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Future wireless communication systems will evolve toward multifunctional integrated systems to improve spectrum utilization and reduce equipment sizes. Joint radar and communication (JRC) systems, which can support simultaneous information transmission and target detection, have been regarded as a promising solution for emerging applications, such as autonomous vehicles. In JRC, data security and privacy protection are critical issues. Thus, we apply covert communication to JRC and propose a joint radar and covert communication (JRCC) system to simultaneously achieve high spectrum utilization and secure data transmission. In the JRCC system, sensitive data transmission is hidden from malicious parties. However, the performance of JRCC is restricted by a severe signal propagation environment and hardware devices. Fortunately, reconfigurable intelligent surfaces (RISs) can intelligently change the signal propagation to improve network performance and cost. We first review fundamental concepts of JRCC and RISs and then propose a RIS-aided JRCC system design. Furthermore, covert communication and radar performance metrics are investigated, and a game theory-based covert rate optimization scheme is designed to achieve secure communication. Finally, we present several promising applications and future directions of RIS-aided JRCC systems. Ministry of Education (MOE) National Research Foundation (NRF) This work was supported, in part, by the National Key R&D Program of China, under grant 2020YFB1806903; National Natural Science Foundation of China, under grants 61971027 and 62102099; Natural Science Foundation of Jiangsu Province, under grant BK20212002; DesCartes program; National Research Foundation, Prime Minister’s Office, Singapore, under its Campus for Research Excellence and Technological Enterprise program; Alibaba Group, through the Alibaba Innovative Research program and Alibaba–Nanyang Technological University Singapore Joint Research Institute; National Research Foundation, Singapore, under AI Singapore Program grant AISG2-RP-2020-019; and Singapore Ministry of Education, under grant RG16/20. This work was also supported, in part, by the National Research Foundation of Korea, under grant 2021R1A2C2007638.

Thanks to the abrupt advances in semiconductor technologies, particularly in terms of the operating frequency, the last decade has seen various efforts and trials in attempts to achieve high-throughput wireless communications at THz frequencies. Based on several potential device technologies, not only III-V heterojunction bipolar and high-electron-mobility transistors but also with silicon CMOSs and photonic technologies, high data rates of 100 Gbps or more have been successfully demonstrated so far. Meanwhile, the next generation of wireless communications systems, so called 6G, is already being discussed in research communities worldwide. A terabit per second peak data rate is envisioned, which essentially requires huge spectral resources. This recent great attention on 6G communications is implicitly going to THz communications but is more than a technical curiosity unlike the past. In this article, we briefly review the progress of THz communications made in the last decade and discuss some of the most challenging issues that need to be overcome for future wireless systems at THz frequencies, including not only the 6G network but also short-range connectivity and fixed wireless links

To expedite research progress on terahertz (THz) communications, we analyze the outage performance of THz communication systems by a compound channel model in this paper. Different from existing models, the compound channel model incorporates the effects of spreading loss, molecular absorption loss, shadowing, and multi-path fading via a composite distribution. By using this model, we maintain an equilibrium of the outage performance analysis between mathematical tractability and the fidelity of realistic THz channels. Specifically, by utilizing the compound channel model, outage performance analysis can get rid of sophisticated case-specific channel modeling relying on field measurement and the ray-tracing assessment. To facilitate the application of the proposed channel model, we also design a maximum likelihood estimation (MLE) based channel parameter estimation approach for the compound channel model. The analytical results of outage performance by using the compound channel model are given in closed form and verified by numerical results.

In this letter, we investigate the use of active elements in reconfigurable intelligent surfaces (RIS) to overcome the double-fading problem introduced in the RIS-aided link in a wireless communications system. Towards this end, each active RIS element amplifies the reflected incident signal rather than only reflecting it has done in passive RIS modules. As revealed in our analysis and simulation, the use of active elements leads to a drastic reduction in the size of RIS to achieve a given performance level. Furthermore, a practical design for active RIS is proposed.

