Collaboration-free passive internet of things communication system and method

Abstract

The application provides a kind of cooperation-free passive Internet of Things communication system and method, it is related to wireless communication technical field.The system includes environment transmitting end, backscattering label and receiving end.The application can reduce system deployment cost, reduce the dependence on special infrastructure and network side cooperation, improve the deployability of environment backscattering system in real non-management scene;It can reduce the power consumption and hardware complexity of label side, suitable for micro-power, low-cost, large-scale Internet of Things nodes;It can enhance the adaptability of system under unknown timing, unknown frequency and unknown payload conditions, improve communication reliability and data recovery ability;It can avoid occupying additional downlink trigger resources or service time slots, reduce the impact on original communication link;It has good protocol extensibility and engineering implementation feasibility at the same time, easy to popularize and apply in different commercial wireless scenarios.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and more particularly to environmental backscatter communication, low-power Internet of Things (IoT) communication, and commercial wireless signal multiplexing communication. Specifically, it relates to a cooperative passive IoT communication system and method. Background Technology

[0002] Compared to traditional active wireless IoT communication technologies, ambient backscatter communication technology communicates by reflecting existing electromagnetic waves in the environment, eliminating the need to actively generate carrier signals. This significantly reduces tag-side communication power consumption, making it suitable for large-scale, low-power IoT node deployments. However, existing ambient backscatter systems for commercial wireless networks heavily rely on the cooperation of the ambient transmitter. For example, some systems require the ambient transmitter to construct data packets according to specific rules to trigger tag wake-up or assist tag synchronization, or to use the receiver to trigger backscatter tags to perform backscatter at a specified time. Other methods require reserving dedicated downlink channels for downlink triggering, mandating the use of fixed-length preambles, or modifying the firmware or hardware of the ambient transmitter. First, when the ambient signal originates from a commercial wireless network, the transmitter's channel, frame transmission time, spreading factor, and payload are typically dynamically determined by the existing service. Third-party backscatter tags usually cannot require the ambient transmitter to modify protocols, reserve spectrum resources, send customized preambles, or provide closed-loop trigger signals. Second, these cooperation requirements affect the normal operation of existing commercial networks, increase the system deployment threshold, and limit its large-scale application in real-world unmanaged scenarios.

[0003] In backscatter communication scenarios in non-cooperative environments, the environmental transmitter freely sends data packets according to existing services, without providing backscatter tags with trigger scheduling, synchronization channels, control channels, or known payload content. Therefore, the backscatter tag cannot obtain the timing, frequency, and payload information of the environmental signal in advance, and the system mainly faces the following technical problems.

[0004] First, the unknown timing presents challenges for low-power symbol-level synchronization. Since the environmental transmitter does not provide triggering, scheduling, or synchronization channels, backscatter tags cannot know in advance the arrival time of environmental data packets, nor can they directly determine symbol boundaries and the start position of payload segments. If tags use continuous high-speed sampling, digital correlation, or digital demodulation for synchronization, power consumption will increase significantly, making it difficult to meet the energy consumption constraints of microwatt-level tags. If only simple energy detection is used, it is easily affected by noise and environmental signal fluctuations, making accurate symbol-level synchronization difficult to achieve. Therefore, how to complete environmental data packet detection and symbol-level synchronization under conditions of no transmitter triggering, no synchronization prior, and extremely low power consumption is the primary problem that needs to be solved in non-cooperative environment backscatter communication.

[0005] Second, the unknown frequency presents challenges for carrier adaptation. In commercial wireless networks, the transmitting end may randomly send data packets across multiple channels or a wide frequency band, and backscatter tags typically cannot know in advance the carrier frequency of the currently active state. If the tag uses an active phase-locked loop, wideband frequency scanning, or high-frequency synthesizer to track the carrier frequency of the environmental signal, it will significantly increase hardware complexity and power consumption, making it unsuitable for low-cost, low-power backscatter tags. Furthermore, carrier frequency variations can introduce frequency-dependent phase shifts during the analog correlation process, weakening the amplitude of the self-differential characteristic and even leading to synchronization failure. Therefore, how to achieve carrier frequency inference, phase compensation, and reflection modulation adaptation in a low-power manner under unknown frequency and wide frequency band environments is the second key problem facing this system.

[0006] Third, decoding difficulties arise from unknown payloads and strong main signal interference. Since non-cooperative systems cannot reserve clean spectrum resources or time windows, the tag-reflected signal is usually superimposed on the original environmental main signal, and its strength is much lower than the environmental main signal. Without knowing the payload content of the environmental data packets, the receiver needs to separate the weak backscattered signal from the strong main signal and unknown payload interference. If the main signal exhibits payload-related phase changes, frequency jumps, or hardware transients, traditional interference cancellation methods based on smooth phase models are prone to large reconstruction errors, causing the residual main signal to mask the tag signal. Therefore, how to reliably separate and decode the weak backscattered signal under conditions of unknown payload, no dedicated channel, and strong main signal interference is the third key problem faced by this system.

[0007] Therefore, it is necessary to provide a new backscatter communication scheme for non-cooperative environments, so that backscatter tags can still extract physical layer features with low power consumption, complete frequency adaptation and symbol-level synchronization, and separate and decode weak backscatter signals by the receiving end without interfering with the original network services, even when the arrival time of the data packets, the carrier frequency and the payload content are unknown. Summary of the Invention

[0008] The purpose of this invention is to provide a passive IoT communication system and method that does not require cooperation, in order to solve the problems of existing commercial wireless network backscattering schemes that rely on environmental transmitter cooperation, tag terminals that have difficulty in completing synchronization and modulation under unknown environmental signal conditions, and weak backscattering signals that are difficult to separate and decode from strong environmental signals under unknown payload conditions.

[0009] To achieve the above objectives, in a first aspect, the present invention provides a passive Internet of Things (IoT) communication system without cooperation, comprising an environmental transmitter, a backscatter tag, and a receiver; the environmental transmitter is used to send environmental data packets and wirelessly transmits the environmental data packets after modulation according to a corresponding wireless communication protocol to form an environmental signal carrying the environmental data packets; the environmental data packets include at least a preamble segment and a payload segment; Backscatter tags are used to extract self-differential features related to the physical layer symbol structure of environmental signals. After the environmental data packet arrives, they perform discrete phase scanning and optimal phase locking in the preamble segment, and perform symbol-level synchronization and payload segment positioning in the optimal phase state. Backscatter tags are also used to generate square wave subcarriers corresponding to the tag data to be transmitted, and perform in-band backscatter modulation in the payload segment to form a composite wireless signal composed of the superposition of the original environmental signal and the reflected signal. The receiver is used to receive composite radio signals, synchronize the composite radio signals, remove chirps and cancel segmented environmental main signals, and recover the tag data to be transmitted through mirror spectrum fusion.

