Analog Beamforming Research Articles

Beamforming Analysis and Design for Wideband THz Reconfigurable Intelligent Surface Communications

Reconfigurable intelligent surface (RIS)-aided terahertz (THz) communications have been regarded as a promising candidate for future 6G networks because of its ultra-wide bandwidth and ultra-low power consumption. However, there exists the beam split problem, especially when the base station (BS) or RIS owns the large-scale antennas, which may lead to serious array gain loss. Therefore, in this paper, we investigate the beam split and beamforming design problems in the THz RIS communications. Specifically, we first analyze the beam split effect caused by different RIS sizes, shapes and deployments. On this basis, we apply the fully connected time delayer phase shifter hybrid beamforming (FC-TD-PS-HB) architecture at the BS and deploy distributed RISs to cooperatively mitigate the beam split effect. We aim to maximize the achievable sum rate by jointly optimizing the hybrid analog/digital beamforming, time delays at the BS and reflection coefficients at the RISs. To solve the formulated problem, we first design the analog beamforming and time delays based on different RISs’ physical directions, and then it is transformed into an optimization problem by jointly optimizing the digital beamforming and reflection coefficients. Next, we propose an alternatively iterative optimization algorithm to deal with it. Specifically, for given the reflection coefficients, we propose an iterative algorithm based on the minimum mean square error technique to obtain the digital beamforming. After, we apply Lagrangian dual reformulation (LDR) and multidimensional complex quadratic transform (MCQT) methods to transform the original problem to a quadratically constrained quadratic program, which can be solved by alternating direction method of multipliers (ADMM) technique to obtain the reflection coefficients. Finally, the digital beamforming and reflection coefficients are obtained via repeating the above processes until convergence. Simulation results verify that the proposed scheme can effectively alleviate the beam split effect and improve the system capacity.

Hybrid Multibeamforming Receiver With High-Precision Beam Steering for Low Earth Orbit Satellite Communication

A hybrid multibeamforming receiver for low Earth orbit (LEO) satellite communication in the Ku-band is designed and tested. The proposed receiver is implemented with eight channels to enable multibeam control. The proposed receiver, including both analog and digital beamforming structures, is capable of multibeam reception using both analog and digital beamforming techniques simultaneously or selectively. Analog beamforming is implemented by employing a local oscillator phase shifter using direct digital synthesis and phase-locked loop (PLL) structures. In digital beamforming, a software-defined radio can control the phase of the signal in the digital baseband. The multibeam received using the proposed hybrid multibeamforming receiver was measured at 11.7 GHz and 12.7 GHz in an anechoic chamber. The phase-control resolutions of analog and digital beamforming were 0.022° and 0.72°, respectively. Analog beam-switching speed is slower than digital beamforming because it depends on the settling time of the PLL circuit, but it has a high phase-control resolution. Therefore, by using analog and digital beamforming when precise beam tilting and fast beam switching are required, respectively, the proposed hybrid multibeamforming is shown to be suitable in accordance with the communication situation.

Low-Resolution Hybrid Beamforming in Millimeter-Wave Multi-User Systems

A new hybrid amalgam of analog and baseband digital beamforming is conceived for millimeter-wave (mmWave) multi-user networks. The base station is equipped with a large-scale antenna-array, which however relies on a limited number of radio frequency chains for mitigating the severe path-loss of mmWave band transmission. Each user is also equipped with a multi-antenna array. The analog beamformer's weight-resolution is set low for the sake of power efficient implementation. The hybrid beamformer design relies on the novel optimization criterion of directly maximizing the geometric means of users' rates, which is shown to result in fair rate-distributions for the users without imposing a minimum user-rate constraint. Furthermore, new computationally efficient algorithms are developed, which are purely based on closed-form low-complexity expressions. Hence these low-complexity solutions are eminently suitable for large-scale mmWave arrays. Numerical examples are provided for demonstrating their efficiency.

