A receiving end beamforming method for backscatter communication and perception integrated system

Abstract

The present invention relates to the field of wireless communication technology, and in particular to a receiving end beamforming method of a backscatter communication perception integrated system. The method is applied to indoor non-line-of-sight scenarios, and the backscatter communication perception integrated system includes a radio frequency source, a receiving end, and a backscatter device. The method includes: when only a direct link exists, obtaining the channel characteristics of the direct link and the direct link arrival angle; when a direct link and a reflection link exist at the same time, obtaining the reflection link arrival angle according to the channel characteristics; constructing an optimization proposition according to the direct link arrival angle and the reflection link arrival angle, calculating the beamforming weight matrix through the optimization proposition, and beamforming the receiving end data. The receiving end data is beamformed through the beamforming weight matrix to suppress the direct link signal, enhance the reflection link signal, and improve the backscatter communication quality.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a receiving end beamforming method of a backscatter communication and perception integrated system. Background Art

[0002] With the rapid development of communication technology, the demand for communication between devices is also increasing. In many emerging application scenarios such as Internet of Vehicles, smart homes, and industrial Internet of Things, many communication devices are required to have efficient communication capabilities and high-precision perception capabilities. Therefore, integrated communication and perception technology (ISAC) is becoming a key technology in the next generation of wireless communications. In the integrated communication and perception system, in addition to the communication capabilities of the wireless communication system, the network can also obtain the perception of device information in the network through the design of the antenna side and waveform measurement, and make perception and communication complement each other.

[0003] In addition to the integrated communication and sensing technology, backscatter communication has also received a lot of attention due to its low power consumption and low cost. Backscatter communication is a technology that combines energy harvesting and impedance adjustment to enable passive devices to obtain energy to drive their own work 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, which is very suitable for communication scenarios such as the Internet of Things where there are many small devices.

[0004] The indoor environment is a major application scenario for the integration of backscattering and communication perception. There are many IoT devices indoors. Backscattering devices transmit their own information by modulating the incident carrier, such as device ID, temperature and humidity status information. On the other hand, the receiving end can perceive the angle, distance, position, etc. of the backscattering device based on the backscattering signal, thereby realizing the integration of backscattering communication perception.

[0005] Today's indoor scenes are becoming more and more complex and changeable, resulting in serious indoor multipath effects. In many locations, the line-of-sight route is even blocked, and only non-line-of-sight paths exist. In this case, the communication quality of the system will be seriously affected, especially for backscattering devices. Non-line-of-sight scenes will further attenuate the backscattering signal strength, making it less than the direct link in the system, affecting the communication performance of the backscattering device. Summary of the invention

[0006] In order to solve the technical problem in the prior art that the backscatter communication and perception integrated system is greatly affected by the direct link signal due to the weak backscatter signal strength in the indoor non-line-of-sight scenario, resulting in reduced backscatter communication quality, the embodiment of the present application proposes a receiving-end beamforming method for the backscatter communication and perception integrated system.

[0007] The embodiment of the present application provides a receiving end beamforming method of a backscatter communication perception integrated system, the method is applied in an indoor non-line-of-sight scenario, the backscatter communication perception integrated system includes a radio frequency source, a receiving end with a multi-antenna array, and a backscattering device, the method includes:

[0008] When only a direct link exists, obtaining a channel characteristic of the direct link and an arrival angle of the direct link;

[0009] When the direct link and the reflected link exist simultaneously, acquiring an arrival angle of the reflected link according to the channel characteristics;

[0010] An optimization proposition is constructed according to the direct link arrival angle and the reflected link arrival angle, a beamforming weight matrix is ​​calculated by the optimization proposition, and beamforming is performed on the receiving end data.

[0011] In some embodiments, the acquiring the channel characteristics of the direct link and the direct link arrival angle includes:

[0012] Acquire a first received signal, wherein the first received signal is a signal received by the receiving end when only the direct link exists;

[0013] Performing channel estimation on the direct link according to the first received signal to obtain channel characteristics of the direct link;

[0014] The first received signal is calculated using an angle estimation algorithm to obtain the direct link arrival angle.

[0015] In some embodiments, acquiring the reflection link arrival angle according to the channel characteristics includes:

[0016] Acquire a second received signal, wherein the second received signal is a signal received by the receiving end when the direct link and the reflected link exist at the same time;

[0017] Restore and eliminate the radio frequency source signal in the second received signal according to the channel characteristics to obtain a backscattering device signal;

[0018] The backscattering device signal is calculated using an angle estimation algorithm to obtain the arrival angle of the reflection link.

[0019] In some embodiments, assuming that there are L direct links in the environment, different direct links correspond to different incident signals, and the expression formula of the first received signal is:

[0020]

[0021] Among them, y CT(n) is the first received signal, P CT,l is the path loss of the lth direct link, θ l represents the azimuth of the lth incident signal, represents the pitch angle of the lth incident signal, is the steering vector of the lth incident signal, where θ l ∈[0,π], s(n) is the incident signal, d l is the propagation distance of the lth incident signal, λ CT is the wavelength of the incident signal, and u(n) is the Gaussian white noise signal.

[0022] In some embodiments, the channel estimation uses the LS channel estimation algorithm, and the channel characteristics are expressed by the formula Calculated;

[0023] in, is the channel characteristic estimation parameter, x is the pilot symbol of the signal transmitted by the RF source, and y CT is the first received signal.

[0024] In some embodiments, the angle estimation algorithm is a MUSIC algorithm, comprising:

[0025] The input L-path multipath coherent signal is divided into a plurality of sub-arrays at equal intervals along the azimuth dimension and the elevation dimension, each of the sub-arrays is vectorized separately, and forward and backward smoothing is performed respectively;

[0026] Obtaining a covariance matrix after bidirectional spatial smoothing according to the smoothing results of all the sub-surface arrays;

[0027] Perform eigenvalue decomposition on the covariance matrix after bidirectional spatial smoothing and calculate the two-dimensional spatial spectrum;

[0028] The incident azimuth angles and incident elevation angles of L coherent signals are acquired according to the two-dimensional spatial spectrum.

[0029] In some embodiments, restoring and eliminating the radio frequency source signal in the second received signal according to the channel characteristics to obtain the backscatter device signal includes:

[0030] Performing equalization processing on the second received signal according to the channel characteristics, and demodulating the radio frequency source transmission signal;

[0031] Restoring the RF source signal according to the channel characteristics and the RF source transmission signal;

[0032] The radio frequency source signal is eliminated from the second received signal to obtain a backscatter device signal.

