This paper investigates the secrecy performance of a keyhole-aided multi-user communication network in the presence of multiple eavesdroppers. The communication happens through the same keyhole for legitimate users and eavesdroppers. In this context, the secrecy performance is evaluated for a user scheduling technique by obtaining the exact closed-form expression of secrecy outage probability (SOP). Further, a simplified asymptotic SOP expression is derived assuming high signal-to-noise ratio (SNR) scenario for a better understanding of the impact of system parameters. The effect of the keyhole parameters, number of users, number of eavesdroppers, and threshold secrecy rate on the SOP performance are also investigated for the considered system model. In the high-SNR regime, the asymptotic SOP saturates to a constant value and does not depend on the keyhole parameter and the channel parameter of the source-to-keyhole channel.

Rate-splitting multiple access (RSMA) is a technique that is widely used in next-generation wireless systems to efficiently manage multiple users. RSMA splits the transmission into two parts using rate splitting, which increases spectral efficiency. However, this technique also makes a portion of the transmission vulnerable to eavesdropping, which can compromise information security. This vulnerability is not limited to external eavesdroppers but also includes internal eavesdropping among users who share the same transmission. Therefore, there is an increasing need to develop secure RSMA systems to address these critical security issues among untrusted users. This paper focuses on a single-antenna RSMA downlink system with multiple untrusted users undergoing Rician channel fading. In this novel system framework considered for performance analysis, each user interprets its own common and private streams while attempting to eavesdrop on the private streams of other users. We evaluate the system-level performance in practical settings involving line-of-sight (LoS) paths using the Rician channel model and derive a tight closed-form approximate expression of the ergodic secrecy rate. Finally, we conduct numerical simulations to validate the theoretical analysis and provide valuable insights into the critical system parameters that impact the achievable ergodic secrecy performance of the RSMA system with untrusted users.

Non-Orthogonal Multiple Access (NOMA) is a wireless communication technique that uses the Successive Interference Cancellation (SIC) strategy to achieve high efficiency. However, SIC can pose security risks in an untrusted NOMA environment where users can suffer from internal eavesdropping. In this research paper, we propose security solutions for downlink NOMA transmission involving two untrusted user terminals and imperfect SIC. Specifically, we investigate the ergodic secrecy rate performance in NOMA for two user terminals against mutual eavesdropping. To achieve the maximum weighted ergodic sum secrecy rate of the system while meeting the quality of service (QoS) requirements of both user terminals, we formulate an optimization problem for power allocation. Our solution approach considers a decoding order that yields the best possible outcome and employs an iterative method to obtain the optimal power allocation. Simulation results confirm the analytical claims and provide key insights on the optimal design parameters. Lastly, we numerically demonstrate that our proposed power control and decoding order design outperforms the benchmark schemes in terms of weighted ergodic sum secrecy rate performance.

In this paper, we propose an opportunistic user scheduling scheme in a multi-user reconfigurable intelligent surface (RIS) aided wireless system to improve secrecy. We derive the secrecy outage probability (SOP) and its asymptotic expression in approximate closed form. The asymptotic analysis shows that the SOP does not depend on the transmitter-to-RIS distance and saturates at a high signal-to-noise ratio to a fixed value that depends on the ratio of the path-loss of the RIS-to-destination and RIS-to-eavesdropper links and the number of users. It is shown that the asymptotic SOP decreases exponentially with the number of RIS elements. We also compare the secrecy performance of our scheme with that of a non-orthogonal multiple access (NOMA) scheduling scheme, which chooses a pair of users to schedule in each time slot. The comparison shows that the secrecy performance of the NOMA scheme is compromised and that our proposed scheduling scheme has better performance.

This paper analyzes the performance of a reconfigurable intelligent surface (RIS)-assisted monostatic backscatter communication system. The system under consideration consists of a reader, a distant tag, and an RIS. The reader sends radio frequency (RF) signal in forward phase to read the information from the distant tag via RIS and the tag reflects the signal with information in backscatter phase back to the reader via same RIS. It is assumed that the channel gains of forward and backscatter links follow Rayleigh distribution. Average achievable rate is computed for the system by deriving the closed-form expressions of its upper and lower bounds. To gain deeper insights, asymptotic expressions of these bounds are also derived in closed-form. With the help of numerical results, the effect of various parameters on rate performance is presented. Simulation results confirm the bounds tightness of the average achievable rate. The impact of the RIS position on the rate performance is also analyzed.