This letter investigates a wireless communication system deploying distributed reconfigurable intelligent surfaces (RISs). Existing works have assumed that perfect timing synchronization is available among all the cooperative RISs. For practical considerations, we first study cooperative reflection design for multi-RIS-aided communication systems taking into account timing synchronization errors. We aim to minimize the mean-squared error of the recovered data in the presence of timing offsets subject to the unit modulus constraints imposed on the phase shifts of the RISs. In order to handle this sophisticated nonconvex problem, we develop a computationally-efficient algorithm based on the majorization-minimization framework where the RIS phase shift matrices and the timing offset equalizer are respectively developed in a semi-closed form and a closed form. Numerical examples validate the improved performance of our proposed design compared with various schemes.

When the wireless communication system evolves to massive multiple-input multiple-output (MIMO) system, the system becomes more and more complex. Hybrid beamforming architecture provides excellent trade-off between the system performance and the complexity for the massive MIMO system. Hybrid beamforming architecture can be classified as fully-connected (FC) and sub-connected (SC) architecture. Existing studies on the system performance comparison of the two architectures are limited. In this paper, we investigate the performance of the FC and SC architecture in the multi-user multiple-input single-output (MU-MISO) system. We derive the closed-form sum rate of two architectures under the same total transmission power constraint. From the results, we conclude that the system performance of FC architecture is always better than that of SC architecture. When the number of users is small or the signal noise ratio (SNR) is low, the performance difference between the FC and SC architecture is small. Our analysis can serve as a guideline of choosing hybrid beamforming architectures.

The information security and functional safety are fundamental issues of wireless communications sytems. The endogenous security principle based on Dynamic Heterogeneous Redundancy provides a direction for the development of wireless communication security and safety technology. This paper introduces the concept of wireless endogenous security from the following four aspects. First, we sorts out the endogenous security problems faced by the current wireless communications system, and then analyzes the endogenous security and safety attributes of the wireless channel. After that, the endogenous security and safety structure of the wireless communications system is given, and finally the applications of the existing wireless communication endogenous security and safety functions are listed.

Aerostat platforms could serve as potential aerial platforms because of their low cost, long flight times, and easy load recovery. They are suitable for emergency communication, early warnings, Earth observations, and other fields. The air-ground communication link between an aerostat platform and the ground is the basic guarantee for aerostat measurement control and service transmission. In traditional aerostat applications, platform measurement control and service transmission usually use different links. The load and ground equipment are complex, and the energy, load, and size of the platform are greatly occupied. In this paper, we propose a Beidou-assisted air-ground communication ground for a near-space platform that uses Beidou's positioning and communication functions to provide tracking and guidance information for the ground station. An air-ground wireless communication mode integrating measurement control and service transmission is achieved. The flight test shows that the system can effectively meet the practical application requirements.

Contribution: A do-it-yourself (DIY) light wave sensing (LWS) and communication project was developed to generate interest and clarify basic electromagnetic (EM) and wireless sensing/communication concepts among students at different education levels from middle school to undergraduate. This article demonstrates the nature of the project and its preliminary effectiveness. Background: Concepts in wireless sensing and communication are generally considered hard to comprehend being underpinned only by theoretical coursework and occasional simulations. Further, K–12 schools and small academic institutions may not have the resources necessary to produce tangible demonstrations for clarification. The consequent lack of affordable hands-on experiences fails to motivate and engage students. Intended Outcomes: The DIY-LWS is intended to make wireless concepts more understandable and less esoteric by linking fundamental concepts with student-relevant technologies, such as solar cells, visible lights, and smartphones. It is also intended to pique student interest by allowing them to personally assemble, operate, and explore a light-based wireless communication system. Students complete assessments before and after the project to quantify its effectiveness. Application Design: A preliminary assessment is used to determine the student base knowledge level and enthusiasm for wireless and related core topics. Students are instructed to assemble and test their own DIY-LWS hardware to provide a hands-on experience and stimulate further exploration. Short lectures are given to link conceptual ideas to the real-world phenomena students personally observed. Finally, students are reassessed to quantify any change in conceptual understanding. Findings: The DIY-LWS kits have been used in multiple events with students at different levels from secondary to high schools to college. As part of a triangulated assessment methodology, pre- and post-assessments revealed pronounced improvements (the number of correct answers doubled) in student understanding of EM concepts. Instructors observed tremendous interest and excitement among the students during and after the experiments.

