The presence of irregularities in measurement causes poor filtering performance to well-celebrated Gaussian filters. The reason is that these filters are traditionally designed with an ideal measurement model, ignoring the possibility of any irregularity in the measurements. In this paper, we address a new measurement irregularity wherein an inaccurate measurement is received, which is stochastically composed of the current and past hypothetically true measurements. The proposed method reformulates the measurement model for incorporating the possible existence of the concerned irregularity. Subsequently, it re-derives the traditional Gaussian filtering method for the reformulated measurement model, resulting into the proposed filtering method. In summary, the paper first proposes a new measurement equation to model the concerned irregularity, resulting into a new state-space model. With the new measurement model, the parameters associated to the measurement update step of Gaussian filtering,i.e., measurement estimate, covariance, and cross-covariance are re-derived accordingly. Interestingly, any of the existing Gaussian filters, such as the extended Kalman filter (EKF) and cubature Kalman filter (CKF), can be designed under the proposed filtering method. We study the stability of the proposed method for its EKF-based formulation. The improved accuracy of the proposed method is validated for two nonlinear filtering problems.

In this work, we investigate the secrecy performance of a wireless network that enables an aerial intelligent reflecting surface-unmanned aerial vehicle for non-orthogonal multiple access (NOMA) transmissions in the presence of a friendly jammer. For a practical NOMA-based system with imperfect successive interference cancellation, we develop a theoretical framework for the secrecy outage probability (SOP) and the strictly positive secrecy capacity. However, the derived expressions are complex and therefore, do not provide important insights into the system design. In this regard, explicit and simplified formulas of the asymptotic SOP are derived under high signal-to-noise ratio conditions for scenarios with and without jamming. Through extensive simulations, we verify the correctness of the proposed theoretical framework. Notably, numerical results reveal the superior performance of the jamming-enabled system over its non-jamming counterpart and demonstrate the efficacy of the proposed scheme.

Energy and spectral efficiency of Internet of Things (IoT) networks can be improved by integrating energy harvesting (EH), cognitive radio, and nonorthogonal multiple access (NOMA) techniques, while unmanned aerial vehicles (UAVs), on the other hand, are a quick and adaptable entity for improving the coverage performance. In this article, we assess the performance of a UAV-assisted overlay cognitive NOMA (OC-NOMA) system by employing an EH-based IoT-inspired cooperative spectrum sharing transmission (I-CSST) scheme. Herein, an energy-constrained UAV-borne secondary node harvests radio-frequency energy from the primary source and uses it to send both its own information signal and the primary information signal using the NOMA approach. We consider the impact of the imperfect successive interference cancellation in NOMA and the distortion noises caused by hardware impairments (HIs) in signal processing, which are unavoidable in real-world systems. We obtain the complicated expressions of outage probability (OP) for primary and secondary IoT networks using the I-CSST scheme under heterogeneous Rician and Nakagami-${m}$fading channels. We continue to investigate asymptotic analysis for OP in order to gain insightful knowledge on the high signal-to-noise ratio (SNR) slope and practicable diversity order. We also assess the system throughput and energy efficiency for the considered OC-NOMA system. Our results demonstrate the benefits of the suggested I-CSST scheme over the benchmark primary direct transmission and orthogonal multiple access schemes. We create a deep neural network (DNN) architecture for real-time OP prediction in order to combat the complications in model-based approaches.

Non-orthogonal multiple access (NOMA) is consid-ered as one of the predominant multiple access techniques for next-generation cellular networks. We consider a 2-user pair downlink NOMA system with imperfect successive interference cancellation (SIC). We consider bounds on the power allocation factors and then formulate the power allocation as an optimization problem to achieve α-Fairness among the paired users. We show that α-Fairness based power allocation factor coincides with lower bound on power allocation factor in case of perfect SIC and$\alpha > 2$. Further, as long as the proposed criterion is satisfied, it converges to the upper bound with increasing imperfection in SIC. Similarly, we show that for$0 < \alpha < 1$, the optimal power allocation factor coincides with the derived lower bound on power allocation. Based on these observations, we then propose a low complexity sub-optimal algorithm. Through extensive simulations, we analyze the performance of the proposed algorithm and compare it against the state-of-the-art algorithms. We show that the proposed optimal and sub-optimal algorithms ensure that each user achieves a rate at least equivalent to its orthogonal multiple access counterparts. Further, we also show significant improvements in terms of fairness with the proposed algorithm as compared to the state-of-the-art algorithms.

