High-speed LoRa backscatter communication method and system

Abstract

The invention discloses a high-speed LoRa backscatter communication method and system, and belongs to the technical field of wireless communication. The LoRa backscatter communication system comprises a reflection label and a receiving end. And the reflection label receives and acquires the environment LoRa data packet, and receives the environment LoRa data packet through the antenna. And after the existence of the environment LoRa data packet is judged, a time-frequency joint modulation method is adopted to perform time domain segmentation on the long-period chirp symbols to generate short-period sub-chirp symbols, and multi-system frequency modulation is realized through a pointer dynamic addressing access wave table method, so that the throughput of the LoRa backscatter communication system is remarkably improved. A receiving end adopts a receiver with double antennas to respectively receive an environment LoRa data packet and a reflection LoRa data packet, and after synchronous error correction is carried out on the reflection LoRa data packet, a time domain bipolar correlation analysis and differential demodulation method is adopted to ensure effective demodulation of reflection information, so that the LoRa backscatter communication system has double advantages of long distance and high rate at the same time. And reliable transmission of LoRa long-distance communication is realized.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology and relates to a high-speed LoRa backscatter communication method and system. Background Technology

[0002] With the rapid development of IoT technology, the demand for low-power wide-area communication has surged. Environmental backscatter communication technology has attracted widespread attention due to its advantages of simple hardware structure design and low power consumption.

[0003] An environmental backscatter communication system consists of a reflective tag and a receiver. The reflective tag receives the ambient radio frequency (RF) signal, uses the ambient RF signal as a carrier, modulates the reflected information onto the ambient RF signal, and reflects the ambient RF signal, transforming it into a reflected RF signal. The receiver demodulates the reflected information by receiving the reflected RF signal carrying the reflected information, thus completing the transmission of the reflected information. Compared with traditional communication systems, the environmental backscatter system does not require the active generation of RF signals, and has advantages such as simple hardware structure and low power consumption, making it suitable for low-power IoT scenarios with massive device access.

[0004] Environmental backscatter communication can be categorized into different systems depending on the ambient radio frequency (RF) signal. LoRa environmental backscatter communication is backscatter communication under the condition that the ambient RF signal is a LoRa signal. Because LoRa is based on chirped linear spread spectrum (CSS) modulation technology, LoRa environmental backscatter communication features long-distance transmission and can be applied in wide-area low-power IoT transmission scenarios such as smart agriculture. However, due to the long chirped symbol period characteristic of LoRa, the data throughput of LoRa environmental backscatter communication is relatively low. Existing LoRa environmental backscatter communication systems all suffer from a performance trade-off between distance and data rate. LoRa environmental backscatter communication systems that can support long-distance transmission have low data rates (below 20kbps), while LoRa environmental backscatter communication systems that can support high-speed transmission have short communication distances (below 200m). This technological bottleneck restricts its application in wide-area real-time communication scenarios. Developing LoRa backscatter communication methods and systems that balance long distance and high data rate is of great significance for overcoming existing technological limitations and promoting the development of the Internet of Things, and will provide innovative solutions for the deployment of low-power devices in wide-area high-speed communication scenarios. Summary of the Invention

[0005] The purpose of this invention is to provide a high-speed LoRa backscatter communication method and system. By converting the modulation unit from long-period chirped symbols to short-period sub-chirped symbols and performing multi-level frequency modulation on the short-period sub-chirped symbols, multi-bit reflection information transmission is achieved in a short time, significantly improving the throughput of the LoRa backscatter communication system. Simultaneously, the receiving end employs a receiver with dual antennas to receive ambient LoRa data packets and reflected LoRa data packets respectively. After correcting the synchronization error of the reflected LoRa data packets, time-domain bipolar correlation analysis and differential demodulation are used to achieve reliable transmission of LoRa long-distance communication, enabling the LoRa backscatter communication system to possess the dual advantages of long distance and high speed.

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

[0007] This invention discloses a high-speed LoRa backscatter communication method and system. The LoRa backscatter communication system includes a reflective tag and a receiver. The reflective tag receives ambient LoRa data packets via an antenna, extracts the ambient signal envelope value, and inputs it to a voltage comparator. The voltage comparator makes a decision based on a preset decision threshold. If the preset decision threshold is continuously output with a high level for a preset duration, it is determined that an ambient LoRa data packet exists in the environment. After determining the presence of the ambient LoRa data packet, a time-frequency joint modulation scheme is used to divide the long-period chirped symbols in the time domain to generate short-period sub-chirped symbols. Using the short-period sub-chirped symbols as modulation units, multi-level frequency modulation is achieved through a pointer dynamic addressing access wavetable method. The reflection information is embedded into the ambient LoRa data packet to generate a reflected LoRa data packet carrying the reflection information, which is then reflected to the receiver. The receiver uses a receiver with dual antennas to receive both the ambient LoRa data packet and the reflected LoRa data packet, and performs synchronization error correction on the reflected LoRa data packet to align the decoding window of the reflected LoRa data packet with the payload data portion of the reflected LoRa data packet, ensuring effective demodulation of the reflection information. The frequency difference between adjacent short-period sub-chirped symbols in the aligned reflected LoRa data packets is extracted, and time-domain bipolar correlation analysis is performed in conjunction with the environmental LoRa data packets. Reflection information is obtained through differential demodulation, thereby realizing high-speed LoRa environmental backscatter communication.

[0008] This invention discloses a high-speed LoRa backscatter communication method, comprising the following steps:

[0009] Step 1: The reflective tag receives and acquires ambient LoRa data packets. The reflective tag receives ambient LoRa data packets through its antenna, extracts the ambient signal envelope value, and inputs it into a voltage comparator. The voltage comparator makes a decision based on a preset decision threshold. If the preset decision threshold is continuously output with a high level for a preset duration, it is determined that ambient LoRa data packets exist in the environment.

