Chirp spread spectrum signal based backscatter communication sensing integration system and method

Abstract

The application discloses a backscattering communication and sensing integrated system and method based on a chirp spread spectrum signal, and relates to the technical field of wireless communication.The system comprises a chirp spread spectrum signal source, a backscattering device and a receiving end.The chirp spread spectrum signal source is used for sending a chirp spread spectrum modulated signal.The chirp spread spectrum modulated signal reaches the backscattering device through a reflection link, and the chirp spread spectrum modulated signal reaches the receiving end through a direct link.The backscattering device modulates the chirp spread spectrum modulated signal, and then transmits the modulated signal to the receiving end.The receiving end is used for realizing signal reception.The receiving end demodulates the signal of the direct link, estimates the sensing parameters of the reflection link, and realizes signal demodulation of the reflection link.The application has the beneficial effect of increasing the communication range and coverage area, and can realize sensing of the backscattering device at a long distance.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and more specifically, to an integrated system and method for backscatter communication and sensing based on chirped spread spectrum signals. Background Technology

[0002] Wireless communication and radar sensing have developed independently for a long time. However, they share many similarities in signal processing, equipment, and system architecture. In the future, 5.5G and 6G wireless communication systems will provide various high-precision sensing services, such as indoor positioning for robot navigation, WiFi sensing for smart homes, and radar sensing for autonomous vehicles. Due to the widespread deployment of millimeter-wave and massive MIMO technologies, communication signals in future wireless systems will tend to have high resolution in both the time and angular domains, making it possible to achieve high-precision sensing using communication signals. This has inspired recent research on the joint design of these two fields, namely Integrated Sensing and Communication (ISAC). Therefore, to improve spectral efficiency and reduce hardware costs, it is necessary to jointly design sensing and communication systems so that they can share the same frequency bands and hardware. These two functions are no longer considered as separate end goals, but rather designed together for mutual benefit, namely, communication-assisted sensing and sensing-assisted communication.

[0003] LoRa is one of the leading Low-Power Wide-Area Network (LPWAN) technologies designed to maintain long-distance connections between IoT devices. LoRa's low-bandwidth signal reduces interference from adjacent signals and provides high signal power. Therefore, its propagation range can reach 10 kilometers in rural areas and several kilometers in urban areas. LoRa employs chirped spread spectrum modulation, enabling signal reception at a very low signal-to-noise ratio (SNR), thus achieving coding gain.

[0004] Chirped spread spectrum communication involves linearly increasing or decreasing the carrier frequency of a signal within one symbol period, resulting in a signal spectrum over a wide frequency range. Its low power consumption and long-range capabilities make chirped spread spectrum signals ideal for rapid deployment in particularly remote, extreme, or even hazardous environments. However, current technology does not yet offer a way to apply chirped spread spectrum signals to integrated long-range backscatter communication scenarios for long-distance sensing of backscattering devices. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides an integrated system and method for backscatter communication and sensing based on chirped spread spectrum signals, which increases the communication range and coverage area, and enables long-distance sensing of backscatter devices.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for integrated backscatter communication and sensing based on chirped spread spectrum signals, the improvement of which is that the method includes the following steps:

[0007] A chirped spread spectrum signal source transmits a chirped spread spectrum modulated signal;

[0008] The chirped spread spectrum modulation signal reaches the backscattering device via a reflection link. The backscattering device modulates the chirped spread spectrum modulation signal and then transmits the modulated signal to the receiving end. The chirped spread spectrum modulation signal reaches the receiving end via a direct link. The signal received by the receiving end includes the signal from the direct link, the signal from the reflection link, and noise.

[0009] The receiving end demodulates the signal of the direct link and estimates the sensing parameters of the reflected link to achieve signal demodulation of the reflected link.

[0010] In the above method, the chirped spread spectrum modulation signal uses CSS linear spread spectrum modulation.

[0011] In the above method, the frame structure of the chirped spread spectrum modulation signal includes a preamble and a payload;

[0012] The preamble consists of a first part and a second part, wherein the first part is a fixed N all-"1" signal and the second part is a continuous p upchirp symbol;

[0013] The payload consists of several chirp symbols with random initial frequencies that increase linearly with time.

[0014] In the above method, the baseband signal expression is:

[0015]

[0016] Where f0 is the starting frequency of the chirp symbol, and k is the slope of the chirp sign, and BW is the signal bandwidth, T is the period of a single chirp signal, and SF is the spreading factor;

[0017] The expression for the frequency band signal is:

[0018]

[0019] Where f c The center frequency of the carrier wave.

[0020] In the above method, the formula for the signal emitted by the backscattering device is:

[0021]

[0022] Where B is ±1.