A cooperative non-orthogonal multiple access (CNOMA) system and an orbital angular momentum (OAM) -based multiple-input multiple-output multiplexing system is proposed as full-duplex relaying (referred to as CNOMF) by the cell center user to the cell edge user in this letter. The proposed CNOMF scheme can significantly improve the capacity of cell edge user and sum channel capacity via user-assisted decode and forward based full-duplex relaying by utilizing different ranges of OAM modes for a 6G (Sixth generation) wireless communication system, compared to other existing schemes (For example, CNOMA-MIMO with FDR, and orthogonal multiple access with OAM-MIMO and half duplex relaying); this was demonstrated via numerical result analysis.

Large intelligent surfaces (LIS) present a promising new technology for enhancing the performance of wireless communication systems. Realizing the gains of LIS requires accurate channel knowledge, and in practice the channel estimation overhead can be large due to the passive nature of LIS. Here, we study the achievable rate of a LIS-assisted single-input single-output communication system, accounting for the pilot overhead of a least-squares channel estimator. We demonstrate that there exists an optimal $K^{*}$, which maximizes achievable rate by balancing the power gains offered by LIS and the channel estimation overhead. We present analytical approximations for $K^{*}$, based on maximizing an analytical upper bound on average achievable rate that we derive, and study the dependencies of $K^*$ on statistical channel and system parameters., Comment: Published in IEEE Wireless Communications Letters

The integrated communication system has received increasing attention to establish a fully connected world in the eras of beyond fifth generation wireless communication and sixth generation wireless communication systems, where a wide range of services with distinct requirements needs to be accommodated, covering distinct scenarios such as terrestrial, ocean, outer space, and underwater. In this article, we first propose the idea of feeder communication, which aims to provide truly seamless and ubiquitous on-demand coverage for any human activity. Compared to the traditional integrated networks, feeder communication focuses on reliable data transmission over multiple propagation media such as outer space, stratosphere, troposphere, and underwater. Due to the significant differences of radio propagation characteristics in different media, feeder communication requires a large number of feeder nodes for inter-medium transmissions, a well-designed network structure, and intelligent wireless transmission and control schemes. The basic concepts, features, application scenarios, network architecture, and the corresponding wireless transmission technologies of feeder communication are presented in detail, and challenges and future directions are also pointed out in this article.

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. We address the evaluation of dynamic (estimation-based) user-decoding order in successive interference cancellation (SIC) in a proof-of-concept multiple access satellite setting in which many code-division multiple access users employ non-orthogonal spreading codes and the same encoder. We consider the practical setting where user symbol energies, unknown to the receiver, are estimated by preamble cross-correlations. Thereafter, SIC proceeds in non-increasing order of the former estimates. In contrast with small networks evaluated in the literature, we analyze the large-user regime and derive a simple system model to analyze the asymptotic network performance. Monte Carlo simulations validate our infinite-user analysis for hundreds of users and report the benefits of their application. Work supported in part by Agencia Estatal de Investigación (AEI, Spain) and by European Regional Development Fund (ERDF) through project WIN-TER (TEC2016-76409-C2-1-R) and project RODIN (PID2019-105717RB-C22), and in part by the Catalan administration (AGAUR) under Grant 2017SGR 578 and predoctoral Fellowship 2019FIB1 00085

In this letter, a new general composite fading model, namely $\alpha $ - $\eta $ - $\kappa $ - $\mathcal {F}$ model, is proposed. It considers most of the well-known propagation phenomena in wireless fading channels, such as shadowing, multi-path fading, non-linearity of the propagation medium, power of the dominant components, and power of the scattered waves. Additionally, most of the important statistical fading models are included in the $\alpha $ - $\eta $ - $\kappa $ - $\mathcal {F}$ model as special cases. The envelope probability density function (PDF) and cumulative distribution function (CDF) are derived and then employed to derive the PDF and CDF of the instantaneous signal-to-noise ratio. The performance of a wireless communication system operating under the $\alpha $ - $\eta $ - $\kappa $ - $\mathcal {F}$ composite model is evaluated in terms of outage probability and symbol error rate. Numerical results are supported by Monte-Carlo simulations to validate the analysis.

The aim of this article is to show the role of electromagnetic theory in fixing the final limitations of wireless communication systems. Some examples regarding the introduction of sidelobe constraints on the fields radiated by antennas are discussed, showing the large impact of constraints on the capacity of wireless communication systems that are based on space coding. The examples are obtained using a GUIbased program that can be freely downloaded by interested readers.