[0010] The reflective tag inputs the ambient LoRa data packets received by the antenna into an envelope detector for signal processing to extract the baseband envelope signal. The ambient signal envelope value output by the envelope detector is input to the positive input of a voltage comparator. A decision threshold voltage is set at the negative input of the voltage comparator. When the ambient signal envelope value continuously exceeds the decision threshold, the voltage comparator outputs a high level and triggers a timer to start counting. If the high level lasts for a preset duration, it is determined that ambient LoRa data packets are present in the environment.

[0011] Step 2: Using a time-frequency joint modulation scheme, the long-period chirped symbols are divided in the time domain to generate short-period sub-chirped symbols. The short-period sub-chirped symbols are used as modulation units. Multi-level frequency modulation is achieved by using a pointer dynamic addressing access wavetable method. The reflection information is embedded into the environmental LoRa data packet to generate a reflected LoRa data packet carrying the reflection information, and then reflected to the receiver.

[0012] After receiving the LoRa data packet from the environment, the reflection tag divides the LoRa data packet into multiple short-period sub-chirped symbols of equal length through time-domain segmentation. Using these short-period sub-chirped symbols as the basic modulation unit, and based on the frequency generated by the pointer dynamic addressing wavetable method, multi-level frequency modulation is applied to the short-period sub-chirped symbols. This maps the reflected information onto different carrier frequencies, causing the short-period sub-chirped symbols to exhibit different degrees of frequency shift according to the reflected information they carry. Let the period of the long-period chirped symbol in the environment be T, the bandwidth be Bw, and the initial frequency be F. The frequency of this long-period chirped symbol increases with time t at a rate of k. The long-period chirped symbol S... a (t) can be expressed as:

[0013]

[0014] In the time-frequency joint modulation scheme, if each long-period chirp symbol in the payload of the environmental LoRa data packet is divided into four short-period sub-chirp symbols, and 4FSK frequency modulation is applied to the short-period sub-chirp symbols, then each short-period sub-chirp symbol carries 2 (log24) bits of reflection information. When the reflection information carried by the four short-period sub-chirp symbols is 00, 01, 10, and 11 respectively, the pointer dynamic addressing access to the wavetable needs to generate four frequencies: f1, f2, f3, and f4. These four frequencies are then multiplied sequentially by the four short-period sub-chirp symbols to produce a frequency offset, resulting in the reflection chirp symbol S carrying the reflection information. b (t) is:

[0015]

[0016] The receiver receives short-period sub-chirped symbols with different frequency offsets. It can demodulate the reflection information based on the frequency offset of the short-period sub-chirped symbols relative to the long-period chirped symbols in the environment, thereby realizing communication of the reflection information.

[0017] The pointer dynamic addressing wavetable access method generates the frequencies reflecting the reflection information. N digital sine wave sampling points are pre-stored in the waveform memory of the reflection tag. In the time-frequency joint modulation scheme, the pointer dynamically addresses the addresses of the digital sine wave sampling points stored in the waveform memory. By adjusting the pointer step frequency and pointer step size, multiple frequencies can be generated with low power consumption. Specifically, the pointer dynamic addressing access strategy is as follows: the pointer moves forward to address based on the rising edge frequency of the reference clock. The number of points the pointer moves each time is adaptively adjusted according to the required frequency. After the pointer address traverses the waveform memory, it returns to the starting address of the waveform memory to begin traversal again. The pointer addressing frequency is clk, and the number of points moved each time is len. After N / clk / len seconds, a single sine wave traversal is achieved, generating a frequency of len*clk / N. The carrier frequency generation is positively correlated with the pointer addressing frequency (i.e., pointer step frequency) clk and the number of address movement points (i.e., pointer step size) len. To generate a higher carrier frequency, the pointer step frequency is increased or the pointer step size is increased; to generate a lower carrier frequency, the pointer step frequency is decreased or the pointer is made to point to the same address during multiple consecutive accesses. For example, if the required carrier frequency is 2*len*clk / (N), a pointer step frequency of 2*clk is used or len = 2 is made; if the required carrier frequency is len*clk / (2*N), a pointer step frequency of clk / 2 is used or the pointer moves only one address every two clock triggers. To meet the low-power backscattering requirement, the waveform memory can store only the first quarter wavelength of the sine wave. Since the sine wave is centrally symmetrical, the complete sine wave can be reconstructed by cyclically traversing the pointer using this central symmetry characteristic.

[0018] Step 3: The receiving end receives environmental LoRa data packets and reflected LoRa data packets.

[0019] Step 4: Correct the synchronization error of the reflected LoRa data packets to align the decoding window of the reflected LoRa data packets with the payload data portion of the reflected LoRa data packets, ensuring effective demodulation of the reflected information.

[0020] The receiver receives reflected LoRa data packets and extracts the preamble portion. When there is no synchronization error, the receiver's decoding window is aligned with the preamble portion of the reflected LoRa data packet. The data within the decoding window is processed using the standard chirped signal S. d (t) is matched and multiplied to obtain a single-tone signal S reflecting the initial frequency. p (t). Standard chirped signal S d (t) is:

[0021]

[0022] The LoRaWAN communication protocol specifies that the preamble of reflected LoRa data packets is a long-period chirped symbol with an initial frequency of 0, i.e., in the S... a The initial frequency F in (t) is 0, therefore S p (t) is represented as:

[0023]

[0024] When synchronization errors exist, the frequency deviation of the reflected LoRa data packets will occur because the decoding window start point is misaligned with the reflected LoRa data packet start point. Let the sampling points between the decoding window start point and the reflected LoRa data packet start point be n sampling points, and the sampling rate be f. s The interval between the decoding window start point and the start point of the reflected LoRa data packet is Δt = n / fs. Let the frequency deviation caused by the interval be Δf. In a reflected LoRa data packet with a frequency change rate of k over time, the relationship between the interval Δt and the frequency deviation Δf is: Δt = (Δf*T) / Bw. When the frequency deviation Δf exists, S... p (t) is represented as:

[0025] S p (t)=e 2πjΔft

[0026] For S p (t) Perform a Fourier transform and detect the position of the spectral peak. Then, calculate the frequency deviation Δf caused by the synchronization error based on the offset between the peak position and the theoretical peak position. Derive the sampling point n between the decoding window start point and the reflected LoRa data packet start point from the relationship between the interval time Δt and the frequency deviation Δf. Move the decoding window according to the sampling point n to align it with the reflected LoRa data packet, thus completing the alignment of the decoding window with the reflected LoRa data packet and ensuring effective demodulation of the reflected information.

