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Imperfect Channel State Information at the Transmitter (CSIT) is inevitable in modern wireless communication networks, and results in severe multi-user interference in multi-antenna Broadcast Channel (BC). While the capacity of multi-antenna (Gaussian) BC with perfect CSIT is known and achieved by Dirty Paper Coding (DPC), the capacity and the capacity-achieving strategy of multi-antenna BC with imperfect CSIT remain unknown. Conventional approaches therefore rely on applying communication strategies designed for perfect CSIT to the imperfect CSIT setting. In this work, we break this conventional routine and make two major contributions. First, we show that linearly precoded Rate-Splitting (RS), relying on the split of messages into common and private parts and linear precoding at the transmitter, and successive interference cancellation at the receivers, can achieve larger rate region than DPC in multi-antenna BC with partial CSIT. Second, we propose a novel scheme, denoted as Dirty Paper Coded Rate-Splitting (DPCRS), that relies on RS to split the user messages into common and private parts, and DPC to encode the private parts. We show that the rate region of DPCRS in Multiple-Input Single-Output (MISO) BC with partial CSIT is enlarged beyond that of conventional DPC and that of linearly precoded RS. Gaining benefits from the capability of RS to partially decode the interference and partially treat interference as noise, DPCRS is less sensitive to CSIT inaccuracies, networks loads and user deployments compared with DPC and other existing transmission strategies. [ABSTRACT FROM AUTHOR]

The feasibility of electrically conductive paper as a low-cost and eco-friendly alternative to copper is presented for application as an antenna conductor in UHF radio-frequency identification (RFID) systems. The conductivity of the paper is determined to be 50 S/m and the effect of such a low conductivity on the radiation performance of a half-wavelength dipole is investigated through simulation and experimental measurements. The radiation efficiency of a dipole cut from a 0.4 mm thick conductive paper sheet is measured to be 5.0%, which translates to an RFID tag read range of 22% of that obtained using copper. This performance is deemed unacceptable for most antenna applications. However, through simulation a conductivity of 500 S/m is identified as a reasonable target for the developers of conductive paper as the current distribution and terminal properties of the resulting antenna become similar to those observed when using copper. The radiation efficiency is projected at 56 % in this case, resulting in an RFID read range of 73% of that obtained using copper. [ABSTRACT FROM PUBLISHER]

A complete characterization of the inkjet printing process using metallic nanoparticle inks on a paper substrate for microwave frequencies up to 12.5 GHz as well as its application to low-cost, high gain and wideband antenna design are demonstrated in this work. Laser and heat sintering of metallic nanoparticles are compared on paper substrate for the first time which demonstrate immense cost and time benefits of laser sintering. The antennas fabricated using the characterized process include a Vivaldi for the UWB band which exhibits a significantly higher gain of up to 8 dBi as compared to the currently published inkjet printed antennas, and a novel slow-wave log periodic dipole array which employs a new miniaturization technique to show 20% width reduction. [ABSTRACT FROM PUBLISHER]

This paper deals with a low-cost method for the assembly of flexible substrate antennas and UHF RF identification silicon (Si) chips. Such a method exploits a magnetic coupling mechanism, thus not requiring for galvanic contacts between the Si chip and antenna itself. The magnetic coupling is established by a planar transformer, the primary and secondary windings of which are implemented on flexible substrate and Si chip, respectively. As a result, the Si chip can be assembled on the antenna with a mere placing and gluing process. First, the idea has been validated by theory. Electromagnetic simulations of a square heterogeneous transformer (1.0-mm side) show a maximum available power gain (MAG) of -0.4 dB at 868 MHz. In addition, the heterogeneous transformer is also quite tolerant with respect to misalignment between primary and secondary. An offset error of 150 \mu\ m reduces the MAG to -0.5 dB. A sub-optimal matching strategy, exploiting a simple on-chip capacitor, is then developed for antennas with 50-\Omega input impedances. Finally, the idea has been experimentally validated exploiting printed circuit board (PCB) prototypes. A PCB transformer (1.5-mm side) and a transformer rectifier (two-diode Dickson multiplier) have been fabricated and tested. Measurements indicates a MAG of -0.3 dB at 868 MHz for the transformer and the capability of the developed rectifier to supply a 220-\k\Omega load at 1.5 V with a -2-dBm input power. [ABSTRACT FROM AUTHOR]

This paper presents a wireless, self-powered, affinity-based biosensor based on the integration of paper-based microfluidics with our previously reported method for self-assembling radio-frequency (RF) antennas. At the core of the proposed approach is a silver-enhancement technique that grows portions of a RF antenna in regions where target antigens hybridize with target specific affinity probes. The hybridization regions are defined by a network of nitrocellulose based microfluidic channels which implement a self-powered approach to sample the reagent and control its flow and mixing. The integration substrate for the biosensor has been constructed using polyethylene and the patterning of the antenna on the substrate has been achieved using a low-cost ink-jet printing technique. The substrate has been integrated with passive radio-frequency identification (RFID) tags to demonstrate that the resulting sensor-tag can be used for continuous monitoring in a food supply-chain where direct measurement of analytes is typically considered to be impractical. We validate the proof-of-concept operation of the proposed sensor-tag using IgG as a model analyte and using a 915 MHz Ultra-high-frequency (UHF) RFID tagging technology. [ABSTRACT FROM PUBLISHER]

This paper presents the evolution of the publication of microstrip antenna papers in the IEEE Transactions on Antennas and Propagation. Both the number of papers and the topics of the papers are examined. To set the reference point and the general trends, the most relevant figures and statistics of all the papers published in the journal since 1970 are also analyzed. [ABSTRACT FROM AUTHOR]

This paper considers sparse device activity detection for cellular machine-type communications with non-orthogonal signatures using the approximate message passing algorithm. This paper compares two network architectures, massive multiple-input-multiple-output (MIMO) and cooperative MIMO, in terms of their effectiveness in overcoming inter-cell interference. In the massive MIMO architecture, each base station (BS) detects only the users from its own cell while treating inter-cell interference as noise. In the cooperative MIMO architecture, each BS detects the users from neighboring cells as well; the detection results are then forwarded in the form of a log-likelihood ratio (LLR) to a central unit where final decisions are made. This paper analytically characterizes the probabilities of false alarm and missed detection for both architectures. The numerical results validate the analytic characterization and show that as the number of antennas increases, a massive MIMO system effectively drives the detection error to zero, while as the cooperation size increases, the cooperative MIMO architecture mainly improves the cell-edge user performance. Moreover, this paper studies the effect of LLR quantization to account for the finite-capacity fronthaul. The numerical simulations of a practical scenario suggest that in specific case cooperating three BSs in a cooperative MIMO system achieves about the same cell-edge detection reliability as a non-cooperative massive MIMO system with four times the number of antennas per BS. [ABSTRACT FROM AUTHOR]

