Codebook-based Beamforming Research Articles

Attitude Information Aided mmWave Beam Tracking Based on Codebook

Beam tracking can be utilized to compensate for beam misalignment and avoid performance degradation in millimeter wave (mmWave) systems. In order to reduce the training overhead, attitude information obtained from motion sensors has been proposed to assist beam tracking. In this letter, we extend attitude information aided beam tracking to the practical systems with codebook-based beamforming. Moreover, estimation errors of attitude information are inevitable in practical systems, and lead to a trade-off in codebook design: wider beams suffer more from insufficient power; narrower beams are more sensitive to the error. Therefore, it is necessary to design a codebook with appropriate beamwidth. We first derive the optimal beamwidth that maximizes the average transmission rate based on the sectored beam model. Further, we consider the codebook with overlapping beams, which can prevent misalignment. Then, both the optimal beamwidth and overlap ratio are derived. Finally, simulation results validate the performance of the proposed methods.

Super Resolution-Based Beam Selection With Hierarchical Codebook in mmWave Communication

Beamforming is regarded as a promising technique for future wireless communication systems. In this regard, codebook-based beamforming offers satisfactory performance with acceptable computational complexity; however, it requires a high power-consumed beam overhead. To achieve balance between the utilized beam overhead and the achieved spectral efficiency performance, we propose a super-resolution-based scheme using a hierarchical codebook. We consider beam sweeping as an inference problem, where low-resolution beam radiating responses are used as an input, and high-resolution beam sweeping responses are output. Simulation results confirm that the proposed scheme exhibits extraordinary performance-overhead tradeoffs as compared with state-of-the-art codebook-based beamforming designs.

Codebook Design for Vertical Beamforming by Multi-Cell Coordination

Fifth-generation (5G) mobile communication systems employ beamforming technology using massive multiple-input and multiple-output (MIMO) to improve the reception quality and spectrum efficiency within a cell. Meanwhile, coordinated beamforming among multiple base stations is an effective approach to improving the spectrum efficiency at the cell edges, in which massive MIMO is deployed at geographically distant base stations and beamforming control is conducted in a cooperative manner. Codebook-based beamforming is a method for realizing multi-cell coordinated beamforming, in which each base station selects one of multiple beams that are predefined in a codebook. In codebook-based beamforming, it is important to design an efficient codebook that takes into account the beam allocation and the number of beams. In general, the larger the number of beams defined in a codebook, the more finely tuned the beam control can be and a greater improvement in spectrum efficiency can be expected. However, it requires a huge signal processing to optimize the beam combinations with a large number of beams by coordinated beamforming. This paper proposes a novel codebook design that efficiently assigns beam directions and widths in a vertical plane. Computer simulations showed that the proposed codebook performs as well as the conventional method while requiring fewer beam combinations.

Performance Evaluation of the MU-MIMO Precoding Using the QuaDRiGa Channel Model

The article presents the analysis of characteristics of algorithms of signal precoding in a multi-antenna system with many users (MU-MIMO). This paper presents the numerical evaluation of the multiuser MIMO beamforming algorithms ZF and DFT codebook based on a QUADRIGA channel model, taking into account the real conditions of signal propagation. The generated channels are used to calculate SINR and the spectral efficiency values of each user using the conventional ZF and DFT beamforming codebook. The eigenvalues of the MIMO channel are important in evaluating the MU-MIMO transmission performance characteristics, such as the spectral efficiency of a precoded system. The obtained performance of MU-MIMO ZF and DFT codebook-based beamforming in spatially correlated channels are compared based on the empirical cumulative density function of the sum rate of multiple users. Spatial correlation degrades capacity performance, and in the channels, the DFT precoder has a more robust performance and outperforms the ZF precoder in spectral efficiency. Obtained results can be used by the algorithm evaluation in the system-level simulations.

