Simultaneous transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) have recently gained a great deal of attention due to their ability of providing full-space service coverage. In this paper, a novel concept called irregular STAR-RIS is proposed with a small portion of activated transmitting and reflecting elements, where users in opposite sides of the surface are served simultaneously. In this proposed system, a tabu search-based sparse deployment and neighbor extraction-based cross-entropy method for the beamforming optimization of the proposed irregular STAR-RIS are considered. For the sake of fair comparison and to highlight the achievable gains, the weighted sum-rate (WSR) performance of a regular STAR-RIS-aided wireless system and a traditional system without STAR-RIS is also evaluated. The results show that the proposed irregular STAR-RIS with a small portion of active elements is capable of significantly improving the WSR performance compared to the conventional systems without STAR-RIS. It is also shown that the position of the users has an impact on the WSR performance, and that the near users have better performance than the far ones.

With the continuous integration of wireless communication and intelligent information Technologies, the Internet of Vehicles (IoV) technology has been widely used in Intelligent Transportation Systems (ITS), which has greatly promoted the development of society in the direction of intelligence and information technology. Unfortunately, it is still facing the challenges of spectrum scarcity, ultra-low latency, large-scale connectivity and secure transmission. To this end, we study the covertness performance of multi-antenna assisted ambient backscatter communication (AmBC) Symbiotic ITS. To improve energy efficiency and reduce interference, the optimal antenna of the radio frequency (RF) source is selected to send covert information to covert receiving vehicle via both direct and reflected links with the help of public vehicle, while a monitor vehicle nearby the RF source covertly detects the potential communication behavior between the RF source and covert receiving vehicle. In addition, the RF source transmits a random power signals to interfere with the monitor vehicle’s detection. Specifically, the analytical expressions for the optimal detection threshold and the detection error probability (DEP) of the monitor vehicle are first derived, and then, the closed-form solutions for the outage probability (OP) of the covert receiving vehicle and public vehicle are computed. Then, an optimization scheme based on the maximize effective covert rate (ECR) under covertness and reliability constraints is proposed. Furthermore, the progressivity of OP at high signal-to-noise ratio (SNR) is investigated. The simulation results verify the analysis and prove that: i) the monitor vehicle’s detection performance can be reduced by lowering the power allocated to covert receiving vehicle within a certain range; ii) the OP of covert receiving vehicle is enhanced with the number of antennas; iii) as the RF source’s maximum transmit power increases, the ECR of the considered system increases and converges to a constant; iv) the multi-antenna selection scheme can significantly improve the covertness performance of the considered system.

Smart cities intelligently control the functionalities of the city through the use of various electronic methods, sensors, and advanced communication techniques. An intelligent transport system (ITS) is the backbone of smart cities and refers to a system in which numerous vehicles utilize a communication infrastructure to exchange vital information, such as traffic, congestion, and road conditions. One of the key elements of ITS is vehicle tracking or localization, which is the monitoring of a moving vehicle’s location using a Global Positioning System (GPS). Accurate vehicle localization is required because many safety and traffic management applications depend on the precise positioning of the vehicles. Intelligent reflecting surface (IRS) is a new technology that offers attractive features like improved performance gains, enhanced network coverage, and flexible deployment, and is considered a key enabler for the 6G-driven vehicle-to-everything (V2X) systems that provide a programmable wireless environment. In this paper, a comprehensive view of a 6G-driven vehicle localization mechanism utilizing IRS is provided. The work also lists the benefits of IRS-enabled sensing in 6G vehicular networks including enhanced security, overcoming blockages, and improved localization. A case study to highlight the advantages of the IRS in vehicle tracking is presented. Finally, we also present the research challenges and future work directions in IRS-enabled vehicle tracking.

