Backscattering analog communication method and device based on wifi channel information

Abstract

The application provides a backscattering analog communication method and device based on WiFi channel information, and the method comprises the following steps: acquiring analog voltage data of a sensor; converting the analog voltage data of the sensor into phase data of a reflected radio frequency signal; embedding the phase data of the reflected radio frequency signal into a WiFi data packet sent by a WiFi sending end to obtain a WiFi data packet embedding the phase data of the reflected radio frequency signal, so that the WiFi receiving end decodes the WiFi data packet embedding the phase data of the reflected radio frequency signal to obtain the analog voltage data of the sensor, without additionally setting a microprocessor, the analog voltage of the sensor can be embedded into the WiFi data packet in a low-power consumption mode, and is transmitted to the WiFi receiving end, and the energy budget of the backscattering communication is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of backscatter analog communication technology, and particularly relates to a backscatter analog communication method and device based on WiFi channel information. BACKGROUND

[0002] Backscatter communication is a key technology of passive Internet of Things, and a backscatter device is activated by energy emitted by a carrier wave source, and modulates its own data in the reflected carrier signal, so as to realize passive communication without generating a carrier. Taking the transmission of voltage data of a sensor by backscatter communication as an example, a traditional backscatter communication method is to use a microprocessor to interface between the sensor and a backscatter communication front end, the microprocessor stores a digital signal data packet of the sensor, and the backscatter communication front end sends the digital signal data packet to a receiving end after discrete backscatter. However, the overall power consumption of the microprocessor is high, which increases the energy budget of backscatter communication. SUMMARY

[0003] The present application provides a backscatter analog communication method and device based on WiFi channel information, which solves the defect that the overall power consumption of the microprocessor is high in the prior art, increases the energy budget of backscatter communication, and does not need to additionally set a microprocessor, so that the analog voltage of the sensor can be embedded in a WiFi data packet at low power consumption and transmitted to a WiFi receiving end, thereby reducing the energy budget of backscatter communication.

[0004] The present application provides a backscatter analog communication method based on WiFi channel information, comprising: acquiring analog voltage data of a sensor; converting the analog voltage data of the sensor into phase data of a reflected radio frequency signal; embedding the phase data of the reflected radio frequency signal into a WiFi data packet sent by a WiFi sending end to obtain a WiFi data packet embedded with the phase data of the reflected radio frequency signal, so that a WiFi receiving end decodes the WiFi data packet embedded with the phase data of the reflected radio frequency signal to obtain the analog voltage data of the sensor.

[0005] According to the backscatter analog communication method based on WiFi channel information provided by the present application, the analog voltage data of the sensor is converted into phase data of a reflected radio frequency signal, comprising: establishing a backscatter communication front end; determining a reflection coefficient of the backscatter communication front end according to the analog voltage data of the sensor; and determining the phase data of the reflected radio frequency signal according to the reflection coefficient of the backscatter communication front end.

[0006] According to the application, a method for backscatter analog communication based on WiFi channel information is provided, wherein phase data of the reflected radio frequency signal is embedded into a WiFi data packet sent by a WiFi sending end, and the method comprises: in an embedding state, embedding the phase data of the reflected radio frequency signal into channel embedding state information of the WiFi data packet sent by the sending end and supporting additional space detection; and in a reference state, embedding reference phase data of a preset reflected radio frequency signal into channel reference state information of the WiFi data packet sent by the sending end and supporting additional space detection.

[0007] According to the application, a method for backscatter analog communication based on WiFi channel information is provided, wherein the WiFi receiving end decodes the WiFi data packet embedded with the phase data of the reflected radio frequency signal to obtain analog voltage data of the sensor, and the method comprises: obtaining the phase data of the reflected radio frequency signal according to a phase difference between channel embedding state information of the WiFi data packet and channel reference state information of the WiFi data packet; and converting the phase data of the reflected radio frequency signal into the analog voltage data of the sensor.

[0008] According to the application, a method for backscatter analog communication based on WiFi channel information is provided, and the method further comprises: offsetting a frequency of the WiFi data packet embedded with the reflected radio frequency signal by a preset frequency offset, wherein the preset frequency is a frequency of a WiFi channel, so that the WiFi receiving end receives the WiFi data packet embedded with the reflected radio frequency signal in a channel corresponding to the preset frequency offset.

[0009] The application further provides a backscatter device, which comprises: a sensor for providing analog voltage data; a backscatter communication front end having an input end connected to an output end of the sensor and an output end connected to a first antenna, wherein the backscatter communication front end adopts the method for backscatter analog communication based on WiFi channel information described above; a data packet detection and synchronization circuit having an input end connected to a second antenna and an output end connected to an input end of a control logic module, wherein the data packet detection and synchronization circuit is used to detect an embedding position of the phase data of the reflected radio frequency signal in the WiFi data packet embedded with the phase data of the reflected radio frequency signal, and output a synchronization communication state signal to the control logic module according to the embedding position; and the control logic module having an output end connected to a control end of the backscatter communication front end, wherein the control logic module is used to output a communication state control signal to the backscatter communication front end according to the synchronization communication state signal, so as to control a communication state of the backscatter communication front end, and the communication state of the backscatter communication front end comprises an embedding state and a reference state.