Analog Beamforming Using ESPAR for Single-RF Precoding Systems

A novel analog beamforming technique that utilizes single radio frequency (single-RF) electronically steerable parasitic array radiator (ESPAR) antennas is proposed. The ESPAR beamforming techniques are aimed at precoding in multiple antenna wireless communication systems using the single or hybrid RF approach. One advantage of ESPAR analog beamforming compared to conventional analog beamforming using phase shifters is that arbitrary patterns can be straightforwardly formed. Therefore, ESPAR analog beamforming can provide performance almost identical to digital beamforming. More importantly, ESPAR analog beamforming does not require phase shifters and power splitters, overcoming implementation challenges of conventional analog beamforming. It also has a more compact size compared to conventional beamforming using uniform antenna arrays. We analyze and optimize ESPAR analog beamforming and propose a channel approach based on beamspace pilot transmission to acquire channel state information (CSI). In addition, we propose limited feedback ESPAR analog beamforming based on a beamforming selection strategy. Simulation results for average gain show that ESPAR analog beamforming has almost identical performance to digital beamforming and better performance than analog beamforming using phase shifters. Energy efficiency simulations show that the technique has the highest efficiency among all the beamforming techniques. Therefore, ESPAR analog beamforming has near optimal performance, high energy efficiency, low circuit complexity, low cost, compact size and can be an effective alternative to conventional analog beamforming.

Hybrid Beamforming in mmWave Massive MIMO for IoV With Dual-Functional Radar Communication

The dual-functional radar communication (DFRC) has been regarded as one of the most attractive solutions for facilitating vehicle applications in internet of vehicles (IoV) by utilizing millimeter Wave (mmWave) and massive multiple-in-multiple-out (MIMO) technologies. In this paper, we propose a hybrid beamforming (HBF) scheme with low power consumption and fully directional beamforming gains. The proposed HBF scheme integrates digital beamforming (DBF) with analog beamforming (ABF) to adopt a fully connected (F-C) structure to realize high spectral efficiency (SE) and accurate target sensing. Specifically, for HBF in a single-user MIMO (SU-MIMO) system, we design a fast Riemannian manifold optimization (FRMO) method by minimizing the weighted summation of the communication beamforming error and radar beamforming error. The proposed method can achieve optimal DBF for downlink communication and guarantee the desired beampattern for radar sensing. For HBF in a multiuser MIMO (MU-MIMO) system, we formulate the weighted optimization problem to mitigate multiuser interference (MUI). We design a low-complexity method, namely, the adaptive particle swarm optimization (APSO) algorithm, to obtain a near-optimal solution for HBF based on the criteria of minimizing MUI and the radar beamforming error. We conduct excessive simulations to evaluate the proposed algorithms for the HBF design in both the SU-MIMO system and MU-MIMO system. The numerical results demonstrate that the proposed algorithms achieve near-optimal performance compared to existing HFB methods with high computational efficiency in terms of beamforming gains and SE.

Adaptive Non-Uniform Hybrid Beamforming for mmWave Train-to-Ground Communications in High-Speed Railway Scenarios

Higher frequency bands, especially millimeter wave (mmWave), are a key enabler for future high speed railway (HSR) wireless communication systems. Hybrid analog and digital beamforming (HBF) schemes operating at mmWave frequency bands can exploit the sparse nature of the channel by using large scale antenna arrays (LSAs) to shape multiple beams that overcome the severe path loss. However, due to the long and straight geometric characteristic of the rail track, there is a significant variance in the train-to-ground communication rate when the train is near or far from the BS. To address this issue, a novel hybrid beamforming scheme is developed based on a non-uniform beam design. We first model and investigate different beam design schemes in terms of spectral efficiency. Then, an efficient straight route based adaptively analog beamforming scheme with the non-uniform beam is proposed for HSR, which is designed to resist path loss. Finally, an adaptive non-uniform HBF algorithm based on the orthogonal matching pursuit method (OMP) is developed to minimize the rate gap between different locations by selecting the appropriate predefined beams. Numerical results show that the proposed hybrid beamforming scheme can efficiently ensure signal coverage, and reduce the variance of the train-to-ground communication rate along a straight track route.

Simultaneously Transmitting and Reflecting Surface (STARS) for Terahertz Communications

A simultaneously transmitting and reflecting surface (STARS) aided terahertz (THz) communication system is proposed. A novel power consumption model is proposed that depends on the type and resolution of the STARS elements. The spectral efficiency (SE) and energy efficiency (EE) are maximized in both narrowband and wideband THz systems by jointly optimizing the hybrid beamforming at the base station (BS) and the passive beamforming at the STARS. 1) For narrowband systems, independent phase-shift STARSs are investigated first. The resulting complex joint optimization problem is decoupled into a series of subproblems using penalty dual decomposition. Low-complexity element- wise algorithms are proposed to optimize the analog beamforming at the BS and the passive beamforming at the STARS. The proposed algorithm is then extended to the case of coupled phase-shift STARS. 2) For wideband systems, the spatial wideband effect at the BS and STARS leads to significant performance degradation due to the beam split issue. To address this, true time delayers (TTDs) are introduced into the conventional hybrid beamforming structure for facilitating wideband beamforming. An iterative algorithm based on the quasi-Newton method is proposed to design the coefficients of the TTDs. Finally, our numerical results confirm the superiority of the STARS over the conventional reconfigurable intelligent surface (RIS). It is also revealed that i) there is only a slight performance loss in terms of SE and EE caused by coupled phase shifts of the STARS in both narrowband and wideband systems, and ii) the conventional hybrid beamforming achieves comparable SE performance and much higher EE performance compared with the full-digital beamforming in narrowband systems but not in wideband systems, where the TTD-based hybrid beamforming is required for mitigating wideband beam split.