[0027] Step 5: Extract the frequency difference between adjacent short-period sub-chirped symbols in the aligned reflected LoRa data packets, perform time-domain bipolar correlation analysis with the environmental LoRa data packets, and obtain reflection information through differential demodulation to achieve high-speed LoRa environmental backscatter communication.

[0028] After aligning the reflected LoRa data packets, conjugate mixing between adjacent symbols is performed on the short-period sub-chirp symbols to generate a single-tone signal reflecting the frequency difference. According to step two, the short-period sub-chirp symbols carrying different reflection information have different frequency deviations; therefore, there is a frequency difference between adjacent short-period sub-chirp symbols. The short-period sub-chirp symbols carrying reflection information are:

[0029]

[0030] Let Δf ij Let be the frequency difference between the j-th short-period sub-chirp and the i-th sub-chirp. Then, by conjugating adjacent short-period sub-chirp symbols, three single-tone signals reflecting the frequency difference are obtained. The frequencies of the three single-tone signals are: Δf 21 =f2-f1,Δf 32 =f3-f2,Δf 43 =f4-f3. The single-tone signal reflecting the frequency difference between the j-th short-period sub-chirp and the i-th sub-chirp is called S. ij (t), i.e., Δf 21 ,Δf 32 ,Δf 43 Corresponding to S respectively 21 (t),S 32 (t),S 43 (t). These single-tone signals S, which reflect the frequency difference between adjacent short-period sub-chirp symbols. ij (t) Signal processing is performed using time-domain bipolar correlation analysis: In the first stage of processing, S ij (t) and a single-tone reference signal S with frequency f0 r (t) Perform the first-level time-domain correlation operation to obtain the time-domain correlation function R(τ), where τ is the value of S during the time-domain correlation function operation. r (t) relative to S ij (t) represents the time shift. r R(t) and R(τ) are expressed as follows:

[0031] S r (t)=e j2πf0t

[0032]

[0033] S ij (t) and S r The frequency difference of (t) will be mapped to the peak position L of the time-domain correlation peak, and the mapping relationship is as follows:

[0034] L=T(Δf ij -f0)

[0035] By detecting the time-domain correlation peak, the frequency difference between adjacent sub-chirped symbols can be determined and compensated, reconstructing the complete long-period chirped symbol. In the second-level processing, the complete long-period chirped symbol is correlated in the time domain with the corresponding symbol in the environmental LoRa data packet. Using the mapping relationship between the correlation peak value and the frequency difference, the correlation peak can be detected and the reflection information of the first sub-chirped symbol can be obtained. Since the frequency difference between adjacent sub-chirped symbols has been obtained in the first-level time-domain correlation processing, the reflection information carried by all sub-chirped symbols is derived sequentially through the differential modulation algorithm, realizing high-speed LoRa backscatter communication.

[0036] This invention also discloses a high-speed LoRa backscatter communication system for implementing a high-speed LoRa backscatter communication method. The high-speed LoRa backscatter communication system includes a reflective tag and a receiver. The reflective tag includes an environmental signal synchronization detection module, a microprocessor, and a reflective information transmission module. The receiver is a software-defined radio platform.

[0037] The environmental signal synchronization detection module is used to receive and acquire environmental LoRa data packets from the reflection tag in step one.

[0038] The microprocessor is a low-power microprocessor used to coordinate and control the environmental signal synchronization detection module in step one and the reflection information transmission module in step two. The microprocessor outputs control signals based on the indication signal from the environmental signal synchronization detection module, thus controlling the reflection information transmission module. When the indication signal is high, the control signal output by the microprocessor is also high, used to control the reflection information transmission module to enter the modulation state; conversely, when the indication signal is low, the control signal output by the microprocessor is also low, used to control the reflection information transmission module to enter the "stop modulation" state.

[0039] The reflection information transmission module is used to implement the time-frequency joint modulation scheme in step two. It divides the long-period chirped symbols in the time domain to generate short-period sub-chirped symbols, uses the short-period sub-chirped symbols as modulation units, and implements multi-level frequency modulation by accessing the wavetable through pointer dynamic addressing. It embeds the reflection information into the environmental LoRa data packet, generates a reflection LoRa data packet carrying the reflection information, and reflects it to the receiving end.

[0040] A software-defined radio platform is used to implement step three (receiving ambient LoRa data packets and reflected LoRa data packets), step four (correcting synchronization errors in reflected LoRa data packets to align the decoding window of the reflected LoRa data packets with the payload data portion of the reflected LoRa data packets, ensuring effective demodulation of the reflected information), and step five (extracting the frequency difference between adjacent short-period sub-chirped symbols in the aligned reflected LoRa data packets). Time-domain bipolar correlation analysis is performed on the ambient LoRa data packets, and reflection information is obtained through differential demodulation, achieving high-speed LoRa ambient backscatter communication. The center receiving frequency of the first receiving antenna of the software-defined radio platform is set as the transmission center frequency of the ambient LoRa data packets for receiving them; the center receiving frequency of the second receiving antenna of the software-defined radio platform is set as the center frequency of the frequency-shifted reflected LoRa data packets for receiving them.