[0023] In the above method, the steering vector of the receiving antenna at the receiving end is set as follows:

[0024]

[0025] Where M is the number of receiving antenna elements and the element spacing is... λ is the wavelength corresponding to the center frequency of the antenna;

[0026] The signal received by the receiving end is:

[0027] y RF (t)=r direct +r BD +n(t);

[0028] r direct For signals in a direct link, the expression is:

[0029] r direct =a⊙h D ·s RF (t-τ D ), τ D This refers to the propagation time of the direct link;

[0030] r BD For the signal of the reflected link, the expression is:

[0031] r BD =a⊙h BD ·x BD (t-τ2)·s RF (t-τ1-τ2);

[0032] Where ⊙ represents matrix dot product, τ1 and τ2 are the propagation times from the signal source to the backscattering device and from the backscattering device to the receiver, respectively; n(t) is Gaussian white noise with a mean of 0 and a variance of 1.

[0033] The receiver experiences a carrier frequency offset (CFO) when receiving baseband signals.

[0034]

[0035] In the above method, the receiving end uses a direct link communication demodulation algorithm to demodulate the signal of the direct link, and when demodulating the signal of the direct link, the signal of the reflected link is regarded as an interference item.

[0036] The direct link communication demodulation algorithm includes the following steps:

[0037] S101. Frame synchronization of signals in direct links: Utilizing the characteristics of the preamble of the chirped spread spectrum modulation signal, each chirp symbol is multiplied with the downchirp signal to eliminate the influence of the sweep frequency signal, and then the result is subjected to FFT transformation to obtain the starting frequency of each chirp symbol.

[0038] By detecting the frequency value corresponding to the peak value of the signal after FFT, if the starting frequency corresponding to p consecutive FFT peak values ​​is the same, the start of the preamble is located.

[0039] S102. Carrier frequency offset estimation: Extract the received signal corresponding to the all-"1" preamble, and combine the signal and noise of the reflected link into n'(t). The baseband signal at the receiving end is simplified as follows:

[0040]

[0041] at this time It is a function of time t;

[0042] The formula for carrier frequency offset estimation is as follows:

[0043]

[0044] Among them, f s R is the sampling frequency, N is the number of sampling points, and R is the sampling frequency. sym Symbol rate;

[0045] Using the estimated carrier frequency offset CFO cancellation is performed on the received direct link signal:

[0046]

[0047] S103. Channel estimation and maximum ratio combining for direct links: Maximum ratio combining is used to weight and sum multiple signals to maximize the signal-to-noise ratio (SNR) of the received signal. The weighting coefficient is w. * =h;

[0048] S104. Demodulation of the direct link signal: Multiply the direct link signal with the downchirp signal, and then perform FFT transformation. The index corresponding to the FFT peak is the modulated data.

[0049] In the above method, during the estimation of the sensing parameters of the reflection link, the signal of the reflection link is obtained by filtering the received signal and down-converting it to frequency 0. At this time, the signal received by the k-th antenna at the receiving end is:

[0050]

[0051] The estimation of sensing parameters for the reflection link includes the following steps:

[0052] S201, frame synchronization of the reflected link signal and frame synchronization of the BD signal; wherein frame synchronization of the reflected link signal includes:

[0053] The signal from the reflected link is multiplied with the downchirp signal to eliminate the influence of the frequency sweep signal, and an FFT transformation is performed to calculate the start frequency of each chirp symbol. If the start frequencies of p consecutive chirp symbols are the same, the start of the preamble can be located.

[0054] S202. Sensing parameter estimation: The MUSIC algorithm based on subspace and the Orthogonal Matching Pursuit (OMP) algorithm based on compressed sensing are used to estimate the angle θ and distance L, where L = L1 + L2, L1 is the straight-line distance between the chirped spread spectrum signal source and the backscattering device, and L2 is the straight-line distance between the backscattering device and the receiver. The estimated angle and distance are denoted as... and

[0055] S203. Coordinate estimation of the backscattering device: The distance L2 between the backscattering device and the receiver is calculated using trigonometric relationships, and then determined by angles. Find the coordinates of the backscattering device:

[0056]

[0057] In the above method, the signal demodulation of the reflection link includes:

[0058] S301, Sensing-assisted communication, corrects frequency offset, calculates the TOA steering vector at the receiver, and applies it to the signal of the reflection link to eliminate the influence of frequency offset on the signal demodulation of the reflection link.

[0059] S302. Channel estimation of the reflection link is performed by estimating the channel of the reflection link using the preamble of the chirped spread spectrum signal and the preamble of the backscattering device.

[0060] S303, Maximum ratio combining of the reflection link: The receiving end uses multiple antennas to receive signals, and it is necessary to combine multiple signals into one signal for subsequent signal demodulation. Maximum ratio combining is used to maximize the received signal-to-noise ratio, and the weighting coefficient is w2.

[0061] S304, signal demodulation of the reflection link, making s BD =s(t-τ1-τ2), B=B(t-τ2), and the combined signal is:

[0062] y BD_MRC (t)=α·s BD(t)·B+n(t);

[0063] Demodulating BD signals using ML detection

[0064] make

[0065] By judging y' BD The sign of the real part is used to determine whether the backscattering device is "0" or "1";

[0066]

[0067] The present invention also provides an integrated communication and sensing system based on chirped spread spectrum signals, the improvement of which is that it includes a chirped spread spectrum signal source, a backscattering device and a receiver.

