Analog Beamforming Network Research Articles

Development of a Front End Array for Broadband Phased Array Receiver

The receiver is a signal receiving device placed at the focus of the telescope. In order to improve the observation efficiency, the concept of phased array receiver has been proposed in recent years, which places a small phased array at the focal plane of the reflector, and flexible pattern and beam scanning functions can be achieved through a beamforming network. If combined with the element multiplexing, all beams within the entire field of view can be observed simultaneously to achieve continuous sky coverage. This article focuses on the front-end array of phased array receiver at 0.7–1.8 GHz for QiTai Telescope, and designs a Vivaldi antenna array of PCB structure with dual line polarization. Each polarization antenna is designed to arrange in a rectangle manner by 11 × 10. Based on the simulation results of the focal field, 32, 18, and eight elements were selected to form one beam at 0.7, 1.25, and 1.8 GHz. An analog beamforming network was constructed, and the measured gains of axial beam under uniform weighting were 19.32, 13.72, and 15.22 dBi. Combining the beam scanning method of reflector antenna, the pattern test of different position element sets required for PAF beam scanning was carried out under independent array. The pattern optimization at 1.25 GHz was carried out by weighting method of conjugate field matching. Compared with uniform weighting, the gain, sidelobe level, and main beam direction under conjugate field matching have been improved. Although the above test and simulation results are slightly different, which is related to the passive array and laboratory testing condition, the relevant work has accumulated experience in the development of the front-end array for the phased array receiver, and has good guiding significance for future performance verification after the array is installed on the telescope.

Performance analysis of insertion loss incorporated hybrid precoding for massive MIMO

<abstract> <p>Due to an increase in the number of users and a high demand for high data rates, researchers have resorted to boosting the capacity and spectral efficiency of the next-generation wireless communication. With a limited RF chain, hybrid analog digital precoding is an appealing alternative. The hybrid precoding approach divides the beamforming process into an analog beamforming network and a digital beamforming network of a reduced size. As a result, numerous hybrid beamforming networks have been proposed. The practical effects of signal processing in the RF domain, such as the additional power loss incurred by an analog beamforming network, were not taken into account. The effectiveness of hybrid precoding structures for massive MIMO systems was examined in this study. In particular, a viable hardware network realization with insertion loss was developed. Investigating the spectral and energy efficiency of two popular hybrid precoding structures, the fully connected structure, and the subconnected structure, it was found that in a massive MIMO, the subconnected structure always performed better than the fully connected structure. Characterizing the effect of quantized analog precoding, it was shown that the subconnected structure was able to achieve better performance with fewer feedback bits than the fully connected structure.</p> </abstract>

LoneSTAR: Analog Beamforming Codebooks for Full-Duplex Millimeter Wave Systems

This work develops LONESTAR, a novel enabler of full-duplex millimeter wave (mmWave) communication systems through the design of analog beamforming codebooks. LONESTAR codebooks deliver high beamforming gain and broad coverage while simultaneously reducing the self-interference coupled by transmit and receive beams at a full-duplex mmWave transceiver. Our design framework accomplishes this by tolerating some variability in transmit and receive beamforming gain to strategically shape beams that reject self-interference spatially while accounting for digitally-controlled analog beamforming networks and self-interference channel estimation error. By leveraging the coherence time of the self-interference channel, a mmWave system can use the same LONESTAR design over many time slots to serve several downlink-uplink user pairs in a full-duplex fashion without the need for additional self-interference cancellation. Compared to those using conventional codebooks, full-duplex mmWave systems employing LONESTAR codebooks can mitigate higher levels of self-interference, tolerate more cross-link interference, and demand lower SNRs in order to outperform half-duplex operation—all while supporting beam alignment. This makes LONESTAR a potential standalone solution for enabling simultaneous transmission and reception in mmWave systems, from which it derives its name.

A novel PAPR reduction method for hybrid beamforming transmitter

In orthogonal frequency division multiplexing (OFDM) systems, peak-to-average power ratio (PAPR) is one of the major factors that affect the power efficiency of transmitter. There exist many PAPR reduction methods for the conventional fully digital multiple-input multiple-output (MIMO) systems but there is little discussion on the PAPR reduction for the hybrid beamforming systems. When some output signals of the digital to analogue converter (DAC) are combined by the analogue beamforming network before power amplifier (PA), the one to one mapping between the digital signal and the signal passing through PAs is destroyed. In such hybrid beamforming architectures, the existing methods can only reduce the PAPR of DAC input signal but not PAPR of PA input signal. In this paper, we investigate whether and how we can extend existing PAPR reduction methods to the hybrid beamforming systems. We propose a novel PAPR reduction method, which extends the iteratively clipping and filtering (ICF) to the hybrid beamforming systems. To the best of our knowledge, our proposed algorithm is the first PAPR reduction algorithm dedicated for the hybrid beamforming systems. From the simulation, our proposed algorithm can achieve a smaller PAPR than the improved selective mapping (SLM) algorithm at the cost of minor signal distortion.