[0010] According to the present invention, a passive IoT communication system without cooperation is provided. The backscatter tag includes a receiving antenna, a differential feature extraction circuit, a tag controller, a frequency synthesis module, an RF switch, and a backscatter antenna. The ambient signal is input to the differential feature extraction circuit through the receiving antenna, and the differential feature extraction circuit outputs differential features. After detecting a valid rising edge of the differential feature, the tag controller determines that the ambient data packet has arrived, performs discrete phase scanning and optimal phase locking in the preamble segment, and performs symbol-level synchronization and payload segment positioning in the optimal phase state. The tag controller generates a tag bit sequence based on the tag data to be transmitted and maps the tag bit sequence to different discrete frequency shift states. For different discrete frequency shift states, the tag controller configures the corresponding frequency control word to the frequency synthesis module, and the frequency synthesis module generates square wave subcarriers of different frequencies. The square wave subcarrier controls the radio frequency switch to switch the impedance state of the backscatter antenna, so that the reflection coefficient of the backscatter tag changes with the square wave subcarrier, thereby modulating the environmental signal and generating a composite wireless signal composed of the superposition of the environmental signal and the reflected signal of the backscatter tag.

[0011] According to the present invention, a passive Internet of Things communication system without cooperation includes a self-differential feature extraction circuit comprising a power divider, a delay unit, a voltage-controlled phase shifter, a combiner, a diode mixer, an RC integrator network, a low-pass filter, and an amplifier. The ambient signal is input to the power divider via the receiving antenna. The power divider divides the ambient signal into a first branch signal and a second branch signal. The first branch signal is delayed by a delay unit to form a delayed signal, and the second branch signal is converted into a phase-adjustable phase-shifted signal by a voltage-controlled phase shifter. The delayed signal and the phase-shifted signal are input to the diode mixer via a combiner for self-mixing processing, and the output is a mixed signal of low-frequency difference frequency component and high-frequency sum frequency component that are related to the phase difference between the first branch signal and the second branch signal. The mixed signal passes through an RC integrator network, a low-pass filter and an amplifier in sequence to suppress the high-frequency sum frequency component and extract the low-frequency difference frequency component, forming a self-differential feature.

[0012] According to the present invention, a passive IoT communication system without cooperation is provided. After detecting a valid rising edge of a self-differential feature, the tag controller determines that an environmental data packet has arrived and performs discrete phase scanning and optimal phase locking in the preamble segment. Specifically, this includes: The tag controller controls the voltage-controlled phase shifter to switch multiple candidate phase states sequentially. The tag controller reads the differential features of each candidate phase state, compares the feature peaks of the differential features of each candidate phase state, and selects the candidate phase state with the largest feature peak as the optimal phase state. The tag controller controls the voltage-controlled phase shifter to maintain the optimal phase state, so that the differential feature extraction circuit works in the optimal phase state in the preamble segment, the start-of-frame delimiter segment, and the payload segment.

[0013] According to the present invention, a passive IoT communication system without cooperation performs symbol-level synchronization and payload segment positioning under optimal phase conditions, specifically including: The tag controller detects consecutive rising or falling edges in the self-differential features under the optimal phase state as synchronization features, and records the time corresponding to two adjacent synchronization features. Let the time corresponding to two adjacent synchronization features be respectively... and The symbol period of the environmental signal is then expressed as: ; The tag controller verifies the symbol period based on the periodic characteristics formed by multiple consecutive preamble symbols and determines the symbol boundary of the environmental signal. The tag controller detects the frame start delimiter after the preamble and determines the end position of the preamble, the position of the frame start delimiter, and the start time of the payload segment based on the self-differential feature change corresponding to the frame start delimiter.

[0014] According to the present invention, a passive IoT communication system without cooperation is provided, assuming that the tag controller can generate Given 2 different discrete frequency shift states, the number of tag bits that each backscatter symbol can carry is:

[0015] in, This indicates the number of tag bits that each backscatter symbol can carry. The number of discrete frequency shift states is indicated; the backscatter symbol refers to the basic modulation unit used to carry tag data, which maintains a certain discrete frequency shift state for a preset symbol duration; the backscatter symbol is time-aligned with the physical layer symbol of the environmental signal.

[0016] According to the present invention, a passive IoT communication system without cooperation modulates environmental signals to generate a composite wireless signal composed of the superposition of environmental signals and reflected signals from backscattered tags, specifically including: After the environmental signal is modulated by the reflection coefficient that varies with the square wave subcarrier, mirror sidebands corresponding to the square wave subcarrier frequency are formed on both sides of the center frequency of the environmental signal carrier. The backscatter tag uses the symbol boundary of the environmental signal as a timing reference, switches the frequency control word at the symbol boundary, and generates the corresponding square wave subcarrier according to the updated frequency control word, so that the backscatter symbol and the physical layer symbol of the environmental signal are aligned in time, forming a composite wireless signal composed of the superposition of the environmental signal and the reflected signal.

[0017] According to the present invention, a passive IoT communication system without cooperation is provided, which performs synchronization, chirp removal, and segmented environmental main signal cancellation on composite wireless signals, specifically including: The composite wireless signal is down-converted and sampled to obtain a digital baseband signal; according to the preamble structure of the wireless communication protocol, environmental data packet synchronization and symbol synchronization are performed on the digital baseband signal to determine the arrival location of the environmental data packet and the boundaries of each physical layer symbol in the environmental signal. The digital baseband signal segment corresponding to each physical layer symbol is multiplied with the conjugate signal of the reference chirp, and dechirping is performed to obtain the corresponding dechirped symbol signal. The dechirped symbol signal includes a strong signal component corresponding to the ambient signal and a weak backscattering signal component corresponding to the reflected signal. The strong signal component corresponding to the ambient signal is denoted as the ambient main signal, and the ambient main signal forms a corresponding ambient main peak in the frequency domain. The phase transition position is determined based on the phase change in the dechirped symbol signal, and the phase transition position is used as the segment boundary; Based on the segmentation boundary, the dechirped symbol signal is divided into a left signal segment before the segmentation boundary and a right signal segment after the segmentation boundary. For the left signal segment, the amplitude, frequency, and phase parameters of the main environmental signal are independently estimated using the least squares method, and a left local main environmental signal model is constructed. For the right signal segment, the amplitude, frequency, and phase parameters of the main environmental signal are independently estimated using the least squares method, and a right local main environmental signal model is constructed. Subtract the corresponding local environmental main signal model from the left and right signal segments respectively to obtain the residual signal after the environmental main signal is suppressed.

[0018] According to the present invention, a passive IoT communication system without cooperation is provided, which recovers tag data to be transmitted through mirror spectrum fusion, specifically including: Using the carrier center frequency of the environmental signal as the center of symmetry, two mirror detection windows are set on both sides of the center of symmetry, and the spectral peaks and energy distributions in the two mirror detection windows are compared. If a certain spectral peak does not have a corresponding symmetrical spectral peak on the other side of the center of symmetry, then the spectral peak is identified as asymmetric residual interference and removed from the discrete frequency shift state set. For discrete frequency shift states where corresponding spectral peaks exist in both mirror detection windows, the spectral peak energies on both sides are fused. The target frequency shift state with the largest fusion energy is determined by searching the maximum value of the sliding window. Based on the preset mapping relationship between the target frequency shift state and the tag bit sequence, the tag bits carried by the current backscatter symbol are recovered. The residual signals corresponding to each physical layer symbol in the payload segment are processed sequentially to recover the complete tag bit sequence, and the tag data to be sent is output according to the tag data frame structure.