[0068] The chirped spread spectrum signal source is used to transmit a chirped spread spectrum modulation signal. The chirped spread spectrum modulation signal reaches the backscattering device via a reflection link, and the chirped spread spectrum modulation signal reaches the receiving end via a direct link.

[0069] The backscattering device modulates the chirped spread spectrum modulation signal and then transmits the modulated signal to the receiving end.

[0070] The receiving end is used to receive signals, including signals from the direct link, signals from the reflected link, and noise. The receiving end demodulates the signals from the direct link and estimates the sensing parameters of the reflected link to demodulate the signals from the reflected link.

[0071] The beneficial effects of this invention are as follows: This invention provides an integrated communication and sensing system and method based on chirped spread spectrum signals. Utilizing the advantages of chirped spread spectrum signals—low power consumption and long distance—it uses them as the source radio frequency signal, greatly increasing the communication range and coverage area. Through backscattering technology, it achieves signal detection and sensing location of backscattering devices over long distances. Attached Figure Description

[0072] Figure 1 This is a schematic diagram of the structure of an integrated communication and sensing system based on chirped spread spectrum signals according to the present invention.

[0073] Figure 2 This is a flowchart illustrating a method for integrating backscatter communication and sensing based on chirped spread spectrum signals according to the present invention.

[0074] Figure 3 This is a schematic diagram of the frame structure of the chirped spread spectrum modulation signal in this invention.

[0075] Figure 4 This is a schematic diagram of the frame structure of the backscattering device in this invention.

[0076] Figure 5 This is a schematic diagram illustrating the steps of the direct link communication demodulation algorithm in this invention.

[0077] Figure 6 This is a schematic diagram illustrating the steps of estimating the sensing parameters of the reflection link in this invention.

[0078] Figure 7 This is a schematic diagram showing the relative positions of the system according to the present invention.

[0079] Figure 8 This is a schematic diagram of the signal demodulation process of the reflection link in this invention.

[0080] Figure 9 This is a schematic diagram of the bit error rate curves for demodulating the reflected link signal under different signal-to-noise ratio conditions.

[0081] Figure 10 This diagram illustrates the coordinate estimation error of a backscattering device using the OMP algorithm under different signal-to-noise ratio conditions. Detailed Implementation

[0082] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0083] The following will clearly and completely describe the concept, specific structure, and technical effects of the present invention in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Furthermore, all connections / linkages involved in the patent do not simply refer to direct contact between components, but rather to the ability to form a better connection structure by adding or reducing connecting accessories according to specific implementation conditions. The various technical features in this invention can be combined interactively without contradicting each other.

[0084] Reference Figure 1 As shown, this invention discloses an integrated communication and sensing system based on chirped spread spectrum signals and backscattering. The system includes a chirped spread spectrum signal source, a backscattering device, and a receiver. It should be noted that the receiver in this embodiment is... Figure 1 The backscatter receiver shown is illustrated; for ease of description, the term "receiver" will be used consistently in the following text.

[0085] In this embodiment, the chirped spread spectrum signal source is used to transmit the chirped spread spectrum modulation signal. The transmitted chirped spread spectrum modulation signal reaches the receiving end via two links, one of which is a direct link to the receiving end, i.e. Figure 1The direct link h in the middle; another link reaches the backscattering device via a reflection link, i.e. Figure 1 The backscattering device modulates the chirped spread spectrum signal and then transmits the modulated signal to the receiver. The receiver is used to receive the signal, and the received signal includes the signal from the direct link, the signal from the reflected link, and noise. The receiver demodulates the signal from the direct link and estimates the sensing parameters of the reflected link to achieve demodulation of the reflected link signal.

[0086] Furthermore, in this embodiment, the chirped spread spectrum signal source uses a single antenna to transmit the chirped spread spectrum signal; the backscattering device is a single antenna that backscatters the chirped spread spectrum signal; the receiving end simultaneously receives two signals from the chirped spread spectrum signal source and the backscattering device, demodulates and cancels the radio frequency source signal, demodulates the backscattered signal, and senses the angle and distance of the backscattering device, thereby estimating the coordinates of the backscattering device.

[0087] Reference Figure 2 The diagram shown is a flowchart illustrating a method for integrated backscatter communication and sensing based on chirped spread spectrum signals provided by the present invention; in this embodiment, the method includes steps S10-S40:

[0088] S10. Transmission of chirped spread spectrum modulation signal: The chirped spread spectrum signal source transmits the chirped spread spectrum modulation signal;

[0089] Regarding the chirped spread spectrum signal source, in this embodiment, the chirped spread spectrum signal source transmits a chirped spread spectrum modulation signal, which uses CSS (Chirp Spread Spectrum) linear spread spectrum modulation. CSS modulation refers to carrying different information through different starting frequencies of chirp symbols. Specifically, to clarify the relationship between each symbol and the number of bits transmitted in wireless transmission, the chirped spread spectrum modulation signal defines a spreading factor SF, representing the number of information bits contained in each symbol, that is, spreading one symbol onto one chip for transmission. Different starting frequencies correspond to different information within a range. When demodulating the chirp signal at the receiving end, it is only necessary to identify the starting frequency of different chirp symbols to demodulate the information carried by that symbol. The basic communication unit of the signal is a linear chirp symbol, that is, a signal whose frequency increases (or decreases) linearly with time. A chirp symbol whose frequency increases linearly with time is called an upchirp, and a chirp symbol whose frequency decreases linearly with time is called a downchirp. The frequency sweeps linearly across the entire bandwidth, thus exhibiting extremely strong anti-interference capabilities and resistance to multipath and Doppler effects.