Reinforcement Learning (RL)-based algorithmic solutions have been profusely proposed in recent years for addressing multiple problems in the Radio Access Network (RAN). However, how RL algorithms have to be trained for a successful exploitation has not received sufficient attention. To address this limitation, which is particularly relevant given the peculiarities of wireless communications, this paper proposes a functional framework for training RL strategies in the RAN. The framework is aligned with the O-RAN Alliance machine learning workflow and introduces specific functionalities for RL, such as the way of specifying the training datasets, the mechanisms to monitor the performance of the trained policies during inference in the real network, and the capability to conduct a retraining if necessary. The proposed framework is illustrated with a relevant use case in 5G, namely RAN slicing, by considering a Deep Q-Network algorithm for capacity sharing. Finally, insights on other possible applicability examples of the proposed framework are provided. © 2022 IEEE. This paper is part of ARTIST project (ref. PID2020-115104RB-I00) funded by MCIN/AEI/10.13039/ 501100011033 and PORTRAIT project (ref. PDC2021-120797-I00) funded by MCIN/AEI/10.13039/501100011033 and by European Union Next GenerationEU/PRTR.

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Network slicing has recently been proposed as one of the main enablers for 5G networks. The slicing concept consists of the partition of a physical network into several self-contained logical networks (slices) that can be tailored to offer different functional or performance requirements. In the context of 5G networks, we argue that existing ubiquitous WiFi technology can be exploited to cope with new requirements. Therefore, in this paper, we propose a novel mechanism to implement network slicing in WiFi Access Points. We formulate the resource allocation problem to the different slices as a stochastic optimization problem, where each slice can have bit rate, delay, and capacity requirements. We devise a solution to the problem above using the Lyapunov drift optimization theory, and we develop a novel queuing and scheduling algorithm. We have used MATLAB and Simulink to build a prototype of the proposed solution, whose performance has been evaluated in a typical slicing scenario. This work has been supported in part by the European Commission and the Spanish Government (Fondo Europeo de Desarrollo Regional, FEDER) by means of the EU H2020 NECOS (777067) and ADVICE (TEC2015-71329) projects, respectively.

The past few decades have shown great advancements in wireless communication systems; however, today's explosive increase in data traffic demands even further improvement in such systems toward next-generation platforms. Current 4G mobile systems provide stationary users with data speeds up to 1 Gbit/s and high-mobility users with speeds up to 100 Mbit/s for mobile online access and multimedia applications such as TV streaming, video conferencing, navigation, high-end gaming, high-definition video streaming, and high-performance imaging [1].

Unlike the classical modulation, for instance, quadrature amplitude modulation (QAM) and others, where bits are transmitted via symbols particularly from modulation alphabets, in index modulation (IM), extra information bits can be conveyed via the indices of a particular transmit entities during the transmission process. Transmit antenna elements are example of transmit entities in multi-antenna systems which can be used to convey extra information bits. Recently, frequency diverse array (FDA), as a new type of transmit antenna array which differs from the traditional phased-array has been proposed in the literature. In FDA, the element indices has small frequency increment across them. In this paper, space-frequency increment IM is proposed. The proposed scheme utilizes the indices of the activated transmit FDA antennas and their respective corresponding frequency increments $\Delta f$ to convey additional information bits. The proposed scheme is inspired by the principle of quadrature spatial modulation (QSM) and no additional antenna activation is required. Compared with spatial modulation (SM) and QSM, it is shown that, the proposed scheme achieved higher spectral efficiency. Further, the average bit error rate (ABER), secrecy sum rate (SSR) and system capacity are derived and evaluated. Moreover, a low-complexity decoding algorithm is examined. Finally, via numerical results, the proposed scheme shows to be better than the comparative alternatives (QSM/SM), and may offer promising properties in various contexts.

In this letter, transmitting metasurface using single dielectric substrate for orbital angular momentum (OAM) generation is presented in Ku -band. A dimension extension method is introduced in designing the unit cell of the proposed transmitting metasurface to achieve required phase shift and transmission magnitude for generating OAM. A prototype of the proposed transmitting metasurface is fabricated and measured. Measured results suggest that the proposed transmitting metasurface can generate OAM vortex wave at 18 GHz. The proposed method can be applied in wireless communication systems requiring low-profile transmitted OAM generator.