[0019] In a second aspect, the present invention provides a passive IoT communication method without cooperation, employing the passive IoT communication system of the first aspect, the method comprising: The environmental transmitter sends environmental data packets and modulates the environmental data packets according to the corresponding wireless communication protocol before wireless transmission to form an environmental signal carrying the environmental data packets; The backscatter tag extracts the self-differential features related to the physical layer symbol structure of the environmental signal, and performs discrete phase scanning and optimal phase locking in the preamble segment after the environmental data packet arrives. It also performs symbol-level synchronization and payload segment positioning in the optimal phase state. The backscatter tag is also used to generate square wave subcarriers corresponding to the tag data to be transmitted, and performs in-band backscatter modulation in the payload segment to form a composite wireless signal composed of the superposition of the original environmental signal and the reflected signal. The receiver receives composite radio signals, performs synchronization, dechirping, and segmentation of the main environmental signals to cancel the composite radio signals, and recovers the tag data to be transmitted through mirror spectrum fusion.

[0020] Compared with the prior art, the present invention has at least the following technical effects: This invention provides a passive IoT communication system and method that requires no cooperation from the environmental transmitter. It enables low-power communication by directly utilizing naturally occurring environmental signals, such as LoRa signals, without modifying existing environmental transmitters, reserving dedicated wireless resources, or constructing specific data packets. Furthermore, this invention reduces system deployment costs, decreases reliance on dedicated infrastructure and network-side cooperation, and improves the deployability of environmental backscatter systems in real-world, unmanaged scenarios. It also reduces tag-side power consumption and hardware complexity, making it suitable for low-power, low-cost, large-scale IoT nodes. Additionally, it enhances the system's adaptability under unknown timing, frequency, and payload conditions, improving communication reliability and data recovery capabilities. It avoids occupying additional downlink triggering resources or service time slots, reducing the impact on existing communication links. Its basic operating mechanism does not rely on proprietary implementations of specific wireless protocols; after appropriate design and parameter adjustments based on the physical layer structure of different protocols, it has the feasibility of being extended to other commercial wireless communication protocols and application scenarios. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] In the attached diagram: Figure 1 This is a structural block diagram of the passive IoT communication system without collaboration according to the present invention; Figure 2 This is a physical image of the backscattering tag of the present invention; Figure 3 This is a block diagram of the self-differential feature extraction circuit of the present invention; Figure 4 This is a flowchart of the discrete phase scanning adaptive mechanism of the present invention; Figure 5 This is a schematic diagram of the low-power frequency synthesis module and modulation logic of the present invention; Figure 6 This is a flowchart of the receiving end processing of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] The following detailed description of some embodiments of the present invention will be provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0025] Please see Figure 1 This invention provides a passive IoT communication system that does not require cooperation, including an environmental transmitter, a backscatter tag, and a receiver. The environmental transmitter is used to send environmental data packets and modulates the environmental data packets according to the corresponding wireless communication protocol before wireless transmission to form an environmental signal carrying the environmental data packets. The environmental data packets include at least a preamble segment and a payload segment. Backscatter tags are used to extract self-differential features related to the physical layer symbol structure of environmental signals. After the environmental data packet arrives, they perform discrete phase scanning and optimal phase locking in the preamble segment, and perform symbol-level synchronization and payload segment positioning in the optimal phase state. Backscatter tags are also used to generate square wave subcarriers corresponding to the tag data to be transmitted, and perform in-band backscatter modulation in the payload segment to form a composite wireless signal composed of the superposition of the original environmental signal and the reflected signal. The receiver is used to receive composite radio signals, synchronize the composite radio signals, remove chirps and cancel segmented environmental main signals, and recover the tag data to be transmitted through mirror spectrum fusion.

[0026] It's important to clarify that the term "reflected signal" here differs from "backscatter symbol" in the following text. The distinction is as follows: a "backscatter symbol" is an information symbol generated by the backscatter tag based on the data to be transmitted; it can be understood as an information unit on the tag side. The backscatter tag uses this backscatter symbol to perform backscatter modulation on the incident environmental signal. The "reflected signal," on the other hand, is the actual wireless signal formed after the aforementioned backscatter modulation and propagated to the receiving end. In other words, the backscatter symbol carries information and acts on the environmental signal by changing the reflection state of the backscatter tag, ultimately forming the reflected signal. Therefore, the two belong to a "modulation symbol—physical signal" relationship, rather than being the same concept.

[0027] like Figure 2As shown, the backscatter tag includes a receiving antenna, a downlink processing sub-board, a main control board, an uplink modulation sub-board, a backscatter antenna, and corresponding connection interfaces. The downlink processing sub-board includes a differential feature extraction circuit for receiving environmental signals and extracting their physical layer features. The main control board includes a low-power tag controller, which is primarily used for: (1) Detect the effective rising edge of the output signal of the self-differential feature extraction circuit, and determine the arrival of the environmental data packet based on the effective rising edge; (2) In response to the determination result of the arrival of the environmental data packet, the voltage-controlled phase shifter is controlled to switch multiple candidate phase states sequentially during the preamble stage of the environmental data packet; (3) Read and compare the differential characteristic amplitudes under different candidate phase states, determine the optimal phase state, and control the voltage-controlled phase shifter to maintain the optimal phase state; (4) Based on the characteristic responses formed under different candidate phase states, infer the frequency range or corresponding working channel of the carrier frequency of the currently received environmental signal; (5) Under the optimal phase state, continue to detect the enhanced self-differential characteristic signal, and determine the symbol period and symbol boundaries of the environmental signal based on the continuous periodicity characteristics; (6) Detect the frame start delimiter after the preamble, and determine the end position of the preamble, the position of the frame start delimiter, and the start time of the payload segment; (7) Generate the corresponding frequency control word based on the tag data to be transmitted, and control the low-power frequency synthesis module to generate the corresponding square wave subcarrier; (8) Based on the determined symbol boundary and the start time of the payload segment, control the RF switch to switch the antenna impedance state during the payload segment in order to perform in-band backscatter modulation; (9) After the payload segment of the environmental data packet ends, stop the current backscatter modulation and re-enter the environmental data packet detection state.

[0028] The uplink modulation sub-board includes a low-power frequency synthesis module and an RF switch. The low-power frequency synthesis module generates a square wave subcarrier based on the frequency control word, and the RF switch switches the impedance state of the backscatter antenna based on the square wave subcarrier, thereby completing in-band backscatter modulation.

[0029] The hardware implementation described above does not require a high-power local oscillator, a high-speed analog-to-digital converter, or an active phase-locked loop, making it suitable for low-cost, low-power backscatter tags.

