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Antenna selection (AS) and intelligent reflecting surface (IRS) are two promising technologies to reduce the hardware cost of multi-antenna systems. This letter intends to jointly design the users’ active transmit beamformers, the IRS’s passive beamformer, and the base station’s receive AS network in order to maximize the uplink sum rate of an IRS-aided multiuser multiple-input multiple-output (MU-MIMO) system. An efficient algorithm is proposed to solve the resultant non-convex problem via capitalizing on the block coordinate descent and fractional programming techniques. Numerical results show that compared with other baseline methods, the proposed algorithm can significantly improve the uplink sum rate. [ABSTRACT FROM AUTHOR]

Existing cellular network is designed mainly for terrestrial users (TUs) with down-tilted antennas, which couldn’t provide efficient 3D coverage for UAV users. This letter proposes up-tilted antenna model to provide 3D seamless coverage for cellular-connected UAVs, and derives coverage probability for both aerial users (AUs) and TUs via stochastic geometry, where the mutual interference between up-tilted and down-tilted antennas is characterized. Specifically, practical antenna model with tunable half power beamwidth $\theta _{k}$ is adopted and power constraint between up-tilted and down-tilted antenna is considered by modelling power allocation parameter $\alpha $ , where the interference Laplace transform is rederived considering the mutual interference. In addition, the theoretical analysis is based on semi-closed expression of coverage probability, which can be used to explore the impact of various system parameters. Numerical results show that when 10% of the power is allocated to up-tilted antenna ($\alpha =0.9$), coverage probability of AUs can be significantly increased by 192%, while coverage probability of TUs reduced by less than 1%, compared with only down-tilted antenna. [ABSTRACT FROM AUTHOR]

The direct wave between the transceiver antenna negatively affects the dynamic range and imaging quality of ground penetrating radar (GPR). Suppressing this direct wave is a vital problem in enhancing the performance of the whole GPR system. In this paper, a Minkowski-fractal metamaterial absorber (MMA) with the resistive film is proposed in the GPR transceiver antenna to reduce the mutual coupling. The simulated and measured results indicate that this MMA has an effective wideband absorption in 1.0-8.0 GHz. And the thickness of MMA is only 0.007 λ 0 (with respect to 2.0 GHz). This wideband MMA can reduce the mutual coupling of the proposed GPR transceiver antenna by an average of 10 dB. And it also mitigates the time-domain ringing problem of the transmit antenna. Real-world experiments demonstrate that the direct wave from the transmitting antenna can be reduced and the target echo arriving at the receiving antenna can be increased if this MMA is placed in the proposed transceiver antenna. This resistive film-based MMA offers great promise in realizing low-cost, compact, and lightweight GPR antennas, which can also be extended to high-frequency microwave imaging. [ABSTRACT FROM AUTHOR]

In recent years, the continuous increase in wireless data services and users' traffic demand has been imposing great challenges on traditional multiple access control (MAC) methods. Some existing MAC techniques improve the communication system's spectral efficiency (SE) via signal processing based cochannel interference (CCI) management. However, no interference management (IM) is free, i.e., its realization is based on the consumption of some communication resources, such as power and degree-of-freedom (DoF), which can also be used for the user's desired data transmission. To lessen the resource cost for IM-based MAC, we exploit interactions among multiple wireless signals to propose a new MAC method, namely, Differentiated Reception Modes based Multiple Access (DRM-MA), in this paper. Under DRM-MA, a central control unit (CCU) is adopted to manage and pair multiple transmitting antennas with their serving receivers (Rxs). The CCU first calculates the phase difference of signals sent from each candidate antenna and perceived by the two receiving antennas of an Rx based on the locations of the transmitting antenna and Rx. Then, the CCU selects and pairs a proper transmitting antenna with each Rx, so that various Rxs can adopt either additive or subtractive reception mode to postprocess the signals received by its two antennas to realize in-phase desired signal construction and inverse-phase interference destruction. DRM-MA can avoid transmission performance loss incurred by signal processing-based IM. Our theoretical analysis and simulation results have shown that DRM-MA can enable concurrent data transmissions of multiple antenna-receiver pairs and output a high system's SE. [ABSTRACT FROM AUTHOR]

In order to improve the stability and control effect of the electromechanical control system, this paper designs the electromechanical control system combined with the computer fault-tolerant technology and proposes an electromechanical control signal processing algorithm. In order to improve the accuracy of the path loss calculation, according to Fresnel's law, this paper deduces the expression of the reflection coefficient of electromechanical control signal with the distance between the transmitting antenna and the receiving antenna as the main variable and then compares the path loss with the ground and the ceiling as the reflecting surface. In addition, in order to study the path loss, this paper selects different reflective materials to study their path loss under horizontal polarization and vertical polarization. The results show that under the vertical polarization, the path loss fluctuation is not large, and the agreement is higher than that of the horizontal polarization. The research results show that the electromechanical control system based on computer fault-tolerance technology proposed in this paper has stable performance and can play an important role in the control of electromechanical systems. [ABSTRACT FROM AUTHOR]

