Method for physical layer authentication in MIMO systems

Abstract

A physical layer authentication (PLA) method realized by a multiple input multiple output (MIMO) system comprising a first communication node (101) comprising a first antenna array (111) and a second communication node (102) comprising a second antenna array (112) the method is suitable for detecting attacker communication nodes (103) which pretends to be the first communication unit when the first communication unit performs uplink communication using the second communication node (102).

Description

[0001] DESCRIPTION

[0002] METHOD FOR PHYSICAL LAYER AUTHENTICATION IN MIMO SYSTEMS

[0003] TECHNICAL FIELD

[0004] Invention relates to a physical layer authentication (PLA) method realized by a multiple input multiple output (MIMO) system comprising a first communication node comprising a first antenna array and a second communication node comprising a second antenna array the method is suitable for detecting attacker communication nodes which pretends to be the first communication unit when the first communication unit performs uplink communication using the second communication node.

[0005] PRIOR ART

[0006] MIMO (Multiple-Input Multiple-Output) systems refer to wireless communication frameworks utilizing multiple transmitting and receiving antennas to enhance data transmission rates, reliability, and spectral efficiency. Physical Layer Authentication (PLA) in MIMO systems leverages unique physical characteristics of the wireless channel, such as spatial and temporal properties, to authenticate devices and secure communication without relying solely on cryptographic methods.

[0007] In prior art, PLA in MIMO networks primarily relied on spatial and temporal features, such as channel impulse response (CIR) [1], channel frequency response (CFR) [2], received signal strength (RSS), and angle space representation of the MIMO channel including angle of arrival (AoA) / angle of departure (AoD) and path gain [3]. These features are typically used to create channel-specific signatures for authentication. Commonly, CIR and RSS methods are implemented in environments where rich multipath scattering provides strong spatial diversity, enabling distinct channel characteristics for each user, while angle space representation are implemented in poor multipath scattering environments. This enables authentication by distinguishing legitimate users from unauthorized ones.

[0008] CIR offers unique multipath signatures that help differentiate legitimate users based on the distinct time delays and paths within their channel characteristics. RSS, on the other hand, is simple to measure and implement, making it computationally efficient for environments with abundant reflections. In dense environments like urban and indoor settings, RSS can provide unique signal variations that are beneficial for authentication. However, both CIR and RSS face significant limitations in sparse MIMO environments, where the reduced number of paths limits multipath diversity, making authentication signatures less reliable. RSS values are particularly sensitive to environmental changes, with small movements or fluctuations impacting measurements and reducing reliability in mobile or dynamic scenarios. Additionally, at higher frequencies like millimeter-wave, the limited scattering effects weaken both CIR and RSS signatures, making them less effective for robust authentication in high-frequency, sparse MIMO channels.

[0009] In sparse channel design, few works are represented in the literature for efficient PLA schemes in sparse static system design. Thus, features of multiple antenna channel representation in 5G communication networks can be also used for a better PLA design by exploiting its unique attributes such as beam pattern [4] and channel sparsity in the angle domain [3] [5] [6] [7] [8]. This is effective in scenarios where there are many distinguishable paths. While these methods improved PLA by exploiting spatial features under limited multipath conditions, they still missed out on additional characteristics that could be harnessed, such as polarization. Although some research has investigated polarization as a security feature [9]

[0010] , these works typically assume uniform polarization across the array, suitable only for rich scattering conditions. They often lack focus on near-field effects and channel non-stationarity present in XL-MIMO arrays, and they do not consistently support both TDD and FDD transmission, which limits their adaptability across different network architectures. This invention overcomes these limitations by leveraging unique polarization characteristics specifically tailored to sparse and XL-MIMO settings, filling a critical gap in secure PLA for high-frequency and complex MIMO networks.

[0010] All the problems mentioned above have made it necessary to make an innovation in the relevant technical field as a result.

[0011] References:

[0012] [1] J. K. Tugnait and H. Kim, “A channel-based hypothesis testing approach to enhance user authentication in wireless networks,” in Proc. Int. Conf. Commun. Syst. Netw. (COMSNETS), Bangalore, India, 2010, pp. 1-9.

