ZigBee backscattering method and system with adaptive switching of Bluetooth excitation

Abstract

The present invention relates to the technical field of backscatter communication, and discloses a ZigBee backscatter method and system for adaptively switching Bluetooth excitation. The method comprises: an excitation source periodically sends a batch of backscatter data packets to a ZigBee receiving end via a tag; the ZigBee receiving end counts the number of correctly received backscatter data packets and compares it with a set threshold; if the number of correctly received backscatter data packets exceeds the threshold, a command is sent to the excitation source and tag via a reverse communication link to switch to an operating mode based on ambient Bluetooth excitation; if the number of correctly received backscatter data packets is less than or equal to the threshold, a command is sent to the excitation source and tag via the reverse communication link to switch to an operating mode based on single-frequency Bluetooth excitation. When the signal-to-noise ratio is low, the present invention can adaptively switch the excitation signal to a single-frequency Bluetooth signal, preventing the excitation signal from causing phase interference with the backscatter signal, thereby reducing the communication bit error rate.

Description

Technical Field

[0001] The present invention relates to the technical field of backscatter communication, and in particular to a ZigBee backscatter method and system with adaptive switching of Bluetooth excitation. Background Art

[0002] Traditional ZigBee devices use active communication, and their high power consumption has become a bottleneck hindering the continued development of wireless sensor networks. Backscatter tags utilize ambient RF signals as excitation signals, modulating these signals to carry tag data. Because they don't actively generate RF signals, their power consumption is significantly lower than traditional active devices. Applying this technology to ZigBee communications, replacing active communication with ZigBee backscatter communication, is expected to significantly reduce the power consumption of wireless sensor networks.

[0003] To fully leverage existing commercial protocol equipment and reduce the deployment cost of backscatter systems, current research is focusing on using commercial devices as the system's excitation source. Given the widespread use of Bluetooth devices in everyday life, ZigBee backscatter systems based on Bluetooth excitation offer unique advantages. Research teams have successfully developed a system in which tags modulate ambient Bluetooth signals into ZigBee-compatible backscatter signals. These backscatter signals can then be demodulated using commercial ZigBee devices as receivers. This approach not only enables low-power ZigBee backscatter communication but also leverages the widespread availability of Bluetooth signals as excitation signals, significantly reducing the system's hardware deployment costs.

[0004] However, this system still suffers from a high bit error rate. The ambient Bluetooth signal, acting as the excitation signal, causes phase interference in the backscattered signal, hindering the demodulation of the backscattered signal by the ZigBee receiver. In poor communication environments with low signal-to-noise ratios, the system's bit error rate is too high, making it difficult to effectively transmit tag data. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a ZigBee backscattering method and system with adaptive switching of Bluetooth excitation. The present invention sets up an additional working mode based on single-frequency Bluetooth excitation; when the signal-to-noise ratio is low, the Bluetooth excitation source switches to sending a single-frequency Bluetooth signal as the excitation signal of the tag, thereby avoiding phase interference with the backscattered signal and reducing the bit error rate of the backscattered communication.

[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 ZigBee backscattering method for adaptively switching Bluetooth excitation, which supports a working mode based on environmental Bluetooth excitation and a working mode based on single-frequency Bluetooth excitation, including:

[0008] Working mode based on environmental Bluetooth excitation: the excitation source sends a Bluetooth signal carrying arbitrary data, and the tag modulates the Bluetooth signal to generate a backscattered signal;

[0009] Working mode based on single-frequency Bluetooth excitation: the excitation source sends a Bluetooth extended advertising packet carrying specific payload field content to generate a single-frequency signal, and the tag modulates the single-frequency signal to generate a backscattered signal;

[0010] Adaptive switching of working modes is achieved through the following methods:

[0011] The excitation source periodically sends a batch of backscattered data packets to the ZigBee receiver through the tag;

[0012] The ZigBee receiver counts the number of correctly received backscattered packets and compares it with the set threshold;

[0013] If the number of correct receptions is greater than the threshold, an instruction is sent to the excitation source and the tag via the reverse communication link to switch to the working mode based on the ambient Bluetooth excitation;

[0014] If the number of correct receptions is less than or equal to the threshold, an instruction is sent to the excitation source and the tag via the reverse communication link to switch to a working mode based on single-frequency Bluetooth excitation.