While intelligent reflecting surfaces (IRSs) and non-orthogonal multiple access (NOMA) techniques have shown great potential to boost the spectral and energy efficiency for future wireless networks, unmanned aerial vehicles (UAVs) are committed for enhancing the wireless connectivity with fast and flexible deployment. In this regard, we study an integration of an IRS in UAV-enabled wireless relaying system using NOMA transmissions. We also count on the impacts of residual hardware impairments (HIs) in user devices and imperfect successive interference cancellation (SIC) in NOMA, which are inevitable in practical system implementation. We analyze the system performance by deriving the closed-form expressions of outage probability (OP) and system throughput over the line-of-sight (LoS) Rician fading channels for the aerial links. We further pursue asymptotic OP analysis to reveal useful insights on the achievable diversity order. Above all, we present a deep neural network (DNN) framework for OP prediction with a short execution time under the dynamic stochastic environment. Our results validate the theoretical proposition and accentuate the performance advantages of the proposed UAV-borne IRS relaying NOMA system.

In this paper, we investigate the physical layer security (PLS) of an overlay cognitive non-orthogonal multiple access (NOMA) system with control-jamming (CJ) under Nakagami-m fading. Herein, a cooperative decode-and-forward (DF) relaying technique is adopted at the secondary transmitter, while a maximal ratio combining (MRC) scheme is employed at the primary destination in order to improve the secrecy performance of the underlying system. Under this setup, we derive analytical expressions for the secrecy outage probability (SOP) and the strictly positive secrecy capacity (SPSC). Moreover, we obtain simple and explicit expressions of the SOP in the high signal-to-noise ratio (SNR) region to get useful insights on the system design for both the cases of without and with jamming. Finally, Monte Carlo simulations are provided to: (i) demonstrate the effectiveness and superiority of the proposed system with jamming over its non-jamming counterpart in terms of security; (ii) verify the accuracy of the proposed analytical framework.

Wireless Body Area Networks (WBANs) comprise a network of sensors subcutaneously implanted or placed near the body surface and facilitate continuous monitoring of health parameters of a patient. Research endeavours involving WBAN are directed towards effective transmission of detected parameters to a Local Processing Unit (LPU, usually a mobile device) and analysis of the parameters at the LPU or a back-end cloud. An important concern in WBAN is the lightweight nature of WBAN nodes and the need to conserve their energy. This is especially true for subcutaneously implanted nodes that cannot be recharged or regularly replaced. Work in energy conservation is mostly aimed at optimising the routing of signals to minimise energy expended. In this article, a simple yet innovative approach to energy conservation and detection of alarming health status is proposed. Energy conservation is ensured through a two-tier approach wherein the first tier eliminates “uninteresting” health parameter readings at the site of a sensing node and prevents these from being transmitted across the WBAN to the LPU. The second tier of assessment includes a proposed anomaly detection model at the LPU that is capable of identifying anomalies from streaming health parameter readings and indicates an adverse medical condition. In addition to being able to handle streaming data, the model works within the resource-constrained environments of an LPU and eliminates the need of transmitting the data to a back-end cloud, ensuring further energy savings. The anomaly detection capability of the model is validated using data available from the critical care units of hospitals and is shown to be superior to other anomaly detection techniques.

Energy harvesting with cognitive radio and nonorthogonal multiple access (NOMA) techniques offer a promising solution to enhance the spectral and energy efficiency in Internet of Things (IoT) networks. This article investigates the performance of an overlay cognitive NOMA (OCNOMA) system tailored for IoT applications. Herein, the primary network includes a primary transmitter-receiver pair, whereas the secondary network comprises an energy-constrained full-duplex (FD) relaying-based secondary transmitter (ST) with its intended multiple receivers. Accordingly, ST employs a time-switching (TS)/power-splitting (PS)-based receiver architecture to harvest the energy from the radio-frequency signal of primary transmission and, thereby, uses this energy to relay the primary signal and to transmit its own signals simultaneously using the OCNOMA principle. For this, we propose a cooperative spectrum-sharing transmission (CSST) scheme using the decode-and-forward relaying strategy, while considering the realistic assumptions of FD-based loop self-interference, NOMA-based imperfect successive interference cancelation, and the transceiver hardware impairments in IoT devices. Adopting Nakagami-${m}$fading environments, we comprehensively analyze the performance by deriving the expressions of the outage probability for the primary and secondary networks for the FD-based CSST scheme under both TS and PS protocols. Thereby, we disclose some apposite ceiling effects and provide an insight on deciding the value of the OCNOMA power allocation factor for efficacious spectrum-sharing cooperation. We further quantify throughput and energy efficiency for the overall system. Our results demonstrate the performance advantages of the proposed FD CSST scheme over the benchmark schemes and provide useful guidelines for the practical design of cognitive IoT networks.

