In this paper, a multiple-input multiple-output (MIMO) wireless system incorporating a reconfigurable intelligent surface (RIS) to efficiently operate at terahertz (THz) frequencies is considered. The transmitter, Alice, employs continuous-variable quantum key distribution (CV-QKD) to communicate secret keys to the receiver, Bob, who utilizes either homodyne or heterodyne detection. The latter node applies the least-squares approach to estimate the effective MIMO channel gain matrix prior to receiving the secret key, and this estimation is made available to Alice via an error-free feedback channel. An eavesdropper, Eve, is assumed to employ either a collective Gaussian entanglement attack or an individual attack on the feedback channel to obtain the estimated channel state information. We present novel closed-form expressions for the secret key rate (SKR) performance of the proposed RIS-assisted THz CV-QKD system. An optimization framework to obtain the optimal phase shifts of the RIS to maximize the SKR is proposed, and a particle-swarm optimization (PSO)-based algorithm is deployed to solve the optimization problem. The effect of various system parameters, such as the number of RIS elements and their phase configurations, the channel estimation error, and the detector noise, on the SKR performance is studied via numerical evaluation of the derived formula. It is demonstrated that the RIS contributes to larger SKR for larger link distances, and that heterodyne detection is preferable over homodyne at lower pilot symbol powers.

In reconfigurable intelligent surface (RIS) aided communication implementing space-shift keying at the transmitter for index modulation, the RIS is proposed to perform the dual function of selecting the phases of the reflecting elements optimally according to the phases of the channel gains, and acting as a modulator by transmitting$M$-ary phase-shift keying (PSK) modulated symbols via reflection phase modulation. The target antenna at the receiver is chosen by utilizing the optimal maximum likelihood (ML) detection rule and a hardware- and energy-efficient greedy detector, which performs detection based on the maximum received energy. For these detection scenarios, closed-form expressions for the probability of erroneous detection (PED) of the target antenna are derived, considering Nakagami-$m$channel fading. Numerical results supporting the analytical framework show the role of the rotation of the$M$-PSKconstellation to improve the reliability of the system. In particular,$\pi/M{-}$rotated$M$-PSK constellation is optimal for the greedy detector, whereas the ML detector is not dependent on such rotation to yield minimum PED.

Heart rate and respiratory rate are critical vital signs in infants, used as non-invasive indicators to assess health status and address potential issues. However, many healthcare settings face a limitation: the inability to measure these parameters simultaneously, as most non-invasive medical-grade instruments track either heart rate or respiratory rate, not both. Addressing this gap, the study investigates the use of machine learning techniques for the bi-directional estimation of infant heart and respiratory rates. It evaluates the performance of several machine learning models, including Convolutional Neural Network, Multilayer Perceptron, Gated Recurrent Units, Long Short-Term Memory, and the gradient boosting models Extreme Gradient Boosting and Light Gradient Boosting Machine, in predicting these vital signs using the Medical Information Mart for Intensive Care II dataset. Numerical results show that the gradient boosting models Extreme Gradient Boosting and Light Gradient Boosting Machine outperformed the neural network-based approaches in accuracy.

Index modulation (IM) schemes for reconfigurable intelligent surfaces (RIS)-assisted systems are envisioned as promising technologies for fifth-generation-advanced and sixth-generation (6G) wireless communication systems to enhance various system capabilities such as coverage area and network capacity. In this paper, we consider a receive diversity RIS-assisted wireless communication system employing IM schemes, namely, space-shift keying (SSK) with binary modulation and spatial modulation (SM) with M-ary modulation for data transmission. The RIS lies in close proximity to the transmitter, and the transmitted data is subjected to a fading environment with a prominent line-of-sight component statistically modeled by a Rician distribution. A receiver structure based on a greedy detection rule is employed to select the receive diversity branch with the highest received signal energy for demodulation. The performance of the considered system is evaluated by obtaining a series-form expression for the probability of erroneous index detection (PED) of the considered target antenna using a characteristic function approach. In addition, closed-form and asymptotic expressions at high and low signal-to-noise ratios (SNRs) for the bit error rate (BER) of the SSK-based system, and the SM-based system employing M-ary phase-shift keying and M-ary quadrature amplitude modulation schemes are derived. The dependencies of the system performance on various parameters are corroborated via numerical results. The asymptotic expressions and results of PED and BER at high and low SNR values lead to the observation of a performance saturation and the presence of an SNR value as a point of inflection, which is attributed to the greedy detector.

