A Method for Forming Radio Frequency Fingerprint of Resource Grid Elements Diagram Based on Synchronization Sub - frames

Abstract

The present invention discloses a method for forming a radio frequency fingerprint of a resource grid element diagram based on a synchronous subframe. The main steps of the method include: S1: collecting the output signal of a wireless device in an actual environment and performing preprocessing. S2: estimating the carrier frequency offset by calculating the differential function of the signal cyclic prefix and the repeated time domain signal, and removing the carrier frequency offset of the signal to achieve carrier synchronization. S3: dividing the signal into single symbols in the time domain and removing the physical signals related to the transmitted data. S4: performing a half-wave frequency shift on each symbol and extracting the subcarrier modulation elements for each symbol. Integrate into a resource grid matrix. S5: rendering the resource grid matrix into a resource grid element diagram as the radio frequency fingerprint of the synchronous subframe. The present invention extracts information in two dimensions, namely, the time domain and the frequency domain, which can retain the device-related features in the received signal to the greatest extent, and can quickly obtain the radio frequency fingerprint of the Internet of Vehicles device, and can be used as a radio frequency fingerprint extraction method for the Internet of Vehicles.

Description

Technical Field

[0001] The present invention belongs to the technical field of communication and information security, and relates to a method for forming a radio frequency fingerprint of a resource grid element graph based on a synchronous subframe. Background Art

[0002] Just as each person has a unique fingerprint, each RF device also has hardware differences, known as "device fingerprints." These differences are reflected in electromagnetic wave signals, and device characteristics can be extracted by analyzing the received RF signal. Transmitter local oscillator deviation, in-phase / quadrature (I / Q) imbalance, filter frequency response characteristics, power amplifier nonlinearity, antenna coupling differences, and other factors all have unique effects on the transmitted signal. Using the extracted characteristics of a wireless device's transmitted signal as a unique identifier to accurately identify individual transmitters is a feasible and reliable solution.

[0003] In recent years, with the emergence of urban congestion problems, the vehicle-road Internet system has attracted people's attention. The Internet of Vehicles is an important component for realizing autonomous driving and even unmanned driving, and is also a core component of the future intelligent transportation system. The core technology in the Internet of Vehicles system is vehicle wireless communication technology (Vehicle to Everything, V2X), of which C-V2X is a vehicle wireless communication technology based on the evolution of cellular network communication technologies such as 3G / 4G / 5G, including a short-range direct communication interface (PC5) and a communication interface (Uu) between the terminal and the base station. In the absence of base station coverage, C-V2X uses the PC5 interface based on the LTE-V2X protocol to support communication between different devices. The Internet of Vehicles device sends a synchronization subframe every 160ms, where the synchronization symbol is independent of the data. The present invention proposes a radio frequency fingerprint formation method for Internet of Vehicles user authentication based on the synchronization subframe. Summary of the Invention

[0004] Purpose of the invention: In view of the high requirements for timeliness of identity recognition in the high-speed mobile environment of the Internet of Vehicles, the present invention proposes a radio frequency fingerprint method that can quickly extract features relying solely on the physical layer. Based on a data-independent synchronization signal, the method converts the amplitude characteristics of the modulation information into easily recognizable color characteristics to quickly obtain the radio frequency fingerprint information of the device. In real-world scenarios, the radio frequency fingerprint extracted by the present invention can be subjected to dimensionality reduction operations to obtain radio frequency fingerprint features, or used for neural network training to automatically learn radio frequency fingerprint features and then guide classification, thereby achieving the effect of device identification or device authentication.

[0005] Technical solution: A method for forming a radio frequency fingerprint of a resource grid element graph based on a synchronous subframe, characterized by comprising the following steps:

[0006] S1: Collect the output signals of wireless devices in the actual environment and perform preprocessing.

[0007] S2: Estimate the carrier frequency offset by calculating the differential function between the signal cyclic prefix and the repeated time domain signal, and remove the carrier frequency offset from the signal to achieve carrier synchronization.

[0008] S3: Divide the signal into individual symbols in the time domain and remove the physical signals related to the transmitted data.

[0009] S4: Perform a half-wave frequency shift on each symbol and extract the subcarrier modulation elements for each symbol. The results are integrated into a resource grid matrix.

[0010] S5: Render the resource grid matrix into a resource grid element graph as the radio frequency fingerprint of the synchronization subframe.

[0011] Furthermore, the pre-processing in step S1 includes signal detection, signal interception, energy normalization, and time domain synchronization, wherein signal detection is to determine the subframe type by demodulating the reference signal position and retaining the synchronized subframe signal for subsequent fingerprint extraction.

