This article proposes a cooperative friendly jamming framework for swarm unmanned aerial vehicle (UAV)-assisted amplify-and-forward (AF) relaying networks with wireless energy harvesting. We consider a swarm of hovering UAVs that relays information from a terrestrial source to a distant mobile user and simultaneously generates jamming signals to obfuscate an eavesdropper. Due to the limited energy of the UAVs, we develop a collaborative time-switching relaying protocol that allows the UAVs to collaborate to harvest wireless energy, relay information, and jam the eavesdropper. To evaluate the secrecy rate, we derive the expressions of the secrecy outage probability (SOP) in the integral form for two popular detection techniques used by the eavesdropper, i.e., selection combining and maximum-ratio combining in high signal-to-noise ratio regime. Monte Carlo simulations validate the derived SOP and show that the proposed framework outperforms the conventional AF relaying system, in terms of SOP. The insights from SOP and analysis in this work sheds light on optimizing the energy harvesting time, the number of UAVs in the swarm as well as their placements, to achieve the required secrecy protection level.

This article proposes a cooperative friendly jamming framework for swarm unmanned aerial vehicle (UAV)-assisted amplify-and-forward (AF) relaying networks with wireless energy harvesting (EH). In particular, we consider a swarm of hovering UAVs that relays information from a terrestrial base station to a distant mobile user and simultaneously generates friendly jamming signals to interfere/obfuscate an eavesdropper. Due to the limited energy of the UAVs, we develop a collaborative time-switching relaying protocol that allows the UAVs to collaborate in harvesting wireless energy, relay information, and jam the eavesdropper. To evaluate the performance, we derive the secrecy outage probability (SOP) for two popular detection techniques at the eavesdropper, i.e., selection combining and maximum-ratio combining. Monte Carlo simulations are then used to validate the theoretical SOP derivation. Using the derived SOP, one can obtain engineering insights to optimize the EH time and the number of UAVs in the swarm to achieve a given secrecy protection level. Furthermore, simulations show the effectiveness of the proposed framework in terms of SOP compared to the conventional AF relaying system. The analytical SOP derived in this work can also be helpful in future UAV secure-communication optimizations (e.g., trajectory and locations of UAVs). As an example, we present a case study to find the optimal corridor to locate the swarm so as to minimize the system SOP. Our proposed framework helps secure communications for various applications that require large coverage, e.g., industrial IoT, smart city, intelligent transportation systems, and critical IoT infrastructures, such as energy and water.

In an UAV‐ (unmanned aerial vehicle‐) aided relaying system, the transmitted signal is exposed to free space in two transmission hops which may be overheard by eavesdroppers. Accordingly, physical layer security should be exploited to improve information security. This paper analyzes both (security and reliability) performance aspects of such a system where only one UAV among multiple UAVs, all capable of harvesting energy from radio frequency signals, is adopted. Towards this end, the tight approximated and exact closed‐form expressions of the outage probability at the legitimate destination and the intercept probability at the eavesdropper are first derived. Then, Monte‐Carlo simulations are conducted to verify the derived expressions. Based on these expressions, the protected zone of the selected UAV is also proposed through an exhaustive search. Finally, various results are provided to illustrate the impact of key operation parameters on the system performance and the efficacy of the UAV selection.

Artificial noise, energy harvesting, and overlay communications can assure design metrics of modern wireless networks such as data security, energy efficiency, and spectrum utilization efficiency. This paper studies impact of artificial noise on security capability of energy harvesting overlay networks in which the cognitive transmitter capable of self‐powering its operation by harvesting radio frequency energy and self‐securing its communications against eavesdroppers by generating artificial noise amplifies and forwards the signal of the primary transmitter as well as transmits its individual signal concurrently. To quantify this impact, the current paper firstly suggests accurate expressions of crucial security performance indicators. Then, computer simulations are supplied to corroborate these expressions. Finally, numerous results are demonstrated to expose insights into this impact from which optimum specifications are determined. Notably, primary/cognitive communications can be secured at distinct degrees by flexibly controlling multiple specifications of the suggested system model.