Codebook Designs for Millimeter-Wave Communication Systems in Both Low- and High-Mobility: Achievements and Challenges

More connectivity, higher data rates, more reliability, massive network capacity, higher performance and fewer delays are required in the fifth generation (5G) of cellular networks. The last ten years have contained explosive growth in mobile data traffic due to the rapid proliferation of Internet-connected smart devices. For 5G mobile and wireless networks, one of the challenges is to discover how to solve the dilemma between capacity requirements and spectrum shortage. Millimeter-wave communication is therefore a key enabler for 5G technologies. Due to the high path and penetration losses at millimeter wavelengths, antenna beamforming assumes a pivotal role in establishing and maintaining a robust communication link. Recently, codebook-based beamforming has been proposed to achieve a fair balance between complexity and performance and to eliminate the overheads. In this paper, we track the techniques of codebook-based beamforming for millimeter-wave communications in the context of the distinct requirements for low-mobility channel and high-mobility channel scenarios. Subsequently, we will provide a comparison of existing codebook-based beamforming techniques in terms of their respective benefits and shortcomings. Finally, some open directions of research are discussed, and challenges that need to be met are pointed out.

Codebook-Based Hybrid Beamforming Using Combined Phase Shifters of High and Low Resolutions

The hybrid beamforming architecture where a combination of analog and digital precoders is employed has attracted much attention recently for its flexible trade-off between power consumption and performance. A codebook-based beamforming scheme is generally considered as a more practical solution rather than the adaptive beamforming schemes due to the large number of antennas. However, the constant amplitude constraint brought by the phase shifters (PSs) in the analog precoder always makes the codebook design problem a tricky and complicated one. In this work, we consider a novel combined PS (CPS) architecture where one high-resolution PS is connected to each RF chain in parallel with low-resolution PSs to each antenna. The corresponding codebook design aiming for ideal flat beam gains is then proposed for the CPS architecture. Simulation results reveal that the proposed scheme achieves a good trade-off between performance and energy efficiency compared with conventional single PS (SPS) and the recently proposed double PS (DPS) architecture.

In Situ Assessment of 5G NR Massive MIMO Base Station Exposure in a Commercial Network in Bern, Switzerland

This paper describes the assessment of radiofrequency (RF) electromagnetic field (EMF) exposure from fifth generation (5G) new radio (NR) base stations in a commercial NR network in Bern, Switzerland. During the measurement campaign, four base station sites were investigated and the exposure induced by the NR massive multiple-input-multiple-output (MaMIMO) antennas was assessed at 22 positions, at distances from the base station between 30 m and 410 m. The NR base stations operated at 3.6 GHz and used codebook-based beamforming. While the actual field levels without inducing downlink traffic were very low (<0.05 V/m) due to a low traffic load and low antenna input powers of up to 8 W, setting up a maximum downlink traffic stream towards user equipment resulted in a time-averaged exposure level of up to 0.4 V/m, whereas the maximum extrapolated exposure level reached 0.6 V/m. Extrapolated to an antenna input power of 200 W, values of 4.3 V/m and 4.9 V/m, respectively, were obtained, which amount to 0.5–0.6% of the reference level recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). In Bern, it was found that the impact of the NR network on the total environmental RF exposure was very limited; with maximum downlink, it contributed 2% on average. Finally, it was also concluded that extrapolation to the maximum exposure level can be done without prior knowledge of the radiation patterns, directly based on the measurement of the Physical Downlink Shared Channel (PDSCH) resource elements.

Bidirectional Positioning Assisted Hybrid Beamforming for Massive MIMO Systems

The integration of the massive multiple-input multiple-output (MIMO) and millimeter-wave (mmWave) communication can increase the throughput of 5G networks. As an attractive technique in the MIMO systems, hybrid beamforming (HBF) can improve the 5G capacity by employing spatial domain resources. However, with the increase of the number of antennas, the traditional beamforming algorithms fail to efficiently keep a balance between the hardware complexity and beamforming gains. In this paper, with the aid of bidirectional location information, a bidirectional positioning assisted HBF (BPA-HBF) scheme is proposed. Specifically, we first propose a new scheme to decouple the optimal problem of traditional HBF as two phases. In the analog beamforming (ABF) phase, the dominated path among the multi-path components is determined by the transmitter and receiver. In addition, the codebook-based beamforming weight vectors are bidirectionally and synchronously determined according to the angle parameters of the dominated path. In the second phase, based on the ABF matrices, the digital beamformers are designed to maximize the energy efficiency. Simulation results indicate that the proposed BPA-HBF scheme can lead to a lower convergence time and complexity than the conventional schemes. In addition, the results show that the algorithm convergence time can be significantly reduced by increasing the positioning precision.

