Hybrid Beamforming Systems Research Articles

Limited Feedback Hybrid Beamforming for Multi-Mode Transmission in Wideband Millimeter Wave Channel

A major bottleneck in millimeter wave hybrid beamforming (BF) system is the limited number of radio frequency (RF) chains at the base station (BS). For example, when the number of users is large, the joint user scheduling and BF design is needed under the hardware constraint. Fortunately, if multiple RF chains are available at both BS and users, the system performance can significantly be improved by multi-mode transmission, which assigns different numbers of streams to the users. However, the optimal multi-mode scheme may require high feedback-feedforward overhead and complexity. Furthermore, since the mmWave BF system operates in a large bandwidth, the wideband channel should be considered. To tackle this problem, we propose the single-carrier (SC) hybrid BF scheme based on the limited feedback information. We maximize the weighted sum rate by adopting the multi-mode transmission based on the RF beam alignment. The proposed SC hybrid BF scheme outperforms the existing orthogonal frequency division multiplexing (OFDM)-based hybrid BF schemes. From the analysis, we find that full spatial multiplexing gain is guaranteed if we scale the number of RF chains at the BS as smaller than the square root of the number of antennas in a large number of users regime.

Beam Tracking Particle Filter for Hybrid Beamforming and Precoding Systems

Because millimeter wave (mmWave) systems can span notably wide spectral bands, mmWave systems are expected to dominate fifth-generation (5G) communication systems. Due to the short wave-length of mmWave radiation, multiple-input multiple-output (MIMO) systems can use massive antennas and precoding technology to overcome signal attenuation in mmWave channels. However, the cost and power consumption of radio frequency (RF) chains would increase substantially with the number of antennas. Hence, hybrid beamforming was proposed to reduce the number of RF chains in massive MIMO systems. Hybrid beamforming involves RF beamforming matrix construction and baseband precoding matrix derivation. This study focused on the design and implementation of an algorithm for the RF beamforming matrix construction for mobile environments. Accordingly, this study presents a mixture particle filter that exploits the temporal continuity of beam clusters in a mobile mmWave channel to reduce the computational complexity of RF beamforming matrix construction. Moreover, this beam-tracking particle filter is based on parallel processing architecture to support the tracking of multiple beam clusters in the mmWave channel. Finally, the beam-tracking particle filter was implemented on a field-programmable gate array platform and was verified in a hybrid beamforming system for mmWave MIMO systems. The particle filter processor achieved a maximal throughput of 9.198k matrices/s with a clock rate of 192 MHz, which could support a speed of up to 88.5 km/h for mobile users.

Hybrid Precoding Technique With Iterative Algorithm for MIMO-OFDM System

This paper proposes a hybrid precoding technique based on multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system to improve bit error rate (BER) performance in hybrid beamforming system. The conventional hybrid beamforming system cannot outperform the performance of full-digital beamforming system in OFDM. In the proposed algorithm, the analog precoding matrices are designed by iterative algorithm and one proper analog precoding matrix with the highest power of hybrid precoder is selected to achieve the highest performance. According to the number of analog precoding matrices, the diversity gain is increased and the performance is improved. The simulation results show that the BER performance and average sum rate for the proposed scheme are higher than the conventional hybrid beamforming system.

Multi-User Hybrid Beamforming System Based on Deep Neural Network in Millimeter-Wave Communication