Abstract Due to the exponential growth of interconnected devices and reduced cell coverage, beyond fifth‐generation networks will be dense. Thus, instead of wired backhaul, wireless backhaul will be cost‐effective and flexible. For security in multi‐transmitter systems, sub‐optimal and optimal transmitter selection schemes exist. However, including backhaul activity knowledge available (BKA) and backhaul activity knowledge unavailable (BKU) cases and transmitter selection schemes, there is no generalized secrecy analysis method. Moreover, evaluation of the ergodic secrecy rate (ESR) of the optimal selection schemes is impossible using existing solution approaches. To address these, two sub‐optimal and optimal transmitter selection schemes are proposed for a small‐cell multi‐transmitter system in BKU or BKA cases in the presence of multiple colluding eavesdroppers. The distribution of the ratio of the destination channel SNR and eavesdropping channel SNR is derived, thereby providing different secrecy performance metrics uniformly irrespective of selection schemes and BKU or BKA cases. Simplified asymptotic expressions are provided to elucidate the influence of the system parameters and of the backhaul reliability. It is observed that the secrecy performance improves when the knowledge of backhaul link activity is utilized, and the improvement is most noticeable when the backhaul is highly unreliable. It is also observed that while the secrecy performance degrades with an increasing number of eavesdroppers, neither the asymptotic saturation value of the secrecy outage probability nor the rate of improvement of the ESR with signal‐to‐noise‐ratio depends on the number of eavesdroppers.

This paper analyzes the secrecy performance of a reconfigurable intelligent surface (RIS) assisted wireless communication system with a friendly jammer in the presence of an eavesdropper. The friendly jammer enhances the secrecy by introducing artificial noise towards the eavesdropper without degrading the reception at the destination. Approximate secrecy outage probability (SOP) is derived in closed form. We also provide a simpler approximate closed-form expression for the SOP in order to understand the effect of system parameters on the performance and to find the optimal power allocation for the transmitter and jammer. The optimal transmit and jamming power allocation factor is derived by minimizing the SOP assuming a total power constraint. It is shown that the SOP performance is significantly improved by the introduction of the jammer and a gain of approximately 3 dB is achieved at an SOP of 10–4by optimally allocating power compared to the case of equal power allocation.

Inclusion of massive machine-type-communication (mMTC) devices in 5G cellular Internet of Things (IoT) has significantly raised the issue of network congestion. To address this challenge, a successive interference cancellation-rate splitting random access (SIC-RSRA) mechanism is proposed in this paper. Unlike traditional mechanisms, all selected mMTC devices are allowed to make a finite number of repeated message requests in randomly selected time slots within a radio frame. The gNodeB, on the other hand, applies both intra-slot SIC (utilizing RSRA) and inter-slot SIC to decode messages from a larger number of devices. For the proposed mechanism, the impact of increasing the number of devices as well as the received power difference is investigated. Through extensive simulations, we show that the proposed mechanism outperforms the other mechanisms in terms of number of RACH successes and number of supported devices.

The cellular Internet-of-Things has resulted in the deployment of millions of machine type communication (MTC) devices under the coverage of a single gNodeB (gNB). These massive number of devices should connect to the gNodeB (gNB) via the random access channel (RACH) mechanism. Moreover, the existing RACH mechanisms are inefficient when dealing with such large number of devices. To address this issue, we propose the rate-splitting random access (RSRA) mechanism, which uses rate splitting and decoding in rate-splitting multiple access (RSMA), to improve the RACH success rate. The proposed mechanism divides the message into common and private messages and enhances the decoding performance. We demonstrate, using extensive simulations, that the proposed RSRA mechanism significantly improves the success rate of MTC in cellular IoT networks. We also evaluate the performance of the proposed mechanism with increasing number of devices and received power difference.

In this paper, a communication network using single carrier with cyclic prefix modulation over frequency selective channels is considered, where an access point provides connectivity to a legitimate destination through multiple transmitters with unreliable backhaul links in the presence of an eavesdropper. A sub-optimal and an optimal transmitter selection scheme are proposed to improve the secrecy of the system, depending on whether the active backhaul channel knowledge is available a priori or not. The secrecy outage probability (SOP) and its asymptotic limit are presented in closed-form. This provides some insights regarding how knowledge of the active backhaul links affects the secrecy performance of the network. Our results show that the optimal transmitter selection scheme obtains a larger benefit than the sub-optimal scheme from the knowledge of the active backhaul links, resulting in a significantly improved system performance; however, the sub-optimal transmitter selection scheme can reduce the complexity and feedback overhead.