Miniaturized Pattern-Reconfigurable Multimode Antennas With Continuous Beam-Steering Capability

In this paper, two miniaturized multi-mode pattern steering antennas for Internet of Things (IoTs) applications are proposed. A compact multi-mode cavity functions both the hybrid and radiator. A continuous 360° pattern scanning in the azimuth plane is controlled by the amplitude and phase of three excitation ports. The first design achieves the smallest size with TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> modes. In contrast, the second design has improved impedance bandwidth and mode isolation by introducing TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> and high-order TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> modes. Eight dipole chokes are attached to the cavity for surface current suppression. This approach eliminates the unwanted patch mode radiation. The antennas support multibeam applications with digital beamforming and analog beamforming with the 0°/180° phase switch and variable gain amplifier (VGA). The direction of arrival (DOA) can be estimated by directly measuring the amplitude and phase of the receiving signal. No full phase shifter and signal classification algorithm are required. The prototypes are fabricated and measured at 2.4 GHz. The diameters of the two antennas are 0.4 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and 0.9 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . The achieved antenna size is very miniature as shown by the literature comparison. The radiation and DOA performance is evaluated. The peak system efficiency is better than 60% after calibration and a good DOA estimation result is obtained.

Hybrid Beamforming With Sub-Connected Structure for MmWave Massive Multi-User MIMO Relay Systems

In this paper, we investigate the hybrid beamforming design with sub-connected structure for millimeter-wave (mmWave) massive multi-user multiple-input multiple-output (MU-MIMO) amplify-and-forward (AF) relay systems. Considering the constant-modulus and block-diagonal constraints, an iterative algorithm is proposed to sequentially design the analog beamforming of the base station, relay, and users. Next, the relay baseband combiner is designed by transforming the highly complicated non-convex mutual information maximization problem into an easily tractable weighted minimum mean squared error one. To mitigate the inter-user interference, a successive serial interference cancellation based and a piecewise successive approximation based methods are developed for the uniform sparse distribution and dense distribution scenarios, respectively. Simulation results demonstrate that the two proposed hybrid beamforming schemes can achieve good performance in terms of sum-rate and energy efficiency, and outperform benchmarks significantly. In addition, the two proposed schemes are shown to be robust to imperfect channel state information (CSI), even though they are studied based on perfect CSI.

Optimal Antenna Pattern Design for the Instantaneous MIMO Channel

Due to the rapid attenuation of the millimeter wave, it is necessary to use very large-scale antenna arrays in millimeter wave communications to get ultra-high directivity which improves the transmission distance and the signal-to-noise ratio. Considering the cost of large-scale RF links, analog beamforming plays an important role in large-scale MIMO communications. This paper discusses the calculation method of the antenna pattern that best matches the instantaneous MIMO channel in analog beamforming. By giving piecewise modeling on the antenna pattern, singular value decomposition and the water-filling algorithm are used to obtain the antenna pattern and the power distribution among antennas. The optimal antenna pattern can provide the target pattern for antenna synthesis to get the maximum capacity. The simulation results show that the method is effective.

Optimization of the Compressive Measurement Matrix in a Massive MIMO System Exploiting LSTM Networks

Massive multiple-input multiple-output (MIMO) technology, which is characterized by the use of a large number of antennas, is a key enabler for the next-generation wireless communication and beyond. Despite its potential for high performance, implementing a massive MIMO system presents numerous technical challenges, including the high hardware complexity, cost, and power consumption that result from the large number of antennas and the associated front-end circuits. One solution to these challenges is the use of hybrid beamforming, which divides the transceiving process into both analog and digital domains. To perform hybrid beamforming efficiently, it is necessary to optimize the analog beamformer, referred to as the compressive measurement matrix (CMM) here, that allows the projection of high-dimensional signals into a low-dimensional manifold. Classical approaches to optimizing the CMM, however, are computationally intensive and time consuming, limiting their usefulness for real-time processing. In this paper, we propose a deep learning based approach to optimizing the CMM using long short-term memory (LSTM) networks. This approach offers high accuracy with low complexity, making it a promising solution for the real-time implementation of massive MIMO systems.