Time-modulated arrays (TMAs) have been found useful to construct directional modulation (DM) transmitters, offering physical-layer security. Two issues, however, exist in conventional TMA DM, which are high power loss and generation of mirror harmonic frequency signals that may compromise wireless security. In this letter, we propose to construct DM transmitters using a high efficiency TMA. By carefully designing the time sequences of the selected phase shifters, the DM symbols modulated upon multicarrier can be synthesized with suppressed mirror harmonic frequencies. It is shown that the proposed TMA DM transmitters here enjoy feeding network efficiency of 100%, and the transmit DM symbols can be synthesized at a pre-selected frequency only, significantly enhancing security performance. The effectiveness of the proposed scheme is validated via bit error rate (BER) simulations. Meanwhile, The TMA DM also can be used as a potential technique for the integrated sensing and communication (ISAC).

This paper investigates covert communication in simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) assisted non-orthogonal multiple access (NOMA) systems, assuming for the sake of being more practical that the successive interference cancellation (SIC) is defective. To assess the covertness performance of the considered system, we first derive closed-form expressions for the detection error probability, the optimal detection threshold and the average minimum detection error probability of the warden, as well as the outage probability of the NOMA user pair. Then an optimization problem to maximize the effective covert rate (ECR) is proposed. According to the results of the simulation, it is possible to increase the maximum ECR of the considered system by varying the amount of components of the STAR-RIS.

In this paper, we study the outage and ergodic rate performance of a rate-splitting multiple access (RSMA)-based cognitive radio (CR) system, where the secondary transmitter aims to communicate with two RSMA users. Imperfect successive interference cancellation (ipSIC) and channel estimation errors (CEEs) are considered in the proposed analysis. Analytical expressions for the outage probability (OP) and the ergodic rate (ER) are calculated. For a deeper understanding, the asymptotic behavior of OP and ER at high signal-to-noise ratio (SNR) regimes are carried out. Illustrative simulation results are presented and reveal that: i) The OP decreases and the ER gradually increases with the increase of SNR, and eventually approaching a constant; ii) ipSIC and CEEs have a negative impact on the considered system; iii) The outage and ergodic rate performance of RSMA-based CR network outperforms CRNOMA network due to flexible power allocation between common and private messages; iv) The OP first decreases and then increases with the power allocated to the common message, and there exists an optimal power allocation factor to ensure the reliable performance.

A document by Taissir Elganimi . Click on the document to view its contents.

Low power consumption and high spectrum efficiency as the great challenges for multi-device access to Internet-of-Things (IoT) have put forward stringent requirements on the future intelligent network. Ambient backscatter communication (ABcom) is regarded as a promising technology to cope with the two challenges, where backscatter device (BD) can reflect ambient radio frequency (RF) signals without additional bandwidth. However, minimalist structural design of BD makes ABcom security vulnerable in wireless propagation environments. By virtue of this fact, this paper considers the physical layer security (PLS) of a wireless-powered ambient backscatter cooperative communication network threatened by an eavesdropper, where a BD with nonlinear energy harvesting model cooperates with decode-andforward (DF) relay for secure communication. The PLS performance is investigated by deriving the secrecy outage probability (SOP) and secure energy efficiency (SEE). Specifically, the closed-form and   asymptotic expressions of SOP are derived as well as the secrecy diversity order for the first time. As an energy-constrained device, balancing power consumption and security is major concern for BD, thus the SEE of the proposed network is studied. The results from numerical analysis show that the performance improvement of SOP and SEE is impacted by system parameters, including transmission power, secrecy rate threshold, reflection efficiency and distance between the source and BD, which provide guidance on balancing security and energy efficiency in ambient backscatter cooperative relay networks.  

