A general backscattering system and method based on ambient OFDM WiFi signals

Abstract

The application discloses a kind of general backscattering system and method based on environment OFDM WiFi signal, system includes: at least one backscattering label and a backscattering receiver;Wherein, the backscattering label, can detect single stream or multi-stream OFDM WiFi signal in environment and backscatter it, while backscattering, it is modulated to single stream or multi-stream OFDM WiFi signal with general label data;The backscattering receiver can capture the single stream or multi-stream OFDM WiFi signal backscattered by the backscattering label, and it is decoded from the single stream or multi-stream OFDM WiFi signal with general label data modulation to obtain label data.The system has general symbol level label data modulation, increase the general property and throughput of system.

Description

Technical Field

[0001] This invention relates to the field of Internet of Things (IoT) communication, and in particular to a universal backscattering system and method based on ambient OFDM WiFi signals. Background Technology

[0002] Backscatter communication is a low-power communication technology that allows backscatter tags (such as IoT nodes) to achieve passive communication by reflecting radio frequency (RF) excitation signals. WiFi signals are a commonly used RF excitation signal source for backscatter communication systems because existing WiFi infrastructure is already well-developed, providing ample excitation signals for backscatter systems. WiFi-based backscatter systems can achieve low-power communication simply by utilizing existing signals in the environment, without requiring a dedicated excitation signal generator. Most WiFi signals in the environment are Orthogonal Frequency Division Multiplexing (OFDM) signals. Newer WiFi protocols use multi-stream technology to improve throughput; for example, 802.11ac WiFi supports up to 8 antennas for multi-stream signal transmission, with a throughput eight times that of a single-stream signal. The expectation is that backscatter systems based on OFDM WiFi signals in the environment can universally and efficiently utilize both single-stream and multi-stream signals as excitation sources for low-power communication, but existing systems do not meet this expectation. Considering that the signal receiver may perform signal stream merging operations when receiving multi-stream signals, this can cause interference with tag modulation, preventing the receiver from correctly demodulating tag data.

[0003] To address this issue, existing backscatter communication systems either employ inefficient packet-level modulation or use different modulation methods for single-stream and multi-stream signals. WiFi Backscatter, published in SIGCOMM in 2014, achieves packet-level modulation of environmental signals, but suffers from low throughput. MOXcatter, published in MobiSys in 2018, can achieve OFDM symbol-level modulation of single-stream OFDM WiFi signals in the environment, offering higher throughput, but it can only achieve packet-level modulation for multi-stream OFDM WiFi signals, resulting in both different modulation methods and limited throughput. VMscatter, published in NSDI in 2020, can achieve OFDM symbol-level modulation of both single-stream and multi-stream OFDM WiFi signals, but it still uses different modulation methods for single-stream and multi-stream signals. In fact, a low-power, low-cost backscatter tag lacks the ability to identify the number of antennas and signal streams in the environment; therefore, the non-universal modulation methods of existing backscatter communication systems severely hinder their deployment and application in passive IoT.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a universal backscattering system and method based on ambient OFDM WiFi signals, which can realize universal symbol-level modulation of ambient OFDM WiFi signals and solve the problem that existing technologies cannot universally and efficiently utilize existing OFDM WiFi signals in the environment.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A universal backscattering system based on ambient OFDM WiFi signals includes: at least one backscattering tag and a backscattering receiver; wherein,

[0008] The backscatter tag can detect single-stream or multi-stream OFDM WiFi signals in the environment and backscatter them, while applying general tag data modulation to the single-stream or multi-stream OFDM WiFi signals during backscattering.

[0009] The backscatter receiver can capture and demodulate the single-stream or multi-stream OFDM WiFi signal backscattered by the backscatter tag, and decode the tag data from the demodulated single-stream or multi-stream OFDM WiFi signal with universal tag data modulation.

[0010] A universal backscattering method based on ambient OFDM WiFi signals, employing the universal backscattering system based on ambient OFDM WiFi signals described in this invention, includes the following steps:

[0011] The system detects single-stream or multi-stream OFDM WiFi signals in the environment by backscattering tags and backscatters them. At the same time as backscattering, a common tag data modulation is applied to the single-stream or multi-stream OFDM WiFi signals.

