A backscatter communication perception integrated system and method based on OFDM

Abstract

The invention discloses an integrated backscatter communication perception system and method based on OFDM, and relates to the technical field of wireless communication. The method comprises the following steps: S10, synchronizing a backscatter device with an OFDM signal sent by a radio frequency source; S20, performing channel estimation on a receiving device to obtain a channel state information matrix; S30, performing parameter estimation to obtain multiple groups of departure angles, arrival angles and relative flight times of a direct link and a reflection link; S40, determining the direct link parameters, and filtering the reflection link parameters from the relative flight time to form a backscatter device parameter set; S50, calculating the two-dimensional coordinates of the backscatter device relative to the user using the backscatter device parameter set; S60, performing spatial filtering; S70, performing signal judgment on the filtered signal to obtain the information sent by the backscatter device. The invention has the beneficial effects of realizing simultaneous backscatter communication and positioning the backscatter device without affecting broadband OFDM communication.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and more specifically, to an OFDM-based backscatter communication and perception integrated system and method. Background Art

[0002] With the rapid development of communication technology, the application scenarios of the Internet of Things are also expanding, such as Internet of Vehicles, smart homes, industrial Internet of Things, etc. In these scenarios, many communication devices are required to have efficient communication capabilities and high-precision perception capabilities to achieve real-time information interaction. In order to meet these needs, ISAC and backscatter communication technology are becoming key technologies in the next generation of wireless communications.

[0003] Synaesthesia integration technology is a process that integrates communication and perception into a unified process. In addition to the communication capabilities of wireless communication systems, the network can also obtain the ability to perceive the information of devices in the network through the design of the antenna side and the waveform side, and make perception and communication complement each other. Synaesthesia integration technology is one of the three new application scenarios of 6G communication. By designing communication and perception algorithms, communication and perception resources are jointly scheduled to improve the overall performance of communication and perception.

[0004] Backscatter communication technology is a technology that combines energy harvesting and impedance adjustment to enable passive devices to obtain energy to drive themselves through energy harvesting, and then modulate the signal by changing the amplitude and phase of the received signal and reflecting it. This communication method can achieve low-power or even zero-power communication, and is very suitable for communication scenarios such as the Internet of Things where there are many small devices. Backscatter communication technology is an important part of the new generation of green Internet of Things. It gets rid of the battery requirements of traditional active communications and overcomes the inherent defects of high energy consumption of existing active communications.

[0005] Indoor environment is a major application scenario for the integration of backscattering and synaesthesia. There are many IoT devices indoors. Backscattering devices transmit their own information by modulating the incident carrier, such as device ID, temperature and humidity, and other status information. On the other hand, the receiver can sense the angle, distance, position, etc. of the backscattering device based on the backscattering signal to achieve backscattering synaesthesia integration. To this end, it is urgent to study the integrated design of backscattering synaesthesia under the premise of low cost and extremely low power consumption, so as to realize new IoT applications such as warehouse positioning, item tracking, posture recognition, and motion monitoring. Summary of the invention

[0006] In order to overcome the deficiencies of the prior art, the present invention provides an OFDM-based backscatter communication perception integrated system and method; through this method, the functions of simultaneous backscatter communication and positioning backscatter equipment can be realized without affecting broadband OFDM communication.

[0007] The technical solution adopted by the present invention to solve the technical problem is: an OFDM-based backscatter communication perception integrated method, the improvement of which is that the method comprises the following steps:

[0008] S10, the backscattering device is synchronized with the OFDM signal sent by the radio frequency source, and the signal is periodically reflected by the backscattering device;

[0009] S20, the receiving device performs channel estimation to obtain a channel state information matrix;

[0010] S30, performing parameter estimation to obtain multiple groups of departure angles, arrival angles, and relative flight times for the direct link and the reflected link;

[0011] S40, determining straight link parameters, and selecting reflection link parameters from the departure angle, arrival angle, and relative flight time to form a backscatter device parameter set;

[0012] S50, using the backscatter device parameter set, calculating the two-dimensional coordinates of the backscatter device relative to the user;

[0013] S60, the backscatter device sends a random OOK modulated signal, and the receiving device calculates the optimal receiving beamforming weight vector using the arrival angle parameters of the direct link and the reflected link, and multiplies it with the received signal to achieve spatial domain filtering;

[0014] S70: Perform signal judgment on the filtered signal to obtain information sent by the backscattering device.

[0015] Furthermore, in step S20, in T consecutive transmission cycles, the receiving device uses the pilot of the OFDM signal to perform channel estimation to obtain a channel state information matrix.