[0010] According to the application, the backscattering communication front end comprises a first microstrip transmission line, a second microstrip transmission line, a third microstrip transmission line, a varactor, a bias inductor and a series capacitor; in the embedded state, the first end of the first microstrip transmission line is connected with the first end of the second microstrip transmission line and the first end of the third microstrip transmission line respectively, the second end of the second microstrip transmission line is grounded, the second end of the third microstrip transmission line is connected with the anode of the varactor, the cathode of the varactor is connected with the first end of the bias inductor and the first end of the series capacitor respectively, the second end of the series capacitor is grounded, and the second end of the bias inductor serves as the input end of the backscattering communication front end.

[0011] According to the application, the backscattering communication front end further comprises a reference state capacitor, a reference state microstrip transmission line and a radio frequency switch; the radio frequency switch is arranged between the reference state microstrip transmission line, the anode of the varactor and the second end of the third microstrip transmission line, the control end of the radio frequency switch serves as the control end of the backscattering communication front end, and is used for connecting the reference state microstrip transmission line with the second end of the third microstrip transmission line according to the reference state control signal of the control logic module; connecting the anode of the varactor with the second end of the third microstrip transmission line according to the embedded state control signal of the control logic module; the first end of the reference state capacitor is grounded, and the second end of the reference state capacitor is connected with the first end of the reference state microstrip transmission line.

[0012] According to the application, the backscattering communication front end further comprises a first impedance matching module, the first end of the first impedance matching module is connected with the second end of the first microstrip transmission line, and the second end of the first impedance matching module serves as the output end of the backscattering communication front end, and is used for matching the impedance of the backscattering communication front end with the first antenna.

[0013] The data packet detection and synchronization circuit comprises an envelope detector, an output end of which is connected with an input end of a comparator, for detecting WiFi signal energy sent by a WiFi sending end and outputting signal energy of the WiFi data packet to the comparator; the comparator, an output end of which serves as an output end of the data packet detection and synchronization circuit, for outputting a first level signal to a control logic module when the signal energy of the WiFi data packet is greater than a preset signal energy threshold and outputting a second level signal to the control logic module when the signal energy of the WiFi data packet is not greater than the preset signal energy threshold, the first level signal being opposite to the second level signal; and a second impedance matching module, an input end of which is connected with the input end of the envelope detector and an output end of which serves as an input end of the data packet detection and synchronization circuit, for matching the data packet detection and synchronization circuit with impedance of the second antenna.

[0014] The application provides a backscattering simulation communication method and device based on WiFi channel information, which comprises the following steps: acquiring analog voltage data of a sensor; converting the analog voltage data of the sensor into phase data of a reflected radio frequency signal; embedding the phase data of the reflected radio frequency signal into a WiFi data packet sent by a WiFi sending end to obtain a WiFi data packet embedded with the phase data of the reflected radio frequency signal, so that the WiFi receiving end decodes the WiFi data packet embedded with the phase data of the reflected radio frequency signal to obtain the analog voltage data of the sensor, without the need of additionally setting a microprocessor, so that the analog voltage of the sensor can be embedded into the WiFi data packet and transmitted to the WiFi receiving end in a low-power consumption mode, and the energy budget of the backscattering communication is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the present application or prior art, the following will briefly introduce the drawings needed in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0016] Figure 1 is a flow diagram of a backscattering simulation communication method based on WiFi channel information provided by the present application;

[0017] Figure 2 is a principle diagram of a backscattering simulation communication method based on WiFi channel information provided by the prior art;

[0018] Figure 3 is a principle diagram of a backscattering simulation communication method based on WiFi channel information provided by the present application;

[0019] Figure 4 is a structure diagram of a data packet with extra space sounding (ESS) channel information (CSI) provided by the present application;

[0020] Figure 5 is a principle diagram of a communication process of a backscattering communication front end provided by the present application;

[0021] Figure 6 is a principle diagram of a reflection coefficient provided by the present application;

[0022] Figure 7 is a principle diagram of a reflection coefficient in a Smith chart provided by the present application;

[0023] Figure 8 is a structure diagram of a short-circuit capacitance reflection model provided by the present application;

[0024] Figure 9 is a schematic diagram of a varactor diode and its capacitance-reverse bias voltage curve provided by the present application;

[0025] Figure 10 is a principle diagram of a reflection circuit design provided by the present application;

[0026] Figure 11 is a simulation result diagram of the relationship between reflection phase, amplitude and bias voltage provided by the present application;

[0027] Figure 12 is a diagram of problems introduced by directly using a switch to switch a bias voltage provided by the present application;

[0028] Figure 13 is a structure diagram of a backscattering device provided by the present application;

[0029] Figure 14 is a partial structure diagram of a backscattering device provided by the present application. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described below in connection with the drawings in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without any creative work fall within the protection scope of the present application.

[0031] Reference is made to Figure 1 , Figure 1 is a flow diagram of a backscattering simulation communication method based on WiFi channel information provided by the present application.

[0032] Please refer to Figure 2 , Figure 2 A principle schematic diagram of a backscatter analog communication method based on WiFi channel information provided by the prior art.

[0033] Please refer to Figure 3 , Figure 3 A principle schematic diagram of a backscatter analog communication method based on WiFi channel information provided by the present application.

[0034] Backscatter communication is a key technology of passive Internet of Things, and a backscatter device is activated by the energy emitted by a carrier wave source, and modulates its own data in the reflected carrier signal, so as to realize passive communication without generating a carrier. The collection of sensor 1 data is the mainstream application of backscatter: when the backscatter communication front end 2 and the sensor 1 module are connected, the whole becomes a passive sensor 1, and the sensor 1 data is transmitted to the receiver with extremely low power consumption.

[0035] In recent years, backscatter technology has received extensive research attention, and has made great progress in the throughput, range, and application of communication.