[0033] In some embodiments, the demodulating the signal transmitted by the radio frequency source includes:

[0034]

[0035] in, is the estimated value of the signal transmitted by the RF source, y(n) is the second received signal, is the channel characteristic estimation parameter, and s(n) is the signal transmitted by the RF source.

[0036] In some embodiments, restoring the radio frequency source signal includes:

[0037]

[0038] in, is the estimated value of the RF source signal, is the channel characteristic estimation parameter, Estimated value of the signal transmitted by the RF source.

[0039] In some embodiments, the optimization proposition is:

[0040]

[0041] ||w H || 2 ≤1

[0042] Where w represents the beamforming weight matrix, α k represents the signal strength factor of the Kth reflection link, is the direct link arrival angle, is the arrival angle of the reflection link.

[0043] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0044] The embodiment of the present application proposes a receiving end beamforming method of a backscatter communication perception integrated system, which is applied to indoor scenes. The backscatter communication perception integrated system includes a radio frequency source, a receiving end, and a backscatter device, and there is only a non-line-of-sight path between the backscatter device and the receiving end. The method constructs an optimization proposition by obtaining the arrival angle of the direct link and the arrival angle of the reflection link, obtains a beamforming weight matrix through the optimization proposition, and beamforms the receiving end data according to the beamforming weight matrix, suppresses the direct link signal, enhances the reflection link signal, and reduces the interference of the direct link to the reflection link communication, so as to improve the communication quality of the reflection link, that is, improve the backscatter communication quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0046] Figure 1 It is a schematic diagram of an application environment of a receiving-end beamforming method of a backscatter communication and perception integrated system provided in an embodiment of the present application;

[0047] Figure 2 It is a flow chart of a receiving end beamforming method of a backscatter communication and perception integrated system provided in an embodiment of the present application;

[0048] Figure 3 yes Figure 2 A detailed flow chart of step S201 in FIG.

[0049] Figure 4 is a flowchart of an angle estimation algorithm in an embodiment of the present application;

[0050] Figure 5 yes Figure 2 A detailed flow chart of step S202 in FIG.

[0051] Figure 6 It is a schematic diagram of a simulation application scenario of a receiving-end beamforming method of a backscatter communication and perception integrated system proposed in an embodiment of the present application;

[0052] Figure 7 is a signal constellation diagram of a second received signal in a simulation application scenario of an embodiment of the present application;

[0053] Figure 8 is a signal constellation diagram of a backscatter device signal in a simulation application scenario in an embodiment of the present application;

[0054] Fig. 9 is a signal constellation diagram of a signal after beamforming in a simulation application scenario in an embodiment of the present application;

[0055] Fig.10 is a curve diagram showing the variation of the simulation bit error rate performance with the signal-to-noise ratio in the simulation application scenario in the embodiment of the present application;

[0056] 100. Application environment; 101. RF source; 102. Receiver; 103. Backscatter device; 104. Obstruction. DETAILED DESCRIPTION

[0057] The present application is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements can also be made without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0058] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0059] It should be noted that, if there is no conflict, the various features in the embodiments of the present application can be combined with each other, all within the scope of protection of the present application. In addition, although the functional module division is performed in the device schematic diagram and the logical order is shown in the flow chart, in some cases, the steps shown or described can be performed in a sequence different from the module division in the device or the flow chart. In addition, the words "first", "second", "third", etc. used herein do not limit the data and execution order, but only distinguish the same items or similar items with basically the same functions and effects.

[0060] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used in this specification and in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used in this specification includes any and all combinations of one or more of the related listed items.

[0061] In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0062] Before introducing the embodiments of the present application, a brief introduction is first given to backscattering, synaesthesia integration, and backscattering combined with synaesthesia integration involved in the present application, so as to facilitate subsequent understanding of the embodiments of the present application.

[0063] Backscatter is a wireless communication technology that uses existing wireless signals to transmit information without generating radio frequency energy. In this technology, a passive or semi-active tag or sensor modulates the existing wireless signal by changing its own reflection characteristics to achieve information transmission.

[0064] Specifically, an external wireless signal is irradiated onto the backscatter tag, and the backscatter tag modulates the wireless signal by changing the impedance of its antenna or circuit, or by switching the circuit, so that the signal carries the backscatter tag's own information, such as device ID, temperature and humidity status information. This modulation can be amplitude modulation (AM), frequency modulation (FM) or phase modulation (PM). The modulated signal is reflected back from the tag into space and captured by the receiving device. The receiving device receives the backscatter signal and demodulates it to extract the backscatter tag's own information.

[0065] Integrated Sensing and Communication (ISAC), also known as ISAC, is a technology that combines traditional communication systems with perception functions. This technology allows wireless communication systems to be used not only for data transmission, but also to perform perception tasks such as environmental detection, object detection, and imaging. ISAC technology uses the reflection and scattering characteristics of wireless signals during propagation to obtain information about the surrounding environment.

[0066] Specifically, wireless communication systems transmit and receive wireless signals to achieve data transmission. Perception refers to detecting the state of the surrounding environment, the position, direction, speed, distance of objects, and the shape of objects by certain means. The perception device in the prior art is a radar, and its perception principle is to send out wireless signals. When the wireless signals encounter different media or objects, the wireless signals will undergo different changes due to reflection, refraction, scattering, etc., and the characteristic information of the object or medium is obtained by detecting and analyzing the changes of the received reflected signals relative to the emitted wireless signals, thereby achieving perception. In the synaesthesia integration technology, perception is to use the wireless signals used for data transmission in the wireless communication system to perform perception tasks. Specifically, the wireless signals in the wireless communication system encounter different media or objects during the data transmission process, which undergo reflection, refraction, scattering, etc., and produce changes. The characteristic information of the object or medium is obtained by detecting and analyzing the changes, and the perception task is performed while achieving data transmission.

[0067] Backscattering combined with synaesthesia integration means that the wireless signal in the wireless communication system is irradiated onto the backscattering tag during the data transmission process. The backscattering tag modulates the wireless signal so that the wireless signal carries the backscattering tag's own information, such as device ID, temperature and humidity and other status information. The modulated signal is reflected back into space from the tag and received by the receiving device. In addition, the wireless signal changes during the data transmission process due to reflection, refraction, scattering, etc. caused by the backscattering tag, thereby carrying the characteristic information of the backscattering tag, such as the position, shape, distance, etc. of the reflected scattering tag. While realizing communication, the receiving device performs the perception task of the backscattering tag and obtains the backscattering tag's own information, realizing the integration of backscattering communication perception.