A new far-field valid angle equation for rectilinear planar near-field measurements is derived. The new valid angle equation is derived by viewing the near-field to far-field transformation process as the generation of a pseudo plane wave by a synthetic phased array and subjecting the antenna-under-test (AUT) to the radiation from this synthetic array. The synthetic phased array does not physically exist; rather, the array is formed during the postprocessing of the planar near-field measurements. The resultant valid far-field angle computed with the new equation is compared against previously established and popularly accepted valid angle equations. A brief discussion is offered on the measurement of low-directivity antennas with a planar near-field measurement system and on amplitude tapering of the near-field measurements to improve the quality of the pseudo plane wave inside the test zone. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate an approach for local reduction of the electric field amplitude of the transmitted radio-frequency signal in ultrahigh-field magnetic resonance imaging (MRI). We excite a suitable combination of three coupled dipole hybrid resonances composing a single transmit antenna array element. Using numerical optimization, we designed a feeding network for three coupled dipoles placed over an electromagnetic phantom mimicking a human body. This network of discrete elements provides the appropriate amplitudes and phases of three dipole currents excited by a single input port. It allows controlling the electric field distribution in the vicinity of the antenna. Our goal was to obtain a minimum of the electric field at the given relatively small depth inside the phantom, where body implants are typically located while keeping a tolerable level of the magnetic field toward the phantom’s center. We designed and manufactured a three-dipole antenna prototype optimized for MRI of the human body at 7 T (proton Larmor frequency of 298 MHz). The experimental validation showed a 40 dB reduction of the electric field amplitude at a depth of 4 cm compared to a conventional single-dipole antenna. The coupling network can be rearranged to target different depths. Therefore, a principle of electric field minimization at a controllable position inside the body has been shown, which may be useful for designing transmit MRI antennas with improved safety of implants. [ABSTRACT FROM AUTHOR]

In this article, a capacity-oriented envelope correlation coefficient (ECC) that incorporates a preferred channel model for assessing a multiple antenna system of a multiple-input-multiple-output (MIMO) mobile device is proposed. Originated from the rudimentary law of ergodic channel capacity, the ECC for multiple antennas (ECC-M) is proven to holistically reflect the impact of radiation patterns and total efficiencies of multiple antennas on channel capacity. The closed-form ECC-M expressions for Rayleigh fading channel model and ray-based spatial channel model are studied, leading to an easy-to-use ECC-M expression that approximately incorporates a realistic channel model. The correlation of the proposed ECC-M to the channel capacity is demonstrated through the Monte Carlo (MC) simulation of three four-element MIMO antenna testbeds in two channel models, showing that the antenna total efficiency and a realistic channel model involved in the ECC-M play an important role in assessing the performance of multiple antennas. It is justified that the difference in channel capacities of two multiple antenna systems is highly relevant to their ECC-Ms at high signal-to-noise ratios (SNRs). The proposed ECC-M is also experimentally validated through over-the-air (OTA) throughput measurement, revealing that the ECC-M can effectively assess the OTA performance of multiple antenna systems for MIMO terminal devices. [ABSTRACT FROM AUTHOR]

This article introduces a transmitarray antenna presenting excellent filtering and dual-polarization properties. Conventional transmitarrays resort to multilayered frequency-selective surfaces (FSSs) for filtering responses. In contrast, we propose a planar dual-polarized filtering antenna as an illumination source to enable a filtering transmitarray. The V-band dual-polarized filtering antenna is excited by a substrate integrated waveguide (SIW) feeding structure. By a novel trisection feed and a well-design radiating element, up to four radiation nulls are produced, leading to an excellent filtering response validated with experimental results. Subsequently, the antenna is employed to illuminate a phase-shifting surface (PSS), achieving outstanding filtering response, stable dual-polarization characteristics, low profile, and ease of integration. The proposed antenna and transmitarray demonstrate significant potential in V-band millimeter-wave (mmW) applications. [ABSTRACT FROM AUTHOR]

This article presents an optimized multicoil array transceiver antenna design to localize the position of a human hand for a touchless artificial human interface. The functioning of the system is evolved from combined principles of a two-coil and three-coil magnetic resonance coupling-based wireless power transfer techniques. The proposed system comprises a transceiver antenna platform made of spatially distributed multicoil arrays as transmitter and receiver antennas, and a resonator coil. The resonator coil attached to the fingertip of the user is localized by comparing the voltage gains of the receiver antenna array working as sensors with the decision thresholds. Therefore, the coil arrays of the transceiver platform and the resonator coil are jointly optimized to enhance the localization accuracy by maximizing the separation of receiver antenna readings from the decision thresholds. The fabricated prototype of the optimized antenna system is measured, and performance is analyzed for various movements of the user fingertip. The results reveal the decision threshold limits of the design for localization and prove that the proposed transceiver antenna system is able to track the human hand movement successfully. Unlike other vision and sensor-based interfacing, the proposed transceiver antenna system provides a cost-effective, user-friendly, and hygienic solution. [ABSTRACT FROM AUTHOR]

Mechanical antennas have garnered interest as a potential method of transmitting extremely low-frequency (ELF) to very-low-frequency (VLF) radiation in a manner that possesses a high efficiency of radiation and a low form factor. In this article, we investigate these claims by solving for the exact field solutions for one particular example, a rotational-oscillating charged thin spherical shell. The field solutions allow the analysis of the radiation pattern, radiation efficiency, and spectral output as a function of several geometric and kinematic quantities of the sphere. The results indicate that high efficiency with a low form-factor appears to be plausible, assuming that the required mechanical conditions for the motion can be achieved. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surfaces (RISs) have attracted major attention in the last few years, due to their useful characteristics. An RIS is a nearly passive thin surface that can dynamically change the reradiated field and can therefore realize anomalous reflection, refraction, focalization, or other wave transformations for engineering the radio propagation environment or realizing novel surface-type antennas. Evaluating the performance and optimizing the deployment of RISs in wireless networks need physically consistent frameworks that account for the electromagnetic characteristics of dynamic metasurfaces. In this article, we introduce a general macroscopic model for evaluating the scattering from an RIS. The proposed method decomposes the wave reradiated from an RIS into multiple scattering contributions and is aimed at being embedded into ray-based models. Since state-of-the-art ray-based models can already efficiently simulate specular wave reflection, diffraction, and diffuse scattering but not anomalous reradiation, we enhance them with an approach based on Huygens’ principle and propose two possible implementations for it. Multiple reradiation modes can be modeled through the proposed approach using the power conservation principle. We validate the accuracy of the proposed model by benchmarking it against several case studies available in the literature, which are based on analytical models, full-wave simulations, and measurements. [ABSTRACT FROM AUTHOR]

