The fifth-generation new radio (NR) cellular communication introduces numerous advancements over Long Term Evolution and earlier technologies. It enables more flexible resource scheduling across multiple dimensions, with beamspace transmissions and time-frequency numerology selection as representative techniques. However, lightweight physical-layer secure transmission in NR remains under investigation, particularly taking NR beamspace into account. In this study, we propose an efficient beamwidth adaptation scheme for NR physical-layer wireless key generation (KG). Given the pivotal role of NR beamspace in determining the channel probing window in the spatial dimension, it directly influences channel probing results and, consequently, KG efficiency. To address this issue, we study NR beamwidth adaptation for enhancing KG performance. Specifically, we optimize NR beamwidth to maximize secrecy-delay efficiency, revealing the tradeoff involved in adapting beamwidth, where smaller beamwidth improves channel estimation accuracy but increases beam sweeping delay.
The fifth-generation new radio (NR) cellular communication introduces numerous advancements over Long Term Evolution and earlier technologies. It enables more flexible resource scheduling across multiple dimensions, with beamspace transmissions and time-frequency numerology selection as representative techniques. However, lightweight physical-layer secure transmission in NR remains under investigation, particularly taking NR beamspace into account. In this study, we propose an efficient beamwidth adaptation scheme for NR physical-layer wireless key generation (KG). Given the pivotal role of NR beamspace in determining the channel probing window in the spatial dimension, it directly influences channel probing results and, consequently, KG efficiency. To address this issue, we study NR beamwidth adaptation for enhancing KG performance. Specifically, we optimize NR beamwidth to maximize secrecy-delay efficiency, revealing the tradeoff involved in adapting beamwidth, where smaller beamwidth improves channel estimation accuracy but increases beam sweeping delay.
The fifth-generation new radio (NR) cellular communication is featured with numerous advancements over Long Term Evolution (LTE) and earlier technologies. It enables more flexible physical-layer resource scheduling across multiple dimensions, and two representative techniques are beamspace transmissions and time-frequency numerology selection. Nevertheless, the lightweight physical-layer secure transmission in NR remains under investigation, especially taking NR beamspace and mobility into consideration. In this work, we propose a physical-layer wireless key generation (KG) efficient beamspace adaptation scheme for NR, where the KG capacity is theoretically characterized by critical NR components including beam direction and beamwidth. In addition, we consider the impacts of user mobility on KG performance. Since NR beamspace plays a key role in deciding the channel probing window in the spatial dimension, the NR beamspace directly affects channel probing results and hence the KG efficiency. To this end, NR beam parameters are obtained to improve the KG performance. Especially, we propose to optimize the NR beamwidth for maximizing the secrecy-delay efficiency, because a tradeoff exists in adapting the beamwidth where smaller beamwidth can improve the channel estimation accuracy but increase the beam sweeping delay. Theoretical analysis and simulation results show that the beam direction adaptation provides spatial degrees of freedom for NR to enhance KG, by enabling beam selection pointing at target areas with richer multipath scatterings. Experimental results demonstrate that the narrow beam is beneficial to enhancing the channel estimation accuracy and the resultant key agreements.
The rapid advancement and deployment of 5G NR technology in diverse applications have introduced new challenges to network security. While 5G NR’s architecture allows flexible customization of subcarrier spacing and frame structures, enabling devices to optimize configurations based on mobility, service characteristics, and coverage, research has largely neglected the potential of fine-tuning system parameters to enhance key generation efficiency and security. This paper addresses this gap by analyzing time-frequency domain correlation and key generation rate as key metrics. We explore the impact of parameter selection on the key generation process in 5G NR systems. Using the Pearson correlation coefficient of channel estimates in the time-frequency domain, we propose a parameter selection strategy to improve physical layer security, validated through simulations. Results show that in fast-fading environments, smaller subcarrier spacing yields better results, while in frequency-selective fading channels, larger subcarrier spacing significantly enhances key generation performance.
The wireless channel is inherently an open medium which exposes wireless communication users to the risk of interception. The vulnerabilities of the wireless channel have led to the search for innovative and efficient security solutions at different levels of the network protocol. In particular, the physical layer level allows for implementing some security functions, such as key generation and exchange, by exploiting the intrinsic randomness of the wireless communication channel. In this paper, we analyze the effect of wireless channel and of antenna characteristics on physical layer security (PLS) key generation. The aim is to put in evidence the relation between physical quantities, such as radio channel characteristics or antenna directivity, with higher level secrecy performance indicators, such as the key mismatch between the different communication nodes and the key randomness. For this purpose, we developed a comprehensive numerical model, which implements all the different steps, from signal generation and wireless propagation modeling to key generation through spectral quantization. The reported results show that the multipath richness of the radio channel, as in outdoor urban scenarios, improves the PLS secrecy performances with respect to simpler propagation scenarios. Moreover, we show that the use of more directive antennas in the legitimate communication link improves secrecy. An opposite effect is achieved when the directivity of the eavesdropper antenna is increased, thus improving its ability to perform passive attacks.