Performance Evaluation of Hybrid Precoder Design for Multi-User Massive MIMO Systems with Low-Resolution ADCs/DACs

This paper presents a comprehensive analysis and design of a hybrid precoding system tailored for mmWave multi-user massive MIMO systems in both downlink and uplink scenarios. The proposed system employs a two-stage precoding approach, incorporating UQ and NUQ techniques, along with low-resolution DACs in downlink and ADCs in uplink to address hardware limitations. The system considers Zero Forcing and Minimum Mean Square Error algorithms as digital precoding methods for the uplink scenario, while exploring the impact of different DAC resolutions on system performance. Extensive simulations reveal that the proposed system surpasses conventional analog beamforming methods, particularly in multi-user scenarios involving inter-user interference. In downlink, the system demonstrates a trade-off between SE and EE, achieving higher Energy Efficiency with NUQ. In uplink, NUQ and UQ converters exhibit similar performance trends regardless of the chosen combiner algorithm. The proposed system attains enhanced Spectral and Energy Efficiency while maintaining reduced complexity and overhead. The study significantly contributes to the advancement of efficient and effective mmWave multi-user massive MIMO systems by providing a thorough analysis of various quantization schemes and precoding techniques. The findings of this research are expected to aid in the optimization of 5G and beyond technologies, particularly in high-density deployment scenarios.

A Framework of Hybrid Transceiver Optimizations With Eigenvalue Constraints for Multi-Hop Networks

In this paper, we propose a general framework on the hybrid analog-digital transceiver design for multi-hop communications. For the inclusive purpose, a transceiver model unifying both linear and nonlinear transceivers has been taken into account. Various performance metrics, including the most representative capacity and weighted mean-squared error (MSE), have been investigated in a unified manner. In particular, to meet practical needs for the quality of services (QoS), a general eigenvalue power constraint model is introduced, which contains a sum power constraint and box eigenvalue constraints as special cases. Specifically, by carefully designing the auxiliary analog and digital beamformers, the multi-hop transceiver optimization is decomposed into a series of independent sub-problems, where the analog beamformers for different hops are completely decoupled. Based on that, this framework establishes a majorization-minimization (MM) based analog beamformer design algorithm, which is able to handle the complicated weighted unit-modulus matrix optimizations by finding their semi-closed-form solutions. Furthermore, an efficient waterfilling algorithm is proposed for the digital beamformer designs to deal with the difficulties of optimizations subject to the multiple eigenvalue power constraints. The numerical results are provided to demonstrate the performance advantages of the proposed framework.

Regularized Zero-Forcing Aided Hybrid Beamforming for Millimeter-Wave Multiuser MIMO Systems

This paper considers hybrid beamforming consisting of analog beamforming (ABF) coupled with digital baseband beamforming (DBF) which is designed for multi-user (MU) multiple input multiple output (MIMO) millimeter-wave (mmWave) communications. ABF uses a limited number of radio frequency (RF) chains and finite-resolution phase-shifters to alleviate the power consumption at the base station (BS), while DBF uses either zero-forcing beamforming (ZFB) or regularized zero forcing beamforming (RZFB) to restrain MU interference. The joint design of ABF and DBF constitutes a computationally challenging mixed discrete continuous optimization problem. The paper develops efficient algorithms for its solution, which iterate scalable-complex expressions. Furthermore, we conceive a new class of MU RZFB for attaining higher rates. Simulations are provided to demonstrate the viability of the proposed algorithms and the advantages of the conceived RZFB.

Low-Overhead Localization and VR Identification for Subarray-Based ELAA Systems

Extremely large aperture arrays (ELAAs) represent a promising architecture in the sixth-generation mobile communication systems with improved spatial division multiplexing gain and spectral efficiency (SE) potential. However, spatial non-stationary channel characteristics kick in because of signal blockage and near-field propagation. To deal with them, this letter models the non-stationary channel by considering an environment-based visibility region (VR) and spherical wavefronts, respectively. Then, we propose a low-overhead channel reconstruction scheme, which can simultaneously locate the user and identify its VR. Our method is designed for subarray-based hybrid structures while the training overhead caused by analog beamforming is limited. Numerical results demonstrate that the proposed method achieves accurate UE localization and VR identification, while the achievable SE can be close to that of using a perfectly known channel in a fully digital system.