[0041] Beneficial effects:

[0042] 1. This invention discloses a high-speed LoRa backscatter communication method and system, which uses environmental LoRa data packets as carriers for high-speed backscatter communication. The reflection tag uses time-frequency joint modulation to segment long-period chirped symbols in the time domain and performs multi-level frequency modulation on the segmented short-period sub-chirps, mapping the reflected information to different initial frequencies of the short-period sub-chirps to achieve information transmission. The receiving end uses two-stage time-domain correlation and peak detection to achieve frequency compensation and reconstruction decoding of the long-period chirped symbols, successfully extracting the reflected information, thus realizing high-speed LoRa long-distance backscatter communication.

[0043] 2. The high-speed LoRa backscatter communication method and system disclosed in this invention, during the embedding of reflection information at the reflective tag end, segments the long-period chirped symbols based on the concept of time-division multiplexing and modulates the segmented short-period sub-chirped symbols. Compared with traditional LoRa backscatter communication schemes, the time-frequency joint modulation method reduces the modulation unit from long-period chirped symbols to short-period sub-chirped symbols, significantly improving the transmission rate of tag information, and is more suitable for applications requiring high-speed wide-area communication, such as smart agriculture and forest fire prevention.

[0044] 3. The high-speed LoRa backscatter communication method and system disclosed in this invention employs a time-domain two-stage correlation analysis decoding method at the receiving end. It obtains the frequency difference between adjacent short-period sub-chirped symbols through time-domain correlation, achieving long-period chirped symbol reconstruction. A second time-domain correlation is performed between the reconstructed symbols and the ambient LoRa symbols, and the tag information is demodulated based on the peak position of the correlation result. Because noise cancels out during weighted accumulation in the time-domain correlation process, the correlation curve between the reconstructed symbols and the ambient LoRa symbols is smoother, resulting in better noise immunity. Therefore, this invention maintains good noise immunity and robustness even under high-noise conditions, supporting high-speed reliable reflection information transmission over long distances.

[0045] 4. This invention discloses a high-speed LoRa backscatter communication method and system for achieving low-power environmental backscatter communication. The tag end of this system only needs to control the radio frequency switch via a microprocessor to achieve the environmental LoRa data packet reception function in step one and the time-domain segmentation function in the time-frequency joint modulation method in step two. Simultaneously, in the time-frequency joint modulation method in step two, this system generates the required frequency through a pointer dynamic addressing wavetable access method. Compared to the traditional backscatter communication system that uses a phase-locked loop to generate the frequency, the pointer dynamic addressing wavetable access method only needs to adjust the pointer addressing step frequency and step size to complete the fine-grained frequency generation, greatly reducing the power consumption required by the time-frequency joint modulation method. All devices in the tag end of this system adopt a low-power design, possessing the advantages of simple system structure, low complexity, and low energy consumption. Attached Figure Description

[0046] Figure 1 This is a flowchart of the high-speed LoRa backscatter communication method disclosed in this invention.

[0047] Figure 2 This is a schematic diagram of a traditional LoRa environment backscatter communication system that uses long-period chirped symbols as the modulation unit.

[0048] Figure 3 This is a schematic diagram of the high-speed LoRa backscatter communication method and the transmission of reflective tag information.

[0049] Figure 4 This is a schematic diagram of a high-speed LoRa backscatter communication method and the demodulation of reflected information at the receiver.

[0050] Figure 5 This is a diagram of the high-speed LoRa backscatter communication method and system architecture disclosed in this invention. Detailed Implementation

[0051] The present invention will be fully described below with reference to the accompanying drawings and specific embodiments. The embodiments are intended to clearly demonstrate the technical implementation of the present invention and help to understand the core innovations of this solution. It should be noted that these embodiments are merely illustrative examples of the technical solution and do not constitute a limitation on the scope of protection of the present invention. Furthermore, this document will systematically describe the key technical problems solved by the present invention and the significant progress achieved compared to the prior art.

[0052] This embodiment uses a software-defined radio platform to generate environmental LoRa data packets conforming to the LoRaWAN communication protocol as the environmental excitation source. The transmission center frequency of the environmental LoRa data packets is set to 433MHz, bandwidth to 500kHz, spreading factor to 9, and transmit power to 20dBm. The reflecting tag uses an omnidirectional antenna with a gain of 5dB, and the reflecting tag performs a 1MHz fundamental frequency shift on the environmental LoRa data packets. This embodiment uses the software-defined radio platform as the receiver. The first receiving antenna of the software-defined radio platform receives the environmental LoRa data packets at a center frequency of 433MHz and bandwidth to 500kHz. The second receiving antenna of the software-defined radio platform receives the reflected LoRa data packets at a center frequency of 434MHz and bandwidth to 1000kHz.

[0053] The specific implementation steps of the high-speed LoRa backscatter communication method and system designed using environmental LoRa signals generated by software radio are as follows:

[0054] like Figure 1 As shown in the figure, the high-speed LoRa backscatter communication method disclosed in this embodiment is implemented in the following specific steps:

[0055] Step 1: The reflective tag receives and acquires ambient LoRa data packets. The reflective tag receives ambient LoRa data packets through its antenna, extracts the ambient signal envelope value, and inputs it into a voltage comparator. The voltage comparator makes a decision based on the ambient signal envelope value. If the dynamic decision threshold is continuously outputting a high level for a preset duration, it is determined that ambient LoRa data packets exist in the environment.

[0056] Step 1.1: Extract the environmental signal envelope from the reflection tag and input the envelope signal into the voltage comparator.

[0057] Step 1.2: Dynamically adjust the appropriate voltage comparator reference voltage to achieve reliable detection of ambient LoRa data packets. In a no-signal environment, adjust the reference voltage slightly higher than the output noise floor of the envelope detector; when ambient LoRa data packets are present, the reference voltage is lower than the envelope voltage value, and the voltage comparator outputs a high level; if the voltage comparator outputs a high level for a duration exceeding a preset duration, it is determined that ambient LoRa data packets are present in the current environment.

[0058] Step 1.3: If LoRa data packets are detected in the environment, proceed to the next step; otherwise, continue detecting.