Land mobile satellite (LMS) systems and unmanned aerial vehicles (UAVs) are the key enablers for broadband wireless networks to serve terrestrial mobile users over a broad area with low cost. However, with the increasing dependency on the aerospace communication infrastructure, the wiretapping and security threats would be a major concern. In this paper, we investigate the secrecy performance of a downlink LMS system by employing a UAV-based friendly jammer in the presence of an eavesdropper on the ground. Specifically, we derive the secrecy outage probability (SOP) of the considered LMS system under the pertinent heterogeneous channels for the satellite links and the air-to-ground jammer. We further derive an asymptotic SOP expression to gain more insights into the system performance. Our theoretical results are validated through simulations and they reveal the impact of UAV position and other key parameters on the secrecy performance of LMS systems.

In this paper, we consider an overlay cognitive satellite-terrestrial relay network comprising a primary satellite source-receiver pair and a secondary transmitter-receiver pair on the ground while taking into account the practical relay transceiver hardware impairments. Herein, a primary satellite source communicates with its terrestrial user by utilizing both direct and relay links, using an amplify-and-forward based cooperative communication technique. Considering distortion noises in relay signal processing, we obtain new closed-form expressions for the outage probability of primary satellite network and secondary terrestrial network and explicitly derive the asymptotic outage behaviour for primary network by adopting pertinent heterogeneous fading models. Both primary and secondary networks satisfy their quality-of-service criteria for the low data rate requirements only. However, for the high data rate requirements, a ceiling effect is shown to occur which eventually makes the spectrum sharing infeasible.

In this paper, we investigate the physical layer security of a non-orthogonal multiple access (NOMA) based downlink hybrid satellite-terrestrial relay network where the satellite communicates with terrestrial NOMA users in the presence of an eavesdropper via an amplify-and-forward relay. To analyze the secrecy performance of this network, we derive new closed-form expressions of secrecy outage probability (SOP) and the probability of positive secrecy capacity by adopting shadowed-Rician fading for the satellite link and Nakagami-m fading for terrestrial links. To get more insights, we further derive the closed-form expression for asymptotic SOP and illustrate the behavior of SOP at high signal-to-noise ratio regime. The analytical results are corroborated through Monte-Carlo simulations.

In this paper, we investigate the performance of an underlay cognitive hybrid satellite-terrestrial network comprising a primary satellite source with its terrestrial receiver and the secondary transmitter (ST) with its pre-paired users on the ground. Herein, the ST employs a cooperative non-orthogonal multiple access (C-NOMA) scheme in which a nearby NOMA user acts as a relay and detects and forwards the information of the far-away NOMA user during the cooperation phase. Further, the widely adopted shadowed-Rician fading and Nakagami-m fading models are considered for the pertinent hybrid channels. For this overall set-up, we obtain a novel closed-form expression for the outage probability of secondary network in the presence of primary interference power constraint imposed by the adjacent primary satellite network. Finally, our analytical findings are corroborated through various numerical and simulation results.

A downlink multi-user hybrid satellite-terrestrial relay network (HSTRN) is considered in this paper, where a multi-antenna satellite communicates with the multiple terrestrial users via an interference-limited amplify-and-forward relay. For this network, we investigate the average symbol error probability (SEP) performance by employing opportunistic scheduling of multiple ground users with outdated channel state information (CSI) of the pertaining channels and considering co-channel interference (CCI) at the relay. Specifically, we derive closed-form analytical and asymptotic expressions of the average SEP for the considered network. Further, numerical and Monte-Carlo simulation results are implemented to vindicate the accuracy of our hypothesis as well as to demonstrate the influence of outdated CSI, CCI, and various channel/system parameters on the system performance. Our analysis provides useful trends in the design of HSTRNs for future wireless communication systems.

This study investigates the physical layer security of a downlink hybrid satellite‐terrestrial relay network (HSTRN) where the satellite channel follows shadowed‐Rician fading and terrestrial channels are assumed to undergo independent and non‐identically distributed Nakagami‐ m fading. Herein, the authors consider a multi‐antenna satellite, which communicates with a terrestrial user via an amplify‐and‐forward relay in the presence of multiple colluding eavesdroppers at the earth. They derive novel expressions of secrecy outage probability (SOP), ergodic secrecy capacity, and probability of positive secrecy capacity for the proposed network. They further obtain the achievable secrecy diversity order of the considered HSTRN by employing asymptotic analysis of SOP expression. Finally, numerical and simulation results are provided to validate the accuracy of the proposed analysis and to highlight the impact of a multi‐antenna satellite on future wireless systems.