A 28 GHz 8 × 8 Gapwaveguide Phased Array Employing GaN Front-End With 60 dBm EIRP

A cost-efficient, high equivalent isotropic radiated power (60 dBm), large-bandwidth (26.5-29.5 GHz) active phased array antenna system has been designed and experimentally verified. The proposed design methodology results in a reduction of production costs by employing GaN-based radio frequency front-ends with 31 dBm output power allowing a reduced number of antenna elements. A fully metallic gapwaveguide technology has been employed achieving efficient heat dissipation per aperture area of the array as well as low-loss easy-to-manufacture antenna elements. The phased array is realized by subarraying an 8×8 slot array antenna with horizontal polarization. A ±60° analog beamforming in the E-plane is demonstrated. The presented antenna is a potential candidate for compact-size high-performance 5G base station antennas with excellent temperature stability.

Deployment and Robust Hybrid Beamforming for UAV MmWave Communications

We deploy an unmanned aerial vehicle (UAV) equipped with a large-scale uniform planar array (UPA) to serve multiple ground users in millimeter-wave band. Particularly, the practical UAV jitter is carefully considered, which may affect the beam gains and impact the communication quality. To provide a stable service, we first model the attitude change of the UPA caused by UAV jitter. Then, an optimization problem is formulated to maximize the minimum achievable rate of the users by optimizing the position and robust hybrid beamforming of the UAV. To solve the non-convex problem with highly coupled variables, a two-stage optimization strategy is developed. The first stage aims to decouple the beamforming from the original problem and design the UAV deployment under the assumption of an ideal beam pattern. The second stage aims to design robust hybrid beamforming with the obtained UAV position. Specifically, we first design analog beamforming for wide beams to cover the potential jitter angle range for each user via a chirp sequence-inspired method. Then, with equivalent channel estimation, we design digital beamforming by combining zero-forcing and water-filling power allocation algorithms. Extensive simulation results show the performance superiority of the proposed solution compared to the benchmark algorithms.

A Two-Stage Fast Beam Search for Multi-User Millimeter-Wave Massive MIMO Systems

Millimeter-wave systems deploy spatial beam search for initial access. A narrow beam search results in significant discovery delays whereas wide beams cause high user misdetection. In this work, a novel two-stage fast beam search algorithm is proposed that utilizes a beamforming architecture with an appropriate antenna spacing for subarray design. The first stage employs analog beamforming to identify the coarse beam space. The second stage based on hybrid beamforming makes use of pattern multiplication for beam space refinement. Simulation results demonstrate that the proposed scheme achieves improved performance in comparison to existing techniques in terms of significantly reduced beam search latency with a marginal increase in user misdetection.

Power-Efficient Analog Front-End Interference Suppression With Binary Antennas

Digital and analog beamforming are well-known methods to suppress interference using multiple-antenna structures, but they have practical limitations: (i) Digital beamforming requires multiple analog-to-digital converters (ADCs) to enable digital conversion, which increases the cost and complexity; (ii) Although analog beamforming does not require expensive ADCs, it uses phase shifters, which cause quantization errors, insertion losses, and reduced power efficiency. In this paper, we consider a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> -user uplink interference channel and propose a low-complexity algorithmic interference-suppression solution relying on simple switch-based reconfigurable antennas at the receivers. We utilize switches to enable/disable antennas to maximize each user’s signal-to-interference-plus-noise ratio (SINR). We present an optimization approach to approximate the optimal solution. To evaluate the results, we compare our method with relevant benchmarks. Moreover, we derive a lower bound on the minimum number of antenna elements per receiver to attain the desired SINR and verify the findings via simulations.

BSA-OMP: Beam-Split-Aware Orthogonal Matching Pursuit for THz Channel Estimation

Terahertz (THz)-band has been envisioned for the sixth generation wireless networks thanks to its ultra-wide bandwidth and very narrow beamwidth. Nevertheless, THz-band transmission faces several unique challenges, one of which is beam-split which occurs due to the usage of subcarrier-independent analog beamformers and causes the generated beams at different subcarriers split, and point to different directions. Unlike the prior works dealing with beam-split by employing additional complex hardware components, e.g., time-delayer networks, a beam-split-aware orthogonal matching pursuit (BSA-OMP) approach is introduced to efficiently estimate the THz channel and beamformer design without any additional hardware. Specifically, we design a BSA dictionary comprised of beam-split-corrected steering vectors which inherently include the effect of beam-split so that the proposed BSA-OMP solution automatically yields the beam-split-corrected physical channel directions. Numerical results demonstrate the superior performance of BSA-OMP approach against the existing state-of-the-art techniques.