Backscatter downlink communication method and system for commercial radio

Abstract

The present invention relates to the field of backscatter communication technology, and discloses a backscatter downlink communication method and system for commercial radio. The method comprises: dividing a received ambient signal into a first signal and a second signal; processing the first signal through a delay module composed of cascaded acoustic wave filters to obtain a delayed signal; causing the second signal to produce a fixed phase offset relative to the ambient signal through a phase shifter to obtain a phase-shifted signal; vector superposition of the obtained signals, where the envelope amplitude of the obtained composite signal is determined by the relative phase offset between the delayed signal and the phase-shifted signal; detecting the envelope amplitude change of the composite signal and outputting an analog signal, converting the analog signal into a digital signal through a comparator, and converting the analog signal into a bit stream or a chip sequence. The present invention does not require additional auxiliary equipment, reduces deployment costs, and better meets the needs of tag data downlink transmission in low-power wireless transmission systems.

Description

Technical Field

[0001] The present invention relates to the technical field of backscatter communications, and in particular to a backscatter downlink communication method and system for commercial radio. Background Art

[0002] With the rapid growth of IoT devices, backscatter communication technology, due to its ultra-low power consumption, has become a key technology supporting the interconnection of massive devices. Traditional radio frequency identification (RFID) systems rely on dedicated readers and writers, making them incompatible with existing wireless infrastructure. Environmental backscatter technology, on the other hand, can carry data on widely available wireless signals such as ZigBee, Bluetooth, and WiFi, providing communication capabilities for passive or low-power devices, making it a research hotspot in this field. However, existing technologies primarily focus on uplink transmission (from tag to receiver), while the downlink (from transmitter to tag) still faces key bottlenecks such as strong hardware dependence and poor protocol compatibility, hindering the large-scale deployment of backscatter tags.

[0003] Existing downlink technologies fall into three main categories: 1) Device-dependent solutions: These offload energy-intensive tasks (such as carrier generation and signal demodulation) to external devices by deploying dedicated devices or modifying transmitter hardware, thereby reducing tag power consumption. For example, the Battery-free 802.15.4 Receiver solution relies on an external device to provide an unmodulated carrier, achieving frame reception with a power consumption of 361 μW. The MIXIQ solution modifies 802.11ax signals to generate auxiliary signals, reducing power consumption to 40 μW. The BiBlue solution utilizes an edge server to convert Bluetooth signals into amplitude-shift keying (ASK) waveforms, achieving 250 kbps throughput. The drawbacks of these solutions are the need to deploy dedicated devices or modify transmitter hardware, resulting in increased system complexity, surging deployment costs, and limited compatibility with unmodified commercial wireless devices. 2) Filter-dependent solutions: These utilize fixed-frequency-response filters (such as SAW filters) to convert frequency-modulated signals into amplitude-modulated signals. For example, the Saiyan solution uses a surface acoustic wave (SAW) filter to convert frequency-modulated chirp signals into amplitude-modulated signals. However, its disadvantages include a fixed filter frequency response, which cannot cover the dynamic frequency bands of multiple protocols such as ZigBee, Bluetooth, and WiFi (e.g., Bluetooth's 40 channels), making it difficult to adapt to the channel diversity found in real-world communication environments. 3) Protocol-customized solutions. These solutions design demodulation mechanisms for specific protocols. For example, the Chameleon solution uses the pulse characteristics of 802.11b differential binary phase-shift keying (DBPSK) to achieve demodulation. However, these solutions cannot be extended to constant-envelope protocols (e.g., ZigBee and Bluetooth), and lack effective means to distinguish the phase symmetry of higher-order modulations (e.g., 802.11b differential binary phase-shift keying), limiting their applicability.

[0004] In summary, existing downlink technology suffers from two fundamental flaws: 1) Strong hardware dependency: Dedicated auxiliary equipment or modifications to transmitter hardware are required, making it difficult to integrate with existing wireless infrastructure; 2) Poor protocol compatibility: Customized filters or protocol solutions cannot cover multi-band and multi-protocol scenarios, limiting scalable application. These issues limit existing backscatter tags to one-way beacons, preventing bidirectional interaction (such as channel switching, rate adaptation, and configuration updates), severely hindering the intelligentization and scalable deployment of IoT devices. Therefore, a downlink communication solution that requires no auxiliary equipment, is compatible with commercial wireless protocols (such as ZigBee, Bluetooth, and WiFi), and adapts to dynamic channel environments is urgently needed to promote the integration of backscatter technology into the ubiquitous IoT ecosystem. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a backscatter downlink communication method and system for commercial radio.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a backscatter downlink communication method for commercial radio, which enables a tag to demodulate multiple environmental signals modulated by a transmitter, comprising the following steps:

[0008] The received ambient signal is divided into a first signal and a second signal; the first signal is processed by a delay module composed of cascaded acoustic wave filters to generate a time delay that matches the modulation period of the protocol type used by the ambient signal to obtain a delayed signal; the second signal is caused to generate a fixed phase offset relative to the ambient signal by a phase shifter to obtain a phase-shifted signal;

[0009] The delayed signal and the phase-shifted signal are vector-superimposed, and the envelope amplitude of the resulting composite signal is determined by the relative phase offset between the delayed signal and the phase-shifted signal;

[0010] detecting the envelope amplitude change of the synthesized signal and outputting an analog signal, and converting the analog signal into a digital signal through a comparator;

[0011] The digital signal is converted into a bit stream or a chip sequence to realize demodulation of the ambient signal.

