Active/Passive Secure Transmission Techniques For Battery-Free Backscatter Communication Systems

Battery-free backscatter is emerging as a cutting-edge technique in the context of ultra-low-power communication.In contrast to the conventional wireless communication that relies on power-hungry radio frequency links for data transmission,backscatter can significantly reduce the power consumption and hardware cost of the system by harvesting and reflecting ambient wireless signals for information transmission.These advantages make battery-free backscatter one of the critical technologies for pervasive sustainable Internet of Everything(Io E)applications.In the future,more and more user privacy and sensitive information will be transmitted in the backscatter system,raising higher requirements for the security of the system.However,the inherent broadcast nature of wireless channels makes wireless signals vulnerable to eavesdropping attacks.Additionally,due to computation and communication resource constraints arising from hardware limitations of battery-free backscatter devices,highly complex cryptography as well as coding or modulation techniques are not suitable for such a paradigm to secure communication.Therefore,it is imperative to design secure transmission schemes that take into account the characteristics of battery-free backscatter communication.Growing attempts have been devoted to exploring physical layer-based secure transmission techniques,which aim to enhance security using the inherent randomness of the wireless channel independently of the hardware conditions of the device.This provides a lightweight security protection idea for backscatter,while the related research is still in the exploratory stage.On this ground,focusing on the security threats of eavesdropping attacks faced by data transmission with the typical application scenarios of backscatter,this paper thoroughly investigates the physical layer-based passive secure transmission techniques for battery-free backscatter,including the physical layer security and the covert communication.Further,the beneficial effect of the inherently stochastic nature of passive backscatter transmission on active transmission in terms of security is explored.The main contributions are summarized as follows:Firstly,a secure transmission scheme for protecting the content of passive backscatter communication is studied.In view of the security of communication contents of multiple concurrently transmitted backscatter devices,we propose an efficient transmission scheme based on artificial noise-assisted secure beamforming.This greatly improves the system fairness and information transmission efficiency while guaranteeing secure communication against eavesdropping by using artificial noise to interfere with the eavesdropper and performing beamforming towards backscatter tags.Second,a secure transmission scheme for hiding the behaviors of passive backscatter communication is studied.To solve the problem that backscatter covert communication relies on a dedicated carrier generator and is challenging to extend,we propose a novel full-duplex receiver-based backscatter covert communication scheme.The scheme enables effective covert transmission of backscatter signals by sending jamming signals with variable power at the receiver to confuse the warden’s detection of the communication.Finally,a secure transmission scheme with passive backscatter communication assisted to hide active communication behaviors is investigated.We propose a covert communication scheme based on distributed backscattered random interference for the limitation that covert communication relies on additional overhead.The scheme achieves covert communication that backscatter benefits active transmission by exploiting the inherent episodic and uncertainty of backscatter transmissions to produce background chatter to deteriorate the detection performance of the warden.In conclusion,this thesis focuses on the efficient physical layer secure transmission of battery-free backscatter communication system,backscatter transmission and its assisted covert communication,which provides a theoretical basis and method support for realizing lightweight secure communication for battery-free backscatter systems.