A rotated quadrature phase-shift keying (QPSK) based semi-orthogonal multiple access (SOMA) data transmission is considered for a visible light communication (VLC) system with two users. The rotation of the QPSK constellation at the transmitter followed by a data pre-processing technique at the receiver of each user ensures the elimination of the successive interference cancellation unit. An optimal maximum likelihood receiver is proposed for the system under consideration using which, the closed-form expressions for the symbol error probability (SEP) for both the users in the VLC system are derived. The optimization problem to obtain the optimal angle of rotation of the QPSK constellation which minimizes the SEP of the users is formulated and solved. The dependency of the optimality of the QPSK rotation angle on various VLC system parameters is studied via numerical results which lead to the observation of a value of the signal-to-noise ratio of the system around 8.8 dB about which the dependency of the optimal rotation angle on the other VLC system parameters interchange, thus providing design aspects for a SOMA-VLC system.

This paper presents one of the first explorations of transparency and explainability of Heart Rate Variability (HRV) based deep learning models designed for stress detection. We employed Shapley additive explanations (SHAP) as an explainable AI (XAI) method, and cross-validated the results with saliency maps, which provides valuable insights into the main contributing factors for decision-making process of these deep models.

Over recent years, reflective intelligent surface (RIS) and index modulation (IM) technologies have proven to be potential technologies for improving the performance of the fifth generation (5G) and beyond 5G wireless communication systems. In this paper, a space-shift keying (SSK) (an IM scheme)-based receive diversity and Nakagami-m faded wireless system is considered, which utilizes a RIS system in between the transmitter and the receiver. A greedy detector is proposed for the system, which chooses a target receiver antenna based on the maximum received energy at the diversity branches. An analytical framework is proposed based on a characteristic function approach to obtain a closed-form expression of the probability of erroneous detection of the target antenna. Asymptotic expressions at high and low average signal-to-noise ratios lead to the observation of a performance saturation, attributed to the structure of the greedy detector. Furthermore, numerical results are presented to show the dependency of the system’s performance on the various system parameters.

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.

This paper considers a receive diversity wireless communication system in which the transmitter uses a one-sided multi-level amplitude shift keying (ASK) modulation scheme to transmit data symbols over Rician fading channels. A channel magnitude-based receiver structure having partial knowledge of the instantaneous channel gains is employed to detect the received data symbols. The system’s error performance is analyzed by deriving a series-form expression for the symbol error probability (SEP). Further, an optimization framework is proposed to minimize the SEP under the average system energy constraint for obtaining the optimal ASK constellation. Numerical results are presented to corroborate the analytical framework where the superior performance of the optimal ASK constellation over the traditional equally-spaced ASK scheme is studied.

This study investigates the application of ensemble learning techniques for automatic modulation classification (AMC) in a reflective intelligent surface (RIS)-aided wireless communication system. The transmitter is considered to utilize five possible phase-shift keying and quadrature-amplitude modulation schemes for data transmission. The receiver extracts cumulant-based and spectral-based features from the received data, and employs three ensemble classifiers, namely XGBoost, LightGBM, and Random Forest for AMC. Furthermore, the important features for each classifier are identified, and their performance is computed and compared with the classifiers using all the features. Numerical results show that the LightGBM classifier performs the best in terms of AMC for the considered system and effectively classifies the modulation schemes at low signal-to-noise ratio values.