[0012] In one embodiment, the vector superposition of the delayed signal and the phase-shifted signal, wherein the envelope amplitude of the synthesized signal is determined by the relative phase offset between the delayed signal and the phase-shifted signal, specifically includes:

[0013] ;

[0014] is the envelope amplitude of the synthetic signal, Represent the insertion loss of the delayed signal and the phase-shifted signal respectively, is the imaginary unit, is the relative fixed phase offset between the phase-shifted signal and the delayed signal, is the relative phase offset between the phase-shifted signal and the delayed signal.

[0015] In one embodiment, the number n of cascaded acoustic wave filters in the delay module is configured according to the protocol type of the ambient signal: when the ambient signal is a ZigBee signal and a Bluetooth signal, n=3 is used to achieve a delay of 45ns; when the ambient signal is a WiFi signal, n=4 is used to achieve a delay of 60ns.

[0016] In one embodiment, the acoustic wave filter uses a thin film bulk acoustic wave resonator chip.

[0017] In one embodiment, the step size of the phase shifter is And the insertion loss is 3.2 dB.

[0018] In one embodiment, converting the digital signal into a bit stream or a chip sequence specifically includes:

[0019] By performing cross-correlation calculation on a preset template and a digital signal sequence output by a comparator, a digital signal sequence whose cross-correlation result exceeds a threshold is marked as synchronized.

[0020] In a second aspect, the present invention provides a backscatter downlink communication system for commercial radio, comprising:

[0021] Matching network for receiving ambient signals;

[0022] A power splitter, configured to split the ambient signal into a first signal and a second signal;

[0023] A delay module, composed of cascaded acoustic wave filters, is used to process the first signal, generate a time delay that matches the modulation period of the protocol type used by the environmental signal, and obtain a delayed signal;

[0024] a phase shifter, causing the second signal to generate a fixed phase shift compared to the ambient signal to obtain a phase-shifted signal;

[0025] The combiner performs vectorial superposition of the delayed signal and the phase-shifted signal. The envelope amplitude of the resulting composite signal is determined by the relative phase offset between the delayed signal and the phase-shifted signal.

[0026] Envelope detector, detects the envelope amplitude change of the synthesized signal and outputs an analog signal,

[0027] a comparator, converting the analog signal into a digital signal;

[0028] A field programmable gate array converts the digital signal into a bit stream or a chip sequence.

[0029] In one embodiment, the vector superposition of the delayed signal and the phase-shifted signal, wherein the envelope amplitude of the synthesized signal is determined by the relative phase offset between the delayed signal and the phase-shifted signal, specifically includes:

[0030] ;

[0031] is the envelope amplitude of the synthetic signal, Represent the insertion loss of the delayed signal and the phase-shifted signal respectively, is the imaginary unit, is the relative fixed phase offset between the phase-shifted signal and the delayed signal, is the relative phase offset between the phase-shifted signal and the delayed signal.

[0032] In one embodiment, the number n of cascaded acoustic wave filters in the delay module is configured according to the protocol type of the ambient signal: when the ambient signal is a ZigBee signal and a Bluetooth signal, n=3 is used to achieve a delay of 45ns; when the ambient signal is a WiFi signal, n=4 is used to achieve a delay of 60ns.

[0033] In one embodiment, the acoustic wave filter uses a thin film bulk acoustic wave resonator chip.

[0034] Compared with the prior art, the beneficial technical effects of the present invention are:

[0035] To address the limitations of existing low-power backscatter tag downlink communications, this paper proposes a novel interferometrically driven backscatter downlink method and system (InterfereX) for commercial radios. This method converts the phase modulation of the ambient signal into envelope amplitude and utilizes envelope detection for efficient decoding. Positive phase modulation produces a high level, while negative phase shifts produce a low level. Because protocols such as ZigBee, Bluetooth, and 802.11b WiFi encode data through differential phase modulation, this method is scalable to commercial radios operating in the 2.4 GHz ISM (Industrial, Scientific, and Medical) band. By modifying only the tag's RF front-end and eliminating the need for additional auxiliary equipment, this method significantly reduces deployment costs and better meets the requirements for downlink tag data transmission in low-power wireless transmission systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 4 is a flow chart of a method in an embodiment of the present invention.

[0037] Figure 2 Schematic diagram of a system in an embodiment of the present invention.

[0038] Figure 3 Schematic diagram of the principle of interference-based amplitude conversion in an embodiment of the present invention.