This paper selects an unlicensed relay among available self‐powered relays to not only remain but also secure information transmission from an unlicensed source to an unlicensed destination. The relays harvest energy in signals of the unlicensed source and the licensed transmitter. Then, they spend the harvested energy for their relaying operation. Conditioned on the licensed outage restriction, the peak transmission power restriction, Rayleigh fading, and the licensed interference, the current paper proposes an exact closed‐form formula of the secrecy outage probability to quickly evaluate the secrecy performance of the proposed relay selection method in cognitive radio networks with energy harvesting. The proposed formula is corroborated by computer simulations. Several results illustrate the effectiveness of the relay selection in securing information transmission. Additionally, the security capability is saturated at large peak transmission powers or large preset outage probabilities of licensed users. Furthermore, the security capability depends on many specifications among which the power splitting ratio, the relays’ positions, and the time switching ratio can be optimally selected to obtain the best security performance.

Relay selection is proposed in this paper as an efficient solution to secure information transmission of secondary users against eavesdroppers in energy harvesting cognitive networks. The proposed relay selection method selects a secondary relay among available secondary relays, which are capable of harvesting radio frequency energy in signals of the secondary transmitter and correctly restore secondary message, to curtail signal-to-noise ratio at the wire-tapper. In order to evaluate the security performance of the suggested relay selection method, an exact intercept outage probability formula accounting for peak transmit power confinement, Rayleigh fading, and interference power confinement is firstly derived. Monte-Carlo simulations are then generated to corroborate the proposed formula. Numerous results expose that positions of relays, the number of relays, and parameters of the energy harvesting method significantly influence the security performance while the power confinements on secondary transmitters cause the performance saturation.

In this paper, we propose an underlay two-way relaying scheme with the successive interference cancellation (SIC) solution in which two secondary sources transmit simultaneously their data to each other through secondary relays. The proposed scheme is operated in only two time slots and under an interference constraint of a primary receiver, denoted as the UTW-2TS scheme. In the UTW-2TS scheme, the secondary relays employ the SIC operation to decode successively the data from received broadcast signals and then encode these data by two techniques: digital network coding (DNC) enforced by XOR operations (denoted as the UTW-2TS-DNC protocol) and superposition coding (SC) enforced by power domain additions (denoted as the UTW-2TS-SC protocol). A selected secondary relay which subjects to maximize decoding capacities and to minimize collection time of channel state information in two protocols UTW-2TS-DNC and UTW-2TS-SC experiences residual interferences from imperfect SIC operations. Outage probabilities and throughputs are solved in terms of exact closed-form expressions to evaluate the system performance of the proposed protocols. Simulation and analysis results provide performance enhancement of the proposed protocols UTW-2TS-DNC and UTW-2TS-SC owing to increase the number of the cooperative secondary relays, the interference constraints, and the distances from the secondary network to the primary receiver. The best throughputs are pointed at optimal interference power allocation coefficients and optimal locations of the selected secondary relay. Considering the same power consumption, the UTW-2TS-DNC protocol outperforms the UTW-2TS-SC protocol. Finally, the simulation results are collected to confirm the exact analysis values of the outage probabilities and throughputs.

This study investigates two‐way relaying where an energy harvesting capable relay exchanges information between two sources. Legitimate information is wire‐tapped by an eavesdropper. To intercept wire‐tapping, this study exploits a friendly jammer. Secrecy outage analysis of the energy harvesting two‐way relaying network with the friendly jammer over Rayleigh fading channels is first proposed in terms of individual secrecy outage probabilities and then validated by computer simulations. Various results demonstrate the efficacy of the jammer in preventing the eavesdropper from stealing the source information and significant impacts of relay location, jammer location, jammer's transmit power, energy conversion efficiency, time switching ratio on the security performance.

This paper exploits a self-powered secondary relay to not only maintain but also secure communications between a secondary source and a secondary destination in cognitive radio networks when source-destination channel is unavailable. The relay scavenges energy from radio frequency (RF) signals of the primary transmitter and the secondary source and consumes the scavenged energy for its relaying activity. Under the maximum transmit power constraint, Rayleigh fading, the primary outage constraint, and the interference from the primary transmitter, this paper suggests an accurate closed-form expression of the secrecy outage probability to promptly assess the security performance of relaying communications in energy scavenging cognitive networks. The validity of the proposed expression is verified by computer simulations. Numerous results demonstrate the security performance saturation in the range of large maximum transmit power or high required outage probability of primary users. Moreover, the security performance is a function of several system parameters among which the relay’s position, the power splitting factor, and the time splitting factor can be optimized to achieve the minimum secrecy outage probability.