Robust Analog Beamforming for Periodic Broadcast V2V Communication

We generalize an existing low-cost analog signal processing concept that takes advantage of the periodicity of vehicle-to-vehicle broadcast service to the transmitter side. In particular, we propose to process multiple antennas using either an analog beamforming network (ABN) of phase shifters, or an antenna switching network (ASN) that periodically alternates between the available antennas, to transmit periodic messages to receivers that have an analog combining network (ACN) of phase shifters, which has been proposed in earlier work. To guarantee robustness, we aim to minimize the burst error probability for the worst receiving vehicular user, in a scenario of bad propagation condition that is modeled by a single dominant path between the communicating vehicles. In absence of any form of channel knowledge, we analytically derive the optimal parameters of both ABN and ASN. The ABN beamforming vector is found to be optimal for all users and not only for the worst receiving user. Further, we demonstrate that Alamouti scheme for the special case of two transmit antennas yields similar performance to ABN and ASN. At last, we show that the derived parameters of the two proposed transmission strategies are also optimal when hybrid ACN-maximal ratio combining is used at the receiver.

An Optimal Procedure for the Design of Discrete Constrained Lens Antennas with Minimized Optical Aberrations. Part II: Three-Dimensional Multifocal Architectures

Novel three-dimensional discrete lens antennas characterized by a number of focal points ranging from one to five and defined explicitly via analytical equations are presented in the paper. A procedure to derive rotationally symmetric afocal lenses starting from multifocal lenses that are not rotationally symmetric is proposed as well. In addition, an innovative method to identify the focal surface minimizing the optical aberrations is derived. The lenses are compared in terms of optical aberrations and accommodation constraints. The most suitable lens architectures depend mainly on the required angular field of view and magnification factor. It is shown that a reduction by a factor close to 3 in the optical aberrations can be obtained when selecting the most appropriate lens architecture and keeping comparable accommodation constraints. The results, derived exploiting a geometrical optics (GO) formulation, provide useful indications for the preliminary design of constrained lens antennas before adopting full wave rigorous techniques. Three-dimensional discrete lens antennas can offer significant advantages as compared to conventional analog beamforming networks (as those based on Butler matrixes) in terms of frequency bandwidth, number of beams and number of radiating elements.

Equivalent Orthogonal Beam Steering for Fast Determination of Reactions Between Two Phased Arrays of Antennas With Analog Beamforming Networks for Maximum Wireless Power Transfer

A practical methodology to maximize wireless power transfer (WPT) efficiency between two sets of antenna arrays phased by analog beamforming networks (BFNs) with digital phase shifters (DPSs) for excitation weightings is presented. The method is particularly useful to obtain the reaction matrix of transmission coefficients between transmitting antenna (TXA) and receiving antenna (RXA) elements in real WPT systems in operation. Afterward, the obtained reaction matrix can be further processed by the singular value decomposition (SVD) method to determine the required array excitation weightings for TXA and RXA arrays to achieve maximum WPT efficiency. The technique takes advantage of electronically beam steering functionality by a set of orthogonal weightings in phased arrays of antennas. The received signals during beam steering may be instantly processed to recover the reaction matrix as required at the time of system operation. The theoretic concepts are first summarized with full-wave simulation results shown to validate the feasibility of this concept.

A Fast Algorithm to Solve Delay Vandermonde Systems in Phased-Array Digital Receivers

Phased-array multibeam RF beamformers require calibration of receivers used in an array of elements before the signals can be applied to an analog beamforming network. This article presents a fast <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> (n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) algorithm for solving linear systems having a delay Vandermonde matrix (DVM) for the analog beamforming matrix. The structure of the DVM enables to obtain a fast algorithm to efficiently reverse multibeams at the DVM output such that calibration of the input low noise amplifiers can be achieved. The arithmetic complexity of the proposed DVM system solving algorithm is preferable over the standard matrix inversion consuming <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> (n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) operations. Numerical experiments are presented for forward accuracy of the proposed algorithm computed at the calibration frequency. Moreover, numerical results are shown to compare the order of the arithmetic complexity and the execution time of the proposed algorithm. Signal flow graphs are presented for four- and eight-element multibeam phased arrays.