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works Optical switching techniques have the potential to enable the optical data center network (DCN) interconnections providing high capacity and fast switching capabilities, overcoming thus the bandwidth and latency bottleneck of present electrical switch-based multi-tiered DCNs. The rapid growth of multi-tenant applications with heterogeneous traffic require specialized quality of service (QoS) in terms of packet loss and latency to the DCN infrastructure. Slicing the DCNs into dedicated pieces according to the deployed applications, differentiated QoS, and high resource utilization can be provided. However, slicing the optical DCNs still needs to be investigated because the Software-defined Networking (SDN) technique is developed for the electrical networks, not fully supporting the properties of the optical network. Additionally, Network Slices (NS) need to be automatically provisioned and reconfigured, to provide flexible slice interconnections in support of the multi-tenant applications to be deployed. In this article, we propose and experimentally assess the automatic and flexible NSs configurations of optical OPSquare DCN controlled and orchestrated by an extended SDN control plane for multi-tenant applications with differentiated QoS provisioning. Optical Flow Control (OFC) protocol has been developed to prevent packet losses at switch sides caused by packet contentions. The extended OpenFlow (OF) protocol of SDN is deployed as well in support of the optical switching characteristics. Based on the collected resource topology of data plane, the optical network slices can be dynamically provisioned and automatically reconfigured by the SDN control plane. Meanwhile, experimental results validate that the priority assignment of application flows supplies dynamic QoS performance to various slices running applications with specific requirements in terms of packet loss and transmission latency. In addition, the capability of exposing traffic statistics information of data plane to SDN control plane enables the implementation of load balancing algorithms further improving the network performance with high QoS. No packet loss and less than 4.8 µs server-to-server latency can be guaranteed for the sliced network with highest priority at a load of 0.5. This work is supported by Olympics project (ESTAR17207) and Metro-Haul project (G.A. 761727).

This paper investigates basic trade-offs between energy and delay in wireless communication systems using finite blocklength theory. We first assume that data arrive in constant stream of bits, which are put into packets and transmitted over a communications link. Our results show that depending on exactly how energy is measured, in general energy depends on $\sqrt {d^{-1}}$ or $\sqrt {d^{-1}\log {d}}$ , where $d$ is the delay. This means that the energy decreases quite slowly with increasing delay. Furthermore, to approach the absolute minimum of −1.59 dB on energy, bandwidth has to increase very rapidly, much more than what is predicted by infinite blocklength theory. We then consider the scenario when data arrive stochastically in packets and can be queued. We devise a scheduling algorithm based on finite blocklength theory and develop bounds for the energy-delay performance. Our results again show that the energy decreases quite slowly with increasing delay.

The accurate measurement of electromagnetic exposure and its application is expected to become more and more important in future wireless communication systems, given the explosion in both the number of wireless devices and equipment radiating electromagnetic fields (EMF) and the growing concerns in the general public linked to it. Indeed, the next generation of wireless systems aims at providing a higher data rate, better quality of service, and lower latency to users by increasing the number of access points, i.e., densification, which in turn will increase EMF exposure. Similarly, the multiplication of future connected devices, e.g., Internet of things devices, will also contribute to an increase in EMF exposure. This paper provides a detailed survey relating to the potential health hazards linked with EMF exposure and the different metrics that are currently used for evaluating, limiting, and mitigating the effects of this type of exposure on the general public. This paper also reviews the possible impacts of new wireless technologies on EMF exposure and proposes some novel research directions for updating the EMF exposure evaluation framework and addressing these impacts in future wireless communication systems. For instance, the impact of mmWave or massive multiple-input multiple-output/beamforming on EMF exposure has yet to be fully understood and included in the exposure evaluation framework.

