Mission-critical applications in underwater communication need to handle data transfer with high reliability and low latency. Moreover, coverage of a large number of underwater sensors gains significance in harsh aquatic environments. These goals can be fulfilled by deploying simultaneously transmitting and reflecting optical reconfigurable intelligent surface (STAR-ORIS), which can enhance the coverage, reliability, and security. However, data broadcasting in underwater optical wireless communication (UOWC) by deploying STAR-ORIS remains a concern since optical signals are highly directional. Hence, we propose a multiple STAR-ORIS aided UOWC system, for which we perform design of a STAR-ORIS prototype and conduct experimental validation of the broadcasting system in terms of bit error rate (BER). The experimental results reveal that the proposed system requires only half or less than half of the transmit power to achieve the same BER performance as that of a single STAR-ORIS-aided UOWC system.

This article proposes a multiple simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) aided underwater optical wireless communication (UOWC) system, where the STAR-RISs can transmit and reflect data simultaneously in two modes of operation: 1) energy splitting (ES) and 2) mode switching (MS). Such a system enables us to broadcast data and enhance the coverage at reduced error rates even for moderate turbulence in UOWC systems. The phase shifts of the multiple STAR-RISs are intricately coupled, for which the optimization problem is formulated for both ES and MS modes, and solved by particle swarm optimization (PSO) and differential evolution (DE) techniques. It is demonstrated that PSO can obtain more sum-rate as compared to DE. Hence, the phase shift values obtained from PSO are utilized to validate the ensuing performance evaluation in terms of average bit error rate (ABER) and channel capacity, for which tractable expressions are derived in terms of bivariate Fox-H function. Further, outage probability expressions are derived in terms of Meijer-G function. Finally, the ABER results reveal that our proposed system can generate a minimum signal-to-noise ratio (SNR) gain of 5 dB over a conventional single RIS system.

This work amalgamates spatial modulation (SM) with ambient backscattering (ABSc) to address the spectral and energy efficiency demands of the power constrained device-to-device (D2D) communications in the Internet-of-things. Though incorporating reconfigurable intelligent surfaces (RISs) in the communication process can help in extending the coverage of such power constrained devices, rich scattering in the operation environment, or broken links between the nodes involved in the end-to-end communication, can adversely affect the system performance. To cope up with this challenge, a selection-based cooperative RIS protocol is proposed, and the performance of the D2D communication system, founded on SM and ABSc at the transmitter and cooperative RISs, is evaluated in terms of the bit error rate, outage probability, and energy efficiency. A link budget analysis is conducted to comprehend the effects of the RIS sizes in countering the path loss effects, and the imperfection of the channel estimation and timing synchronization of multiple RISs are also analyzed. The results reveal that the proposed communication model with cooperative RISs can overcome the path loss effects and enhance the received power levels, thereby outperforming the baseline system where a single RIS intervenes in the end-to-end communication, with a signal-to-noise ratio gain of around 10 dB for the bit error rate, outage probability, and energy efficiency. Considering different prominent SM techniques for the system operation and comparing the performance in different set-ups, it is shown that the system implementing generalized SM performs the best.

Keeping in mind the device size and power constraints of future wireless devices, transmitters free of radio frequency chains need to be designed using reconfigurable intelligent surfaces (RIS) as modulators. In this context, spatial modulation (SM) can be applied to selectively activate the desired RIS elements for fulfilling spectral- and energy-efficient communications with low error rates. In this paper, we deploy a RIS as a modulator and propose SM and generalized SM (GSM) based on irregular activation of the RIS elements, where the elements are activated with different probabilities. This can be further combined with element selection, where channel conditions are considered for element activation. It is shown that element selection based on channel conditions in conjunction with irregularly activated SM schemes perform better than conventional SM and GSM schemes in terms of error rates and energy efficiency while maintaining an acceptable signalling overhead and computational complexity.

In future wireless networks, device-to-device (D2D) communications are expected to play an important role to support a plethora of applications. To meet the target quality of service while ensuring high reliability, and high spectral and energy efficiencies, manipulation of the radio waves by reconfigurable intelligent surfaces (RIS) will be critical. In this context, leveraging concepts of polarization, this paper proposes a framework for bidirectional D2D communications, where the data exchange between a central node and devices operating in distinct polarization states, is multiple-input multiple-output in nature and takes place via a dual-polarized RIS, in the presence of hardware impairments and imperfect interference cancellation, as well as impairments caused by the spatial correlation and cross-polarization. Performance evaluation of such a framework is conducted in terms of key metrics, namely, bit error rate, outage probability, channel capacity, and energy efficiency, for which closed-form expressions are obtained considering transmissions over Nakagami fading channels. An asymptotic analysis is also conducted to evaluate the achievable diversity gains, by approximating the Nakagami model with a tractable Gamma model. Further, the impact of imperfect channel estimation on performance is also investigated. Comparative numerical results are provided, and the effects of the main system parameters on performance are analyzed. The proposed framework is shown to provide significant performance improvements as compared to D2D communications via non-polarized RIS.

Thanks to their capability in controlling the wireless channels in a dynamic way, metamaterial-based reconfigurable intelligent surfaces (RIS) can help in providing low error rates and high data rates, as per the requirements of future wireless applications. In many of the envisioned applications, devices need to interchange data within close proximity. In this context, this paper proposes a RIS-assisted full-duplex MIMO bidirectional model for communication between multiple devices, and analyzes its performance while considering a realistic model for the communication channels, which accounts for key physical charac-teristics and impairments. The system performance is evaluated in terms of the symbol error probability, outage probability, and channel capacity, for which closed-form expressions are derived while taking into account residual hardware impairments and residual self-interference at the devices, and considering operations in both indoor and outdoor environments. The results reveal that system operations in indoor environments yield better performance as compared to outdoor scenarios, and quantify the impacts of the hardware impairments and self-interferences.