Millimeter-wave (mmWave) communication with a large bandwidth can result in a significantly improved data rate in wireless communications. To overcome high path-loss in the mmWave frequency band, beamforming technology is necessary. Especially, there has been widespread interest in development of hybrid beamforming (HB) technologies, in view of reducing cost and power consumption in massive multiple input multiple output (MIMO) systems. Some of existing researches on HB algorithms assumed perfect channel state information (CSI) and the others used beam training process in case of assuming imperfect CSI. When beam training process is used, enough beam training has to be conducted to achieve sufficient system performance in massive MIMO systems, which results in significant training overhead. Thus, it is necessary to reduce beam training complexity. Compared to state-of-the-art technology, we propose a multi-user HB system using codebooks based on a deep neural network (DNN) in this paper. In our proposed scheme, beam codewords for the base station (BS) and all users can be inferred using limited beam training in cases when the channel state information (CSI) is unknown. In order to apply the proposed scheme to situations where the CSI is unknown, reference radio frequency (RF) beamformers were introduced. Also, the proposed DNN structure is designed considering introduced reference RF beamformers. By using the proposed DNN with reference RF beamformers, the proposed system can inferred optimal beam codewords with limited beam training. Results obtained from simulations indicate that the proposed scheme can achieve almost the same performance as a conventional scheme with less beam training complexity. We also show that the performances achieved by the proposed scheme are gradually increased as training epoch is increased, eventually converging to a steady-state value.

Self-Interference Cancellation and Channel Estimation in Multicarrier-Division Duplex Systems With Hybrid Beamforming

Design of full-duplex (FD) wireless systems faces many challenges, including self-interference cancellation (SIC), capability to provide high capacity, high flexibility for operation, best usage of resources, etc. In this paper, we propose and investigate a multicarrier-division duplex (MDD) based hybrid beamforming system operated in FD mode, which is endowed with the advantages of both time-division duplex and frequency-division duplex. It also shares some merits of FD and allows to be free of self-interference (SI) in digital domain, but faces the same challenge of SI as the FD in analog domain. Hence in this paper, we first propose an adaptive beamforming assisted SI cancellation scheme with taking into account the practical requirement of analog-to-digital conversion (ADC). It can be shown that the proposed approach is capable of jointly coping with the desired signals' transmission and SI suppression. Then, channel estimation (CEst) in MDD/MU-MIMO system is proposed by exploiting the reciprocity between the uplink and downlink subcarrier channels that is provided by MDD. Correspondingly, the orthogonality-achieving pilot symbols are designed, and the least-square (LS) CEst as well as linear minimum mean-square error (LMMSE) CEst are derived. Finally, the performance of MDD/MU-MIMO systems employing the proposed SIC method is investigated, with respect to the SI cancellation capability, sum-rate potential, CEst performance, and the effect of CEst on the achievable performance. Our studies show that MDD/MU-MIMO provides an effective option for design of future wireless transceivers.

Beamforming with Precoders Based Millimeter Wave Communication System

The 5G communications are used with baseband Precoders and Beamforming. The Technology is needed to update, all available characteristics in the present Wireless Communication System (WCS). The Hybrid Beamforming systems are across in the RF and Digital domain. In the mmWave MIMO system, the numbers of antennas has increased to improve the Spectral Efficiency of the system. The proposed algorithms observe that system performance for different SNR range.

Energy Efficiency of mmWave MIMO Systems With Spatial Modulation and Hybrid Beamforming

This work addresses the problem of energy-efficient radio resource allocation in large-scale multiple-input multiple-output (MIMO) systems using hybrid beamforming and spatial modulation, communicating using mmWaves. The problem is formulated as the maximization of the bit-per-Joule energy efficiency with respect to the transmit power and number of active radio-frequency (RF) chains, enforcing constraints on maximum power, maximum and minimum number of active RF chains, and minimum achievable rate guarantee. The optimization is carried out considering both the standard linear power consumption model, as well as the case in which the transmit amplifier operates in the non-linear region. In both cases, the globally optimal solution is derived with affordable complexity. Numerical results confirm the optimality of the proposed optimization framework, showing that spatial modulation with hybrid beamforming is more energy-efficient than a hybrid beamforming system without spatial modulation for realistic hardware power dissipation values.

Improving Energy Efficiency of Hybrid Beamforming System

Hybrid beamforming which combines conventional digital beamforming with analog beamforming system is promising model in wireless communication. The problem is using RF chain in digital precoder spends high cost and variable phase shifter exist at analog precoder processing network. Dealing with this problem, many architectures emerge to make lower hardware complexity and power consumption. This paper proposes low-resolution solution using phase over-sampling(POS) and switches(SW) on Radio Frequency(RF) chain to improve energy efficiency. We analyze proposed POS-SW hybrid beamforming system. In the simulation, the estimate is channel capacity in different signal-to-noise and energy efficiency during increasing number of RF chain on 3 dimension(3D) channel environment. It is shown that the proposed system has almost same channel capacity and high energy efficiency compared to the conventional system.