Achieving ultra-high reliability for short packets is a core challenge for future wireless communication systems, as current systems are designed only to transmit long packets based on classical information-theoretic principles. To tackle this challenge, this letter relies on multi-hop unmanned aerial vehicle (UAV) relay links to deliver short ultra-reliable and low-latency (URLLC) instruction packets between ground Internet of Things (IoT) devices. To accomplish this task, we perform non-linear optimization to minimize the overall decoding error probability in order to find the optimal values of the distance and the blocklength. In this vein, a novel, semi-empirical based non-iterative algorithm is proposed to solve the quasi-optimization problem. The algorithm executes in quasilinear time and converges to a globally optimal/sub-optimal solution based on the chosen parameters. Simulation results demonstrate that our algorithm allows operation under the ultra-reliable regime (URR), and yields the same performance as exhaustive search algorithms.

Spectrum sensing, which helps to resolve the coexistence issue and optimize spectrum efficiency, plays an important role in future wireless communication systems. However, the upcoming 5G communication involves diversified scenarios with different characteristics and diverse requirements. This tendency makes it difficult for spectrum sensing methods to flexibly serve various applications while maintaining satisfactory performance. Motivated by such a challenge, this article combines the reinforcement learning concept with spectrum sensing technique, seeking a feasible way to adaptively deploy spectrum sensing configurations so as to optimize system performance under multifarious scenarios in 5G communications. In this article, we first categorize several major optimization targets for spectrum sensing in future communications. Then we elaborate the full details of the proposed sensing technique. Three dedicated modes with respective optimization objectives are designed thereafter. Numerical results manifest that the proposed sensing technique has the capability of adapting to various scenarios, which is appealing in practice.

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Wireless communications play a central role in our modern connected lives; at the same time, they constitute a very broad and deep area of research. The elements that make wireless communications possible are a transmitter, which sends information through electromagnetic waves; a medium that is able to transport these waves; and, finally, a receiver, which extracts the information from the-usually very small-amount of energy it is able to collect from the medium.

A wideband folded reflectarray antenna (FRA) based on single-layered polarization rotating metasurface (PRM) is proposed. The FRA is composed of a wideband polarization grid (PG), a wideband PRM and a wideband circular waveguide as the primary source. First, a wideband polarization rotating unit cell consisting of rhombus-shaped metal patch etched on dielectric substrate is designed, which can be used to rotate polarization of the reflective wave 90° relative to that of the incident wave. The element and its mirror image can provide 0°, 90°, 180° and 270° phase shifts with 2-bit phase quantization and relatively higher polarization conversion rates in the Ku band. Due to the introduction of PG and PRM, the distance between the PG surface and the feed phase center can be reduced to about 1/2 of the distance between the imaginary feed and PRM reflectarray. Finally, a wideband FRA consisting of 315 elements with circular aperture is designed, fabricated and measured. The measured results indicate that the proposed antenna achieves 39.5% 3-dB gain bandwidth with 25.5 dBi peak gain at 15 GHz. Its maximum aperture efficiency is about 40%. Low-profile and wideband features of the FRA make it be a candidate in the wireless communication systems.

The Orbital Angular Momentum (OAM) wireless communication technology has received much attention in recent years for its natural orthogonality between different OAM states. Combining the OAM technology with the Orthogonal Frequency Division Multiplexing (OFDM) technology, we proposed a new OAM-OFDM wireless communication system to explore a new approach for enhancing the transmission capacity of the wireless communication system. Atmospheric turbulence is an important factor for influencing the capacity of the OAM-OFDM wireless communication system. In consideration of the effect of the atmospheric turbulence, we derived a crosstalk model of the proposed OAM-OFDM wireless communication system. Furthermore, a capacity model of the OAM-OFDM wireless communication system is proposed in consideration of the effect of atmospheric turbulence on both the OAM and OFDM signals. Compared with the conventional OAM wireless communication system, the capacity performance of the proposed OAM-OFDM wireless communication system is significantly improved and the average improvement is 751%.