[0039] Figure 4 Schematic diagram of the envelope of ZigBee signal demodulation in an embodiment of the present invention.

[0040] Figure 5 Schematic diagram of the envelope of Bluetooth signal demodulation in an embodiment of the present invention.

[0041] Figure 6 The fixed phase offset in the embodiment of the present invention is Schematic diagram of envelope amplitude changes caused by different phase modulations.

[0042] Figure 7 The fixed phase offset in the embodiment of the present invention is Schematic diagram of envelope amplitude changes caused by different phase modulations.

[0043] Figure 8 Schematic diagram of the envelope of 802.11b WiFi signal demodulation in an embodiment of the present invention.

[0044] Figure 9 The figure is a schematic diagram of the bit error rate of the ZigBee signal in line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios according to an embodiment of the present invention.

[0045] Figure 10 The figure is a schematic diagram of the bit error rate of the Bluetooth signal in line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios according to an embodiment of the present invention.

[0046] Figure 11 The figure is a schematic diagram of the bit error rate of an 802.11b WiFi signal in line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios according to an embodiment of the present invention.

[0047] Figure 12 Schematic diagram of demodulation bit error rates of Bluetooth signals under different channels in an embodiment of the present invention.

[0048] Figure 13 Schematic diagram of the demodulation bit error rate of ZigBee signals under different channels in an embodiment of the present invention.

[0049] Figure 14 FIG. 1 is a schematic diagram of demodulation bit error rates of 802.11b WiFi signals under different channels according to an embodiment of the present invention. DETAILED DESCRIPTION

[0050] A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0051] like Figure 1 As shown, the present invention provides a backscatter downlink communication method for commercial radio, which enables the tag to demodulate multiple environmental signals modulated by the transmitter, including the following steps:

[0052] S1: Split the received ambient signal into a first signal and a second signal; Process the first signal through a delay module composed of cascaded acoustic wave filters to generate a time delay that matches the modulation period of the protocol type used by the ambient signal, thereby obtaining a delayed signal; Use a phase shifter to cause the second signal to generate a fixed phase offset relative to the ambient signal, thereby obtaining a phase-shifted signal;

[0053] S2: Perform vectorial superposition of the delayed signal and the phase-shifted signal. The envelope amplitude of the resulting composite signal is determined by the relative phase offset between the delayed signal and the phase-shifted signal.

[0054] S3: detecting the envelope amplitude change of the synthesized signal and outputting an analog signal, and converting the analog signal into a digital signal through a comparator;

[0055] S4: Convert the digital signal into a bit stream or a chip sequence to achieve demodulation of the ambient signal.

[0056] Specifically, if Figure 2As shown, the present invention designs a novel interferometric RF front-end in the tag, which converts the phase information modulated by the ambient signal into a distinguishable envelope amplitude. The incident ambient signal first passes through a matching network and is then split into two signals by a power divider. The first signal is precisely time-delayed by a cascaded film bulk acoustic resonator (FBAR) chip. The second signal passes through a phase adjustment module, where a precision phase shifter adjusts the fixed phase offset between the two signals. The two processed signals are recombined in a combiner. The envelope amplitude of the combined signal is determined by the phase difference between the two signals: a high level corresponds to a positive phase shift, while a low level corresponds to a negative phase shift. An envelope detector detects envelope changes, and its output signal is converted to a digital signal by a comparator. A field-programmable gate array (FPGA) converts these digital signals into a bit stream or chip sequence. Furthermore, an RF switch (RF switch) is responsible for implementing uplink data transmission. This section first introduces the principle of interference-based demodulators, then analyzes the factors that affect amplitude conversion efficiency. Finally, it explains how to apply amplitude conversion to demodulate ZigBee, Bluetooth, and WiFi signals.

[0057] The field programmable gate array converts these digital signals into bit streams or chip sequences. Specifically, for ZigBee signals and WiFi signals, the field programmable gate array converts the digital signals into chip sequences; for Bluetooth signals, the field programmable gate array converts the digital signals into bit streams.

[0058] Specifically, interference-based ambient signal demodulation works as follows: It aims to reveal the characteristics of the superposition of the original ambient signal and its delayed replica. When the two signals are superimposed, their envelope amplitude is determined by the phase difference. This aligns with the modulation scheme of commercial protocols (such as ZigBee, Bluetooth, and 802.11b WiFi), where data is determined by the phase difference between adjacent chips or codewords. This invention converts phase-shift modulation into varying envelope amplitudes, making envelope detection a powerful tool for decoding ambient signals.

[0059] In one embodiment, step S2 of vector superposition of the delayed signal and the phase-shifted signal, wherein the envelope amplitude of the synthesized signal is determined by the relative phase offset between the delayed signal and the phase-shifted signal, specifically includes:

[0060] ;

[0061] is the envelope amplitude of the synthetic signal, Represent the insertion loss of the delayed signal and the phase-shifted signal respectively, is the imaginary unit, is the relative fixed phase offset between the phase-shifted signal and the delayed signal, is the relative phase offset between the phase-shifted signal and the delayed signal.