[0059] Step 2: Using a time-frequency joint modulation scheme, the long-period chirped symbols are divided in the time domain to generate short-period sub-chirped symbols. The short-period sub-chirped symbols are used as modulation units. Multi-level frequency modulation is achieved by using a pointer dynamic addressing access wavetable method. The reflection information is embedded into the environmental LoRa data packet to generate a reflected LoRa data packet carrying the reflection information, and then reflected to the receiver.

[0060] Step 2.1: Perform time-domain segmentation on the LoRa data packets in the environment to generate several short-period sub-chirped symbols.

[0061] Step 2.2: Using the short-period sub-chirp symbols as the basic modulation unit, the reflected information is mapped to different carrier frequencies through multi-level frequency modulation;

[0062] Step 2.3: When generating the carrier frequency, the pre-stored waveform memory in the chip is accessed using pointer addressing, and the step frequency and step size of the pointer accessing the waveform memory are dynamically adjusted to generate the target modulation frequency.

[0063] First, the reference waveform is pre-stored in the waveform memory of the chip. When modulation begins, the pointer dynamically addresses the waveform memory address to achieve low-power frequency synthesis.

[0064] The specific reference waveform selection strategy is as follows: the reference waveform is a set of N sine wave sampling points. The set of N sampling points is stored in the waveform memory.

[0065] The specific pointer dynamic addressing strategy is as follows: the pointer moves forward to address based on the rising edge frequency of the reference clock. The number of points the pointer moves each time is adaptively adjusted according to the required frequency. After the pointer address traverses the waveform memory, it returns to the starting address of the waveform memory to start traversing again. The pointer addressing frequency is clk, and the number of points moved each time is len. A single sine wave traversal is achieved after N / clk / len seconds, generating a frequency of len*clk / N. That is, the carrier frequency generation is positively correlated with the pointer step frequency clk and the pointer step size len. If a higher frequency carrier frequency needs to be generated, the pointer step frequency is increased or the pointer step size is increased; if a lower frequency carrier frequency needs to be generated, the pointer step frequency is decreased or the pointer is made to point to the same address in multiple consecutive accesses. For example, if the required carrier frequency is 2*len*clk / (N), a pointer step frequency of 2*clk is used or len=2 is made; if the required carrier frequency is len*clk / (2*N), a pointer step frequency of clk / 2 is used or the pointer moves only one address every two clock triggers. To meet the low power consumption requirement of backscattering, the waveform memory can store only the first quarter wavelength of the sine wave. Since the sine wave is centrally symmetrical, the complete sine wave can be reconstructed by cyclically traversing the pointer using the central symmetry characteristic of the sine wave.

[0066] In this embodiment, the long-period chirped symbol with a period of 1.024 milliseconds is evenly divided into 4 segments in the time domain, and each short-period sub-chirped symbol has a period of 0.256 milliseconds. Each short-period sub-chirped symbol is modulated using 8FSK, enabling each short-period sub-chirped symbol to transmit 3 bits. Therefore, a single chirped symbol can transmit 12 bits of data under the high-speed LoRa backscatter communication method disclosed in this invention. Compared to the traditional LoRa backscatter communication method that uses long-period chirped symbols as the modulation unit, this method reduces the modulation unit from long-period chirped symbols to short-period sub-chirped symbols, significantly improving the transmission rate of the reflective tag information and meeting the requirements of high-speed wide-area communication applications.

[0067] The high-speed LoRa backscatter communication method disclosed in this invention achieves low-power, high-precision frequency synthesis by optimizing waveform storage strategies and pointer addressing mechanisms. Simultaneously, the combination of time-domain segmentation and multi-level modulation effectively solves the throughput limitation problem in traditional LoRa backscatter communication, meeting the high-speed wide-area communication needs of applications such as smart agriculture and industrial IoT.

[0068] Step 3: The receiving end receives environmental LoRa data packets and reflected LoRa data packets.

[0069] Step 3.1: The receiver's first receiving antenna receives the environmental LoRa data packets.

[0070] Step 3.2: The receiver's second receiving antenna receives the reflected LoRa data packet. To ensure the reflected LoRa data packet is completely received, the center receiving frequency of the receiver's second receiving antenna is set to the center frequency of the reflected LoRa data packet, and the receiving bandwidth is set to twice the bandwidth of the reflected LoRa data packet.

[0071] Step 4: Correct the synchronization error of the reflected LoRa data packets to align the decoding window of the reflected LoRa data packets with the payload data portion of the reflected LoRa data packets, ensuring effective demodulation of the reflected information.

[0072] Step 4.1: Initialize the sliding window. Set the sliding window length to the duration T of a complete long-period chirp symbol.

[0073] Step 4.2: Demodulate the signal within the window based on the standard LoRa chirped demodulation scheme and detect the frequency domain peak value.

[0074] Step 4.3: Establish the frequency offset-time offset conversion model described in the invention content section based on the LoRa symbol characteristics: Δt = (Δf*T) / Bw. Map the frequency offset to the number of time offset sampling points, and move the sliding window to achieve data packet window alignment.

[0075] Step 5: Extract the frequency difference between adjacent short-period sub-chirped symbols in the aligned reflected LoRa data packets, perform time-domain bipolar correlation analysis with the environmental LoRa data packets, and obtain reflection information through differential demodulation to achieve high-speed LoRa environmental backscatter communication.

[0076] Step 5.1: Starting with the first short-period chirped symbol, perform conjugate mixing operations on adjacent short-period chirped symbols sequentially to extract the frequency difference. In this embodiment, a complete long-period chirped symbol is divided into four short-period chirped symbols, and conjugate mixing is performed sequentially on the first and second, second and third, and third and fourth short-period chirped symbols. Specifically, the second symbol in the two short-period chirped symbols participating in the conjugate mixing undergoes a conjugate transformation, i.e., its real part remains unchanged, and its imaginary part is negated; then, it is multiplied point-by-point with the first short-period chirped symbol. Since the reflection information carried by the two symbols differs, a frequency difference exists. After conjugate mixing, the result is a single-tone signal with a frequency equal to the frequency difference between the two symbols.