The demand for mobile data is likely to grow at a pace more than envisaged in the coming years. Further, as applications such as the Internet of Things (IoT) come to fruition, there will be increased diversity in the types of devices demanding Internet connectivity and their requirements. Significant increase in data rate requirements is also expected due to services such as Ultra High Definition (UHD) video streaming and cloud computing. To meet all these demands, physical layer waveform candidates for future generations of communications need to be robust and inherently capable of extending into multiple domains (space, time, frequency, users, transmission media, code etc.) to ensure efficient utilization of resources. Multiple domains can be innately integrated into the design process of modulation schemes by using tensors, which are multi-way arrays. This paper introduces a unified tensor framework, providing a foundation for multi-domain communication systems that can be used to represent, design and analyse schemes that span several domains. Transmitted signals are represented by $N$ th order time function tensors which are coupled, using a system tensor of order $N+M$ , with the received signals which are represented by another tensor of order $M$ through the contracted convolution. We begin with the continuous time representation of the tensor system model and present both the strict multi-domain generalization of the Nyquist criterion for zero interference (inter-tensor and intra-tensor interference) as well as a relaxation. We present an equivalent discrete time system model, and as an example of using the tensor framework we derive tensor based linear equalization methods to combat multi-domain interference. An application to multi-user MIMO-GFDM illustrates the utility of this novel framework for derivation of joint domain signal processing techniques.

With the expected increase in data traffic (e.g., video) and in the user devices generating new traffic (e.g., device-to-device communication, Internet of Things, etc.), the evolution of next-generation mobile networks (e.g., 5G networks) has gone towards heterogeneous deployments where multiple small cells coexist in the same area covered by a macro base station. To reduce the capital expenses in the network, a wireless mesh can be used, which is made of millimeter-wave links that route the data traffic of the mobile users inside the backhaul network. Such an increase in the number of deployed base stations inevitably increases the power consumption; hence, the operating expenses and the CO2 consumption also increase. To achieve greener mobile communications, sleep-mode strategies have been considered in order to switch off the unused network components. However, the switching on/off should be made according to the traffic demanded by the users and with the aim of guaranteeing the demanded service at any time. Given that the traffic demand and networking traffic fluctuate over time at each location, we propose a robust mixed integer linear problem that jointly solves the user association, the backhaul routing paths in the wireless mesh and the switching off of the unused links with the aim of minimizing the power consumption. The robust strategy is based on the $\Gamma $ -robust approach and is able to guarantee the user demand while taking into account its intrinsic variability. A thorough evaluation has been performed in order to analyze the impact of the robust strategy on the network performance.

The mechanism of the passive intermodulation (PIM) distortion caused by the loose contact in coaxial connectors is of great importance in wireless communication systems. This paper focuses on the effect of the additional impedance on PIM levels in coaxial connectors. First, the additional impedance and PIM levels of the loose contact coaxial connectors are measured. Then, the S-parameters and the additional impedance with three different loose contact cases are simulated. Finally, a modified coaxial connector with different values of conductive tapes is designed to verify the additional impedance impacts on the PIM level. It is shown that the increase of the additional impedance of the metal–metal loose contact will lead to the deterioration of PIM levels in the coaxial connector.

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

We propose a novel positioning-communication integrated signal, which superposes the configurable positioning signal on the communication one to achieve a sub-meter range measurement accuracy. Different from other positioning schemes, there are multi positioning signals on different sub-carriers for different positioning users. The powers and bandwidths of these positioning signals are controllable, which reduces the near-far effect, and improves the range measurement accuracy. Other major contributions are: we analyze the interference of the positioning signal to the communication one; we give the lower-bound and measurement accuracy of the range estimation in both flat and fading channels, and derive their simple expressions. The results show the interaction between the communication and positioning signals is limited, and it is feasible to use the proposed signal for high accuracy positioning.

This article gives us the unmanned aircraft guide parking solution. we can only use UWB devices and drones to realize the complex cooperation between cars, park, wireless communication system, let it become easy to set up

Recently, there has been quite a bit of discussion about the safety of newer 5G wireless communication systems [1]. It is not uncommon to find articles that compare RF safety standards developed by different organizations and accept the validity of each without comment [2] or dismiss the validity of a given standard by claiming a conflict of interest [3]. Given this, it is reasonable to ask about the legitimacy of the standards setting process. In regulating human RF exposure, most countries in the world refer to standards generated by either the International Committee on Electromagnetic Safety (IEEE/ICES) and its Committee on Man and Radiation (COMAR) or the International Commission on Nonionizing Radiation (ICNIRP). Hence, it is reasonable to discuss the processes by which these bodies arrive at their standards or guidelines for human exposure to RF electromagnetic fields. That is the purpose of this document. Prior to equating the validity of any alternative standard to those of COMAR or ICNIRP, a similar analysis of the alternative should be done. One example of such an analysis is presented in [4].