[0036] For the sensor 1, the traditional method of acquiring and transmitting data is to use a microprocessor (μP) to interface between the sensor 1 and the backscatter communication front end 2. Even if the power consumption of the backscatter communication front end 2 can be as low as microwatt (μW), the power consumption of the microprocessor is still the bottleneck of the overall energy consumption of the sensor 1. The typical energy consumption of a microsensor 1 is at the milliwatt (mW) level, and considering the strict energy budget of a passive sensor 1, the microprocessor is usually difficult to bear for the backscatter communication front end 2.

[0037] In order to solve the technical problems existing in the prior art, the present application provides a backscatter analog communication method based on WiFi channel information, comprising:

[0038] 101: acquiring analog voltage data of the sensor 1;

[0039] 102: converting the analog voltage data of the sensor 1 into phase data of a reflected radio frequency signal;

[0040] 103: embedding the phase data of the reflected radio frequency signal into a WiFi data packet sent by a WiFi sending end to obtain a WiFi data packet embedded with the phase data of the reflected radio frequency signal, so that the WiFi receiving end decodes the WiFi data packet embedded with the phase data of the reflected radio frequency signal to obtain the analog voltage data of the sensor 1.

[0041] Specifically, the backscatter communication front end 2 converts the analog voltage data of the sensor 1 into phase data of the reflected radio frequency signal, and embeds the phase data of the reflected radio frequency signal into the WiFi data packet sent by the WiFi sender, for example, directly modulates the analog sensor 1 voltage data into the channel state information (CSI) of the backscatter WiFi data packet, and coexists with the WiFi carrier data packet, which can be directly received and decoded by the WiFi receiver to obtain the analog voltage data of the sensor 1. The analog sensor 1 usually outputs signals in the form of voltage, and the backscatter communication front end 2 takes the analog voltage of the sensor 1 as input and directly converts it into the phase of the reflected radio frequency signal in the analog domain. The radio frequency phase is more stable in propagation than amplitude modulation, and more compatible with WiFi networks than pulse width modulation. In this way, the backscatter communication front end 2 avoids using a microprocessor as an interface and reduces energy consumption to an affordable level.

[0042] In addition, the WiFi sender is a standard commercial WiFi sender, which is upgraded by a driver program to be able to send a data packet with ESS CSI. On this basis, the backscatter communication front end 2 reflects the WiFi data packet sent by the WiFi sender and embeds the analog voltage data of the sensor 1 in this part of the CSI. The basic principle of the backscatter communication front end 2 to realize analog backscatter is the reflection model of the short-circuit capacitor. Through the design of a specific reflection circuit, the backscatter communication front end 2 can convert the voltage value of the analog sensor 1 into the phase value in the radio frequency reflection signal. Then, the backscatter communication front end 2 performs phase embedding, that is, correctly embeds the converted phase value into the ESS CSI field of the WiFi data packet. Finally, the receiver extracts the CSI and calculates the difference between two CSIs in a WiFi data packet to extract the sensor 1 data. The design of the backscatter communication front end 2 supports the commercial WiFi receiver to directly extract the voltage data of the sensor 1 in the reflected data packet, and can retain the original WiFi data packet sent by the WiFi sender, which is not particularly limited in the present application.

[0043] In summary, the backscatter analog communication method based on WiFi channel information of the present application does not need to additionally set a microprocessor, can realize low-power embedding of the analog voltage of the sensor 1 into the WiFi data packet, and transmit it to the WiFi receiver, thereby reducing the energy budget of the backscatter communication.

[0044] On the basis of the above embodiment:

[0045] Please refer to Figure 4 , Figure 4This is a schematic diagram of the structure of a data packet with Additional Space Probe (ESS) Channel Information (CSI) provided by the present invention.

[0046] Please refer to Figure 5 , Figure 5 This is a schematic diagram illustrating the communication process of the backscattering communication front-end provided by the present invention.

[0047] Please refer to Figure 6 , Figure 6 This is a schematic diagram illustrating the principle of the reflection coefficient provided by the present invention.

[0048] Please refer to Figure 7 , Figure 7 This is a schematic diagram illustrating the principle of the reflection coefficient in the Smith chart provided by the present invention.

[0049] In a preferred embodiment, converting the analog voltage data of sensor 1 into phase data of the reflected radio frequency signal includes: establishing a backscattering communication front-end 2; determining the reflection coefficient of the backscattering communication front-end 2 based on the analog voltage data of sensor 1; and determining the phase data of the reflected radio frequency signal based on the reflection coefficient of the backscattering communication front-end 2.

[0050] Specifically, for the backscattering communication front-end 2, its signal consists of forward and reverse electromagnetic waves within the radio frequency transmission line. In transmission line theory, these electromagnetic waves are quantized as voltage and current waves. The reflection coefficient of the backscattering communication front-end 2 represents the reverse (or reflected) voltage wave (V) at a specific port. - ) and positive (or incident) voltage wave (V + The ratio of ) . Since a wave has two variables, amplitude and phase, the reflection coefficient is a complex number. The terminal of a transmission line with characteristic impedance Z0 is connected to a line with impedance Z L The load, here the load impedance Z L It is a complex number. At this time, the reflection coefficient Γ is:

[0051]

[0052] Where |Γ| and θ represent the relative amplitude attenuation and relative phase change of the reflected wave relative to the incident wave, respectively. To put the reflection coefficient simply, if the incident voltage wave signal at the port is Asin(2πft), it is a sinusoidal signal with amplitude A and initial phase of 0. The reflected signal of this circuit is represented as A|Γ|sin(2πft+θ). In S-parameter theory, the reflection coefficient is also referred to as S... 11 To indicate. The remainder of this invention will also use S. 11 To represent the reflection coefficient.