The integration of antennas into disposable paper drones using inkjet printing technology is presented. These drones or unmanned aerial vehicles (UAVs) are developed using origami folding structures. Two vertical monopole antennas based on the same design concept are proposed and their performance assessed for two different conditions. The conditions relate to the placement of the other electronic components and circuits on the origami drones as reported in the literature. The first is when the electromechanical components and corresponding metallic layers are located in the wings. In this case, the effect of the possible location of the antenna as well as the deformation of the wings on S11 is discussed. The second is a more general case scenario which includes when the components and motors are placed at the tail and lower part of the body of the drone. The antenna elements are directly printed onto a photo paper substrate using silver nanoparticle conductive ink. Subsequently, the substrate is folded to create a paper drone. Low-cost desktop inkjet printing equipment is used to deposit the metallic tracks of the antenna. The designs target the current frequency bands employed in the control and wireless communication of commercial drones (2.4 GHz and 5 GHz bands). The purpose of this work is to investigate potential antenna scenarios for disposable drones which may one day be fully fabricated using inkjet printing technology. All antenna designs and studies have been simulated using CST Microwave Studio and compared well with experimental results. [ABSTRACT FROM AUTHOR]

In this paper, we study the diversity-multiplexing-gain tradeoff (DMT) of wireless relay networks under the half-duplex constraint. It is often unclear what penalty if any, is imposed by the half-duplex constraint on the DMT of such networks. We study two classes of networks; the first class, called KPP(I) networks, is the class of networks with the relays organized in K parallel paths between the source and the destination. While we assume that there is no direct source-destination path, the K relaying paths can interfere with each other. The second class, termed as layered networks, is comprised of relays organized in layers, where links exist only between adjacent layers. [ABSTRACT FROM PUBLISHER]

This paper studies the effectiveness of relaying for interference mitigation in an interference-limited communication scenario. We are motivated by the observation that in a cellular network, a relay node placed at the cell edge observes a combination of intended signal and inter-cell interference that is correlated with the received signal at a nearby destination, so a relaying link can effectively allow the antennas at the relay and at the destination to be pooled together for both signal enhancement and interference mitigation. We model this scenario by a multiple-input multiple-output (MIMO) Gaussian relay channel with a digital relay-to-destination link of finite capacity, and with correlated noise across the relay and destination antennas. Assuming a compress-and-forward strategy with Gaussian input distribution and quantization noise, we propose a coordinate ascent algorithm for obtaining a stationary point of the non-convex joint optimization of the transmit and quantization covariance matrices. For fixed input distribution, the globally optimum quantization noise covariance matrix can be found in closed-form using a transformation for the relay’s observation that simultaneously diagonalizes two conditional covariance matrices by congruence. For fixed quantization, the globally optimum transmit covariance matrix can be found via convex optimization. This paper further shows that such an optimized achievable rate is within a constant additive gap of the MIMO relay channel capacity. The optimal structure of the quantization noise covariance enables a characterization of the slope of the achievable rate as a function of the relaying link capacity. Moreover, this paper shows that the improvement in spatial degrees of freedom by MIMO relaying in the presence of noise correlation is related to the aforementioned slope via a connection to the deterministic relay channel. [ABSTRACT FROM AUTHOR]

In this paper, we revisit the fundamental problem of computing MIMO capacity under per-antenna power constraint (PAPC). Unlike the sum power constraint counterpart which likely admits water-filling-like solutions, MIMO capacity with PAPC has been largely studied under the framework of generic convex optimization. The two main shortcomings of these approaches are 1) their complexity scales quickly with the problem size, which is not appealing for large-scale antenna systems and/or 2) their convergence properties are sensitive to the problem data. As a starting point, we first consider a single user MIMO scenario and propose two provably-convergent iterative algorithms to find its capacity, the first method based on fixed-point iteration and the other based on alternating optimization and minimax duality. In particular, the two proposed methods can leverage the water-filling algorithm in each iteration and converge faster, compared with current methods. We then extend the proposed solutions to multiuser MIMO systems with dirty paper coding-based transmission strategies. In this regard, capacity regions of Gaussian broadcast channels with PAPC are also computed using closed-form expressions. Numerical results are provided to demonstrate the outperformance of the proposed solutions over existing approaches. [ABSTRACT FROM AUTHOR]

In this paper, a quad-mode endfire planar phased antenna array with wide scan angle and 1.2 mm clearance is proposed for 5G mobile terminals. The proposed antenna can obtain over 8 GHz of impedance bandwidth. In this paper, it is suggested to efficiently combine a multimode array element with different radiation patterns for each mode into a phased antenna array. In the array, similar and wide embedded radiation patterns are obtained for the all four modes. Furthermore, a coaxial to differential stripline transition is designed in this paper. The differential feeding structure is very compact and utilizes only MMPX connector and vias. The total scan pattern and coverage efficiency of the measured and simulated phased array antenna are calculated in the range from 25 to 33 GHz, and good agreement between measured and simulated results is observed. The mean coverage efficiency along the frequency range is very similar, but minor difference in variance of coverage efficiency is observed in the measurements. The coverage efficiency of around 50% for the threshold gain of 5 dBi is achieved in the chosen frequency range. [ABSTRACT FROM AUTHOR]

RFID-based pose perception can enable industrial automation applications such as industrial robot grasping. In this paper, a RFID pose estimation method based on classification algorithm and phase-position transformation model for moving objects is proposed, which converts the traditional pose estimation problem into a machine learning classification problem by dividing the direction angle value domain of the object into several classes. The phase information of multiple RFID tags attached to the object is transformed into position information using an unwrapped phase-position model, on which the input features of the classifier is constructed. A classifier based on the LightGBM framework is constructed and trained to realize the mapping between RFID phase information and the object’s pose. Extensive experiments demonstrate that the proposed method in this paper can accurately estimate the pose of moving objects in real time and successfully complete the robot grasping task for objects on the conveyor belt. [ABSTRACT FROM AUTHOR]