[0068] Indoor environment is a major application scenario for the backscattering combined with synaesthesia integration technology. However, in complex indoor environments, the multipath effect is serious. Wireless signals propagate through different paths, and each component field arrives at the receiving end at different times. They are superimposed on each other according to their respective phases, causing interference and signal distortion. In addition, in complex indoor environments, the line of sight of wireless communication between the backscattering device and the receiving end is blocked, and only non-line-of-sight paths exist. Non-line-of-sight scenarios will further attenuate the backscattering signal strength to be less than the direct link signal strength in the system. The direct link signal interferes with the backscattering signal, thereby affecting the communication performance of the backscattering device.

[0069] Based on this, in order to solve the technical problem in the prior art that the backscatter communication perception integrated system is greatly affected by the direct link signal due to the weak backscatter signal strength in the indoor non-line-of-sight scenario, resulting in reduced backscatter communication quality, the embodiment of the present application proposes a receiving-end beamforming method for the backscatter communication perception integrated system.

[0070] See also Figure 1 , Figure 1 It is a schematic diagram of an application environment of a receiving-end beamforming method of a backscatter communication and perception integrated system provided in an embodiment of the present application;

[0071] like Figure 1 As shown, the application environment 100 is an indoor environment, which includes a backscatter communication sensing integrated system and an obstruction 104. The backscatter communication sensing integrated system includes: a radio frequency source 101, a receiving end 102 with a multi-antenna array, and a backscatter device 103.

[0072] It can be understood that a multi-antenna array refers to an array composed of multiple antennas, which are arranged in a specific geometric shape and are used to transmit or receive wireless signals.

[0073] Specifically, the RF source 101 and the receiving end 102 are within the line of sight, and the wireless signal between the RF source 101 and the receiving end 102 is transmitted unobstructed. The signal propagation path between the RF source 101 and the receiving end 102 is a direct link, and the direct link includes the path from the RF source 101 to the receiving end 102 and the path from the RF source 101 to the wall or object to the receiving end 102. Figure 1 As shown, the solid arrows represent partial direct links.

[0074] The receiving end 102 and the backscattering device 103 are in a non-line-of-sight range. There is an obstruction 104 between the receiving end 102 and the backscattering device 103, and the wireless communication line of sight is blocked. The signal propagation path between the receiving end 102 and the backscattering device 103 is a reflection link. In the embodiment of the present application, the reflection link is a non-line-of-sight path. The reflection link includes the path of the backscattering device 103-wall or object-receiving end 102. Figure 1 As shown, the dotted arrow represents a partially reflective link.

[0075] The RF source 101 refers to a device or system capable of generating wireless signals, and the number of transmitting antennas of the RF source 101 is at least one. It can be understood that the transmitting antenna is a component that converts electrical signals in a transmission line or a feeder into wireless signals and effectively transmits these wireless signals into free space. The RF source 101 can be an oscillator, a RF transmitter, a radar system, etc., but is not limited thereto.

[0076] The receiving end 102 refers to a device that can receive wireless signals and demodulate them to extract original information, which can be a software radio device, an indoor small base station, an RFID reader, etc., but is not limited thereto.

[0077] The backscatter device 103 refers to a passive or semi-active tag or sensor that can modulate an external wireless signal irradiated thereon and reflect the modulated signal back into space. The number of transmitting antennas and receiving antennas of the backscatter device 103 is at least one each. It can be understood that the receiving antenna is a component that converts wireless signals in free space into electrical signals and transmits the electrical signals to a receiving device for further processing. The backscatter device 103 can be an RFID tag, a wireless sensor network node, a biomedical sensor, etc., but is not limited thereto.

[0078] The shielding object 104 refers to an object that blocks the direct line of sight between the receiving end 102 and the backscattering device 103. It can be a table, a chair, a wall, a bookshelf, etc., but is not limited thereto.

[0079] See also Figure 2 , Figure 2 It is a flow chart of a receiving-end beamforming method of a backscatter communication and perception integrated system provided in an embodiment of the present application.

[0080] like Figure 2 As shown, the method includes:

[0081] Step S201: When only a direct link exists, the channel characteristics of the direct link and the arrival angle of the direct link are obtained.

[0082] It can be understood that the direct link refers to the signal propagation path between the RF source 101 and the receiving end 102, which includes the direct path of the RF source 101-receiving end 102 and the path of the RF source 101-wall or object-receiving end 102.

[0083] Channel characteristics refer to parameters that describe signal propagation characteristics in wireless communications. By obtaining the channel characteristics of the direct link, the signal data from the RF source 101 can be restored in the signal received by the receiving end 102 using the channel characteristics of the direct link to obtain an estimated value of the signal transmitted by the RF source 101.

[0084] The direct link arrival angle refers to the angle position of the RF source transmission signal from the RF source 101 to the receiving end 102. The direct link arrival angle includes the direct link incident azimuth angle and the direct link incident elevation angle. By obtaining the direct link arrival angle, when performing the receiving end data beamforming optimization, the signal in the direct link incident direction is suppressed to reduce the interference of the direct link signal on the backscatter communication.

[0085] For details, see Figure 3 , Figure 3 yes Figure 2 Detailed flowchart of step S201 in FIG.

[0086] like Figure 3 As shown, step S201: when there is only a direct link, obtaining the channel characteristics of the direct link and the direct link arrival angle includes:

[0087] Step S2011: Acquire a first received signal, wherein the first received signal is a signal received by the receiving end when only a direct link exists.

[0088] Specifically, by controlling the transmission power of the RF source 101, the transmission power of the RF source 101 is made lower than the activation threshold of the backscatter device 103. Under this transmission power, the backscatter device 103 does not receive, modulate, or reflect the RF source transmission signal emitted by the RF source 101. There is only a direct link in the environment, and the receiving end 102 only receives the RF source transmission signal. Among them, the signal from the RF source 101 in the signal received by the receiving end 102 is called the RF source signal. At this time, the signal received by the receiving end 102 is the first received signal. The first received signal is the sum of the RF source signal and the Gaussian white noise signal.

[0089] Assuming that there are L direct links in the environment, different direct links correspond to different incident signals. The expression formula of the first received signal is:

[0090]

[0091] Among them, y CT(n) is the first received signal, P CT,l is the path loss of the lth direct link, θ l represents the azimuth of the lth incident signal, represents the pitch angle of the lth incident signal, is the steering vector of the lth incident signal, where θ l ∈[0,π], s(n) is the incident signal, d l is the propagation distance of the lth incident signal, λ CT is the wavelength of the incident signal, and u(n) is the Gaussian white noise signal.

[0092] Step S2012: performing channel estimation on the direct link according to the first received signal to obtain channel characteristics of the direct link.

