In this paper, we present a novel communication system model that integrates reconfigurable intelligent surfaces (RIS), spatial shift keying (SSK), and code index modulation (CIM) based on Hadamard coding called RIS based transmit SSK-CIM (RIS-CIM-TSSK). By leveraging RIS, the system adapts rapidly to dynamic environments, enhancing error rates and overall reliability. SSK facilitates the transmission of additional passive information while eliminating the need for multiple radio frequency (RF) chains, thereby reducing complexity. CIM enhances passive information transmission through frequency domain spreading, which may increase signal obfuscation. This proposed scheme not only improves energy efficiency but also offers a robust solution for reliable communication in modern wireless networks, paving the way for smarter and more adaptable implementations. We consider a suboptimal, low-complexity detector for the proposed scheme and also address the blind case for phase adjustment of the RIS. Finally, we present the simulation results for the proposed system model across various configurations, including different numbers of receive and transmit antennas, varying reflecting elements of the RIS, and different code lengths.

This paper proposes the orthogonal time frequency space-based code index modulation (OTFS-CIM) scheme, a novel wireless communication system that combines OTFS modulation, which enhances error performance in high-mobility Rayleigh channels, with CIM technique, which improves spectral and energy efficiency, within a single-input multiple-output (SIMO) architecture. The proposed system is evaluated through Monte Carlo simulations for various system parameters. Results show that increasing the modulation order degrades performance, while more receive antennas enhance it. Comparative analyses of error performance, throughput, spectral efficiency, and energy saving demonstrate that OTFS-CIM outperforms traditional OTFS and OTFS-based spatial modulation (OTFS-SM) systems. Also, the proposed OTFS-CIM system outperforms benchmark systems in many performance metrics under high-mobility scenarios, making it a strong candidate for sixth generation (6G) and beyond.

This paper proposes a new orthogonal time frequency space (OTFS)-based index modulation system called OTFS-aided media-based modulation (MBM) scheme (OTFS-MBM), which is a promising technique for high-mobility wireless communication systems. The OTFS technique transforms information into the delay-Doppler domain, providing robustness against channel variations, while the MBM system utilizes controllable radio frequency (RF) mirrors to enhance spectral efficiency. The combination of these two techniques offers improved bit error rate (BER) performance compared to conventional OTFS and OTFS-based spatial modulation (OTFS-SM) systems. The proposed system is evaluated through Monte Carlo simulations over high-mobility Rayleigh channels for various system parameters. Comparative throughput, spectral efficiency, and energy efficiency analyses are presented, and it is shown that OTFS-MBM outperforms traditional OTFS and OTFS-SM techniques. The proposed OTFS-MBM scheme stands out as a viable solution for sixth generation (6G) and next-generation wireless networks, enabling reliable communication in dynamic wireless environments.

This paper investigates the error performance of Reconfigurable Intelligent Surfaces (RIS) assisted communication systems employing two prominent space-time coding techniques, namely Space-Time Block Coding (STBC) and Space-Time Line Coding (STLC), under time-selective fading channels. The STBC (STLC) network comprises a single base station (BS) with two (one) transmit antenna(s) and a user equipment (UE) with one (two) receive antenna(s), respectively. A RIS with N elements facilitates communication between the BS and the UE, particularly in scenarios without Line-of-Sight (LOS) channels. Simulation results reveal that time-selective fading significantly degrades the error performance of space-time coding techniques. However, utilizing RIS in "Intelligent" mode mitigates these adverse effects by applying necessary phase shift adjustments, thereby improving system reliability in fast-fading environments. In contrast, in "Blind" mode, the results indicate that the RIS has a minimal impact on improving error performance under fast-fading channel conditions.