[0015] In one embodiment, the stimulus source sends a Bluetooth extended advertising packet carrying specific payload field content to generate a single frequency signal, specifically comprising:

[0016] The payload field of the Bluetooth extended advertising packet of the single-frequency signal is all 0 data.

[0017] In one embodiment, the reverse communication link includes: a communication link from the ZigBee receiver to the excitation source and a communication link from the excitation source to the tag;

[0018] The communication link between the ZigBee receiver and the stimulus source uses cross-protocol communication technology. The Bluetooth device in the stimulus source establishes a mapping table between ZigBee symbols and Bluetooth bit sequences by adding sampling offsets, and demodulates the instructions in the form of ZigBee signals.

[0019] Communication link from the excitation source to the tag: The WiFi module of the excitation source sends an amplitude modulated signal, and the tag demodulates the amplitude modulated signal through an envelope detector to obtain the instruction.

[0020] In one embodiment, the amplitude modulated signal is implemented by alternately transmitting a constant OFDM symbol and a random OFDM symbol, wherein one random OFDM symbol and one constant OFDM symbol represent bit 1, and two random OFDM symbols represent bit 0.

[0021] In one embodiment, 90% of the number of backscattered data packets sent by the tag to the ZigBee receiver is set as the threshold.

[0022] In a second aspect, the present invention provides a ZigBee backscatter system with adaptive switching Bluetooth excitation, which supports an operating mode based on ambient Bluetooth excitation and an operating mode based on single-frequency Bluetooth excitation, including:

[0023] Data packet sending module: The excitation source periodically sends a batch of backscattered data packets to the ZigBee receiver through the tag;

[0024] Excitation mode switching module: The ZigBee receiver counts the number of correctly received backscattered data packets and compares it with a set threshold. If the number of correctly received packets is greater than the threshold, a command is sent to the excitation source and tag via the reverse communication link to switch to an operating mode based on ambient Bluetooth excitation. If the number of correctly received packets is less than or equal to the threshold, a command is sent to the excitation source and tag via the reverse communication link to switch to an operating mode based on single-frequency Bluetooth excitation.

[0025] Among them, the working mode based on environmental Bluetooth excitation is: the excitation source sends a Bluetooth signal carrying arbitrary data, and the tag modulates the Bluetooth signal to generate a backscattered signal; the working mode based on single-frequency Bluetooth excitation is: the excitation source sends a Bluetooth extended broadcast packet carrying specific payload field content to generate a single-frequency signal, and the tag modulates the single-frequency signal to generate a backscattered signal.

[0026] In one embodiment, the stimulus source sends a Bluetooth extended advertising packet carrying specific payload field content to generate a single frequency signal, specifically comprising:

[0027] The payload field of the Bluetooth extended advertising packet of the single-frequency signal is all 0 data.

[0028] In one embodiment, the reverse communication link includes: a communication link from the ZigBee receiver to the excitation source and a communication link from the excitation source to the tag;

[0029] The communication link between the ZigBee receiver and the stimulus source uses cross-protocol communication technology. The Bluetooth device in the stimulus source establishes a mapping table between ZigBee symbols and Bluetooth bit sequences by adding sampling offsets, and demodulates the instructions in the form of ZigBee signals.

[0030] Communication link from the excitation source to the tag: The WiFi module of the excitation source sends an amplitude modulated signal, and the tag demodulates the amplitude modulated signal through an envelope detector to obtain the instruction.

[0031] In one embodiment, the amplitude modulated signal is implemented by alternately transmitting a constant OFDM symbol and a random OFDM symbol, wherein one random OFDM symbol and one constant OFDM symbol represent bit 1, and two random OFDM symbols represent bit 0.

[0032] In one embodiment, 90% of the number of backscattered data packets sent by the tag to the ZigBee receiver is set as the threshold.

[0033] The system in the present invention corresponds to the method, and the specific technical solutions applicable to the method are also applicable to the system.