In this paper, the B-scan technique is applied to a reverberation chamber (RC) for the first time to characterize the time-domain behavior of the chamber. Based on B-scan measurement results, three things are studied in this paper. 1) The statistical behavior of the fields in the time domain is investigated, and it is found that the received power of the impulse response follows chi-square distribution with one degree of freedom. 2) The stirrer efficiency is quantified based on the equivalent total scattering cross section (TSCS) of stirrers, and this definition is not sensitive to the antenna position and load in the RC. It is shown that the stirrer efficiency defined in this paper provides, for the first time, a quantitative way to evaluate the stirrer design and the chamber performance. 3) A time-gating technique is proposed which provides an alternative method to eliminate the early time response and obtain the chamber transfer function of the RC accurately. This could be potentially used to increase the stirrer efficiency without changing the stirrers physically. It is demonstrated that the B-scan technique is a very useful approach for the study and evaluation of an RC. [ABSTRACT FROM PUBLISHER]

In this paper, an antenna gain measurement method for millimeter-wave antennas in an on-wafer probe station environment is studied. The one-antenna gain measurement has been known since the 1940s. However, the authors believe that this extension of their previous work is the first time when the method is systematically studied in the on-wafer probe station environment. The main difference between the original one-antenna gain measurement and our method is that in the probe station environment, the space is limited and, therefore, the reflecting plate dimensions are limited. We have studied the effect of the reflector size limitation through computations using physical optics and through measurements with a standard gain horn (SGH) and with a printed microstrip patch antenna. The necessary size of the reflecting plate naturally depends on the beamwidth of the antenna under test and on the distance. Time gating has been applied in the retrieving calculation to filter out multiple reflections. According to this paper, the one-antenna gain measurement in the $W$ -band results in the correct antenna gain with very high accuracy for the highly directional SGH. For the patch antenna, the gain measured in the on-wafer probe station environment agrees well with the simulated one. [ABSTRACT FROM AUTHOR]

Intelligent fault detection is an important application of artificial intelligence and has been widely used in many mechanical systems. The shipborne antenna that is a typical and an important mechanical system plays an irreplaceable role in ships. Considering the tough working environment and heavy background noise, fault detection is difficult for the shipborne antenna. Therefore, the paper presents an intelligent fault detection method via multiscale inner product with locally connected feature extraction for shipborne antenna fault detection. Inspired by inner product principle, this paper takes advantage of inner product to capture fault information in the vibration signals and detect the faults in rolling bearing of the shipborne antenna. Meanwhile, multiscale analysis is employed in two layers of the network to improve the feature extraction ability. The local features under different scales are collected and used for fault classification. Finally, the proposed method is verified by three datasets and comparison methods are also developed to show its superiority. Results show that the proposed method can learn sensitive features directly from raw vibration signals and detect the faults in rolling bearing of shipborne antenna effectively. [ABSTRACT FROM AUTHOR]

This paper compares three modern and two classical multiobjective optimizers (MOOs) as applied to real-world problems in electromagnetics. The behavior of sophisticated optimizers on simple test functions has been studied exhaustively. In contrast, the algorithms here are tested on practical applications, where the function evaluations are computationally expensive, making the convergence rate a crucial factor. The examples considered include the optimization of a narrowband slot antenna, a mushroom-type electromagnetic bandgap structure, and an ultrawideband Vivaldi antenna. Another popular topic in the literature is in comparing classical MOOs on electromagnetics problems. The modern optimizers chosen in this paper are state of the art and each has a distinct design philosophy. This paper introduces two unique MOOs to the electromagnetics community: BORG, an auto-adaptive genetic algorithm and the Multi-Objective Covariance Matrix Adaptation Evolutionary Strategy (MO-CMA-ES), an extension of the popular single-objective CMA-ES. These algorithms are compared to the Multi-objective Evolutionary Algorithm based on Decomposition (MOEA/D), a Chebysheff scalarization algorithm, and two classical MOOs. This paper will study the behavior of these algorithms on problems in electromagnetics with a limited number of function evaluations using five distinct metrics and will provide useful guidelines and recommended optimizer settings. [ABSTRACT FROM AUTHOR]

The multi-user Holographic Multiple-Input and Multiple-Output Surface (MU-HMIMOS) paradigm, which is capable of realizing large continuous apertures with minimal power consumption, has been recently considered as an energy-efficient solution for future wireless networks, offering increased flexibility in impacting electromagnetic (EM) wave propagation according to the desired communication, localization, and sensing objectives. The tractable channel modeling in MU-HMIMOS wireless systems is one of the most critical research challenges, mainly due to the coupling effect induced by the excessively large number of closely spaced patch antennas. In this paper, we focus on this challenge for the downlink of multi-user MIMO communications and extend an EM-compliant channel model to multi-user case, which is expressed in the wavenumber domain using the Fourier plane wave approximation. Based on the presented channel model, we investigate the spectral efficiency of maximum-ratio transmission and Zero-Forcing (ZF) precoding schemes. We also introduce a novel hardware efficient ZF precoder, leveraging Neumann series (NS) expansion to replace the required matrix inversion operation, which is very hard to be computed in the conventional way due to the extremely large number of patch antennas in the envisioned MU-HMIMOS communication systems. In comparison with the conventional independent and identical Rayleigh fading channels that ignore antenna coupling effects, the proposed EM-compliant channel model captures the mutual couplings induced by the very small antenna spacing. Our extensive performance evaluation results demonstrate that our theoretical performance expressions approximate sufficiently well the simulated achievable spectral efficiency with the considered linear precoding schemes, even for the highly correlated cases, thus verifying the effectiveness and robustness of the presented analytical framework. In addition, it is verified that the proposed NS-based ZF precoder achieves similar performance to conventional ZF, while requiring lower hardware complexity, thus, providing a hardware efficient solution for practical design of MU-HMIMOS communications systems. [ABSTRACT FROM AUTHOR]