The gyromagnetic nonlinear transmission line (GNLTL) is a special kind of coaxial transmission line partially loaded with the ferrite material. A GNLTL system can modulate the input high-power pulses into wideband high-power microwaves without relying on the electron beam and confining magnetic field. The unique working mechanism gives the GNLTL system the potential to be a small portable wideband high-power microwave radiation source. In this study, a wideband high-power microwave radiation source based on a GNLTL system is designed and constructed. In order to effectively radiate the wideband microwaves into the air, a high-power wideband Vlasov antenna and a special absorption high-pass filter are developed. The designs of key subsystems and high-power radiation experiments have been introduced and discussed in detail. In the test experiments, a radiated pulse with a peak electric field strength of 23 kV/m was measured at 20 m away from the transmitting antenna and the effective potential of radiation is 460 kV/m. The pulse width of the radiation pulse is about 4 ns, the center frequency is about 2.25 GHz, and the highest repetition rate can reach 25 Hz. [ABSTRACT FROM AUTHOR]

In this article, we will show how to improve the standard procedure in the Annex G of IEC 61000-4-21 on the shielding effectiveness (SE) of materials and gaskets through measurements performed in reverberation chambers. We thoroughly analyze and discuss measurement models (MMs), which are already present in the literature including the standardized model. Moreover, we further derive one of these MMs in a different way and introduce a different application, which is suitable to measure high SE values. We apply such MMs and compare results. By the analysis, discussion, and comparisons of measurement results, we clearly provide a robust improvement to the standard measurement procedure. [ABSTRACT FROM AUTHOR]

Unmanned aerial vehicle (UAV), when illuminated by high-power microwave (HPM), is vulnerable to losing control and even falling to the ground with damage. To explore the mechanism of the UAV's falling and its damage caused by HPM, the HPM radiation experiments on a certain kind of UAV are carried out. It is concluded that the UAV's cable is the main energy coupling path from HPM according to the analysis of the cable connection relationships among the flight control system (FCS), the electronic speed control (ESC) board, and the motors based on the experiment. Furthermore, the coupled voltages of the cable's termination load are obtained when the UAV is radiated by HPM with different carrier frequencies or incident directions using numerical calculation and typical test verification. To facilitate the analysis of circuit level, the equivalence of radiation and injection test is analyzed, so the waveform of the control signal related to the UAV's flight is recorded by the injection test. According to the experimental results and the principle of the UAV's flight dynamics, the effect mechanisms of the UAV's falling and its damage are clarified. The experimental results show that the carrier frequency of the HPM leading to the falling and damage of the UAV mainly depends on the length of the internal cable inside the UAV. The pulsewidth and the repetition frequency of HPM resulting in the UAV's falling are related to the pulsewidth and the period of the control signal of FCS. In addition, the coupled voltages induced on the twisted three-wire cables due to the illumination of HPM are verified to enter into the control signal port through parasitic capacitance and, finally, to damage the vulnerable components, including the metal–oxide–semiconductor field-effect transistor inside the ESC and the motor of the UAV. The damage mechanism is determined to be the high-voltage breakdown and large current burning. [ABSTRACT FROM AUTHOR]

Full-duplex (FD) relay systems including a transmit antenna selection and a non-orthogonal multiple access (NOMA) methods are analyzed under presence of multiple eavesdroppers. A channel state information of both the considered system and eavesdroppers is assumed to be outdated and eavesdroppers eavesdrop information signals independently. A closed-form of secure outage probability (SOP), secrecy throughput of every user is derived to evaluate the secrecy performance, and the mathematical analysis approach is verified by the Monte-Carlo simulation. Furthermore, the Golden-Section Search algorithm is proposed to find the maximum of the secrecy throughput of the considered FD-NOMA system. Numerical results indicate that there exists the SOP floor in the considered system and it is constrained by the channel gain of near user. Moreover, there is the optimal signal to interference plus noise ratio value which minimizes the SOP of the system regardless of the number of eavesdroppers. In comparison with half-duplex NOMA model, the SOP of FD-NOMA model is better. [ABSTRACT FROM AUTHOR]

With innovative applications of unmanned aerial vehicle (UAV) ad hoc networks in various areas, their demands on broad bandwidth, large capacity and low latency become prominent. The combination of millimeter wave, directional antenna and time division multiple access techniques, which enables concurrent transmissions, is promising to deal with it. In this paper, we study the resource allocation problem in UAV ad hoc networks. Specifically, the slot assignment, antenna boresight and transmit power are jointly optimized to promote the network capacity. First, we formulate the optimization problem as the maximization of the fairness-weighted network capacity, subject to the constraint on priority guarantee. Then, because the formulated problem is a mixed integer non-linear programming problem (MINLP), which is NP-hard, two algorithms called dual-based iterative search algorithm (DISA) and sequential exhausted allocation algorithm (SEAA) are respectively proposed to efficiently solve it with acceptable complexity. DISA slacks the MINLP into a continuous-variable optimization problem and solves it with the Lagrangian dual method in an iterative manner. As a heuristic method, SEAA schedules links sequentially, i.e., from high-priority to low-priority ones. Numerical results demonstrate that both DISA and SEAA can efficiently allocate resources for UAVs, while guaranteeing the fairness and priority of links. [ABSTRACT FROM AUTHOR]