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

[0035] In response to the defect of high bit error rate of existing Zigbee backscatter systems based on Bluetooth excitation, the present invention provides an additional working mode based on single-frequency Bluetooth excitation. When the signal-to-noise ratio is low, the present invention can adaptively switch the excitation signal to a single-frequency Bluetooth signal to prevent the excitation signal from causing phase interference to the backscatter signal, thereby reducing the bit error rate of communication. The present invention switches the working mode based on the packet loss rate. The tag regularly sends a batch of backscatter data packets to the receiving end, which records the number of correctly received data packets and compares it with a pre-set threshold. According to the comparison result, instructions are transmitted to the excitation source and the tag to adjust the working mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Flowchart of a method in an embodiment of the present invention.

[0037] Figure 2 The following is a schematic diagram of the working process of Bluetooth devices.

[0038] Figure 3 Schematic diagram of the allowable phase error range when demodulating ZigBee backscattered signals based on ambient Bluetooth excitation in an embodiment of the present invention.

[0039] Figure 4 Schematic diagram of the allowable phase error range when demodulating ZigBee backscatter signals based on single-frequency Bluetooth excitation in an embodiment of the present invention.

[0040] Figure 5 Schematic diagram of ZigBee backscatter data packet loading in two working modes in an embodiment of the present invention.

[0041] Figure 6Schematic diagram of a working mode switching strategy based on backscatter packet loss rate in an embodiment of the present invention.

[0042] Figure 7 Schematic diagram of a reverse communication link in an embodiment of the present invention.

[0043] Figure 8 Schematic diagram of the mapping relationship between ZigBee symbols and Bluetooth bit sequences in an embodiment of the present invention.

[0044] Figure 9 is a schematic diagram of an amplitude modulation signal in an embodiment of the present invention.

[0045] Figure 10 FIG. 1 is a schematic diagram of demodulating an AM signal by dynamically setting a threshold value according to an embodiment of the present invention.

[0046] Figure 11 Schematic diagram of the effective throughput of two working modes under various signal-to-noise ratios in an embodiment of the present invention.

[0047] Figure 12 Schematic diagram of packet loss rates of data packets sent by backscatter at various signal-to-noise ratios in an embodiment of the present invention.

[0048] Figure 13 Schematic diagram of effective throughput under various signal-to-noise ratios after the strategy of adaptively switching working modes is adopted in an embodiment of the present invention.

[0049] Figure 14 A schematic diagram of a symbol error rate of ZigBee symbols restored by a Bluetooth device in an embodiment of the present invention.

[0050] Figure 15 Schematic diagram of the bit error rate of a tag demodulating an amplitude modulated signal in a communication link from an excitation source to a tag in an embodiment of the present invention. DETAILED DESCRIPTION

[0051] A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0052] like Figure 1 As shown, the present invention provides a ZigBee backscattering method for adaptively switching Bluetooth excitation, which supports a working mode based on environmental Bluetooth excitation and a working mode based on single-frequency Bluetooth excitation, including the following steps:

[0053] S1, the excitation source periodically sends a batch of backscattered data packets to the ZigBee receiver through the tag;

[0054] S2, the ZigBee receiver counts the number of correctly received backscattered data packets and compares it with the set threshold;

[0055] S3, if the number of correct receptions is greater than the threshold, a command is sent to the excitation source and the tag via the reverse communication link to switch to the working mode based on the ambient Bluetooth excitation;

[0056] S4: If the number of correct receptions is less than or equal to the threshold, an instruction is sent to the excitation source and the tag via the reverse communication link to switch to a working mode based on single-frequency Bluetooth excitation.

[0057] Among them, the working mode based on environmental Bluetooth excitation is: the excitation source sends a Bluetooth signal carrying arbitrary data, and the tag modulates the Bluetooth signal to generate a backscattered signal; the working mode based on single-frequency Bluetooth excitation is: the excitation source sends a Bluetooth extended broadcast packet carrying specific payload field content to generate a single-frequency signal, and the tag modulates the single-frequency signal to generate a backscattered signal;

[0058] The following first introduces how the present invention switches between the two working modes, and then introduces the implementation method of each communication link.

[0059] 1. Working mode adaptive switching method.

[0060] The following first introduces how to implement the working mode based on single-frequency Bluetooth excitation in the present invention, and then introduces how to switch between the working mode based on single-frequency Bluetooth excitation and the working mode based on ambient Bluetooth excitation in the present invention.