This study suggests an energy-scavenging capable unlicensed relay not only to retain communications between an unlicensed sender-recipient pair in underlay cognitive networks but also to secure these communications against eavesdropping of malicious users. Message-securing capability of such a network configuration is assessed through secrecy outage probability (SOP). For this purpose, a precise closed-form formula of the SOP accounting for interference power restriction, Nakagami-m fading, and maximum transmit power restriction is first proposed. Then, the proposed formula is validated by computer simulations. Ultimately, various results are supplied to contrive that the relay position, the time percentage, and the power percentage of the energy-scavenging technique should be appropriately chosen for achieving the best security performance. Moreover, the SOP decreases with lower severity fading level and is constant in the range of high maximum interference power or high maximum transmit power.

Underlay cognitive networks allow unlicenced/secondary users (SUs) to opportunistically access licenced frequency bands, and hence information transmission is undoubtedly wire‐tapped by eavesdroppers. This study analyses security performance of a relay selection scheme, which selects a secondary relay to minimise information wire‐tapping of eavesdroppers, in underlay cognitive networks. Toward this end, the authors propose approximate and asymptotic intercept outage probability expressions which account for interference power constraint for licenced/primary users, maximum transmit power constraint for SUs, independent non‐identical fading channels, and direct channel between secondary source and eavesdropper. Moreover, they determine diversity order and coding gain of this relay selection based on the proposed asymptotic expression. Monte Carlo simulations validate these expressions and numerous results demonstrate that the investigated relay selection prevents the eavesdropper from obtaining full diversity order offered by all relays and source, induces the intercept outage probability saturated at either large maximum transmit power or large maximum interference power, and improves information security performance with respect to the increase in the number of relays.

Cognitive radio networks (CRNs) allow coexistence of unlicensed users (UUs) and licensed users (LUs) and hence, mutual interference between UUs and LUs is neither ignored nor considered as Gaussian‐distributed quantity. Additionally, exploiting jamming signals to purposely interfere with signal reception of eavesdroppers is a feasible solution to improve security performance of CRNs. This paper analyzes reliability‐security trade‐off, which accounts for maximum transmit power constraint, interference power constraint, jamming signal, and Rayleigh fading, and considers interference from LUs as non‐Gaussian‐distributed quantity. Toward this end, exact closed‐form expressions of successful detection probability and successful eavesdropping probability, from which reliability‐security trade‐off is straightforwardly visible, are first suggested and then validated by Monte‐Carlo simulations. Various results demonstrate that interference from LUs considerably decreases both probabilities while jamming signal enlarges the difference between them, emphasizing its effectiveness in improving security performance.

Energy detection has been for long constituting the most popular sensing method in RADAR and cognitive radio systems. The present paper investigates the sensing behaviour of an energy detector over Hoyt fading channels, which have been extensively shown to provide rather accurate characterization of enriched multipath fading conditions. To this end, a simple series representation and an exact closed-form expression are firstly derived for the corresponding average probability of detection for the conventional single-channel communication scenario. These expressions are subsequently employed in deriving novel analytic results for the case of both collaborative detection and square-law selection diversity reception. The derived expressions have a relatively tractable algebraic representation which renders them convenient to handle both analytically and numerically. As a result, they can be utilized in quantifying the effect of fading in energy detection based spectrum sensing and in the determination of the trade-offs between sensing performance and energy efficiency in cognitive radio communications. Based on this, it is shown that the performance of the energy detector depends highly on the severity of fading as even slight variations of the fading conditions affect the value of the average probability of detection. It is also clearly shown that the detection performance improves substantially as the number of branches or collaborating users increase. This improvement is substantial in both moderate and severe fading conditions and can practically provide full compensation for the latter cases.