[0053] In traditional backscatter designs, the backscatter communication front-end 2 modulates bits 0 and 1 by providing two discrete reflection coefficient values. For example, the RFID backscatter communication front-end 2 provides a reflection coefficient Γ1 = 0 as a matched state where the incident wave is completely absorbed, and a reflection coefficient |Γ2| = 1 as a state where the incident wave is completely reflected. These two values ​​can be represented in polar coordinates on a Smith chart. Besides this OOK-style reflection in RFID, there is also a BPSK-based backscatter modulation method, which provides two reflection coefficients Γ1 = j and Γ2 = -j, where j is the imaginary unit. These two reflection coefficients have the same amplitude, meaning they both completely reflect the incident wave, but they provide a 180-degree phase difference, thus forming the BPSK reflection signal modulation method.

[0054] This invention proposes using analog modulation to convert the voltage data of sensor 1 into the phase of the reflected radio frequency signal. Specifically, this invention designs an radio frequency circuit whose reflection coefficient changes according to the voltage data of external sensor 1; this change is analog and continuous. Since the phase of the reflected signal depends on the reflection coefficient, the reflection coefficient, determined by the voltage data of sensor 1, correspondingly determines the phase of the reflected radio frequency signal, thereby adjusting the voltage data of external sensor 1 into the phase of the reflected radio frequency signal.

[0055] Please refer to Figure 8 , Figure 8 This is a schematic diagram of the short-circuit capacitor reflection model provided by the present invention.

[0056] A potential method to achieve the aforementioned phase change is to use a short-circuited variable capacitor, which replaces the circuit load with a variable capacitor, thus reducing the reflection coefficient Γ. C This can be achieved by replacing the load impedance with the capacitive impedance Z. C To calculate:

[0057]

[0058] θ C = -2arctan(2πfCZ0)

[0059] Where f is the frequency of the reflected RF signal, C is the capacitance, and Z0 is the characteristic impedance of the antenna or transmission line, typically 50 ohms. The reflection coefficient of a short-circuited capacitor is a unit complex number. Since the signal frequency remains almost constant during reflection (2.4GHz for WiFi) and the characteristic impedance remains constant (50 ohms), the phase of the reflection coefficient depends only on the capacitance. In summary: a short-circuited capacitor will completely reflect the incident RF signal, and its capacitance value will determine the phase of the reflected RF signal.

[0060] Please refer to Figure 9 ,Figure 9 The present invention provides a varactor diode and a schematic diagram of its capacitance-reverse bias voltage curve.

[0061] To apply the varactor diode model described above to the signal of sensor 1, this invention establishes a correspondence between the data of sensor 1 and the capacitance value. Considering the system's universality, this invention uses the common analog voltage signal output by sensor 1, converting its analog voltage value into the capacitance value of the varactor diode to achieve a variable capacitance and thus a variable reflection coefficient. For this purpose, this invention introduces a varactor diode to convert the external analog voltage into a small capacitance.

[0062] A varactor diode is a reverse-biased PN junction that generates a junction capacitance that varies smoothly with the bias voltage. The value of the junction capacitance depends on the reverse bias voltage V:

[0063]

[0064] In the formula, C0 is the junction capacitance without bias voltage; V0 and γ are two constants, which are related to the specific diode type. Currently available commercial varactor diodes can provide various capacitance ranges. Considering that the system of this invention operates under WiFi signals, this invention sets f = 2.4GHz and Z0 = 50. Calculations show that if the capacitance of the varactor diode varies from 0.1pF to 1.5pF, the phase difference can reach nearly 90 degrees; while if the capacitance varies from 100pF to 10000pF, the phase difference is only 1.5 degrees. It can be seen that a varactor diode with a smaller capacitance should be used, and existing commercial diodes such as SMV2201 and GMV9822 can provide a variation range of approximately 0.1pF to 2pF. Therefore, this type of varactor diode should be used.

[0065] Please refer to Figure 10 , Figure 10 A schematic diagram illustrating the principle of the reflection circuit design provided by this invention.

[0066] By using a varactor diode, the backscattering communication front-end 2 correlates the external analog voltage of sensor 1 with a changing capacitance value, and thus with the reflection coefficient of the backscattering communication front-end 2. The passive reflection circuit designed in this invention provides a continuously variable reflection coefficient, thereby converting the analog voltage signal of sensor 1 into the phase of the reflected radio frequency signal. This circuit includes three microstrip transmission lines TL. 1,2,3 varactor diode D V The bias inductor L acts as a radio frequency choke (RFC) to isolate the DC and RF branches. Bias ; and a series capacitor C SThis is used to block DC bias while providing a short circuit to ground for the RF branch. The short-to-ground transmission line TL2 is, on one hand, one of the RF components operating at 2.4 GHz, and on the other hand, a reverse-biased varactor diode D. V Provide DC grounding.

[0067] All components used in this circuit are passive and require no power supply. The analog signal conversion process of the backscattering communication front-end 2 consumes almost no energy because its main DC path is blocked by capacitor C. S and varactor diode D V The only DC current blocked is the reverse saturation current of the varactor diode, which is typically less than 0.01 μA. Therefore, the backscattering communication front-end 2 completes the conversion of the sensor 1 voltage to the radio frequency reflected signal at a negligible energy cost.