[0061] (1) Working mode based on single-frequency Bluetooth excitation.

[0062] Bluetooth devices can generate single-frequency Bluetooth signals by sending Bluetooth packets carrying specific data. The existing ZigBee backscatter system based on ambient Bluetooth excitation uses overwrite modulation technology. The tag can apply phase shift and cover the phase interference caused by the ambient Bluetooth signal, thereby carrying the tag data. The working process of the Bluetooth device is as follows: Figure 2 As shown. Bluetooth uses Gaussian frequency shift keying (GFSK) to carry data bit sequences by applying frequency shift to the signal; among them, GFSK technology is obtained by introducing a Gaussian filter based on BFSK (binary frequency shift keying) technology. The signal passing through the Gaussian filter also needs to pass through a digital integrator, a digital-to-analog converter and an up-converter. Because frequency shift will cause phase shift, when the ambient Bluetooth signal is used as the excitation signal, the phase of the backscattered signal will be disturbed. However, because the phase shift range imposed by the tag during backscattering is greater than the range of phase interference caused by the ambient Bluetooth signal, the positive and negative phase shift of the backscattered signal is controlled by the tag. The ZigBee receiver can restore the tag data based on the positive and negative phase shift between sampling points. The allowable phase error range when the ZigBee receiver demodulates the backscattered signal is as follows Figure 3 shown. Figure 3 A label is given by modulating Phase shift to carry data bits 1, modulation The constellation diagram of an example of using the phase shift to carry the data bit 0 (the in-phase component is the horizontal axis and the orthogonal component is the vertical axis). Using the ambient Bluetooth signal as the excitation signal will cause the phase shift between two adjacent sampling points of the ZigBee receiver to be as large as 0. is centered and has a range of Therefore, the total phase shift obtained by the ZigBee receiver is The ZigBee receiver is in the range of ) demodulates the backscattered signal to obtain bit 1, thus correctly recovering the tag data. Although the ZigBee receiver can correctly recover the tag data using this method, the phase interference introduced by the ambient Bluetooth signal reduces the acceptable phase error range when demodulating the backscattered signal. This results in a higher bit error rate (BER) at low signal-to-noise ratios.

[0063] To reduce the bit error rate (BER) of backscatter communication, phase interference caused by the excitation signal should be avoided. This paper proposes an operating mode for ZigBee backscatter communication based on single-frequency Bluetooth excitation. In this mode, the Bluetooth device transmits all zeros, ensuring a consistent frequency shift when modulating the signal, thus generating a single-frequency Bluetooth signal. Figure 4 A label is given by modulating Phase shift to carry data bits 1, modulation The constellation diagram of an example of carrying data bit 0 with a phase shift (the in-phase component is the horizontal axis and the orthogonal component is the vertical axis); Figure 4 As shown, using a single-frequency Bluetooth signal as the excitation signal does not introduce phase interference to the backscattered signal. Therefore, the permissible error range of the ZigBee receiver when demodulating the backscattered signal is increased. Implementing ZigBee backscatter communication using this method can reduce the bit error rate.

[0064] Figure 4 This paper demonstrates the permissible phase error range for a ZigBee receiver demodulating a backscattered signal in single-frequency Bluetooth excitation mode. The Bluetooth excitation source device is controlled to transmit data, generating a single-frequency Bluetooth signal. The tag uses the single-frequency Bluetooth signal as the excitation signal, preventing phase interference in the backscattered signal.

[0065] Compared to the working mode based on ambient Bluetooth excitation, the backscattered signal in the working mode based on single-frequency Bluetooth excitation proposed by the present invention is not subject to phase interference. Therefore, in this working mode, the ZigBee receiver has a lower bit error rate when demodulating the backscattered signal.

[0066] (2) Working mode switching strategy based on backscatter packet loss rate.

[0067] The packet loss rate of the backscattered data packets received by the receiving device can be used as a basis for the system to switch the working mode.