Mobile-to-mobile communications are offering clear benefits including spectrum and energy efficiency and low latency. However, these systems have to deal with various constraints with the most notable being related to the power consumption as well as the various peculiarities of the time varying wireless medium. In order to improve these systems' performance, antenna selection (AS) techniques have been proposed as an efficient approach to satisfy the hardware/power limitations that exist. However, these systems' performance is directly affected by the fast varying wireless medium, since AS is frequently performed using outdated estimates of the signal-to-noise ratio. In this paper, we propose a transmit AS scheme, whose operation is based on the shadowing side information (SSI) that is acquired in every stationarity region. By adopting SSI as an AS criterion, the negative consequences of the outdated channel state information (CSI) can be alleviated, since large-scale fading varies more slowly as compared to small-scale fading. The performance of this scheme is analyzed using the measures of the outage probability and the average bit error probability. It is shown that the proposed scheme outperforms the corresponding one that is based on (outdated) CSI, especially in scenarios with good channel conditions.

In this paper, we analyze the performance of simultaneous wireless information and power transfer (SWIPT) in two-way relay systems with an active direct link under Nakagami-m fading environment. We consider a three-node based cooperative relaying system consisting of two source nodes and a battery-enabled relay node. Herein, one round of information exchange between source nodes can be accomplished in three time phases. Relay node relies on amplify-and-forward (AF) operation to broadcast the signals, while the destination nodes utilize maximal-ratio combining (MRC) technique to make use of both the direct and relay links. Moreover, the relay node harvests energy from the radio-frequency (RF) signals in the first two phases using power-splitting (PS) approach and then utilizes the harvested energy for information processing and broadcasting the received signals in the third phase. For the considered setup, we proficiently derive accurate expressions for the outage probability (OP), system throughput, and energy efficiency. Numerical results enlighten the importance of considering direct link with MRC in the SWIPT-enabled two-way relay systems.

In this paper, we propose an energy harvesting-based overlay hybrid satellite-terrestrial spectrum sharing system which exploits both direct and relay links from a primary satellite source to terrestrial user with the coexistence of a secondary transmitter-receiver pair on the ground. It is assumed that an energy-constrained secondary transmitter deploys the time switching-based relaying protocol to harvest energy from the primary satellite's signal and then performs an amplify-and-forward based relay cooperation with the primary satellite network to explore an opportunity for spectrum access. By adopting Shadowed-Rician fading for satellite links and Nakagami-m fading for terrestrial links, we derive analytical expressions for the outage probability of primary satellite network and secondary terrestrial network. In addition, to get useful insights, expressions for throughput and energy efficiency of primary satellite network are also provided assuming a delay-limited scenario. Moreover, our results illustrate the impact of power splitting factor and energy harvesting time fraction on the system performance.

In this paper, we examine the performance of simultaneous wireless information and power transfer (SWIPT) in the two-way relay networks under Nakagami-m fading. We consider a three-node wireless communications system, where two source nodes communicate to each other via a half-duplex battery-enabled relay node. A hybrid decode-amplify-forward (HDAF) based relaying scheme is proposed to make the communication links more reliable. With this scheme, the relay node can harvest energy from the radio-frequency (RF) signals, and destination nodes can exploit the direct link. For harvesting energy from RF signals, we adopt time switching (TS) approach, whereby relay node first harvests energy from the received signals in the first phase (energy harvesting phase), and then utilizes the harvested energy to process and broadcast the received signals in next three consecutive (information processing) phases. At the destination nodes, selection combining (SC) technique is employed to make use of two intended signals received via direct and relay links. For this setup, we derive the closed-form expressions for user outage probability (OP) and achievable system throughput under Nakagami-m fading. Numerical and simulation results are provided to highlight the impact of various system and channel parameters on the SWIPT-enabled wireless system and to verify the accuracy of derived expressions.

Important statistical properties of the double-generalized Gamma (dGG) distribution are studied in this paper. The dGG distribution is suitable for modeling non-homogeneous double-scattering radio propagation fading conditions, which can be frequently observed in vehicle-to-vehicle (V2V) communications. In this context, important statistical metrics for the bivariate dGG distribution, such as the joint probability density function, cumulative distribution function, and the moments, are derived for the first time, while simplified expressions for the corresponding marginal statistical metrics are presented. Moreover, the second-order statistics of this distribution are also analytically studied. The derived analytical framework has been employed to analyze the performance of a transmit antenna selection system operating in V2V communication channels modeled by the dGG distribution. In this scenario, the impact of outdated channel state information (CSI) to the system's performance is investigated in terms of various metrics, including the level crossing rate and the average fade duration. Furthermore, simplified asymptotic closed-form expressions for the outage probability have been derived to examine the achievable diversity and coding gains. Based on our analysis, insightful discussions are provided. It is shown that the diversity gain is independent from the number of transmit antennas when the available CSI becomes outdated.