[0068] Please refer to Figure 11 , Figure 11 This is a schematic diagram of the simulation results of the relationship between reflection phase, amplitude and bias voltage provided by the present invention.

[0069] This invention utilizes the Keysight Advanced Design System (ADS) to construct and simulate the passive conversion circuit described above. By adjusting the impedance and transmission line length, the backscattering communication front-end 2 provides a flat phase change across the entire 2.4 GHz WiFi band, demonstrating the relationship between the reflected phase and bias voltage at a signal frequency of 2.45 GHz. From an RF circuit design perspective, the reflection circuit of the backscattering communication front-end 2 is essentially an analog phase shifter, albeit a reflective one. Compared to expensive commercial chips, the circuit design of this invention is low-cost, low-power, and precisely meets the "reflective" requirement of the backscattering communication front-end 2.

[0070] In a preferred embodiment, embedding the phase data of the reflected radio frequency signal into the WiFi data packet sent by the WiFi transmitter includes: in the embedding state, embedding the phase data of the reflected radio frequency signal into the channel embedding state information of the WiFi data packet supporting additional space detection sent by the transmitter; and in the reference state, embedding the preset reference phase data of the reflected radio frequency signal into the channel reference state information of the WiFi data packet supporting additional space detection sent by the transmitter.

[0071] Considering that large-scale deployment of backscatter depends on its ability to utilize existing carriers in the environment as excitation, backscatter traffic is often difficult to coexist with carrier traffic. Existing technologies typically require modifying the data packet information of the carrier traffic, such as modifying the packet payload or corrupting the entire data frame. These operations inevitably disrupt the carrier traffic and may lead to decoding failure at the receiver. To address the technical problems existing in the prior art, this embodiment embeds the phase data of the reflected radio frequency signal into the channel embedding state information of the WiFi data packet supporting additional space probing transmitted by the transmitter in the embedded state; and embeds the preset reference phase data of the reflected radio frequency signal into the channel reference state information of the WiFi data packet supporting additional space probing transmitted by the transmitter in the reference state information.

[0072] The principle of payload-transparent analog modulation is as follows: The backscattering communication front-end 2 utilizes the "Extra Spatial Sounding" (ESS) feature in 802.11n to carry the signal of analog sensor 1 using the CSI. For example, the backscattering communication front-end 2 can use an envelope detector to accurately locate the Long Training Field (LTF) portion of the data packet, and then embed a precise analog phase value using a reference circuit, thereby embedding the sensor 1 signal into the extra CSI of the WiFi data packet. When receiving the backscattered data packet, the receiver can extract the embedded sensor 1 reading and cancel the influence of the channel itself on the embedded phase by calculating the phase difference between the two CSIs in the same data packet. During this process, since the WiFi payload remains unchanged, the backscattering communication front-end 2 has payload-transparent properties, and the original payload in the data packet can also be decoded simultaneously.

[0073] Specifically, in terms of phase embedding, the backscattering communication front end 2 transparently embeds the converted radio frequency phase information into the WiFi data packet, so that commercial WiFi devices can decode the readings of the analog sensor 1 without affecting their decoding of normal WiFi data packets.

[0074] The backscattering communication front-end 2 embeds the phase information of the reflected radio frequency signal into the CSI of the WiFi data packet to achieve analog communication. However, the CSI itself characterizes the characteristics of the wireless channel between the transmitter and receiver, thus helping the WiFi receiver decode the WiFi data packet. In the backscattering scenario, the backscattering communication front-end 2 affects the wireless channel by introducing attenuation and phase changes into the radio frequency signal. The backscattering communication front-end 2 utilizes this influence to modify the phase of the CSI based on the voltage of the analog sensor 1. However, the CSI also includes the environmental dynamics of the wireless channel, and the influence of these environmental dynamics can easily overwhelm the intentionally embedded CSI phase of the backscattering communication front-end 2. Therefore, to obtain an accurate phase embedded by the backscattering communication front-end 2, the influence of the environment must be completely avoided.

[0075] The backscattering communication front-end 2 achieves this using Extra Spatial Sounding (ESS) of the 802.11n standard. ESS was originally used to probe the extra spatial stream (i.e., extra channels) of Multiple-Input Multiple-Output (MIMO) channels that are not used to transmit WiFi data. It inserts the same Long Training Field (LTF) into the physical layer header of the WiFi packet to calculate the CSI. In the 802.11n preamble, the ESS LTF (or HT-ELTF, where E stands for extra) immediately follows the regular HT-DLTF (D stands for data), and they contain the same baseband signal. In a Single-Input Single-Output (SISO) scenario, these two LTFs traverse the same channel, thus giving two identical CSI channel measurements.

[0076] To embed the analog voltage of sensor 1 into the WiFi data packet, the backscattering communication front-end 2 precisely embeds the phase of the converted reflected RF signal into the HT-ELTF portion of the WiFi data packet supporting ESS. The other portions of the WiFi data packet, including the original HT-DLTF, are reflected with a constant phase as a reference. We refer to the state of the backscattering communication front-end 2 when reflecting the HT-ELTF symbol as the "embedding state," and the corresponding additional CSI measurement as the "ESS CSI." Similarly, when the backscattering communication front-end 2 reflects other portions of the WiFi data packet, we refer to the state of the backscattering communication front-end 2 as the "reference state," and the original CSI as the "regular CSI." Thus, the phase difference between the ESS CSI and the regular CSI should be equal to the phase of the converted reflected RF signal. Since the ESS CSI and the regular CSI operate on the exact same wireless channel, environmental influences are completely canceled out when calculating the phase difference between the two CSIs.