[0012] The system's backscatter receiver captures and demodulates the single-stream or multi-stream OFDM WiFi signal backscattered by the backscatter tag, and decodes the tag data from the demodulated single-stream or multi-stream OFDM WiFi signal with universal tag data modulation.

[0013] Compared with existing technologies, the universal backscattering system and method based on ambient OFDM WiFi signals provided by this invention have the following advantages:

[0014] By using backscattering tags to apply universal tag data modulation to single-stream or multi-stream OFDM WiFi signals while simultaneously backscattering them, the tag data is decoded from the demodulated single-stream or multi-stream OFDM WiFi signals using a backscattering receiver. Compared to existing technologies like MOXcatter and VMscatter, this invention's system features universal symbol-level tag data modulation, increasing the system's versatility and throughput. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the configuration of a universal backscattering system based on ambient OFDM WiFi signals provided in an embodiment of the present invention.

[0017] Figure 2 A comparison chart of the bit error rate of tag data under a single-stream excitation signal between the method provided in this embodiment of the invention and the existing MOXcatter method.

[0018] Figure 3 Provided for embodiments of the present invention Figure 2 A comparison chart of the bit error rate of multi-stream excitation signal labeled data between the method provided in this embodiment of the invention and the existing MOXcatter method.

[0019] Figure 4 A comparison chart of the error throughput of tag data under a single-stream excitation signal between the method provided in this embodiment of the invention and the existing MOXcatter method.

[0020] Figure 5 Provided for embodiments of the present invention Figure 2 A comparison chart of the multi-stream excitation signal tag data throughput of the method provided in this embodiment of the invention and the existing MOXcatter method. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the specific content of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments, which do not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0022] First, the following explanations are provided for the terms that may be used in this article:

[0023] The term "and / or" means that either or both can be achieved simultaneously. For example, X and / or Y means that it includes both "X" or "Y" as well as the three cases of "X and Y".

[0024] The terms “including,” “comprising,” “containing,” “having,” or other similar semantic descriptions should be interpreted as non-exclusive inclusion. For example, “including a technical feature element (such as raw material, component, ingredient, carrier, dosage form, material, size, part, component, mechanism, device, step, process, method, reaction conditions, processing conditions, parameter, algorithm, signal, data, product or article of manufacture, etc.)” should be interpreted as including not only the expressly listed technical feature element, but also other technical feature elements that are not expressly listed and are well-known in the art.

[0025] The term "composed of" excludes any technical features not expressly listed. When used in a claim, it closes the claim to exclude all technical features other than those expressly listed, except for associated conventional impurities. If the term appears only in a clause of a claim, it limits the claim to the elements expressly listed in that clause; elements recited in other clauses are not excluded from the overall claim.

[0026] Unless otherwise explicitly specified or limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this document according to the specific circumstances.

[0027] The terms “center,” “longitudinal,” “lateral,” “length,” “width,” “thickness,” “upper,” “lower,” “front,” “back,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” “outer,” “clockwise,” and “counterclockwise” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience and simplification of description and do not imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this document.

[0028] The following is a detailed description of the universal backscattering system based on ambient OFDM WiFi signals provided by this invention. Contents not described in detail in the embodiments of this invention are prior art known to those skilled in the art. Where specific conditions are not specified in the embodiments of this invention, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used in the embodiments of this invention, unless otherwise specified, are all commercially available products.

[0029] like Figure 1 As shown, this embodiment of the invention provides a universal backscattering system based on ambient OFDM WiFi signals, comprising: at least one backscattering tag and a backscattering receiver; wherein,

[0030] The backscatter tag can detect single-stream or multi-stream OFDM WiFi signals in the environment and backscatter them, while applying general tag data modulation to the single-stream or multi-stream OFDM WiFi signals during backscattering.

[0031] The backscatter receiver can capture and demodulate the single-stream or multi-stream OFDM WiFi signal backscattered by the backscatter tag, and decode the tag data from the demodulated single-stream or multi-stream OFDM WiFi signal with universal tag data modulation.