[0062] Specifically, Figure 3 The demodulation process of the ambient signal based on interference is explained. Assume that the phase shift signal of the original ambient signal is , Indicates that at the current moment, the delayed signal of the environmental signal is , is the signal delay between the ambient signal and the delayed signal. The phase difference between the delayed signal and the phase-shifted signal Determined by the phase change between adjacent codewords or chips, there is a fixed phase offset between the delayed signal and the phase-shifted signal When the delayed signal and the phase-shifted signal are vector-superimposed and the composite signal is calculated, if , constructive interference occurs, the envelope amplitude of constructive interference Enhanced; on the contrary, if , destructive interference occurs, the envelope amplitude of destructive interference This process can be expressed mathematically as:

[0063]

[0064]

[0065]

[0066] . (1)

[0067] in, Indicates the envelope amplitude of the synthetic signal; Represent the insertion loss of delayed signal and phase-shifted signal respectively; is the center frequency of the ambient signal; and Represent the phases of the phase-shifted signal and the delayed signal respectively; and represent the fixed phase offsets of the phase-shifted signal and the delayed signal, respectively; Indicates the relative fixed phase offset between the phase-shifted signal and the delayed signal; represents the relative phase shift between the phase-shifted signal and the delayed signal. In formula (1), since all parameters ( , and ) are fixed, the envelope amplitude of the synthetic signal Determined by the relative changing phase offset between the phase-shifted signal and the delayed signal.

[0068] In one embodiment, the number n of cascaded acoustic wave filters in the delay module is configured according to the protocol type of the ambient signal: when the ambient signal is a ZigBee signal and a Bluetooth signal, n=3 is used to achieve a delay of 45ns; when the ambient signal is a WiFi signal, n=4 is used to achieve a delay of 60ns.

[0069] In one embodiment, the acoustic wave filter uses a thin film bulk acoustic wave resonator chip.

[0070] In one embodiment, the step size of the phase shifter is And the insertion loss is 3.2 dB.

[0071] Specifically, factors affecting amplitude conversion efficiency include time delay and phase offset.

[0072] Latency: The time delay between the ambient signal and the delayed signal It is an important factor affecting amplitude conversion. To achieve the best performance, the time delay between the ambient signal and the delayed signal Should be the same as the modulation period of the codeword or chip to maximize the phase difference between the signals and their corresponding envelope amplitude difference For example, the ideal delays for ZigBee, Bluetooth, and WiFi signals are 、 as well as This requirement seems simple, but existing delay solutions are difficult to achieve. For example, the Biscatter solution attempts to use microstrip lines to introduce delay: the longer the microstrip line, the greater the delay. However, due to the extremely fast propagation speed of electromagnetic waves, the delay that can be introduced per meter of microstrip line is only 0.47 ns, and the loss is as high as 6 dB / m. To achieve a delay of 1 μs, the tag needs meters long delay line with losses up to dB.

[0073] To overcome delay size limitations, the present invention exploits the properties of acoustic wave filters. Due to the low propagation speed of acoustic waves (approximately 180 m / s), these filters can provide significant delay within a compact size. For example, the QPQ1287 acoustic wave filter can achieve a delay of 9 ns with a loss of 3 dB; the AFS2442.0S4 acoustic wave filter can achieve a delay of 12.5 ns with a loss of 2 dB; the MP07497 acoustic wave filter can achieve a delay of 16 ns with a loss of 3.2 dB; and the M359-2595M1 acoustic wave filter can achieve a delay of 1200 ns with a loss of 31 dB. These acoustic wave filters can achieve delays ranging from 9 ns to 1200 ns. However, even the acoustic wave filters with the highest delays exhibit high insertion loss. For example, achieving a delay of 1 μs using the M35-2595M1 acoustic wave filter introduces at least 31 dB of loss, which can severely attenuate weak input signals.

[0074] In order to strike a balance between increasing delay and insertion loss, the present invention cascades multiple acoustic wave filters to avoid excessive loss introduced by a single filter while maintaining a high delay / insertion loss ratio. Specifically, the present invention stacks film bulk acoustic resonator (FBAR) chips with the model number ACFF-1024. A single ACFF-1024 film bulk acoustic resonator (FBAR) chip can form a delay of 15 ns, and its loss is only 1.3 dB. Cascading three ACFF-1024 film bulk acoustic resonator (FBAR) chips successfully increases the delay from 15 ns of a single filter to more than 45 ns. Accordingly, the present invention models the insertion loss of the delayed signal as , the accumulated delay is Where n is the number of FBAR chips; IL is the insertion loss of a single FBAR chip; and dl is the delay introduced by a single FBAR chip. This article will later describe the optimal filter configurations for different IoT protocols.