In this paper, we investigate the performance of a spectrum sharing decode-and-forward multiple-relay network (SSDMN) with direct link under the joint impact of two practical and detrimental imperfections, called transceiver hardware impairments (HIs) and channel estimation errors (CEEs). Here, we consider the hardware distortions induced by all the non-ideal secondary nodes and residual interferences originating from imperfect channel estimations. By taking these imperfections into account, we derive an exact closed-form expression for the outage probability of the considered SSDMN employing selection cooperation over independent and non-identical Rayleigh fading channels. We identify three important ceiling effects invoked by HIs, namely relay cooperation ceiling (RCC), direct link ceiling (DLC), and overall system ceiling. Specifically, we highlight the impact of these prevailing effects on the system's performance and provide some useful insights about the tolerable level of HIs while designing the practical systems for a given rate requirement. We also illustrate that a potential direct link and a relaying link can, respectively, partially compensate for the incurred performance losses due to RCC and DLC effects. Moreover, we investigate the asymptotic behavior of outage probability to highlight the impact of HIs and CEEs on the achievable diversity and coding gains.

In this paper, important statistical properties of the double- generalized Gamma (dGG) distribution, a generic modelthat has been used for modeling the double-scattering radio propagation fading conditions, are obtained and investigated. In this context, useful statistical metrics, such as the probability density function, cumulative distribution function, and the moments, are derived. Moreover, the second-order statistics of this distribution are also analytically studied for the first time. Based on them, exact expressions for the outage probability, the average symbol error probability, and the capacity of a transmit antenna selection system operating in a vehicle-to-vehicle (V2V) communication environment are obtained. In addition, the level crossing rate and the average fade duration are studied. Simplified asymptotic closed-form expressions have been also obtained and used to investigate the diversity and coding gains.

In this paper, we analyze the performance of a cognitive amplify-and-forward multi-relay network (CAFMRN) with direct link under the joint impact of transceiver hardware impairments (HIs) and channel estimation errors (CEEs). Herein, we consider hardware distortions induced by all the non-ideal secondary nodes and residual interferences originating from imperfect channel estimations. Taking these imperfections into account, we derive a new closed-form expression for the outage probability of the considered CAFMRN employing selection cooperation over independent and non-identical Rayleigh fading channels. Furthermore, we derive an asymptotic outage behavior to assess achievable diversity order. We illustrate that HIs may invoke ceiling effects into the system, namely relay cooperation ceiling (RCC) and overall system ceiling (OSC). Specifically, we showcase that the RCC ceases the full cooperation, whereas, the OSC may further aggravate the system outage performance under a high-rate requirement. By modeling the CEEs as decreasing function of signal-to-noise-ratio, we demonstrate that CEEs pose critical impact on the coding gain only and not on the diversity gain of the system. Finally, numerical and simulation results are presented to validate our theoretical findings.

Transmit antenna selection (TAS) schemes have been adopted in various communication systems to provide improved performance with relatively reduced complexity. The quality-of-service (QoS) in these systems depends on the availability of perfect channel state information (CSI). In practice, it is difficult to acquire perfect CSI, since it may get outdated due to feedback process. In this paper, we investigate the impact of outdated CSI in a TAS system that operates in a vehicle-to-vehicle (V2V) communication environment. The V2V channel is modeled by the double-Weibull (DW) distribution, a widely adopted distribution for modelling scenarios where both the transmitter and the receiver are in motion. In this context, we introduce and derive important statistical metrics for the bivariate DW distribution, such as the probability density function, the cumulative distribution function, and the moments. Based on them, exact expressions for the outage probability and the average bit error probability of the TAS scheme are derived under the assumption of outdated CSI. Moreover, simplified asymptotic closed-form expressions have been obtained. These expressions are then used to study the performance of the system under consideration.

We consider a hybrid satellite-terrestrial spectrum sharing system wherein multiple terrestrial secondary networks coexist with a primary satellite network. We propose an amplify-and-forward based cooperative spectrum sharing protocol by employing an opportunistic secondary network selection (OSNS) scheme. The best secondary network is selected to minimize the outage probability of primary satellite system and to achieve spectrum access. With overlay approach, the selected secondary network allocates its partial power to relay the satellite signal and utilizes the remaining power to transmit its own signal. We derive closed-form expressions of outage probability for both primary and secondary networks and examine their achievable diversity order over hybrid fading channels. Numerical and simulation results validate our analysis and highlight the performance gains of the considered system with OSNS scheme.

