Research On Reconfigurable Intelligent Surface-Assisted Physical Layer Key Generation Technology

The evolution of 6G networks from “Internet of Everything” to “Internet of Intelligent Everything” will significantly enhance future services and data value.Correspondingly,the capability for data security protection must also shift from traditional higher-layer protection to foundational physical-layer safeguards.Physical layer security technologies utilize unique physical layer attributes to protect communication security.Physical layer key generation(PKG)techniques utilize wireless channel characteristics to establish symmetric keys for both communicating parties,adding new endogenous security means that can be integrated but do not rely on classic cryptography technology.Currently,PKG primarily aims to enhance the key generation rate(KGR)to achieve a high-security communication vision to the “one-time pad”.However,the exponential growth of wireless services and the diversification of application scenarios in B5G/6G systems pose challenges for existing PKG protocols.These protocols rely on the natural fading characteristics of the wireless channel and lack proactive manipulation of the wireless environment,making it difficult for them to keep pace with the ever-increasing communication rates.Reconfigurable intelligent surfaces(RIS)have been identified as a potential key technology for 6G,which can flexibly manipulate electromagnetic waves,creating new opportunities for PKG.Existing research has deployed RIS in-between transceivers acting as intelligent reflecting surfaces(IRS)to facilitate key generation.However,there are still several unresolved issues:(1)Current schemes are unable to reconstruct the full space wireless environment,which results in limitations on sum KGR;(2)The entropy of secret keys by existing approaches fails to closely approximate the channel entropy,leading to lower actual KGR;(3)Present solutions often compromise communication data rates to enhance KGR,thus failing to achieve an integrated communication and security;(4)It is challenging for current methods to realize an integrated communication and security within single-radio frequency(RF)chain nodes.To address the issues above,this dissertation conducts in-depth research on“Reconfigurable Intelligent Surface-Assisted Physical Layer Key Generation Technology,”establishing two technical approaches: enhancing channel degrees of freedom(Do F)and increasing antenna Do F to meet high-security requirements and integrating communication and security requirements.Subsequently,we employ RIS’s various electromagnetic manipulation capabilities to tackle the problems in current PKG studies.The specific research contents are as follows:1.To address the issue of existing schemes being unable to reconstruct the full-space wireless environment,which leads to limitations in sum KGR,we propose simultaneously transmitting and reflecting-RIS(STAR-RIS)-assisted multi-user PKG schemes for both SISO and MISO scenarios.For the case of uncorrelated eavesdropping channels in SISO environments,a novel STAR-RIS-assisted SISO multi-user PKG protocol is introduced,along with closed-form expressions for the sum KGR.Subsequently,under both independent and coupled phase shift models,an optimization problem is formulated that jointly optimizes phase shifts and amplitude coefficients to maximize the sum KGR.To tackle this non-convex problem,exact optimal phase shifts are derived through monotonicity analysis,and an alternating optimization algorithm based on Lagrangian duality and quadratic transformation is employed to solve it.Numerical simulations demonstrate improved KGR performance over conventional reflective or transmissive RIS,regardless of whether the STAR-RIS employs independent or coupled phase shifts.For MISO scenarios with correlated eavesdropping channels,we introduce a STAR-RIS-assisted MISO multi-user PKG protocol,which derives closed-form solutions for sum KGR.Considering both independent and coupled phase shifts models,an optimization problem is formulated to maximize the sum KGR by jointly optimizing the base station precoding matrix and STAR-RIS coefficients.A penalty-based alternating optimization algorithm is proposed to address this non-convex problem.Simulation results show that STAR-RIS achieves a higher sum KGR than traditional reflective or transmissive RIS.2.To address the problem of low KGR resulting from the entropy of the secret key failing to approach channel entropy,we propose a radiation RIS-assisted fine-grained channel characteristic PKG mechanism.For passive eavesdropping scenarios,this dissertation first analyzes the enhancing effect of multipath fine-grained channel features on channel entropy.It then presents a radiation RIS-assisted fine-grained channel feature PKG scheme.This scheme utilizes the pattern diversity of the radiation RIS to estimate angle-of-arrival,designs transmit and receive beamforming to estimate path gains,and ultimately generates keys from this finegrained channel.In the context of active attacks,the dissertation first examines the impact of RIS jamming attacks on channel reciprocity.Following this,a radiation RIS-assisted anti-RISjamming attack PKG scheme is proposed.Based on the separation of multipath by the radiation RIS,attacked paths are detected and removed,allowing for the reconstruction of reciprocal channels to generate keys.Simulation and experimental results demonstrate that the proposed scheme can extract fine-grained channel features even in single-RF conditions,achieving a higher KGR than the current combined multipath channel.Additionally,when compared against scenarios affected by RIS jamming attacks,the scheme reduces the KDR by two orders of magnitude.3.To address the problem of the existing scheme improving the key rate at the expense of the communication rate and failing to achieve seamless integration of communication and security,we propose an IRS-assisted integrated communication and security mechanism.Initially,leveraging the sparse character of the channel,an IRS subchannel estimation algorithm based on adaptive sparse matching pursuit is adopted to estimate IRS subchannels accurately.Subsequently,considering both continuous phase shift IRS and discrete phase shift IRS,the dissertation proposes two tailored phase shift configuration methods.For continuous phase shift IRS,a novel method randomly rotates the phase of the received signal while maintaining maximum signal amplitude.Meanwhile,a dual-functional integration method is put forward for discrete phase shift IRS,wherein part of the IRS elements are used to optimize communication quality.In contrast,the remaining elements are deployed to increase channel randomness.Finally,a 4.9 GHz IRS-assisted prototype system for integrated communication and security has been developed and experimentally validated in terms of both communication and security aspects.The simulation results for continuous phase shift IRS demonstrate that the mechanism can enhance the randomness of the received signal phase while maintaining communication quality.Meanwhile,experimental outcomes for the discrete phase shift IRS indicate that the proposed mechanism significantly boosts the KGR and signal-to-noise ratio(SNR).Under static conditions,the KGR reaches 30.81 bits/s,improving 10.6 dB in the average received power.4.To address the challenge of integrating communication and security for a single RF chain node,we propose a radiation RIS array-assisted integrated communication and security solution.To begin with,a novel architecture for the radiation RIS array is designed,where each antenna element can reconfigure its radiation pattern dynamically.Subsequently,a radiation RIS array-assisted integrated communication and security protocol is introduced.This protocol optimizes both the phase shifter and the radiation RIS elements,using observed multipath information to maximize the SNR.Ultimately,physical layer keys are generated upon overcoming multipath fading.Simulation results indicate that the proposed scheme effectively mitigates multipath fading effects under a single RF chain,enhancing both the SNR and the KGR,thus achieving a cohesive fusion of communication and security functionalities.Furthermore,an experimentation platform is constructed to demonstrate the anti-fading capabilities of the radiating RIS.Experimental results confirm that the proposed approach reduces fading by up to 27 dB.