Spectral efficiency improvement is a key focus in most wireless communication systems and achieved by various means such as using large antenna arrays and/or advanced modulation schemes and signal formats. This work proposes to further improve spectral efficiency through combining non-orthogonal spectrally efficient frequency division multiplexing (SEFDM) systems with index modulation (IM), which can efficiently make use of the indices of activated subcarriers as communication information. Recent research has verified that IM may be used with SEFDM to alleviate inter-carrier interference (ICI) and improve error performance. This work proposes new SEFDM signal formats based on novel activation pattern designs, which limit the locations of activated subcarriers and enable a variable number of activated subcarriers in each SEFDM subblock. SEFDM-IM system designs are developed by jointly considering activation patterns, modulation schemes and signal waveform formats, with a set of solutions evaluated under different spectral efficiency scenarios. Detailed modelling of coded systems and simulation studies reveal that the proposed designs not only lead to better bit error rate (BER) but also lower peak-to-average power ratio (PAPR) and reduced computational complexity relative to other reported index-modulated systems. [ABSTRACT FROM AUTHOR]

Digital beamforming (DBF) with full Radio-Frequency (RF) complexity requires a separate RF chain per transmit antenna, which is not only difficult to realize for large-scale MIMO systems but also vulnerable to hardware imperfection. In this paper, we show that DBF architectures don’t necessarily require the number of RF chains to be the same as the number of transmit antennas. We propose a low RF-complexity transmit DBF architecture that enables to use a small number of RF chains to serve a large number of transmit antennas. In our architecture, the transmit antennas are divided into groups. All antennas in the same group share the same RF chain in a time-multiplexed manner to preserve the signal from baseband till the antenna aperture. A novel antenna grouping algorithm is proposed to dynamically group the transmit antennas in a way that each antenna group forms a close-to-rank-one channel matrix with the receive antennas. Under ideal hardware conditions, we show that our DBF architecture can achieve nearly the same performance as that of the conventional full RF-complexity DBF in terms of bandwidth and spectral efficiency. However, when hardware imperfection is considered, our architecture outperforms full RF-complexity DBF in both spectral and energy efficiency because it is more robust to inter RF-chain cross-talk effects due to the reduction on the number of required RF chains. [ABSTRACT FROM AUTHOR]

With the gradual promotion of the fifth generation (5G) mobile communication and Internet of Things (IoT) applications, wireless communication transmission will be more vulnerable to illegal interceptions and/or attacks. To ensure communication security, we study covert communication of downlink nonorthogonal multiple access (NOMA) systems, where the channel knowledge of users is uncertain. A multiantenna transmitter tries to covertly transmit information to a covert user (strong user) through the shield of a public communication link (weak user), while the warden tries to detect the communication behavior between the transmitter and the covert user. To improve security and energy efficiency, the ${k}$ th best antenna of the transmitter is selected, since the optimal antenna may be not available due to some schedule and/or other reasons. Aiming to evaluate the proposed framework performance, we start by deriving exact expressions for the minimum detection error probability and the optimal detection threshold of the warden, followed by a calculation analysis of the expected minimum detection error probability (EMDEP) and the outage probability of NOMA users. The asymptotic behavior for the outage probability is investigated at high signal-to-noise ratio (SNR) to acquire greater useful insights. With the goal of improving the system covertness performance, we propose that a scheme is optimized to enhance the covert throughput of the system to the maximum. Simulation results show that the following hold: 1) channel estimation errors have a significant effect on system performance; 2) reliability performance tends to build up, as the total number of antennas grows large; and 3) as the transmitting power and number of antennas increases, there is an upper bound for maximizing the covert throughput. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Antenna arrays have a long history of more than 100 years and have evolved closely with the development of electronic and information technologies, playing an indispensable role in wireless communications and radar. With the rapid development of electronic and information technologies, the demand for all-time, all-domain, and full-space network services has exploded, and new communication requirements have been put forward on various space/air/ground platforms. To meet the ever increasing requirements of the future sixth generation (6G) wireless communications, such as high capacity, wide coverage, low latency, and strong robustness, it is promising to employ different types of antenna arrays (e.g., phased arrays, digital arrays, and reconfigurable intelligent surfaces, etc.) with various beamforming technologies (e.g., analog beamforming, digital beamforming, hybrid beamforming, and passive beamforming, etc.) in space/air/ground communication networks, bringing in advantages such as considerable antenna gains, multiplexing gains, and diversity gains. However, enabling antenna array for space/air/ground communication networks poses specific, distinctive and tricky challenges, which has aroused extensive research attention. This paper aims to overview the field of antenna array enabled space/air/ground communications and networking. The technical potentials and challenges of antenna array enabled space/air/ground communications and networking are presented first. Subsequently, the antenna array structures and designs are discussed. We then discuss various emerging technologies facilitated by antenna arrays to meet the new communication requirements of space/air/ground communication systems. Enabled by these emerging technologies, the distinct characteristics, challenges, and solutions for space communications, airborne communications, and ground communications are reviewed. Finally, we present promising directions for future research in antenna array enabled space/air/ground communications and networking. [ABSTRACT FROM AUTHOR]

Millimeter wave (MmWave) dual-functional radar-communication (DFRC) technology is believed to hold the ability to alleviate spectrum congestion and inter-radar interference in 5G vehicle-to-everything (V2X) systems. The radar target sizes in V2X system may not be ignored in views of the demands of short-range sensing and ultra-narrow beams supported by massive MIMO mmWave beamforming. Under such scenario, a novel single-target-multi-beams (STMB) radar beam alignment scheme is proposed to acquire more accurate information on estimated ranges and velocities by allocating multiple radar beams to a certain target. For instance, the relative velocity direction can be accurately estimated based on STMB scheme by using a weighted linear estimation methods. Then, the hybrid analog-digital beamforming under STMB scheme is formulated and optimized by maximizing transmission rate subject to radar signal-to-interference-and-noise (SINR) constraints, where a radar beam cancellation algorithm is proposed to adjust adaptively the radar beam number pointing to a certain target, which can guarantee strict radar SINR constraint under different transmission power levels. The numerical results verify the effectiveness and reliability of STMB scheme and show that the proposed beamformer outperforms the benchmark in both spectral efficiency and minimum radar SINR. [ABSTRACT FROM AUTHOR]