[0090] The frame structure of the chirped spread spectrum modulated signal transmitted by the chirped spread spectrum signal source is as follows: Figure 3As shown, it mainly includes a preamble and a payload. The preamble consists of two parts: the first part is a fixed N all-"1" signal used to eliminate carrier frequency offset at the receiving end; the second part is a continuous p upchirp symbol. The payload consists of several chirp symbols with random starting frequencies that increase linearly with time. Specifically, when the data portion does not modulate information and all starting frequencies are 0, the original chirped spread spectrum modulation signal degenerates into a chirped spread spectrum excitation source signal without any information. Unless otherwise specified, the following descriptions of this invention will use a chirped spread spectrum modulation signal carrying information as an example for signal model explanation.

[0091] In this embodiment, the baseband signal expression is:

[0092]

[0093] Where f0 is the starting frequency of the chirp symbol, and k is the slope of the chirp sign, and BW is the signal bandwidth, T is the period of a single chirp signal, and SF is the spreading factor;

[0094] The expression for the frequency band signal is:

[0095]

[0096] Where f c The center frequency of the carrier wave.

[0097] S20. Reflection of the chirped spread spectrum modulation signal: The chirped spread spectrum modulation signal reaches the backscattering device via the reflection link. The backscattering device modulates the chirped spread spectrum modulation signal and then transmits the modulated signal to the receiving end.

[0098] In this embodiment, the backscattering device employs BPSK modulation, controlling the phase change of the incident signal by inputting different binary data: sending "0" reverses the phase of the incident signal by 180°, while sending "1" does not change the phase of the incident signal. The frame structure of the backscattering device is as follows: Figure 4 As shown, the signal includes a preamble and data. The preamble is implemented using a Barker code sequence. The data portion begins with M consecutive "1"s, used for sensing parameter estimation at the receiver. The second portion consists of random "0 / 1" data. Because the Barker code sequence has good autocorrelation properties, accurate synchronization of the backscattering device can be achieved at the receiver. After bipolar coding mapping, bit "0" corresponds to "-1", and bit "1" corresponds to "1". The chirped spread spectrum modulated signal reaches the receiver after backscattering. The formula for the signal transmitted by the backscattering device is:

[0099]

[0100] Where B is ±1.

[0101] S30. Reception of chirped spread spectrum modulation signal: The chirped spread spectrum modulation signal arrives at the receiving end via a direct link. The signal received at the receiving end includes the signal from the direct link, the signal from the reflected link, and noise.

[0102] In this embodiment, the receiver employs a multi-antenna configuration, with the antennas arranged in a uniform linear array. It receives signals from the direct link of the chirped spread spectrum source and signals from the reflected link of the backscattering device. Because multiple antennas are used, the received backscattered signal contains the angle information of the backscattering device.

[0103] Furthermore, in this embodiment, the steering vector of the receiving antenna at the receiving end is set as follows:

[0104]

[0105] Where M is the number of receiving antenna elements and the element spacing is...

[0106] The signal received by the receiving end is:

[0107] y RF (t)=r direct +r BD +n(t);

[0108] r direct For signals in a direct link, the expression is:

[0109] r direct =a⊙h D ·s RF (t-τ D );

[0110] r BD For the signal of the reflected link, the expression is:

[0111] r BD =a⊙h G ·y BD (t-τ2)

[0112] =a⊙h BD ·x BD (t-τ2)·s RF (t-τ1-τ2)·x BD (t-τ2);

[0113] Where ⊙ represents matrix dot product, n(t) is Gaussian white noise with a mean of 0 and a variance of 1.

[0114] Because the receiver and the chirped spread spectrum signal source are separate, independent of each other, and lack clock synchronization, there is a certain deviation in the carrier frequency, resulting in a carrier frequency offset (CFO) in the received baseband signal, which can be expressed by the following formula:

[0115] The receiver experiences a carrier frequency offset (CFO) when receiving baseband signals.

[0116]

[0117] S40. Demodulation of received signal: The receiving end demodulates the signal of the direct link and estimates the sensing parameters of the reflected link to achieve demodulation of the signal of the reflected link.