[0093] During signal transmission, the signal will be affected by the channel, including attenuation, phase shift, and noise. In order to correctly decode the received data, it is necessary to remove the influence of the channel from the received signal. The main purpose of channel estimation is to extract the channel characteristics of the channel from the received data, so as to understand the influence of the channel on the signal and facilitate the correct decoding of the received data.

[0094] Channel estimation methods can be roughly divided into two categories, one is non-blind channel estimation and the other is blind channel estimation. Non-blind channel estimation requires the use of pilot sequences known to both the transmitter and the receiver for channel estimation, and uses different time-frequency domain interpolation techniques to estimate the channel response on subcarriers between pilots or symbols. The main non-blind channel estimation methods currently used include least squares channel estimation (LS channel estimation), minimum mean square error channel estimation (MMSE channel estimation), DFT-based channel estimation, and decision feedback-based channel estimation, etc.; while the estimation process of blind channel estimation does not rely on known information, and mainly includes maximum expectation-based channel estimation, subspace-based channel estimation technology, etc.

[0095] In the embodiment of the present application, the LS channel estimation algorithm is used to perform channel estimation on the direct link. The basic idea of ​​the LS channel estimation algorithm is to estimate the channel parameters by minimizing the square sum of the errors between the data received by the receiving end and the data sent by the transmitting end.

[0096] In the embodiment of the present application, a pilot symbol is periodically provided in the radio frequency source transmission signal. The pilot signal in the radio frequency source transmission signal and the first received signal are used to perform channel estimation on the direct link. According to the LS channel estimation algorithm, the channel characteristics of the direct link can be calculated by the following formula:

[0097]

[0098] in, is the channel characteristic estimation parameter, x is the pilot symbol in the RF source transmission signal, y CT is the first received signal.

[0099] when When the sum of squared errors of the estimation is minimized, the channel characteristic estimation parameters obtained at this time are is the best approximation of LS channel estimation.

[0100] Step S2013: Calculate the first received signal using an angle estimation algorithm to obtain a direct link arrival angle.

[0101] When beamforming the receiving end data, it is necessary to suppress the signal in the incident direction of the direct link. Therefore, it is necessary to obtain the direct link arrival angle before beamforming the receiving end data. In the case of only a direct link, the signals received by the receiving end all come from the RF source. The first received signal is the sum of the RF source signal and the Gaussian white noise signal. The angle of arrival of the direct link can be obtained by estimating the angle of the first received signal.

[0102] The angle estimation algorithm is a perception algorithm. The main angle estimation algorithms currently used include the ESPRIT (Estimating Signal Parameters via Rotational Invariance Techniques) algorithm, the MUSIC (Multiple Signal Classification) algorithm, and the OMP (Orthogonal Matching Pursuit) algorithm.

[0103] In the embodiment of the present application, the MUSIC algorithm is used to calculate the direct link arrival angle. Specifically, the 2D-MUSIC algorithm based on two-dimensional spatial smoothing is used to calculate the first received signal to obtain the direct link arrival angle.

[0104] The 2D-MUSIC algorithm based on two-dimensional space smoothing is an algorithm used to estimate the signal arrival angle in two-dimensional space. The algorithm is used to smooth the received coherent signals on a two-dimensional array. The problem it solves is how to remove the coherence between coherent signals to better estimate the angle.

[0105] See also Figure 4 , Figure 4 It is a flowchart of the angle estimation algorithm in the embodiment of the present application.

[0106] like Figure 4 As shown, the 2D-MUSIC algorithm based on two-dimensional spatial smoothing specifically includes:

[0107] Step S301: the input L-path multipath coherent signal is divided into a plurality of sub-arrays at equal intervals along the azimuth dimension and the elevation dimension, each sub-array is vectorized separately, and forward and backward smoothing is performed respectively.

[0108] In the embodiment of the present application, since the first received signal is a multipath signal composed of the same RF source transmitted signal transmitted by the same RF source through L direct links and received by the receiving end 102, there is a strong correlation between the multiple signals. The first received signal is divided into multiple sub-arrays at equal intervals along the direction dimension and the elevation dimension, and each sub-array is vectorized separately, and forward and backward smoothing is performed respectively.

[0109] Specifically, for a surface array with a directional dimension of M and a pitch dimension of N, the sub-surface array is divided into interlaced sub-arrays in two dimensions. Assuming that the directional dimension is divided into m sub-arrays and the pitch dimension is divided into n sub-arrays, the size of the sub-array is M s =M+1-m columns, N s =N+1-n rows.

[0110] Among them, the first y ,i z ) The element selection matrix of the sub-array can be expressed as:

[0111]

[0112] in, and They are respectively the forward spatial smoothing (i y ,i z ) array element selection matrices of the azimuth and elevation dimensions of the subarrays, and They are the backward spatial smoothing (i y ,i z ) array element selection matrices of the azimuth and elevation dimensions of the subarrays, M s ×M s The identity matrix of M is an M whose anti-diagonal elements are 1 and the rest of the elements are 0. s ×M s matrix; N S ×N S The identity matrix of N is an N whose anti-diagonal elements are 1 and the rest of the elements are 0 S ×N S The matrix of .

[0113] Step S302: Obtain the covariance matrix after bidirectional spatial smoothing according to the smoothing results of all sub-surface arrays.

[0114] Specifically, the forward and backward covariance matrices of each subarray are obtained according to the array element selection matrix: The covariance matrix results of all sub-arrays are averaged to obtain the smoothed forward covariance matrix and the backward covariance matrix

[0115]

[0116] Then the covariance matrices after bidirectional spatial smoothing are

[0117]

[0118] Step S303: performing eigenvalue decomposition on the covariance matrix after bidirectional spatial smoothing to calculate the two-dimensional spatial spectrum.

[0119] Specifically, the covariance matrix after bidirectional spatial smoothing is Perform eigenvalue decomposition to distinguish the signal subspace and the noise subspace and calculate their two-dimensional spatial spectrum

[0120]

[0121] in, is the steering vector corresponding to the angle of the obtained array, E n is the covariance matrix after bidirectional spatial smoothing The noise subspace.

[0122] Step S304: Obtain incident azimuth angles and incident elevation angles of L coherent signals according to the two-dimensional spatial spectrum.

[0123] Specifically, the largest L peaks are searched at different angles in the two-dimensional spatial spectrum, and the L peaks are taken to obtain the incident azimuth and incident elevation angles of the L coherent signals. The incident azimuth and incident elevation angle constitute the direct link arrival angle.

[0124] Step S202: Obtain the arrival angle of the reflection link.