Today's wireless communication networks have many requirements such as high data rate, high reliability, low latency, low error data transmission, and high energy efficiency. High-performance index modulation (IM) techniques and reconfigurable intelligent surface (RIS) technology, which has recently attracted the attention of researchers, are strong candidates to meet these requirements. This paper introduces a novel RIS-supported code IM-based receive spatial modulation (RIS-CIM-RSM) system. The proposed RIS-CIM-RSM system uses quadrature amplitude modulation (QAM) symbols, receive antenna indices, and spreading code indices for wireless data transmission. In the proposed system, an RIS applies a phase rotation that maximizes signal-to-noise ratio (SNR) to the signals coming to the reflecting elements and directs them to the selected receive antenna. Performance analyses of the proposed RIS-CIM-RSM system such as data rate, throughput, and energy saving are obtained. The results obtained show that the proposed RIS-CIM-RSM system is superior to the counterpart RIS-based IM systems in the literature in terms of data rate, throughput, energy saving, and error performance.

Reconfigurable intelligent surface (RIS) structures reflect incident signals by adjusting phase adaptively according to the channel condition during transmission to increase signal quality at the receiver. Spatial modulation (SM) technique is a potential candidate for future energy-efficient wireless communications due to its ability to provide better throughput, low-cost implementation, and good error performance. Also, Alamouti's space-time block coding (ASBC) is an important space and time coding technique for the diversity gain and simplified maximum likelihood (ML) detection. In this paper, we propose the RIS-assisted received spatial modulation (RSM) scheme with ASBC, namely RIS-RSM-ASBC, for next-generation wireless networks. The RIS in the proposed system model is separated into two parts, each used as an access point (AP) to transmit its Alamouti coded information while reflecting passive signals to the selected receive antenna. We design the optimal ML detector for the proposed RIS-RSM-ASBC scheme. Furthermore, we present the greedy detector (GD) to reduce the complexity of the ML detector. Extensive computer simulations are performed to corroborate theoretical derivations. The results show that the RIS-RSM-ASBC system is highly reliable and provides data rate enhancement compared to traditional RIS-assisted transmit SM (RIS-TSM), RIS-assisted transmit quadrature SM (RIS-TQSM), RIS-assisted received SM (RIS-RSM), RIS-assisted transmit space shift keying with ASBC (RIS-TSSK-ASBC), and RIS-assisted TSSK with Vertical-Bell Laboratories Layered Space-Time (RIS-TSSK-VBLAST) schemes.

Reconfigurable intelligent surfaces (RISs) are software-controlled passive devices that can be used as relay$(R)$systems to reflect incoming signals from a source$(S)$to a destination$(D)$in a cooperative manner with optimum signal strength to improve the performance of wireless communication networks. The configurability and flexibility of an RIS deployed in an Internet of Things (IoT)-based network can enable network designers to devise stand-alone or cooperative configurations that have considerable advantages over conventional networks. In this article, two new deep neural network (DNN)-assisted cooperative RIS (CRIS) models, namely, DNN$_{R} -$CRIS and DNN$_{R, D} -$CRIS, are proposed for cooperative communications. In DNN$_{R} -$CRIS model, the potential of RIS deployment as an IoT-based relay element in a next-generation cooperative network is investigated using deep-learning (DL) techniques for RIS phase optimization. In addition, to reduce the maximum-likelihood (ML) complexity at$D$, a new DNN-based symbol detection method is presented with the DNN$_{R, D} -$CRIS model combined with DNN-assisted phase optimization. For a different number of relays and receiver configurations, the bit error rate (BER) performance results of the proposed DNN$_{R} -$CRIS and DNN$_{R, D} -$CRIS models and traditional CRIS scheme (without a DNN) are presented for a multirelay cooperative communication scenario with path loss effects. It is revealed that the proposed DNN-based models show promising results in terms of BER, even in high-noise environments with low system complexity.

Vehicular ad hoc networks (VANETs) have recently become more significant to intelligent transport systems (ITS). Recent works focused on improving throughput and decreasing delay. In this paper, a novel MIMO-OFDM based MAC Protocol is proposed for VANETs to enhance their performance. Multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) are integrated to exploit the benefit of both MIMO and OFDM. To accord MIMO with OFDM, a novel access mechanism is proposed. 3D Markov chain model-based analytical study is presented, considered a non-saturated condition. Nakagami-m fading channels are taken into account in the study. Parameters affecting performance are taken into consideration, and relationships are derived. The probability of successful transmission, probability of outage, bit error rate (BER), throughput, and delay expressions are achieved. Moreover, numerical results are presented, which verify analytical studies.