A small-cell network with multiple transmitters and unreliable wireless backhaul is considered for secrecy enhancement. The small-cell network is operating under a spectrum sharing agreement with a primary network in a cognitive radio system. A constraint on the desired outage probability at the primary receiver is assumed as a part of the spectrum sharing agreement. The reliability of the wireless backhaul links are modeled by a set of independent and identically distributed Bernoulli random variables. A sub-optimal and an optimal small-cell transmitter selection (TS) scheme is proposed to improve the performance of the system, depending on the availability of channel state information. Selection schemes are designed for the scenario where knowledge is available regarding which backhaul links are active. The corresponding secrecy outage probabilities along with their asymptotic expressions are derived. It is shown that the secrecy performance is significantly improved compared to the case where knowledge of the active backhaul links is unavailable.

In this study, the authors propose a hybrid power line communication (PLC)/visible light communication (VLC)/radio frequency (RF) fronthaul with a fibre‐based wired backhaul system to support massive number of smart devices (SDs). Since a signal‐to‐noise ratio‐based access point (AP) association and bandwidth (BW) allocation for each SD do not necessarily improve the system capacity, they propose novel and efficient AP association and BW allocation strategies to maximise the sum rate capacity (SRC) of the hybrid system under consideration. An optimisation problem is formulated for the SRC with the AP association and BW allocation as the optimisation parameters and a hierarchical decomposition method is used to convert the non‐linear optimisation problem into a set of convex optimisation problems. Then, the proposed strategies are used to solve the optimisation problem in an iterative manner until the SRC converges to an optimal value. Further, an analytical approximation for the BW allocated to each SD for a given AP association is derived using the Lagrangian multiplier method. The performance of the proposed system is evaluated through extensive numerical results. Moreover, the effect of the increased number of SDs on the optimal SRC is analysed.

In this paper, an incremental selective decode-and-forward (ISDF) relay strategy is proposed for power line communication (PLC) systems to improve the spectral efficiency. Traditional decode-and-forward (DF) relaying employs two time slots by using half-duplex relays which significantly reduces the spectral efficiency. The ISDF strategy utilizes the relay only if the direct link quality fails to attain a certain information rate, thereby improving the spectral efficiency. The path gain is assumed to be log-normally distributed with very high distance dependent signal attenuation. Furthermore, the additive noise is modeled as a Bernoulli-Gaussian process to incorporate the effects of impulsive noise contents. Closed-form expressions for the outage probability and the fraction of times the relay is in use, and an approximate closed-form expression for the average bit error rate (BER) are derived for the binary phase-shift keying signaling scheme. We observe that the fraction of times the relay is in use can be significantly reduced compared to the raditional DF strategy. It is also observed that at high transmit power, the spectral efficiency increases while the average BER decreases with increase in the required rate.

MOTIVATION: The extraction of sequence variants from the literature remains an important task. Existing methods primarily target standard (ST) mutation mentions (e.g. 'E6V'), leaving relevant mentions natural language (NL) largely untapped (e.g. 'glutamic acid was substituted by valine at residue 6'). RESULTS: We introduced three new corpora suggesting named-entity recognition (NER) to be more challenging than anticipated: 28-77% of all articles contained mentions only available in NL. Our new method nala captured NL and ST by combining conditional random fields with word embedding features learned unsupervised from the entire PubMed. In our hands, nala substantially outperformed the state-of-the-art. For instance, we compared all unique mentions in new discoveries correctly detected by any of three methods (SETH, tmVar, or nala ). Neither SETH nor tmVar discovered anything missed by nala , while nala uniquely tagged 33% mentions. For NL mentions the corresponding value shot up to 100% nala -only. AVAILABILITY AND IMPLEMENTATION: Source code, API and corpora freely available at: http://tagtog.net/-corpora/IDP4+ . CONTACT: [email protected]. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