[0032] Preferably, in the above system, the backscattering tag applies general tag data modulation to the single-stream or multi-stream OFDM WiFi signal while backscattering, including:

[0033] The corresponding tag data is modulated by applying a phase shift to the OFDM WiFi signal in the time slot of each symbol;

[0034] The backscatter receiver includes a signal demodulator and a tag data decoder, wherein the signal demodulator is capable of demodulating the single-stream or multi-stream OFDM WiFi signal backscattered by the backscatter tag.

[0035] The tag data decoder decodes tag data from a single-stream or multi-stream OFDM WiFi signal demodulated by the signal demodulator and subjected to common tag data modulation in the following manner:

[0036] If the signal demodulator captures a single-stream OFDM WiFi signal backscattered by the backscattering tag, the tag data can be directly decoded after demodulation.

[0037] If the signal demodulator captures that the backscattered signal from the backscattered tag is a multi-stream OFDM WiFi signal, then the tag data is obtained by demodulating and decoding before the multi-stream OFDM WiFi signals are merged.

[0038] Preferably, in the above system, when the backscatter tag applies general tag data modulation to a single-stream or multi-stream OFDM WiFi signal, if a phase shift is applied to a certain symbol in the OFDM WiFi signal, the binary tag data to be transmitted is modulated as 1; if no phase shift is applied to a certain symbol in the OFDM WiFi signal, the binary tag data to be transmitted is modulated as 0.

[0039] The backscatter receiver further includes a phase error estimator connected between the signal demodulator and the tag data decoder. This estimator can correct the channel error of each symbol's subcarrier based on the channel estimation result. Each corrected subcarrier retains the phase offset applied by the backscatter tag to the entire symbol time slot. The subcarrier corresponding to each symbol is obtained by removing the cyclic prefix of the symbols in each OFDM WiFi signal stream from the signal demodulator and then demodulating it using a Fast Fourier Transform before combining the multi-stream OFDM WiFi signals.

[0040] The tag data decoder calculates the phase offset applied by the backscatter tag to the backscatter signal by comparing the phase difference between the received subcarrier and the original subcarrier of the ambient signal, and then decodes the tag data.

[0041] Preferably, in the above system, the phase error estimator of the backscatter receiver corrects the channel error of each symbol's subcarrier based on the channel estimation result in the following manner:

[0042] The backscatter receiver uses the first K symbols of the received OFDM WiFi signal to estimate the phase error caused by the i-th symbol through linear regression. intercept With slope If K = 1, then let The first K symbols are the first K symbols of the backscatter tag that are not subjected to general tag data modulation each time an OFDM WiFi signal is detected;

[0043] For symbols containing modulation tag data, use the intercept. and slope estimation results and According to the formula To estimate phase error i > K;

[0044] Then subtract the phase estimation result Φi The tag phase used for tag data decoding is obtained.

[0045] Preferably, in the above system, as i increases, it is updated in real time in the following manner. include:

[0046] For the i-th symbol, i > K, after decoding the tag data, the phase of the i-th symbol is subtracted from the phase of the tag data to obtain the result. use Reusing linear regression calculation and However, this approach has high time complexity. To reduce time complexity, calculation is performed using a formula. Then use the following formula Update slope

[0047]

[0048] Here, parameter α is the update rate, and the value of α is between (0,1), that is, 0 < α < 1. The larger the value of α, the higher the update rate. The greater the impact.

[0049] See Figure 1 This invention also provides a universal backscattering method based on ambient OFDM WiFi signals, employing the aforementioned universal backscattering system based on ambient OFDM WiFi signals, and including the following steps:

[0050] The system detects single-stream or multi-stream OFDM WiFi signals in the environment by backscattering tags and backscatters them. At the same time as backscattering, a common tag data modulation is applied to the single-stream or multi-stream OFDM WiFi signals.

[0051] The system's backscatter receiver captures and demodulates the single-stream or multi-stream OFDM WiFi signal backscattered by the backscatter tag, and decodes the tag data from the demodulated single-stream or multi-stream OFDM WiFi signal with universal tag data modulation.

[0052] Preferably, in the above method, the backscattering tag of the system applies general tag data modulation to the single-stream or multi-stream OFDM WiFi signal during backscattering in the following manner: modulating the corresponding tag data by applying a phase shift to the OFDM WiFi signal in the time slot of each symbol.