A Novel Two-Stage Beam Selection Algorithm in mmWave Hybrid Beamforming System

A hybrid beamforming structure, which consists of digital precoding and analog beamforming, is a low-cost solution to millimeter wave (mmWave) large-scale antenna systems. In this letter, we study the sum rate maximization problem where an analog beamformer is selected from a discrete codebook. A two-stage scheme is proposed in order to avoid an exhaustive search. First, the lower bound of the sum rate is derived, and the trace inverse of the equivalent channel is determined as a novel metric for beam selection. Based on this metric, we formulate a convex problem to derive an initial beam set. Finally, an iterative algorithm is designed to update beams for further performance improvement. Simulation results demonstrate that the proposed scheme achieves a near-optimal sum rate performance and outperforms existing schemes.

Hybrid beamforming for millimetre wave massive MU‐MIMO systems with IQ imbalance

The downlink communication of a single-cell millimetre wave (mmWave) massive multi-user multiple-input multiple-output (MU-MIMO) system with hybrid beamforming (HBF) is studied. The authors consider the system with in-phase and quadrature-phase imbalance (IQI) at the radio-frequency (RF) chains. Firstly, they provide the HBF designs based on the complex-valued effective channel and augmented real-valued equivalent channel, respectively. Then, they study the impact of IQI on the achievable downlink sum rate and derive the approximation of the achievable sum rate on various HBF schemes. Results show that the sum rate of the receiver designed based on real-valued equivalent channel increases without bound, but the performance of the receiver designed based on complex-valued presentation exhibits a finite ceiling, as the number of BS antennas increases. Furthermore, both receivers limit to finite ceiling rates due to IQI as the transmit power goes to infinity. Moreover, the HBF system reaches a peak sum rate at a certain value of the number of users, and IQI has an ignorable impact on the value. Meanwhile, the impact of the amplitude imbalance is more significant on the performance degradation of the HBF system than that of the phase imbalance.

User Scheduling for Millimeter Wave Hybrid Beamforming Systems With Low-Resolution ADCs

We investigate uplink user scheduling for millimeter wave (mm-wave) hybrid analog/digital beamforming systems with low-resolution analog-to-digital converters (ADCs). Deriving new scheduling criteria for the mm-wave systems, we show that the channel structure in the beamspace, in addition to the channel magnitude and orthogonality, plays a key role in maximizing the achievable rates of scheduled users due to quantization error. The criteria show that to maximize the achievable rate for a given channel gain, the channels of the scheduled users need to have 1) as many propagation paths as possible with unique angle-of-arrivals (AoAs) and 2) even power distribution in the beamspace. Leveraging the derived criteria, we propose an efficient scheduling algorithm for mm-wave zero-forcing receivers with low-resolution ADCs. We further propose a chordal distance-based scheduling algorithm that exploits only the AoA knowledge and analyze the performance by deriving ergodic rates in closed form. Based on the derived rates, we show that the beamspace channel leakage resulting from phase offsets between AoAs and quantized angles of analog combiners can lead to sum rate gain by reducing quantization error compared to the channel without leakage. The simulation results validate the sum rate performance of the proposed algorithms and the derived ergodic rate expressions.

Joint Precoding and Combining Design for Hybrid Beamforming Systems With Subconnected Structure

Hybrid analog and digital structure with reduced radio frequency (RF) chains is a key enabler to reach a compromise between system complexity and performance in future fifth-generation high-frequency communications. A fully connected architecture that each antenna connects to all RF chains has been proven to achieve similar performance compared to a traditional full-digital system where the number of RF chains is equal to the number of antennas. However, such a structure is difficult for practical implementation owing to the problem of circuit layout for high-frequency antenna array structures. Therefore, a subconnected alternative where each RF chain only connects to a disjoint subset of antennas becomes more attractive. In this paper, we study the system with the subconnected subarray architecture employed by both the transmitter and the receiver, and aim to maximize the sum-rate by taking joint precoding and combining into consideration. We propose two schemes, named joint-SIC and MU-SIC, for single-user and multi-user communications, respectively. Moreover, we provide an upper bound of the sum-rate achieved by such a subconnected subarray structure. The simulation results show the fast convergence and effectiveness of the proposed schemes.