This paper considers the uplink performance of a multi-user massive multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system with mobile users. Mobility brings two major problems to a MIMO-OFDM system: inter carrier interference (ICI) and channel aging. In practice, it is common to allot multiple contiguous subcarriers to a user as well as schedule multiple users on each subcarrier. Motivated by this, we consider a general subcarrier allocation scheme and derive expressions for the ICI power, uplink signal to interference plus noise ratio and the achievable uplink sum-rate, taking into account the ICI and the multi-user interference due to channel aging. We show that the system incurs a near-constant ICI power that depends linearly on the ratio of the number of users per subcarrier to the number of subcarriers per user, nearly independently of how the UEs distribute their power across the subcarriers. Further, we exploit the coherence bandwidth of the channel to reduce the length of the pilot sequences required for uplink channel estimation. We consider both zero-forcing and maximal-ratio combining at the receiver and compare the respective sum-rate performances. In either case, the subcarrier allocation scheme considered in this paper leads to significantly higher sum-rates compared to previous work, owing to the near-constant ICI property as well as the reduced pilot overhead. [ABSTRACT FROM AUTHOR]

This two-part paper aims to quantify the cost of device activity detection in an uplink massive connectivity scenario with a large number of devices but device activities are sporadic. Part I of this paper shows that in an asymptotic massive multiple-input multiple-output (MIMO) regime, device activity detection can always be made perfect. Part II of this paper subsequently shows that despite the perfect device activity detection, there is nevertheless significant cost due to device detection in terms of overall achievable rate, because of the fact that nonorthogonal pilot sequences have to be used in order to accommodate the large number of potential devices, resulting in significantly larger channel estimation error as compared to conventional massive MIMO systems with orthogonal pilots. Specifically, this paper characterizes each active user's achievable rate using random matrix theory under either maximal-ratio combining (MRC) or minimum mean-squared error (MMSE) receive beamforming at the base station (BS), assuming the statistics of their estimated channels as derived in Part I. The characterization of user rate also allows the optimization of pilot sequences length. Moreover, in contrast to the conventional massive MIMO system, the MMSE beamforming is shown to achieve much higher rate than the MRC beamforming for the massive connectivity scenario under consideration. Finally, this paper illustrates the necessity of user scheduling for rate maximization when the number of active users is larger than the number of antennas at the BS. [ABSTRACT FROM AUTHOR]

In this paper, we consider routing in random wireless-ad hoc-networks, where each node is equipped with a single antenna. Our analysis uses a proper model of the physical layer together with an abstraction of higher communication layers. We assume that the nodes are distributed according to a Poisson-point-process and consider routing schemes that select the next relay based on the geographical locations, the channel gains of its neighbor nodes and the statistical characterization of all other nodes. While many routing problems are formulated as optimization problems, the optimal distributed solution is rarely accessible. In this paper, we present the exact optimal solution for the scenario analyzed. The optimal routing is given as a maximization of a routing metric, which depends solely on the known partial channel state information and includes an expectation with respect to the interference statistics. The optimal routing scheme is important because it gives an upper bound on the performance of any other routing scheme. We also present sub-optimal routing schemes that only use part of the available knowledge and require much lower computational complexity. Numerical results demonstrate that the performance of the low complexity schemes is close to optimal and outperforms other tested routing schemes. [ABSTRACT FROM PUBLISHER]

In this paper, we present a new and significant theoretical discovery. If the absolute height difference between base station (BS) antenna and user equipment (UE) antenna is larger than zero, then the network performance in terms of both the coverage probability and the area spectral efficiency will continuously decrease toward zero as the BS density increases in ultra-dense networks (UDNs). Such findings are completely different from the conclusions in the existing works, both quantitatively and qualitatively. In particular, this performance behavior has a tremendous impact on the deployment of the 5th-generation UDNs. Network operators may invest large amounts of money in deploying more network infrastructure only to obtain even less network capacity. This paper’s results reveal that one way to address this issue is to lower the BS antenna height to the UE antenna height. However, this requires a revolutionized approach of the BS architecture and deployment, which is also explored in this paper. [ABSTRACT FROM PUBLISHER]

This paper presents the Greene second-order parabolic equation (PE) solution to model radio propagation over irregular terrain. This solution is implemented by finite-difference and shift-map technique. The second-order finite-difference approach performs well for slopes up to about 15°, and discontinuous slope changes up to about 30°, which is better than can be achieved using the split-step/Fourier approach. The results prove that the Greene PE solution has greater propagation angles than does the Claerbout PE solution. Thus, the Greene second-order solution can certainly give better results for large angle propagation over complicated terrain boundaries. Besides, we treat the important problem of accuracy of the different approximations of the PE-based propagation models, and derive the general PE solutions with respect to the terrain slope for the different approximations. It is useful to have collected in one paper, the most important PE approximations for radio propagation. [ABSTRACT FROM AUTHOR]

This paper is concerned with obtaining closed-form exact solution for the 2-D canonical problem of the reflected field from a moving planar discontinuity of a dielectric–magnetic medium that is excited by an impulsive line current. The spectral theory of transient (STT) that originally deals with nondispersive frequency-domain plane-wave spectra is used in this paper for addressing a time-variant scattering problem. The scattering from a moving object yields dispersive and anisotropic PW spectra. Nevertheless, we demonstrate that the STT is capable of dealing with these types of spectra and obtain the desired exact time-dependent solutions. The unique wave phenomena that are associated with the medium and scatterer velocity are explored. [ABSTRACT FROM PUBLISHER]

This paper considers a massive random access problem in which a large number of sporadically active devices wish to communicate with a base station (BS) equipped with massive multiple-input multiple-output (MIMO) antennas. Each device is preassigned a unique signature sequence, and the BS identifies the active devices by detecting which sequences are transmitted. This device activity detection problem can be formulated as a maximum likelihood estimation (MLE) problem for which the sample covariance matrix of the received signal is a sufficient statistic. The goal of this paper is to characterize the feasible set of problem parameters under which this covariance based approach is able to successfully recover the device activities in the massive MIMO regime. Through an analysis of the asymptotic behaviors of MLE via its associated Fisher information matrix, this paper derives a necessary and sufficient condition on the Fisher information matrix to ensure a vanishing probability of detection error as the number of antennas goes to infinity, based on which a numerical phase transition analysis is obtained. This condition is also examined from a perspective of covariance matching, which relates the phase transition analysis to a recently derived scaling law. Further, we provide a characterization of the distribution of the estimation error in MLE, based on which the error probabilities in device activity detection can be accurately predicted. Finally, this paper studies a random access scheme with joint device activity and data detection and analyzes its performance in a similar way. [ABSTRACT FROM AUTHOR]