[0068] While the single-frequency Bluetooth excitation operating mode proposed in this invention can reduce the bit error rate of backscatter communication, the Bluetooth excitation source device must send specific data to generate the single-frequency Bluetooth signal in this mode, making data transmission impossible. Furthermore, only the data carried in the payload field of a Bluetooth packet can be controlled by the Bluetooth device, so only the signal corresponding to this field is a single-frequency Bluetooth signal. Therefore, when using this mode, the excitation signal duration available to the tag is relatively short, reducing the amount of data transmitted in each backscatter transmission.

[0069] The two working modes based on environmental Bluetooth excitation and based on single-frequency Bluetooth excitation have their own advantages and disadvantages, so the present invention will adaptively switch between these two working modes. When the signal-to-noise ratio is large, the backscatter communication bit error rate is low. At this time, the working mode based on environmental Bluetooth excitation is adopted. In this mode, the Bluetooth excitation source can send a Bluetooth extended broadcast packet carrying any valid data. The tag can use the signal corresponding to the entire Bluetooth extended broadcast packet as the excitation signal to carry the tag data. When the signal-to-noise ratio is small, the backscatter communication bit error rate is high. At this time, the system switches to a working mode based on single-frequency Bluetooth excitation, and lets the Bluetooth excitation source send a Bluetooth extended broadcast packet with a payload of all 0s to generate a single-frequency Bluetooth signal. This working mode can prevent the excitation signal from causing phase interference to the backscatter signal, thereby reducing the bit error rate of the backscatter communication. The carrying of ZigBee backscatter data packets in the two working modes is shown as follows. Figure 5 As shown in the figure, the tag can transmit 58 bytes and 55 bytes of valid data in a single backscattering operation based on ambient Bluetooth excitation and single-frequency Bluetooth excitation, respectively.

[0070] The difficulty in implementing adaptive switching of working modes lies in how the excitation source and the tag switch working modes at the right time. This invention proposes a working mode switching strategy based on backscatter packet loss rate, such as Figure 6 The excitation source and tag in the present invention periodically send a batch of backscattered data packets to the ZigBee receiver. The ZigBee receiver device records the number of packets correctly received. , and the pre-set threshold If the number of correctly received packets exceeds the threshold, the device switches to an ambient Bluetooth stimulus mode; otherwise, it switches to a single-band Bluetooth stimulus mode. The ZigBee receiver transmits instructions to the stimulus source and tag to adjust their operating modes.

[0071] The present invention can adaptively adjust the excitation signal type, using the ambient Bluetooth signal as the excitation signal when the signal-to-noise ratio is high, and using a single-frequency Bluetooth signal as the excitation signal when the signal-to-noise ratio is low. At high signal-to-noise ratios, the backscatter system is based on the ambient Bluetooth excitation, and the Bluetooth excitation source can transmit valid data while providing the excitation signal to the tag. At low signal-to-noise ratios, the backscatter system switches the excitation signal to a single-frequency Bluetooth signal, allowing backscatter communication to maintain a low bit error rate even at low signal-to-noise ratios. In summary, by adaptively switching operating modes, the present invention can achieve optimal performance at all signal-to-noise ratios.

[0072] 2. Establish reverse communication link.

[0073] In the above-mentioned working mode switching strategy based on backscatter packet loss rate, the ZigBee receiving device needs to transmit the instruction of switching working mode to the excitation source and the tag. The following will introduce how to implement the reverse communication link from the receiving end to the excitation source and the tag. Figure 7 As shown. The present invention establishes the reverse communication link by respectively realizing the communication from the ZigBee receiving end to the excitation source and the communication from the excitation source to the tag. The communication from the ZigBee receiving end to the excitation source is realized by cross-protocol decoding technology, and the Bluetooth module in the excitation source can demodulate the ZigBee signal. The communication from the excitation source to the tag is realized by an amplitude modulated signal. The excitation source device in the present invention has a WiFi module added, which can be used to send an amplitude modulated signal, and the tag can use an envelope detector to demodulate the amplitude modulated signal. The implementation methods of these two communication links will be introduced separately below.

[0074] (1) Cross-protocol communication from ZigBee devices to Bluetooth devices.

[0075] ZigBee signals use offset quadrature phase shift keying (OQPSK) modulation to modulate information through phase shift, and Bluetooth devices also demodulate signals based on phase shift.

