Dual-band wi-fi backscattering system and implementation method

Abstract

The application provides a dual-band WiFi backscattering system and an implementation method, comprising a dual-band ultra-low power consumption modulator and a dual-band tag data decoder; the dual-band ultra-low power consumption modulator adjusts the reflection coefficient of a radio frequency front end according to the load data of a tag, and carries the data on the incident WiFi signal; the dual-band tag data decoder restores the tag data by analyzing the reflected WiFi signal. The application realizes that the reflective tag supports WiFi dual-band at the same time, so that more excitation signals can be used to realize higher throughput, and the reliability of the reflective communication is improved by using almost no other devices working in the 5GHz frequency band except WiFi; meanwhile, the backscattering system has the characteristics of low power consumption, so as to guide the communication of a large number of Internet of Things devices and provide support for the development of the Internet of Things field.

Description

Technical Field

[0001] This invention relates to the field of Internet of Things (IoT) technology, and more specifically, to a dual-band WiFi backscattering system and its implementation method. Background Technology

[0002] The Internet of Things (IoT) has rapidly penetrated various industries, such as logistics warehousing, smart retail, and smart manufacturing. Backscatter communication technology has attracted widespread attention due to its microwatt-level power consumption caused by passively reflecting incident wireless signals. However, traditional RFID technology based on reflection communication requires customized dedicated transceivers, resulting in high deployment costs. WiFi backscatter can utilize widely deployed WiFi devices for data transmission, effectively reducing deployment complexity.

[0003] Patent document CN115499106B discloses a tag data decoding method based on a codeword conversion WiFi backscattering system. This method infers the tag's modulation type by calculating the reflected signal strength, thereby selecting the corresponding demodulation method at the receiver. Specifically, the receiver demodulates BPSK / QPSK signals by calculating the similarity between the reflected signal and the excitation signal, and demodulates 16QAM signals using differential summation or majority voting. Patent document CN115833925A discloses a backscattering processing method based on ambient OFDM WiFi. This method iteratively separates the tag's phase information from the received reflected signal, thereby correctly demodulating the tag data. Patent document CN116232443A discloses an ambient WiFi backscattering system and method based on a single commercial AP receiver. This method uses a single AP to infer all possible tag data and excitation signal data from the reflected signal, and then selects the correct tag data and excitation signal data from all candidate data using CRC checksum.

[0004] Although mainstream WiFi protocols such as 802.11n / ac / ax support dual-band operation at 2.4GHz and 5GHz, current WiFi backscatter communication systems can only operate in the 2.4GHz band. This is partly due to the large frequency gap between the two WiFi bands, making it difficult to find suitable commercial components for designing dual-band tags. Secondly, the 2.4GHz RF circuitry is easier to design than the 5GHz band. However, the limited bandwidth of the 2.4GHz band restricts its throughput, and the presence of numerous wireless devices such as Bluetooth, ZigBee, and wireless keyboards operating in the 2.4GHz band causes significant co-channel interference. Therefore, current WiFi devices generally operate in the cleaner 5GHz band. This situation means that WiFi backscatter tags operating only in 2.4GHz cannot obtain sufficient excitation signals to carry their data, and are also subject to severe co-channel interference, compromising communication quality. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a dual-band WiFi backscattering system and its implementation method.

[0006] The dual-band WiFi backscattering system provided by the present invention includes a dual-band ultra-low power modulator and a dual-band tag data decoder;

[0007] The dual-band ultra-low power modulator adjusts the reflection coefficient of the radio frequency front end according to the tag's load data, and loads the data onto the incident WiFi signal;

[0008] The dual-band tag data decoder reconstructs the tag data by analyzing the reflected WiFi signal.

[0009] Preferably, the dual-band ultra-low power modulator uses a pHEMT transistor with impedance regulated by bias voltage to change the reflection coefficient, thereby achieving the same constellation diagram for different operating frequency bands.

[0010] Preferably, the pHEMT transistor has different bias voltage-impedance transformation relationships at different operating frequencies, and the dual-band ultra-low power modulator switches to the corresponding bias voltage sequence according to the operating frequency band.

[0011] The bias voltage sequence is obtained through prior measurement, and the corresponding information is stored in the tag's memory. The bias voltage sequence remains unchanged for a certain operating frequency band.