[0075] Phase offset: Another key factor affecting amplitude conversion is the constant phase offset between the two signal paths. .like Figure 3 As stated, and The relative phase change between The trajectory of The arc of Indicates frequency deviation (for Bluetooth signals 250 kHz for ZigBee signals is 500 kHz); the chord length corresponding to this arc is It shows that 、 and Form a triangle. The triangle satisfies .when and When fully aligned, the amplitude conversion efficiency is the highest. This paper tests the effect of different phase offsets on the demodulation efficiency of ZigBee signals. The results show that different phase offset changes may lead to This results in a difference of more than 20 dB. The precise control of can significantly improve the demodulation quality. In practical applications, the present invention uses a step size of The fine-grained phase shifter (model MAPS-010164) has an insertion loss of only 3.2 dB.

[0076] In one embodiment, converting the digital signal into a bit stream or a chip sequence in step S4 specifically includes:

[0077] By performing cross-correlation calculation on a preset template and a digital signal sequence output by a comparator, a digital signal sequence whose cross-correlation result exceeds a threshold is marked as synchronized.

[0078] Specifically, ZigBee and Bluetooth signal demodulation involves envelope amplitude, envelope optimization, synchronization, and decoding.

[0079] (1) Envelope amplitude. Both ZigBee and Bluetooth signals use binary phase modulation, where A phase shift of represents a bit (or chip) 1, while A shift of 0 represents a bit (or chip) 0. As mentioned earlier, these phase differences are converted into different envelope amplitudes, enabling low-power RF demodulation through envelope detection. Figure 4 and Figure 5 The demodulated envelopes of a ZigBee signal and a Bluetooth signal are shown. The ZigBee signal generates a high level when the modulation code is 1 and a low level when the modulation code is 0; the Bluetooth signal generates a high level when the modulation bit is 1 and a low level when the modulation bit is 0. Given the binary nature of these amplitude levels, a single comparator can effectively digitize the signal: if the amplitude exceeds the comparator threshold, the output is 1; otherwise, the output is 0.

[0080] Figure 4The demodulated ZigBee signal envelope is shown. After being converted by the interference-based RF front-end, the modulation phase of the ZigBee signal exhibits a distinct envelope variation. A high level corresponds to modulated chip 1, and a low level corresponds to chip 0. By setting the comparator threshold, this signal can be converted into a digital signal and input into a field-programmable gate array (FPGA).

[0081] Figure 5 The demodulated Bluetooth signal envelope is shown. After being converted by the interference-based RF front-end, the modulation phase of the Bluetooth signal exhibits a distinct envelope variation. A high level corresponds to modulated chip 1, and a low level corresponds to chip 0. By setting the comparator threshold, this signal can be converted into a digital signal and input into a field-programmable gate array (FPGA).

[0082] (2) Envelope optimization. The demodulation quality depends on the amplitude difference between the envelope when constructive and destructive interference occurs. The amplitude difference depends on the time delay, phase offset and insertion loss. As shown in formula 1, the present invention defines the insertion loss as (in from the phase shifter) and (in and IL = 1.5 dB comes from the film bulk acoustic resonator (FBAR) chip), its total delay .therefore, Only a constant phase shift and the number of cascaded acoustic wave filters n. It has been verified that under normalized RF power, with a step size of Stacking three film bulk acoustic resonator (FBAR) chips will maximize the amplitude conversion efficiency by increasing the phase shift increment. For ZigBee signals, it is 0.1173 (-9.3 dB), and for Bluetooth signals, it is 0.0588 (-12.3 dB). The tag can maximize the amplitude conversion efficiency by fine-tuning the phase offset between RF links. It is worth noting that due to the phase difference of Bluetooth signals (limited by ) is smaller than the phase difference of the ZigBee signal (limited by ) Therefore, the optimal envelope amplitude of Bluetooth signals is lower than that of ZigBee signals.

[0083] (3) Synchronization and decoding. Tag demodulation needs to be synchronized with the input environmental signal first. The data packets of ZigBee signals and Bluetooth signals themselves contain synchronization fields. For example, the synchronization header (SHR) of the ZigBee signal lasts for 160 μs, while the Bluetooth signal provides an 8 μs preamble. The present invention uses the 8 μs field as a template on a field programmable gate array (FPGA) and calculates its cross-correlation with each comparator output sequence. Sequences exceeding a predefined threshold are marked as synchronized, and their outputs are directly mapped to digital bits. Given that the bandwidth of the Bluetooth signal is 1 MHz and the bandwidth of the ZigBee signal is 2 MHz, the present invention sets the sampling rates to 2 MHz and 4 MHz respectively according to the Nyquist criterion.

[0084] Specifically, the demodulation of 802.11b WiFi signals involves amplitude symmetry, generating different envelopes, envelope optimization, synchronization, and decoding.

[0085] Unlike ZigBee and Bluetooth signals, 802.11b WiFi signals use Differential Quadrature Phase Shift Keying (DQPSK), which is a phase shift keying scheme. The main challenge in applying the interferometer-based envelope demodulator to DQPSK demodulation is that multiple phase states produce the same envelope amplitude, resulting in amplitude symmetry.