Particle Swarm Optimization Based Beamforming in Massive MIMO Systems

<p>This research puts forth an optimization- based analog beamforming scheme for millimeter-wave (mmWave) massive MIMO systems. Main aim is to optimize the combination of analog precoder / combiner matrices for the purpose of getting near-optimal performance. Codebook-based analog beamforming with transmit precoding and receive combining serves the purpose of compensating the severe attenuation of mmWave signals. The existing and traditional beamforming schemes involve a complex search for the best pair of analog precoder / combiner matrices from predefined codebooks. In this research, we have solved this problem by using Particle Swarm Optimization (PSO) to find the best combination of precoder / combiner matrices among all possible pairs with the objective of achieving near-optimal performance with regard to maximum achievable rate. Experiments prove the robustness of the proposed approach in comparison to the benchmarks considered. <strong></strong></p><p class="IndexTerms"> </p>

Positioning-Aided 3D Beamforming for Enhanced Communications in mmWave Mobile Networks

The extension from centimeter wave frequencies to millimeter wave (mmWave) frequencies has triggered an enormous transformation in terms of radio access architecture for future wireless networks, and it has therefore empowered unlimited opportunities for the user-oriented services and applications. Besides mmWave as a driving element, beamforming (BF) will be incorporated as a key enabling technology for the future wireless networks. In this paper, we propose a positioning-aided beamforming (PA-BF) framework for enhanced downlink communications in a cloud-oriented mmWave mobile networks. We show that the proposed PA-BF achieves a higher effective transmit ratio that is equivalent to a lower initial access latency than the conventional codebook-based BF, which in turn manifests its capability to support high-velocity mobile users. We also analyze the impact of positioning accuracies on the performance of PA-BF and discuss the trade-offs between different BF strategies with varied system parameters. Our simulation results demonstrate that, with a narrow beam phased array and reasonably good positioning accuracy, the PA-BF framework is capable of achieving higher spectral efficiency than the considered codebook-based BF especially at higher velocities.

A Hybrid Model-Based and Data-Driven Approach to Spectrum Sharing in mmWave Cellular Networks

Inter-operator spectrum sharing in millimeter-wave bands has the potential of substantially increasing the spectrum utilization and providing a larger bandwidth to individual user equipment at the expense of increasing inter-operator interference. Unfortunately, traditional model-based spectrum sharing schemes make idealistic assumptions about inter-operator coordination mechanisms in terms of latency and protocol overhead, while being sensitive to missing channel state information. In this paper, we propose hybrid model-based and data-driven multi-operator spectrum sharing mechanisms, which incorporate model-based beamforming and user association complemented by data-driven model refinements. Our solution has the same computational complexity as a model-based approach but has the major advantage of having substantially less signaling overhead. We discuss how limited channel state information and quantized codebook-based beamforming affect the learning and the spectrum sharing performance. We show that the proposed hybrid sharing scheme significantly improves spectrum utilization under realistic assumptions on inter-operator coordination and channel state information acquisition.

Beam Training for Millimeter-Wave Communication Based on Tabu Table Enhanced Rosenbrock Algorithm

The codebook-based beamforming for millimeter-wave (mm Wave) communication systems is usually used to compensate the severe attenuation of the mm Wave region. The beam training process based on pre-specified beam codebooks is considered a global optimization problem in 2-D planes formed by the potential beam index. The Rosenbrock algorithm (RA) is adopted to implement optimum beam searching whereas the simulated annealing (SA) algorithm is used to solve the problem of falling into the local optimum, due to the unavailable gradient information of the objective function. However, the RA implements rounding to the integer which leads to the problem of repeated search and beam space discontinuity caused by beam index will impair the powerful local search ability. Thus, in this paper, an enhanced RA based on tabu search and combined with SA algorithm is proposed as an alternative solution for beam search success rate. The proposed algorithm reduces the search times by forbidding the repeat search with tabu table and design of neighbor region. Moreover, to prevent the search failure, the search candidate index is defined to keep the local search ability of the original algorithm and wrap around of beam index is applied to maintain continuity of the search direction. Experimental simulations show that the proposed technique can improve the search efficiency in terms of reduced steps and increase search success rate during the beam training procedure compared to existing techniques.