[0077] In a preferred embodiment, the WiFi receiver decodes the WiFi data packet containing the phase data of the reflected radio frequency signal to obtain the analog voltage data of the sensor 1, including: the WiFi receiver obtaining the phase data of the reflected radio frequency signal based on the phase difference between the channel embedding state information of the WiFi data packet and the channel reference state information of the WiFi data packet; and converting the phase data of the reflected radio frequency signal into the analog voltage data of the sensor 1.

[0078] The WiFi receiver can operate on another WiFi channel adjacent to the transmitter by 20MHz to listen for WiFi data packets. After acquiring the CSI from the WiFi receiver, the phase difference between the two CSI measurements is calculated, and the corresponding voltage value is then calculated. This completes the simulated transmission of the voltage value of sensor 1. Specifically, in terms of data extraction at the receiver, this invention corresponds to the voltage of sensor 1 by calculating the phase difference between the two CSIs. During backscattering, apart from the phase change caused by the embedded state of the communication front-end 2 during backscattering, the ESS CSI and the conventional CSI experience the same wireless channel. If the phase difference between the embedded state and the reference state is θ... V Then the two CSIs are:

[0079] H regular =H air ·H err

[0080] H ess =H air ·e jθV ·H err

[0081] Among them, H air H is the wireless channel response of the environment. err This includes all phase errors, such as those caused by carrier frequency offset, sampling frequency offset, etc. The phase difference is obtained by calculating the quotient of the two CSI values:

[0082]

[0083] After obtaining the phase difference, it needs to be converted back to a voltage value through the voltage-phase correspondence. Since voltage and phase are basically linearly related, the voltage can be obtained by modeling a linear function. In this way, the backscattering communication front-end 2 realizes the transmission of sensor 1 data in completely analog form without using digital communication. The backscattering communication front-end 2 does not contain a power-consuming microprocessor, and the specific analog voltage sampling process is transferred to the WiFi receiver.

[0084] Please refer to Figure 12 , Figure 12 A schematic diagram illustrating the problems introduced by directly using a switch to switch the bias voltage, as provided by this invention.

[0085] As a preferred embodiment, the method further includes: shifting the frequency of the WiFi data packet embedding the reflected radio frequency signal by a preset frequency, wherein the preset frequency is the frequency of the WiFi channel, so that the WiFi receiver receives the WiFi data packet embedding the reflected radio frequency signal on the channel corresponding to the preset frequency shift.

[0086] Specifically, the backscattering communication front-end 2 embeds the phase of the converted reflected radio frequency signal into the WiFi CSI by changing the phase of the wireless channel. If the original link from the WiFi transmitter to the WiFi receiver still exists, the signal path will include a portion that does not pass through the backscattering communication front-end 2, potentially confusing the phase difference of the CSI. This embodiment solves this problem by introducing a preset frequency offset to the reflected signal, for example, ±20MHz. The WiFi receiver then receives WiFi data packets in an adjacent 20MHz WiFi channel. This frequency offset is achieved by multiplying the incident signal by a 20MHz square wave. Specifically, this embodiment achieves the multiplication by switching the reflection switch with a 20MHz frequency shift. This square wave can be generated using a ring oscillator, resulting in very low power consumption in integrated circuit implementations.

[0087] Please refer to Figure 13 , Figure 13 This is a schematic diagram of the structure of a backscattering device provided by the present invention.

[0088] The present invention also provides a backscattering device, comprising: a sensor 1 for providing analog voltage data; a backscattering communication front-end 2 whose input terminal is connected to the output terminal of the sensor 1 and whose output terminal is connected to a first antenna 3, the backscattering communication front-end 2 employing a backscattering analog communication method based on WiFi channel information; a data packet detection and synchronization circuit 5 whose input terminal is connected to a second antenna 6 and whose output terminal is connected to the input terminal of a control logic module 4, for detecting the embedding position of the phase data of the reflected radio frequency signal in the WiFi data packet containing the phase data of the reflected radio frequency signal, and outputting a synchronization communication status signal to the control logic module 4 according to the embedding position; and a control logic module 4 whose output terminal is connected to the control terminal of the backscattering communication front-end 2, for outputting a communication status control signal to the backscattering communication front-end 2 according to the synchronization communication status signal, so as to control the communication status of the backscattering communication front-end 2, the communication status of the backscattering communication front-end 2 including an embedding state and a reference state.

[0089] Please refer to Figure 14 , Figure 14 This is a partial structural schematic diagram of a backscattering device provided by the present invention.

[0090] In a preferred embodiment, the backscattering communication front-end 2 includes a first microstrip transmission line, a second microstrip transmission line, a third microstrip transmission line, a varactor diode, a bias inductor, and a series capacitor. In the embedded state, the first end of the first microstrip transmission line is connected to the first ends of the second and third microstrip transmission lines, respectively. The second end of the second microstrip transmission line is grounded. The second end of the third microstrip transmission line is connected to the anode of the varactor diode. The cathode of the varactor diode is connected to the first end of the bias inductor and the first end of the series capacitor, respectively. The second end of the series capacitor is grounded. The second end of the bias inductor serves as the input terminal of the backscattering communication front-end 2.