[0118] Regarding the demodulation of the received signal, this embodiment designs a direct link communication demodulation algorithm to demodulate the signal from the direct link and to estimate the location information of the backscattering device through the backscattered signal. Specifically, the receiving end uses the direct link communication demodulation algorithm to demodulate the signal from the direct link, and when demodulating the signal from the direct link, the signal from the reflected link is treated as interference. In this embodiment, the direct link communication demodulation algorithm is combined with... Figure 5 As shown, it includes the following steps:

[0119] S101. Frame synchronization of the direct link signal: Since the preamble of the chirped spread spectrum modulation signal is known to contain p consecutive upchirp symbols with a starting frequency of 0, and the data part of the chirped spread spectrum modulation signal of the chirped spread spectrum signal source is randomly modulated information, it is almost impossible for p consecutive bits of the same data to appear. Therefore, the corresponding starting frequencies will not be the same. This invention determines the start of the direct link signal frame by detecting when p consecutive upchirp symbols appear in the received signal.

[0120] Therefore, in this embodiment, the characteristics of the preamble of the chirp spread spectrum modulation signal are utilized. Each chirp symbol is multiplied with the downchirp signal to eliminate the influence of the sweep frequency signal. Then, the result is subjected to FFT transformation to obtain the starting frequency of each chirp symbol. By detecting the frequency value corresponding to the peak value of the signal after FFT, if the starting frequency corresponding to p consecutive FFT peak values ​​is the same, the start of the preamble is located.

[0121] S102. Carrier Frequency Offset Estimation: Since the transmitted signal preamble contains all "1"s, in order to eliminate CFO, it is necessary to truncate the received signal corresponding to the all "1"s preamble. Furthermore, since the reflected signal is much weaker than the direct link signal, it is combined with noise to form n'(t). The simplified baseband signal at the receiving end is as follows:

[0122]

[0123] at this time It is a function of time t;

[0124] The formula for carrier frequency offset estimation is as follows:

[0125]

[0126] Among them, f s R is the sampling frequency, N is the number of sampling points, and R is the sampling frequency. sym Symbol rate;

[0127] Using the estimated carrier frequency offset CFO cancellation is performed on the received direct link signal:

[0128]

[0129] S103, Channel estimation and maximum ratio combining for direct links;

[0130] In this embodiment, channel estimation of the direct link is performed using the known preamble. Since the receiver uses multiple antennas to receive data simultaneously, a combining method is needed to merge the multiple signals into a single signal before demodulation. This invention employs maximum ratio combining to perform a weighted summation of the multiple signals, maximizing the signal-to-noise ratio of the received signal. The weighting coefficient at this point is w. * =h;

[0131] S104, Direct Link Signal Demodulation;

[0132] In this embodiment, the modulation information of the chirped spread spectrum modulation signal corresponds one-to-one with the start frequency of the chirp symbol. Therefore, the core idea is to calculate the start frequency of each chirp symbol in the received signal payload and map it to 0 to 2. SF -1. First, it is necessary to eliminate the influence of the sweep signal and obtain the starting frequency of each chirp symbol. Specifically, the received signal is multiplied by the downchirp signal, and then an FFT is performed. The index corresponding to the peak value is the modulated data.

[0133] Specifically, when the data portion of the chirped spread spectrum modulation signal does not carry any information, the chirped spread spectrum modulation signal degenerates into a simple chirped spread spectrum excitation signal. In this case, demodulation of the direct link signal is not required; only frame synchronization of the direct link signal and determination of the signal frame header are needed.

[0134] Additionally, step S40 includes a step of estimating the sensing parameters of the reflection link, combined with... Figure 6As shown, steps S201-S203 are included. In this embodiment, during the estimation of the sensing parameters of the reflection link, the signal of the reflection link is obtained by filtering the received signal and down-converting it to frequency 0. At this time, the signal received by the k-th antenna at the receiving end is:

[0135]

[0136] Furthermore, the estimation of sensing parameters for the reflection link includes the following steps:

[0137] S201, frame synchronization of the reflected link signal and frame synchronization of the BD signal;

[0138] The frame synchronization of the reflected link signal includes: the reflected link signal is modulated with backscatter device data on the chirped spread spectrum modulation signal, thereby shifting the source chirped spread spectrum modulation signal by 1MHz. After filtering and downconversion, the frame structure of the source signal is not destroyed. Therefore, similar to the frame synchronization of the direct link signal, the reflected link signal is multiplied with the downchirp signal to eliminate the influence of the sweep frequency signal and to prepare for the estimation of subsequent sensing parameters. Then, an FFT transformation is performed to calculate the starting frequency of each chirp symbol. If 10 consecutive chirp symbols have the same starting frequency, the start of the preamble can be located.

[0139] In addition, step S201 also includes the step of BD signal frame synchronization:

[0140] Since the BD signal preamble is a Barker code sequence, which has good autocorrelation characteristics, the formula in step S303 below only eliminates the influence of the sweep frequency signal, but the influence of the lower frequency BD data signal B(t) still exists. Therefore, it is necessary to extract the sequence of N "1" parts corresponding to the BD data frame. The BD signal frame is synchronized by correlating the above signal with the known Barker code sequence and finding the maximum peak value to locate the BD frame header; the signal corresponding to the M "1" parts of the data part, i.e., B(t) = 1, is extracted and used for sensing parameter estimation.