[0053] Tag data is decoded from a demodulated single-stream or multi-stream OFDM WiFi signal subjected to universal tag data modulation by the system's backscatter receiver in the following manner:

[0054] If the backscatter receiver captures a single-stream OFDM WiFi signal backscattered by the backscatter tag, the tag data can be directly decoded after demodulation.

[0055] If the backscatter receiver captures the backscattered signal of the backscatter tag as a multi-stream OFDM WiFi signal, then the tag data is obtained by demodulating and decoding before the multi-stream OFDM WiFi signals are merged.

[0056] Preferably, in the above method, when applying general tag data modulation to a single-stream or multi-stream OFDM WiFi signal using the backscatter tag of the system, if a phase shift is applied to a certain symbol in the OFDM WiFi signal, the binary tag data to be transmitted is 1; if no phase shift is applied to a certain symbol in the OFDM WiFi signal, the binary tag data to be transmitted is 0.

[0057] Preferably, in the above method, the backscatter receiver demodulates and then decodes the tag data before combining the multi-stream OFDM WiFi signals in the following manner:

[0058] The backscatter receiver's phase error estimator corrects the channel error of each symbol's subcarrier based on the channel estimation result. Each corrected subcarrier retains the phase offset applied to the entire symbol time slot by the backscatter tag. The subcarrier of each symbol is obtained by removing the cyclic prefix of each symbol in each OFDM WiFi signal stream through the backscatter receiver's signal demodulator before combining the multi-stream OFDM WiFi signals, and then demodulating it using a fast Fourier transform.

[0059] The tag data is obtained by comparing the phase difference between the received subcarrier and the original subcarrier of the ambient signal using the tag data decoder of the backscatter receiver to determine the phase offset applied by the backscatter tag to the backscatter signal.

[0060] Preferably, in the above method, the backscatter receiver corrects the channel error of each symbol's subcarrier based on the channel estimation result in the following manner:

[0061] The backscatter receiver uses the first K symbols of the received OFDM WiFi signal to estimate the phase error caused by the i-th symbol through linear regression. intercept With slope If K = 1, then let The first K symbols are the first K symbols of the backscatter tag that are not subjected to general tag data modulation each time an OFDM WiFi signal is detected;

[0062] For symbols containing modulation tag data, use the intercept. and slope estimation results and According to the formula To estimate phase error i > K;

[0063] Then subtract the phase estimation result. The tag phase is used to decode the tag data.

[0064] Preferably, in the above method, as i increases, it is updated in real time in the following manner. include:

[0065] For the i-th symbol, i > K, after decoding the tag data, the phase of the i-th symbol is subtracted from the phase of the tag data to obtain the result. use Reusing linear regression calculation and However, this approach has high time complexity. To reduce time complexity, a formula is used for calculation. Then use the following formula Update slope

[0066]

[0067] Here, parameter α is the update rate, and the value of α is between (0,1), that is, 0 < α < 1. The larger the value of α, the higher the update rate. The greater the impact.

[0068] In summary, the system and method of this invention, compared to existing technologies such as MOXcatter and VMscatter, offer general symbol-level tag data modulation, increasing the system's versatility and throughput. Furthermore, our proposed method for eliminating phase errors reduces the system's bit error rate.

[0069] To more clearly demonstrate the technical solution and its effects provided by the present invention, the following detailed description of the universal backscattering system and method based on ambient OFDM WiFi signals provided by the present invention is given by specific embodiments.

[0070] Example 1

[0071] like Figure 1 As shown in the figure, this embodiment of the invention provides a universal backscattering system based on ambient OFDM WiFi signals. The system mainly includes the following parts: a backscattering excitation signal, a backscattering tag, and a backscattering receiver. The technical details of each part will be described below.

[0072] (1) Backscattering excitation signal

[0073] The system of this invention uses the OFDM WiFi signal in the environment as the backscattering excitation signal. The OFDM WiFi signal here can be a single-stream signal or a multi-stream signal. The excitation signal of the system of this invention comes from the existing WiFi infrastructure in the environment, without the need for a dedicated excitation signal generator, or special design or firmware modification, which will not be described in detail here.