[0091] In a preferred embodiment, the backscattering communication front-end 2 further includes a reference state capacitor, a reference state microstrip transmission line, and an RF switch. The RF switch is disposed between the reference state microstrip transmission line, the positive terminal of the varactor diode, and the second terminal of the third microstrip transmission line. The control terminal of the RF switch serves as the control terminal of the backscattering communication front-end 2, used to connect the reference state microstrip transmission line to the second terminal of the third microstrip transmission line according to the reference state control signal of the control logic module 4; and to connect the positive terminal of the varactor diode to the second terminal of the third microstrip transmission line according to the embedded state control signal of the control logic module 4. The first terminal of the reference state capacitor is grounded, and the second terminal of the reference state capacitor is connected to the first terminal of the reference state microstrip transmission line.

[0092] Specifically, the backscattering communication front-end 2 uses the CSI phase difference between the embedded state and the reference state to encode the voltage of the analog sensor 1. The reflection phase of the reference state is also determined by the backscattering communication front-end 2. For example, the reflection phase of the backscattering communication front-end 2 in the reference state is set to the phase corresponding to 0V in the embedded state. In this way, a 0° phase difference indicates that the analog voltage of the sensor 1 is 0V. The reference state circuit design, for example, switches the DC bias voltage of the varactor diode between the input voltage in the embedded state and 0V in the reference state. However, since the RF choke and capacitor together form the LC resonant circuit of the input voltage, there is a transient process when switching from 0V to the input voltage. This causes the voltage of the varactor diode to gradually stabilize instead of changing instantaneously. This transition process may last for more than 2 microseconds, which seriously affects the synchronization accuracy. To avoid this transient process and reduce the switching time, the backscattering communication front-end 2 in this embodiment adds an RF switch before the varactor diode. The RF switch can switch between the varactor diode branch and the constant phase branch, corresponding to the embedded state and the reference state, respectively. Common RF switches such as ADG918 / 919 have switching times of less than 10 nanoseconds and do not have transient processes.

[0093] The RF switch can be a single-pole double-throw switch, capable of switching between reference and embedded states. Its control signal is output by control logic module 4. After detecting the arrival of a data packet, it waits 36 microseconds before switching to the embedded branch, and then switches back to the reference branch after 4 microseconds. The clock of control logic module 4 is derived from a 20MHz clock, which is not specifically limited in this application.

[0094] In a preferred embodiment, the backscattering communication front-end 2 further includes a first impedance matching module 21. The first end of the first impedance matching module 21 is connected to the second end of the first microstrip transmission line. The second end of the first impedance matching module 21 serves as the output end of the backscattering communication front-end 2, used to match the impedance of the backscattering communication front-end 2 with that of the first antenna 3.

[0095] In addition, the first impedance matching module 21 may include a first impedance inductor and a first impedance matching capacitor; the first end and the second end of the first impedance matching inductor are respectively connected to the first antenna 3 and the first end of the first impedance matching capacitor, and the second end of the first impedance matching capacitor is grounded.

[0096] In a preferred embodiment, the packet detection and synchronization circuit 5 includes: an envelope detector 52, whose output is connected to the input of a comparator 51, for detecting the signal energy of a WiFi data packet emitted by a WiFi transmitter and outputting the signal energy of the WiFi data packet to the comparator 51; a comparator 51, whose output is the output of the packet detection and synchronization circuit 5, for outputting a first-level signal to the control logic module 4 when the signal energy of the WiFi data packet is greater than a preset signal energy threshold, and outputting a second-level signal to the control logic module 4 when the signal energy of the WiFi data packet is not greater than the preset signal energy threshold, wherein the first-level signal and the second-level signal are opposite; and a second impedance matching module 53, whose output is connected to the input of the envelope detector 52 and whose input is the input of the packet detection and synchronization circuit 5, for matching the impedance of the packet detection and synchronization circuit 5 with that of the second antenna 6.

[0097] To locate the HT-ELTF symbol, in this embodiment, since the backscattering communication front-end 2 only enters the embedded state when the HT-ELTF symbol in the WiFi data packet enters the embedded state, it needs to be synchronized with this part to determine the switching time. This embodiment adds an envelope detector 52 to the backscattering communication front-end 2 and cascades a comparator 51 to achieve this. When the detector detects the packet header, it uses a clock to locate the HT-ELTF symbol, for example, waiting 36 microseconds, switching to the embedded state for 4 microseconds, and then switching back. This part requires a 4MHz clock for timing, which is provided to the comparator 51. This clock can be derived from an existing 20MHz clock.

[0098] In addition, comparator 51 can be clocked; envelope detector 52 may include envelope detector capacitor and envelope detector diode; second impedance matching module 53 may include second impedance inductor and second impedance matching capacitor; the first terminal of envelope detector capacitor is connected to the input terminal of comparator 51 and the cathode of envelope detector diode respectively, the second terminal of envelope detector capacitor is grounded, the anode of envelope detector diode is connected to the first terminal of second impedance matching inductor and the first terminal of second impedance matching capacitor respectively, the second terminal of second impedance matching capacitor is grounded, and the second terminal of second impedance matching inductor is connected to second antenna 6.

[0099] The first level signal can be a high level signal, and the second level signal can be a low level signal; this invention does not impose any particular limitation on these signals.

[0100] The backscattering communication front-end 2, data packet detection and synchronization circuit 5, and control logic module 4 of the present invention can be, but are not limited to, implemented in a PCB on an FR4 substrate.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A backscattering analog communication method based on WiFi channel information, characterized in that, include: Acquire analog voltage data from the sensor; The analog voltage data of the sensor is converted into phase data of the reflected radio frequency signal; The phase data of the reflected radio frequency signal is embedded into the WiFi data packet sent by the WiFi transmitter to obtain a WiFi data packet with the phase data of the reflected radio frequency signal embedded, so that the WiFi receiver can decode the WiFi data packet with the phase data of the reflected radio frequency signal embedded to obtain the analog voltage data of the sensor.