[0141] S202. Sensing parameter estimation: The MUSIC (Multiple Signal Classification) algorithm based on subspace and the Orthogonal Matching Pursuit (OMP) algorithm based on compressed sensing are used to estimate the angle θ and distance L, where L = L1 + L2, L1 is the straight-line distance between the chirped spread spectrum signal source and the backscattering device, and L2 is the straight-line distance between the backscattering device and the receiver. The estimated angle and distance are denoted as... and

[0142] The relevant content regarding the subspace-based MUSIC (Multiple Signal Classification) algorithm and the compressed sensing-based Orthogonal Matching Pursuit (OMP) algorithm is as follows:

[0143] The MUSIC algorithm utilizes the fundamental principle that the received signal steering vector and the eigenvectors of the noise subspace are orthogonal to perform angle-distance estimation through spectral peak search. The specific algorithm flow is as follows:

[0144] 1. First, calculate the signal covariance matrix R. XX ;

[0145] 2. Perform singular value decomposition on the covariance matrix, arrange the singular values ​​in descending order, and extract the eigenvectors corresponding to the smaller eigenvalues;

[0146] 3. Construct a steering vector orthogonal to the noise feature vector, and use it as the denominator to construct a two-dimensional spectral peak search expression.

[0147] Orthogonal matching pursuit (ORP) is a powerful tool for signal processing and sparse signal reconstruction. It approximates a target signal by selecting the atom most relevant to the actual received signal from a complete dictionary matrix, and has wide applications in many fields, including image processing, compressed sensing, and machine learning.

[0148] Overcomplete dictionary matrix: The number of atoms in the dictionary exceeds the dimension of the signal. In the Orthogonal Matching Pursuit (OMP) algorithm, overcomplete dictionaries are typically used to process high-dimensional signals, where the dimension of the signal is smaller than the number of atoms in the dictionary. In this case, the signal cannot be linearly represented by a single atom in the dictionary, and it is necessary to approximate the signal by combining multiple atoms. In this invention, the dictionary matrix is ​​a matrix composed of angles and time-delay steering vectors.

[0149] Sparse representation of signals: Sparse representation means that although a large number of atoms are available, only a small fraction is needed to accurately represent a specific signal. In this invention, since there is only one backscattering device, there is only one incident angle and time delay relative to the antenna array at the receiving end (assuming that the signals received by the antennas at the receiving end are all plane waves, i.e., the incident angles are the same between different antennas), corresponding to only one column of steering vectors in the dictionary matrix. The specific algorithm flow is as follows:

[0150] 1. Construct the dictionary matrix A corresponding to the angular guidance vector;

[0151] 2. Initialize the residual as the reflected link signal r0 = y, and initialize the target guidance vector set Λ to be empty;

[0152] 3. Take the inner product of the dictionary matrix and the current residual |<α j ,r k-1 >|, select the atom α with the largest inner product. j Add to set Λ;

[0153] 4. Solving the least squares problem Find the sparse representation of x k ;

[0154] 5. Update the residuals, r k =y-Ax k .

[0155] The time delay estimation algorithm is the same as above, except that the dictionary matrix is ​​replaced with a matrix composed of time delay steering vectors, and the received signal is transposed.

[0156] S203, Coordinate estimation of the backscattering device;

[0157] Combination Figure 7 The diagram shown is a schematic representation of the relative positions of the system. L1 is the straight-line distance between the chirped spread spectrum signal source and the backscattering device, and L2 is the straight-line distance between the backscattering device and the receiver. The distance L2 between the backscattering device and the receiver is calculated using trigonometric relationships, and then determined by angles. Find the coordinates of the backscattering device:

[0158]

[0159]

[0160] Furthermore, combining Figure 8 As shown, the signal demodulation of the reflection link in step S40 includes steps S301-S304, the contents of which are as follows:

[0161] S301, Sensing-Assisted Communication: The frequency offset caused by propagation delay directly leads to a phase rotation in the received backscattered signal, significantly interfering with the BPSK signal and potentially causing a 180-degree phase rotation, resulting in demodulation errors. Therefore, frequency offset correction is necessary. Based on the delay information estimated in step 2, the receiver's TOA steering vector can be directly calculated. Applying this vector to the received backscattered signal eliminates the impact of frequency offset on backscattered signal demodulation.

[0162] S302. Channel estimation of the reflection link is performed by estimating the channel of the reflection link using the preamble of the chirped spread spectrum signal and the preamble of the backscattering device.

[0163] S303, Maximum ratio combining of the reflection link: The receiving end uses multiple antennas to receive signals, and it is necessary to combine multiple signals into one signal for subsequent signal demodulation. Maximum ratio combining is used to maximize the received signal-to-noise ratio, where w2 is the weighting coefficient.