Low-Complexity Beam Training for 5G Millimeter-Wave Massive MIMO Systems

We consider a 5G millimeter-wave (mmWave) massive MIMO system with subconnected hybrid structure, where each transceiver unit (TXRU) is connected to a subarray at the transmitter (TX) or the receiver (RX). Beam training is the first step for codebook-based beamforming in the absence of ideal channel state information (CSI). The complexity of the optimal exhaustive search beam training is exponentially increased with the number of TXRUs (or subarrays) at the TX and the RX, which is infeasible in practice. The conventional beam training schemes are mainly based on the idea of mathematical search algorithms and novel beam codebook designs. In this study, we explore a novel low-complexity beam training scheme by fully exploiting the sparse nature of the mmWave channel and the strong correlations of large-scale antenna arrays. Specifically, we propose a training scheme to reduce beam search space for 5G mmWave system, which consists of the following two key stages: 1) a beam subset optimization method from the perspective of array gain for capturing the energy of dominant channel propagation paths, and 2) a class of linear iterative beam search algorithms within the optimized beam subset utilizing the idea of limiting the degrees of freedom of the subarray indices during beam training. The range of the optimized beam subset size and linear search condition are also given. The performances of the proposed two algorithms, beam subset optimization-single subarray linear search and beam subset optimization-subarray pair linear search, are evaluated in a 5G mmWave system. Analysis has shown that the complexity of the proposed scheme is linear with the number of channel propagation paths, which can considerably reduce the complexity of conventional schemes. Simulation results have verified the near-optimal performance of the proposed schemes when compared with exhaustive search as well as other existing training methods.

Millimeter Wave SDMA With Limited Feedback: RF-Only Beamforming Can Outperform Hybrid Beamforming

Millimeter wave (mmWave) beamforming (BF) system can increase the spatial capacity by being installed in hotspot areas where a number of users exist. However, it is hard to obtain the channel state information of a large array system at transmitter. Even with the codebook-based BF scheme, the digital-analog hybrid BF structure may require a two-step feedback procedure. In order to reduce the feedback and feedforward overhead required for joint user scheduling and hybrid BF, we propose a codebook-based radio frequency (RF) only BF scheme with one-step feedback procedure. We show that the achievable sum rate of the RF-only BF scheme double-logarithmically scales with the number of users in mmWave channel model, which coincides with the results for the digital BF schemes in rich scattering channel model. We also show that the RF-only BF scheme can outperform the hybrid BF scheme with limited feedback. In addition, we examine the error performance in extremely sparse channel, and find the number of transmitted beams to achieve the desired rate per user in a small number of users regime.

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.

Benefits of the sparsity of mmWave outdoor spatial channels for beamforming and interference cancellation

Future outdoor communication networks are expected to make use of the mmWave bands. In this context, this paper investigates the use of sparse signal processing for efficient angular frequency estimation. Compressive sensing (CS) and correlation-based method are shown to provide accurate estimates of the Power Angular Profile (PAP). The recovered PAP is used to perform analogue beamforming. When tracking mobile users it is shown that codebook based analogue beamforming, as used in IEEE 802.11ad, results in a large signalling overhead. This adversely affects net throughput. Our CS approach requires just 2% of the resources consumed by codebook-based beamforming while providing similar SNR performance.Interference cancellation is implemented by exploiting the accurate PAP recovered by CS. This method estimates the beamforming vector required to optimise the signal to leakage and noise ratio (SLNR), allowing the coexistence of both non-interfering and interfering links. To maximise user fairness the interference cancellation capabilities of CS beamforming are combined with a Space–Time Division Multiple Access (STDMA) scheduling scheme. Considerable network throughput enhancement is demonstrated when compared to the IEEE 802.11ad codebook based beamforming approach.