[0030] Based on the same inventive concept, another embodiment of the present invention provides a passive IoT communication method without cooperation, employing the passive IoT communication system of the aforementioned embodiment. The method includes the following steps: S1. The environmental transmitter sends environmental data packets and modulates the environmental data packets according to the corresponding wireless communication protocol before wireless transmission, so as to form an environmental wireless signal (hereinafter referred to as environmental signal) carrying the environmental data packets.

[0031] In some implementations, the environmental data packet is a LoRa (LongRange, a low-power wide-area network protocol designed for IoT applications) data packet, which includes at least a preamble segment, a frame start delimiter, and a payload segment. The preamble segment and the frame start delimiter are used to provide extractable physical layer timing features, and the payload segment is used to carry the original service data.

[0032] It should be noted that the environmental transmitter of this invention has not been modified and can send environmental data packets according to the original wireless communication protocol and service scheduling method. The environmental transmitter does not need to know the location, tag data or working status of the backscatter tag, nor does it need to provide the backscatter tag with triggering instructions, synchronization channels, control channels, dedicated preambles or known payloads.

[0033] Furthermore, the environmental transmitter is an existing commercial wireless transmitting device in the environment, which sends environmental data packets according to its original business requirements, without needing to send customized waveforms, provide trigger signals, reserve dedicated channels, modify payload content, or change the original transmission timing for backscatter communication.

[0034] S2. Environmental Data Packet Detection and Self-Difference Feature Extraction In non-cooperative environments, backscatter tags cannot obtain the transmission time of environmental data packets, the carrier frequency of environmental signals, and physical layer symbol boundaries in advance. If backscatter tags use continuous high-speed sampling, complete digital demodulation, or digital correlation operations to extract synchronization information, it will significantly increase tag power consumption and hardware complexity, making it difficult to meet the application requirements of low-power backscatter tags.

[0035] Therefore, the present invention sets up a backscattering tag side. Figure 3 The self-differential feature extraction circuit shown extracts analog synchronization features, i.e., self-differential features, related to the physical layer symbol structure of the environmental signal without performing complete digital demodulation of the environmental signal.

[0036] like Figure 3 As shown, the self-differential feature extraction circuit includes a power divider, a delay unit, a voltage-controlled phase shifter, a combiner, a diode mixer, an RC integrator network, a low-pass filter, and an amplifier.

[0037] After the environmental signal is input into the differential feature extraction circuit by the receiving antenna of the backscatter tag, it is first divided into the first branch signal and the second branch signal by the power divider.

[0038] The first branch signal has a delay time of... A broadband surface acoustic wave delay unit is used to form a delayed signal. The second branch signal passes through a voltage-controlled phase shifter to form a phase-adjustable phase-shifted signal. The phase state of the voltage-controlled phase shifter is controlled by a tag controller to enable subsequent discrete phase scanning between different candidate phase states.

[0039] The delayed signal and the phase-shifted signal are input to a diode mixer via a combiner for self-mixing. By self-mixing the ambient signal and its delayed signal, the mixer outputs a low-frequency differential characteristic related to the phase difference between the first and second branch signals.

[0040] The mixing output passes sequentially through an RC integrator network, a low-pass filter, and an amplifier. The RC integrator network accumulates the mixing output within a preset time window to enhance the correlation characteristics within the environmental signal symbol; the low-pass filter filters out high-frequency components and out-of-band noise generated by self-mixing; and the amplifier increases the amplitude of the differential characteristic signal to form the output signal for detection by the tag controller, i.e., the aforementioned self-differential characteristic.

[0041] The self-differential characteristic reflects the physical layer symbol changes of the environmental signal. When the environmental data packet arrives, the self-differential characteristic changes from its original stable state and generates a valid rising edge.

[0042] After the tag controller detects a valid rising edge of the self-differential feature, it determines that the environmental data packet has arrived and starts the subsequent discrete phase scanning process.

[0043] It should be noted that the valid rising edge is only used to provide initial triggering information for the arrival of environmental data packets and is not directly used as the final symbol synchronization result. The main function of the self-differential feature extraction circuit is to provide simulated physical layer features for subsequent phase scanning and symbol-level synchronization.

[0044] The output of step S2 includes: (1) The arrival of environmental data packets triggers the signal; (2) Self-differential characteristic output signal.

[0045] Among them, the environmental data packet arrival trigger signal is used to start the discrete phase scan in step S3, and the self-differential feature output signal is used to evaluate the synchronization feature strength under different candidate phase states.

[0046] S3. Perform discrete phase scanning and optimal phase locking in the preamble segment of the environmental data packet. During the differential feature extraction process, different carrier frequencies introduce different static phase residuals into the correlation output. When this phase residual makes the integral result close to zero, the symbol boundary features of the front-end output will be significantly weakened, leading to synchronization failure. Therefore, under unknown carrier frequency conditions, it is necessary to compensate for the frequency-related phase offset. This invention employs a discrete phase scanning mechanism for blind estimation and phase locking in the preamble segment. For example... Figure 4 As shown, after the tag controller detects the valid rising edge of the self-differential feature in step S2, it determines that the environmental data packet has arrived and starts discrete phase scanning in the preamble segment of the environmental data packet.

[0047] The tag controller sequentially controls the voltage-controlled phase shifter to switch between multiple candidate phase states. Let the set of M candidate phase states be:

[0048] The tag controller reads the self-difference features of each candidate phase state. Let the candidate phase state be... The corresponding self-difference feature is This forms the feature response vector:

[0049] In one implementation, the candidate phase states are set as four orthogonal phase states, and the four candidate phase states are tested sequentially using a series of consecutive preamble symbols in the environmental data packet.

[0050] The tag controller compares the peak values ​​of the self-difference characteristics of each candidate phase state and selects the candidate phase state with the largest peak value of the self-difference characteristics as the optimal phase state:

[0051] Determine the optimal phase state Then, the tag controller controls the voltage-controlled phase shifter to maintain the optimal phase state, so that... Figure 3 The self-differential feature extraction circuit shown operates in the optimal phase state during the subsequent preamble, start-of-frame delimiter (SFD) and payload stages.

[0052] The phase scanning described above can reduce the static phase residual caused by the carrier frequency of the environmental signal, enhance the synchronization characteristics of the output of the self-differential feature extraction circuit, and provide a feature signal with a higher signal-to-noise ratio for symbol-level synchronization in step S4.

[0053] The tag controller can also base its actions on the feature response vectors formed under different candidate phase states. Infer the frequency range or corresponding working channel of the carrier frequency of the currently received environmental signal (K=arg max(S)).

[0054] The output of step S3 includes at least: 1. Optimal phase state ; 2. Enhanced self-differential characteristic signal under optimal phase state; 3. Optional environmental operating channel or frequency range information.

[0055] The optimal phase state and the enhanced self-differential characteristic signal are used in step S4 to perform precise symbol-level synchronization.

[0056] S4. Perform symbol-level synchronization and payload positioning under optimal phase conditions. After completing the discrete phase scan and optimal phase locking in step S3, the backscattering tag is in the optimal phase state. Continue to utilize Figure 3 The self-differential feature extraction circuit shown processes environmental signals.