[0012] Furthermore, in step S3, the PSBCH symbol containing data in the signal needs to be removed from the single symbol, and the complete OFDM symbol needs to be intercepted, discarding the cyclic prefix part of the symbol.

[0013] Furthermore, the specific steps of step S4 are:

[0014] Perform a Fourier transform on each symbol, extract the subcarriers with modulation symbols in the symbol frequency domain, and exclude the empty subcarriers with no signal to obtain the resource grid elements of a single symbol. After normalizing the subcarrier modulation elements of each symbol, arrange the resource grid elements of each symbol in a vertical row according to the subcarrier sequence size. Each OFDM symbol is demodulated to obtain an M×1 subcarrier modulation element matrix, and the resource grid elements of multiple symbols are merged in the order in which the symbols appear in the synchronization subframe to obtain a resource grid matrix of size M×N. Where M is the number of subcarriers with non-empty modulation elements, N is the number of symbols excluding data symbols, and the elements in the resource grid matrix are:

[0015]

[0016] Furthermore, the specific steps of step S5 are:

[0017] The elements in the resource grid matrix are divided into two groups according to their modulus value a. r,lSizes are mapped to different colors based on a unified color model, the same color classification range, and the same number of combined colors, resulting in a resource grid element diagram. A color model here refers to a set of visible sublights in a three-dimensional color space, encompassing a specific color and all colors. In the resource grid element diagram, the horizontal axis represents the time domain, representing different symbols, and the vertical axis represents the frequency domain, representing subcarriers with different center frequencies.

[0018] Beneficial Effects: Compared with existing methods, this present invention has the following significant advantages: In the context of the Internet of Vehicles (IoV), this method leverages the data-independent nature of the unique synchronization subframes in LTE-V2X to extract resource grid elements and convert them into an image format, enabling rapid acquisition of IoV device radio frequency fingerprints. This method eliminates the need for complex mathematical calculations, transforming the radio frequency fingerprint into three dimensions, extracting information in both the signal's time and frequency domains, and largely preserving device-related features in the received signal. Simulations and experiments have shown that this method can accurately identify devices using physical layer information, with an accuracy rate of up to 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of an embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram of the LTE-V2X physical layer frame structure.

[0021] Figure 3 This is a schematic diagram of the frame structure after removing the PSBCH symbol.

[0022] Figure 4 It is a schematic diagram of the fingerprint structure obtained by extracting radio frequency fingerprints in a specific example. DETAILED DESCRIPTION

[0023] The technical solutions provided by the present invention will be described in detail below with reference to specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0024] The present invention provides a method for forming a radio frequency fingerprint of a resource grid element diagram based on a synchronous subframe. The overall solution is as follows: Figure 1 , comprising the following steps:

[0025] S1: Collect the output signal of the wireless device in the actual environment and perform preprocessing. The specific example uses the synchronous subframe under the LTE-V2X standard, and the acquisition frequency is f s , the frequency domain subcarrier spacing is Δf, and the physical layer frame structure is as follows Figure 2 , the synchronization subframe length is N subslotEach symbol is preceded by a cyclic prefix (CP) that copies the tail information of the OFDM symbol. This frame structure is used to design coarse synchronization and fine synchronization to obtain the subframe synchronization point n. syn , and each symbol synchronization point In the frame structure, the PSBCH is a broadcast channel used to transmit user data. The PSSS is the primary synchronization signal and is located in symbols 2 and 3 of the subframe. The SSSS is the secondary synchronization signal and is located in symbols 12 and 13 of the subframe. The frame structure is designed to contain two adjacent and identical PSSS and SSSS signals in each synchronization subframe. The DMRS is the demodulation reference signal and is located in symbols 5, 7, and 10 of the subframe. The GP is a guard interval, which is a blank symbol. The PSSS, SSSS, and DMRS signals are only related to the user ID and are data-independent.

[0026] S2: Estimate the carrier frequency offset by calculating the differential function of the signal cyclic prefix and the repeated time domain signal, and remove the carrier frequency offset from the signal to achieve carrier synchronization. The frequency offset estimation formula is:

[0027]

[0028]

[0029]

[0030] where y PSSS (n), y SSSS (n) corresponding PSSS and SSSS time domain symbols, is the principal value of the complex argument, and the obtained signal frequency offset is f o .

[0031] S3: Synchronize the signal at each symbol in the time domain Divide the subframe into individual symbols to obtain the time domain signal of each symbol and remove the PSBCH symbol, such as Figure 3 As shown, it is necessary to intercept the complete OFDM symbol and discard the cyclic prefix part of the symbol.