This study first modifies the traditional partial relay selection in cooperative cognitive networks to prevent error propagation and then proposes exact and asymptotic outage analysis for the modified partial relay selection under practical operation conditions such as channel estimation errors (CEEs) on all wireless channels, independent and non‐identical fading distributions, interference power constraint, and maximum transmit power constraint. The proposed analysis is useful in assessing system performance in important parameters as well as providing insights into performance limits without exhaustive simulations. Moreover, in order to quantitatively evaluate the performance gain of utilising the direct channel between the source and the destination in relaying communications, the authors extend their proposed analysis to dual‐hop cognitive networks. Illustrative results demonstrate that CEEs and outage threshold significantly degrade system performance, and the direct channel dramatically contributes to performance improvement of relaying communications.

This work is devoted to the analysis of the performance of energy detection based spectrum sensing in the presence of enriched fading conditions which are distinct for the large number of multipath components and the lack of a dominant components. This type of fading conditions are characterized efficiently by the well known Nakagami-q or Hoyt distribution and the proposed analysis is carried out in the context of the area under the receiver operating characteristics (ROC) curve (AUC). Unlike the widely used probability of detection metric, the AUC is a single metric and has been shown to be rather capable of evaluating the performance of a detector in applications relating to cognitive radio, radar systems and biomédical engineering, among others. Based on this, novel analytic expressions are derived for the average AUC and its complementary metric, average CAUC, for both integer and fractional values of the involved time-bandwidth product. The derived expressions have a tractable algebraic representation which renders them convenient to handle both analytically and numerically. Based on this, they are employed in analyzing the behavior of energy detection based spectrum sensing over enriched fading conditions for different severity scenarios, which demonstrates that the performance of energy detectors is, as expected, closely related to the value of the fading parameter q.

The aim of this work is the proposition of the κ-μ/Inverse Gaussian distribution which corresponds to a physical fading model. This is a composite distribution which is based on the κ-μ multipath model and the recently proposed Inverse Gaussian shadowing model. The former is a generalised model which includes as special cases the widely known Nakagamim, Rayleigh, Rice and one sided Gaussian distributions and accounts particularly for Non-Line-of-Sight communications. The latter is a convenient model which was recently shown to characterize shadowing effect more accurately than the widely used gamma distribution. As a result, the proposed composite model provides an overall efficient characterisation of multipath and shadowing effects which typically occur simultaneously. The offered modelling accuracy is achieved thanks to the remarkable flexibility of its parameters which is verified by the fact that the model is capable of providing good fittings to measurement data from realistic communication scenarios. Novel analytic expressions are derived for the probability density function (pdf) and the moments of the κ-μ/Inverse Gaussian composite fading model which includes as special cases the Nakagami-m/Inverse Gaussian, Rayleigh/Inverse Gaussian and Rice/Inverse Gaussian composite fading distributions. The offered expressions can be readily utilized in the derivation of vital performance measures in radio and free-space-optical communications over multipath/shadowing and medium-to-strong atmospheric turbulence, respectively. In this context, a closed-form expression is derived for the Amount of Fading over κ-μ/Ig fading channels.

This paper studies the outage performance behaviour of underlay cooperative cognitive networks over Nakagami‐ m fading channels. For time savings in collecting simulation results, the authors propose a new outage probability expression. Notably, this expression is quite general, taking into account practical operation conditions such as interference power constraint, maximum transmit power constraint, correlation among received signal‐to‐noise ratios, non‐identically and independently distributed Nakagami‐ m fading channels and the maximum ratio combining receiver. Moreover, it is useful in obtaining numerical results for performance comparison between dual‐hop communications and cooperative communications in underlay cognitive networks. Interestingly, analytical results illustrate that like dual‐hop cognitive networks, cooperative cognitive ones experience an error floor but the latter significantly outperform the former at almost no cost of power and bandwidth.