[0076] ZigBee signals use offset quadrature phase shift keying (OQPSK) modulation with a bandwidth of 2MHz and a 0.5 Inside The phase shift of The Bluetooth bandwidth is 1MHz. After receiving the signal, the Bluetooth device samples it at a sampling frequency of 1MHz, that is, every 1 The signal is sampled once, then demodulated based on the sign of the phase shift between adjacent sampling points. A sampling offset is added to the Bluetooth device to ensure a fixed mapping between the symbols sent by the ZigBee device and the bit sequence demodulated by the Bluetooth device. A mapping table is established by iterating through the demodulation results of all ZigBee symbols. During actual communication, the Bluetooth device finds the sequence in this table with the smallest Hamming distance to the currently demodulated sequence and restores the corresponding ZigBee symbol.

[0077] The schematic diagram of this method is as follows Figure 8 As shown. By utilizing the sampling offset, a fixed mapping between ZigBee symbols and Bluetooth bit sequences is established, so that the symbols sent by the ZigBee device can be restored on the Bluetooth device. By enabling cross-protocol communication from a ZigBee device to a Bluetooth device, the backscatter system of the present invention can achieve communication from a ZigBee receiver to a Bluetooth excitation source. The present invention sets the left sampling offset and the right sampling offset respectively, so that each 4-bit ZigBee symbol is mapped to two 16-bit Bluetooth sequences.

[0078] (2) Modulation and demodulation of amplitude modulated signals.

[0079] WiFi can generate an AM signal in the time domain by controlling the data carried by the subcarrier. The tag can demodulate the AM signal using its equipped envelope detector.

[0080] The WiFi module in the excitation source device of the present invention can generate an amplitude modulated signal by sending constant OFDM symbols and random OFDM symbols. The constant OFDM symbol means that the current OFDM symbol carries constant data (for example, all 0s), and the random OFDM symbol means that the current OFDM symbol carries random data. The generated amplitude modulated signal is as follows: Figure 9 The figure shows the waveform of an AM signal in the time domain and illustrates how the AM signal encodes data. In an AM signal, a data bit 1 is represented by one random OFDM symbol and one constant OFDM symbol, and a data bit 0 is represented by two random OFDM symbols.

[0081] The tag of the present invention can use the equipped envelope detector to demodulate the AM signal. The tag adopts a dynamic threshold demodulation method, calculates the threshold value according to the signal corresponding to the preamble field in the data packet carried by the AM signal, and then uses the threshold value to demodulate the subsequent AM signal. The schematic diagram of the demodulation method is shown in FIG. Figure 10 shown.

[0082] The technical solution of the present invention is described in more detail below with reference to an embodiment.

[0083] Simulation experiments were carried out in MATLAB R2024b to verify the feasibility and superiority of the present invention.

[0084] To simulate backscatter communication, the experiment uses the bleWaveformGenerator function in the Bluetooth toolbox to send Bluetooth extended advertising packets and generate Bluetooth protocol signals. The awgn function in the Communications toolbox is used to add noise to the signal. The PHYDecoderOQPSKNoSync function in the Communications toolbox is used to simulate the ZigBee receiver and demodulate the backscattered signal.

[0085] To simulate the cross-protocol communication link from ZigBee to Bluetooth, the experiment uses the lrwpanWaveformGenerator function in the Communications Toolbox to send ZigBee data packets and generate ZigBee protocol signals, and uses the awgn function in the Communications Toolbox to add noise to the signal.

[0086] To simulate the communication link from the stimulus source to the tag, the experiment used the wlanWaveformGenerator function in the WLAN toolbox to generate the WiFi protocol signal, the awgn function in the Communications toolbox to add noise to the signal, and the envelope function in the Signal Processing toolbox to implement envelope detection.

[0087] The process of switching the system's operating mode is as follows. The excitation source and tag send 10 data packets to the ZigBee receiver device via backscatter. The ZigBee receiver demodulates the received data packets and checks the preamble field in the data packets. If the data carried in the preamble field is all 0s, the data packet is considered to have been received correctly. The ZigBee receiver device counts the number of correctly received data packets. If the number of correctly received data packets is greater than 9, the system operating mode needs to be switched to an operating mode based on ambient Bluetooth excitation; if the number of correctly received data packets is less than or equal to 9, the system operating mode needs to be switched to an operating mode based on single-frequency Bluetooth excitation. After that, the ZigBee receiver transmits the instruction to switch the operating mode to the excitation source and tag via the reverse communication link.