2. The backscattering analog communication method based on WiFi channel information according to claim 1, characterized in that, The step of converting the analog voltage data of the sensor into phase data of the reflected radio frequency signal includes: Establish a backscatter communication front-end; The reflection coefficient of the backscattering communication front end is determined based on the analog voltage data of the sensor; The phase data of the reflected radio frequency signal is determined based on the reflection coefficient of the backscattering communication front end.

3. The backscattering analog communication method based on WiFi channel information according to claim 1, characterized in that, The step of embedding the phase data of the reflected radio frequency signal into the WiFi data packet sent by the WiFi transmitter includes: In the embedded state, the phase data of the reflected radio frequency signal is embedded into the channel embedding state information of the WiFi data packet that supports additional space detection transmitted by the transmitting end; In the reference state, the reference phase data of the preset reflected radio frequency signal is embedded into the channel reference state information of the WiFi data packet that supports additional space detection transmitted by the transmitting end.

4. The backscattering analog communication method based on WiFi channel information according to claim 3, characterized in that, The WiFi receiver decodes the WiFi data packets containing the phase data of the embedded reflected radio frequency signal to obtain the analog voltage data of the sensor, including: The WiFi receiver obtains the phase data of the reflected radio frequency signal based on the phase difference between the channel embedding state information of the WiFi data packet and the channel reference state information of the WiFi data packet. The phase data of the reflected radio frequency signal is converted into analog voltage data of the sensor.

5. The backscattering analog communication method based on WiFi channel information according to any one of claims 1 to 4, characterized in that, Also includes: The frequency of the WiFi data packet with embedded reflected radio frequency signal is offset by a preset frequency, which is the frequency of the WiFi channel, so that the WiFi receiver receives the WiFi data packet with embedded reflected radio frequency signal on the channel corresponding to the preset frequency offset.

6. A backscattering device, characterized in that, include: Sensors used to provide analog voltage data; The input terminal is connected to the output terminal of the sensor, and the output terminal is connected to the first antenna. The backscattering communication front-end adopts the backscattering analog communication method based on WiFi channel information as described in any one of claims 1 to 5. The input terminal is connected to the second antenna, and the output terminal is connected to the input terminal of the control logic module. The data packet detection and synchronization circuit is used to detect the embedding position of the phase data of the reflected radio frequency signal in the WiFi data packet that embeds the phase data of the reflected radio frequency signal, and output a synchronization communication status signal to the control logic module according to the embedding position. The control logic module, whose output is connected to the control terminal of the backscattering communication front end, is used to output a communication status control signal to the backscattering communication front end according to the synchronization communication status signal, so as to control the communication status of the backscattering communication front end. The communication status of the backscattering communication front end includes an embedded state and a reference state.

7. The backscattering device according to claim 6, characterized in that, The backscattering communication front end includes a first microstrip transmission line, a second microstrip transmission line, a third microstrip transmission line, a varactor diode, a bias inductor, and a series capacitor. In the embedded state, the first end of the first microstrip transmission line is connected to the first end of the second microstrip transmission line and the first end of the third microstrip transmission line, respectively. The second end of the second microstrip transmission line is grounded. The second end of the third microstrip transmission line is connected to the positive terminal of the varactor diode. The negative terminal of the varactor diode is connected to the first end of the bias inductor and the first end of the series capacitor, respectively. The second end of the series capacitor is grounded. The second end of the bias inductor serves as the input terminal of the backscattering communication front end.

8. The backscattering device according to claim 7, characterized in that, The backscattering communication front end also includes a reference state capacitor, a reference state microstrip transmission line, and a radio frequency switch; The radio frequency switch is disposed between the reference state microstrip transmission line, the positive terminal of the varactor diode, and the second terminal of the third microstrip transmission line. The control terminal of the radio frequency switch serves as the control terminal of the backscattering communication front end, and is used to connect the reference state microstrip transmission line and the second terminal of the third microstrip transmission line according to the reference state control signal of the control logic module; and to connect the positive terminal of the varactor diode and the second terminal of the third microstrip transmission line according to the embedded state control signal of the control logic module. The first terminal of the reference state capacitor is grounded, and the second terminal of the reference state capacitor is connected to the first terminal of the reference state microstrip transmission line.

9. The backscattering device according to claim 7, characterized in that, The backscattering communication front end further includes a first impedance matching module. The first end of the first impedance matching module is connected to the second end of the first microstrip transmission line. The second end of the first impedance matching module serves as the output end of the backscattering communication front end, used to match the impedance of the backscattering communication front end with that of the first antenna.

10. The backscattering device according to any one of claims 6 to 9, characterized in that, The data packet detection and synchronization circuit includes: An envelope detector connected to the input of a comparator is used to detect the signal energy of WiFi data packets emitted by a WiFi transmitter and output the signal energy of the WiFi data packets to the comparator. The comparator, whose output terminal serves as the output terminal of the data packet detection and synchronization circuit, is used to output a first-level signal to the control logic module when the signal energy of the WiFi data packet is greater than a preset signal energy threshold, and to output a second-level signal to the control logic module when the signal energy of the WiFi data packet is not greater than the preset signal energy threshold, wherein the first-level signal and the second-level signal are opposite. The output terminal is connected to the input terminal of the envelope detector. The input terminal serves as the second impedance matching module for the data packet detection and synchronization circuit, and is used to match the impedance of the data packet detection and synchronization circuit with that of the second antenna.

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