In this paper, the joint effect of multiple jamming signals and noise at the eavesdropper in wiretap channels is studied in terms of the secrecy outage probability, where all nodes are deployed with multiple antennas. Specifically, the transmitter employs a transmit antenna selection (TAS) technique; the legitimate receiver uses either a selection combining (SC) or a maximal-ratio combining (MRC) scheme; and the eavesdropper adopts the MRC technique. Exact closed-form expressions for the secrecy outage probability are derived for both SC and MRC schemes at the legitimate receiver, which are applicable for arbitrary number of power distributed jamming signals. An asymptotic secrecy outage analysis is conducted, which shows that the diversity gains for all combining schemes equal to the product of the number of antennas at the transmitter and the legitimate receiver. Representative numerical examples are presented to illustrate the effects of the key system parameters on the secrecy outage performance. Finally, the proposed analysis is validated through Monte Carlo simulation results.

In this paper, we investigate the secrecy performance of a hybrid satellite-terrestrial relay network, where a satellite communicates with a terrestrial destination via multiple relays in the presence of eavesdropper. Particularly, to strengthen the system security against wiretapping attack, we present amplify-and-forward (AF) based optimal and partial relay selection schemes to minimize the secrecy outage probability (SOP). Hereby, the optimal scheme depends on both main and wiretapper links, while the partial scheme relies only on the legitimate terrestrial links. We derive the SOP expressions for both schemes by considering Shadowed-Rician fading for satellite channels and Nakagami-m fading for terrestrial channels. We further simplify these expressions at asymptotic high signal-to-noise ratio (SNR) and main-to-eavesdropper ratio (MER) regime to reveal useful insights on achievable diversity gains. Finally, the theoretical analysis is validated through Monte-Carlo simulations.

In this paper, we investigate the secrecy performance of an underlay cognitive decode-and- forward relay network (CDRN) by exploiting an active direct link in the presence of primary user's (PU's) interference. Herein, a secondary user (SU) transmitter strives to maintain a secure communication link with a legitimate SU receiver in presence of a passive eavesdropper. On account of system's viability, we consider the presence of a PU transmitter as well as a PU receiver, wherein the secondary transmissions satisfy the fading- averaged interference constraints at the PU receiver. Specifically, we focus on utilizing the interference from primary transmission as a jamming signal for ameliorating the secrecy performance of secondary network. We derive closed-form expressions of secrecy outage probability for the secondary network with and without PU's interference. Numerical and simulation results validate our analysis and reveal the secrecy performance improvement of considered CDRN.

This study investigates the performance of a cognitive relay sharing system (CRSS) wherein two primary users (PUs) exchange the information bidirectionally. The overall transmission in CRSS takes place using an amplify‐and‐forward‐based multiple access broadcast protocol. Herein, besides assisting the transmission of secondary users, the relay also provides an aid for the bidirectional communication between PUs. In addition, the secondary system employs an opportunistic user scheduling with multiple destinations to further ameliorate the performance of secondary network. Here, by considering Nakagami‐ m fading channels, the authors derive novel closed‐form expressions of outage probability (OP) and average error probability for both primary and secondary systems. Based on the derived expressions of OP, the authors also quantify the average system throughput. With bidirectional primary communications, the proposed CRSS offers higher spectral efficiency and incentivises the secondary communication through multiuser diversity. Finally, numerical and simulation results are provided for the validation of the theoretical analysis.

In this paper, we study a hybrid satellite-terrestrial spectrum sharing system (HSTSSS) in which multiple terrestrial secondary networks cooperate with a primary satellite network for dynamic spectrum access. For complexity-aware HSTSSS design, we propose an amplify-and-forward-based overlay spectrum sharing protocol using partial and opportunistic secondary network selection schemes. The secondary network selection aims to minimize the outage probability of the primary satellite system and, thereby, to explore spectrum sharing opportunities. With the overlay approach, the selected secondary network allocates part of its power to relay the satellite signal and utilizes the remaining power to transmit its own signal. Considering Shadowed-Rician fading for satellite links, and Nakagami-m as well as Rician fading for terrestrial links, we derive closedform expressions for the outage probability of both primary and secondary networks, and examine their achievable diversity orders. Numerical and simulation results validate our analysis and highlight the performance gains of the proposed schemes for an HSTSSS with and without a direct satellite primary communication link.