[0032] S4: Perform a half-wave frequency shift on each symbol and extract the subcarrier modulation elements for each symbol. The results are integrated into a resource grid matrix.

[0033] Each symbol is then Fourier transformed to extract the subcarriers with modulation symbols in the symbol frequency domain, excluding the empty subcarriers without signals to obtain the resource grid elements of a single symbol. After normalizing the subcarrier modulation elements of each symbol, the resource grid elements of each symbol are arranged in a vertical row according to the subcarrier sequence size. Each OFDM symbol is demodulated to obtain an M×1 subcarrier modulation element matrix, and the resource grid elements of multiple symbols are merged according to the order in which the symbols appear in the synchronous subframe to obtain a resource grid matrix of size M×N. For the synchronous subframe signal, where M=72 and N=8, the elements in the resource grid matrix are:

[0034]

[0035] S5: Render the resource grid matrix into a resource grid element diagram as the radio frequency fingerprint of the synchronization subframe. The specific steps of this step are:

[0036] The elements in the resource grid matrix are divided into two groups according to their modulus value a. r，l The size is mapped to different colors based on the standard of a unified color model, the same color classification range, and the same number of combined colors. In this example, the HSV color model is used, the number of color combinations is 64, and the color classification range is [0, 1], resulting in a resource grid element diagram. The horizontal axis of the resource grid element diagram is the time domain, representing different symbols, and the vertical axis is the frequency domain, representing subcarriers with different center frequencies. The obtained resource grid element diagram is the RF fingerprint of the synchronous subframe, such as Figure 4 shown.

[0037] The above disclosure is only a preferred embodiment of the present invention and cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for forming a radio frequency fingerprint of a resource grid element graph based on a synchronous subframe, characterized in that: The following steps are involved: S1: Collect the output signals of wireless devices in the actual environment and perform preprocessing; S2: Estimate the carrier frequency offset by calculating the difference function between the signal cyclic prefix and the repeated time domain signal, and remove the carrier frequency offset from the signal to achieve carrier synchronization; S3: Divide the signal into individual symbols in the time domain and remove the physical signals related to the transmitted data; S4: Perform a half-wave frequency shift on each symbol, extract the subcarrier modulation elements of each symbol, and integrate them into a resource grid matrix; S5: Rendering the resource grid matrix into a resource grid element graph as the radio frequency fingerprint of the synchronization subframe; The specific steps of step S4 are: Perform a Fourier transform on each symbol to extract the subcarriers with modulation symbols in the symbol frequency domain, excluding empty subcarriers with no signal, to obtain the resource grid elements of a single symbol. After normalizing the subcarrier modulation elements of each symbol, arrange the resource grid elements of each symbol in a vertical row according to the subcarrier sequence size. Each OFDM symbol is demodulated to obtain an M×1 subcarrier modulation element matrix, and the resource grid elements of multiple symbols are merged in the order in which the symbols appear in the synchronization subframe to obtain an M×N resource grid matrix. Where M is the number of subcarriers with non-empty modulation elements, and N is the number of symbols excluding data symbols. The elements in the resource grid matrix are: S[r,l]=a r,l e -jbr,l ,r∈[0,M-1],l∈[0,N-1]。 2. A method for forming a radio frequency fingerprint of a resource grid element graph based on a synchronous subframe according to claim 1, characterized in that: The preprocessing in step S1 includes: signal detection, signal interception, energy normalization, and time domain synchronization; wherein the signal detection is to determine the subframe type by demodulating the reference signal position and retain the synchronized subframe signal for subsequent fingerprint extraction.

3. A method for forming a radio frequency fingerprint of a resource grid element graph based on a synchronous subframe according to claim 1, characterized in that: In step S3, the PSBCH symbol containing data in the signal needs to be removed from the single symbol, and the complete OFDM symbol needs to be intercepted, discarding the cyclic prefix part of the symbol.

4. A method for forming a radio frequency fingerprint of a resource grid element graph based on a synchronous subframe according to claim 1, characterized in that: The specific steps of step S5 are: The elements in the resource grid matrix are divided into two groups according to their modulus value a. r,l The sizes are mapped to different colors according to the standards obtained by a unified color model, the same color classification range, and the same number of combined colors, thereby obtaining a resource grid element diagram. The color model here refers to a visible sub-light set in a three-dimensional color space, which includes a certain color and all colors. In the resource grid element diagram, the horizontal axis is the time domain, representing different symbols, and the vertical axis is the frequency domain, representing subcarriers with different center frequencies.

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