The authors presents a study of the effect of correlation among the multi‐hop path gains on the average channel capacity and the outage performance of a power line communication system equipped with decode‐and‐forward relays. The path gain of each hop follows a log‐normal distribution and the joint density is modelled by a multivariate log‐normal distribution with exponential correlation. A distance dependent signal attenuation factor is added to the channel model to incorporate the effect of physical distance between the nodes. Furthermore, a Gaussian mixture (Bernoulli‐Gaussian) noise is included in the system model to analyse the effect of impulsive noise together with thermal noise. Approximate closed‐form expressions for the end‐to‐end average channel capacity and the outage probability are derived. Numerical results showing the impact of the amount of correlation, the number of hops, the impulsive noise power, and the spread of the average power of the path gains on the performance are presented. The results show that for a fixed transmit power and end‐to‐end distance between source and destination, the performance improves with increasing number of hops; however, the amount of improvement reduces with increasing channel correlation.

The authors present a study on the end‐to‐end average bit error rate (BER), the average channel capacity and the outage performance of a multi‐hop power line communication (PLC) system equipped with decode‐and‐forward (DF) relays. To combat the issue of distance dependent signal attenuation, multi‐hop data transmission has recently been introduced for PLC systems. However, apart from the distance dependent signal attenuation, PLC systems also suffer from (i) the variation in signal amplitude (fading) because of reflections and (ii) impulsive noise. Thus, in this study, the channel for each hop of the multi‐hop PLC system is modelled by a log‐normal fading amplitude, which is clubbed to a distance dependent signal attenuation factor. To consider the effect of the impulsive noise along with the background noise, the additive noise at each node is modelled by a Bernoulli–Gaussian process. Analytical expressions for the end‐to‐end average BER for binary phase‐shift keying, the average channel capacity and the outage probability are obtained. The merit of the multi‐hop PLC system over a conventional direct transmission PLC system for fixed transmission power is shown through numerical results. The authors' results show that with increasing number of DF relays, the end‐to‐end average BER, the average channel capacity and the outage performance improve.

The use of repeaters (relays) has recently been introduced in power line communication (PLC) systems for long-distance data transfer and thus, it becomes important to analyze the performance of relay based PLC systems. A simplified system model with distance dependent signal attenuation and additive white Gaussian noise may not cover all the factors affecting the data transfer, such as variation in amplitude (fading) and occurrence of impulsive noise. Hence, a more realistic system model with log-normal fading, distance dependent signal attenuation, and a Bernoulli-Gaussian impulsive noise is considered in this paper to study the end-to-end average bit error rate (BER) and the end-to-end average channel capacity of a PLC system equipped with amplify-and-forward (AF) relays. Approximate closed-form expressions of the end-to-end average BER for binary phase-shift keying and the average channel capacity for high signal-to-noise ratio are obtained. The performance of the PLC system with AF relays is found to be superior compared to that of a direct transmission PLC system for fixed transmission power.

The authors analyse an L ‐channel selection combining (SC) scheme for a power line communication (PLC) system with binary phase‐shift keying. The focus is on improving the reliability in data transfer of the system instead of improving the data rate. To enhance the reliability in data transfer, multiple PLC channels are used to send the same information‐bearing signal to the receiver. The L PLC channels are subject to log‐normal fading, which is modelled by a multivariate log‐normal distribution with an exponential correlation. The channels are also corrupted by additive impulsive noise as well as thermal noise. To consider the effect of both types of noises, they adopt a Gaussian mixture noise model, in which the additive noise samples are taken from a Bernoulli–Gaussian process. The system performance is evaluated in terms of the average bit error rate and the average channel capacity, for which approximate closed form expressions are derived. Numerical results showing the impact of the number of PLC channels, the amount of correlation, the noise scenarios, and the fading environments on the performance are presented. The authors' results show that the performance improves with increasing number of PLC channels; however, the amount of improvement reduces with increasing channel correlation.

This paper proposes a selection combining (SC) scheme for a power line communication (PLC) system with binary phase-shift keying. The main purpose is to utilize multiple of independent and non-interfering channels to send an information-bearing signal and to use SC at the receiver end to improve the reliability of the PLC system. The fading coefficient of each PLC channel is modeled by a log-normal distribution, and to include the effects of both background noise and impulsive noise, the additive noise samples are taken from a Bernoulli-Gaussian process. We obtain a closed-form approximation of the bit error rate and an expression for the outage probability of the proposed scheme. The merit of the L-channel PLC system with SC when compared with a single channel PLC system over different fading and impulsive noise scenarios is demonstrated through numerical results.