[0088] In order to find the optimal threshold for switching working modes, the present invention measures the effective throughput of the two working modes at various signal-to-noise ratios and the packet loss rate of backscatter at various signal-to-noise ratios. The effective throughput is as follows: Figure 11 As shown, the packet loss rate is Figure 12The experimental results show that in order for the present invention to achieve the optimal effective throughput at each signal-to-noise ratio, the working mode should be switched when the packet loss rate is around 10%. After setting the packet loss rate threshold for switching the working mode to 10%, the present invention measured the effective throughput of the system at each signal-to-noise ratio. The experimental results are shown in Figure 2. Figure 13 As shown. Experimental results show that by adaptively switching the excitation signal type, the present invention can achieve the highest effective throughput under various signal-to-noise ratios. In addition, the present invention also verifies the feasibility of the constructed reverse communication link. The symbol error rate of cross-protocol communication from ZigBee devices to Bluetooth devices is shown in Figure 14 The experimental results show that when the signal-to-noise ratio is greater than 8 dB, the error rate of using Bluetooth devices to demodulate ZigBee signals and restore ZigBee symbols can reach The bit error rate of the tag demodulated AM signal is as follows: Figure 15 When the signal-to-noise ratio is greater than 4 dB, the bit error rate of the AM signal demodulated by the tag using the envelope detector can reach Within.

[0089] 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.

[0090] 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.

[0091] A ZigBee backscatter system with adaptive switching of Bluetooth excitation supports both an ambient Bluetooth excitation-based working mode and a single-frequency Bluetooth excitation-based working mode, including:

[0092] Data packet sending module: The excitation source periodically sends a batch of backscattered data packets to the ZigBee receiver through the tag;

[0093] Excitation mode switching module: The ZigBee receiver counts the number of correctly received backscattered data packets and compares it with a set threshold. If the number of correctly received packets is greater than the threshold, a command is sent to the excitation source and tag via the reverse communication link to switch to an operating mode based on ambient Bluetooth excitation. If the number of correctly received packets is less than or equal to the threshold, a command is sent to the excitation source and tag via the reverse communication link to switch to an operating mode based on single-frequency Bluetooth excitation.

[0094] Among them, the working mode based on environmental Bluetooth excitation is: the excitation source sends a Bluetooth signal carrying arbitrary data, and the tag modulates the Bluetooth signal to generate a backscattered signal; the working mode based on single-frequency Bluetooth excitation is: the excitation source sends a Bluetooth extended broadcast packet carrying specific payload field content to generate a single-frequency signal, and the tag modulates the single-frequency signal to generate a backscattered signal.

[0095] 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.

[0096] 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.

[0097] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A ZigBee backscattering method with adaptive switching of Bluetooth excitation, characterized in that: Supports working modes based on environmental Bluetooth excitation and single-frequency Bluetooth excitation, including: Working mode based on environmental Bluetooth excitation: the excitation source sends a Bluetooth signal carrying arbitrary data, and the tag modulates the Bluetooth signal to generate a backscattered signal; Working mode based on single-frequency Bluetooth excitation: the excitation source sends a Bluetooth extended advertising packet carrying specific payload field content to generate a single-frequency signal, and the tag modulates the single-frequency signal to generate a backscattered signal; Adaptive switching of working modes is achieved through the following methods: The excitation source periodically sends a batch of backscattered data packets to the ZigBee receiver through the tag; The ZigBee receiver counts the number of correctly received backscattered packets and compares it with the set threshold; If the number of correct receptions is greater than the threshold, an instruction is sent to the excitation source and the tag via the reverse communication link to switch to the working mode based on the ambient Bluetooth excitation; If the number of correct receptions is less than or equal to the threshold, an instruction is sent to the excitation source and the tag via the reverse communication link to switch to a working mode based on single-frequency Bluetooth excitation.