Hybrid Beamforming for Multi-User Massive MIMO Systems

The large scale multiple-input multiple-output (MIMO) system with hybrid beamforming (HBF) is a promising communications technology due to its excellent tradeoff between hardware complexity and system performance. Assuming perfect channel state information is acquired, we consider a single cell downlink multi-user massive MIMO system working in a generic channel model with a hybrid structure that supports multiple streams per UE. We aim to find an analog and digital precoder/combiner that maximizes the sum-rate of the communication system. Unlike the traditional two-stage design criterion, which separately designs the analog and digital stages, our proposed criterion jointly designs two stages by trying to avoid the loss of information at each stage. When double the least number of radio frequency (RF) chains are available, we provide an asymptotically optimal solution in a massive MIMO regimen, i.e., the sum-rate of such an HBF solution could approach the channel capacity under large base station (BS) antenna arrays. A corresponding solution using the fewest RF chains is then derived. Finally, the simulation results are shown to validate the proposed schemes. Specifically, the solution with the fewest RF chains is shown to outperform the state of the art for HBF systems, even when the number of BS antennas is not very large. It should be noted that the schemes proposed in this paper have low complexity owing to their closed-form solutions.

Two-Stage Analog Combining in Hybrid Beamforming Systems With Low-Resolution ADCs

In this paper, we investigate hybrid analog/digital beamforming for multiple-input multiple-output (MIMO) systems with low-resolution analog-to-digital converters for millimeter wave (mmWave) communications. In the receiver, we propose to split the analog combining subsystem into a channel gain aggregation stage followed by a spreading stage. Both stages use phase shifters. Our goal is to design the two-stage analog combiner to optimize mutual information (MI) between the transmitted and quantized signals by effectively managing quantization error. To this end, we formulate an unconstrained MI maximization problem without a constant modulus constraint on analog combiners, and derive a two-stage analog combining solution. The solution achieves the optimal scaling law with respect to the number of radio frequency chains and maximizes the MI for homogeneous singular values of a MIMO channel. We further develop a two-stage analog combining algorithm to implement the derived solution for mmWave channels. By decoupling channel gain aggregation and spreading functions from the derived solution, the proposed algorithm implements the two functions by using array response vectors and a discrete Fourier transform matrix under the constant modulus constraint on each matrix element. Therefore, the proposed algorithm provides a near-optimal solution for the unconstrained problem, whereas conventional hybrid approaches offer a near optimal solution only for a constrained problem. The closed-form approximation of the ergodic rate is derived for the algorithm, showing that a practical digital combiner with two-stage analog combining also achieves the optimal scaling law. Simulation results validate the algorithm performance and the derived ergodic rate.

RF Lens-Embedded Antenna Array for mmWave MIMO: Design and Performance

The requirement of high data rate in 5G calls for utilization of the mmWave frequency band. Researchers seeking to compensate for mmWave's high path loss have proposed that mmWave MIMO systems make use of beamforming. Hybrid beamforming systems demonstrate promising performance in achieving high gain and directivity by using phase shifters. The actual implementation, however, is costly and complex. To reduce such cost and complexity, this article presents actual prototypes of the lens antenna to be used in 5G mmWave beamforming systems. Using a lens as a passive phase shifter enables beamforming without the heavy network of phase shifters, while gain and directivity are achieved by the energy-focusing property of the lens. Proposed in this article are two types of lens antennas, one for static and the other for mobile usage. The lens antennas' sizes are varied to also discuss the lens design. Their performance is evaluated using measurements and simulation data along with link- and system-level analysis. Results show the lens antenna yields high gain, directivity, and improved beam-switching feasibility compared to when a lens is not used.