[0077] Step 5.2: Perform first-level time-domain correlation processing on the single-tone signal described in Step 5.1 and a reference single-tone signal of known frequency. Specifically, multiply the single-tone signal and the reference signal point by point using a sliding window, and integrate and accumulate the product results within each window to obtain the correlation function on the time axis. The peak positions of the time-domain correlation correspond to a one-to-one mapping relationship between the frequency differences between the two signals.

[0078] Step 5.3: Detect the peak position of the time-domain correlation function and calculate the frequency difference accordingly to achieve frequency compensation. The frequency difference between adjacent short-period chirped symbols can be determined by peak position mapping. The frequency difference is the frequency offset of the second short-period chirped symbol relative to the first. Based on this frequency difference, frequency compensation is performed on the second short-period chirped symbol to make its frequency consistent with the first symbol, and the frequency difference between the two is recorded for subsequent step 5.5 for demodulation of reflection information.

[0079] Step 5.4: Perform a second-level time-domain correlation between the frequency-compensated reflected signal and the ambient signal received by the first receiving antenna at the receiver. The specific operation of the time-domain correlation is the same as in step 5.2. Detect the peak position of the time-domain correlation and determine the frequency difference between the ambient signal and the reflected signal based on the detected peak position.

[0080] Step 5.5: Demodulate the reflection information. The frequency difference between the two reflects the tag information carried by the reflected signal. Based on the frequency difference, the reflection information carried by the first short-period chirped symbol of the reflected signal can be determined. Combining the frequency differences between each adjacent short-period chirped symbol recorded in Step 5.3, the reflection information carried by each of the remaining short-period chirped symbols can be derived step by step, thus completing the demodulation process of the high-speed LoRa backscatter communication method and system.

[0081] The high-speed LoRa backscatter communication method and system disclosed in the above experiment include a reflective tag and a receiver. The reflective tag includes an environmental signal synchronization detection module and a reflective information transmission module. The receiver includes a software-defined radio wireless communication platform with dual antennas.

[0082] The environmental signal synchronization detection module includes an envelope detector and a voltage comparator, used to detect the presence of environmental LoRa data packets that can be used for the transmission of reflected tag information. In this example, the envelope detector and voltage comparator are the LT5534 from Analog Devices and the NCS2200 from Onsemi, respectively.

[0083] The microprocessor is a low-power microprocessor used to coordinate and control the environmental signal synchronization detection module in step one and the reflection information transmission module in step two. The microprocessor outputs control signals based on the indication signals output by the environmental signal synchronization detection module, thereby controlling the reflection information transmission module. In this embodiment, the microprocessor uses an AGLN250 FPGA from Igllo Nano.

[0084] The reflection information transmission module includes an RF switch, a waveform memory, and an omnidirectional antenna operating in the 433MHz band. It is used to implement step two, dynamically addressing the wavetable via pointers to perform time-frequency joint modulation on the environmental LoRa data packets. Specifically, the information to be transmitted is assigned to different short-period sub-chirps, and each short-period sub-chirp is mapped to a different frequency. The wavetable is then dynamically addressed via pointers to generate the modulation frequency corresponding to the short-period sub-chirp. In this embodiment, the reflection information transmission module consists of a ZIISOR TX433-JKD-20P RF antenna connected to an ANALOG DEVICES ADG902 RF switch, and the waveform memory is a read-only core built into an Igllo Nano AGLN250 FPGA.

[0085] The receiving end is a software-defined radio platform with dual antennas, used to implement step three (receiving ambient LoRa data packets and reflected LoRa data packets), step four (correcting synchronization errors in the reflected LoRa data packets), and finally step five (decoding reflected information from the ambient LoRa data packets and reflected LoRa data packets), thus realizing a high-speed LoRa backscatter communication method and system. In this embodiment, the receiving end is the Ettus software-defined radio NI 2920.

[0086] The above description is merely a preferred embodiment of the present invention and does not constitute a limitation on the scope of protection of the present invention. For those skilled in the art, various equivalent substitutions or modifications can be made without departing from the principles and essence of the present invention. All obvious changes made based on the concept of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-speed LoRa backscatter communication method, characterized in that: The reflective tag receives ambient LoRa data packets via its antenna, extracts the ambient signal envelope value, and inputs it to a voltage comparator. The voltage comparator makes a decision based on a preset threshold. If the preset threshold is continuously output with a high level for a preset duration, it is determined that an ambient LoRa data packet exists in the environment. After determining the presence of the ambient LoRa data packet, a time-frequency joint modulation scheme is used to divide the long-period chirped symbol in the time domain to generate a short-period sub-chirped symbol. The short-period sub-chirped symbol is used as the modulation unit, and multi-level frequency modulation is achieved through a pointer dynamic addressing wavetable access method. The reflection information is then embedded into the ambient LoRa data packet. The system generates a reflected LoRa data packet carrying reflection information and reflects it to the receiver. The receiver uses a dual-antenna receiver to receive both the ambient LoRa data packet and the reflected LoRa data packet. It also corrects the synchronization error of the reflected LoRa data packet to align the decoding window of the reflected LoRa data packet with the payload data portion of the reflected LoRa data packet, ensuring effective demodulation of the reflection information. The frequency difference between adjacent short-period sub-chirped symbols in the aligned reflected LoRa data packet is extracted and combined with the ambient LoRa data packet for time-domain bipolar correlation analysis. The reflection information is obtained through differential demodulation, realizing high-speed LoRa ambient backscatter communication.