[0057] Since the voltage-controlled phase shifter is locked in a phase state that yields the maximum peak value of the differential characteristic, the physical layer synchronization characteristics output by the differential characteristic extraction circuit are enhanced. The tag controller determines the symbol period and symbol boundary of the ambient signal based on the enhanced differential characteristic signal.

[0058] Specifically, the tag controller detects the periodic features of consecutive rising or falling edges in the enhanced self-differential feature signal and records the time corresponding to adjacent feature positions.

[0059] Let the times when two adjacent valid synchronization features appear be respectively and Then the symbol period of the environmental signal can be expressed as:

[0060] The tag controller verifies the symbol period based on the periodic characteristics formed by multiple consecutive preamble symbols and determines the symbol boundaries of the environmental signal.

[0061] In one implementation where the environmental signal is a LoRa signal, the tag controller first determines the symbol period and preamble symbol boundary of the LoRa signal based on the periodic self-differential characteristic output formed by continuously chirped preambles.

[0062] Subsequently, the tag controller continues to detect the start-of-frame delimiter after the preamble. Based on the self-differential characteristic changes corresponding to the start-of-frame delimiter, the end position of the preamble, the position of the start-of-frame delimiter, and the start time of the payload segment are determined.

[0063] Therefore, step S4 completes the final symbol-level synchronization, rather than the initial environment data packet triggering. Its synchronization process is based on the optimal phase locking already achieved in step S3.

[0064] The output of step S4 includes at least: 1. Environmental signal symbol period ; 2. The boundary positions of each environmental symbol; 3. Position of the frame start delimiter; 4. Start time of the effective payload segment.

[0065] The above results serve as the time reference for subsequent tag frequency shift state switching and payload segment backscatter modulation.

[0066] S5. Generate a low-power square wave subcarrier corresponding to the tag data to be transmitted. like Figure 4 As shown, the tag controller generates a tag bit sequence based on the tag data to be transmitted and maps the tag bit sequence to different discrete frequency shift states. Different discrete frequency shift states correspond to different square wave subcarrier frequencies. Assume the tag controller can generate... Given 2 different discrete frequency shift states, the number of tag bits that each backscatter symbol can carry is:

[0067] in, This indicates the number of tag bits carried by each backscatter symbol. This indicates the number of discrete frequency shift states that can be selected.

[0068] It should be noted that a backscatter symbol refers to a basic modulation unit used to carry tag data, which maintains a certain discrete frequency shift state within a preset symbol duration for the backscatter tag. In this embodiment, the backscatter symbol is time-aligned with the physical layer symbol of the environmental signal, that is, the backscatter tag maintains a discrete frequency shift state between adjacent environmental symbol boundaries determined in step S4, and switches the discrete frequency shift state at the environmental symbol boundaries.

[0069] In one implementation, Figure 5 The low-power frequency synthesis module shown includes a 16-bit binary adder and a D-type flip-flop group. For different discrete frequency shift states, the tag controller configures a corresponding frequency control word to the low-power frequency synthesis module. This frequency control word is input to the 16-bit binary adder and accumulated with the output state fed back from the D-type flip-flop group. The accumulated result is input to the D-type flip-flop group and updated under the drive of the low-speed master clock CLK. The output state of the D-type flip-flop group is fed back to the 16-bit binary adder, thus forming an accumulator-type frequency synthesis structure. A predetermined bit in the output state, such as the most significant bit, is output as a square wave subcarrier. By changing the frequency control word, the flip period of the predetermined bit can be changed, thereby generating square wave subcarriers of different frequencies. Different square wave subcarrier frequencies correspond to the different discrete frequency shift states mentioned above.

[0070] Therefore, step S5 generates a square wave subcarrier with a corresponding frequency based on the discrete frequency shift state corresponding to the current backscatter symbol, and outputs the square wave subcarrier to the control terminal of the radio frequency switch for step S6 to perform in-band backscatter modulation.

[0071] S6. Perform in-band backscatter modulation in the payload segment. The backscatter tag begins backscatter modulation after the environmental data packet enters the payload phase, based on the payload segment start time determined in step S4. The square wave subcarrier generated in step S5 controls the RF switch to switch the impedance state of the backscatter antenna, causing the reflection coefficient of the backscatter tag to change with the square wave subcarrier, thereby modulating the environmental signal and generating a composite wireless signal composed of the superposition of the environmental signal and the reflected signal from the backscatter tag. The specific modulation process is as follows: After the environmental signal is modulated by the reflection coefficient that varies with the square wave subcarrier, mirror sidebands corresponding to the square wave subcarrier frequency are formed on both sides of the center frequency of the environmental signal carrier.

[0072] When the backscatter label is selected For each discrete frequency shift state, the corresponding mirror sideband is located at:

[0073] and

[0074] in, The center frequency of the carrier wave of the environmental signal. For the first A discrete frequency shift state.

[0075] According to the symbol boundary of the environmental signal determined in step S4, the backscatter tag switches the frequency control word or square wave subcarrier at the symbol boundary to align the backscatter symbol with the physical layer symbol of the environmental signal.

[0076] In this invention, the backscatter tag carries tag data only during the payload phase. The preamble phase is mainly used for environmental data packet arrival detection, symbol-level synchronization, discrete phase scanning, and frequency range inference; the start-of-frame delimiter phase is used to confirm the start time of the payload segment.

[0077] Through the above modulation, a composite wireless signal is formed by superimposing the original environmental signal and the tag reflection signal, and is received by the receiving end.

[0078] S7. Synchronize, dechirp, and cancel segmented environmental main signals for composite signals. like Figure 6 As shown, the receiver receives the composite wireless signal formed by the superposition of the original environmental signal and the tag reflection signal, and down-converts and samples it to obtain a digital baseband signal. This digital baseband signal serves as the input signal for subsequent data packet synchronization, symbol synchronization, chirp removal, segmented environmental main signal reconstruction and cancellation, and mirror spectrum processing.

[0079] The receiver first performs environmental data packet synchronization and symbol synchronization on the digital baseband signal according to the preamble structure of the wireless communication protocol, and determines the arrival position of the environmental data packet and the boundaries of each physical layer symbol in the environmental signal.

[0080] In implementations where the ambient signal is a LoRa signal, for each LoRa physical layer symbol after symbol synchronization, the dedicated receiver multiplies the digital baseband signal segment corresponding to each physical layer symbol with the conjugate signal of the reference chirp, performing dechirping processing to obtain the corresponding dechirped symbol signal. The dechirped symbol signal includes a strong signal component corresponding to the original ambient signal and a weak backscatter signal component corresponding to the tag reflection signal. The strong signal component corresponding to the original ambient signal is referred to as the ambient main signal, which forms a corresponding ambient main peak in the frequency domain.

[0081] Considering that commercial wireless transmitters may generate phase transients within a physical layer symbol during chirp wrap-around, instantaneous frequency jumps, or hardware state switching, the receiver determines the phase jump position based on the phase change in the dechirped symbol signal and uses the phase jump position as the segment boundary.