[0016] Further, in step S20, the signal received by the receiving device includes a direct link signal directly reaching the receiving device from the radio frequency source, a reflected link signal of the backscattering device, and multiple interference link signals generated by reflections of inherent obstacles in the environment, and the interference link signals are classified into static links and dynamic links according to the motion characteristics of the obstacles;

[0017] The total number of links is L, including S static links, W dynamic links, one reflection link and one direct link;

[0018] For the received p-th OFDM symbol, on the k-th OFDM subcarrier, the formula for the received signal is:

[0019]

[0020] Where αl is the complex channel gain of the lth path, H l (k) represents the channel state information matrix of the lth path on the kth subcarrier, obtained by channel estimation; is complex Gaussian white noise;

[0021] Further, in step S30, the receiving device obtains the departure angle, arrival angle and relative flight time of each link signal through a perception estimation algorithm;

[0022] The perception estimation algorithm is an iterative projection MUSIC algorithm, comprising the following steps:

[0023] S301, the obtained P channel state information matrix is ​​divided into multiple sub-matrices with equal spacing along the subcarrier dimension, and each sub-matrix is ​​vectorized and smoothed forward and backward to obtain a forward covariance matrix and the posterior covariance matrix

[0024] S302: Obtaining a bidirectional spatial smoothing covariance matrix

[0025] S303, smoothing the covariance matrix of the two-way space Perform eigenvalue decomposition, sort the eigenvalues ​​from large to small, and select the first L eigenvectors to form the signal subspace E s , the remaining eigenvectors constitute the noise subspace E n ;

[0026] S304, calculating the spatial spectrum:

[0027]

[0028] in, is the departure angle, θ is the arrival angle, τ is the relative flight time, is a guidance vector with departure angle, arrival angle and relative flight time as parameters, and its form is

[0029]

[0030] Where a(θ) = e -jπndsinθ ,n=0,1,…,N-1, m=0,1,…,M-1, k=0,1,…,K-1,f k is the frequency of the kth subcarrier;

[0031] S305, obtain spatial spectrum P RAP-MUSIC The global maximum value in , and obtain the corresponding guidance vector, determine the departure angle Angle of arrival θ and relative flight time τ;

[0032] S306, perform iterative projection, and arrange the estimated steering vectors in parallel to form a matrix A l , calculate the projection matrix Pr l =IA l (A l H A l ) -1 A l H , where I represents the identity matrix, and then the signal subspace E is converted into s The guiding vector for the peak search is projected and the spatial spectrum is repeatedly calculated:

[0033]

[0034] in is the aforementioned steering vector;

[0035] By searching L spectral peaks, we can obtain L parameter sets including departure angle, arrival angle and relative flight time, which are recorded as:

[0036] S307 , filtering out parameters of the backscatter device from the parameter set in step S306 .

[0037] Further, in step S50, calculating the two-dimensional coordinates of the backscattering device relative to the user includes:

[0038] S501, according to the frame structure of the signal sent by the backscattering device, the departure angle, arrival angle and relative flight time parameters of the reflection link in the estimation result of the receiving device will obey the distribution determined by the modulation state of the backscattering device, thereby obtaining the estimated values ​​of the parameters of the reflection link;

[0039] S502: Calculate the distance of the backscatter device relative to the user using the sine theorem based on the selected backscatter device parameter set.

[0040]

[0041] in, θ AOA with rtof TAG are the estimated departure angle, arrival angle and relative flight time of the backscattering device, c is the speed of light, and the two-dimensional coordinates of the backscattering device relative to the user are expressed as

[0042] Furthermore, the radio frequency source is equipped with M transmitting antennas, and the receiving device is equipped with N receiving antennas.

[0043] Further, in step S60, the receiving device calculates the optimal receiving beamforming weight vector using the arrival angle parameters of the straight link and the reflected link, and multiplies it with the received signal to implement spatial domain filtering, including:

[0044] S601, setting λ m,n (k) is the frequency domain response of the kth sub-band on the link composed of the mth transmitting antenna and the nth receiving antenna, and the reflection link is a flat channel; v m With g n are the channel responses between the mth transmitting antenna and the nth receiving antenna and the backscattering device respectively;

[0045] S602: Let the reflection coefficient of the backscattering device be Γ, then the frequency domain expression of the pth OFDM symbol received by the nth receiving antenna on the kth subcarrier is:

[0046]

[0047] Among them, s m,p (k) is the symbol loaded by the mth transmitting antenna on the kth subcarrier, c p is the symbol for the backscatter device, is complex Gaussian white noise d is the number of sampling periods that the reflection link lags behind the direct link;