[0012] The prior measurement refers to analyzing the electric field model of the reflected signal from the receiver's perspective, and matching the corresponding tag data components in the electric field model with the desired constellation diagram, thereby calculating the bias voltage corresponding to the required reflection coefficient.

[0013] The receiver perspective refers to the zero-shot receiver filtering out the static components in the received signal while retaining the changing dynamic components, which are caused by the reflection coefficient of the RF front-end due to the frequent switching of tags.

[0014] Preferably, after receiving the reflected signal, the dual-band tag data decoder searches for suitable amplitude and phase thresholds to demodulate the PAM symbols modulated by the tag.

[0015] Preferably, the selection of the amplitude threshold depends on the fact that the reflecting tag does not change the WiFi preamble, so that the high-energy preamble and the reflected PAM symbol have a fixed energy difference, and the receiver calculates the energy of the preamble to obtain a suitable amplitude threshold.

[0016] Preferably, the fixed energy difference means that the energy of the signal at the preamble is the same as that of symbols 0 and 3 in 4-PAM modulation, but 9.5 dB higher than that of symbols 1 and 2.

[0017] Preferably, the phase threshold needs to be set to π / 2 after eliminating the phase error in the received WiFi signal;

[0018] The phase error elimination is achieved by embedding a training sequence into the data to be transmitted using tags, and the receiver eliminates the phase error by observing the phase of the training sequence.

[0019] The dual-band WiFi backscattering system implementation method provided by the present invention includes:

[0020] Step S1: Map the bit stream to be transmitted on the tag to 4-PAM symbols, and select the bias voltage corresponding to PAM according to the current operating frequency band of the tag, thereby completing the modulation of the data;

[0021] Step S2: After detecting the WiFi signal, the WiFi receiver calculates the average energy of each OFDM symbol and the phase of the pilot signal for demodulating tag data.

[0022] Preferably, step S1 includes:

[0023] Step S1.1: Use a vector network analyzer to measure the reflection parameters of the pHEMT under different bias voltages and different operating frequency bands;

[0024] Step S1.2: Establish a reflection signal model and separate the dynamic components in the reflection signal;

[0025] Step S1.3: Map the 4-PAM constellation point trajectory to the dynamic component trajectory, and select the reflection coefficient sequence corresponding to the 4-PAM constellation point on the dynamic component trajectory;

[0026] Step S1.4: Find the bias voltage sequence corresponding to the reflection coefficient sequence obtained in step S1.3 in the reflection signal model, and store the bias voltage sequence in the tag's memory;

[0027] Step S1.5: The tag maps the data to be transmitted to 4-PAM symbols and selects the appropriate bias voltage to apply to the pHEMT transistor according to the operating frequency band;

[0028] Step S1.6: The tag needs to shift the reflected signal to another independent WiFi channel.

[0029] Preferably, step S2 includes:

[0030] Step S2.1: After the WiFi receiver detects the reflected WiFi signal based on the short training sequence in the WiFi frame, it uses the short training sequence to correct the frequency offset of the received signal.

[0031] Step S2.2: The WiFi receiver extracts long training data from the received signal to perform channel estimation, and uses the estimated channel information to equalize the channel;

[0032] Step S2.3: The WiFi receiver counts the energy of the preamble and calculates the amplitude threshold;

[0033] Step S2.4: The WiFi receiver uses the training sequence embedded in the tag to estimate the phase error of the first 16 OFDM symbols of the WiFi frame, and uses linear fitting to obtain the rate of change of the phase error over time, which is used to correct the phase error of all subsequent OFDM symbols.

[0034] Step S2.5: The WiFi receiver calculates the average phase of the pilot in each OFDM symbol;

[0035] Step S2.6: The decoder uses π / 2 as the phase threshold and the calculated amplitude threshold to demodulate the PAM symbols.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] This invention enables WiFi backscatter communication to utilize the excitation signals of both WiFi bands simultaneously, improving communication reliability while increasing throughput, thereby guiding the communication of a large number of IoT devices and providing support for the development of the IoT field. Attached Figure Description

[0038] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0039] Figure 1 This is a flowchart illustrating the operation of the dual-band WiFi backscattering system of the present invention.