Compressive Sensing Based Beamforming forMillimeter-Wave OFDM Systems

In this paper, we address codebook-based beamforming for multi-antenna orthogonal frequency division multiplexing (OFDM) systems operating in 60-GHz millimeter-wave band. Given a pre-specified codebook, the task of the beamforming process is to identify the best transmit and receive beam vectors to maximize the spectral efficiency. By properly modeling the multipath structure in 60-GHz channels, we transform the above task into the estimation of several sparse signal vectors. Furthermore, we tailor compressive sensing (CS) technology to efficiently estimate such sparse signals, wherein the CS measurement matrix is specifically designed by minimizing the inner products between different columns of the CS effective dictionary. As a result, CS-based iterative and non-iterative beamforming schemes are proposed. Due to the ability to judiciously exploit multipath sparsity inherent in 60-GHz channels, the proposed schemes significantly outperform the existing counterparts in terms of training overhead and success probability, which is confirmed by theoretical analysis and extensive simulations.

On the Feasibility of Codebook-Based Beamforming in Millimeter Wave Systems With Multiple Antenna Arrays

The use of the millimeter (mm) wave spectrum for next generation (5G) mobile communication has gained significant attention recently. The small carrier wavelengths at mmwave frequencies enable synthesis of compact antenna arrays, providing beamforming gains that compensate the increased propagation losses. In this work, we investigate the feasibility of employing multiple antenna arrays (at the transmitter and/or receiver) to obtain diversity/multiplexing gains in mmwave systems, where each of the arrays is capable of beamforming independently. Considering a codebook-based beamforming system (the set of possible beamforming directions is fixed a priori, e.g., to facilitate limited feedback), we observe that the complexity of jointly optimizing the beamforming directions across the multiple arrays is highly prohibitive, even for very reasonable system parameters. To overcome this bottleneck, we develop reduced complexity algorithms for optimizing the choice of beamforming directions, premised on the sparse multipath structure of the mmwave channel. Specifically, we reduce the cardinality of the joint beamforming search space, by restricting attention to a small set of dominant candidate directions. To obtain the set of dominant directions, we develop two complementary approaches: 1) based on computation of a novel spatial power metric; a detailed analysis of this metric shows that, in the limit of large antenna arrays, the selected candidate directions approach the channel's dominant angles of arrival and departure, and 2) precise estimation of the channel's (long-term) dominant angles of arrival, exploiting the correlations of the signals received across the different receiver subarrays. Our methods enable a drastic reduction of the optimization search space (a factor of 100 reduction), while delivering close to optimal performance, thereby indicating the potential feasibility of achieving diversity and multiplexing gains in mmwave systems.

MAC-layer concurrent beamforming protocol for indoor millimeter-wave networks

In this paper, we study concurrent beamforming issue for achieving high capacity in indoor millimeter-wave (mmWave) networks. The general concurrent beamforming issue is first formulated as an optimization problem to maximize the sum rates of concurrent transmissions, considering the mutual interference. To reduce the complexity of beamforming and the total setup time, concurrent beamforming is decomposed into multiple single-link beamforming, and an iterative searching algorithm is proposed to quickly achieve the suboptimal transmission/reception beam sets. A codebook-based beamforming protocol at medium access control (MAC) layer is then introduced in a distributive manner to determine the beam sets. Both analytical and simulation results demonstrate that the proposed protocol can drastically reduce total setup time, increase system throughput, and improve energy efficiency.

Low Complexity Codebook-Based Beamforming for MIMO-OFDM Systems in Millimeter-Wave WPAN

In this paper, we consider a beamforming system in millimeter-wave wireless personal area networks (WPAN), where transmit and receive weight vectors are jointly derived by exchanging a training sequence repeatedly with different combinations of transmit and receive weight vectors. We propose a low complexity codebook-based beamforming scheme that consists of multiple levels and level-adaptive antenna selection in order to reduce the beamforming setup time. For each level, 1) the transmit and receive antennas are selected according to pre-determined inter-element spacings, 2) the training sequences are sent with different weight vectors from a pre-defined codebook and 3) the receiver selects the best transmit and receive weight vectors in order to optimize an effective signal-to-noise ratio (SNR) and these vectors are used to determine the codebook for the next following level. Even with low complexity, we show from the numerical results that our proposed scheme can provide an effective SNR gain and an average spectral efficiency approaching those of the codebook-based beamforming with exhaustive search.