[0048] S603, change the formula in step S602 into a matrix form, m,n (k)} forms a complex matrix H with N rows and M columns 1 (k), let g = [g 1 ,…,g N ] T 、v=[v 1 ,…,v M ] T , H 2 (k) = Γe -j2πkd / K gv T ;

[0049] but:

[0050] Among them, z p (k) = [z 1,p (k),…,z N,p (k)] T ,s p (k) = [s 1,p (k),…,s M,p (k)] T ,

[0051] S604: The receiving device uses the shortest relative flight time estimation result as the direct link parameter and uses its arrival angle information Constructing Steering Vectors Using the arrival angle information of the reflection link Constructing Steering Vectors

[0052] S605, by constructing a receive beamforming weight vector, the problem of minimizing the direct link power and maximizing the reflected link power is transformed into solving an optimization problem:

[0053]

[0054] ||w H || 2 ≤1;

[0055] Solve and obtain the closed expression of the optimal spatial domain filter weight vector:

[0056]

[0057] Multiplying the received signal with the weight vector implements spatial domain filtering.

[0058] Furthermore, in step S501, the characteristics of different links are reflected by the characteristics of the trajectory, and the links corresponding to the backscattering devices are screened by distinguishing the characteristics.

[0059] Furthermore, in step S40, the direct link parameters are determined by using the characteristic of the shortest direct link delay, and the reflection link parameters are determined by using the modulation state characteristics of the backscattering device, and the reflection link parameters are selected from the relative flight time.

[0060] The present invention also provides an OFDM-based backscatter communication and perception integrated system, the improvement of which is that the system includes a backscatter device, a radio frequency source and a receiving device;

[0061] The backscatter device is synchronized with the OFDM signal sent by the radio frequency source and the signal is periodically reflected by the backscatter device;

[0062] The receiving device performs channel estimation to obtain a channel state information matrix; after performing parameter estimation, multiple groups of departure angles, arrival angles and relative flight times of direct links and reflection links are obtained; direct link parameters are determined, and reflection link parameters are selected from the departure angles, arrival angles and relative flight times to form a backscattering device parameter set; thereafter, the two-dimensional coordinates of the backscattering device relative to the user are calculated using the backscattering device parameter set;

[0063] The backscatter device sends a random OOK modulated signal, and the receiving device uses the arrival angle parameters of the direct link and the reflected link to calculate the optimal receiving beamforming weight vector, and multiplies it with the received signal to achieve spatial domain filtering; thereafter, the filtered signal is subjected to signal judgment to obtain the information sent by the backscatter device.

[0064] The beneficial effects of the present invention are: it is able to estimate the angle and relative flight time of the backscattering device based on the result of channel estimation, and then obtain the position of the backscattering device using a triangulated positioning method, while performing spatial filtering according to the incident angle of the received signal to achieve interference suppression of the radio frequency source, and can achieve communication with the backscattering device, thereby having both backscattering communication capability and perception capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 Schematic diagram of an indoor backscattering synaesthesia integrated system model in one embodiment of the present invention.

[0066] Figure 2 The present invention is a flowchart of an OFDM-based backscatter communication perception integration method in one embodiment of the present invention.

[0067] Figure 3 The figure is a curve diagram showing the variation of the bit error rate performance of backscatter communication with the signal-to-noise ratio in one embodiment of the present invention.

[0068] Figure 4 This is a curve diagram showing how positioning accuracy performance varies with signal-to-noise ratio in one embodiment of the present invention. DETAILED DESCRIPTION

[0069] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0070] The following will clearly and completely describe the concept, specific structure and technical effects of the present invention in combination with the embodiments and drawings, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by technicians in this field without creative work are all within the scope of protection of the present invention. In addition, all the connection / connection relationships involved in the patent do not refer to the direct connection of components, but refer to the formation of a better connection structure by adding or reducing connection accessories according to the specific implementation situation. The various technical features in the invention can be combined interchangeably without conflicting with each other.

[0071] Example 1

[0072] Reference Figure 1As shown, a backscatter communication and perception integrated system based on OFDM is provided. Figure 1 That is the model diagram of the system, which includes a cellular base station, a reflective tag and a user end. The signal transmitted by the cellular base station is received by the user end after being reflected by the reflective tag, forming a reflective link. If the signal transmitted by the cellular base station is directly received by the user end, its path is called a direct path. Furthermore, if the signal transmitted by the cellular base station is reflected by a moving object and then received by the user end, the path formed is called a dynamic path. If it is reflected by a solid object and then received by the user end, the path formed is called a static path.