Presents corrections to conference information for the paper, ," (Bhattacharyya, S.),IEEE Antennas Propag. Mag., vol. 62, no. 5, pp. 13–15, Oct. 2020. doi: 10.1109/MAP.2020.3014528. [ABSTRACT FROM AUTHOR]

In this paper, we study the average throughput performance of energy beamforming in a multi-antenna wireless-powered communication network (WPCN). The considered network consists of one hybrid access point (AP) with multiple antennas and a single-antenna user. The user has no constant power supply and, thus, needs to harvest energy from the signals broadcast by the AP in the downlink (DL) before sending its data back to the AP with the harvested energy in the uplink (UL). We derive closed-form expressions of the average throughput and their asymptotic expressions at a high SNR for both delay-limited and delay-tolerant transmission modes. The optimal DL energy harvesting time, which maximizes the system throughput, is then obtained for high SNR. All analytical expressions are validated by numerical simulations. The impact of various parameters, such as the AP transmit power, the energy harvesting time, and the number of antennas, on the system throughput is also investigated. [ABSTRACT FROM AUTHOR]

This paper discusses a method to regularize linear problems in presence of incomplete and noisy data generated by partially or totally unknown sources. The idea is to identify the “simplest” solution, looking for the system having the minimum number of degrees of freedom (NDF) compatible with the available data. It is shown that a normalized version of the trace norm (known as 1-Schatten norm in functional analysis) is a good convex approximation of the NDF of the field. This allows to use the trace norm as a convex surrogate of the NDF in the minimization process, taking advantage of the recent literature on rank minimization. Examples regarding MIMO beamforming from incomplete channel matrix, field interpolation with no a priori information on the sources, and land-mine identification using the total field are discussed. [ABSTRACT FROM PUBLISHER]

This paper studies the ergodic rate performance of regularized zero-forcing (RZF) precoding in the downlink of a multi-user multiple-input single-output (MISO) system, where the channel between the base station (BS) and each user is modeled by the double scattering model. This non-Gaussian channel model is a function of both the antenna correlation and the structure of scattering in the propagation environment. This paper makes the preliminary contribution of deriving the minimum-mean-square-error (MMSE) channel estimate for this model. Then under the assumption that the users are divided into groups of common correlation matrices, this paper derives deterministic approximations of the signal-to-interference-plus-noise ratio (SINR) and the ergodic rate, which are almost surely tight in the limit that the number of BS antennas, the number of users, and the number of scatterers in each group grow infinitely large. The derived results are expressed in a closed-form for the special case of multi-keyhole channels. The simulation results confirm the close match provided by the asymptotic analysis for moderate system dimensions. We show that the maximum number of users that can be supported simultaneously, while realizing large-scale MIMO gains, is equal to the number of scatterers. [ABSTRACT FROM AUTHOR]

This paper deals with the efficient computation of scattering problems by fast oscillating periodic surfaces using two-scale expansion homogenization techniques. The proposed method splits the field between an effective field and a boundary layer corrector and applies an asymptotic expansion. Then, the evaluation of these boundary layers leads to the extraction of effective parameters, modeling the effects of the highly oscillating surface on the scattered field. A previous paper has already presented such a technique to deal with TM polarization. First, this paper extends the approach to TE polarization and completes it by pointing out all the key points. Especially it shows the map of the split fields underlining the physical contribution of each term. Second, this paper exposes and compares two different uses of these computed effective parameters. Numerical examples show the validity of the method, especially by justifying the asymptotic expansion ansatz. Computational efficiency is discussed. [ABSTRACT FROM AUTHOR]

This paper discusses the design and implementation of a biomimetic, flexible antenna system consisting of flexible dipoles on Pyralux AP. They are implemented into a novel, airborne atmospheric sensor system. The antennas and substrate serve a secondary function as a rotor system, forcing the sensor nodes to autorotate when falling to maximize drag and decrease their fall speed. The designed antenna system works both in the industrial, scientific, and medical band and the GPS L1 band with the designed antennas having bandwidths of 100 and 130 MHz, respectively. This paper also presents a test procedure to characterize the antenna performance at different bend angles. [ABSTRACT FROM AUTHOR]

Singular divergence-conforming bases have been proposed for the solution of integral equations although they have seen only occasional use in practical applications. The existing singular bases are not hierarchical, which prevents their use in adaptive $ {p}$ -refinement applications. In this paper, a new family of singular hierarchical basis functions is proposed for quadrilateral cells. These functions model the singularities associated with current and charge density at edges and are more convenient for modeling such singularities than triangular bases of the same kind. The basis functions are of the additive kind and combine a hierarchical polynomial representation on quadrilaterals with linearly independent singular terms that incorporate general exponents that may be adjusted for the specific wedge angle of interest. Moreover, the added singular basis functions are computed on the fly. On the basis of various reported numerical results, this paper also illustrates the difficulties, the advantages, the accuracy, and the cost of using such bases in the method of moment solutions of integral equations. [ABSTRACT FROM AUTHOR]

This paper presents a novel surface-wave (SW)-based high-impedance surface (HIS) multibeam antenna with 360° scanning capability in azimuth. The proposed antenna consists of four rotationally symmetric beamforming networks (BFNs) and a microstrip patch array-based HIS. Regarding to the BFN, it is formed by a planar offset parabolic reflector fed by multiple substrate integrated waveguides. Through proper design, the proposed BFN can efficiently launch guided SWs with TM0 mode. With the perturbation of the HIS structure, the bounded SWs can be transformed to $m=-1$ space harmonic mode leaky-wave radiation. Combining the feature of the leaky-wave radiation in the elevation plane and the manipulation of the propagation direction of the SWs by switching the feeding ports, beam scanning in the azimuth direction with a tilted elevation angle can be realized. As the HIS is shared by the four BFNs, the size of the antenna can be reduced and a broadened antenna scanning range is achieved. In this paper, a prototype of the proposed antenna with 28 feeding ports, 7 in each BFN, is numerically analyzed and experimentally demonstrated. The proposed antenna features low-cost, low-profile, and single layer configuration. [ABSTRACT FROM PUBLISHER]