[0125] It can be understood that the reflection link is a signal propagation path between the backscatter device 103 and the receiving end 102. Since the backscatter device 103 and the receiving end 102 are in a non-line-of-sight situation, the reflection link includes a path from the backscatter device 103 to the receiving end 102.

[0126] The arrival angle of the reflection link refers to the arrival direction of the backscatter signal propagating from the backscatter device 103 to the receiving end 102, which includes the incident direction angle of the reflection link and the incident elevation angle of the reflection link. When performing data beamforming at the receiving end, it is necessary to enhance the signal in the incident direction of each reflection link to achieve the effect of maximizing the overall backscatter signal receiving power. Therefore, before performing data beamforming at the receiving end, it is necessary to obtain the arrival angle of the reflection link.

[0127] For details, see Figure 5 , Figure 5 yes Figure 2 A detailed flow chart of step S202 in FIG.

[0128] like Figure 5 As shown, step S202: obtaining the arrival angle of the reflection link includes:

[0129] Step S2021: Acquire a second received signal, wherein the second received signal is a signal received by the receiving end when both the direct link and the reflected link exist.

[0130] Specifically, the transmission power of the RF source 101 is controlled to be higher than the activation threshold of the backscatter device 103, so as to activate the backscatter device 103. Under the transmission power, the backscatter device 103 receives and modulates the RF source transmission signal sent by the RF source 101 and reflects the modulated signal back into space, and the modulated signal is received by the receiving end 102. The signal transmitted by the backscatter device 103 is called a backscatter signal.

[0131] At this time, there are both direct links and reflected links in the environment, and the receiving end 102 receives the RF source transmission signal emitted by the RF source 101 and the backscattering signal emitted by the backscattering device 103. Among them, the part of the signal received by the receiving end 102 from the backscattering device 103 is called the backscattering device signal. At this time, the signal received by the receiving end 102 is the second received signal. The second received signal is composed of the RF source signal, the backscattering device signal and the Gaussian white noise signal.

[0132] The signal received by the backscatter device is called the backscatter device received signal. Since the backscatter device is modulated based on the RF source transmission signal emitted by the RF source, the backscatter device received signal can be expressed as Where g represents the signal attenuation experienced by the signal transmitted from the RF source to the backscattering device; represents the carrier of the backscattered signal, which is expressed as s(n) represents the signal transmitted by the RF source, d represents the propagation distance of the signal transmitted by the RF source to the backscattering device, and λ CTIndicates the wavelength of the signal emitted by the RF source.

[0133] The backscatter signal transmitted by the backscatter device 103 to the receiving end 102 can be described as:

[0134]

[0135] Where b(n) represents the backscattered signal, g is the signal attenuation experienced by the signal transmitted from the RF source to the backscattering device, represents the carrier of the backscattered signal, represents the backscatter device receiving the signal, and c(n) represents the backscatter device sending the symbol. The backscatter device sending the symbol is the information that the backscatter device needs to transmit to the receiving end, such as the backscatter device ID.

[0136] Assume that there are K reflection links, and different reflection links correspond to different incident signals. The incident signal refers to the multipath signal of the same backscattered signal after passing through K reflection links. Then the expression of the backscattered device signal at the receiving end is:

[0137]

[0138] Among them, y BD (n) represents the backscattered device signal, P BD,k represents the path loss from the backscattered signal in the kth reflection link to the receiving end, b(n) represents the backscattered signal, θ k represents the azimuth of the kth incident signal, represents the elevation angle of the kth incident signal, is the steering vector of the kth incident signal, where θ k ∈[0,π], d k represents the propagation distance of the kth incident signal, λ BD is the wavelength of the backscattered signal.

[0139] The second received signal is composed of the RF source signal, the backscattering device signal and the Gaussian white noise signal. The expression of the second received signal is:

[0140]

[0141] Wherein, y(n) represents the second received signal, and u(n) is a Gaussian white noise signal.

[0142] Step S2022: restore and eliminate the RF source signal in the second received signal according to the channel characteristics to obtain a backscatter device signal.

[0143] The RF source signal in the second received signal is restored based on the channel characteristics of the direct link. Since the backscatter device signal is modulated based on the RF source signal and the reflection link only has a non-line-of-sight path, the strength of the backscatter device signal is much smaller than the RF source signal. The second received signal is equalized using the channel characteristics of the direct link, and the estimated value of the RF source transmission signal that accounts for the main energy is demodulated from the second received signal based on the minimum code distance principle. The demodulation formula is as follows:

[0144]

[0145] in, is the estimated value of the signal transmitted by the RF source, y(n) is the second received signal, is the channel characteristic estimation parameter, and s(n) is the signal transmitted by the RF source.

[0146] According to the demodulated RF source transmission signal estimation value And the channel characteristic estimation parameters of the direct link Restore the RF source signal. The restoration formula is as follows:

[0147]

[0148] in, is the estimated value of the RF source signal, is the channel characteristic estimation parameter, Estimated value of the signal transmitted by the RF source.

[0149] The estimated value of the RF source signal is eliminated from the second received signal to obtain the backscattering device signal after Successive Interference Cancellation (SIC). The elimination formula is as follows:

[0150]

[0151] Among them, y SIC (n) is the backscattered device signal, y(n) is the second received signal, is the estimated value of the RF source signal.

[0152] Since only the RF source signal that accounts for the main energy is restored and eliminated in this step, some RF source signals still remain. The signal strength of the RF source signal is much greater than the backscatter device signal, so the residual RF source signal will still have a great impact on the backscatter communication. Therefore, it is necessary to use the perception ability of the receiving end 102 to obtain the arrival angle of the reflection link, and enhance the signal in the incident direction of the reflection link and suppress the signal in the incident direction of the direct link to reduce the impact of the residual RF source signal on the backscatter communication.

[0153] Step S2023: Calculate the backscatter device signal using an angle estimation algorithm to obtain the arrival angle of the reflection link.

[0154] When beamforming is performed on the receiving end data, the signal in the incident direction of the reflection link needs to be enhanced. Therefore, the arrival angle of the reflection link needs to be obtained before beamforming is performed on the receiving end data.

[0155] In the embodiment of the present application, the angle estimation algorithm used is the MUSIC algorithm.

[0156] Specifically, a 2D-MUSIC algorithm based on two-dimensional spatial smoothing is used to sense the backscattering device signal to obtain the arrival angle of the reflection link.