[0073] In this embodiment, in an OFDM-based backscatter communication perception integrated system, the backscatter device is synchronized with the OFDM signal sent by the radio frequency source, and the signal is periodically reflected by the backscatter device; the receiving device performs channel estimation to obtain a channel state information matrix; after parameter estimation, multiple groups of departure angles, arrival angles and relative flight times of the direct link and the reflection link are obtained; the direct link parameters are determined, and the reflection link parameters are filtered out from the departure angle, arrival angle and relative flight time to form a backscatter device parameter set; thereafter, the two-dimensional coordinates of the backscatter device relative to the user are calculated using the backscatter device parameter set.

[0074] Furthermore, the backscatter device sends a random OOK modulated signal, and the receiving device uses the arrival angle parameters of the direct link and the reflected link to calculate the optimal receiving beamforming weight vector, and multiplies it with the received signal to achieve spatial domain filtering; thereafter, the filtered signal is subjected to signal judgment to obtain the information sent by the backscatter device.

[0075] Example 2

[0076] The present invention provides an integrated backscatter communication perception method based on OFDM, which is implemented based on the system shown in Example 1; the present invention includes a radio frequency source, a backscatter device and a receiving device. In this embodiment, the radio frequency source is the cellular base station, the backscatter device is a reflective tag, and the receiving device is a user terminal. In this solution, the user terminal is a mobile phone.

[0077] The invention provides an OFDM-based backscatter communication perception integrated method, combined with Figure 2 As shown, the following steps are included:

[0078] S10, the backscattering device is synchronized with the OFDM signal sent by the radio frequency source, and the signal is periodically reflected by the backscattering device; in this embodiment, a fixed 01 sequence is sent by alternating reflection and absorption;

[0079] S20, the receiving device performs channel estimation to obtain a channel state information matrix;

[0080] In this embodiment, in step S20, in T consecutive transmission cycles, the receiving device uses the pilot of the OFDM signal to perform channel estimation to obtain a channel state information matrix;

[0081] S30, performing parameter estimation to obtain multiple groups of departure angles, arrival angles, and relative flight times for the direct link and the reflected link;

[0082] In this embodiment, the forward and backward smoothing RAP-MUSIC (Recursively Applied and Projected Multiple Signal Classification, RAP-MUSIC) algorithm is used for parameter estimation;

[0083] S40, determining direct link parameters, and filtering out reflection link parameters from the relative flight time to form a backscatter device parameter set; in step S40, the direct link parameters are determined using the characteristic of the shortest direct link delay, and the reflection link parameters are filtered out from the relative flight time using the modulation state characteristics of the backscatter device;

[0084] S50, using the backscatter device parameter set, calculating the two-dimensional coordinates of the backscatter device relative to the user;

[0085] S60, the backscatter device sends a random OOK modulated signal, and the receiving device calculates the optimal receiving beamforming weight vector using the arrival angle parameters of the direct link and the reflected link, and multiplies it with the received signal to achieve spatial domain filtering;

[0086] S70: Perform signal judgment on the filtered signal to obtain information sent by the backscattering device.

[0087] Through the above method, the present invention can estimate the angle and relative flight time of the backscatter device according to the result of channel estimation, and then obtain the position of the backscatter device by using triangulation positioning. At the same time, spatial filtering is performed according to the incident angle of the received signal to achieve interference suppression of the radio frequency source (direct link), so that the system can communicate with the backscatter device, thereby having both backscatter communication capability and perception capability.

[0088] Example 3

[0089] Continue to combine Figure 1 , Figure 2As shown, the present invention provides an integrated method for backscatter communication perception based on OFDM, which is implemented based on the system shown in Example 1, and the RF source of the system is equipped with M transmitting antennas, the receiving device is equipped with N receiving antennas, and also includes a backscatter device equipped with a single antenna.

[0090] In this embodiment, an OFDM-based backscatter communication sensing integrated method of the present invention includes the following steps:

[0091] S10, the backscattering device is synchronized with the OFDM signal sent by the radio frequency source, and the signal is periodically reflected by the backscattering device; in this embodiment, normal communication between the radio frequency source and the receiving device needs to be ensured; a fixed 01 sequence is sent by alternating reflection and absorption;

[0092] S20, the receiving device performs channel estimation to obtain a channel state information matrix; in this embodiment, in step S20, in T consecutive transmission cycles, the receiving device performs channel estimation using the pilot of the OFDM signal to obtain a channel state information matrix;