Very recently, signed quadrature spatial modulation (sQSM) is developed as a competent technique that expands the spatial constellation diagram of QSM system by adding a bipolar dimension. Despite the enhanced spectral efficiency, the existing optimal maximum likelihood (ML) presents a serious computational challenge for large scale sQSM systems. Therefore, developing a reduced complexity detector for sQSM schemes is of significant importance to enable implementing and enjoying the inherent advantages of this promising system. Toward this end, a Tree Search (TS) optimal low complexity detector, called TSopt, for sQSM Multiple Input Multiple Output (MIMO) system is proposed and analyzed in this paper. The proposed detector expands the computationally complex ML detector for sQSM into a tree-structure representation. The idea of the suggested algorithm is to employ an efficient searching strategy that can expeditiously find the branch corresponding to the minimum error without tracing the entire nodes as in the ML case. It is reported that the proposed TSopt algorithm achieves the exact error performance as ML detector but with substantial reduction in computational complexity. Besides, complexity analysis in terms of the number of visited nodes of the TSopt algorithm is analyzed and a closed-form expression for the expected complexity at high SNR values is derived. Reported results disclose agreement between simulation and expected analytical complexity with substantial gains of around 60–80% in complexity reduction for different system parameters. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Posts & Telecommunications (Natural Science Edition) is the property of Chongqing University of Posts & Telecommunications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The wearable localization system for wireless capsule endoscopy (WCE) is a potential technology to realize rapid diagnosis and treatment of the gastrointestinal (GI). However, the electromagnetic localization accuracy of WCE still needs to be improved. In this paper, based on RSSI electromagnetic fading model, the accurate fitting parameter values are obtained by Kalman filter and the least square method. A novel weighted centroid localization (WCL) algorithm based on exponential weights is proposed, which can achieve high-accuracy localization by using only sparse reception matrix. The simulation results show that when the standard deviation of the localization data is 7.85, the localization root mean square error (RMSE) is 25.4 mm; when the standard deviation of the localization data is 5.475, the localization RMSE is 2.5 mm. These two localization RMSEs are 38% and 79% less than those of the conventional centroid localization algorithm, respectively. An experimental platform of wearable wireless communication and localization system using 24 array receiving antennas is developed in human phantom environment. The experimental results show that the wearable WCE electromagnetic localization system based on the proposed algorithm achieves a localization RMSE of 36.3 mm, which is 17% lower than that of the conventional centroid localization algorithm and meets the needs of clinical diagnosis. [ABSTRACT FROM AUTHOR]

A novel concept for utilizing a single dielectric resonator (DR) to fulfill a dual-mode bandpass filter (BPF) and a power divider (PD) simultaneously is proposed. A stepped rectangular DR is employed and two of its modes are, respectively, applied to the two functions. The fields of the modes are orthogonal and their frequencies can be flexibly controlled so that the BPF and PD are able to operate with high isolation and adjustable frequency bands. In the BPF part, one of the shielding cavity modes is also introduced to form a dual-mode characteristic. According to the symmetry of the electromagnetic fields, the PD part is designed in three forms: 1-to-2 PD with in-phase outputs, 1-to-2 PD with antiphase outputs, and 1-to-4 PD. As a result, three dual-functional combinations are achieved. For demonstration, the proposed dual-function applications sharing the common DR in high circuit integration are implemented and measured. [ABSTRACT FROM AUTHOR]

This letter presents a flat-top radiation transmitter (Tx), which is composed of 2 × 2 array patches connected to the ground plane of the aperture by four shorting vias, which can generate a mushroom structure resulting in back lobe level reduction. The final design exhibits an overall size of 1.93 $\lambda _{0}$  × 1.93 $\lambda _{0}$  × 0.075 $\lambda _{0}$ at 5.8 GHz. The measured results agree well with the simulated results, which achieves a maximum left-hand circular polarization gain of 8.5 dBi with a sidelobe level of $< $ −13.5 dB, and 3 dB beamwidths of 80 $^{\circ }$ in both the E- and H-planes. Moreover, the proposed transmitter is tested with the rectenna showing that a stable received energy of 5.93 mW is obtained with an exciting 1 W input power in case of receiving antenna lateral misalignment of up to 60 mm, which demonstrates feasibility in practical deployment. Compared with the other works, the proposed antenna has the advantage in compactness and wide 3 dB beamwidth. [ABSTRACT FROM AUTHOR]

The design of an antenna requires a careful selection of its parameters to retain the desired performance. However, this task is time-consuming when the traditional approaches are employed, which represents a significant challenge. On the other hand, machine learning presents an effective solution to this challenge through a set of regression models that can robustly assist antenna designers to find out the best set of design parameters to achieve the intended performance. In this paper, we propose a novel approach for accurately predicting the bandwidth of metamaterial antenna. The proposed approach is based on employing the recently emerged guided whale optimization algorithm using adaptive particle swarm optimization to optimize the parameters of the long-short-term memory (LSTM) deep network. This optimized network is used to retrieve the metamaterial bandwidth given a set of features. In addition, the superiority of the proposed approach is examined in terms of a comparison with the traditional multilayer perceptron (ML), Knearest neighbors (K-NN), and the basic LSTM in terms of several evaluation criteria such as root mean square error (RMSE), mean absolute error (MAE), and mean bias error (MBE). Experimental results show that the proposed approach could achieve RMSE of (0.003018), MAE of (0.001871), and MBE of (0.000205). These values are better than those of the other competing models. [ABSTRACT FROM AUTHOR]