[0074] (2) Backscattering label

[0075] The backscattering tag used in this invention can detect OFDM WiFi signals in the environment and backscatter them. The tag does not distinguish between single-stream and multi-stream OFDM WiFi signals. Simultaneously with backscattering, the tag applies universal tag data modulation to both single-stream and multi-stream OFDM WiFi signals.

[0076] The tag detection of environmental signals follows the method in the existing MOXcatter technology, which uses an envelope detector and a comparator to achieve low-power environmental signal detection. When an OFDM WiFi signal is present in the environment, the envelope detector will output a high voltage, and when there is no signal, it will output a low voltage. A voltage comparator is used to convert the output of the envelope detector into a binary signal. The rising edge of the voltage comparator output signal is used to drive the backscattered tag to reflect and modulate the tag data.

[0077] A general method for modulating tag data at the symbol level is proposed. The core technology of tag data modulation is applying a phase shift to the symbol. Applying a phase shift to a symbol indicates the transmission of tag data 1, while not applying a phase shift indicates the transmission of tag data 0. Similar to the existing MOXcatter technology, an RF switch is used to achieve backscattering and modulation of the ambient signal. Only a square wave control signal with a phase shift needs to be input to the RF switch to apply frequency and phase shift to the backscattered signal. The modulation method differs from MOXcatter. MOXcatter requires the tag to ensure that the modulated signal has a valid codeword, which imposes requirements on the modulation method of the ambient signal and the transmitted data, and is not applicable to all ambient signals. The proposed system only uses phase modulation information and does not require the original signal to use a specific modulation method or transmit specific data, making it a general design.

[0078] The tag applies a phase offset to the ambient signal within each symbol's time slot. This modulation method is universal for both single-stream and multi-stream signals. For single-stream signals, one and only one symbol is transmitted in each time slot, and the phase offset carried by each symbol in the modulated signal indicates the tag data it modulates. For multi-stream signals, since symbols with the same index on different signal streams are transmitted in the same time slot, and each symbol does not span time slots, this method allows the backscattering tag to modulate symbols with the same index on all signal streams in the same way. By applying a phase offset in different time slots, universal and efficient modulation of ambient OFDM WiFi signals is achieved.

[0079] (3) Backscatter receiver

[0080] This invention uses a backscatter receiver to capture backscattered OFDM WiFi signals and decode tag data. During baseband signal processing, tag data is decoded before multi-stream signal merging to prevent tag modulation interference caused by signal stream merging.

[0081] Before combining multi-stream signals, the backscatter receiver removes the cyclic prefix from each symbol in each stream and then demodulates it into a series of subcarriers using a Fast Fourier Transform (FFT). After demodulation, the receiver corrects for channel errors in each subcarrier based on channel estimation. Since the tag applies the same phase offset across the entire symbol slot, this offset is retained on each subcarrier after the FFT. Therefore, the phase offset applied by the tag to the backscattered signal can be determined by comparing the phase difference between the received subcarrier and the original phase of the ambient signal subcarrier, thus decoding the tag data.

[0082] At this point, note that some phase errors are introduced during signal transmission and reception. These phase errors, combined with the phase offset of tag modulation, cause the backscatter receiver to fail to decode the tag data. Note that among all phase errors, the phase error introduced by the carrier frequency offset (CFO) is dominant. The phase error introduced by the CFO for the i-th symbol of the OFDM signal can be expressed by the following formula:

[0083]

[0084] Here, Q represents the number of subcarriers of the symbol, and L... cp Where Q is the symbol cyclic prefix length, T is the sampling duration, Δω is the CFO, and i is the symbol index or position. For a given signal, Q,L cp T are both fixed values. It increases linearly with increasing Δω,i. Δω can sometimes be very large. Assuming the crystal oscillators used in the WiFi signal transmitter and receiver have an error of ±20ppm (typical for portable electronic products), then for signals transmitted in the 5GHz band, Δω can reach 5 × 10⁻⁶. 9 ×20×10 -6 =100kHz. Using the built-in frequency correction of the WiFi receiver, the long training field of the OFDM signal is utilized to estimate and eliminate most of the CFO. The higher the signal-to-noise ratio of the received signal, the more accurate the CFO elimination. For environmental signals with long durations, the symbol 'i' is larger in the later transmission time slots. Considering that backscattered signals are generally weak and have low signal-to-noise ratios, the phase error may still affect tag data decoding due to the combined effect of the remaining CFO after frequency correction and the larger 'i'.