A practical visible light communications (VLC) system accounting for the effect of the random orientation and the random location of the photo-detector receiver is considered in this paper. The characterizations of the random orientation of the receiver, modeled as the receiver employing wide field of view (FOV) for data detection, and the random location of the receiver are utilized to derive the statistics for the scenarios in which (i) only the orientation of the receiver is random, (ii) only the location of the receiver is random, and (iii) both the orientation and location of the receiver are random. Furthermore, the receiver structures for a fully coherent VLC system and a VLC system employing the least-squares technique for channel estimation are proposed. Employing the receiver structures, the closed/series-form expressions for the symbol error probabilities are derived for all three scenarios of practical VLC channel models. The numerical results particularly show the crucial role of the ratio of the distance of the location of the receiver from the center of the receiving plane to the distance from the light-emitting diode (LED) to the center of the receiving plane in the performance of all the considered VLC systems.

In this work, we consider a two-user receive diversity wireless communication system with a rotated M-ary phase-shift keying (M-PSK) modulation, also known as semi-orthogonal multiple access (SOMA), for data transmission at the transmitter. At the receiver of the considered wireless communication system, each user utilizes a maximum ratio combining (MRC) technique and an optimal maximum-likelihood (ML) rule for transmitted data detection. We provide an analytical framework for the error analysis of the receive diversity wireless communication system and derive the closed-form expressions of the symbol error probability (SEP) for the users. Further, we also obtain the asymptotic expressions of the SEP at a high signal-to-noise ratio (SNR). We provide a numerical solution for the problem of finding the optimal rotation angle for the M-PSK constellation minimizing the SEP. The effects of the system parameters, namely, the number of diversity branches, SNR, and M, on the optimal rotation angle are demonstrated via numerical results. Furthermore, the simulation results corroborate the presented analytical results.

We study the secret key rate (SKR) of a multiple-input multiple-output (MIMO) continuous variable quantum key distribution (CVQKD) system operating at terahertz (THz) frequencies, accounting for the effects of channel estimation. We propose a practical channel estimation scheme for the THz MIMO CVQKD system which is necessary to realize transmit-receive beamforming between Alice and Bob. We characterize the input-output relation between Alice and Bob during the key generation phase, by incorporating the effects of additional noise terms arising due to the channel estimation error and detector noise. Furthermore, we analyze the SKR of the system and study the effect of channel estimation error and overhead. Our simulation results reveal that the SKR may degrade significantly as compared to the SKR upper bound that assumes perfect channel state information, particularly at large transmission distances.

The sixth-generation (6G) communication networks being highly data-intensive and enabled by the Internet of Everything (IoE) are envisaged to find applications in various domains including smart healthcare, smart industry, and gaming. In this article, a novel hybrid 6G-based cybertwin cooperative architecture is studied and an analytical framework for the secrecy outage analysis is presented. The base station (BS) considered utilizes nonorthogonal-multiple-access for content request transmission to the cybertwin host and the server with a direct communication link present between the BS and the server. A wireless link experiencing Nakagami-$m$fading is considered which is further assisted in the communication network by a wired link which is a power line communication link and experiences Rayleigh fading, for the communication between the cybertwin host and the server. Secrecy error probability expressions are derived for the cybertwin host and the server for the scenario when both the wireless and the wired links are available for communication and only the wireless link is available for communication. Furthermore, the presented analytical results are corroborated with simulation results which demonstrate the optimality of operating the wireless links at lower signal-to-noise ratio (SNR) values. It is observed that for the lower values of Nakagami fading parameter, better secrecy performance is observed with the usage of wired link along with the wireless link, and also the secrecy performance of the cybertwin host and the server is dependent on the system parameters like the fading parameter and the average SNR.