[0164] S304, signal demodulation of the reflection link, making s BD =s(t-τ1-τ2), B=B(t-τ2), to obtain the combined signal:

[0165] y BD_MRC (t)=α·s BD (t)·B+n(t);

[0166] Demodulating BD signals using ML detection

[0167] make

[0168] By judging y' BD The sign of the real part is used to determine whether the backscattering device is "0" or "1";

[0169]

[0170] Through the above steps, this invention provides an integrated system and method for backscatter communication and sensing based on chirped spread spectrum signals. A chirped spread spectrum signal source transmits a chirped spread spectrum signal, and the receiving end can recover backscattering device information and locate it using the reflected link signal. When the chirped spread spectrum signal source transmits a modulated signal carrying information, the receiving end can simultaneously recover the chirped spread spectrum modulated signal. The use of chirped spread spectrum modulated signals significantly improves the system's coverage. This invention designs the frame structure of the chirped spread spectrum signal source and the backscattering device signal, performs carrier frequency offset estimation and interference cancellation on the received signal to reduce the impact of frequency offset on tag positioning, and designs frame synchronization algorithms and signal detection algorithms for the receiving end source signal and tag signal, thereby improving the system's bit error rate and positioning accuracy. This invention designs an OMP algorithm to sense the tag's angle and distance, and simultaneously uses the sensing results to assist in the demodulation of the tag's communication signal, achieving decimeter-level accuracy at a distance of 100 meters.

[0171] This invention also includes a simulation to verify the effect. The parameters are set as follows: system carrier frequency of 433MHz, bandwidth of 500kHz, spreading factor of SF=7, distance between transmitter and backscattering device of 40m, distance from backscattering device to receiver of 70m, total length of reflection link of 110m, and relative angle between backscattering device and receiver of 30 degrees. The number of receiver antennas is 4 and 16, and the number of experiments is set to 5000.

[0172] Figure 9The diagram shows the bit error rate (BER) curves for demodulating the reflected link signal under different signal-to-noise ratio (SNR) conditions. The horizontal axis represents the received SNR, and the vertical axis represents the BER. The relative angle between the backscattering device and the receiver is 30 degrees. The black solid line represents a receiver with 4 antennas, and the red solid line represents a receiver with 16 antennas. The SNR is set to vary within the range of -10:5:20 (dB). It can be observed that as the SNR increases, the BER decreases significantly, and the BER of the receiver with 16 antennas is significantly lower than that with 4 antennas. At an SNR of 10 dB, the BER of the receiver with 4 antennas reaches 10 dB. -3 Order of magnitude.

[0173] Figure 10 This paper demonstrates the coordinate estimation error of a backscattering device using the OMP algorithm under different signal-to-noise ratio (SNR) conditions. The horizontal axis represents the received SNR, and the vertical axis represents the RMSE of the coordinate estimation. The relative angle between the backscattering device and the receiver is 30 degrees. The black solid line represents a receiver with 4 antennas, and the red solid line represents a receiver with 16 antennas. The SNR is set to vary within the range of -10:5:20 (dB). It can be observed that the coordinate estimation error is stable at 0.7m when there are 4 antennas, and the angle estimation error is stable at 0.2m when there are 16 antennas.

[0174] This invention provides a long-distance, low-cost, and low-power chirped spread spectrum modulation backscattering inductive integrated system structure. By designing the frame structure of the radio frequency source signal and the backscattering device signal, the receiver performs carrier frequency offset estimation, frame synchronization, and signal detection to recover the radio frequency source signal and the backscattering signal. At the same time, the backscattering link signal is used to estimate the angle and distance of the device, and then the coordinates of the backscattering device are calculated by triangulation.