[0157] The backscatter device signal is a multipath signal composed of the same backscatter signal emitted by the same backscatter device and received by the receiving end through K reflection links. There is a strong correlation between the multiple signals. The backscatter device signal is divided into multiple sub-arrays with equal spacing along the direction dimension and the pitch dimension. Each sub-array is vectorized separately and forward and backward smoothed respectively. The forward and backward covariance matrices of each sub-array are calculated based on the smoothing results of all sub-arrays. The covariance matrix results of all sub-arrays are averaged to obtain the smoothed forward covariance matrix and the backward covariance matrix

[0158]

[0159] Then the covariance matrices after bidirectional spatial smoothing are

[0160]

[0161] The covariance matrix after bidirectional spatial smoothing is subjected to eigenvalue decomposition to calculate the two-dimensional spatial spectrum. The largest K peaks are searched at different angles in the two-dimensional spatial spectrum, and the K peaks are taken to obtain the incident azimuth and incident elevation angles of the K coherent signals. The incident azimuth and incident elevation angle constitute the arrival angle of the reflection link.

[0162] Step S203: construct an optimization proposition according to the direct link arrival angle and the reflected link arrival angle, calculate the beamforming weight matrix through the optimization proposition, and perform beamforming on the receiving end data.

[0163] An optimization proposition is constructed based on the direct link arrival angle and the reflected link arrival angle obtained in step S201 and step S202. The optimization proposition is as follows:

[0164]

[0165] ||w H || 2 ≤1

[0166] Where w is the beamforming weight matrix, α k is the signal strength factor of the kth reflection link, is the direct link arrival angle, is the arrival angle of the reflection link.

[0167] Specifically, the signal strength factor α k It can be obtained according to the eigenvalue size of the covariance matrix. Since the steering vector is actually the signal subspace of the covariance matrix, the first K largest eigenvalues ​​of the covariance matrix are selected as signal strength factors for substitution.

[0168] The solution target of this optimization problem is the beamforming weight matrix w. The solution logic of this optimization problem is: and ||w H || 2 Among all values ​​of the beamforming weight matrix w with ≤ 1, find the value such that The beamforming weight matrix w with the largest value.

[0169] Among them, the beamforming weight matrix w needs to satisfy It means that the beamforming weight matrix w needs to suppress the signal in the incident direction of the direct link and force the signal in the incident direction of the direct link to zero, so as to minimize the interference of the direct link communication on the reflected link communication.

[0170] In addition, the beamforming weight matrix w needs to satisfy ||w H || 2 ≤1, which means that the power of the beamforming weight matrix w needs to be limited to achieve power normalization and avoid The value of the term becomes infinitely large as the modulus of the beamforming weight matrix w increases.

[0171] In the beamforming weight matrix w that satisfies the above two conditions, find The beamforming weight matrix w with the largest value is the ultimate goal of solving this optimization problem. The maximum value of indicates that the signal in the incident direction of each reflection link is enhanced to maximize the overall reflection link signal receiving power.

[0172] make Then the optimization proposition is a tag Find the direction perpendicular to a source The beamforming weight matrix of , so the closed-form expression of the beamforming weight matrix is ​​transformed into:

[0173]

[0174] The beamforming weight matrix is ​​calculated through the above optimization proposition, and beamforming is performed on the receiving end data to suppress the direct link, enhance the reflected link, and reduce the impact of the direct link signal on the backscatter communication. This solves the technical problem in the prior art that the backscatter communication perception integrated system is greatly affected by the direct link signal due to the weak backscatter signal strength in the indoor non-line-of-sight scenario, resulting in reduced backscatter communication quality.

[0175] See also Figure 6 , Figure 6 It is a schematic diagram of a simulation application scenario of a receiving-end beamforming method of a backscatter communication and perception integrated system proposed in an embodiment of the present application.

[0176] by Figure 6 Taking the simulation application scenario shown as an example, the receiving end beamforming method of the backscatter communication and perception integrated system proposed in the embodiment of the present application is further explained.

[0177] Model simulation is used to verify the receiving end beamforming method proposed in the embodiment of the present application. Figure 6 As shown, the simulation application scenario 100 is an indoor office scenario, in which an obstruction 104 and a backscatter communication perception integrated system are arranged.

[0178] The integrated backscatter communication sensing system includes a radio frequency source 101, a receiving end 102, and a backscatter device 103. The carrier frequency of the system is set to 900 MHz; the number of transmitting antennas of the radio frequency source 101 is 1, and the coordinates of the radio frequency source 101 are (2.4, 5, 1.5), in meters; the antenna array dimension of the receiving end 102 is M×N=8×8, and the coordinates of the receiving end 102 are (0.01, 4.5, 2.3), in meters; the number of transmitting antennas and the number of receiving antennas of the backscatter device 103 are both 1, and the coordinates of the backscatter device 103 are (2, 4.4, 0), in meters.

[0179] The shielding object 104 is located between the receiving end 102 and the backscattering device 103, so that the backscattering device 103 and the receiving end 102 are in a non-line-of-sight scenario. There are two reflection links. In the embodiment of the present application, the shielding object 104 is a bookshelf.

[0180] The RF source transmission signal emitted by the RF source is a QPSK signal, the backscatter signal emitted by the backscatter device is a BPSK signal, and the RF source transmission signal strength is 10 times the backscatter signal strength. The angle scanning interval of the angle estimation algorithm is 1 degree.

[0181] Verification was performed based on the above model parameters.

[0182] The transmission power of the RF source 101 is controlled to be lower than the activation threshold of the backscattering device. Under this transmission power, the backscattering device 103 is not activated and does not perform backscattering. The receiving end 102 only receives the RF source transmission signal sent by the RF source 101. At this time, the signal received by the receiving end 102 is the first received signal, which is composed of the RF source signal and Gaussian white noise. The RF source signal is the signal from the RF source 101 part of the signal received by the receiving end 102.

[0183] Channel estimation of the direct link is performed according to the first received signal, and an angle estimation algorithm is used to estimate the arrival angle of the direct link.

[0184] The transmission power of the RF source 101 is controlled to be higher than the activation threshold of the backscattering device. Under this transmission power, the backscattering device 103 is activated to perform backscattering. The receiving end 102 receives the RF source transmission signal sent by the RF source 101 and the backscattering signal sent by the backscattering device. At this time, the signal received by the receiving end 102 is a second received signal, which is composed of the RF source signal, the backscattering device signal and the new Gaussian white noise signal.

[0185] See also Figure 7 , Figure 7 It is a signal constellation diagram of the second received signal in the simulation application scenario of the embodiment of the present application.

[0186] Among them, QPSK modulation uses four phase states, namely 0 degrees, 90 degrees, 180 degrees and 270 degrees. On the constellation diagram, the QPSK signal appears as four points, which are equally spaced on the horizontal and vertical axes to form a square distribution.