2. The high-speed LoRa backscatter communication method as described in claim 1, characterized in that: Includes the following steps: Step 1: The reflective tag receives and acquires ambient LoRa data packets; the reflective tag receives ambient LoRa data packets through its antenna, extracts the ambient signal envelope value and inputs it into a voltage comparator. The voltage comparator makes a decision on the ambient signal envelope value based on a preset decision threshold. If the preset decision threshold is continuously outputting a high level for a preset duration, it is determined that ambient LoRa data packets exist in the environment. Step 2: Using a time-frequency joint modulation scheme, the long-period chirped symbols are divided in the time domain to generate short-period sub-chirped symbols. The short-period sub-chirped symbols are used as modulation units. Multi-level frequency modulation is achieved by using a pointer dynamic addressing method to access the wavetable. The reflection information is embedded into the environmental LoRa data packet to generate a reflected LoRa data packet carrying the reflection information, and then reflected to the receiver. Step 3: The receiving end receives environmental LoRa data packets and reflected LoRa data packets; Step 4: Correct the synchronization error of the reflected LoRa data packets to align the decoding window of the reflected LoRa data packets with the payload data portion of the reflected LoRa data packets, ensuring effective demodulation of the reflected information; Step 5: Extract the frequency difference between adjacent short-period sub-chirped symbols in the aligned reflected LoRa data packets, perform time-domain bipolar correlation analysis with the environmental LoRa data packets, and obtain reflection information through differential demodulation to achieve high-speed LoRa environmental backscatter communication.

3. The high-speed LoRa backscatter communication method as described in claim 2, characterized in that: In step one, The reflective tag inputs the ambient LoRa data packets received by the antenna into an envelope detector for signal processing to extract the baseband envelope signal. The ambient signal envelope value output by the envelope detector is input to the positive input of a voltage comparator. A decision threshold voltage is set at the negative input of the voltage comparator. When the ambient signal envelope value continuously exceeds the decision threshold, the voltage comparator outputs a high level and triggers a timer to start counting. If the high level lasts for a preset duration, it is determined that an ambient LoRa data packet exists in the environment.

4. The high-speed LoRa backscatter communication method as described in claim 3, characterized in that: In step two, After receiving the LoRa data packet from the environment, the reflection tag divides the LoRa data packet into multiple short-period sub-chirped symbols of equal length through time-domain segmentation. Using these short-period sub-chirped symbols as basic modulation units, and based on frequencies generated by the pointer dynamic addressing wavetable access method, multi-level frequency modulation is applied to the short-period sub-chirped symbols. This maps the reflected information onto different carrier frequencies, causing the short-period sub-chirped symbols to exhibit different degrees of frequency shift according to the reflected information they carry. Let the period of the long-period chirped symbol in the environment be T, the bandwidth be Bw, and the initial frequency be F. The frequency of this long-period chirped symbol increases with time t at a rate of k. The long-period chirped symbol S... a (t) can be expressed as: In the time-frequency joint modulation scheme, if each long-period chirp symbol in the payload of the environmental LoRa data packet is divided into four short-period sub-chirp symbols, and 4FSK frequency modulation is applied to the short-period sub-chirp symbols, each short-period sub-chirp symbol carries 2 (log24) bits of reflection information; when the reflection information carried by the four short-period sub-chirp symbols are 00, 01, 10, and 11 respectively, the pointer dynamic addressing access to the wavetable needs to generate four frequencies: f1, f2, f3, and f4, and multiply these four frequencies sequentially by the four short-period sub-chirp symbols to produce a frequency offset, resulting in the reflection chirp symbol S carrying the reflection information. b (t) is: The receiver receives short-period sub-chirped symbols with different frequency offsets. It can demodulate the reflection information based on the frequency offset of the short-period sub-chirped symbols relative to the long-period chirped symbols in the environment, thereby realizing communication of the reflection information.

5. The high-speed LoRa backscatter communication method as described in claim 4, characterized in that: The pointer dynamic addressing wavetable access method generates the frequencies reflecting the reflection information. N digital sine wave sampling points are pre-stored in the waveform memory of the reflection tag. In the time-frequency joint modulation scheme, the pointer dynamically addresses the addresses of the digital sine wave sampling points in the waveform memory. By adjusting the pointer step frequency and pointer step size, multiple frequencies are generated with low power consumption. Specifically, the pointer dynamic addressing strategy is as follows: the pointer moves forward to address based on the rising edge frequency of the reference clock. The number of points the pointer moves each time is adaptively adjusted according to the required frequency. After the pointer address traverses the waveform memory, it returns to the starting address of the waveform memory to begin traversal. The pointer addressing frequency is clk, and the number of points moved each time is len. A single sine wave traversal is achieved after N / clk / len seconds, generating a frequency of len*clk / N. The frequency, i.e., the carrier frequency generation, is positively correlated with the pointer step frequency clk and the pointer step length len. If a higher frequency carrier frequency needs to be generated, the pointer step frequency is increased or the pointer step length is increased; if a lower frequency carrier frequency needs to be generated, the pointer step frequency is decreased or the pointer is made to point to the same address in multiple consecutive accesses; if the required carrier frequency is 2*len*clk / (N), the pointer step frequency of 2*clk is used or len=2 is made; if the required carrier frequency is len*clk / (2*N), the pointer step frequency of clk / 2 is used or the pointer is made to move only one address every two clock triggers; in order to meet the low power consumption requirement of backscattering, the waveform memory can only store the first quarter wavelength of the sine wave. Since the sine wave is centrally symmetrical, the complete sine wave can be reconstructed by cyclically traversing the pointer using the central symmetry characteristic of the sine wave.