The downlink performance of two-tier (macro/pico) multi-antenna cellular heterogeneous networks employing space division multiple access (SDMA) technique with zero-forcing precoding is analyzed in this paper. The number of users simultaneously served with SDMA by a base-station (BS) depends on the number of active users in its cell, with the maximum served users limited to L\text {max} . To protect the pico users from severe macro-interference, part of the antennas at each macro BS is proposed to be utilized toward interference nulling to pico users. The partitioning of macro antenna resources to serve macro-users and to null interference to pico users for optimal performance is investigated in this paper. Biased-nearest-distance-based user association scheme is proposed, where the bias value accounts for the natural bias due to the differences in multi-antenna transmission schemes across tiers, as well as the artificial bias for load balancing. The signal-to-interference-ratio coverage probability, rate distribution, and average rate of a typical user are then derived. Our results demonstrate that the proposed interference nulling scheme has strong potential for improving performance if the macro antennas partitioning is carefully done. The optimal L\text {max}^{*} for both macro and pico-tier, which maximize the average data rate, is also investigated and it is found to outperform both single-user beamforming and full-SDMA. Finally, the impact of imperfect channel state information due to limited feedback is analyzed. [ABSTRACT FROM PUBLISHER]

The use of unmanned aircraft systems (UAS) is expanding rapidly. For safe and reliable integration of UAS into the National Airspace System (NAS), control and nonpayload communication (CNPC) system requirements are being developed. The air-to-ground (AG) channel characteristics essentially determine CNPC link performance. The National Aeronautics and Space Administration (NASA) Glenn Research Center has sponsored a comprehensive AG channel measurement campaign in 2013 in both the L- and C-bands recently allocated for UAS. These measurements covered nearly all typical ground site (GS) local environments, including over water, hilly, mountainous, suburb, and near urban. As a continuation of results reported for the over-water scenarios, a description of the measurement campaign, measured results, and complete AG channel models for hilly and mountainous terrains are provided in this paper. The path loss is modeled by a modified log-distance path loss model with a correction for flight direction; path loss results are close to those of free space. A strong ground reflection was observed only for some small portions of some of the flight paths. The small-scale fading is well modeled by the Ricean distribution with a $K$-factor of 29.4 dB in the C-band and 12.8 dB in the L-band. The interband signals are uncorrelated. The spatial correlation for the two intraband channels with an aircraft antenna separation of 1.8 m is greater than 0.85. The C-band root-mean-square delay spread (RMS-DS) is 10 ns most of the time, with a maximum of 1 \mu\text{s} in hilly terrain and 180 ns in mountainous terrain. Tapped delay line (TDL) models accounting for the line of sight (LOS) and up to seven intermittent multipath components (MPCs) were developed, including the MPCs' probability of occurrence, relative power, phase, duration, and excess delay. [ABSTRACT FROM PUBLISHER]

In this paper, we present a scalable architecture in silicon that allows synthesis and dynamic waveform shaping of periodic mm-wave signals, either generated on-chip or quasi-optically through radiation in free space capable of producing pulse trains with picosecond time signatures. This is achieved through an architecture that allows extraction of multiple harmonics above f\mathrm {max} with simultaneous amplitude and phase control. Signal synthesis is achieved through controlled interference of multiple traveling waves with rich harmonic components and delays. The first example, presented in this paper, is where the signal synthesis is achieved on-chip demonstrating a pulse train at the output with a measured pulsewidth of 2.6 ps and a 0.46-mW output power. The second example is a four-element array with integrated antennas, which allows signal synthesis in space and is demonstrated to show reconfigurable radiation of pulse trains with a 2.6-ps pulsewidth, pure tones at a fundamental frequency of 107.5 GHz with an effective isotropic radiated power (EIRP) of 4.6 dBm and a second harmonic of 215 GHz with EIRP of 5.0 dBm, as well as any combination of these two harmonics with arbitrary amplitudes and delays. To the best of the authors’ knowledge, this paper demonstrates the sharpest on-chip and radiated pulses with dynamic waveform shaping in any integrated circuit technology. This can open the door to innovations in broadband terahertz imaging, sensing, and spectroscopy. [ABSTRACT FROM AUTHOR]

This paper analyzes the performance of the recently proposed quadrature spatial modulation (QSM) multiple-input–multiple-output (MIMO) system over Nakagami- $m$ fading channel. In the analysis, the general distribution of the Nakagami- m$ channel phase is considered. In the literature, performance analysis of spatial modulation (SM) over Nakagami- m$ channel with uniform phase is conducted. However, apart from the very special case of , where Nakagami- $m$ fading corresponds to Rayleigh fading, the phase of the Nakagami- $m$ distribution is not uniformly distributed. It is shown in this paper that the phase of the channel has major impact on the performance of spatial multiplexing MIMO systems such as SM and QSM systems. A general upper bound expression for the average bit error ratio (ABER) performance of QSM is derived, and the impact of different channel parameters is studied. Monte Carlo simulation results are provided to corroborate the exactness of the derived analysis. [ABSTRACT FROM PUBLISHER]

This paper presents a new theory for analyzing the leaky-wave (LW) mechanism supported by planar metasurfaces (MTSs) described by continuous, anisotropic, nonuniform, locally periodic boundary conditions (BCs), and excited by a vertical dipole at the interface. These BCs well represent a dense distribution of subwavelength metal patches of infinitesimal thickness, printed on a grounded slab. We denote succinctly this theoretical formulation as flat optics for LWs. This formulation is based on an adiabatic, asymptotic form of the Floquet theorem, introduced here for the first time. The adiabatic Floquet-wave analysis allows for: 1) describing the mechanism of global interaction between the cylindrical surface wave (SW) launched by the dipole and the modulated MTS; 2) introducing a generalized curvilinear-wavefront LW field that can be used for controlling the radiation-pattern shaping; 3) describing the local and global transfer of energy from SW to LW; 4) establishing an analytical relationship between the aperture field polarization and the anisotropic parameters of the MTS and 5) between the leakage parameter $\alpha $ and the MTS modulation index. Concerning the latter point, a closed-form formula for $\alpha $ is introduced, which allows for unprecedented control of the aperture field amplitude. The theoretical results are successfully validated by comparison with a full-wave analysis, showing impressive accuracy. In a companion paper published in this Journal issue, the present theory is used for the synthesis of a large class of planar aperture antennas. [ABSTRACT FROM AUTHOR]