In this paper, a novel cooperative ad hoc medium access control (MAC) protocol is proposed for autonomous vehicles (AVs) referred to as CoMACAV. Three data transmission modes have been offered to increase the throughput which are direct transmission (DT), cooperative relaying (CR) and multi-hop relaying (MHR). The IEEE 802.11 standard defined mechanism only for direct communication which is not suitable for cooperative communication. Therefore, new control packets are introduced, and format of existing control packets is modified for cooperative communication. An analytical model based on the Markov chain model is presented. Simulation results show that the proposed CoMACAV protocol increases throughput.

Vehicular ad hoc networks (VANETs) have recently attracted interest for automation and intelligent transportation system (ITS). Two major factors which influence the performance of VANETs in practical transmission are bit error and channel capture. In this paper, to assess the performance of the IEEE 802.11 medium access control (MAC) for VANETs under channel fading and capture effect, an analytical model based on Markov chain model is presented. The parameters that could impact performance are studied. The relationship among parameters and performance metrics are derived. The probability of successful and unsuccessful transmission, probability of frame capture, and throughput expressions are obtained. Furthermore, to verify the analytical studies numerical results are presented.

In vehicular ad hoc networks (VANETs), mobility among vehicles can result in rapid topology changes with frequent link breakage and unstable communications, which cause collision and packet loss. Conversely, cooperative transmission can improve communication reliability and can enhance communication rate with lower delay by alleviating wireless channel impairments caused by mobility in VANETs. In this study, a novel reliable and efficient cooperative medium access control protocol for VANETs (RECV‐MAC) is proposed. Since a random access mechanism is suitable and efficient because of the dynamic and open nature of VANETs, authors used the random access approach, i.e. carrier sense multiple access with collision avoidance, which is used by IEEE 802.11p. The RECV‐MAC protocol is compatible with IEEE 802.11p. New control messages are introduced to support cooperative communication. The mechanism is defined to choose suitable transmission mode as well as to select optimal helper. To investigate the performance of RECV‐MAC protocol, Markov chain model‐based analytical analysis is provided. The RECV‐MAC protocol is validated by numerical results which demonstrate that RECV‐MAC protocol improves the performance with higher throughput, enhances the reliability of communication by decreasing packet dropping rate (PDR), and decreases delay, in particular, satisfies the delay constraint of 100 ms for sm.

Cooperative wireless communication has attracted intense interest as an alternative way to multiple-antenna systems to obtain spatial diversity. In this paper, we investigate the performance of a vehicle-to-vehicle cooperative scheme where another vehicle in the vicinity of the source vehicle acts as a relay. The underlying source-to-relay, relay-to-destination, and source-to-destination links are modeled as cascaded Nakagami-m fading which provides a realistic description of an intervehicular channel. Unlike the most studies on cooperative intervehicular communications in the literature which are based on analog relaying, we employ digital relaying approach and investigate the performance of the techniques developed for mitigating error propagation in decode and forward based wireless relay systems such as maximum likelihood, cooperative maximal ratio combining, link adaptive relaying, virtual noise based detection and soft information relaying. Simulation results show that detection schemes with these techniques outperform the noncooperative system that involves direct transmission between the source and destination terminals and overcome the diversity gain reduction due to error propagation.

In this paper, two different antenna selection models based on signal-to-noise ratio (SNR) have been proposed in order to reduce the end-to-end bit error rate (BER) of decode and forward (DF) relaying cooperative system where source and destination terminals contain single antenna while relay terminal has multiple antennas. Specifically, by using instantaneous and average SNR of source-to-destination, source-to-relay and relay-to-destination links, optimal decision rules are derived theoretically for antenna selection at the relay terminal. Later, BER expressions of considered system have been derived for two antenna selection models over Rayleigh fading channels. Theoretical and simulation results show the validity of proposed mathematical analysis and point out the confirmation of theoretical results.