[0093] In step S20, the signal received by the receiving device includes a direct link signal (corresponding to Figure 1 direct path in the backscatter device), the reflected link signal of the backscatter device (corresponding to Figure 1 The interference link signals are classified into static links (corresponding to Figure 1 Dynamic path in) and dynamic link (corresponding to Figure 1 In this embodiment, the total number of links is set to L, including S static links, W dynamic links, one reflection link and one direct link;

[0094] For the received p-th OFDM symbol, on the k-th OFDM subcarrier, the formula for the received signal is:

[0095]

[0096] Among them, α l is the complex channel gain of the lth path, H l (k) represents the channel state information matrix of the lth path on the kth subcarrier, obtained by channel estimation; is complex Gaussian white noise;

[0097] S30, performing parameter estimation to obtain multiple groups of departure angles, arrival angles, and relative flight times for the direct link and the reflected link;

[0098] In this embodiment, the forward and backward smoothing RAP-MUSIC (Recursively Applied and Projected Multiple Signal Classification, RAP-MUSIC) algorithm is used for parameter estimation;

[0099] In step S30, the receiving device obtains the departure angle, arrival angle and relative flight time of each link signal through a perceptual estimation algorithm; the perceptual estimation algorithm is an iterative projection MUSIC algorithm, namely the forward and backward smoothing RAP-MUSIC algorithm mentioned above, comprising the following steps:

[0100] S301, the obtained P channel state information matrix is ​​divided into multiple sub-matrices with equal spacing along the subcarrier dimension, and each sub-matrix is ​​vectorized and smoothed forward and backward to obtain a forward covariance matrix and the posterior covariance matrix

[0101] S302: Obtaining a bidirectional spatial smoothing covariance matrix

[0102] S303, smoothing the covariance matrix of the two-way space Perform eigenvalue decomposition, sort the eigenvalues ​​from large to small, and select the first L eigenvectors to form the signal subspace E s , the remaining eigenvectors constitute the noise subspace E n ;

[0103] S304, calculating the spatial spectrum:

[0104]

[0105] in, is the departure angle, θ is the arrival angle, τ is the relative flight time, is a steering vector with departure angle, arrival angle and relative flight time as parameters, and its form is:

[0106]

[0107] Where a(θ) = e -jπndsinθ ,n=0,1,…,N-1, m=0,1,…,M-1, k=0,1,…,K-1,f k is the frequency of the kth subcarrier;

[0108] S305, obtain spatial spectrum P RAP-MUSIC The global maximum value in , and obtain the corresponding guidance vector, determine the departure angle Angle of arrival θ and relative flight time τ;

[0109] S306, perform iterative projection, and arrange the estimated steering vectors in parallel to form a matrix A l , calculate the projection matrix Pr l =IA l (A l H A l ) -1 A l H , where I represents the identity matrix, and then the signal subspace E is converted into s The guiding vector for the peak search is projected and the spatial spectrum is repeatedly calculated:

[0110]

[0111] in is the aforementioned steering vector;

[0112] By searching L spectral peaks, we can obtain L parameter sets including departure angle, arrival angle and relative flight time, which are recorded as:

[0113] S307 , filtering out parameters of the backscatter device from the parameter set in step S306 .

[0114] S40, determining straight link parameters, and selecting reflection link parameters from the relative flight time to form a backscatter device parameter set;

[0115] In step S40, the direct link parameters are determined by using the characteristic of the shortest direct link delay, and the reflection link parameters are determined by using the modulation state characteristics of the backscattering device, and the reflection link parameters are selected from the relative flight time;

[0116] S50, using the backscatter device parameter set, calculating the two-dimensional coordinates of the backscatter device relative to the user;

[0117] In step S50, calculating the two-dimensional coordinates of the backscattering device relative to the user includes:

[0118] S501, according to the frame structure of the signal sent by the backscattering device, the departure angle, arrival angle and relative flight time parameters of the reflection link in the estimation result of the receiving device will obey the distribution determined by the modulation state of the backscattering device, thereby obtaining the estimated values ​​of the parameters of the reflection link;

[0119] S502: Calculate the distance of the backscatter device relative to the user using the sine theorem according to the selected backscatter device parameter set:

[0120]

[0121] in, θ AOA with rtof TAG are the estimated departure angle, arrival angle and relative flight time of the backscattering device, c is the speed of light, and the two-dimensional coordinates of the backscattering device relative to the user are expressed as

[0122]

[0123] S60, the backscatter device sends a random OOK modulated signal, and the receiving device calculates the optimal receiving beamforming weight vector using the arrival angle parameters of the direct link and the reflected link, and multiplies it with the received signal to achieve spatial domain filtering;