6. The high-speed LoRa backscatter communication method as described in claim 5, characterized in that: In step four, The receiver receives reflected LoRa data packets and extracts the preamble portion of the reflected LoRa data packets. When there is no synchronization error, the receiver's decoding window is aligned with the preamble portion of the reflected LoRa data packets. The data within the decoding window is processed using the standard chirped signal S. d (t) is matched and multiplied to obtain a single-tone signal S reflecting the initial frequency. p (t); Standard chirped signal S d (t) is: The LoRaWAN communication protocol specifies that the preamble of reflected LoRa data packets is a long-period chirped symbol with an initial frequency of 0, i.e., in the S... a The initial frequency F in (t) is 0, therefore S p (t) is represented as: When synchronization error exists, the frequency deviation of the reflected LoRa data packet will occur because the decoding window start point is not aligned with the start point of the reflected LoRa data packet. Let the interval between the start of the decoding window and the start of the reflected LoRa data packet be n sampling points, and the sampling rate be f. s The interval between the decoding window start point and the start point of the reflected LoRa data packet is Δt = n / fs. Let the frequency deviation caused by the interval be Δf. In a reflected LoRa data packet with a frequency changing rate of k over time, the relationship between the interval Δt and the frequency deviation Δf is: Δt = (Δf*T) / Bw. When the frequency deviation Δf exists, S... p (t) is represented as: S p (t)=e 2πjΔft For S p (t) Perform Fourier transform and detect the position of the spectral peak. Then, calculate the frequency deviation Δf caused by the synchronization error based on the offset between the peak position and the theoretical frequency peak position. The sampling point n between the decoding window start point and the reflected LoRa data packet start point is derived from the relationship between the interval time Δt and the frequency deviation Δf. The decoding window is moved according to the sampling point n to align with the reflected LoRa data packet, thus completing the alignment of the decoding window with the reflected LoRa data packet and ensuring effective demodulation of the reflected information.

7. The high-speed LoRa backscatter communication method as described in claim 6, characterized in that: Step five is implemented as follows: After aligning the reflected LoRa data packets, conjugate mixing between adjacent symbols is performed on the short-period sub-chirp symbols to generate a single-tone signal reflecting the frequency difference. According to step two, the short-period sub-chirp symbols carrying different reflection information have different frequency deviations, therefore there is a frequency difference between adjacent short-period sub-chirp symbols. The short-period sub-chirp symbols carrying reflection information are: Let Δf ij Let be the frequency difference between the j-th short-period sub-chirp and the i-th sub-chirp. Then, by conjugating adjacent short-period sub-chirp symbols, three single-tone signals reflecting the frequency difference are obtained. The frequencies of the three single-tone signals are: Δf 21 =f2-f1,Δf 32 =f3-f2,Δf 43 =f4-f3; The single-tone signal reflecting the frequency difference between the j-th short-period sub-chirp and the i-th sub-chirp is called S. ij (t), i.e., Δf 21 ,Δf 32 ,Δf 43 Corresponding to S respectively 21 (t),S 32 (t),S 43 (t); these single-tone signals S reflecting the frequency difference between adjacent short-period sub-chirp symbols ij (t) Signal processing is performed using time-domain bipolar correlation analysis: In the first stage of processing, S ij (t) and a single-tone reference signal S with frequency f0 r (t) Perform the first-level time-domain correlation operation to obtain the time-domain correlation function R(τ), where τ is the value of S during the time-domain correlation function operation. r (t) relative to S ij (t) represents the time shift; S r R(t) and R(τ) are expressed as follows: S ij (t) and S r The frequency difference of (t) will be mapped to the peak position L of the time-domain correlation peak, and the mapping relationship is as follows: L=T(Δf ij -f0) By detecting the time-domain correlation peak, the frequency difference between adjacent sub-chirped symbols can be determined and compensated, thus reconstructing the complete long-period chirped symbol. In the second-level processing, the complete long-period chirped symbol is correlated with the corresponding symbol in the environmental LoRa data packet in the time domain. The correlation peak can be detected and the reflection information of the first sub-chirped symbol can be obtained by utilizing the mapping relationship between the correlation peak value and the frequency difference. Since the frequency difference between adjacent sub-chirped symbols has been obtained in the first-level time-domain correlation processing, the reflection information carried by all sub-chirped symbols is derived sequentially through the differential demodulation algorithm, realizing high-speed LoRa backscatter communication.

8. A high-speed LoRa backscatter communication system for implementing a high-speed LoRa backscatter communication method as described in claims 1, 2, 3, 4, 5, 6, or 7, characterized in that: It includes a reflective tag and a receiver; the reflective tag includes an environmental signal synchronization detection module, a microprocessor, and a reflective information transmission module; the receiver is a software-defined radio platform; The environmental signal synchronization detection module is used to receive and acquire environmental LoRa data packets from the reflection tag in step one. The microprocessor is a low-power microprocessor used to coordinate and control the environmental signal synchronization detection module in step one and the reflection information transmission module in step two. The microprocessor outputs a control signal based on the indication signal output by the environmental signal synchronization detection module to control the reflection information transmission module. When the indication signal is high, the control signal output by the microprocessor is also high, used to control the reflection information transmission module to enter the modulation state. When the indication signal is low, the control signal output by the microprocessor is also low, used to control the reflection information transmission module to enter the "stop modulation" state. The reflection information transmission module is used to implement the time-frequency joint modulation method in step two, which divides the long-period chirped symbols in the time domain to generate short-period sub-chirped symbols, uses the short-period sub-chirped symbols as modulation units, and implements multi-level frequency modulation by accessing the wavetable through pointer dynamic addressing. The reflection information is embedded into the environmental LoRa data packet, generating a reflection LoRa data packet carrying the reflection information, and reflecting it to the receiving end. A software-defined radio platform is used to implement step three: receiving ambient LoRa data packets and reflected LoRa data packets; step four: correcting synchronization errors in the reflected LoRa data packets to align the decoding window of the reflected LoRa data packets with the payload data portion of the reflected LoRa data packets, ensuring effective demodulation of the reflected information; and step five: extracting the frequency difference between adjacent short-period sub-chirped symbols in the aligned reflected LoRa data packets. Time-domain bipolar correlation analysis is performed in conjunction with the ambient LoRa data packets, and reflection information is obtained through differential demodulation to achieve high-speed LoRa ambient backscatter communication. The center receiving frequency of the first receiving antenna of the software-defined radio platform is set as the transmission center frequency of the ambient LoRa data packets for receiving them; the center receiving frequency of the second receiving antenna of the software-defined radio platform is set as the center frequency of the frequency-shifted reflected LoRa data packets for receiving them.

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