Radio-frequency chain selection for energy and spectral efficiency maximization in hybrid beamforming under hardware imperfections

The next-generation wireless communications require reduced energy consumption, increased data rates and better signal coverage. The millimetre-wave frequency spectrum above 30 GHz can help fulfil the performance requirements of the next-generation mobile broadband systems. Multiple-input multiple-output technology can provide performance gains to help mitigate the increased path loss experienced at millimetre-wave frequencies compared with microwave bands. Emerging hybrid beamforming architectures can reduce the energy consumption and hardware complexity with the use of fewer radio-frequency (RF) chains. Energy efficiency is identified as a key fifth-generation metric and will have a major impact on the hybrid beamforming system design. In terms of transceiver power consumption, deactivating parts of the beamformer structure to reduce power typically leads to significant loss of spectral efficiency. Our aim is to achieve the highest energy efficiency for the millimetre-wave communications system while mitigating the resulting loss in spectral efficiency. To achieve this, we propose an optimal selection framework which activates specific RF chains that amplify the digitally beamformed signals with the analogue beamforming network. Practical precoding is considered by including the effects of user interference, noise and hardware impairments in the system modelling.

Fully-/Partially-Connected Hybrid Beamforming Architectures for mmWave MU-MIMO

Hybrid digital analog (HDA) beamforming has attracted considerable attention in practical implementation of millimeter wave (mmWave) multiuser multiple-input multiple-output (MU-MIMO) systems due to the low power consumption with respect to its fully digital baseband counterpart. The implementation cost, performance, and power efficiency of HDA beamforming depends on the level of connectivity and reconfigurability of the analog beamforming network. In this paper, we investigate the performance of two typical architectures that can be regarded as extreme cases, namely, the fully-connected (FC) and the one-stream-per-subarray (OSPS) architectures. In the FC architecture each RF antenna port is connected to all antenna elements of the array, while in the OSPS architecture the RF antenna ports are connected to disjoint subarrays. We jointly consider the initial beam acquisition and data communication phases, such that the latter takes place by using the beam direction information obtained by the former. We use the state-of-the-art beam alignment (BA) scheme previously proposed by the authors and consider a family of MU-MIMO precoding schemes well adapted to the beam information extracted from the BA phase. We also evaluate the power efficiency of the two HDA architectures taking into account the power dissipation at different hardware components as well as the power backoff under typical power amplifier constraints. Numerical results show that the two architectures achieve similar sum spectral efficiency, while the OSPS architecture is advantageous with respect to the FC case in terms of hardware complexity and power efficiency, at the sole cost of a slightly longer BA time-to-acquisition due to its reduced beam angle resolution.

A Noncoherent Massive MIMO System Employing Beamspace Techniques

Noncoherent detection schemes are an appealing and low-complexity alternative in multi-user massive MIMO uplink systems compared to classical coherent detection algorithms, since no actual channel knowledge is required at the receiver. For noncoherent multi-user detection to function, the induced power at the base station is utilized to separate the different users. However, spatial separation is impossible when the users are located in the far-field of the receiving antenna array. Consequently, noncoherent detection fails in such scenarios. To this end, beamspace techniques can be applied, focusing the energy of the incident wave to a smaller subset of the receive antennas and enabling again the noncoherent detection scheme. This paper analyzes the beamspace capabilities of a dielectric lens and an analog beamforming network applied at the receiver. Furthermore, a sub-array architecture is proposed, relaxing the design requirements for practical implementation. It is shown that noncoherent detection in combination with beamspace techniques performs comparably to channel-estimation-based detection. In addition, the sub-array architecture revealed a significant performance enhancement accompanied by a reduced user separability.

High-Efficiency and Wideband Aperiodic Array of Uniformly Excited Slotted Waveguide Antennas Designed Through Compressive Sensing

A uniformly excited slotted waveguide (WG) antenna array for point-to-point communication is presented. The European Telecommunications Standards Institute class-II sidelobe level requirements are satisfied in all planes at almost all frequencies by the aperiodic arrangement of several parallel ridge WGs in the E-plane, each with a different number of equally spaced radiating slots along the H-plane. Both the optimal separation and number of slots per WG are determined through a compressive sensing approach. This results in 160 slots organized in 16 columns offering 29 dBi peak gain at $Ka$ -band. A dedicated 16-way analog beamforming network is designed to provide the optimal nonuniform and in-phase excitation of the 16 WG channels, thereby compensating for the variable number of slots per column and the phase difference due to the E-plane aperiodicity. The measurements confirm the simulated reflection coefficient and radiation pattern characteristics, as well as the high aperture efficiency (70%–90%) over a 13.6% relative bandwidth (27.5–31.5 GHz) and <2 dB gain variation over 3.75 GHz (12.7%).