[0175] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A method for integrated backscatter communication and sensing based on chirped spread spectrum signals, characterized in that, The method includes the following steps: A chirped spread spectrum signal source transmits a chirped spread spectrum modulated signal; The chirped spread spectrum modulation signal reaches the backscattering device via a reflection link. The backscattering device modulates the chirped spread spectrum modulation signal and then transmits the modulated signal to the receiving end. The chirped spread spectrum modulation signal reaches the receiving end via a direct link. The signal received by the receiving end includes the signal from the direct link, the signal from the reflection link, and noise. The receiving end demodulates the signal of the direct link and estimates the sensing parameters of the reflected link to achieve signal demodulation of the reflected link. The frame structure of the chirped spread spectrum modulation signal includes a preamble and a payload; the preamble consists of a first part and a second part, wherein the first part is a fixed N all-"1" signal and the second part is a continuous p upchirp symbol; the payload consists of a number of chirp symbols with random start frequencies and whose frequencies increase linearly with time. The baseband signal expression is: Where f0 is the starting frequency of the chirp symbol, and k is the slope of the chirp sign, and BW is the signal bandwidth, T is the period of a single chirp signal, and SF is the spreading factor; The expression for the frequency band signal is: Where f c The center frequency of the carrier wave; The formula for the signal emitted by the backscattering device is: Where B is ±1; The steering vector of the receiving antenna at the receiving end is set as follows: Where M is the number of receiving antenna elements and the element spacing is... λ is the wavelength corresponding to the center frequency of the antenna; The signal received by the receiving end is: y RF (t)=r direct +r BD +n(t); r direct For signals in a direct link, the expression is: r direct =a⊙h D ·s RF (t-τ D ), τ D This refers to the propagation time of the direct link; r BD For the signal of the reflected link, the expression is: r BD =a⊙h BD ·x BD (t-τ2)·s RF (t-τ1-τ2); Where ⊙ represents matrix dot product, These are the propagation times from the signal source to the backscattering device and from the backscattering device to the receiver, respectively. n(t) is Gaussian white noise with a mean of 0 and a variance of 1; The receiver experiences a carrier frequency offset (CFO) when receiving baseband signals. The receiving end uses a direct link communication demodulation algorithm to demodulate the signal of the direct link, and when demodulating the signal of the direct link, the signal of the reflected link is regarded as an interference item. The direct link communication demodulation algorithm includes the following steps: S101. Frame synchronization of signals in direct links: Utilizing the characteristics of the preamble of the chirped spread spectrum modulation signal, each chirp symbol is multiplied with the downchirp signal to eliminate the influence of the sweep frequency signal, and then the result is subjected to FFT transformation to obtain the starting frequency of each chirp symbol. By detecting the frequency value corresponding to the peak value of the signal after FFT, if the starting frequency corresponding to p consecutive FFT peak values ​​is the same, the start of the preamble is located. S102. Carrier frequency offset estimation: Extract the received signal corresponding to the all-"1" preamble, and combine the signal and noise of the reflected link into n'(t). The baseband signal at the receiving end is simplified as follows: at this time It is a function of time t; The formula for carrier frequency offset estimation is as follows: Among them, f s R is the sampling frequency, N is the number of sampling points, and R is the sampling frequency. sym Symbol rate; Using the estimated carrier frequency offset CFO cancellation is performed on the received direct link signal: S103. Channel estimation and maximum ratio combining for direct links: Maximum ratio combining is used to weight and sum multiple signals to maximize the signal-to-noise ratio (SNR) of the received signal. The weighting coefficient is w. * =h; S104. Demodulation of the direct link signal: Multiply the direct link signal with the downchirp signal, and then perform FFT transformation. The index corresponding to the FFT peak is the modulated data. In the estimation of the sensing parameters of the reflection link, the signal of the reflection link is obtained by filtering the received signal and down-converting it to frequency 0. At this time, the signal received by the k-th antenna at the receiving end is: The estimation of sensing parameters for the reflection link includes the following steps: S201, frame synchronization of the reflected link signal and frame synchronization of the BD signal; wherein frame synchronization of the reflected link signal includes: The signal from the reflected link is multiplied with the downchirp signal to eliminate the influence of the frequency sweep signal, and an FFT transformation is performed to calculate the start frequency of each chirp symbol. If the start frequencies of p consecutive chirp symbols are the same, the start of the preamble can be located. S202. Sensing parameter estimation: The MUSIC algorithm based on subspace and the Orthogonal Matching Pursuit (OMP) algorithm based on compressed sensing are used to estimate the angle θ and distance L, where L = L1 + L2, L1 is the straight-line distance between the chirped spread spectrum signal source and the backscattering device, and L2 is the straight-line distance between the backscattering device and the receiver. The estimated angle and distance are denoted as... and S203. Coordinate estimation of the backscattering device: The distance L2 between the backscattering device and the receiver is calculated using trigonometric relationships, and then determined by angles. Find the coordinates of the backscattering device: The signal demodulation of the reflection link includes: S301, Sensing-assisted communication, corrects frequency offset, calculates the TOA steering vector at the receiver, and applies it to the signal of the reflection link to eliminate the influence of frequency offset on the signal demodulation of the reflection link. S302. Channel estimation of the reflection link is performed by estimating the channel of the reflection link using the preamble of the chirped spread spectrum signal and the preamble of the backscattering device. S303, Maximum ratio combining of the reflection link: The receiving end uses multiple antennas to receive signals, and it is necessary to combine multiple signals into one signal for subsequent signal demodulation. Maximum ratio combining is used to maximize the received signal-to-noise ratio, and the weighting coefficient is w2. S304, signal demodulation of the reflection link, making s BD =s(t-τ1-τ2), B=B(t-τ2), and the combined signal is: y BD_MRC (t)=α·s BD (t)·B+n(t); Demodulating BD signals using ML detection make By judging y' BD The sign of the real part is used to determine whether the backscattering device is "0" or "1"; 2. The method for integrated backscatter communication and sensing based on chirped spread spectrum signals according to claim 1, characterized in that, The chirped spread spectrum modulation signal uses CSS linear spread spectrum modulation.

3. A backscatter communication and sensing integrated system based on chirped spread spectrum signals, characterized in that, The system is used to implement the integrated backscatter communication and sensing method based on chirped spread spectrum signals as described in claim 1 or 2, including a chirped spread spectrum signal source, a backscattering device, and a receiver. The chirped spread spectrum signal source is used to transmit a chirped spread spectrum modulation signal. The chirped spread spectrum modulation signal reaches the backscattering device via a reflection link, and the chirped spread spectrum modulation signal reaches the receiving end via a direct link. The backscattering device modulates the chirped spread spectrum modulation signal and then transmits the modulated signal to the receiving end. The receiving end is used to receive signals, including signals from the direct link, signals from the reflected link, and noise. The receiving end demodulates the signals from the direct link and estimates the sensing parameters of the reflected link to demodulate the signals from the reflected link.

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