[0124] In step S60, the receiving device calculates the optimal receiving beamforming weight vector using the arrival angle parameters of the straight link and the reflected link, and multiplies it with the received signal to implement spatial domain filtering, including:

[0125] S601, setting λ m,n (k) is the frequency domain response of the kth sub-band on the link composed of the mth transmitting antenna and the nth receiving antenna, and the reflection link is a flat channel; v m With g n are the channel responses between the mth transmitting antenna and the nth receiving antenna and the backscattering device respectively;

[0126] S602: Let the reflection coefficient of the backscattering device be Γ, then the frequency domain expression of the pth OFDM symbol received by the nth receiving antenna on the kth subcarrier is:

[0127]

[0128] Among them, s m,p (k) is the symbol loaded by the mth transmitting antenna on the kth subcarrier, c p is the symbol for the backscatter device, is complex Gaussian white noise d is the number of sampling periods that the reflection link lags behind the direct link;

[0129] S603, change the formula in step S602 into a matrix form, m,n (k)} forms a complex matrix H with N rows and M columns 1 (k), let g = [g 1 ,…,g N ] T 、v=[v 1 ,…,v M ] T , H 2(k) = Γe -j2πkd / K gv T ;

[0130] but:

[0131] Among them, z p (k) = [z 1,p (k),…,z N,p (k)] T ,s p (k) = [s 1,p (k),…,s M,p (k)] T ,

[0132] S604: The receiving device uses the shortest relative flight time estimation result as the direct link parameter and uses its arrival angle information Constructing Steering Vectors Using the arrival angle information of the reflection link Constructing Steering Vectors

[0133] S605, by constructing a receive beamforming weight vector, the problem of minimizing the direct link power and maximizing the reflected link power is transformed into solving an optimization problem:

[0134]

[0135] ||w H || 2 ≤1;

[0136] Solve and obtain the closed expression of the optimal spatial domain filter weight vector:

[0137]

[0138] Multiplying the received signal with the weight vector implements spatial domain filtering.

[0139] S70: Perform signal judgment on the filtered signal to obtain information sent by the backscattering device.

[0140] In this embodiment, since the modulation mode of the backscatter device is OOK, and considering that spatial domain filtering cannot completely eliminate interference, the filtered signal will present an OOK signal pattern with a non-zero mean; therefore, the judgment above the mean is 1, and the judgment below the mean is 0.

[0141] In the above embodiments of the present invention, since the symbols on the reflection link remain consistent on the links between all subcarriers and the transmitting and receiving antennas, diversity gain can be achieved in the spatial dimension of the antenna and the frequency dimension of the subcarrier.

[0142] In this embodiment, a backscatter communication perception integration method based on OFDM provided by the present invention is simulated and verified, and the parameters are set as follows: the system carrier frequency is 5GHz, the number of OFDM subcarriers is 64, the system bandwidth is 40MHz, the number of transmitting and receiving antennas is 3, the number of multipaths is 5, the distance between the transmitting and receiving devices is 10 meters, the backscatter device is synchronized with the OFDM symbol, and OOK modulation is used. When the power of the reflection link relative to the direct link is set to -10dB, the transmission bit error rate of the reflection device is reduced to below 10-4 after the SNR is greater than 10dB. Figure 3 When the signal-to-noise ratio of the reflection link is 30 dB, the positioning error drops below 10 cm, as shown in Figure 4 As shown, the positioning accuracy of the proposed backward smoothing MUSIC algorithm is better than that of the traditional MUSIC algorithm.

[0143] Through the above method, the present invention can estimate the angle and relative flight time of the backscatter device according to the result of channel estimation, and then obtain the position of the backscatter device by triangulation positioning. At the same time, spatial filtering is performed according to the incident angle of the received signal to suppress interference with the RF source (direct link), so that the system can communicate with the backscatter device, thereby having both backscatter communication capability and perception capability. Through the existing environmental RF source and receiver, the parameters of the reflected signal of the backscatter device can be estimated while performing broadband OFDM communication, providing the perception capability of locating the backscatter device.

[0144] In addition, the present invention can rely on the angle information obtained by the perception system, suppress the direct signal in the direction of the RF source through receiving beamforming and enhance the reflected signal of the backscattering device, so as to achieve the effect of system perception-assisted communication. The simulation verifies that the system can achieve high perception accuracy and communication capability, and after using the perception capability to assist communication, when the power of the reflection link is attenuated by 3dB relative to the direct link, the BD signal bit error rate is reduced to below 10-4 after the SNR is greater than 10dB; as the power of the reflection link decreases, the BD bit error rate increases, while the direct link is not greatly affected, realizing the mutual benefit of communication and perception, and has certain engineering practice value.