[0013] [2] L. Xiao, L. Greenstein, N. Mandayam, and W. Trappe, “Fingerprints in the ether: Using the physical layer for wireless authentication,” in Proc. Int. Conf. Commun. (ICC), Glasgow, U.K., 2007, pp. 4646-4651 . [3]. J. Tang, A. Xu, Y. Jiang, Y. Zhang, H. Wen, and T. Zhang, “MmWave MIMO physical layer authentication by using channel sparsity,” in Proc. IEEE Int. Conf. Artif. Intell. Inf. Syst. (ICAIIS), Mar. 2020, pp. 221-224.

[0014] [4] S. Balakrishnan, S. Gupta, A. Bhuyan, P. Wang, D. Koutsonikolas, and Z. Sun, “Physical layer identification based on spatial-temporal beam features for millimeter-wave wireless networks,” IEEE Trans. Inf. Forensics Security, vol. 15, pp. 1831-1845, 2020

[0015] [5] Jie Tang Hong Wen Huanhuan Song. “Physical layer authentication for 5G / 6G millimeter wave communications by using channel sparsity “IET Commun, January 2022.

[0016] [6] L. Afeef, H. M. Furqan, and H. Arslan, "Physical Layer Authentication Scheme in Beamspace MIMO Systems” IEEE Communication letters, Vol. 26, no. 7, July 2022.

[0017] [7] L. Afeef, H. M. Furqan, and H. Arslan, "Enhanced physical layer authentication framework in MIMO systems” Apr. 28, 2022, Turk Patent (EPATS), App. No: 2022 / 007102.

[0018] [8] L. Afeef, H. M. Furqan, A. Bendaimi, and H. Arslan, " Sparse Domains Exploitation for Physical Layer Authentication” Nov. 13, 2023, European Patent, App. No: 23209427.6

[0019] [9] Sun, D., Zhang, Q., Wei, D. and Zhang, M., 2020. A secure constellation design for polarized modulation in wireless communications. IEEE Access, 8, pp.130588-130597.

[0020]

[0010] Henarejos, P. and Perez-Neira, A.L, 2023. Polarization-Based Security: Safeguarding Wireless Communications at the Physical Layer. arXiv preprint arXiv:2307.07244.

[0021] BRIEF DESCRIPTION OF THE INVENTION

[0022] The present invention relates to a method to eliminate the above-mentioned disadvantages and bring new advantages to the relevant technical field.

[0023] An object of the invention is achieving reliable PLA in wireless networks with sparse channel conditions.

[0024] Another object of the invention is enhancing spoofing resistance in sparse network conditions and XL-MIMO.

[0025] To achieve all the objects mentioned above and that will emerge from the following detailed description, the present invention relates to a physical layer authentication (PLA) method realized by a multiple input multiple output (MIMO) system comprising a first communication node comprising a first antenna array and a second communication node comprising a second antenna array the method is suitable for detecting attacker communication nodes which pretends to be the first communication unit when the first communication unit performs uplink communication using the second communication node. Accordingly, comprising the steps of:

[0026] - initiating, by the first communication node, access to the second communication node using a pilot signal using a channel;

[0027] - receiving, by the second communication node, a pilot signal using an upper layer authentication method;

[0028] - performing, by the second communication node, channel estimation on the channel using the pilot signal;

[0029] - identifying, by the second communication node, a visibility region of the first communication node on the second antenna array of the second communication node;

[0030] - measuring, by the second communication node, polarization characteristics of the channel over each antenna element in the first antenna array and in each visibility region in the second antenna array wherein measured polarization characteristics comprise at least a polarization angle;

[0031] - generating, a reference polarization signature using polarization characteristics and storing the polarization signal assigned to the first communication device;

[0032] - repeating steps starting from channel estimation and generating a test polarization signature;

[0033] - comparing the reference polarization signature and the test polarization signature;

[0034] - if comparing results with a match authenticating the communication node that the test polarization signature is generated from as the first communication node. Thus, standard PLA (Physical Layer Authentication) techniques that rely on spatial or temporal features can be vulnerable to spoofing in sparse MIMO environments or struggle with latency requirements in real-time applications. By utilizing polarization, a characteristic stable yet unique across devices, this invention strengthens physical layer security, particularly in high-frequency, large- scale deployments, enabling secure and efficient authentication where standard methods fall short.

