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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 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]