[0040] Figure 2 Based on the principles of modulation and frequency shift;

[0041] Figure 3 The effect of reducing the bit error rate is shown in the diagram;

[0042] Figure 4 The effect of increasing throughput is shown in the diagram. Detailed Implementation

[0043] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0044] Example 1:

[0045] The dual-band WiFi backscattering system provided by the present invention includes a dual-band ultra-low power modulator and a dual-band tag data decoder;

[0046] The dual-band ultra-low power modulator adjusts the reflection coefficient of the radio frequency front end according to the tag's load data, and loads the data onto the incident WiFi signal;

[0047] The dual-band tag data decoder reconstructs the tag data by analyzing the reflected WiFi signal.

[0048] The dual-band ultra-low power modulator changes the reflection coefficient by using a pHEMT transistor with impedance regulated by bias voltage, thereby achieving the same constellation diagram for different operating frequency bands.

[0049] The pHEMT transistor has different bias voltage-impedance transformation relationships at different operating frequencies, and the dual-band ultra-low power modulator switches to the corresponding bias voltage sequence according to the operating frequency band.

[0050] The bias voltage sequence is obtained through prior measurement, and the corresponding information is stored in the tag's memory. The bias voltage sequence remains unchanged for a certain operating frequency band.

[0051] The prior measurement refers to analyzing the electric field model of the reflected signal from the receiver's perspective, and matching the corresponding tag data components in the electric field model with the desired constellation diagram, thereby calculating the bias voltage corresponding to the required reflection coefficient.

[0052] The receiver's perspective refers to the ability of a zero-shot receiver to filter out static components in the received signal while retaining dynamic components that are caused by the reflection coefficient of the RF front-end due to the frequent switching of tags.

[0053] The dual-band tag data decoder can receive reflected signals and find suitable amplitude and phase thresholds to demodulate the PAM symbols modulated by the tags.

[0054] The selection of the amplitude threshold depends on the fact that the reflecting tag does not change the WiFi preamble, so that the high-energy preamble and the reflected PAM symbol have a fixed energy difference. The receiver counts the energy of the preamble to obtain a suitable amplitude threshold.

[0055] The fixed energy difference refers to the fact that the energy of the signal at the preamble is the same as that of symbols 0 and 3 in 4-PAM modulation, but 9.5 dB higher than that of symbols 1 and 2.

[0056] The phase threshold needs to be set to π / 2 after eliminating the phase error in the received WiFi signal.

[0057] The phase error elimination is achieved by embedding a certain amount of training sequence into the data to be transmitted using tags, and the receiver eliminates the phase error by observing the phase of the training sequence.

[0058] like Figure 1 The specific implementation process includes:

[0059] Step S1: Map the bit stream to be transmitted on the tag to 4-PAM symbols, and select the bias voltage corresponding to PAM according to the current operating frequency band of the tag, thereby completing the modulation of the data;

[0060] Step S2: After detecting the WiFi signal, the WiFi receiver calculates the average energy of each OFDM symbol and the phase of the pilot signal for demodulating tag data.

[0061] Specifically, step S1 includes:

[0062] Step S1.1: Use a vector network analyzer to measure the reflection parameters of the pHEMT under different bias voltages and different operating frequency bands;

[0063] Step S1.2: Establish a reflection signal model and separate the dynamic components in the reflection signal;

[0064] Step S1.3: Map the 4-PAM constellation point trajectory to the dynamic component trajectory, and select the reflection coefficient sequence corresponding to the 4-PAM constellation point on the dynamic component trajectory;

[0065] Step S1.4: Find the bias voltage sequence corresponding to the reflection coefficient sequence obtained in step S1.3 in the reflection signal model, and store the bias voltage sequence in the tag's memory;

[0066] Step S1.5: The tag maps the data to be transmitted to 4-PAM symbols and selects the appropriate bias voltage to apply to the pHEMT transistor according to the operating frequency band;

[0067] Step S1.6: To avoid interference with the excitation signal, the tag needs to shift the reflected signal to another independent WiFi channel.

[0068] Specifically, step S2 includes:

[0069] Step S2.1: After the WiFi receiver detects the reflected WiFi signal based on the short training sequence in the WiFi frame, it uses the short training sequence to correct the frequency offset of the received signal.