[0086] (1) Amplitude symmetry. Amplitude symmetry occurs when different phase states produce the same amplitude when superimposed, making them indistinguishable. Figure 6 As shown, when the constant phase offset When the envelope amplitude and This mirror symmetry about the I axis makes This ambiguity is not limited to 802.11b DQPSK; it also poses a significant obstacle to higher-order modulation schemes such as 8PSK and 16PSK, limiting current demodulation strategies to binary protocols such as Bluetooth and ZigBee.

[0087] Figure 6 Shown When the phase modulation is different, the amplitude changes. correspond ; Phase modulation correspond ; Phase modulation correspond ; Phase modulation correspond .in, .

[0088] (2) Generate different envelopes. The key to overcoming amplitude symmetry is to generate an asymmetric vector sum so that each phase state corresponds to a unique envelope amplitude. The present invention introduces a constant phase offset To achieve this, this will destroy the different modulation states and Symmetry between. Figure 7 As shown, set will break the mirror symmetry of the combined signal, resulting in different envelope amplitudes ( This separation enables the tag to establish specific comparator thresholds for each symbol, enabling efficient demodulation of 802.11b DQPSK. For higher-order modulations, similar customized phase offset methods can be used to break the inherent symmetry. Figure 8 It further illustrates how the introduction of phase offset can distinguish the envelope amplitudes of different phase offsets. It is worth noting that since each 802.11b symbol contains an 11-bit long Barker code sequence and the phase offset within the symbol is limited to 0 and , so there will be significant amplitude changes during the symbol transition. In order to accurately capture these changes, the present invention uses three parallel comparators as low-precision analog-to-digital converters (ADCs). The output of each comparator is based on Importantly, the duration of these distinguishable pulses is at least , so the comparator sampling rate needs to be at least To achieve reliable demodulation.

[0089] Figure 7 Shown When the phase modulation is different, the amplitude changes. correspond ; Phase modulation correspond ; Phase modulation correspond ; Phase modulation correspond .in, .

[0090] (3) Envelope optimization. As with ZigBee and Bluetooth signals, the performance indicators of demodulation quality are This invention will Defined as the minimum difference between all pairs of envelopes: It has been verified that stacking four film bulk acoustic resonator (FBAR) chips can maximize the amplitude conversion efficiency, making (-12.8 dB), while stacking three film bulk acoustic resonator (FBAR) chips can also achieve 0.0349 (-14.5dB). In addition, for 802.11b DQPSK, the step size is The phase shifter can provide at least eight different offset positions, effectively breaking the amplitude symmetry. These findings provide an important basis for optimizing envelope characteristics, ensuring reliable demodulation of 802.11b WiFi signals by backscatter tags.

[0091] (4) Synchronization and decoding. Similar to ZigBee and Bluetooth signals, 802.11b WiFi signal demodulation uses template matching technology to achieve tag demodulation. The difference is that WiFi signal decoding uses a comparator with three different thresholds to map the envelope amplitude to 2 bits (for example, 000 represents 0; 011 represents 01; 111 represents 2), which is different from the 1-bit output of Bluetooth and ZigBee signals. Field Programmable Gate Array (FPGA) is used to The tag samples at a rate of 1 μs. When the cross-correlation between the input sequence and the template exceeds a threshold, the tag starts decoding. It is worth noting that effective amplitude transitions only occur at symbol boundaries every 1 μs. Once synchronized, the tag evaluates the WiFi symbol every 1 μs and ignores the amplitude changes in between. Figure 8 As shown, the amplitude conversion occurs every 1 μs, and each level corresponds to a unique .

[0092] Figure 8 This figure demonstrates the demodulated envelope of an 802.11b WiFi signal. After the modulation phase of the 802.11b WiFi signal is converted by the interferometer-based RF front-end, the signal exhibits a distinct envelope change every microsecond at codeword switching points. Since there are four envelope types, three comparators with three thresholds are used to distinguish between different phase modulations. The comparator outputs are fed into a field-programmable gate array (FPGA).

[0093] ZigBee signal demodulation: Figure 9 The downlink bit error rate (BER) of the tag decoding ZigBee signals at different distances in line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios is demonstrated. The experiment shows that the present invention can reliably demodulate ZigBee signals within a range of 5 meters. It is worth noting that the performance in the LOS scenario is better due to reduced environmental noise and stronger signal reception. At 1.0 meter, the BER of LOS is as low as , NLOS is , and remains below 1% until the distance exceeds 4 meters.

[0094] Bluetooth signal demodulation: Figure 10The downlink bit error rate (BER) of Bluetooth signal decoding by the tag at different distances in line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios is demonstrated. Experiments show that the demodulation performance of the present invention remains stable within a range of 5 meters.