[0085] In standard WiFi transmission and reception, pilot subcarriers can be used to correct these phase errors. However, since the pilot subcarriers in the backscattered signal also carry the phase offset of tag modulation, existing correction methods may eliminate the tag modulation information along with it. A new method is invented here. Because... The phase error increases linearly with increasing i, and a number of training symbols can be used to estimate it. It is stipulated that no phase offset is applied to the first K symbols each time the tag detects an environmental signal. In the backscatter receiver, these first K symbols of the received signal are used to estimate the phase error. Since it does not contain the phase offset introduced by the tag, linear regression is used to estimate it. intercept With slope (If K = 1, then let) For a symbol i (i>K) containing tag modulation data, use and estimation results To estimate

[0086] Then subtract the phase estimation result Φi The obtained tag phase can then be used for tag data decoding. The phase estimation is the same as that of a typical WiFi receiver, ensuring the accuracy of the estimated phase. The value increases linearly with increasing i, ensuring the correctness of tag data decoding. Furthermore, it can be updated in real time as i increases. For the i-th symbol (i>K), after decoding the tag data, subtracting the phase of the tag data from the phase of the symbol yields the result. Can be used Reusing linear regression calculation However, this results in high time complexity. To reduce time complexity, we can calculate... Simply use renew

[0087]

[0088] Where the parameter α is the update rate, the larger α is, the higher the update rate. The greater the impact, the more efficient the implementation can be. Real-time updates improve the accuracy of phase error estimation.

[0089] Compared to existing technologies such as MOXcatter and VMscatter, the system and method of this invention offer universal symbol-level tag data modulation, increasing the system's versatility and throughput. Furthermore, the proposed method for eliminating phase errors reduces the system's bit error rate.

[0090] Example 2

[0091] This invention provides a universal backscattering system based on ambient OFDM WiFi signals. For example... Figure 1 As shown, the system consists of three parts: a backscatter excitation signal from the transmitter, a backscatter tag, and a backscatter receiver. The backscatter excitation signal can be a single-stream or multi-stream OFDM WiFi signal. The backscatter tag modulates the excitation signal using common tag data. The backscatter receiver first estimates the phase error and then decodes the tag data.

[0092] The backscatter tag uses a logarithmic envelope detector with a filter circuit to detect WiFi signals in the environment. A high-speed comparator TLV3501 is used as the comparator circuit. A Xilinx ZYNQ FPGA development board EBAZ4205 is used to modulate the tag data and generate a square wave control signal with phase shift; the control logic is written in Verilog. This control signal is used to control an RF switch with an antenna to achieve backscattering and tag data modulation. The RF switch used for the backscatter signal is passive, but the circuitry for ambient signal detection and control signal generation requires a 5V power supply.

[0093] The Xilinx Zedboard ZYNQ-7000 and AD-FMCOMMS3 were used as backscatter receivers, supporting 2x2 multi-stream signals and a 40MHz bandwidth. Signal processing, including baseband signal processing, phase error estimation, and tag data decoding, was performed using the Xilinx ZYNQ Radio Extensions package in MATLAB.

[0094] Figure 1 , Figure 2 The system of the present invention (i.e.) was compared. Figure 1, Figure 2 The bit error rate (BER) of this system and the existing MOXcatter system are compared. It can be seen that the BER of this system is superior to that of MOXcatter. When the tag-receiver distance is 2 meters, the BER of this system is 0.0081% under single-stream excitation and 0.006% under multi-stream excitation, which is 471.9 and 433.3 times better than MOXcatter (3.8% and 2.6%), respectively. As the tag-receiver distance increases, the BER of this system also increases, but it remains lower than that of MOXcatter. When the tag-receiver distance reaches 8 meters under single-stream excitation and 4 meters under multi-stream excitation, the BER of MOXcatter exceeds 10%, while the BERs of this system are 0.024% and 0.012%, respectively, which is sufficient to support low-power communication in IoT applications. The lower BER of this system is due to the use of a phase error estimation method, which corrects for errors introduced by the residual CFO that lead to tag data decoding errors.