[0070] Step S2.2: The WiFi receiver extracts long training data from the received signal to perform channel estimation, and uses the estimated channel information to equalize the channel;

[0071] Step S2.3: The WiFi receiver counts the energy of the preamble and calculates the amplitude threshold;

[0072] Step S2.4: The WiFi receiver uses the training sequence embedded in the tag to estimate the phase error of the first 16 OFDM symbols of the WiFi frame, and uses linear fitting to obtain the rate of change of the phase error over time, which is used to correct the phase error of all subsequent OFDM symbols.

[0073] Step S2.5: The WiFi receiver calculates the average phase of the pilot in each OFDM symbol;

[0074] Step S2.6: The decoder uses π / 2 as the phase threshold and the calculated amplitude threshold to demodulate the PAM symbols.

[0075] Example 2:

[0076] Example 2 is a preferred example of Example 1.

[0077] WiFi backscattering requires the tag to frequency-shift the reflected signal to a separate channel independent of the excitation signal to avoid self-interference. The tag's encoding and frequency-shifting process for the excitation signal is as follows:

[0078] Step S1: Assume the four symbols of 4-PAM are s1, s2, s3, and s4, and their corresponding bias voltages are v1, v2, v3, and v4, respectively. The energies of s1 and s4 are greater than those of s2 and s3; the symbols corresponding to s1 and s2 have the same phase and are out of phase with s3 and s4.

[0079] Step S2: Generate a control waveform, which is a peak-to-peak waveform with a variable reference voltage and a frequency of f. s Square wave.

[0080] Specifically, step S2 includes

[0081] Step S2.1: Set the frequency shift to f s When the tag transmits symbol s1, the tag generates an initial level of v1, followed by a level of v4, with a frequency of f. s A square wave controlled pHEMT transistor.

[0082] Step S2.2: Set the frequency shift to f s When the tag transmits symbol s2, the tag generates an initial voltage level of v2, followed by a voltage level of v3, with a frequency of f. s A square wave controlled pHEMT transistor.

[0083] Step S2.3: Set the frequency shift to f s When the tag transmits symbol s3, the tag generates an initial voltage level of v3, followed by a voltage level of v2, with a frequency of f. s A square wave controlled pHEMT transistor.

[0084] Step S2.4: Set the frequency shift to f s When the tag transmits symbol s4, the tag generates an initial level of v4, followed by a level of v1, with a frequency of f. s A square wave controlled pHEMT transistor.

[0085] This modulation process is as follows Figure 2 As shown, those skilled in the art can understand this embodiment as a more specific description of the modulator behavior in Embodiment 1.

[0086] Example 3:

[0087] Example 3 is a preferred example of Example 1.

[0088] The dual-band WiFi backscattering system described in this patent can achieve reliable reflective communication by utilizing the cleaner spectrum of the 5GHz band. Simultaneously, it improves throughput by leveraging the fact that the amount of data transmitted by a WiFi device in the 5GHz band within a certain timeframe far exceeds the amount transmitted in the 2.4GHz band. Its specific implementation process includes:

[0089] Step S1: Configure the reflective tag so that it operates in the 2.4GHz band for the first millisecond and in the 5GHz band for the remaining 9 milliseconds, with a period of 10 milliseconds.

[0090] Step S2: The tag uses the modulator to modulate its own payload data and transmits the data to the WiFi signal in the environment.

[0091] Step S3: The WiFi receiver demodulates the tag data based on the calculated phase threshold and amplitude threshold. The bit error rate and throughput results obtained at different distances are as follows: Figure 3 , Figure 4 As shown.

[0092] Figure 3 In this invention, the bit error rate of the dual-band WiFi backscattering system is 7 to 10 times lower than that of the traditional single-band WiFi backscattering system. Figure 4 The dual-band WiFi backscatter system described in this patent has a throughput that is 8 to 11 times higher than that of a traditional single-band WiFi backscatter system.