[0145] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A backscatter communication perception integrated method based on OFDM, characterized in that: The method comprises the following steps: S10, the backscattering device is synchronized with the OFDM signal sent by the radio frequency source, and the signal is periodically reflected by the backscattering device; S20, the receiving device performs channel estimation to obtain a channel state information matrix; S30, performing parameter estimation to obtain multiple groups of departure angles, arrival angles, and relative flight times for the direct link and the reflected link; In step S30, the receiving device obtains the departure angle, arrival angle and relative flight time of each link signal through a perception estimation algorithm; The perception estimation algorithm is an iterative projection MUSIC algorithm, comprising the following steps: S301, the obtained P channel state information matrix is ​​divided into multiple sub-matrices with equal spacing along the subcarrier dimension, and each sub-matrix is ​​vectorized and smoothed forward and backward to obtain a forward covariance matrix and the posterior covariance matrix S302: Obtaining a bidirectional spatial smoothing covariance matrix S303, smoothing the covariance matrix of the two-way space Perform eigenvalue decomposition, sort the eigenvalues ​​from large to small, and select the first L eigenvectors to form the signal subspace E s , the remaining eigenvectors constitute the noise subspace E n ; S304, calculate spatial spectrum P RAP-MUSIC ; S305, obtain spatial spectrum P RAP-MUSIC The global maximum value in , and obtain the corresponding guidance vector, determine the departure angle Angle of arrival θ and relative flight time τ; S306, performing iterative projection, recalculating the spatial spectrum, and obtaining a parameter set including a departure angle, an arrival angle, and a relative flight time through a spectrum peak search; S307, filtering out parameters of the backscatter device from the parameter set of step S306; S40, determining straight link parameters, and selecting reflection link parameters from the departure angle, arrival angle, and relative flight time to form a backscatter device parameter set; S50, using the backscatter device parameter set, calculating the two-dimensional coordinates of the backscatter device relative to the user; S60, the backscatter device sends a random OOK modulated signal, and the receiving device calculates the optimal receiving beamforming weight vector using the arrival angle parameters of the direct link and the reflected link, and multiplies it with the received signal to achieve spatial domain filtering; S70: Perform signal judgment on the filtered signal to obtain information sent by the backscattering device.

2. The OFDM-based backscatter communication sensing integrated method according to claim 1, characterized in that: In step S20, in T consecutive transmission periods, the receiving device uses the pilot of the OFDM signal to perform channel estimation to obtain a channel state information matrix.

3. The OFDM-based backscatter communication sensing integrated method according to claim 1, characterized in that: The step S304 includes: Compute the spatial spectrum: in, is the departure angle, θ is the arrival angle, τ is the relative flight time, is a steering vector with departure angle, arrival angle and relative flight time as parameters, and its form is: Where a(θ) = e -jπndsinθ ,n=0,1,…,N-1, f k is the frequency of the kth subcarrier.

4. The OFDM-based backscatter communication sensing integrated method according to claim 3, characterized in that: The step S306 includes: S306, perform iterative projection, and arrange the estimated steering vectors in parallel to form a matrix A l , calculate the projection matrix Pr l =IA l (A l H A l ) -1 A l H , where I represents the identity matrix, and then the signal subspace E is converted into s The guiding vector for the peak search is projected and the spatial spectrum is repeatedly calculated: in is the aforementioned steering vector; By searching L spectral peaks, we can obtain L parameter sets including departure angle, arrival angle and relative flight time, which are recorded as:

5. The OFDM-based backscatter communication sensing integrated method according to claim 1, characterized in that: In step S50, calculating the two-dimensional coordinates of the backscattering device relative to the user includes: S501, according to the frame structure of the signal sent by the backscattering device, the departure angle, arrival angle and relative flight time parameters of the reflection link in the estimation result of the receiving device will obey the distribution determined by the modulation state of the backscattering device, thereby obtaining the estimated values ​​of the parameters of the reflection link; S502: Calculate the distance of the backscatter device relative to the user using the sine theorem according to the selected backscatter device parameter set: in, θ AOA with rtof TAG are the estimated departure angle, arrival angle and relative flight time of the backscattering device, c is the speed of light, and the two-dimensional coordinates of the backscattering device relative to the user are expressed as 6. The OFDM-based backscatter communication sensing integrated method according to claim 5, characterized in that: The radio frequency source is equipped with M transmitting antennas, and the receiving device is equipped with N receiving antennas.