In this paper, we consider a device-to-device (D2D) cellular communication network where the wireless communication link among the devices and the base stations (BS), and between two devices is subjected to Rician fading and Nakagami-m fading distributions, respectively. The BSs and the devices are assumed to be placed randomly as independent Poisson point processes with the typical cellular user experiencing interference from both the D2D users and the BSs. We have investigated two scenarios, firstly both the BSs and the D2D users transmit orthogonal frequency division multiplexing with cyclic prefix (CP-OFDM) symbols for data transmission, and secondly, the BSs transmit CP-OFDM symbols while the D2D users transmit orthogonal quadrature amplitude (OQAM) modulated symbols over a filter bank based multi carrier (FBMC) transmitter system. Using the techniques of stochastic geometry, series form expression of the coverage probability of the cellular users is derived for the underlying interference-limited D2D cellular network. Moreover, the optimal coverage values that maximize the energy efficiency of the network are also obtained analytically. The study of the performance metrics obtained by numerical results provides insights on the dependence of the type of interference from the D2D users and of the type of modulation to be employed at the D2D users on the performance of the system.

A receive diversity powerline communication system subject to uncorrelated Rayleigh distributed channel gains and corrupted by background noise modeled by Nakagami-m distribution is considered in this paper. For the transmitter utilizing multi-level amplitude-shift keying (ASK) modulation for data transmission and the receiver employing the optimal noncoherent decision rule for symbol estimation, the closed-form expression for the symbol error probability (SEP) of the system with an even number of diversity branches is derived using the union bound approach. Further, the constrained optimization problem for obtaining the optimal ASK signaling levels minimizing the SEP of the system with constrained total energy at the transmitter is formulated and solved numerically. It is observed that the optimal ASK constellation thus obtained outperforms the traditional equally-spaced ASK constellation for higher values of signal-to-noise ratio and diversity branches and at lower values of the shape parameter of the noise.

This paper considers a device-to-device (D2D) cellular communication network with the wireless communication link among the devices and the base station (BS) modeled by the Rician fading and the wireless communication link between the devices modeled by Nakagami-m fading distribution. The devices and the BSs are assumed to be placed randomly as independent Poisson point processes with the devices experiencing interference from both D2D users and the cellular users. Using the techniques of stochastic geometry, series form expressions of the coverage probability of the cellular users are derived for the underlying interference-limited D2D cellular network. Furthermore, the optimal coverage values that maximize the energy efficiency of the network are also obtained analytically. The effect of the Rician factor and other system parameters on the performance of the system is studied by numerical results. The study of the variations of the optimal coverage analysis with the system parameters presented in this paper gives an insight into the design of cellular D2D communication networks.

The cooperative device‐to‐device (D2D) network employing non‐orthogonal multiple access (NOMA) is expected to play an important role in the next‐generation wireless networks. In this work, the authors derive outage probability expressions of a cooperative NOMA D2D network which employs decode‐and‐forward relaying. A wireless link experiencing Nakagami‐ m fading is considered which is further assisted in the communication network by a wired link which is a powerline communication link and experiences Rayleigh fading. The outage analysis, shown for both the strong user and the weak user, is derived assuming that at the receiver there is perfect successive interference cancellation. Employing power division NOMA, optimum value for the coefficient of power allocation is obtained corresponding to the minimum probability of outage of the strong user. Furthermore, a range of the NOMA power allocation coefficient is provided for the communication link at the weak user which is between the wireless and the powerline link. Symbol error probability expressions are also derived for the strong and the weak users for the scenario when: i) both the wireless and the wired links are available for communication and ii) only the wireless link is available for communication.

Cooperative device-to-device communication with non- orthogonal multiple access (NOMA) employing additional power line communication technology is an effective way to increase the coverage and spectral efficiency of the next generation hybrid networks. In this paper, we present the outage analysis of a cooperative network with NOMA and decode-and-forward relaying assuming a direct link between the base station and the users. We consider a relaying network consisting of a wireless link for the strong user and the weak user having both wireless and a wired link which is assumed as a power line link. The wireless links are subjected to Nakagami-m fading and the power line link experiences Rayleigh fading. The outage probability expressions for both the strong and the weak users are derived assuming power division NOMA and perfect successive interference cancellation at the receivers. We also derive the optimal value of the NOMA power allocation coefficient minimizing the outage probability at the strong user and obtain the range of the power allocation coefficient between the power line and the wireless link at the weak user. Furthermore, numerical results validate the derived analytical results.