This work is devoted to the error rate analysis of underlay multi‐hop cognitive networks with arbitrary number of hops in the presence of multipath fading. Novel analytic expressions are derived in closed‐form for the case of Rayleigh fading, which are validated extensively through extensive comparisons with results from computer simulations. In addition, the corresponding asymptotic performance for large maximum transmit power or large maximum interference power is investigated in detail. The derived expressions provide useful insights on the behaviour of the network performance under different operation parameters and include several previous works as special cases. Furthermore, their algebraic representation is relatively simple which renders them convenient to handle both analytically and numerically. The offered results also demonstrate that underlay multi‐hop cognitive networks suffer significantly from the error floor phenomenon, the channel estimation error and the order of locating unlicensed users of different maximum transmit power levels, whereas for the linear network model their performance is highly dependant on the number of hops. Moreover, it is shown that optimum positioning of helpers in underlay multi‐hop cognitive networks depends on numerous factors and differs substantially from those in traditional multi‐hop networks.

To protect digital subscriber loop (DSL) systems against impulse noise (IN), interleaving combined with Reed-Solomon (RS) coding has been used. Nevertheless, interleaving introduces a long delay. This paper considers retransmission instead of interleaving to reduce such delay and proposes an approach using the available RS decoding failure status to trigger retransmission request. Retransmission probability, average delay and bit error rate (BER) are derived and validated by simulation. Illustrative results show that retransmission can offer a much shorter delay than interleaving while efficiently avoiding transmission errors in various channel conditions.

Reed-Solomon (RS) coding and interleaving are usually combined to protect digital subscriber line (DSL) systems against impulse noise (IN) but introducing a long delay. It is proved that interleaving delay can be significantly reduced by error and erasure decoding (EED). This paper proposes an erasure marking technique to enhance the reliability of the erasure information in order to completely exploit the capability of EED for interleaving delay reduction. Selection of proper parameters for the proposed erasure marking technique is analyzed. Simulation results show that the proposed technique can guarantee efficient erasure marking and reduce the interleaving delay by a factor of two.

In this paper, the exact symbol error probability expression for a decode-and-forward cooperative relaying scheme using quadrature amplitude modulation (QAM) in the presence of Rayleigh fading and Bernoulli-Gaussian impulsive noise is derived. Different from, we only consider the practical receiver structure at the destination without requiring any knowledge of impulsive noise. Also, the source retransmission when the relay fails to detect the source signal is discussed. Analytical results show that cooperative relaying in impulsive noise environment still achieves space diversity and better performance than direct transmission under same bandwidth efficiency and power consumption for any impulse power and impulse rate. However, the source retransmission-assisted cooperative relaying brings negligible improvement.

This paper evaluates the performance of a decode-and-forward scheme using orthogonal frequency-division multiplexing (OFDM) over both time-selective and frequency-selective fading channels. We consider a simple detection based on the zero-forcing (ZF) principle to eliminate inter-carrier interference (ICI) caused by high mobility and to combine signals received from the source and the relay for high spatial diversity at the destination. The symbol error rate (SER) of the ZF-based cooperative relaying scheme is derived and validated by computer simulations. Various results show the superiority of cooperative relaying to direct transmission under same transmission power and bandwidth efficiency for any relay position, signal-to-noise ratio (SNR), path-loss exponent, and normalized Doppler frequency.

Abstract This paper considers a coded cooperative relaying scheme in which all successfully decoded signals from multiple sources are simultaneously forwarded by a multi‐antenna relay to a common multi‐antenna destination to increase bandwidth efficiency. Iterative decoding with hard interference cancellation is used at destination to recover user information. By using orthogonal transmission from sources to avoid their mutual interference, the multi‐antenna relay offers receive space diversity that greatly enhances the decoding performance at the relay. This makes the source‐relay transmission more robust, less sensitive to the source‐relay link SNR, and hence increases the contribution of the relay in cooperative transmission. Simulation results show that the proposed scheme significantly outperforms direct transmission under the same transmit power and bandwidth efficiency. Copyright © 2009 John Wiley & Sons, Ltd.

A coded cooperative transmission scheme based on turbo encoding/decoding, in which only newly generated parity bits of the partner are sent if the user successfully decodes its partner's information in order to improve bandwidth efficiency is proposed. The proposed encoding structure introduces correlation between users' data over multiple frames, which offers effectively longer codes and facilitates high-performance iterative multi-user decoding at the destination. Additionally, the iterative decoding over multiple frames can provide time diversity besides spatial diversity inherent in user cooperation even for flat block fading channels. Simulation results show that the proposed scheme significantly outperforms direct transmission for the same transmitted power and bandwidth efficiency.