[0095] Figure 3 , Figure 4 The system of the present invention (i.e.) is shown Figure 3 , Figure 4 The throughput of this system and the existing MOXcatter system are compared. Under single-stream excitation, the throughput of this system is always higher than that of MOXcatter, and almost twice that of MOXcatter. At a tag-to-receiver distance of 2 meters, the throughput of this system is 228.0 kbps, while that of MOXcatter is only 109.6 kbps. This is because this system implements single-symbol-level tag data modulation, modulating 1 bit of tag data in each 4-microsecond symbol slot, while MOXcatter, to reduce the bit error rate, requires twice the redundancy modulation, modulating 1 bit of tag data in every two 4-microsecond symbol slots, resulting in a 50% reduction in data transmission rate compared to this system. Under multi-stream excitation, since MOXcatter can only achieve packet-level modulation, its maximum throughput is only 2.92 kbps, far lower than its performance under single-stream excitation. In contrast, this system uses a common modulation scheme under both single-stream and multi-stream excitation, achieving a maximum throughput of 230.0 kbps, similar to its performance under single-stream excitation.

[0096] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A universal backscattering system based on ambient OFDM WiFi signals, characterized in that, include: At least one backscatter tag and one backscatter receiver; wherein, The backscatter tag can detect single-stream or multi-stream OFDM WiFi signals in the environment and backscatter them, while applying general tag data modulation to the single-stream or multi-stream OFDM WiFi signals during backscattering. The backscatter receiver can capture and demodulate the single-stream or multi-stream OFDM WiFi signal backscattered by the backscatter tag, and decode the tag data from the demodulated single-stream or multi-stream OFDM WiFi signal with universal tag data modulation. The backscatter tag applies common tag data modulation to single-stream or multi-stream OFDM WiFi signals while backscattering, including: The corresponding tag data is modulated by applying a phase shift to the OFDM WiFi signal in the time slot of each symbol; The backscatter receiver includes a signal demodulator and a tag data decoder, wherein the signal demodulator is capable of demodulating the single-stream or multi-stream OFDM WiFi signal backscattered by the backscatter tag. The tag data decoder decodes tag data from a single-stream or multi-stream OFDM WiFi signal demodulated by the signal demodulator and subjected to common tag data modulation in the following manner: If the signal demodulator captures a single-stream OFDM WiFi signal backscattered by the backscattering tag, the tag data can be directly decoded after demodulation. If the signal demodulator captures that the backscattered signal of the backscattered tag is a multi-stream OFDM WiFi signal, then the tag data is obtained by demodulating and decoding before the multi-stream OFDM WiFi signals are merged. When the backscatter tag applies general tag data modulation to a single-stream or multi-stream OFDM WiFi signal, if a phase shift is applied to a certain symbol in the OFDM WiFi signal, the binary tag data to be transmitted is 1; if no phase shift is applied to a certain symbol in the OFDM WiFi signal, the binary tag data to be transmitted is 0. The backscatter receiver further includes a phase error estimator, communicatively connected between the signal demodulator and the tag data decoder, capable of correcting the channel error of each symbol's subcarrier based on the channel estimation result. Each corrected subcarrier retains the phase offset applied by the backscatter tag to the entire symbol time slot. The subcarrier corresponding to each symbol is obtained by the signal demodulator removing the cyclic prefix of the symbols in each OFDM WiFi signal stream before combining the multi-stream OFDM WiFi signals, and then demodulating it using a fast Fourier transform. The tag data decoder calculates the phase shift applied by the backscatter tag to the backscatter signal by comparing the phase difference between the received subcarrier and the original subcarrier of the ambient signal, and then decodes the tag data. The phase error estimator of the backscatter receiver corrects the channel error of each symbol's subcarrier based on the channel estimation results in the following manner: The phase error estimator uses the received OFDM WiFi signal as a front end. The sign is estimated by linear regression. Phase error caused by each symbol intercept With slope ,like Then let ,forward The symbol represents the backscatter tag, which, each time an OFDM WiFi signal is detected, does not apply general tag data modulation. One symbol; For symbols containing modulation tag data ,use intercept and slope estimation results and According to the following formula To estimate phase error , i > K; Then the phase estimation results minus The tag phase used for tag data decoding is obtained.