Underwater communication is a mode of transmitting or receiving the signals below water. Many applications such as shipments, autonomous vehicle, climate recording etc. use the antennas for transmitting and receiving the signals below water. The antenna design for underwater sensor networks is an emerging field for the researchers, as many of the antenna design have proposed in order to get the better radiation patterns and return loss during the data transmission but the researches are done mostly with narrow band and low frequencies which results in low data rate during transmission of the data. Here in this research paper a novel patch antenna design is proposed with circular insulation provided for its circuitry called as a circular quad band bowtie antenna works with high frequencies and also capable of radiate multiple frequencies from its four tapers. The lack of work in this field is a driving force for the development of an underwater UWB antenna. UWB antennas come in a variety of shapes and sizes, although the majority of them are designed for air communications. To acquire a result, UWB technology is required a high level of resolution for device placement in order to enhance the underwater communication applications. The radiation patterns of the proposed design are omnidirectional and it results the return loss of less than − 25 dB and due to the robust design of the proposed antenna, it can transmit the multiple frequencies via different tapers. The parameters of the proposed antenna are taken for considerations after testing at different frequencies. The future scope of circular quad band bow tie antenna is to use of it in other MIMO applications used in fifth generation of mobile communications. [ABSTRACT FROM AUTHOR]

We propose a 1 × 32 silicon photonics transceiver integrated optical phased array (OPA) with a large scanning angle. It can process receive and transmit signals simultaneously, which effectively increases the on-chip signal transmission efficiency. The simulation shows that the phase-tuned 62.2° lateral beam steering without grating lobe and the wavelength-tuned 31.2° longitudinal beam steering can be achieved in the transmitting mode, and the overall optical loss is less than 9.1 dB. In the receiving mode, the combination of the two detection methods reduces the complexity of the system while ensuring the sensitivity of the system. According to statistics, an effective collection area of 43.3% per unit area can be achieved in the receiving mode, which provides a reliable guarantee for subsequent high-quality signal processing. [ABSTRACT FROM AUTHOR]

In this letter, we propose using a reconfigurable intelligent surface (RIS) to improve the performance of integrated sensing and communication (ISAC) systems since it can customize the wireless propagation environment by tuning phase shifts. However, it is not straightforward to integrate the RIS into ISAC systems. As the waveform design for the ISAC system is highly dependent on the channel conditions, the phase shift design of the RIS is fully coupled with the waveform design at the base station (BS). To address this challenge, we jointly optimize the beamformer at the BS and the phase shifts at the RIS in order to maximize the communication data rate and the mutual information (MI) for sensing, and then develop an efficient algorithm to solve this problem. Simulation results show that the proposed algorithm can effectively improve both sensing and communication performance. [ABSTRACT FROM AUTHOR]

Since millimeter wave (mmWave) and sub-terahertz bands are highly vulnerable to blockage and penetration loss effects, wireless coverage enhancement is one of the critical challenges in indoor mmWave deployments. In particular, when the line-of-sight (LoS) link is blocked, a strong non-LoS (NLoS) path can provide a stable link quality. One of the efficient ways to improve the NLoS link is the use of strategically placed passive reflectors. In this letter, we study the indoor coverage improvement by using a transparent passive reflector attached on a wall. We consider an indoor open-door scenario, where the LoS link is blocked by the walls for receivers inside the room, and the coverage can only be achieved via an NLoS link through a passive reflector. We analytically derive closed-form equations of the reflection visibility probability and the coverage probability. By simulation and analytical results, we show the coverage dependency on the location and size of the reflector. [ABSTRACT FROM AUTHOR]

This letter investigates the capacity for the multiple-input multiple-output (MIMO) optical intensity channels in the high signal-to-noise ratio (SNR) regime from a sphere-packing (SP) perspective. In such a channel, the inputs represent optical intensities, hence are nonnegative. Considering the peak- and average-power constraints for the inputs, the high-SNR capacity can be expressed in terms of the volume of an image signal space through an SP argument. When the number of transmit antennas $n_{\mathrm{T}} $ and receive antennas $n_{\mathrm{R}} $ satisfies $n_{\mathrm{T}} \leq n_{\mathrm{R}} $ , the image-space volume is derived in terms of singular values of the channel matrix. While for $n_{\mathrm{T}} > n_{\mathrm{R}} $ , the image-space volume is derived by decomposing the image space into multiple non-overlapping subpolytopes, whose volumes can be conveniently calculated. [ABSTRACT FROM AUTHOR]

The performance of symbol detection in multiple-input multiple-output (MIMO) systems is largely determined by the achievable diversity order. The inter antenna interference (IAI), however, can limit detectors’ ability to take full advantage of diversity. This occurs because off-diagonal channel coefficients of the MIMO channel matrix are not mutually orthogonal. Nevertheless, this can be mitigated with the aid of lattice reduction (LR), which aims to increase the orthogonality among these coefficients. We propose a LR aided probability data association (PDA) detector that achieves a similar diversity order to that of the optimum detector but with significant less computational complexity. [ABSTRACT FROM AUTHOR]