[0187] BPSK modulation uses only two phase states, usually 0 degrees and 180 degrees. On the constellation diagram, the BPSK signal appears as two points, located at the two extremes of the horizontal axis (I axis), while the value on the vertical axis (Q axis) is 0.

[0188] like Figure 7 As shown, the second received signal is concentrated and distributed at four points, forming a square distribution as a whole. The part that accounts for the main power is the QPSK signal, and the BPSK signal is very weak. Since the signal sent by the RF source 101 is a QPSK signal, and the signal sent by the backscattering device 103 is a BPSK signal, it can be inferred that the RF source signal accounts for the main power in the second received signal. At this time, the direct link signal greatly interferes with the backscattering communication.

[0189] The radio frequency source signal in the second received signal is restored and eliminated according to the channel estimation of the direct link to obtain the backscattering device signal.

[0190] See also Figure 8 , Figure 8 It is a signal constellation diagram of the backscatter device signal in the simulation application scenario in the embodiment of the present application.

[0191] Since only the RF source signal that accounts for the majority of the energy is restored and eliminated in this step, some RF source signals still remain. Figure 8 As shown in the figure, the backscatter device signal is evenly spread outward at one point, and the QPSK signal and the BPSK signal are mixed together, making it difficult to distinguish the BPSK signal. It can be seen that the residual RF source signal seriously interferes with the identification of the backscatter device signal and still has a great impact on the backscatter communication.

[0192] The angle of arrival of the reflected link is estimated using an angle estimation algorithm based on the backscattered device signal.

[0193] According to the arrival angle of the direct link and the arrival angle of the reflected link, an optimization proposition is constructed and the beamforming weight matrix is ​​solved, and beamforming is performed at the receiving end. The signal in the incident direction of the direct link is suppressed and forced to zero, so that the interference of the direct link signal to the backscatter communication is minimized; at the same time, the signal in the incident direction of the reflected link is enhanced to maximize the overall backscatter power.

[0194] See also Fig. 9 , Fig. 9 It is a signal constellation diagram of the signal after beamforming in the simulation application scenario in the embodiment of the present application.

[0195] like Fig. 9 As shown in the figure, the signal after beamforming is concentrated and distributed at two points, showing a clearer BPSK symbol form. It can be seen that the residual high-power RF source signal is suppressed and the backscatter communication quality is improved.

[0196] Use an energy detector and a maximum likelihood detector to demodulate the backscatter device signal and the signal after beamforming and calculate the bit error rate, and compare the bit error rate before beamforming with the bit error rate after beamforming to verify the effect of beamforming. The bit error rate refers to the ratio of the number of bits transmitted in error to the total number of bits transmitted in a given time. In the embodiment of the present application, the lower the bit error rate of the signal, the better the backscatter communication quality.

[0197] Specifically, an energy detector is a technology used to detect the presence or absence of a signal in wireless communication. It determines whether a signal is being transmitted by monitoring the energy level of the received signal.

[0198] The demodulation of the backscatter device signal using an energy detector is taken as an example for specific description.

[0199] When the backscatter device is in a reflective state, the information it carries is bit 1; when the backscatter device is in a non-reflective state, the information it carries is bit 0. The average energy of the backscatter device signal is:

[0200]

[0201] Where g is the signal attenuation experienced by the RF source transmitting the signal to the backscattering device, P BD,k represents the path loss from the backscatter signal in the kth reflection link to the receiving end, c(n) represents the symbol sent by the backscatter device, σ 2 is the variance of Gaussian white noise.

[0202] Let the average energy when sending bit 1 be P1, and the average energy when sending bit 0 be P0. These two can be obtained based on the reference symbol in the backscatter signal sent by the backscatter device. Then the energy detector decision formula is:

[0203]

[0204] Where c(n) represents the symbol sent by the backscatter device, and y BD (n) represents the backscatter device signal.

[0205] The backscatter device signal is decision-demodulated by the energy detector and the bit error rate is calculated.

[0206] Similarly, the beamformed signal is demodulated by the energy detector and the bit error rate is calculated. The bit error rate of the backscatter device signal and the beamformed signal are compared.

[0207] See also Fig.10 , Fig.10 It is a curve chart showing the variation of the simulated bit error rate performance with the signal-to-noise ratio in the simulation application scenario in the embodiment of the present application.

[0208] like Fig.10 As shown in the figure, the signal-to-noise ratio SNR is set to -5:20 (dB), the solid rectangular line represents the bit error rate of the backscattering device signal demodulated by the energy detector, and the dotted rectangular line represents the bit error rate of the beamformed signal demodulated by the energy detector. As shown in the figure, the signal beamformed by the method proposed in the embodiment of the present application improves the performance of 6.5 dB compared with the backscattering device signal directly. -2 The signal-to-noise ratio required for the bit error rate is reduced from about 16.4 dB to about 9.1 dB. It can be seen that the backscatter communication performance can be improved by beamforming the receiving end data using the method proposed in the embodiment of the present application.

[0209] The maximum likelihood detector is an optimal detector in digital communication, which is used to determine the most likely transmitted signal in a given received signal. Its basic idea is to estimate the value of the transmitted signal based on the received signal samples and select the hypothesis that maximizes the conditional probability of the received signal.

[0210] The demodulation of the backscatter device signal using the maximum likelihood detector is taken as an example for specific description.

[0211] pass:

[0212]

[0213] The decision formula of the maximum likelihood detector can be obtained by sorting out:

[0214]

[0215] Where c(n) represents the symbol sent by the backscatter device, σ 2 is the variance of Gaussian white noise, ρ(y|H1) represents the probability density function when bit 1 is sent, μ1+iω1 is the mean of the probability density function when bit 1 is sent, ρ(y|H0) represents the probability density function when bit 0 is sent, μ0+iω0 is the mean of the probability density function when bit 0 is sent, y real is the real part of the backscatter device signal, y imag is the imaginary part of the backscatter device signal.

[0216] The backscatter device signal is demodulated and the bit error rate is calculated using the decision formula of the maximum likelihood detector.

[0217] Similarly, the beamformed signal is demodulated and the bit error rate is calculated by the decision formula of the maximum likelihood detector. The bit error rate of the backscatter device signal and the beamformed signal are compared.