In this paper, we investigate the outage performance of a decode-and-forward (DF) underlay cognitive two-way relay system with direct link using time division broadcast protocol in the presence of primary user's interference. Herein, relying on the practicability and low-complexity of statistical channel state information (CSI), the secondary transmissions satisfy the fading-averaged interference constraints at the primary receiver. We study an efficient link utilization scheme that can exploit both direct and relay links with appropriate combining methods to improve the performance of secondary users. Considering Nakagami-m fading channels, we derive a tight closed-form expression of outage probability for the secondary communications. We further perform the asymptotic high signal-to-interference noise ratio (SINR) analysis to gain more insight. We quantify the implications of primary user's interference on the secondary system performance and present several useful insights. With the proposed scheme, secondary system is shown to harness full diversity as long as the primary interference remains limited otherwise outage floor phenomenon occurs. Numerical and simulation results corroborate our theoretical developments.

In this paper, we consider an overlay spectrum sharing system with two-way communications in the presence of multiple co-channel interferers under Nakagami-m fading. By employing three-phase time-division broadcast protocol, a secondary user allocates its partial power to amplify-and-forward the two-way primary signals and the remaining power to transmit its own signal. For such a set-up, we derive tight closed-form expressions of the outage probability for both primary and secondary communications. We further obtain their high signal-to-noise ratio (SNR) equivalent expressions to determine the achievable diversity gains. Moreover, we quantify the impact of co-channel interference on the spectrum sharing and present useful insights into the system performance. Numerical and simulation results conform to our theoretical findings.

In this paper, we consider a two-way relay system that employs transmit/receive beamforming for bidirectional communication using analog network coding (ANC) protocol in the presence of channel estimation error (CEE). For this set-up, we first obtain the instantaneous end-to-end signal-to-noise ratios (SNRs) with partial self-interference cancellation pertaining to imperfect channel estimation. Then, by considering asymmetric traffic requirements, we derive an accurate expression of overall outage probability (OOP) of the considered system under Nakagami-m fading. We further derive a tight lower bound on OOP that has a simple and compact closed-form representation. Moreover, we present an asymptotic OOP expression at high SNR to examine the achievable diversity order with CEE. Numerical and simulation results validate our theoretical analysis and highlight the impact of CEE and different traffic patterns on the system performance with various antenna configurations and fading severity parameters.

In this study, the authors conduct the performance evaluation and resource allocation for two‐way multiple‐input multiple‐output‐based device‐to‐device (D2D) communications overlaying a cellular network. The considered system model comprises of a base station, a mobile user, and a pair of D2D users, where each of them is equipped with multiple antennas and employs transmit/receive zero forcing. Based on overlaying approach, both D2D and cellular communications take place bidirectionally by employing analogue network coding with a best selected D2D user as two‐way relay for the cellular links. The authors analyse the outage performance of cellular and D2D systems in a Rayleigh fading environment. They also deduce asymptotic outage behaviour of cellular system and highlight the achievable diversity order. In addition, they derive the expressions of ergodic sum rate for both the systems. Above all, they provide a selection algorithm for the best relaying D2D user and describe feasible range of power splitting factor to maximise the data rate of cellular system for a given data rate of D2D system. Numerical and simulation results validate the authors’ theoretical findings and illustrate the performance gains of the considered scheme under various antenna configurations.

In this study, the authors consider a cooperative spectrum sharing network with multiple primary users (PUs) and multiple secondary users (SUs). Hereby, one end‐PU communicates bidirectionally with one of the best selected other end‐PUs with the cooperation of the best selected SU using time division broadcast protocol. Based on an overlay approach, the selected SU allocates its partial power to relay the PUs’ signals and utilises the remaining power to transmit its own signal. The authors devise a low‐complexity distributed PU–SU selection strategy to minimise the overall outage probability of the primary system. For Nakagami‐ m fading, the authors derive tight expressions of outage probability for both primary and secondary systems of the considered scheme. Further, by deriving their asymptotic behaviour at high signal‐to‐noise ratio, the authors highlight the performance gain accrued by cooperative and multiuser diversity along with that offered by the channels under Nakagami‐ m fading. Besides, the authors demonstrate the effective locations for the SUs to access the spectrum. Above all, the authors illustrate that the increase of the number of SUs is more desirable than the number of PUs to explore the spectrum sharing opportunities. Numerical and simulation results substantiate the effectiveness of the proposed scheme and the theoretical analysis.