Holographic Multiple Input Multiple Output (HMIMO), which integrates massive antenna elements into a compact space to achieve a spatially continuous aperture, plays an important role in future wireless networks. With numerous antenna elements, it is hard to implement the HMIMO via phased arrays due to unacceptable power consumption. To address this issue, reconfigurable refractive surface (RRS) is an energy-efficient enabler of HMIMO since the surface is free of expensive phase shifters. Unlike traditional metasurfaces working as passive relays, the RRS is used as transmit antennas, where the far-field approximation does not hold anymore, urging a new performance analysis framework. In this letter, we first derive the data rate of an RRS-based single-user downlink system, and then compare its power consumption with the phased array. Simulation results verify our analysis and show that the RRS is an energy-efficient way to HMIMO. [ABSTRACT FROM AUTHOR]

Multiple-input multiple-output (MIMO) technology is helpful with improving the communication throughput and performance of molecular communication (MC) systems. Though index modulation (IM) approaches aid to alleviate intersymbol interference (ISI) and interlink interference (ILI) issues in molecular MIMO systems by encoding the information in the antenna index, ISI and ILI problems still exist in such environments. Coded modulation strategies show promising results in terms of system error performance due to their better ISI and ILI combating capability. In this letter, a novel coded modulation scheme is proposed where the pulse position constellation is incorporated with the coded antenna indices. The proposed scheme is shown to yield an improved error performance owing to its better ILI mitigating strength. [ABSTRACT FROM AUTHOR]

This paper introduces a novel approach for dense antenna arrays, which integrates beamforming and antenna selection. The proposed method aims to optimize the number of transmit antennas to reduce power consumption and enhance spectral efficiency at the transmitter. By employing optimal beamforming weights, our approach steers signals toward the intended receiver to maximize the transmit power of the desired signal while mitigating side-lobe interference under channel uncertainty. To adapt beamforming parameters dynamically to changing channel conditions, we develop a channel estimation approach that obtains accurate channel state information (CSI). In contrast to prior studies, our channel estimation method utilizes a generalized Gaussian distribution (GGD) model, capable of accommodating both matched and mismatched CSI features by modeling heavy-tailed and light-tailed distributions. This allows our method to capture diverse channel statistical behaviors resulting from phenomena such as fading and interference under various propagation conditions. Furthermore, we introduce an angle entropy metric, which measures angle of departure (AoD) variations, indicating the degree of uncertainty regarding the directionality of transmitted signals. Simulation results validate the accuracy of our analytical findings and demonstrate the superior performance of the proposed approach in terms of robustness and bit-error-rate (BER) performance. [ABSTRACT FROM AUTHOR]

In-band full duplex (IBFD) communications are a potential solution to spectrum scarcity. IBFD communications offer greater spectral efficiency than traditional half-duplex communications by transmitting and receiving on the same frequency channel. However, IBFD operation requires overcoming the challenge of eliminating the self-interference coupled from the transmit antenna to the receive subsystem. Knowledge of the characteristics of the loopback propagation channel makes it easier to cancel out the self-interference. Nevertheless, complex field trials are required to adequately characterize loopback channels, which is still lacking in the recent literature. This paper proposes a measurement campaign in a real and ongoing broadcast transmission center to characterize the main characteristics of loopback channels. The work proposes a set of loopback channels based on field trials and an empirical analysis of the most relevant parameters of the channel model, such as the Doppler spectrum, the delay spread, and the K-factor. • A new methodology for measuring and characterizing broadcast loopback channels. • Characterizing the loopback channel in terms of the amplitude and the delay of the paths. • An analysis of the obtained delay spread and K-factor values. • Characterizing the Doppler spectrum of the loopback channel in broadcast transmitters. • Performance evaluation of the proposed channel models under an ATSC 3.0 compliant transceiver chain. [ABSTRACT FROM AUTHOR]

Socionext, a company based in Yokohama, Japan, has introduced its 60GHz radio-frequency range sensors for Advanced Driver Assistance Systems (ADAS) applications. These sensors utilize time-division multiplexing (TDM-MIMO) operation with multiple transmitting and receiving antennas to accurately detect the position and movement of vehicle passengers. CHASM, a company based in Canton, Massachusetts, has launched a series of transparent heaters for ADAS sensors. These heaters integrate carbon nanotubes (CNT) and metal micromesh to provide exceptional optoelectronic performance and are compatible with camera, lidar, and radar sensors. [Extracted from the article]

Abstract Two‐dimensional (2‐D) transmit arrays offer many advantages over traditional over‐the‐horizon radar (OTHR) arrays, including the capability to steer and mitigate auroral clutter, a clutter type prevalent in polar operation, in all azimuth and elevation directions. The approaches of previous studies on OTHR 2‐D transmit arrays are considered suboptimal, but it can be shown that the 2‐D array is an effective OTHR transmitter when operated in an appropriate manner. A reference system derived from publicly available information on an operational OTHR array is used as a benchmark to compare the performance of various 2‐D OTHR transmit systems with respect to effective isotropic radiated power on target, sidelobe levels, and elevation selectivity.

Summary: Incorporation of multiple antennas in downlink non‐orthogonal multiple access (NOMA) system helps in achieving better performance by exploiting different diversity schemes. To this end, we propose a general framework of transmit antenna selection (TAS)‐assisted orthogonal space‐time block code (OSTBC) transmission for multiple NOMA users. We derive exact expressions of probability density function of the TAS‐OSTBC processed signal‐to‐noise ratio (SNR) at the output of maximum‐ratio combiner of the NOMA users. Using well‐known moment generating function approach, we evaluate the error performance of TAS‐OSTBC assisted NOMA users over generalized η−μ fading channel in presence of perfect and imperfect successive interference cancelation. We investigate the proposed system in different multi‐antenna scenarios and accordingly observe better error performance of the users by increasing the number of transmit and receive antennas. We perform their asymptotic analysis leading to full‐diversity order at high SNR. For numerical evaluation, we truncate the infinite series in derived results and examine the upper bound of truncation error. We evaluate nth moment of the output SNR and obtain channel quality estimation index as a performance measure of the proposed NOMA system. Moreover, we investigate the influence of power coefficients and fading parameters, η and μ, on the error performance of TAS‐OSTBC‐assisted NOMA users. We also compare the derived error performances with the existing schemes, wherein we observe that the proposed system shows remarkable improvement in the bit error rate (BER) of the NOMA users. For validation, we execute simulations which closely match with the derived analytical results. [ABSTRACT FROM AUTHOR]