[0035] A possible embodiment of the invention is characterized in that the first antenna array is MIMO antenna array and the second antenna array is XL-MIMO antenna array.

[0036] Another possible embodiment of the invention is characterized in that comprising steps of;

[0037] - monitoring test polarization signatures over a predetermined time;

[0038] - after predetermined time have passed, updating the reference polarization signature.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a drawing illustrating top schematic view of the system.

[0040] Figure 2 is flow chart of the method.

[0041] REFERENCE NUMBERS GIVEN IN THE FIGURE

[0042] 100 Communication node

[0043] 101 First communication node

[0044] 102 Second communication node

[0045] 103 Attacker communication node

[0046] 110 Antenna array

[0047] 111 First antenna array

[0048] 112 Second antenna array

[0049] DETAILED DESCRIPTION OF THE INVENTION

[0050] In this detailed description, the subject matter is explained with references to examples without forming any restrictive effect only in order to make the subject more understandable.

[0051] The invention is a physical layer authentication (PLA) method realized by a multiple input multiple output (MIMO) system. Referring to figure 1 , the system comprising a first communication node (101 ) comprising a first antenna array (111 ) and a second communication node (102) comprising a second antenna array (112) and an attacker communication nodes (103). As is well known in the art, PLA is a security technique that performs the authentication of devices in wireless communication systems at the physical layer.

[0052] MIMO is an antenna technology for wireless communications that utilize multiple antennas simultaneously (at both, the transmitter and receiver) to transfer data. This improves the wireless range, and bandwidth, minimizes interference.

[0053] The first communication node (101 ) is a legitimate transmitting node. First communication node (101 ) can be a base station, a user equipment, IOT device etc. The first antenna array (111 ) is MIMO antenna array (110). First antenna The MIMO antenna array (100) is well know in the art and it is an antenna used in MIMO systems to increase data rates, reliability, and spectral efficiency in wireless communications. The second communication node (102) is a legitimate receiving node. Second communication node (102) can be a base station, a user equipment etc. The second antenna array (112) is XL-MIMO antenna array (100). The XL-MIMO antenna array (112) is well know in the art and could have extremely large MIMO configuration with hundreds or thousands of antennas, where near-field propagation effects create non-stationarity, resulting in each antenna element experiencing slightly different channel characteristics, including polarization phase.

[0054] The attacker communication node (103) is a device designed to interfere with a communications system or use it for a malicious purpose, such as a router or a jammer.

[0055] In figure 2, an embodiment of the method is given. The method is suitable for detecting attacker communication nodes (103) which pretends to be the first communication unit when the first communication unit performs uplink communication using the second communication node (102).

[0056] First communication node (101 ) initiates access to the second communication node (102) using a pilot signal using a channel, as the legitimate transmitter, while the second communication node (102) serves as the intended legitimate receiver tasked with authenticating the first communication node (101 ). The attacker aims to impersonate first communication node's (101 ) a pilot signal by transmitting to second communication node (102).

[0057] A pilot signal is received from the first communication node (101 ) to the second communication node (102) and authenticates the first communication node (101 ) using the upper layer authentication method. Authentication verifies the legitimacy of communicating entities. It explains how a wireless system can distinguish between legitimate and malicious users by verifying the identity of a network node on the receiving end of a transmission.

[0058] The channel between first communication node (101 ) and second communication node (102) is estimated performing by the second communication node (102) using the received pilot signal.

[0059] In the method, using traditional VR identification approaches, the visibility regions of first communication node (101 ) in the XL-MIMO antenna array (112) of second communication node (102) if any are determined. The traditional VR identification approaches can be energy sensing, location-based or ray scanning, power and ray field-based. By the second communication node (102), measuring polarization characteristics of the channel over each antenna element in the first antenna array (111 ) and in each visibility region in the second antenna array (112).