2. The universal backscattering system based on ambient OFDM WiFi signals according to claim 1, characterized in that, along with Add real-time updates as follows ,include: For the The symbol, i > K, is used after decoding the tag data. Subtracting the phase of the tag data from the phase of each symbol yields... ,use Reusing linear regression calculation and Then calculate using the formula Then follow the formula use Update the slope of the linear regression; in the formula, the parameters... For update rate, The value of is between (0,1), that is, 0 < 1. <1.

3. A universal backscattering method based on ambient OFDM WiFi signals, characterized in that, The universal backscattering system based on ambient OFDM WiFi signals as described in any one of claims 1-2 includes the following steps: The system detects single-stream or multi-stream OFDM WiFi signals in the environment by backscattering tags and backscatters them. At the same time as backscattering, a common tag data modulation is applied to the single-stream or multi-stream OFDM WiFi signals. The system captures and demodulates the single-stream or multi-stream OFDM WiFi signal backscattered by the backscatter tag using a backscatter receiver, and decodes the tag data from the demodulated single-stream or multi-stream OFDM WiFi signal with universal tag data modulation applied. The backscattering tag of the system applies general tag data modulation to single-stream or multi-stream OFDM WiFi signals during backscattering in the following manner: modulating the corresponding tag data by applying a phase shift to the OFDM WiFi signal in the time slot of each symbol. Tag data is decoded from a demodulated single-stream or multi-stream OFDM WiFi signal subjected to universal tag data modulation by the system's backscatter receiver in the following manner: If the backscatter receiver captures a single-stream OFDM WiFi signal backscattered by the backscatter tag, the tag data can be directly decoded after demodulation. If the backscatter receiver captures the backscattered signal of the backscatter tag as a multi-stream OFDM WiFi signal, then the tag data is obtained by demodulating and decoding before the multi-stream OFDM WiFi signals are merged. When the backscattered tag of the system applies general tag data modulation to a single-stream or multi-stream OFDM WiFi signal, if a phase shift is applied to a symbol in the OFDM WiFi signal, the binary tag data to be transmitted is 1; if no phase shift is applied to a symbol in the OFDM WiFi signal, the binary tag data to be transmitted is 0. The backscatter receiver demodulates and then decodes the tag data before combining the multi-stream OFDM WiFi signals in the following manner: The backscatter receiver's phase error estimator corrects the channel error of each symbol's subcarrier based on the channel estimation result. Each corrected subcarrier retains the phase offset applied to the entire symbol time slot by the backscatter tag. The subcarrier of each symbol is obtained by removing the cyclic prefix of each symbol in each OFDM WiFi signal stream through the backscatter receiver's signal demodulator before combining the multi-stream OFDM WiFi signals, and then demodulating it using a fast Fourier transform. The tag data is obtained by comparing the phase difference between the received subcarrier and the original subcarrier of the ambient signal using the tag data decoder of the backscatter receiver to determine the phase offset applied by the backscatter tag to the backscatter signal. The channel error estimator of the backscatter receiver corrects the channel error of each symbol's subcarrier based on the channel estimation results in the following manner: The channel error estimator uses the received OFDM WiFi signal as a reference. The sign is estimated by linear regression. Phase error caused by each symbol intercept With slope ,like Then let ,forward The symbol represents the backscatter tag, which, each time an OFDM WiFi signal is detected, does not apply general tag data modulation. One symbol; For symbols containing modulation tag data, use the intercept. and slope estimation results and According to the formula To estimate phase error , i > K; Then the phase estimation results minus The tag phase used for tag data decoding is obtained.

4. The universal backscattering method based on environmental OFDM WiFi signals according to claim 3, characterized in that, In the method described, as Add real-time updates as follows ,include: For the first The symbol, i > K, is used after decoding the tag data. Subtracting the phase of the tag data from the phase of each symbol yields... ,use Reusing linear regression calculation and Then calculate using the formula Then follow the formula use Update the slope of the linear regression In the formula, the parameters For update rate, The value of is between (0,1), that is, 0 < 1. <1.

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