This letter presents a compact dual-polarized over-the-air testing antenna with low radar cross section (RCS) for the fifth-generation and emerging wireless communication systems. The proposed antenna design is achieved by slotting two orthogonal Vivaldi antennas in a cross-shaped form into a two-part three-dimensional printed radome and loading microwave-absorbing materials (MAMs) at the antenna's outer edges. The proposed antenna has a rocket-nest shape with a diameter of 63.4 and 113.68 mm length. The −10 dB impedance bandwidth ( S 11) is obtained from a range of 2.1 up to 6 GHz. The two-part radome is formed by polylactic acid and acrylonitrile butadiene styrene dielectric materials, respectively. Their respective dielectric constants are approximately 2.6 and 4.5 within the −10 dB impedance bandwidth. The MAMs geometry and distribution location are optimized to suppress induced current over the antenna. An antenna prototype has been fabricated and measured. The measured results agree reasonably well with the simulated results. The results show that the use of the two-part radome enables the achievement of low RCS with compact form factor. Furthermore, a low bistatic RCS of between 2 and 6 GHz is observed in simulation for angular ranges of ${{\boldsymbol \theta }} \in [ { - {\text{30}^\circ }, + {\text{30}^\circ }} ]$ and $\boldsymbol{\Phi } \in [ { - {\text{90}^\circ }, + {\text{90}^\circ }} ]$ .

Future wireless communication networks tend to be intelligentized to accomplish the missions that cannot be preprogrammed. In the new intelligent communication systems, optimizing the network performance has become a challenge due to the ever-increasing complexity of the network environment. New theories and technologies for intelligent wireless communications have obtained widespread attention, among which deep reinforcement learning (DRL) is an excellent machine learning technology. DRL has great potential in enhancing the intelligence of wireless communication systems while overcoming the above challenge. This paper presents a review on applications of DRL in intelligent wireless communications with focuses on millimeter wave (mmWave), intelligent caching and unmanned aerial vehicle (UAV) scenarios. We first introduce the concepts and basic principles of single/multi-agent DRL techniques. Then, we review the related works where DRL algorithms are used to address emerging issues in wireless communications. These issues include mmWave communication, intelligent caching, UAV aided communication, and handover/access control in HetNets. Finally, critical challenges and future research directions of applying DRL in intelligent wireless communications are outlined.

Power amplifiers (PAs) will receive significant attention in the 5G era because of increasing wireless communication requirements. The development trends of PAs with broader bandwidth, higher efficiency, and higher power using conventional concepts are no longer the primary focus of PA technologies for 5G applications. The PA is not a stand-alone device but rather a closely related part of the wireless communication system (WCS). Here, we analyze PA design technology over the last few decades and look at possible future requirements for 5G applications, the characteristics of these PAs for 5G applications, and possible future applications of 5G PA technologies.

To support different standards simultaneously within a wireless communication system, research on dual-/multi-band components has been conducted extensively. However, the operating frequencies of existing works are usually fixed resulting in a low flexibility. To solve this problem, a highly reconfigurable coupler whose two operating frequencies can be controlled independently is proposed for the first time in this paper. Based on the analysis of a basic configuration, the conditions for realizing the desired independent frequency tuning can be obtained. To realize this unique property, varactors loaded coupled line sections are introduced on a conventional branch line coupler. Owing to the symmetrical structure of the proposed coupler, explicit theoretical analysis can be conducted. For demonstration, two reconfigurable couplers are designed, fabricated, and measured. The first coupler can provide frequency tunability from 3.4 to 4.2 GHz at the upper band with the lower band fixed at 2.4 GHz. The other one can not only provide a tunable frequency from 1.3 to 1.6 GHz at the lower band with the higher band fixed at 3.4 GHz, but also give a tunable higher band from 2.9 to 3.4 GHz with the lower band fixed at 1.55 GHz. The measured results agree well with the simulated results, validating the proposed design methodologies.

The birth of wireless communication systems nearly 1 century ago has transformed and redefined the way humans communicate and interact. This transformation, which has opened boundaries between societies and eliminated cultural barriers, has evolved from the original paradigm of wireless electromagnetic communication systems. This paradigm has experienced numerous evolutionary developments that have not only brought along seamless connectivity for human interactions but also communication between machines and devices.