The authors propose novel spectrum sensing and utilisation schemes for cognitive radio networks using the chirp ‐z transform. To improve the spectral efficiency, a dispersed chirp ‐z transform is introduced with the energy detection method. The dispersed chirp‐ z transform enables one to analyse the dispersed frequency spectrum of any frequency range of interest. The analysis is first focused on the sensing part, including the derivations of closed‐form expressions for the optimal detection thresholds minimising the total error rate over additive white Gaussian noise (AWGN), Rayleigh, Rician and log‐normally distributed fading channels. Then, the performance analysis of the proposed system is investigated for efficient spectrum utilisation over AWGN and fading channels by presenting the receiver operating characteristics. Conventional and segmented chirp ‐z transform‐based spectrum utilisation techniques are also introduced for performance comparison purposes. Finally, the theoretical framework and the optimal threshold derivations through simulations are verified. The analyses reveal that the proposed schemes have a considerable potential to improve the non‐cooperative spectrum sensing and utilisation performance.

In this letter, we investigate the error rate performance of two-way amplify-and-forward (AF) relaying communication system over independently but not necessarily identically distributed (i.n.i.d.) cascaded Nakagami-$m$fading channels. We have derived a closed-form expressions of cumulative distribution function (CDF) and moment generating function (MGF) for considering system. By using these expressions, we analyse the performance of two-way AF relaying system in terms of outage probability and symbol error rate (SER). Numerical and simulation results show the validity of the proposed mathematical analysis and point out the confirmation of the analytical results.

In this study, the authors investigate the error rate performance of amplify-and-forward relaying over N*Nakagami fading channels. This is a recently introduced channel model that involves the product of N Nakagami-m-distributed random variables. Employing the moment generating function approach, the authors derive symbol error rate expressions for a single-relay system under instantaneous power scaling (IPS) and average power scaling (APS) factors at the relay node, that is, variable and fixed gains. The results achieved by the authors demonstrate that the achievable diversity order is a function of Nakagami fading parameter (m) and degree of cascading (N). An identical diversity order is obtained under both scaling factors when the relay is close to the destination. When the relay is close to the source, IPS becomes advantageous over APS. Monte–Carlo simulations are further provided to confirm the analytical results.

Cooperative communication techniques promise the advantages of MIMO (multi-input multi-output) communications for wireless scenarios with single-antenna terminals. In this paper, we investigate the performance of a vehicle-to-vehicle cooperative scheme where another vehicle in the vicinity of the source vehicle acts as a relay. The underlying source-to-relay, relay-to-destination, and source-to-destination links are modeled as cascaded (double) Rayleigh fading. This statistical model provides a realistic description of inter-vehicular channel where two or more independent Rayleigh fading processes are assumed to be generated by independent groups of scatterers around the two mobile terminals. We derive a pairwise error probability (PEP) expression for the inter-vehicular cooperative scheme under consideration and show that the full distributed spatial diversity is extracted. Based on the derived PEP expressions, we obtain union bounds on the bit error rate performance which are then minimized to optimally allocate power between broadcasting and relaying phases. Optimum power allocation brings performance gains up to 3dB depending on the relay location and deployed modulation scheme.

Although there has been a growing literature on cooperative diversity, the current literature is mainly limited to Rayleigh fading channel model which typically assumes a wireless communication scenario with a stationary base station antenna above roof-top level and a mobile station at street level. In this paper, we investigate cooperative diversity for inter-vehicular communication based on cascaded Rayleigh fading. This channel model provides a realistic description of inter-vehicular channel where two or more independent Rayleigh fading processes are assumed to be generated by independent groups of scatterers around the two mobile terminals. We investigate the performance of amplify-and-forward relaying for an inter-vehicular cooperative scheme assisted by a road-side access point which acts as a relay. Our diversity analysis reveals that the cooperative scheme is able to extract the full distributed spatial diversity. We further formulate a power allocation problem for the considered scheme to optimize the power allocated to broadcasting and relaying phases. Performance gains up to 2.8 dB are observed through optimum power allocation depending on the relay location.