section (RCS) values and Doppler velocities in monostatic MIMO radar systems. These schemes are based on the fast block least mean squares (FBLMS) and fast block recursive least squares (FBRLS) algorithms considering both stationary as well as mobile targets and/or radar platform. For the stationary scenario, schemes are proposed for estimation of RCS coefficients, target number and their angle, range locations. In addition, a procedure is also developed to obtain the 2D-image of the MIMO radar scene in angle-range dimensions. Analysis is presented for the first and second order moments of the observation as well as estimation errors resulting from the proposed FBLMS, FBRLS techniques, along with their global convergence. Both the proposed schemes are shown to converge globally to the optimal Wiener filter, which is lacking in existing schemes. Further, a Bayesian information criterion based selection rule is employed to enhance the estimation and imaging performance of the proposed adaptive frameworks. Cramer-Rao bounds are derived to characterize the mean squared error of the estimated RCS coefficients for stationary scenarios and also for joint RCS, Doppler velocity estimation in mobile MIMO radar scenarios. The FBLMS and FBRLS schemes are shown to have significantly lower computational complexities in comparison to existing MIMO radar schemes. Simulation results demonstrate the improved performance of the proposed schemes and also validate the derived analytical expressions.

Particle Swarm Optimization for Weighted Sum Rate Maximization in MIMO Broadcast Channels

In this paper, we investigate the downlink multiple-input-multiple-output (MIMO) broadcast channels in which a base transceiver station (BTS) broadcasts multiple data streams to K MIMO mobile stations (MSs) simultaneously. In order to maximize the weighted sum-rate (WSR) of the system subject to the transmitted power constraint, the design problem is to find the pre-coding matrices at BTS and the decoding matrices at MSs. However, such a design problem is typically a nonlinear and nonconvex optimization and, thus, it is quite hard to obtain the analytical solutions. To tackle with the mathematical difficulties, we propose an efficient stochastic optimization algorithm to optimize the transceiver matrices. Specifically, we utilize the linear minimum mean square error Wiener filters at MSs. Then, we introduce the constrained particle swarm optimization algorithm to jointly optimize the precoding and decoding matrices. Numerical experiments are exhibited to validate the effectiveness of the proposed algorithm in terms of convergence, computational complexity and total WSR.

Multiband printed mobile MIMO antenna for WWAN and LTE applications

Multiband printed mobile MIMO antenna for WWAN and LTE applications