In this study, the authors investigate the impact of channel estimation error (CEE) on the performance of a multiple‐input–multiple‐output (MIMO) two‐way relay system under Rayleigh fading. Herein, transmit/receive zero‐forcing (ZF) is employed at the two source nodes, whereas analogue network coding is used at the relay node. Fundamentally, for making use of transmit/receive ZF, all nodes must be aware of channel state information (CSI). As perfect CSI may not always be available in practical scenarios, the CEE does exist in the considered system. By taking the imperfect CSI into account, they enucleate that the residual self‐interference and additional noise pertaining to the CEE have effect of reducing end‐to‐end signal‐to‐noise ratios (SNRs) at the two source nodes. Based on the statistical characterisations of these post‐processing SNRs, they carry out the overall system outage probability analysis. Further, they investigate the asymptotic outage behaviour to deduce the achievable diversity order. They substantiate that the diversity order may reduce to zero under severe impact of CEE. In addition, they derive a closed‐form expression of ergodic sum‐rate of the considered system with CEE. Numerical and simulation investigations are conducted to support all the theoretical findings using various values of CEE and antenna configurations.

In this paper, we investigate the performance of an overlay spectrum sharing system by employing an opportunistic multiuser two-way relaying with time division broadcast (TDBC) protocol over Nakagami-m fading channels. Herein, one-end primary user (PU) exchanges information with one of the best selected other end-PUs with the assistance of a secondary user (SU) using TDBC protocol. With an overlay approach, the SU allocates its partial power to relay the PUs' signals and uses the remaining power to transmit its own signal. The underlying PU selection strategy is designed to minimize the primary system outage probability. For such a set-up, we derive a closed-form expression for the overall outage probability. Based on its asymptotic representation at high signal-to-noise ratio (SNR), we illustrate that the primary system can achieve maximum diversity order and allows spectrum sharing as long as its outage constraints are met. Numerical and simulation results are provided to validate our theoretical analysis.

In this paper, we investigate the impact of channel estimation errors on the overall outage performance of a two-way multi-relay system that employs three-phase analog network coding (ANC) with opportunistic relay selection. We first represent the two end-to-end instantaneous signal-to-noise ratios (SNRs) with imperfect self-interference cancellation owing to the channel estimation errors. Based on these, we derive a tight closed-form expression for the overall system outage probability over Rayleigh fading channels. We also derive an asymptotic outage expression in high SNR regime, from which the effect of imperfect estimation on the achievable diversity order is examined. The theoretical findings are verified through numerical and simulation results.

Alterations in transients during awake, slow wave sleep (SWS), and rapid eye movement (REM) sleep stages due to an exposure to high environmental heat have been studied using continuous wavelet transform (CWT) method and artificial neural network (ANN). After two hours long EEG (Electroencephalogram) recordings from healthy rats, EEG data representing three sleep states was visually selected and further subdivided into 2 seconds long epoch. After extracting features in terms of wavelet coefficients for all the epochs multilayer perceptron neural network (MLPNN) has been trained to detect changes in the vigilance states of the subjects exposed to environmental heat stress. It reveals that, the classifications of wavelet coefficients of EEG signals in acute as well as chronic heat conditions along with the control data show the overall accuracy of 94.5% in SWS, 91.75% in REM sleep and 91.75% in AWAKE state.

We consider a two-way relay system where multi-antenna sources employ beamforming to communicate bidirectionally via a single-antenna relay with analog network coding over Nakagami-m fading channels. We address the problem of both separate and joint optimization of power allocation and relay location in order to minimize the overall system outage probability. Our results demonstrate that separate optimization of relay location is more significant than that of power allocation to improve the overall system outage performance. We further emphasize that the joint optimization of power allocation and relay location can provide noticeable outage performance improvement over unbalanced per-hop fading conditions and/or nonidentical antenna configurations.

This paper evaluates the performance of an opportunistic scheduling scheme for a multiuser two-way relay network, wherein an analog network coding (ANC)-based relay assists the communication between multiple pairs of users. To ensure fairness for each user pair, we consider a scheduler based on maximizing the normalized minimum of the instantaneous signal-to-noise ratios (SNRs) at each user of the pair. Under a high SNR assumption, we derive upper and lower bound expressions for the outage probability and the average sum-rate in a Rayleigh fading environment and establish that a multiuser diversity of order equal to the number of user pairs is harnessed by the scheme. Numerical and simulation results are presented to confirm the performance gain of the proposed scheme.

In a distributed cooperative environment, synchronization is a major issue. Especially when OFDM is employed in the physical layer, frequency offset synchronization is of great significance. In addition, transmitter and receiver IQ imbalances are known to be important implementation issues in OFDM systems. In this paper, a novel precoding strategy is proposed that enables blind estimation of carrier frequency offsets (CFOs) of each transmitter (separately) in cooperative scenario when the SFBC OFDM is employed in the physical layer, even when the transmitter and receiver IQ imbalances are present, and the channel is frequency selective. This non-redundant precoding strategy involves multiplication of the symbols to be transmitted by a random phase precoding sequence, and results in no loss in rate or bandwidth. Computer simulations are presented to demonstrate the effectiveness of the algorithm.