We consider an ultra-reliable low-latency system in which a reconfigurable intelligent surface (RIS) is deployed to assist the simultaneous wireless information and power transfer between the access point and multiple devices. The data transmission, in the form of short packets, is performed using the rate splitting mechanism with chase-combining hybrid automatic repeat request error control. Using a realistic channel model and considering operation in the presence of hardware impairments at the RIS and the devices, the system performance is investigated in two folds. First, the average block error rate and the outage probability in the information transfer are evaluated. Then, the battery recharging time in the power transfer and its statistics are determined. Numerical results are provided to illustrate the system performance and quantify the impacts of key parameters including the packet size, the maximum number of packet retransmissions, and the RIS size.

This paper investigates the power coverage probability in cooperative wireless powered communication networks, where multiple access points collaborate to meet the energy demands of low-power devices. Based on the theory of Poisson-Delaunay triangulation, the probability density functions (PDF) of the Euclidean distance between the access points of the Poisson-Delaunay triangular cell and typical devices are derived. By using the theory of stochastic geometry and the obtained PDFs, the closed-form expressions of the wireless power coverage probability are obtained for three typical locations of the devices. As the wireless power coverage probability expressions involve the extended generalized multivariate MeijerG function (EGMMGF), a new implementation enabling numerical calculation of the EGMMGF is also proposed. The impacts of the main network parameters on the performance of the proposed framework are analyzed. In particular, comparative results show the significant gains that can be achieved in the wireless power coverage when multiple access points participate in the wireless power transfer or when the density of the network’s access points is increased, as compared to the non-cooperative scheme.

In wireless communications, reconfigurable intelligent surfaces (RIS) are emerging as a promising technology that is made possible by the advent of software controlled metamaterial sheets for controlling the wireless channels dynamically. In future applications, IoT devices will have small sizes and limited power supply. To make these devices spectrally and energy efficient in accordance with the advanced 5G and 6G specifications, we propose ambient backscattering (ABSc) technique along with spatial modulation (SM) and space shift keying (SSK) for data transfer assisted with RIS. We also conduct a thorough performance analysis of these schemes in terms of outage probability, and bit error rate, validated by Monte-Carlo simulations, and provide comparative results that illustrate the merits of the proposed techniques. In particular, it is shown that RIS-empowered SM and SSK along with ABSc perform much better than conventional communications.

In this paper, spectral efficiency of free-space optical (FSO) communication is enhanced by the utilization of advanced schemes of optical spatial modulation (OSM). Optical generalized spatial modulation (OGSM), optical enhanced spatial modulation (OESM), and optical improved quadrature spatial modulation (OIQSM) are proposed for performance improvement of FSO systems over Gamma-Gamma (G-G) channel incorporating pointing errors and path loss effect. These methods are investigated in terms of bit error rate (BER) and the analytical BER upper bound results are corroborated by Monte Carlo simulations. Both spatial domain and symbol domain errors are considered while calculating BER upper bounds. The specifications required to implement the schemes are also presented. The proposed methods offer benefits of reduced cost and power consumption, and BER performance improvement over OSM for higher spectral efficiencies. The upper bounds of BER are tight for all values of transmit power for various configurations of the proposed schemes.

Underwater optical wireless communication (UOWC) is an alternative to the existing acoustic and radio frequency (RF) underwater communication. In this paper, advanced schemes of UOWC like transmit laser selection (TLS) and TLS combined with optical spatial modulation (TLS-OSM) are proposed for weak oceanic turbulence based UOWC cooperative communication, which can enhance the performance of conventional UOWC communication. The performance is analyzed in terms of average symbol error probability (ASEP) and corroborated by Monte Carlo simulations. It is observed that TLS can achieve a signal to noise ratio (SNR) gain of at least 2 dB over the existing methods while TLS-OSM achieves a SNR gain of at least 3 dB over TLS scheme at any ASEP value of more than 10-2, thereby validating the efficiency of our schemes.

In this paper, performance analysis of a relay based hybrid free space optical and radio frequency (FSO/RF) communication system is achieved by calculating outage probability. Some advanced concepts like hybrid spatial modulation (HSM), transmit source selection (TSS) and HSM along with TSS for such hybrid systems are proposed for the first time. These cooperative systems employ decode and forward (DF) scheme at the relay. The performance of these schemes are compared with the existing ones analytically and validated by means of Monte Carlo simulations. The FSO channel model incorporates pointing errors for outdoor scenarios. The system performance is influenced by various parameters which is explored extensively in this paper.

In this study, advanced multiple‐input multiple‐output (MIMO) techniques for body‐to‐body (B2B) sensor‐based communication for sporting activities like running and cycling under different scenarios have been proposed. Enhanced spatial modulation and spatial media‐based modulation have been investigated for efficient MIMO‐based B2B communication. Special sensors have been proposed to deploy such techniques. Lognormal (LN) mixture model has been used because it can address the shadowing effects in B2B communication for such activities. Since LN mixture cannot yield closed‐form expressions, it has been approximated using mixture of gamma (MG) distribution to achieve closed‐form expressions for bit error rate (BER) in MIMO‐based B2B communication for the first time. The system performance for the proposed methods has been analysed in terms of BER and theoretical upper bound expressions using MG distribution have been verified by Monte Carlo simulations.