In this paper, we consider an unmanned aerial vehicle (UAV)-enabled massive multiple-input multiple-out (MIMO) non-orthogonal multiple access (NOMA) full-duplex (FD) two-way relay (TWR) system with low-resolution analog-to-digital converters/digital-to-analog converters (ADCs/DACs) architecture. Minimum mean-square error (MMSE) channel estimator and maximum ratio combining/maximum ratio transmission (MRC/MRT) at the UAV are utilized to obtain the UAV-GUs channel state information (CSI) and process the signals of multi-pair ground user (GUs), respectively. By adopting the additive quantization noise model (AQNM), the approximate sum spectrum/energy efficiency (SE/EE) with imperfect CSI and imperfect successive interference cancellation (SIC) are derived. To evaluate the effects of the parameters on system performance, the asymptotic analysis is presented. Then, the power scaling laws are provided to characterize the asymptotic performance. The numerical results verify the accuracy of theoretical analysis and show that the interference and noise can be effectively eliminated by deploying large-scale antennas, lager Rician factors, and applying proper power scaling law. We also find that the proposed system can obtain better SE performance by adjusting the height of the UAV. Moreover, the performance of the proposed system is related to the ADCs/DACs quantization bits, where the SE saturate values increase with the increasing number of quantization bits, while the EE first increases and then decreases. Finally, the SE/EE trade-off of this low-resolution ADC/DAC quantized system can be achieved by choosing the appropriate number of quantized bits, and the trade-off region grows as Rician factor increases.

This paper investigates the performance of non-orthogonal multiple access (NOMA) based hybrid satellite-unmanned aerial vehicle (UAV) systems, where a low Earth orbit (LEO) satellite communicates with the ground users via a decode and forward (DF) UAV relay. We investigate a two NOMA users system, where a far user (FU) and a near user (NU) are served by the UAV which is located at a certain height above the origin of the coverage circle. The channel between satellite and UAV is assumed to follow a Shadowed-Rician fading and the channels between UAV and users are assumed to follow a Nakagami-m fading. New closed-form expressions of the outage probabilities for the two users and the system are derived. Different from other work in literature, we take into consideration different parameters affecting the total link budget. Additionally, we propose an algorithm for minimizing the system outage probability. The mathematical analysis is verified by extensive representative Monte-Carlo (MC) simulations. Finally, simulations are provided to demonstrate the impact of important parameters on the considered system as well as the superiority of the NOMA scheme the over reference scheme.

Non-orthogonal multiple access (NOMA) and ambient backscatter communication (AmBC) play major roles to enhance spectrum efficiency in wireless communication systems. Besides, the AmBC provides good reinforcement for the current trend toward dispensing batteries for battery-free Internet-of-Things (IoT) devices. In this paper, we propose a symbiotic battery-free IoT system, that exploits the downlink transmission of a NOMA multiplexing enabled cellular network, to permit an IoT spectrum-efficient uplink communication. The IoT backscatter device (BD) performs a symbiotic radio (SR) relation with the cellular source to power its communication by intelligently reflecting the received power. We derive a closed-form expression of the ergodic capacity (EC) of the BD transmission and tight approximations of the ECs of the cellular source transmission, where all channels undergo Nakagami-m fading. Additionally, we validate the analytical results obtained using Monte-Carlo simulations. The influences of several system parameters such as power allocation factor, reflection coefficient, and channels’ severity factors have been investigated. Finally, the performance of the proposed system is compared with a benchmark OMA-based system to highlight the achievable performance improvement.

To meet the demands of massive connections, diverse quality of services (QoS), ultra-reliable and low latency in the future sixth-generation (6G) Internet-of-vehicle (IoV) communications, we propose non-orthogonal multiple access (NOMA)-enabled small-cell IoV network (SVNet). We aim to investigate the trade-off between system capacity and energy efficiency through a joint power optimization framework. In particular, we formulate a nonlinear multi-objective optimization problem under imperfect successive interference cancellation (SIC) detecting. Thus, the objective is to simultaneously maximize the sum-capacity and minimize the total transmit power of NOMA-enabled SVNet subject to individual IoV QoS, maximum transmit power and efficient signal detecting. To solve the nonlinear problem, we first exploit a weighted-sum method to handle the multi-objective optimization and then adopt a new iterative Sequential Quadratic Programming (SQP)-based approach to obtain the optimal solution. The proposed optimization framework is compared with Karush-Kuhn-Tucker (KKT)-based NOMA framework, average power NOMA framework, and conventional OMA framework. Monte Carlo simulation results unveil the validness of our derivations.