[0093] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0094] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A dual-band WiFi backscattering system, characterized in that, Includes a dual-band ultra-low power modulator and a dual-band tag data decoder; The dual-band ultra-low power modulator adjusts the reflection coefficient of the radio frequency front end according to the tag's load data, and loads the data onto the incident WiFi signal; The dual-band tag data decoder reconstructs the tag data by analyzing the reflected WiFi signal; The dual-band ultra-low power modulator changes the reflection coefficient by using a pHEMT transistor with impedance regulated by bias voltage, thereby achieving the same constellation diagram for different operating frequency bands. The pHEMT transistor has different bias voltage-impedance transformation relationships at different operating frequencies, and the dual-band ultra-low power modulator switches to the corresponding bias voltage sequence according to the operating frequency band. The bias voltage sequence is obtained through prior measurement, and the corresponding information is stored in the tag's memory. The bias voltage sequence remains unchanged for a certain operating frequency band. The prior measurement refers to analyzing the electric field model of the reflected signal from the receiver's perspective, and matching the corresponding tag data components in the electric field model with the desired constellation diagram, thereby calculating the bias voltage corresponding to the required reflection coefficient. The receiver perspective refers to the zero-shot receiver filtering out the static components in the received signal while retaining the changing dynamic components, which are caused by the reflection coefficient of the RF front-end due to the frequent switching of tags.

2. The dual-band WiFi backscattering system according to claim 1, characterized in that, After receiving the reflected signal, the dual-band tag data decoder searches for appropriate amplitude and phase thresholds to demodulate the PAM symbols modulated by the tag.

3. The dual-band WiFi backscattering system according to claim 2, characterized in that, The selection of the amplitude threshold depends on the fact that the reflecting tag does not change the WiFi preamble, so that the high-energy preamble and the reflected PAM symbol have a fixed energy difference. The receiver counts the energy of the preamble to obtain a suitable amplitude threshold.

4. The dual-band WiFi backscattering system according to claim 3, characterized in that, The fixed energy difference refers to the fact that the energy of the signal at the preamble is the same as that of symbols 0 and 3 in 4-PAM modulation, but 9.5 dB higher than that of symbols 1 and 2.

5. The dual-band WiFi backscattering system according to claim 4, characterized in that, The phase threshold needs to be set after eliminating phase errors in the received WiFi signal. ; The phase error elimination is achieved by embedding a training sequence into the data to be transmitted using tags, and the receiver eliminates the phase error by observing the phase of the training sequence.

6. A method for implementing a dual-band WiFi backscattering system, characterized in that, The dual-band WiFi backscattering system according to any one of claims 1-5 includes: Step S1: Map the bit stream to be transmitted on the tag to 4-PAM symbols, and select the bias voltage corresponding to PAM according to the current tag's operating frequency band to complete the modulation of the data; Step S2: After detecting the WiFi signal, the WiFi receiver calculates the average energy of each OFDM symbol and the phase of the pilot signal for demodulating tag data.

7. The implementation method of the dual-band WiFi backscattering system according to claim 6, characterized in that, Step S1 includes: Step S1.1: Use a vector network analyzer to measure the reflection parameters of the pHEMT under different bias voltages and different operating frequency bands; Step S1.2: Establish a reflection signal model and separate the dynamic components in the reflection signal; Step S1.3: Map the 4-PAM constellation point trajectory to the dynamic component trajectory, and select the reflection coefficient sequence corresponding to the 4-PAM constellation point on the dynamic component trajectory; Step S1.4: Find the bias voltage sequence corresponding to the reflection coefficient sequence obtained in step S1.3 in the reflection signal model, and store the bias voltage sequence in the tag's memory; Step S1.5: The tag maps the data to be transmitted to 4-PAM symbols and selects the appropriate bias voltage to apply to the pHEMT transistor according to the operating frequency band; Step S1.6: The tag needs to shift the reflected signal to another independent WiFi channel.

8. The implementation method of the dual-band WiFi backscattering system according to claim 6, characterized in that, Step S2 includes: Step S2.1: After the WiFi receiver detects the reflected WiFi signal based on the short training sequence in the WiFi frame, it uses the short training sequence to correct the frequency offset of the received signal. Step S2.2: The WiFi receiver extracts the long training sequence from the received signal to perform channel estimation, and uses the estimated channel information to equalize the channel; Step S2.3: The WiFi receiver counts the energy of the preamble and calculates the amplitude threshold; Step S2.4: The WiFi receiver uses the training sequence embedded in the tag to estimate the phase error of the first 16 OFDM symbols of the WiFi frame, and uses linear fitting to obtain the rate of change of the phase error over time, which is used to correct the phase error of all subsequent OFDM symbols. Step S2.5: The WiFi receiver calculates the average phase of the pilot in each OFDM symbol; Step S2.6: The decoder... The phase threshold is used, and the calculated amplitude threshold is used to demodulate the PAM symbols.

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