There is an on-going need for faster, more accurate, and easier to implement threat identification systems for concealed electronics, to thwart terrorism and espionage attempts. Common electronics are used in the design of improvised explosive devices (IEDs), targeting military, and civilian populations, while concealed recording devices steal proprietary/confidential data, compromising both government and industrial resources. This paper discusses a novel, nonintrusive, repeatable, reliable, expandable, and simple-to-implement detection and identification (D&I) system for identifying threats by using unintended radiated emissions (URE). This paper differs from current URE proposals, by avoiding energy radiation. The proposed process also addresses big data problems involved in capturing and building databases of URE characteristics. Issue interpretation is utilized with URE data to distinguish between threat/nonthreat devices using multiple criteria decision analysis and other decision-making techniques to determine model and mode of hidden devices. System optimization, verified by testing, is used to improve the speed and accuracy of the identification algorithm. The system is developed with data from 130 devices and validated with 33 separate devices, which are representative of IED and espionage threats. Due to slow progress in the URE D&I field, the properties and potential of a more effective D&I system, compared to current methods, will be of interest to the explosive ordnance disposal, security services, electronic systems manufacturing, automated inventory, mobile application development communities, and potentially others as well. For a field that is not well documented, this paper provides a clear, concise, and detailed model for future research and applications of URE D&I. [ABSTRACT FROM AUTHOR]

The calibration of phase offsets between RF chains on commodity WiFi chips has been an key obstacle for many WiFi-based applications. In this paper, we conduct extensive experiments to explore the characteristics of the phase offsets. The real experimental results reveal that the phase offsets are actually deterministic. We explain such a phenomena via the circuit design of WiFi chips. We also show that the phase offsets are even the same among different chips. With extensive experiments, we obtain and report the measured phase offset values for the commodity Intel 5300 and Atheros AR9380 WiFi chips. With the observation illustrated in this paper, the calibration of the phase offsets can be simplified greatly. [ABSTRACT FROM AUTHOR]

In this paper, we focus on the downlink ergodic sum rate of a single-cell large-scale multiuser MIMO system in which the base station employs $N$ antennas to communicate with $K$ single-antenna user equipments (UEs). A regularized zero-forcing (RZF) scheme is used for precoding under the assumption that each UE uses a specific power and each link forms a spatially correlated MIMO Rician fading channel. The analysis is conducted assuming that $N$ and $K$ grow large with a given ratio and perfect channel state information is available at the base station. New results from random matrix theory and large system analysis are used to compute an asymptotic expression of the signal-to-interference-plus-noise ratio as a function of system parameters, spatial correlation matrix, and Rician factor. Numerical results are used to validate the accuracy of asymptotic approximations in the finite system regime and to evaluate the performance under different operating conditions. It turns out that the asymptotic expressions provide accurate approximations even for relatively small values of $N$ and $K$. [ABSTRACT FROM AUTHOR]

This paper investigates the achievable performance of cell-free massive multiple-input multiple-output (MIMO) systems with low resolution analog-to-digital converters (ADCs) at both the access points (APs) and users. A closed-form expression for the achievable rate is derived, which enables the study of the effects of AP number, antenna number per AP, user number, and ADC resolution on the achievable rate. In addition, a simple asymptotic approximation for the individual user rate is presented, which shows that the user rate is mainly constrained by the ADC resolution at the user. Moreover, we propose an ADC resolution bits allocation scheme aiming at maximizing the sum rate subject to the total ADC resolution bits constraint, which substantially outperforms the equal ADC resolution bits allocation scheme. Furthermore, a max–min power control scheme is proposed, which not only ensures user fairness, but also improves the achievable rate. Finally, simulation results are provided to corroborate the analytical results. [ABSTRACT FROM AUTHOR]

The problem of multiple-input multiple-output (MIMO) channel estimation at millimeter-wave frequencies, both in single-user setting and in multi-user setting, is tackled in this paper. Using a subspace approach, we develop a protocol enabling the estimation of the right (respectively, left) singular vectors at the transmitter (respectively, receiver) side; then, we adapt the projection approximation subspace tracking with deflation and the orthogonal Oja algorithms to our framework and obtain two-channel estimation algorithms. We also present an alternative algorithm based on the least squares approach. The hybrid analog/digital nature of the beamformer is also explicitly taken into account at the algorithm design stage. In order to limit the system complexity, a fixed analog beamformer is used at both sides of the communication links. The obtained numerical results, showing the accuracy in the estimation of the channel matrix dominant singular vectors, the system achievable spectral efficiency, and the system bit error rate, prove that the proposed algorithms are effective and that they compare favorably, in terms of the performance-complexity tradeoff, with respect to several competing alternatives. [ABSTRACT FROM AUTHOR]

The thirteen papers in this special section focus on antenna considerations for future millimeter-wave and terahertz wireless sytems. Recent developments in data-intensive applications and emergence of Internet-of-Things (IoT) have exponentially increased the wireless data traffic. IoT also requires fusion of multiple sensors and wireless devices operating in real time. These papers present state-of-the-art research on a wide range of antenna technologies, analysis techniques, and application scenarios in millimeter-wave and terahertz regimes. The 13 letters of this cluster are categorized in five groups based on the type of the antenna/broader focus. [ABSTRACT FROM AUTHOR]

Multiple signal classification (MUSIC) has been widely applied in multiple-input multiple-output (MIMO) receivers for direction-of-arrival (DOA) estimation. To reduce the cost of radio frequency (RF) chains at millimeter-wave bands, hybrid analog-digital structure has been adopted in massive MIMO transceivers. In this situation, received signals at the antennas are unavailable to the digital receiver, and as a consequence, the spatial covariance matrix (SCM), which is essential in MUSIC algorithm, cannot be obtained using traditional sample average approach. Based on our previous work, we propose a novel algorithm for SCM reconstruction in hybrid massive MIMO systems with multiple RF chains in this paper. By switching the analog beamformers to a group of predetermined DOAs, SCM can be reconstructed through the solutions of a set of linear equations. Furthermore, a low-complexity algorithm, as well as a careful selection of the predetermined DOAs, will be also presented in this paper. Simulation results show that the proposed algorithms can reconstruct the SCM accurately so that MUSIC algorithm can be well used in hybrid massive MIMO systems with multiple RF chains. [ABSTRACT FROM AUTHOR]

