Reconfigurable intelligent surface (RIS)-aided communication is considered as an exciting research topic in academic and industrial communities since it provides an emerging affordable solution to achieve high quality and secure next-generation wireless systems. Especially, the deployment of RIS in multi-user wireless networks promises to reduce system hardware costs, signal processing complexity, as well as energy consumption due to small size, lightweight and ability to actively shape the wireless propagation environment. Further, by realizing a cost-effective radio environment, RIS-aided communication can be implemented to be an appealing technology for future integration with other emerging wireless applications and communication systems. Despite the positive appeal, RISs face new challenges that hinder integrating efficiently into wireless networks, such as network secrecy performance and system sum-rates, as well as achieving efficient deployment design in highly dynamic and time-varying wireless environments. To this end, we overview recent state-of-the-art techniques to address the above issues faced in the integration of RISs with various emerging multi-user communication techniques, such as Unmanned Aerial Vehicles (UAVs), Non-Orthogonal Multiple Access (NOMA), Millimeter Wave (mmWave) and Terahertz (THz) communications, Physical Layer Security (PLS), massive antennas, and Simultaneous Wireless Information and Power Transfer (SWIPT). Finally, we highlight promising future research directions of RIS-aided communication in Cell-Free Massive Multiple-Input-Multiple-Output (MIMO) systems, Rate-Splitting Multiple Access (RSMA), Light Fidelity (LiFi), and Cognitive Radio (CR) systems.

With the introduction of wireless communications in a diverse range of security-sensitive scenarios such as healthcare, Smart Cities, internet-of-things (IoT) infrastructure, nuclear power plants, so forth, it has become necessary to protect the wireless network against malicious eavesdroppers via physical layer security (PLS). We analyze and study the impact of an eavesdropper located in an underlay cooperative cognitive radio network (CRN). A reconfigurable intelligent surface is used to improve the secrecy outage probability of the proposed system. CRs resolve spectrum scarcity by enabling spectrum sharing. On the other hand, RIS is a planar surface device equipped with signal enhancing reflecting elements that enhance signals at desired users and suppress signal power at undesired eavesdroppers in PLS networks. Therefore, the integration of RIS in cooperative underlay CR networks can enable secure wireless communications. To this end, we derive closed-form secrecy outage probability (SOP) expressions for a network that consists of a primary destination, secondary source, secondary user and a passive eavesdropper. The obtained equations are verified via simulation.

In this article, we investigate the design of reconfigurable intelligent surface (RIS)-aided transmission as a smart method to reflect signals received from access points to users and, hence, improving users’ performance. To implement smart Internet of Things (IoT) networks, massive connectivity and low-cost deployment are essential in designing such systems. In particular, we consider two practical scenarios (dual-hop and single-hop transmissions). These scenarios highlight the potential of RIS in enhancing the system’s outage probability performance. Furthermore, to characterize channel conditions in practice, we pay particular attention to two-channel distributions that are non-central chi-square (NCCS) distributions that approximate the channel distribution of the RIS-aided wireless system and the squared $K_G$ distribution. In addition, the RIS-aided system may face imperfect hardware-related issues in practice. Therefore, we need to consider the degraded performance of practical RIS-aided systems by considering the detrimental impact of in-phase and quadrature-phase imbalance (IQI). To characterize the main system performance metric, we provide closed-form formulas of outage probability and ergodic capacity. We then evaluate system performance under the impacts of signal-to-noise ratio (SNR), the number of meta-surfaces, and channel parameters. All closed-form outage expressions are validated via Monte Carlo simulations. Simulation results indicate that the considered RIS scheme at dual-hop and single hop under the impact of IQI and RIS hardware impairment achieves significant improvements in terms of outage probability at high SNR and high meta-surface number N. Additionally, the simulation results demonstrate that the impact of IQI on the proposed system is limited. It is worth noting that, in terms of ergodic capacity, ergodic capacity faces an upper limit. Despite this limitation, the proposed system can still work well once some parameters are controlled well, such as the transmit SNR, levels of IQI, and the number of RIS components.

This paper designs an experimental scheme to monitor the tool wear state by extracting the vibration signal of tool wear. The data acquisition and signal processing hardware includes a T-type cutting tool, a vibration sensor, an amplifier, a data acquisition card, and a computer. In the time domain, the vibration signal is analyzed by statistical analysis method, and it is concluded that the variance of vibration signal of X-axis wear is positively correlated with the degree of tool wear. Moreover, the vibration signal is converted from time domain to frequency domain by Fourier transform, and the characteristic frequency bands of vibration signal are 2–4 kHz and 7–9 kHz in frequency domain. In addition, in time-frequency domain, the vibration signal is decomposed by wavelet packet decomposition technology, and the energy statistics of the decomposed frequency band is carried out. It is further judged that the energy percentage of 2.5–3.75 kHz and 7.5–8.25 kHz is closely related to tool wear, so the energy percentage of the two characteristic frequency bands is selected as the characteristic value of tool wear monitoring.

Renewable energy is one of the critical solutions to address the ever-increasing demand for energy. In developing countries such as Zimbabwe where the conventional generation hardly sustains half of the nation’s energy demands, renewable energy solutions are compensating for the deficit. Among these renewables, solar energy technologies have witnessed rapid growth. In most cases, solar energy installers assume to have all the knowledge required in the field. However, many technical barriers still exist within the field of solar energy systems. For solar energy systems which are synchronized to the grid, the integration of these renewables pose a serious stability and protection threat to the already unstable and even stable grids. In this paper, some of the technical problems being faced are discussed. Policy issues as well as the possible solutions needed in order to realize full, unhindered growth of solar energy are addressed.

Since WBAN has limited bandwidth, its performance in the industrial, scientific, and medical (ISM) band degrades as the number of active devices sharing the same spectrum increases. The increasing device density challenges device and packet synchronization mechanism that raise collision probabilities during carrier sense. In this view, access to the transmission channel for health care applications with WBAN coexistence is limited, and the transmission of aperiodic data becomes unreliable. Therefore, in this article, we propose WBAN performance improvement through adaptive channel access mechanisms. We propose device synchronization, dynamic backoff and channel access mechanism (CCA) in stationary and mobile networks. We implement the proposed mechanism using carrier sense multiple access with collision avoidance (CSMA-CA) for multiple WBAN scheme in IEEE 802.15.4 wireless standard and analyze its end to end delay performance. Moreover, we analyze the effect of the different beacon (BO) and superframe (SO) order for device synchronization in multiple existence cases. The implementation of the proposed mechanism outperforms the conventional IEEE 802.15.4 and the transmission scheme applied in Traffic Class Prioritization Medium Access Control (TCP-MAC) protocols. Simulation results show the average delay of the proposed protocol decreased by 67% and 56.8% at a WBAN speed of 0.5m/s and by 54.1% and 26.31% at a WBAN speed of 1m/s when compared to the standard protocol and the TCP-MAC, respectively.