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Nonorthogonal multiple access (NOMA) superposes several user signals for simultaneous transmission, considerably ameliorating spectral efficiency. To exploit efficiently radio frequency energy sources surrounding NOMA transmitters for improved energy efficiency, NOMA networks further employ energy harvesting, which practically possesses nonlinear characteristic. In addition, multiple antennas can be deployed at users to transfer-and-harvest energy efficiently and to transmit/receive information reliably with antenna array processing. As such, this paper evaluates numerically the throughput and the outage probability of NOMA networks accounting for practical factors such as nonlinear energy harvesting, all multi-antenna users, and imperfect channel information. Illustrative results expose that nonlinear energy harvesting and channel information imperfection considerably degrade system performance, which is governed flexibly by multiple parameters. Notably, NOMA networks can prevent a total outage and achieve the best performance with a proper parameter selection. Moreover, their performance is considerably ameliorated with accreting the number of antennas. [ABSTRACT FROM AUTHOR]

Relay selection not only maintains but also improves the reliability of source-destination communication when the direct communication link cannot be established because of deep fading and/or shadowing. Nevertheless, two-hop communication makes wireless networks more vulnerable to overhearing as compared to single-hop/direct communication, raising a serious concern about security. To exploit relay selection with both high reliability and security, we propose a jamming-and-relaying (JaR) strategy to adopt one user as a jammer and another user as a traditional relay. Specifically, in this way, legitimate messages are protected against wire-tappers over both relay-destination and source-relay hops where the former and the latter are respectively secured by the jamming signals created by the jammer and the source. Meanwhile, the reliability of such cooperative communication systems is improved by selecting one user as a traditional relay with the highest signal-to-noise ratio over the source-relay channels. Moreover, both the jammer and the traditional relay operate with energy scavenged from source signals through a non-linear energy scavenger (NL-ES) to improve energy efficiency as well as motivate them to secure and forward source messages. The proposed JaR strategy is evaluated over Nakagami-m fading channels in terms of reliability and security by derived exact and asymptotic formulas. Illustrative results expose its superiority to two baseline strategies, namely non-jamming-and-relay selection (nJaR) and non-jamming non-relay selection (nJnR); more specifically, the proposed JaR strategy is more secure than two baseline strategies with a signal-to-noise ratio (SNR) gain of at least 7 dB and is more reliable than the nJnR strategy with a SNR gain of 4 dB for the fading severity m = 3 . Nonetheless, the reliability-security trade-off presents in all the considered strategies. Additionally, an appropriate equilibrium between security and reliability is achievable by setting up system parameters in a proper manner. Furthermore, the NL characteristic of the energy scavengers drastically impacts the reliability yet insignificantly affects the security for the JaR strategy. Also, the NL-ES is more secured yet less reliable than the linear ES (L-ES). [ABSTRACT FROM AUTHOR]

This paper studies overlay-based cognitive radio networks (ObCRNs) where transmission from a licensed transmitter (LT) to a licensed receiver (LR) is supported by an unlicensed transmitter (UT) who has its own communication to an unlicensed receiver (UR). To improve power efficiency of UT and diversity gain at UR and LR, UT operates in direct transmission (DT) or amplify-and-forward (AF) mode or decode-and-forward (DF) mode, and UR and LR combine signals with selection combining (SC) and maximum ratio combining (MRC) from LT and UT. Explicit outage probability expressions for ObCRNs with MRC/SC and DT/AF/DF are proposed to promptly rate its performance. Numerous results reveal the efficacy of the proposed solution and its flexibly-controlled performance. [ABSTRACT FROM AUTHOR]

This paper improves energy efficiency and communications reliability for wireless transmission under κ - μ shadowed fading (i.e., integrating all channel impairments including path loss, shadowing, fading) and hardware impairment by employing a nonlinear energy harvester and multi-antenna power transmitter. To this end, this paper provides explicit formulas for outage probability. Numerous results corroborate these formulas and expose that energy-harvesting nonlinearity, hardware impairment, and channel conditions drastically deteriorate system performance. Notwithstanding, energy-harvesting nonlinearity influences system performance more severely than hardware impairment. In addition, desired system performance is accomplished flexibly and possibly by choosing a cluster of specifications. Remarkably, the proposed communications scheme obtains the optimal performance with the appropriate selection of the time-splitting factor. [ABSTRACT FROM AUTHOR]

Summary: This paper investigates a nonlinear energy scavenging overlay network (NLESON) wherein a primary source (PS) communicates with a primary destination (PD) probably under aid of a secondary source (SS) who communicates with a secondary destination (SD). SS is a power‐constrained device, and thence, its operation relies on energy harvested by a practical nonlinear energy scavenger. To support PS and exploit the harvested energy at most, SS adaptively switches between single and superposition modes where the single mode allows SS to transmit solely its signal with the entire harvested energy and the superposition mode asks SS to transmit both—its signal and amplified primary signal—with different power fractions. Moreover, for increasing the probability of successfully decoding primary signal at PD and SD, which then reduces considerably primary interference on secondary signal in the superposition mode, we leverage both direct channels (PS‐PD and PS‐SD) and apply both signal combining paradigms (maximum ratio combining and selection combining). The outage/throughput performance of the NLESON is assessed quickly through the proposed closed‐form expressions over κ−μ shadowed fading channels. Various results exposed the effectiveness of the aforementioned solutions for the NLESON and their flexibility in controlling system performance. [ABSTRACT FROM AUTHOR]