Limited Feedback Hybrid Beamforming Based on Dual Polarized Array Antenna

To satisfy increased data quantity demanded by users, millimeter-wave (mmWave) communication using large bandwidth and numerous antennas has considerable promise as a new technology for wireless communication. Also, it is possible to increase more data rate by using a dual polarized array antenna (DPAA). On the other hand, beamforming techniques have to be used in mmWave communication to overcome high path-loss. Conventional beamformers, however, have problems of high costs, high power consumption, and difficulties of implementation to be used in mmWave communication. Thus, a hybrid analog radio frequency and digital baseband beamformer is used to solve these problems. Since, it is very hard to achieve perfect channel state information, it is necessary to use limited feedback information based on beam training. In this letter, a hybrid beamforming system based on DPAA considering practical antenna radiation pattern is developed in a multi-user channel environment. Furthermore, two hybrid beamforming algorithms using only limited feedback channel information are proposed and analyzed.

Capacity Analysis of a Hybrid Beamforming System with the Characteristics of Channel Clustering

Capacity Analysis of a Hybrid Beamforming System with the Characteristics of Channel Clustering

Retracted: A new codebook design for hybrid beamforming systems using quantized phase shifters

We consider a hybrid beamforming system, where the overall beamformer consists of a low-dimensional baseband beamformer and an radio frequency (RF) beamformer imple­mented by using analog phase shifters. In practice, the analog phase shifters are imperfect and are controlled with several quantized phases. This makes the channel estimation difficult in codebook-based beamforming schemes. In this paper, we propose a new codebook-based beamforming scheme to address the challenge of the quantized phase shifters. The fundamental idea is to design new codebook beams by logically separating a full antenna array into some subarrays and by mirroring a half of weights of subarrays from the rest weights. Numerical results show that the proposed scheme outperforms the conventional scheme using discrete Fourier transform (DFT) beams.

Reconfigurable Hybrid Beamforming for Dual-Polarized mmWave MIMO Channels: Stochastic Channel Modeling and Architectural Adaptation Methods

A reconfigurable hybrid beamforming (HBF) system is presented to dynamically exploit the channel diversities and antenna array directivity in millimeter wave (mmWave) channels. To develop an effective method for HBF architecture adaptation in wideband mmWave channels, the performance of an architecture is evaluated based on its average frequency-domain channel capacity. According to our analysis and simulations, the spatial covariance of the frequency-domain channels of using HBF can still be approximately modeled in a Kronecker form. Furthermore, beamforming directivity and channel spatial diversity have different advantages on capacity improvement in different transceiving conditions. Based on the results of channel modeling, system analysis, and simulations, a reconfigurable HBF architecture is thus proposed to enable flexible adjustments of the active subarrays, the antennas and polarizations of each subarray, and the active analog front-end and radio frequency chains linked to the active subarrays. A training procedure is meanwhile developed for the HBF system to learn proper architectures according to the system constraints, the channel statistics, the baseband precoder structure, and the channel capacity between the transmitter and the receiver. Compared with a fixed HBF system, such a reconfigurable system provides 3–15-dB power gains in channel capacity under various simulated channel conditions.

Arbitrary Beam Synthesis of Hybrid Beamforming Systems for Beam Training

For future millimeter wave mobile communication systems, the use of analog/hybrid beamforming is envisioned to be an important aspect. The synthesis of beams is a key technology to enable the best possible operation during beam search and data transmission. The method for synthesizing beams developed in this letter is based on previous work in radar technology considering only phased array antennas. With this technique, it is possible to generate a desired beam of any shape with the constraints of the desired target transceiver antenna frontend. It can cope with 1-D, 2-D, and even 3-D antenna array geometries, e.g., cylindrical arrays. The numerical examples show that the method can synthesize beams by considering a user defined tradeoff between gain, transition width, and passband ripples. Since this beam synthesis method is computationally complex, it is only suitable for offline calculation during the design or calibration of a device.