Backscattering by objects is a relevant phenomenon in millimeter-wave (mm-wave) propagation. Accordingly, computationally efficient models characterizing this process are now available in the literature. However, these models are restricted to single-surface contributions. In this article, we propose a multiple-scattering model for calculating backscattered fields due to consecutive interactions with several smooth electrically-large rectangular surfaces. The model is fundamentally based on the cascading of single-scattering events. In addition, the model is later extended to capture single-scattering blockage between backscattering events. The model is implemented using a Fresnel-integral-based method and validated by means of electromagnetic (EM) simulations and measurements. Furthermore, insight on the effects of the model parameters—number of surfaces, frequency, surface size, surface height-to-width ratio, surface displacement, and antenna-to-surface and surface-to-surface distances—is provided. Due to its computational efficiency, the proposed model can be suitable for system- and link-level simulations of wireless systems, particularly when Monte Carlo simulations are applied. [ABSTRACT FROM AUTHOR]

A high-efficiency wideband double-layer transmitarray antenna (TA) using miniaturized array elements is proposed in the study for millimeter-wave (mm-Wave) applications. The transmitarray consists of 484 dual-polarized elements. Each element is composed of only two layers of identical modified Jerusalem crosses printed on a dielectric substrate. Additional stubs are used for size reduction, leading to a compact size with a periodicity of only $0.44 \lambda _{0}$. It contributes to a high aperture efficiency for the proposed TA. TA is designed, fabricated, and measured. It achieves a peak gain of 28.67 dBi at 31 GHz and a high aperture efficiency of 44%–61.3% within the 1 dB gain bandwidth, which is 10.3% (29.5–32.7 GHz) in the measurement. The proposed dual-polarized double-layer TA demonstrates simplified design complexity, reduced thickness and mass, and lower cost compared with the conventional TAs. It also exhibits high radiation gain and high aperture efficiency. [ABSTRACT FROM AUTHOR]

This communication presents a dual-polarized transmitarray antenna with wide bandwidth and independent beam control for each polarization. A new low-insertion-loss transmitarray element allowing wideband dual-polarized operation is proposed by using magnetoelectric (ME) dipole with shared radiating structure and interleaved orthogonal feeding probes; 1 bit phase adjustment can be realized individually for each polarization with additional freedom in manipulating the cross-polarization over a fractional bandwidth of 23%. Three transmitarrays that achieve possibly different collimated beams and/or cross-polarization manipulation are designed and carried out at millimeter-wave frequencies covering from 23.5 to 32.5 GHz. Measurement results of the prototypes agree reasonably well with simulations, which validates the wideband operation and independent beam controls. [ABSTRACT FROM AUTHOR]

A low-profile wide-angle reconfigurable transmitarray antenna (RTA) is proposed in this communication. This RTA consists of a feeding antenna, a phase transforming lens, and a 1 bit phase-reconfigurable transmitting antenna (PRTA). The feeding antenna is composed of a 12 $\times12$ slot array fed by 36-way waveguide power divider, which possesses the characteristics of equal amplitude and in-phase distribution to obtain high efficiency. The desired 1 bit PRTA uses 16 $\times16$ array of C-shaped probe-fed patch elements to achieve flexible wide-angle beam scanning. To eliminate the mirror lobe effects of 1 bit phase quantization, the phase transforming lens with a $16\times16$ array of perforated dielectric element is designed to generate a spherical phase front from virtual focal source. By spatially cascading these three components, a low-profile RTA architecture is constituted, where the two spatial separations between adjacent components are $0.20\lambda _{\mathbf {0}}$ and $0.08\lambda _{\mathbf {0}}$ at 12.0 GHz, respectively. Finally, the proposed antenna prototype with an effective aperture of $7.68\lambda _{\mathbf {0}} \times 7.68\lambda _{\mathbf {0}}$ (192 mm $\times192$ mm) is fabricated and measured. The measured peak gain is 23.5 dBi at 12.0 GHz with aperture efficiency of 30.2% and a 3 dB gain bandwidth of 1.1 GHz. The measured results demonstrate that the proposed design has the 2-D wide-angle beam scanning capability up to 60°. [ABSTRACT FROM AUTHOR]

A design method of programmable transmitarray antenna with independent controls of transmission amplitude and phase is proposed in C-band. The unit cell with cascaded structures mainly consists of four parts, including the receiving antenna, reconfigurable attenuator with p-i-n diodes, reconfigurable phase shifter with varactors, and transmitting antenna. Correspondingly, various manipulations of spatial electromagnetic (EM) fields are achieved by varying the bias voltages of p-i-n diodes and varactors in the transmitarray antenna. The fabricated unit cell is measured in a standard waveguide, and the whole array with $8\times 8$ unit cells is measured with two horns for calibration of the programmable EM features. The experimental results show that the transmission amplitude can range from −16 to −3.6 dB, and the transmission phase achieves 270° coverage independently at the operating frequency of 5.67 GHz under 16 bit programmable control. To further exhibit the capability and functionality of the proposed transmitarray antenna, the waveform engineering of adaptive beamforming and power-allocation beamforming is separately realized in the experiment. The measured results have good agreements with our theoretical calculations, verifying the validity of our design method. [ABSTRACT FROM AUTHOR]