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.

In this study, bit error rate (BER) performance of multiple input multiple output (MIMO) systems employing transmit antenna selection with maximal ratio combining (TAS/MRC) and orthogonal space time block codes (OSTBC) is analysed and compared. Analysis has been done for several modulation schemes in equicorrelated Rayleigh fading channels. Novel infinite series expressions for BER of TAS/MRC are proposed in this work. The authors observe that the existing literature on performance analysis of TAS/MRC in correlated channels implicitly or explicitly assume no correlation on the transmitter side. In this work the authors overcome this shortcoming. An alternate closed‐form expression for BER performance of OSTBC MIMO systems is derived. This closed‐form expression is computationally efficient than existing expressions. Monte Carlo simulations were performed to validate the analytical results. It has been observed that TAS/MRC outperforms OSTBC in terms of BER performance in equicorrelated Rayleigh fading channel. As a case study, performance comparison of cognitive radio (CR) links employing OSTBC and TAS/MRC MIMO systems is investigated in order to show the usefulness of the present analytical study. Even though TAS is the optimum transmit antenna technique in terms of BER performance, OSTBC seems to be a promising alternative for more realistic scenarios in CR systems.