[0060] In the method, the polarization characteristics of the wireless channel between the transmitter and the receiver are measured. Polarization characteristic comprises a polarization angle. Specifically, the polarization angle (the orientation of the electric field of the electromagnetic wave) is measured to capture the distinctive signature that the propagation medium imposes on the transmitted signal. The orientation angle of the electric field vector of an electromagnetic wave, often measured relative to a reference axis. It can vary based on the device’s orientation and environmental factors. This measurement is made on each antenna element in the MIMO array and in each visibility region in the XL-MIMO array.

[0061] Then, using the extracted polarization features, a reference polarization signature is generated for each user or device. This signature acts as a "fingerprint" that identifies the specific user or device based on their unique polarization properties. This step provides a unique, identifiable pattern for each user, which can be compared with a stored reference for authentication. The signature encapsulates both static and dynamic polarization characteristics, ensuring it is highly distinctive and difficult to replicate in both sparse MIMO and XL MIMO systems and the generated signature is stored in the database of second communication node (102).

[0062] A pilot signal is received from the unknown node at second communication node (102) and the channel is estimated. The steps are repeated starting from channel estimation and a test polarization signature is generated. The test polarization signatures are monitored for a predetermined period of time and after a predetermined period of time, the reference polarization signature is updated.

[0063] The generated polarization signature of the unknown node is then compared to a stored reference signature associated with the legitimate device or user. This comparison determines whether the observed polarization characteristics match those of an authenticated user. If the observed polarization signature aligns closely with the reference, the authentication is deemed successful. If there is a significant discrepancy, access is denied. The signature comparison step ensures that only devices with the correct, pre-registered polarization characteristics are granted access, adding a robust layer of security. This step involves periodically re-measuring and updating the polarization signature to account for environmental changes or device movement. This is particularly useful in dynamic environment where the channel is varying over time. This dynamicity can be observed from transmitter, receiver, scatters in the environment, or all. This can be more critical in XL-MIMO systems where near-field propagation effects can introduce slight differences causing non- stationarity over the array, leading to unique variations in polarization across antenna elements.

[0064] Over time, small changes in the environment or device orientation might alter the polarization characteristics slightly. Regular updates to the stored polarization signature help maintain authentication accuracy and robustness.

[0065] The scope of protection of the invention is specified in the attached claims and cannot be limited to those explained for sampling purposes in this detailed description. It is evident that a person skilled in the art may exhibit similar embodiments in light of the above-mentioned facts without drifting apart from the main theme of the invention.

Claims

CLAIMS1. A physical layer authentication (PLA) method realized by a multiple input multiple output (MIMO) system comprising a first communication node (101 ) comprising a first antenna array (111 ) and a second communication node (102) comprising a second antenna array (112) the method is suitable for detecting attacker communication nodes (103) which pretends to be the first communication unit when the first communication unit performs uplink communication using the second communication node (102); characterized in that comprising the steps of: initiating, by the first communication node (101 ), access to the second communication node (102) using a pilot signal using a channel; receiving, by the second communication node (102), a pilot signal using an upper layer authentication method; performing, by the second communication node (102), channel estimation on the channel using the pilot signal; identifying, by the second communication node (102), a visibility region of the first communication node (101 ) on the second antenna array (112) of the second communication node (102); measuring, by the second communication node (102), polarization characteristics of the channel over each antenna element in the first antenna array (111 ) and in each visibility region in the second antenna array (112) wherein measured polarization characteristics comprise at least a polarization angle; generating, a reference polarization signature using polarization characteristics and storing the polarization signal assigned to the first communication device; repeating steps starting from channel estimation and generating a test polarization signature; comparing the reference polarization signature and the test polarization signature; if comparing results with a match authenticating the communication node (100) that the test polarization signature is generated from as the first communication node (101 ).

2. The method according to claim 1 , wherein the first antenna array (111 ) is MIMO antenna array (100) and the second antenna array (112) is XL-MIMO antenna array (100).

3. The method according to claim 1 , characterized in that comprising steps of;- monitoring test polarization signatures over a predetermined time; after predetermined time have passed, updating the reference polarization signature.

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