[0082] like Figure 6 As shown, the receiver divides the dechirped symbol signal into a left signal segment before the segment boundary and a right signal segment after the segment boundary, based on the segment boundary. For the left signal segment, the dedicated receiver uses the least squares method to independently estimate the amplitude, frequency, and phase parameters of the main environmental signal and constructs a left-side local main environmental signal model. For the right signal segment, the same method is used to independently estimate the amplitude, frequency, and phase parameters of the main environmental signal and construct a right-side local main environmental signal model.

[0083] The receiver subtracts the corresponding local environmental master signal model from the left and right signal segments respectively to obtain the residual signal after the environmental master signal is suppressed. Compared with fitting the entire physical layer symbol using a single continuous phase model, the segmented reconstruction of this invention can adapt to the local phase transients within the symbol, reduce the reconstruction error of the environmental master signal, and thus reduce the interference of the residual environmental master signal on the weak tag reflection signal.

[0084] Figure 6 The meanings of each parameter are as follows: , : Estimated amplitudes of the main signals in the local environments on the left and right sides; , : Estimated frequencies of the main signals in the local environment on the left and right sides; , : Frequency indices corresponding to candidate peak values ​​in the lower and upper sidebands; The length of the frequency domain interval or the number of frequency points used in the mirror comparison; The allowed symmetry error threshold for the mirror frequency index; Figure 6 The boundaries of the left and right segments are determined by the phase jump position.

[0085] S8. Recover tag data through mirror spectrum fusion After the environmental main signal cancellation is completed in step S7, the receiver performs frequency domain analysis on the residual signal.

[0086] like Figure 6 As shown, the receiver sets up image detection windows located above and below the center frequency of the environmental signal carrier as the center of symmetry, and compares the spectral peaks and energy distributions in the two image detection windows.

[0087] If a certain spectral peak does not have a corresponding symmetrical spectral peak on the other side of the center frequency, then the spectral peak is identified as asymmetric residual interference and removed from the discrete frequency shift state set.

[0088] For discrete frequency shift states where there are corresponding spectral peaks in both the upper and lower mirror windows, the receiver fuses the spectral peak energy from both sides.

[0089] Assume the first The upper sideband energy corresponding to each discrete frequency shift state is: The energy of the lower band is Then the fusion energy of this discrete frequency shift state can be expressed as:

[0090] The receiver determines the target frequency shift state with the largest fusion energy by searching the maximum value of a sliding window:

[0091] Based on the target frequency shift state The receiver recovers the tag bits carried by the current backscatter symbol by establishing a preset mapping relationship between the tag bit sequence and the tag bit sequence.

[0092] The receiving end processes the residual signals corresponding to each physical layer symbol of the payload segment in sequence, recovers the complete tag bit sequence, and outputs the tag data to be transmitted according to the tag data frame structure.

[0093] It should be noted that the decoding process of this invention does not require prior knowledge of the payload content of the environmental data packets. It only utilizes the residual signal after segmented main signal cancellation and the mirror spectrum symmetry formed by in-band backscatter modulation to recover the tag data to be transmitted. Through steps S1 to S8, this invention can achieve data communication from the backscatter tag to the receiver without the environmental transmitter providing trigger scheduling, modifying the original protocol, reserving a dedicated channel, or providing a known payload.

[0094] In summary, the passive IoT communication system and method without collaboration provided by this invention have at least the following characteristics: 1. Adopting an asymmetric system architecture of "lightweight physical feature extraction at the tag end and complex signal processing at the receiver end", the main computational complexity is transferred from the backscattering tag side to the receiver deployed by the user, so that the original network services do not need to be modified.

[0095] 2. In the absence of environmental transmitter cooperation, a self-differential analog front-end consisting of delayed phase shift, diode mixing, integration, filtering and amplification is used to extract the physical layer features of commercial environmental signals. The arrival trigger of environmental data packets is obtained by detecting the effective rising edge of the self-differential feature output signal. Symbol-level synchronization is achieved after completing discrete phase scanning and phase locking.

[0096] 3. Perform discrete phase scanning during the preamble stage, and perform phase locking and blind frequency estimation based on the integral peak vector, enabling the tag to work adaptively in unknown carrier frequencies and wide-band environments.

[0097] 4. Low-speed accumulator-type frequency shift synthesis and RF switch impedance switching are used to achieve in-band backscatter modulation, forming a mirror spectrum feature that can be separated by the receiver while maintaining low power consumption.

[0098] 5. The receiver performs segmented reconstruction and main signal cancellation based on the intra-symbol phase transient of the commercial transmitter, and combines mirror window comparison, asymmetric suppression and peak fusion to achieve tag decoding under unknown payload conditions.

[0099] The following is a specific embodiment of the present invention.

[0100] This embodiment is a cooperative backscatter communication system based on commercial LoRa environmental signals.

[0101] The system in this embodiment includes an unmodified environmental transmitter, backscatter tags, and a dedicated receiver. The unmodified environmental transmitter is an existing commercial LoRa transmitter in the environment, which transmits environmental data packets according to its original service, without needing to send customized waveforms, reserve channels, or provide trigger signals for backscatter communication. The backscatter tag is deployed on the object to be sensed, identified, or communicated with, and is used to extract physical layer features from the environmental LoRa signal and modulate tag data in the payload segment. The dedicated receiver is deployed on the user side and is used to receive the composite signal formed by the superposition of the original environmental signal and the tag's reflected signal, and to recover the tag data.

[0102] Specifically, after receiving the environmental LoRa radio frequency signal, the backscatter tag first utilizes... Figure 3 The self-differential feature extraction circuit shown performs analog domain feature extraction on the environmental signal. The input signal is split into two paths by a power divider: the first path passes through a broadband surface acoustic wave delay unit to form a delayed signal, and the second path passes through a voltage-controlled phase shifter to form a phase-adjustable phase-shifted signal. The two signals are then combined and input to a zero-bias diode mixer for self-mixing. The mixer output passes sequentially through an RC integrator network, a low-pass filter, and an amplifier to form a self-differential feature output signal related to the physical layer symbol structure of the environmental LoRa signal. The low-power tag controller detects the valid rising edge of the self-differential feature output signal. When a valid rising edge is detected, it determines that the environmental data packet has arrived and initiates subsequent discrete phase scanning. This valid rising edge serves only as initial trigger information for the arrival of the environmental data packet and is not directly used as the final symbol synchronization result.

[0103] Upon detecting the arrival of an environmental data packet, the backscatter tag performs a discrete phase scan during the preamble phase of the environmental data packet. The tag controller sequentially controls the voltage-controlled phase shifter to switch between multiple candidate phase states and reads the characteristic amplitude of the self-differential characteristic output signal under each candidate phase state. In one embodiment, the candidate phase states are set as four orthogonal phase states, and each candidate phase state is tested sequentially using multiple consecutive preamble symbols. The tag controller compares the characteristic amplitudes under different candidate phase states, selects the candidate phase state with the largest characteristic amplitude as the optimal phase state, and controls the voltage-controlled phase shifter to lock in the optimal phase state. The tag controller can also infer the frequency range or operating channel of the carrier frequency of the currently received environmental signal based on the characteristic responses formed by different candidate phase states, thereby completing phase adaptation and blind frequency estimation under unknown carrier frequency conditions.