As an alternative and appealing approach to providing information security in wireless communication systems, secret key generation at physical layer has demonstrated its potential in terms of efficiency and reliability over traditional cryptographic methods. Without the necessity of a management centre for key distribution or reliance on computational complexity, physical layer key generation protocols enable two wireless entities to extract identical and dynamic keys from the randomness of the wireless channels associated with them.\nIn this thesis, the reliability of secret key generation at the physical layer is examined in practical wireless channels with imperfect channel state information (CSI). Theoretical analyses are provided to relate key match rate with channel's signal-to-noise ratio (SNR), degrees of channel reciprocity, and iterations of information reconciliation.\nIn order to increase key match rate of physical layer secret key generation, improved schemes in the steps of channel estimation and sample quantization are proposed respectively. In the channel estimation step, multiple observations of the wireless channels are integrated with a linear processor to provide a synthesized and more accurate estimation of the wireless channel. In the sample quantization step, a magnitude based quantization method with two thresholds is proposed to quantize partial samples, where specific quantization areas are selected to reduce cross-over errors. Significant improvements in key match rate are proven for both schemes in theoretical analysis and numerical simulations. Key match rate can even achieve 100% in both schemes with the assistance of information reconciliation process.\nIn the end, a practical application of physical layer secret key generation is presented, where dynamic keys extracted from the wireless channels are utilized for securing secret data transmission and providing efficient access control.
Modern networking technologies involve the interconnection of smart and intelligent physical objects to provide advanced services. These physical objects may be part of various network technologies like WLAN, wireless sensor network (WSN), Internet of Things (IoT), etc., and share data in wireless mode, which should be secured from threats. These physical devices possess many constraints like power, computational complexity and storage, and are required to have lightweight security algorithms. Traditionally, security is achieved by the higher layers of the communication model, which has high computational complexity and consumes more power. In this chapter, a secure-key-generation scheme from physical layer characteristics is introduced as a possible lightweight security alternative to traditional upper-layer security approaches. The proposed scheme is based on the wiretap-channel model and security is achieved by generating keys at both communicating ends independently, based on inherent common-channel characteristics like randomness. It is mainly based on the principle of spatial decorrelation and channel reciprocity for identical carrier frequency. There is no provision for sharing keys as in public-key cryptography, so physical-layer key generation is not vulnerable to threats like key leakage. The generated key at the transmitter encrypts plain text; the generated cipher is transmitted on the common channel and is decrypted at the receiver end using the key generated by the receiver. Key generation consists of fundamental blocks like channel probing and quantization followed by information reconciliation and privacy amplification. The physical-layer key generation is already a power-efficient security solution; this chapter aims to enhance this capacity further. This is done by introducing low-end signal conditioning in the channel-probing step using moving-window averaging. This solution not only improves system performance but also makes it suitable for limited- power applications. The performance of the key-generation system is characterised in terms of the bit-disagreement rate between the generated key sequences of communicating parties and the key randomness by means of the NIST statistical test suite.
This paper investigates physical-layer key generation (PLKG) in multi-antenna base station systems, by leveraging a fluid antenna system (FAS) to dynamically customize radio environments. Without requiring additional nodes or extensive radio frequency (RF) chains, the FAS effectively enables adaptive antenna port selection by exploiting channel spatial correlation to enhance the secret key rate (SKR) at legitimate nodes. To comprehensively evaluate the performance of the FAS in PLKG, we propose an FAS-assisted PLKG model that integrates transmit beamforming and sparse port selection under independent and identically distributed (i.i.d.) and spatially correlated channel models, respectively. Specifically, the PLKG utilizes reciprocal channel probing to derive an approximate SKR expression based on the mutual information between legitimate channel estimates, explicitly accounting for the Eve’s channel observation under spatially correlated channel scenarios. Nonconvex optimization problems for these scenarios are formulated to maximize the SKR subject to transmit power constraints and sparse port activation. We propose an iterative algorithm by capitalizing on successive convex approximation and Cauchy-Schwarz inequality to obtain a locally optimal solution. A reweighted ℓ1-norm-based algorithm is applied to advocate for the sparse port activation of FAS-assisted PLKG. To approximate the optimal activated ports obtained by exhaustive search, a low-complexity sliding window-based port selection is proposed to substitute reweighted ℓ1-norm method based on Rayleigh-quotient analysis. Simulation results demonstrate that the FAS-assisted PLKG scheme significantly outperforms fixed antenna-assisted PLKG schemes in both environments. It is shown that the FAS achieves higher SKR with fewer RF chains through dynamic sparse port selection, which effectively reduces the resource overhead. Also, the sliding window approach closely approximates the globally optimal port selection compared to the reweighted ℓ1-norm method, rendering it suitable for practical deployments.