7. The OFDM-based backscatter communication and sensing integrated method according to claim 6, characterized in that: In step S60, the receiving device calculates the optimal receiving beamforming weight vector using the arrival angle parameters of the straight link and the reflected link, and multiplies it with the received signal to implement spatial domain filtering, including: S601, setting λ m,n (k) is the frequency domain response of the kth sub-band on the link composed of the mth transmitting antenna and the nth receiving antenna, and the reflection link is a flat channel; v m With g n are the channel responses between the mth transmitting antenna and the nth receiving antenna and the backscattering device respectively; S602: Let the reflection coefficient of the backscattering device be Γ, then the frequency domain expression of the pth OFDM symbol received by the nth receiving antenna on the kth subcarrier is: Among them, s m,p (k) is the symbol loaded by the mth transmitting antenna on the kth subcarrier, c p is the symbol for the backscatter device, is complex Gaussian white noise d is the number of sampling periods that the reflection link lags behind the direct link; S603, change the formula in step S602 into a matrix form, m,n (k)} form a complex matrix H1(k) with N rows and M columns, let g = [g1,…,g N ] T 、v=[v1,…,v M ] T 、H2(k)=Γe -j2πkd / K gv T ; but: where z p (k) = [z 1,p (k), …, z N,p (k)] T , s p (k) = [s 1,p (k), …, s M,p (k)] T , S604: The receiving device uses the shortest relative flight time estimation result as the direct link parameter and uses its arrival angle information Constructing Steering Vectors Using the arrival angle information of the reflection link Constructing Steering Vectors S605, by constructing a receive beamforming weight vector, the problem of minimizing the direct link power and maximizing the reflected link power is transformed into solving an optimization problem: ||w H || 2 ≤1； Solve and obtain the closed expression of the optimal spatial domain filter weight vector: Multiplying the received signal with the weight vector implements spatial domain filtering.

8. The OFDM-based backscatter communication and sensing integrated method according to claim 7, characterized in that: In step S501, the characteristics of different links are reflected by the characteristics of the trajectory, and the links corresponding to the backscattering devices are screened by distinguishing the characteristics.

9. The OFDM-based backscatter communication and sensing integrated method according to claim 1, characterized in that: In step S40, the direct link parameters are determined by using the characteristic of the shortest direct link delay, and the reflection link parameters are determined by using the modulation state characteristics of the backscattering device, and the reflection link parameters are selected from the relative flight time.

10. An OFDM-based backscatter communication and perception integrated system, characterized in that: The system includes a backscatter device, a radio frequency source, and a receiving device; The backscatter device is synchronized with the OFDM signal sent by the radio frequency source and the signal is periodically reflected by the backscatter device; The receiving device performs channel estimation to obtain a channel state information matrix; after performing parameter estimation, multiple groups of departure angles, arrival angles and relative flight times of direct links and reflection links are obtained; direct link parameters are determined, and reflection link parameters are selected from the departure angles, arrival angles and relative flight times to form a backscattering device parameter set; thereafter, the two-dimensional coordinates of the backscattering device relative to the user are calculated using the backscattering device parameter set; The receiving device obtains the departure angle, arrival angle and relative flight time of each link signal through a perception estimation algorithm; the perception estimation algorithm is an iterative projection MUSIC algorithm, comprising the following steps: S301, the obtained P channel state information matrix is ​​divided into multiple sub-matrices with equal spacing along the subcarrier dimension, and each sub-matrix is ​​vectorized and smoothed forward and backward to obtain a forward covariance matrix and the posterior covariance matrix S302: Obtaining a bidirectional spatial smoothing covariance matrix S303, smoothing the covariance matrix of the two-way space Perform eigenvalue decomposition, sort the eigenvalues ​​from large to small, and select the first L eigenvectors to form the signal subspace E s , the remaining eigenvectors constitute the noise subspace E n ; S304, calculate spatial spectrum P RAP-MUSIC ; S305, obtain spatial spectrum P RAP-MUSIC The global maximum value in , and obtain the corresponding guidance vector, determine the departure angle Angle of arrival θ and relative flight time τ; S306, performing iterative projection, recalculating the spatial spectrum, and obtaining a parameter set including a departure angle, an arrival angle, and a relative flight time through a spectrum peak search; S307, filtering out parameters of the backscatter device from the parameter set of step S306; The backscatter device sends a random OOK modulated signal, and the receiving device uses the arrival angle parameters of the direct link and the reflected link to calculate the optimal receiving beamforming weight vector, and multiplies it with the received signal to achieve spatial domain filtering; thereafter, the filtered signal is subjected to signal judgment to obtain the information sent by the backscatter device.

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