[0104] After achieving optimal phase locking, the backscatter tag continues to process the environmental LoRa signal using a differential feature extraction circuit under optimal phase conditions. Since the static phase residual caused by the carrier frequency has been compensated, the physical layer synchronization characteristics in the differential feature output signal are enhanced. The tag controller determines the LoRa symbol period and symbol boundaries based on the periodic rising and falling edges corresponding to consecutive preamble symbols, and further detects the frame start delimiter after the preamble. Based on the feature changes corresponding to the frame start delimiter, it determines the preamble end position, the frame start delimiter position, and the payload segment start time. Thus, the tag completes the timing acquisition required for subsequent backscatter modulation in the order of "data packet arrival initial trigger—discrete phase scan—optimal phase locking—symbol-level synchronization—payload positioning."

[0105] After phase locking and symbol-level synchronization are completed, the tag performs in-band backscatter modulation only in the payload segment of the environmental data packet. The tag-side low-power frequency synthesis module adopts an accumulator-type frequency synthesis structure, using a low-speed master clock to drive a binary adder and a D-type flip-flop to generate a square wave subcarrier according to a preset frequency control word. The square wave subcarrier controls the RF switch to switch the impedance state of the backscatter antenna, causing the tag's reflection coefficient to change with the square wave subcarrier, thereby reflecting and modulating the incident environmental signal and forming mirror sidebands corresponding to the square wave subcarrier frequency on both sides of the environmental signal's carrier center frequency. This method does not rely on the explicit or implicit header settings of the environmental protocol, but operates based on the physical layer symbol boundary, thus enabling tag data transmission without changing the original environmental transmitter services.

[0106] After receiving the composite signal, the dedicated receiver first performs synchronization and dechirping processing to compress the ambient LoRa chirped signal into the frequency domain main peak. Then, the receiver determines the phase transition boundary based on the symbol structure, divides the dechirped waveform into multiple local segments, and estimates the amplitude, frequency, and phase parameters of the main ambient signal in each local segment. A local main signal model is constructed and subtracted to suppress strong ambient main signals. After main signal cancellation, the receiver utilizes the symmetry of the mirror spectrum formed by in-band frequency shift modulation for decoding. The target frequency shift is determined through mirror window comparison, asymmetric interference removal, and sliding window maximum value search, and the tag bit information is recovered accordingly.

[0107] Through the above steps, this embodiment can achieve data communication between the backscatter tag and the dedicated receiver without the environmental transmitter cooperating, without modifying the original protocol, without reserving a dedicated channel, and without sending customized data packets.

[0108] The dedicated receiver is implemented using a Universal Software Radio Platform (USRP). This platform receives the composite signal formed by the superposition of the original environmental signal and the tag's reflected signal, and down-converts and samples the received RF signal to output a digital baseband signal. The digital baseband signal is then input to the receiver to perform synchronization, chirp removal, segmented reconstruction, main signal cancellation, mirror window comparison, asymmetric interference suppression, and peak fusion decision to recover the tag data. In this implementation, the USRP serves only as a receiving device deployed on the user side, passively monitoring environmental signals and tag reflection signals. It does not send control commands to the environmental transmitter, nor does it require the environmental transmitter to modify the communication protocol, reserve downlink channels, or provide service time slots. Besides the USRP, this implementation can also be achieved using software-defined radio equipment or dedicated receiving hardware with corresponding RF reception, downconversion, sampling, and digital baseband output capabilities.

[0109] The above embodiments use LoRa environment signals as an example to illustrate the present invention, but the basic principle of the present invention is not limited to the LoRa protocol. For commercial wireless protocols with repeating preambles, training fields, cyclic prefixes, short training sequences, or other extractable physical layer features, the delay parameters, integration windows, phase scanning methods, frequency shift states, and receiver signal processing methods can be designed or adjusted according to the signal structure and physical layer features of the corresponding protocols to realize the application of the non-cooperative backscattering mechanism described in the present invention in other wireless signal scenarios.

[0110] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. It should be understood that the invention is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A passive IoT communication system that requires no cooperation, characterized in that, It includes an environmental transmitter, a backscatter tag, and a receiver; the environmental transmitter is used to send environmental data packets and modulate the environmental data packets according to the corresponding wireless communication protocol before wireless transmission to form an environmental signal carrying the environmental data packets; the environmental data packets include at least a preamble segment and a payload segment; The backscatter tag is used to extract the self-differential features related to the physical layer symbol structure of the environmental signal, and after the environmental data packet arrives, it performs discrete phase scanning and optimal phase locking in the preamble segment, and performs symbol-level synchronization and payload segment positioning in the optimal phase state; the backscatter tag is also used to generate a square wave subcarrier corresponding to the tag data to be transmitted, and perform in-band backscatter modulation in the payload segment to form a composite wireless signal composed of the superposition of the original environmental signal and the reflected signal; The receiving end is used to receive the composite wireless signal, synchronize the composite wireless signal, remove chirp and cancel segmented environmental main signals, and recover the tag data to be transmitted through mirror spectrum fusion.

2. The passive IoT communication system without collaboration according to claim 1, characterized in that, The backscatter tag includes a receiving antenna, a differential feature extraction circuit, a tag controller, a frequency synthesis module, an RF switch, and a backscatter antenna. The environmental signal is input to the differential feature extraction circuit through the receiving antenna, and the differential feature extraction circuit outputs differential features. After detecting a valid rising edge of the differential feature, the tag controller determines that the environmental data packet has arrived, performs discrete phase scanning and optimal phase locking in the preamble segment, and performs symbol-level synchronization and payload segment positioning in the optimal phase state. The tag controller generates a tag bit sequence based on the tag data to be transmitted and maps the tag bit sequence to different discrete frequency shift states. For different discrete frequency shift states, the tag controller configures a corresponding frequency control word to the frequency synthesis module, and the frequency synthesis module generates square wave subcarriers of different frequencies accordingly. The square wave subcarrier controls the radio frequency switch to switch the impedance state of the backscatter antenna, so that the reflection coefficient of the backscatter tag changes with the square wave subcarrier, thereby modulating the environmental signal and generating a composite wireless signal composed of the superposition of the environmental signal and the reflected signal of the backscatter tag.