Learning and Data-Driven Beam Selection for mmWave Communications: An Angle of Arrival-Based Approach

This paper investigates how angle-of-arrival (AoA) information can be exploited by deep-/machine-learning approaches to perform beam selection in the uplink of a mmWave communication system. Specifically, we consider a hybrid beamforming setup comprising an analog beamforming (ABF) network with adjustable beamwidth followed by a zero-forcing baseband processing block. The goal is to select the optimal configuration for the ABF network based on the estimated AoAs of the various user equipments. To that aim, we consider 1) two supervised machine-learning approaches: k -nearest neighbors (kNN) and support vector classifiers (SVC); and 2) a feed-forward deep neural network: the multilayer perceptron. We conduct an extensive performance evaluation to investigate the impact of the quality of CSI estimates (AoAs and powers) obtained via the Capon or MUSIC methods, fluctuations in the received power, the size of the training dataset, the total number of analog beamformers in the codebook, their beamwidth, or the number of active users. The computer simulations reveal that performance, in terms of classification accuracy and sum-rate is very close to that achievable via exhaustive search.

Rotman Lens Based Hybrid Analog–Digital Beamforming in Massive MIMO Systems: Array Architectures, Beam Selection Algorithms and Experiments

Hybrid analog-digital beamforming is a well-known cost-efficient signal processing method for massive MIMO systems. In this paper, we propose a hybrid beamforming massive MIMO system based on Rotman lens analog beamforming with beam selection and digital beamforming. Rotman lens is a low-cost true-time-delay analog beamforming network supporting wide bandwidth signals, which is thus more attractive than the analog beamforming networks based on conventional high-cost phase shifters. To study our system based on Rotman lens, we first examine two potential array architectures, i.e., full-array and subarray architectures, concerning the RF design feasibility, insertion loss, and system scalability. Since the beam selection is required in our system, we propose two beam selection algorithms, i.e., greedy search-based method and branch- and bound-based method, aiming to optimize the hybrid beamforming system in terms of error-rate performance for both the full-array and subarray architectures. To validate our system in practice, the proposed system is also investigated and verified experimentally. In particular, we design and fabricate a sample of Rotman lens operating in the 5-GHz band, whose measured results agrees well with the computer simulation results. The measurement results are incorporated into the Monte-Carlo simulation with the proposed beam selection algorithms to study the error-rate performance. Our simulation results show that the hybrid beamforming system using the low-cost Rotman lens has performance comparable to that of the system using the high-cost phase shifters, and exhibits wideband capability and superior performance over the small-scale MIMO system under the same number of RF transceivers.

Dual Null Steering and Limited Beam Peak Steering Using Triple-Mode Circular Microstrip Patch Antenna

A compact triple-mode circular microstrip patch antenna capable of creating two nulls in the upper hemisphere and steering them independently is presented. The antenna consists of a central circular patch supporting TM11 mode, a TM21 mode shorted annular ring around it and another shorted annular ring supporting TM31 mode encompassing the other two radiators. Each mode is fed using two feed points to create right-handed circular polarization. Analytical and simulation studies show that by controlling the individual mode amplitude and phase ratios, radiation pattern can be reconfigured. Especially, two nulls can be generated in upper hemisphere and can be steered independently based on the ratio of applied excitation to each mode. This is a highly desirable feature for satellite receives antenna system with antijamming capability. To calculate the required modes excitation ratios, a MATLAB optimization code using a hybrid method of particle swarm optimization and pattern search was used. To apply the calculated excitation, an analog beamforming network consisting of digital variable gain attenuators, digital phase shifters, and low-noise amplifiers was used. This antenna was fabricated and tested for radiation patterns showing full hemispherical null steering along with limited beam peak steering.

Hybrid Analog–Digital Precoding Revisited Under Realistic RF Modeling

In this letter, we revisit hybrid analog–digital precoding systems with emphasis on the modeling of their radio-frequency (RF) losses, to realistically evaluate their benefits in 5G system implementations. We focus on fully-connected analog beamforming networks (FC-ABFNs) and on discrete Fourier transform implementations, and decompose these as a bank of commonly used RF components. We then model their losses based on their S-parameters. Our results reveal that the performance and energy efficiency of hybrid precoding systems are severely affected once these, commonly ignored, losses are considered in the overall design. In this context, we also show that hybrid precoder designs similar to Butler matrices are capable of providing better performances than FC-ABFN for systems with a large number of RF chains.