Overlay networks allow the unlicensed transmitter ( UT ) to aid the licensed transmitter ( LT ) by sending the superimposed signal including messages of both UT and LT with a higher prerogative for LT 's message. Such unequal message prerogatives enable efficient non-orthogonal multiple access (NOMA)-assisted decoding, a.k.a. successive interference cancellation, at corresponding receivers. Alongside the license of accessing the frequency band of LT , UT is further beneficial with its transmission powered merely by energy harvested from LT . Realistically, radio frequency energy harvester is not linear and message transmission in overlay networks is prone to wire-tapping of eavesdroppers. Accordingly, this paper recommends an analysis framework for security performance metrics—secrecy throughput and secrecy outage probability—of overlay networks with nonlinear energy scavenging and NOMA-assisted decoding. The proposed framework facilitates in assessing and comparing security performance in indispensable specifications and serves perfectly as a design guideline. Obtained results reveal that overlay networks with NOMA-assisted decoding are more secure than its OMA and NOMA-unsupported decoding counterparts and suffer error floor at high saturation power threshold or high licensed transmit power. Further, their performance is enhanced with an increase in message processing time and distance between unlicensed and licensed transmitters. [ABSTRACT FROM AUTHOR]

In overlay networks, the cognitive sender ( CS ) assists the primary transmitter ( PT ) by broadcasting the superposed signal composed of both cognitive and primary information with a higher priority for the primary information to ameliorate spectral efficiency. Such different information priorities also facilitate efficient successive interference cancellation (SIC) at corresponding receivers for better system performance. To further benefit CS beside licensed spectrum accessing permission, we assume transmission of CS solely with energy scavenged from PT . Practically, energy scavenger has a nonlinear characteristic and circuit components almost suffer hardware imperfections. Further, path loss, shadowing, and fading are all present in practical wireless channels, which affect not only the scavenged energy but also the system performance. Consequently, this paper proposes a framework to analyze the performance metrics— outage probability and throughput—of overlay networks under realistic scenarios subject to hardware imperfections, energy scavenging nonlinearity, SIC-based signal detection, and versatile-and-general κ - μ shadowed fading. This framework facilitates the system performance evaluation-and-comparison in essential specifications and serves well as a design instruction. Obtained results reveal that hardware imperfections affect the system performance more direly than energy scavenging nonlinearity does and the primary transmission performs considerably better than the secondary transmission irrespective of channel severities. Furthermore, the system performance can be adjusted and optimized versatilely by a multi-parameter set. [ABSTRACT FROM AUTHOR]

This paper considers an underlay relaying network where a cognitive relay performs decode-and-forward operation to aid communication between a cognitive source-destination pair. Transmit powers of cognitive users are subject to both interference and peak transmit power constraints. To stimulate support, the relay merely spends power scavenged from source signals with realistic non-linear energy harvester for its operation. Additionally, to secure secret transmission of both the source and the relay, this paper proposes to merge jamming signals with secret ones before their transmission. Relied on practical observations that jamming signals and channel state information at legitimate receivers may not be suppressed and estimated perfectly, respectively, this paper analyzes system performance under inaccuracies of jamming suppression and channel estimation. Purposively, this paper analyzes security-reliability trade-off of underlay relaying networks under joint practical influences of erroneous channel information, Nakagami-m fading severity, jamming suppression error, energy harvesting non-linearity, and power constraints of cognitive users. Towards this end, explicit expressions of intercept and outage probabilities are first derived. Then, they are used to quickly generate numerous results so as to withdraw interesting findings. More specifically, the proposed jamming strategy experienced the trade-off between security and reliability as well as reliability/security saturation at high peak transmit power. Additionally, channel estimation error, fading severity, jamming suppression error, and energy harvesting non-linearity significantly impact system performance. Nonetheless, system parameters can be set properly to achieve different security levels and prevent absolute outage. [ABSTRACT FROM AUTHOR]

We propose a system model for energy harvesting-based underlay relaying networks with transmit antenna selection and jamming where a multi-antenna unlicensed relay performs multiple tasks [received signal combining, transmit antenna selection (TAS), energy harvesting] to save energy consumption, ensure continuous connection of an unlicensed source to an unlicensed destination, and secure transmission against a wire-tapper. Moreover, to guarantee security for source-to-relay transmission, we propose embedding jamming signal into secret information at the source to reduce the wire-tapper's capability of decoding source message. To swiftly illustrate security-and-reliability trade-off of the proposed system model as well as compare with its counterparts so as to highlight our contributions, we propose closed forms of intercept and outage probabilities at the wire-tapper and the destination, correspondingly, under licensed interference and restraints of peak transmit/interference powers. We found from various results that (1) the proposed TAS scheme achieved the best reliability-and-security trade-off in comparison with previous schemes; (2) reliability saturation occurs at high peak transmit/interference power; (3) licensed interference and time for energy harvesting drastically enhance security yet mitigate reliability; (4) distributing power properly to secret and jamming signals at the source brings better security; (5) increasing the number of antennas at the relay dramatically improves both security and reliability for the proposed TAS scheme. [ABSTRACT FROM AUTHOR]

This paper proposes an overlay network wherein a pair of licensed source (LS) and licensed destination (LD) is adaptively assisted by a pair of unlicensed source (US) and unlicensed destination (UD). By processing adaptively at US and UD relied on the decoding statuses of LD and US, licensed communication is always supported with a high diversity gain from which unlicensed communication also benefits from removing licensed interference as well as transmitting with the highest available power, eventually improving reliability of both unlicensed and licensed communication. This paper also proposes closed-form formulas of outage probabilities at LD and UD for prompt reliability evaluation over κ - μ shadowed fading channels. Multiple results illustrate the superiority of the proposed adaptive processing scheme as compared to its counterpart. Further, the reliability of the suggested scheme can be flexibly controlled and optimized with setting specifications reasonably. [ABSTRACT FROM AUTHOR]