[0095] 802.11b WiFi signal demodulation: When the transmitter operates in WiFi mode, the present invention encounters higher noise in NLOS scenarios, limiting the reliable demodulation distance to within 3.75 meters. Figure 11 It shows that at 1.0 m, the BER is as low as 4.90‰ in LOS, but increases to 2.51% in NLOS.

[0096] Channel Diversity: A key advantage of the present invention over filter-based demodulators (such as Saiyan) is its inherent compatibility with multiple wireless channels. Unlike systems that rely on the sharp frequency response of specific channel filters, the present invention can seamlessly adapt to a wide range of frequencies. Figure 12 、 Figure 13 and Figure 14 As shown, the demodulation performance of the present invention for Bluetooth signal, ZigBee signal and WiFi signal transmission is evaluated under different channel conditions. Figure 12 showed that for Bluetooth signals evaluated on 40 channels (center frequencies from 2402 MHz to 2480 MHz), the tags achieved a BER ranging from 2.00‰ to 7.90‰. Figure 13 It is shown that for ZigBee signals evaluated on 16 channels (center frequencies from 2405 MHz to 2480 MHz), the BER of the tag is to 0.97‰. Figure 14 It is shown that for the WiFi signals evaluated on 13 channels (center frequencies ranging from 2412 MHz to 2472 MHz), the BER of the tag does not exceed 1%, with a minimum value of 1.90%.

[0097] In one embodiment, the present invention can be implemented by referring to the following steps:

[0098] (1) Tag prototype construction: The low-power demodulator based on interference first uses a power divider model SCN-2-27+ to split the input environmental signal into two paths. The first signal is delayed by three cascaded ACFF-1024 film bulk acoustic resonator (FBAR) chips, and the other signal is phase-shifted by a phase shifter model MAPS-010164. Subsequently, the two signals are recombined by another combiner model SCN-2-27+, and the superimposed signal is captured by an envelope detector model AD8313. Three parallel comparators model TLV3501 are used to act as low-precision analog-to-digital converters. The field programmable gate array model AGLN250 demodulates Bluetooth signal data at a sampling rate of 2 MSPS, demodulates ZigBee signal data at 4 MSPS, demodulates WiFi signal data at 25 MSPS, and controls the RF switch model ADG902 for backscatter tag uplink communication.

[0099] (2) Environment setup: In the end-to-end experiment, the present invention uses a laptop equipped with a Qualcomm Atheros AR938X network card as the WiFi signal transmitter, with a power setting of 20 dBm. A TI CC1352 chip is used as the ZigBee signal and Bluetooth signal transmitter, with a power setting of 20 dBm.

[0100] (3) Downlink decoding: After receiving the environmental signal and completing the pre-processing, it needs to be converted into usable data through the demodulation process. The present invention designs a demodulation scheme for phase-modulated signals, which includes the following steps: first, the phase-modulated signal is converted into an amplitude signal using an interference-driven demodulation mechanism; second, the analog signal is converted into a digital signal through envelope detection and comparator processing; finally, the field programmable gate array (FPGA) performs signal processing and data decoding. The demodulation process of the present invention has the following characteristics: first, low-power demodulation is achieved through phase-to-amplitude conversion; second, it is compatible with multiple wireless communication protocols, such as ZigBee, Bluetooth, and WiFi; third, innovative demodulation technology is used to improve the accuracy and robustness of demodulation. Experimental verification shows that the demodulation process performs well in different environments and has broad application prospects.

[0101] It should be understood that although the steps in the flowcharts of the accompanying drawings are shown in sequence as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least some of the steps in the flowcharts of the accompanying drawings may include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times. The order of execution of these steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least a portion of the steps or stages in other steps.

[0102] Based on the description of the above method embodiments, the present invention also provides a system. The system can be a system that uses the software (application), module, component, server, client, etc. of the method described in the embodiments of this specification and is combined with the necessary implementation hardware. Based on the same innovative concept, the system in one or more embodiments provided by the embodiments of the present disclosure is as described in the following embodiments. Since the implementation scheme and method for solving the problem of the system are similar, the implementation of the specific system of the embodiments of this specification can refer to the implementation of the aforementioned method, and the repeated parts will not be repeated. As used below, the term "module" or "module" refers to a combination of software and / or hardware that can realize the predetermined function. Although the system described in the following embodiments is preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceived.

[0103] A backscatter downlink communication system for commercial radios, comprising:

[0104] Matching network for receiving ambient signals;

[0105] A power splitter, configured to split the ambient signal into a first signal and a second signal;

[0106] A delay module, composed of cascaded acoustic wave filters, is used to process the first signal, generate a time delay that matches the modulation period of the protocol type used by the environmental signal, and obtain a delayed signal;

[0107] a phase shifter, causing the second signal to generate a fixed phase shift compared to the ambient signal to obtain a phase-shifted signal;

[0108] The combiner performs vectorial superposition of the delayed signal and the phase-shifted signal. The envelope amplitude of the resulting composite signal is determined by the relative phase offset between the delayed signal and the phase-shifted signal.