2. The ZigBee backscattering method for adaptively switching Bluetooth excitation according to claim 1, characterized in that: The excitation source sends a Bluetooth extended advertising packet carrying specific payload field content to generate a single-frequency signal, specifically including: The payload field of the Bluetooth extended advertising packet of the single-frequency signal is all 0 data.

3. The ZigBee backscattering method for adaptively switching Bluetooth excitation according to claim 1, characterized in that: The reverse communication link includes: a communication link from the ZigBee receiving end to the excitation source and a communication link from the excitation source to the tag; The communication link between the ZigBee receiver and the stimulus source uses cross-protocol communication technology. The Bluetooth device in the stimulus source establishes a mapping table between ZigBee symbols and Bluetooth bit sequences by adding sampling offsets, and demodulates the instructions in the form of ZigBee signals. Communication link from the excitation source to the tag: The WiFi module of the excitation source sends an amplitude modulated signal, and the tag demodulates the amplitude modulated signal through an envelope detector to obtain the instruction.

4. The ZigBee backscattering method for adaptively switching Bluetooth excitation according to claim 3, characterized in that: The amplitude modulated signal is realized by alternately sending a constant OFDM symbol and a random OFDM symbol, wherein one random OFDM symbol and one constant OFDM symbol represent bit 1, and two random OFDM symbols represent bit 0.

5. The ZigBee backscattering method for adaptively switching Bluetooth excitation according to claim 1, characterized in that: 90% of the number of backscattered data packets sent by the tag to the ZigBee receiving end is set as the threshold.

6. A ZigBee backscatter system with adaptive switching of Bluetooth excitation, characterized in that: Supports working modes based on environmental Bluetooth excitation and single-frequency Bluetooth excitation, including: Data packet sending module: The excitation source periodically sends a batch of backscattered data packets to the ZigBee receiver through the tag; Excitation mode switching module: The ZigBee receiver counts the number of correctly received backscattered data packets and compares it with a set threshold. If the number of correctly received packets is greater than the threshold, a command is sent to the excitation source and tag via the reverse communication link to switch to an operating mode based on ambient Bluetooth excitation. If the number of correctly received packets is less than or equal to the threshold, a command is sent to the excitation source and tag via the reverse communication link to switch to an operating mode based on single-frequency Bluetooth excitation. Among them, the working mode based on environmental Bluetooth excitation is: the excitation source sends a Bluetooth signal carrying arbitrary data, and the tag modulates the Bluetooth signal to generate a backscattered signal; the working mode based on single-frequency Bluetooth excitation is: the excitation source sends a Bluetooth extended broadcast packet carrying specific payload field content to generate a single-frequency signal, and the tag modulates the single-frequency signal to generate a backscattered signal.

7. The ZigBee backscatter system with adaptive switching of Bluetooth excitation according to claim 6, characterized in that: The excitation source sends a Bluetooth extended advertising packet carrying specific payload field content to generate a single-frequency signal, specifically including: The payload field of the Bluetooth extended advertising packet of the single-frequency signal is all 0 data.

8. The ZigBee backscatter system with adaptive switching of Bluetooth excitation according to claim 6, characterized in that: The reverse communication link includes: a communication link from the ZigBee receiving end to the excitation source and a communication link from the excitation source to the tag; The communication link between the ZigBee receiver and the stimulus source uses cross-protocol communication technology. The Bluetooth device in the stimulus source establishes a mapping table between ZigBee symbols and Bluetooth bit sequences by adding sampling offsets, and demodulates the instructions in the form of ZigBee signals. Communication link from the excitation source to the tag: The WiFi module of the excitation source sends an amplitude modulated signal, and the tag demodulates the amplitude modulated signal through an envelope detector to obtain the instruction.

9. The ZigBee backscatter system with adaptive switching of Bluetooth excitation according to claim 8, characterized in that: The amplitude modulated signal is realized by alternately sending a constant OFDM symbol and a random OFDM symbol, wherein one random OFDM symbol and one constant OFDM symbol represent bit 1, and two random OFDM symbols represent bit 0.

10. The ZigBee backscatter system with adaptive switching of Bluetooth excitation according to claim 6, characterized in that: 90% of the number of backscattered data packets sent by the tag to the ZigBee receiving end is set as the threshold.

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