[0218] like Fig.10As shown in the figure, the solid triangle line represents the bit error rate of the backscatter device signal demodulated by the maximum likelihood detector, and the dotted triangle line represents the bit error rate of the beamformed signal demodulated by the maximum likelihood detector. As shown in the figure, the signal beamformed by the method proposed in the embodiment of the present application improves the performance of the backscatter device signal by 6.5 dB compared with the direct backscatter device signal. -2 The signal-to-noise ratio required for the bit error rate is reduced from about 15.4dB to about 8.7dB. It is further verified that the backscatter communication performance can be improved by beamforming the receiving end data through the method proposed in the embodiment of the present application. For the direct link, since the direct link signal demodulation process occurs before beamforming, beamforming does not affect the communication performance of the direct link.

[0219] To summarize, the receiving-end beamforming method of a backscatter communication perception integrated system proposed in an embodiment of the present application constructs an optimization proposition by acquiring the arrival angle of the direct link and the arrival angle of the reflected link, obtains the beamforming weight matrix through the optimization proposition, and performs beamforming on the receiving-end data according to the beamforming weight matrix to suppress the direct link signal, enhance the reflected link signal, and reduce the interference of the direct link to the reflected link communication, so as to improve the communication quality of the reflected link, that is, improve the backscatter communication quality.

[0220] 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 receiving end beamforming method for a backscatter communication and sensing integrated system, characterized in that: The method is applied in an indoor non-line-of-sight scenario, the backscatter communication perception integrated system includes a radio frequency source, a receiving end with a multi-antenna array, and a backscatter device, and the method includes: When only a direct link exists, obtaining a channel characteristic of the direct link and an arrival angle of the direct link; When the direct link and the reflected link exist simultaneously, acquiring an arrival angle of the reflected link according to the channel characteristics; An optimization proposition is constructed according to the direct link arrival angle and the reflected link arrival angle, a beamforming weight matrix is ​​calculated by the optimization proposition, and beamforming is performed on the receiving end data; The optimization proposition is: ||w H || 2 ≤1 Where w represents the beamforming weight matrix, α k represents the signal strength factor of the Kth reflection link, is the direct link arrival angle, is the arrival angle of the reflection link; Signal strength factor α k According to the eigenvalue size of the covariance matrix, since the steering vector is actually the signal subspace of the covariance matrix, the first K largest eigenvalues ​​of the covariance matrix are selected as signal strength factors for substitution; The solution target of this optimization problem is the beamforming weight matrix w. The solution logic of this optimization problem is: and ||w H || 2 Among all values ​​of the beamforming weight matrix w with ≤ 1, find the value such that The beamforming weight matrix w with the largest value; Among them, the beamforming weight matrix w needs to satisfy It indicates that the beamforming weight matrix w needs to suppress the signal in the incident direction of the direct link and force the signal in the incident direction of the direct link to zero, so as to minimize the interference of the direct link communication to the reflection link communication; The beamforming weight matrix w needs to satisfy ||w H || 2 ≤1, which means that the power of the beamforming weight matrix w needs to be limited to achieve power normalization and avoid The value of the term becomes infinitely large as the modulus of the beamforming weight matrix w increases; In the beamforming weight matrix w that satisfies both conditions, find The beamforming weight matrix w with the largest value is the ultimate goal of solving this optimization problem; among them, The maximum value of indicates that the signal in the incident direction of each reflection link is enhanced to maximize the received power of the overall reflection link signal; make Then the optimization proposition is a tag Find the direction perpendicular to a source The beamforming weight matrix of , so the closed-form expression of the beamforming weight matrix is ​​transformed into:

2. The method according to claim 1, characterized in that The obtaining of the channel characteristics of the direct link and the direct link arrival angle includes: Acquire a first received signal, wherein the first received signal is a signal received by the receiving end when only the direct link exists; Performing channel estimation on the direct link according to the first received signal to obtain channel characteristics of the direct link; The first received signal is calculated using an angle estimation algorithm to obtain the direct link arrival angle.

3. The method according to claim 1, characterized in that The acquiring the reflection link arrival angle according to the channel characteristics comprises: Acquire a second received signal, wherein the second received signal is a signal received by the receiving end when the direct link and the reflected link exist at the same time; Restore and eliminate the radio frequency source signal in the second received signal according to the channel characteristics to obtain a backscattering device signal; The backscattering device signal is calculated using an angle estimation algorithm to obtain the arrival angle of the reflection link.

4. The method according to claim 2, characterized in that: Assuming that there are L direct links in the environment, different direct links correspond to different incident signals, and the expression formula of the first received signal is: Among them, y CT (n) is the first received signal, P CT,l is the path loss of the lth direct link, θ l represents the azimuth of the lth incident signal, represents the pitch angle of the lth incident signal, is the steering vector of the lth incident signal, where θ l ∈[0,π], s(n) is the incident signal, d l is the propagation distance of the lth incident signal, λ CT is the wavelength of the incident signal, and u(n) is the Gaussian white noise signal.

5. The method according to claim 2, characterized in that: The channel estimation adopts LS channel estimation algorithm, and the channel characteristics are obtained by formula Calculated; in, is the channel characteristic estimation parameter, x is the pilot symbol of the signal transmitted by the RF source, and y CT is the first received signal.

6. The method according to claim 2 or 3, characterized in that: The angle estimation algorithm is a MUSIC algorithm, comprising: The input L-path multipath coherent signal is divided into a plurality of sub-arrays at equal intervals along the azimuth dimension and the elevation dimension, each of the sub-arrays is vectorized separately, and forward and backward smoothing is performed respectively; Obtaining a covariance matrix after bidirectional spatial smoothing according to the smoothing results of all the sub-surface arrays; Perform eigenvalue decomposition on the covariance matrix after bidirectional spatial smoothing and calculate the two-dimensional spatial spectrum; The incident azimuth angles and incident elevation angles of L coherent signals are acquired according to the two-dimensional spatial spectrum.

7. The method according to claim 3, characterized in that The method of restoring and eliminating the radio frequency source signal in the second received signal according to the channel characteristics to obtain a backscattering device signal includes: Performing equalization processing on the second received signal according to the channel characteristics, and demodulating the radio frequency source transmission signal; Restoring the RF source signal according to the channel characteristics and the RF source transmission signal; The radio frequency source signal is eliminated from the second received signal to obtain a backscatter device signal.

8. The method according to claim 7, characterized in that The demodulating the radio frequency source transmission signal comprises: in, is the estimated value of the signal transmitted by the RF source, y(n) is the second received signal, is the channel characteristic estimation parameter, and s(n) is the signal transmitted by the RF source.

9. The method according to claim 7, characterized in that: The restoring the radio frequency source signal comprises: in, is the estimated value of the RF source signal, is the channel characteristic estimation parameter, Estimated value of the signal transmitted by the RF source.

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