[0109] Envelope detector, detects the envelope amplitude change of the synthesized signal and outputs an analog signal,

[0110] a comparator, converting the analog signal into a digital signal;

[0111] The field programmable gate array converts the digital signal into a bit stream or a chip sequence to realize the demodulation of the environmental signal.

[0112] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. It is intended that all variations within the meaning and range of equivalents of the claims be embraced herein, and any reference signs in the claims should not be construed as limiting the claims to which they relate.

[0113] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A backscatter downlink communication method for commercial radio, which enables a tag to demodulate multiple environmental signals modulated by a transmitter, characterized in that: The following steps are involved: The received ambient signal is divided into a first signal and a second signal; the first signal is processed by a delay module composed of cascaded acoustic wave filters to generate a time delay that matches the modulation period of the protocol type used by the ambient signal to obtain a delayed signal; the second signal is caused to generate a fixed phase offset relative to the ambient signal by a phase shifter to obtain a phase-shifted signal; The delayed signal and the phase-shifted signal are vector-superimposed, and the envelope amplitude of the resulting composite signal is determined by the relative phase offset between the delayed signal and the phase-shifted signal; detecting the envelope amplitude change of the synthesized signal and outputting an analog signal, and converting the analog signal into a digital signal through a comparator; The digital signal is converted into a bit stream or a chip sequence to realize demodulation of the ambient signal.

2. A commercial radio-oriented backscatter downlink communication method according to claim 1, characterized in that: The delay signal and the phase-shifted signal are vector-superimposed, and the envelope amplitude of the synthesized signal obtained is determined by the relative phase offset between the delay signal and the phase-shifted signal, specifically including: ； is the envelope amplitude of the synthetic signal, Represent the insertion loss of the delayed signal and the phase-shifted signal respectively, is the imaginary unit, is the relative fixed phase offset between the phase-shifted signal and the delayed signal, is the relative phase offset between the phase-shifted signal and the delayed signal.

3. The backscatter downlink communication method for commercial radio according to claim 1, characterized in that: The number n of cascaded acoustic wave filters in the delay module is configured according to the protocol type of the ambient signal: when the ambient signal is a ZigBee signal or a Bluetooth signal, n=3 is used to achieve a delay of 45ns; when the ambient signal is a WiFi signal, n=4 is used to achieve a delay of 60ns.

4. The backscatter downlink communication method for commercial radio according to claim 1, characterized in that: The acoustic wave filter adopts a thin film bulk acoustic wave resonator chip.

5. The backscatter downlink communication method for commercial radio according to claim 1, characterized in that: The step size of the phase shifter is And the insertion loss is 3.2 dB.

6. The backscatter downlink communication method for commercial radio according to claim 1, characterized in that: The converting of the digital signal into a bit stream or a chip sequence specifically includes: By performing cross-correlation calculation on a preset template and a digital signal sequence output by a comparator, a digital signal sequence whose cross-correlation result exceeds a threshold is marked as synchronized.

7. A backscatter downlink communication system for commercial radio, characterized in that include: Matching network for receiving ambient signals; A power splitter, configured to split the ambient signal into a first signal and a second signal; A delay module, composed of cascaded acoustic wave filters, is used to process the first signal, generate a time delay that matches the modulation period of the protocol type used by the environmental signal, and obtain a delayed signal; a phase shifter, causing the second signal to generate a fixed phase shift compared to the ambient signal to obtain a phase-shifted signal; The combiner performs vectorial superposition of the delayed signal and the phase-shifted signal. The envelope amplitude of the resulting composite signal is determined by the relative phase offset between the delayed signal and the phase-shifted signal. Envelope detector, detects the envelope amplitude change of the synthesized signal and outputs an analog signal, a comparator, converting the analog signal into a digital signal; A field programmable gate array converts the digital signal into a bit stream or a chip sequence.

8. A commercial radio-oriented backscatter downlink communication system according to claim 7, characterized in that: The delay signal and the phase-shifted signal are vector-superimposed, and the envelope amplitude of the synthesized signal obtained is determined by the relative phase offset between the delay signal and the phase-shifted signal, specifically including: ； is the envelope amplitude of the synthetic signal, Represent the insertion loss of the delayed signal and the phase-shifted signal respectively, is the imaginary unit, is the relative fixed phase offset between the phase-shifted signal and the delayed signal, is the relative phase offset between the phase-shifted signal and the delayed signal.

9. The commercial radio-oriented backscatter downlink communication system according to claim 7, characterized in that: The number n of cascaded acoustic wave filters in the delay module is configured according to the protocol type of the ambient signal: when the ambient signal is a ZigBee signal or a Bluetooth signal, n=3 is used to achieve a delay of 45ns; when the ambient signal is a WiFi signal, n=4 is used to achieve a delay of 60ns.

10. The commercial radio-oriented backscatter downlink communication system according to claim 7, characterized in that: The acoustic wave filter adopts a thin film bulk acoustic wave resonator chip.

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