Covert communication aims to prevent the warden from detecting the presence of communications,i.e.with a negligible detection probability.When the distance between the transmitter and the legitimate receiver is large,...Covert communication aims to prevent the warden from detecting the presence of communications,i.e.with a negligible detection probability.When the distance between the transmitter and the legitimate receiver is large,large transmission power is needed,which in turn increases the detection probability.Relay is an effective technique to tackle this problem,and various relaying strategies have been proposed for long-distance covert communication in these years.In this article,we first offer a tutorial on the relaying strategies utilized in covert transmission.With the emergence of reflecting intelligent surface and its application in covert communications,we propose a hybrid relay-reflecting intelligent surface(HR-RIS)-assisted strategy to further enhance the performance of covert communications,which simultaneously improves the signal strength received at the legitimate receiver and degrades that at the warden relying on optimizing both the phase and the amplitude of the HR-RIS elements.The numerical results show that the proposed HR-RIS-assisted strategy significantly outperforms the conventional RIS-aided strategy in terms of covert rate.展开更多
Photoelectrochemical(PEC)technology is considered to be a promising approach for solar-driven hydrogen production with zero emissions.Bismuth vanadate(BiVO_(4))is a kind of photocatalytic material with strong photoact...Photoelectrochemical(PEC)technology is considered to be a promising approach for solar-driven hydrogen production with zero emissions.Bismuth vanadate(BiVO_(4))is a kind of photocatalytic material with strong photoactivity in the visible light region and appropriate band gap for PEC water splitting.However,the solar-to-hydrogen efficiency(STH)of BiVO_(4)is far away from the 10%target needed for practical application due to its poor charge separation ability.Therefore,this review attempts to summarize the strategies for improving the photocurrent density and especially hydrogen production of BiVO_(4)materials through PEC techniques in the last three years,such as doping nonmetal and metal elements,depositing noble metals,constructing heterojunctions,coupling with carbon and metalorganic framework(MOF)materials to further enhance the PEC performance of BiVO_(4)photoanode.This review aims to serve as a general guideline to fabricate highly efficient BiVO_(4)-based materials for PEC water splitting.展开更多
基金supported in part by the National Natural Science Foundation of China(Nos.62001116,62271150,62171134,U22A2002 and 62071234)the Natural Science Foundation of Fujian Province under Grant(Nos.2020J05106 and2022J01081)+1 种基金the Major Science and Technology plan of Hainan Province under Grant ZDKJ2021022the Scientific Research Fund Project of Hainan University under Grant KYQD(ZR)-21008
文摘Covert communication aims to prevent the warden from detecting the presence of communications,i.e.with a negligible detection probability.When the distance between the transmitter and the legitimate receiver is large,large transmission power is needed,which in turn increases the detection probability.Relay is an effective technique to tackle this problem,and various relaying strategies have been proposed for long-distance covert communication in these years.In this article,we first offer a tutorial on the relaying strategies utilized in covert transmission.With the emergence of reflecting intelligent surface and its application in covert communications,we propose a hybrid relay-reflecting intelligent surface(HR-RIS)-assisted strategy to further enhance the performance of covert communications,which simultaneously improves the signal strength received at the legitimate receiver and degrades that at the warden relying on optimizing both the phase and the amplitude of the HR-RIS elements.The numerical results show that the proposed HR-RIS-assisted strategy significantly outperforms the conventional RIS-aided strategy in terms of covert rate.
基金supported by the National Key Research and Development Program of China (2016YFA0202401)the 111 Project (B16016)+1 种基金the National Natural Science Foundation of China (51572080, 51702096 and U1705256)the Fundamental Research Funds for the Central Universities (2017XS080)
基金financially supported by the National Natural Science Foundation of China(Nos.21663027,21808189)the Fundamental Research Funds for the Central Universities of Chang’an University(No.300102299304)the Natural Science Basic Research Fund of Shaanxi Province(No.2020JZ20)。
文摘Photoelectrochemical(PEC)technology is considered to be a promising approach for solar-driven hydrogen production with zero emissions.Bismuth vanadate(BiVO_(4))is a kind of photocatalytic material with strong photoactivity in the visible light region and appropriate band gap for PEC water splitting.However,the solar-to-hydrogen efficiency(STH)of BiVO_(4)is far away from the 10%target needed for practical application due to its poor charge separation ability.Therefore,this review attempts to summarize the strategies for improving the photocurrent density and especially hydrogen production of BiVO_(4)materials through PEC techniques in the last three years,such as doping nonmetal and metal elements,depositing noble metals,constructing heterojunctions,coupling with carbon and metalorganic framework(MOF)materials to further enhance the PEC performance of BiVO_(4)photoanode.This review aims to serve as a general guideline to fabricate highly efficient BiVO_(4)-based materials for PEC water splitting.
基金supported by the National Key Research and Development Program of China (2018YFB1500101)the 111 Project (B16016)+1 种基金the National Natural Science Foundation of China (U1705256,51702096 and 61904053)the Fundamental Research Funds for the Central Universities (2019MS026,2019MS027 and 2020MS080)。