This paper describes a multifunctional microwave device that can be reconfigured to behave either as a filter or an antenna. The device is based around a single-resonant element, referred to as a building block element that is connected to four ports. The resonant element is a microstrip square patch working in the 2.45 GHz unlicensed Industrial Scientific and Medical band used for IEEE 802.11 WiFi. The proposed building block is simple in its design and construction. This paper also presents devices composed of three building blocks, which can realize more complex filtering and antenna mode performance. In addition, p-i-n diodes have also been incorporated into the devices in order to facilitate electronic control. Measured results, pertaining to fabricated prototypes, show that filter and antenna operation can be achieved in the same device at a frequency of around 2.45 GHz with acceptable insertion loss and efficiency. In the future, it is anticipated that this could lead to a new paradigm, namely, a device that is analogous to a field programmable gate array operating in the microwave frequency regime. [ABSTRACT FROM AUTHOR]

The use of low-resolution digital-to-analog converters (DACs) for transmit precoding provides crucial energy efficiency advantage for massive multiple-input multiple-output (MIMO) implementation. This paper formulates a quadrature amplitude modulation (QAM) constellation range and a one-bit symbol-level precoding design problem for minimizing the average symbol error rate (SER) in downlink massive MIMO transmission. A tight upper bound for the SER with low-resolution DAC precoding is first derived. The derived expression suggests that the performance degradation of one-bit precoding can be interpreted as a decrease in the effective minimum distance of the QAM constellation. Using the obtained SER expression, we propose a QAM constellation range design for the single-user case. It is shown that in the massive MIMO limit, a reasonable choice for constellation range with one-bit precoding is that of the infinite-resolution precoding with per-symbol power constraint, but reduced by a factor of $\sqrt{2/\pi }$ or about 0.8. The corresponding minimum distance reduction translates to about a 2 dB gap between the performance of one-bit precoding and infinite-resolution precoding. This paper further proposes a low-complexity heuristic algorithm for the one-bit precoder design. Finally, the proposed QAM constellation range and precoder design are generalized to the multiuser downlink. We propose to scale the constellation range for the infinite-resolution zero-forcing (ZF) precoding with per-symbol power constraint by the same factor of $\sqrt{2/\pi }$ for one-bit precoding. The proposed one-bit precoding scheme is shown to be within 2 dB of infinite-resolution ZF. In term of number of antennas, one-bit precoding requires about 50% more antennas to achieve the same performance as infinite-resolution precoding. [ABSTRACT FROM AUTHOR]

The reflectometry diagnostic for demonstration fusion reactor (DEMO) is envisaged to provide the electron density profile and to be used as a control diagnostic for the real-time vertical position controller. An initial conceptual study has been performed defining the position of the antennas and the routing of the waveguides. In the present design, the integration has been driven by the remote handling and blanket interfaces. To progress with the system integration, neutronics simulations were performed to assess the cooling requirements. This paper presents a nuclear and thermal analysis for the initial design of the reflectometry diagnostic for DEMO. The neutronics simulations were performed using the Monte Carlo simulation program MCNP6 and FENDL 2.1 cross sections, while ANSYS mechanical v18 was used to perform the thermal analysis. Simulation results show that the nuclear heat loads reach 8 W/cm3 at the surface of the diagnostics section. Without an active cooling system, the operating temperatures of the components under such heat loads would be well above the acceptable from the thermomechanical point of view. The thermal analysis here presented provides the temperature distribution in the components when subjected to neutron/gamma irradiation and thermal radiation from the plasma, after the implementation of a preliminary design of the active cooling system. The operation temperatures of the plasma-facing antennas, as well as the performance of the diagnostics system from the neutron shielding point of view, are analyzed and discussed in this paper. [ABSTRACT FROM AUTHOR]

In this paper, we consider a full-duplex (FD) and amplify-and-forward (AF) relay with multiple antennas, where hardware impairments of the FD relay are taken into account. Due to the inter-dependence of the transmit relay power and the residual self-interference in an FD-AF relay, we observe a distortion loop that degrades the system performance when relay dynamic range is not high. In this paper, we analyze the relay function, and an optimization problem is formulated to maximize the signal to distortion-plus-noise ratio under relay and source transmit power constraints. Due to the problem complexity, we propose a gradient-projection-based (GP) algorithm to obtain an optimal solution. Moreover, a non-alternating sub-optimal solution is proposed by assuming a rank-1 relay amplification matrix, and separating the design of the relay process into multiple stages (MuStR1). The proposed MuStR1 method is then enhanced by introducing an alternating update over the optimization variables, denoted as AltMuStR1 algorithm. Numerical simulations show that compared to GP, the proposed (Alt)MuStR1 algorithms significantly reduce the required computational complexity at the expense of a slight performance degradation. Moreover, as the hardware impairments increase, or for a system with a high transmit power, the impact of applying a distortion-aware design is significant. [ABSTRACT FROM PUBLISHER]

In this paper, we present modeling of very low frequency (3–30 kHz) through-the-Earth (TTE) radio transmissions in four multistory buildings using the finite-difference time-domain method. These structures are generally made of reinforced concrete, whose steel content is the most important control on bulk conductivity. The floors and walls are represented as sheets of a given conductance, based on the fact that electromagnetic geophysical methods will only resolve conductive sheets in terms of their conductance as opposed to both conductivity and thickness. We validate this approach first using synthetic data and second by comparison with field data. Conductance models were derived from observed data for a variety of propagation environments, including reinforced concrete, steel floors, and basements, and for transmission into, out of, or within a building. The models were able to account for nonintuitive observations, such as increase in signal strength near the edges of buildings and in localized areas in between buildings. Conductances obtained for the floors and walls could be used as representative values in future forward modeling to assess the viability or optimize a TTE radio link in a multistory building. [ABSTRACT FROM PUBLISHER]