The authors consider a single‐channel power line communication (PLC) system in the presence of Middleton Class‐A impulsive noise employing multi‐level amplitude‐shift keying (ASK) modulation at the transmitter and non‐coherent detection at the receiver. An asymptotically optimal detector for the PLC system is obtained using a tight approximation of the noise statistics. The magnitude of the received symbol is obtained as the decision variable, whose statistics is utilised to derive a series expression for the symbol error rate (SER). An asymptotic expression for the SER at high signal‐to‐noise ratio (SNR) is also obtained which is further utilised to find the optimal ASK constellation minimising the SER. It is shown by numerical examples that the optimal solution is extremely close to the equally spaced ASK constellation set at high SNR. It is also observed that the SER variation of the system with the impulsive index of the noise validates the optimality of the proposed detector at high SNR.

In a communication system employing coherent reception, pilot symbols are used for estimating the channel state information (CSI) at the receiver. The amount of training, which is quantified by the fractional pilot duration for a fixed-length pilot-plus-data frame, should be kept as low as possible for saving bandwidth and increasing data rate. However, reducing training leads to degraded error performance due to poor CSI estimate although it increases data rate, while increasing training improves error performance but reduces data rate. Expressing the tradeoff between symbol error probability (SEP) and data rate by the normalized error-free data rate, we present an analytical framework for its maximization with respect to pilot symbol duration fraction in a pilot-aided single-input multiple-output wireless communication system with reception over independent and identically distributed flat Rayleigh fading diversity branches, employing M -ary phase-shift keying, and using maximal-ratio combining. Closed-form expressions for the approximate optimal pilot symbol duration fraction are derived for the high signal-to-noise ratio (SNR) case. Numerical results are presented to highlight the system behavior with changes in parameters like SNR, pilot symbol quality, and number of receive diversity branches. It is found that the optimization maximizes normalized error-free data rate with close to minimum SEP.

This paper proposes to use N-branch diversity reception for a power line communication (PLC) system with binary phase-shift keying to improve the reliability of data transmission. The PLC channel is subject to Rayleigh fading and additive Nakagami-m background noise with m <; 1, which is caused by multiple noise sources. The optimal detector for this system is derived by approximating the noise distribution by Hoyt distribution. A closed form expression and a series expression for the symbol error probability for even and odd N, respectively, are obtained. The advantage of using multiple receive branches in terms of achieving better error performance and its power efficiency are shown through numerical results. The effect of the shape parameter m of the background noise on the performance of the optimal receiver is also demonstrated.

A noncoherent quadratic diversity reception system for multilevel amplitude-shift keying (ASK) signals in Rayleigh fading with different cases of the channel covariance matrix is considered. These include the important case of distributed antennas, which exhibit uncorrelated fading with distinct mean-squared channel gains (uncorrelated nonidentical fading) and weighted energy detectors, and the cases of exponentially correlated and uniformly correlated channels with equal mean-squared channel gains. For these cases, closed-form expressions for the symbol error probability (SEP) of the system are derived using the decision statistics obtained from the maximum likelihood receiver. The problem of determining the optimal amplitude levels that minimize the SEP under a total signal energy constraint is formulated and solved analytically for the high signal-to-noise ratio (SNR) configuration and numerically for the general configuration. For the high SNR configuration, it is shown that the optimal ASK levels should follow an approximately geometric progression. It is also observed that an equally spaced ASK constellation is not optimal in terms of achieving the minimum SEP. Numerical results are presented to highlight performance trends for channel gain imbalance and correlation.