3. The passive IoT communication system without collaboration according to claim 2, characterized in that, The self-differential feature extraction circuit includes a power divider, a delay unit, a voltage-controlled phase shifter, a combiner, a diode mixer, an RC integrator network, a low-pass filter, and an amplifier. The environmental signal is input to the power divider via the receiving antenna, and the power divider divides the environmental signal into a first branch signal and a second branch signal; the first branch signal is delayed by a delay unit to form a delayed signal, and the second branch signal is phase-adjustable by a voltage-controlled phase shifter; The delayed signal and the phase-shifted signal are processed by a combiner input diode mixer to produce a mixed signal that is related to the phase difference between the first branch signal and the second branch signal, as well as a mixed signal of the high-frequency sum frequency component. The mixed signal is then passed through an RC integrator network, a low-pass filter, and an amplifier to suppress the high-frequency sum frequency component and extract the low-frequency difference frequency component, thus forming a self-differential feature.

4. The passive IoT communication system without collaboration according to claim 3, characterized in that, After detecting a valid rising edge of the self-differential feature, the tag controller determines that the environmental data packet has arrived and performs discrete phase scanning and optimal phase locking in the preamble segment, specifically including: The tag controller controls the voltage-controlled phase shifter to sequentially switch between multiple candidate phase states. The tag controller reads the differential features of each candidate phase state, compares the feature peaks of the differential features of each candidate phase state, and selects the candidate phase state with the largest feature peak as the optimal phase state. The tag controller controls the voltage-controlled phase shifter to remain in the optimal phase state, so that the differential feature extraction circuit operates in the optimal phase state in the preamble segment, the start-of-frame delimiter segment, and the payload segment.

5. The passive IoT communication system without collaboration according to claim 4, characterized in that, The process of performing symbol-level synchronization and payload segment positioning under optimal phase conditions specifically includes: The tag controller detects the synchronization features of consecutive rising or falling edges in the self-differential features under the optimal phase state, and records the time corresponding to two adjacent synchronization features. Let the time corresponding to two adjacent synchronization features be respectively... and The symbol period of the environmental signal is then expressed as: ; The tag controller verifies the symbol period based on the periodic characteristics formed by multiple consecutive preamble symbols and determines the symbol boundary of the environmental signal. The tag controller detects the frame start delimiter after the preamble and determines the end position of the preamble, the position of the frame start delimiter, and the start time of the payload segment based on the self-differential feature change corresponding to the frame start delimiter.

6. The passive IoT communication system without collaboration according to claim 5, characterized in that, Assuming the tag controller is capable of generating Given 2 different discrete frequency shift states, the number of tag bits that each backscatter symbol can carry is: in, This indicates the number of tag bits that each backscatter symbol can carry. The number of discrete frequency shift states is indicated; the backscatter symbol refers to the basic modulation unit used to carry tag data, in which the backscatter tag maintains a certain discrete frequency shift state within a preset symbol duration; the backscatter symbol is time-aligned with the physical layer symbol of the environmental signal.

7. The passive IoT communication system without collaboration according to claim 6, characterized in that, Modulating the environmental signal to generate a composite wireless signal consisting of the superposition of the environmental signal and the reflected signal from the backscattering tag, specifically includes: After the environmental signal is modulated by the reflection coefficient that varies with the square wave subcarrier, mirror sidebands corresponding to the square wave subcarrier frequency are formed on both sides of the center frequency of the carrier of the environmental signal. The backscatter tag uses the symbol boundary of the environmental signal as a timing reference, switches the frequency control word at the symbol boundary, and generates the corresponding square wave subcarrier according to the updated frequency control word, so that the backscatter symbol and the physical layer symbol of the environmental signal are aligned in time, forming a composite wireless signal composed of the superposition of the environmental signal and the reflected signal.

8. The passive IoT communication system without collaboration according to claim 7, characterized in that, Synchronization, chirping removal, and segmentation of environmental main signals are performed on composite wireless signals, specifically including: The composite wireless signal is down-converted and sampled to obtain a digital baseband signal; according to the preamble structure of the wireless communication protocol, environmental data packet synchronization and symbol synchronization are performed on the digital baseband signal to determine the arrival location of the environmental data packet and the boundaries of each physical layer symbol in the environmental signal. The digital baseband signal segment corresponding to each physical layer symbol is multiplied by the conjugate signal of the reference chirp, and dechirping is performed to obtain the corresponding dechirped symbol signal. The dechirped symbol signal includes a strong signal component corresponding to the environmental signal and a weak backscattering signal component corresponding to the reflected signal. The strong signal component corresponding to the environmental signal is denoted as the main environmental signal, and the main environmental signal forms a corresponding main environmental peak in the frequency domain. The phase transition position is determined based on the phase change in the dechirped symbol signal, and the phase transition position is used as the segment boundary; Based on the segmentation boundary, the dechirped symbol signal is divided into a left signal segment before the segmentation boundary and a right signal segment after the segmentation boundary. For the left signal segment, the amplitude, frequency, and phase parameters of the main environmental signal are independently estimated using the least squares method, and a left local main environmental signal model is constructed. For the right signal segment, the amplitude, frequency, and phase parameters of the main environmental signal are independently estimated using the least squares method, and a right local main environmental signal model is constructed. Subtract the corresponding local environmental main signal model from the left and right signal segments respectively to obtain the residual signal after the environmental main signal is suppressed.

9. The passive IoT communication system without collaboration according to claim 8, characterized in that, The recovery of the tag data to be transmitted through mirror spectrum fusion specifically includes: Using the carrier center frequency of the environmental signal as the center of symmetry, two mirror detection windows are set on both sides of the center of symmetry, and the spectral peaks and energy distributions in the two mirror detection windows are compared. If a certain spectral peak does not have a corresponding symmetrical spectral peak on the other side of the center of symmetry, then the spectral peak is identified as asymmetric residual interference and removed from the discrete frequency shift state set. For discrete frequency shift states where corresponding spectral peaks exist in both mirror detection windows, the spectral peak energies on both sides are fused. The target frequency shift state with the largest fusion energy is determined by searching the maximum value of the sliding window. Based on the preset mapping relationship between the target frequency shift state and the tag bit sequence, the tag bits carried by the current backscatter symbol are recovered. The residual signals corresponding to each physical layer symbol of the payload segment are processed sequentially to recover the complete tag bit sequence, and the tag data to be sent is output according to the tag data frame structure.

10. A passive IoT communication method without cooperation, characterized in that, The method employs the passive IoT communication system without collaboration as described in any one of claims 1-9, and includes: The environmental transmitter sends environmental data packets and modulates the environmental data packets according to the corresponding wireless communication protocol before wireless transmission, so as to form an environmental signal carrying the environmental data packets; The backscatter tag extracts the self-differential features related to the physical layer symbol structure of the environmental signal, and performs discrete phase scanning and optimal phase locking in the preamble segment after the environmental data packet arrives, and performs symbol-level synchronization and payload segment positioning in the optimal phase state; the backscatter tag is also used to generate square wave subcarriers corresponding to the tag data to be transmitted, and performs in-band backscatter modulation in the payload segment to form a composite wireless signal composed of the superposition of the original environmental signal and the reflected signal; The receiving end receives the composite wireless signal, performs synchronization, dechirping, and segmentation of the main environmental signal cancellation on the composite wireless signal, and recovers the tag data to be transmitted through mirror spectrum fusion.

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