Backscatter communication synchronization and control method based on ambient cellular OFDM signal

Abstract

A backscatter communication synchronization and control method based on an ambient cellular OFDM signal, which method relates to the technical field of wireless communications. The method comprises the following steps: S10, a sending end sending an ambient cellular OFDM signal, wherein the ambient cellular OFDM signal carries synchronization and control information; and S20, a backscatter tag acquiring the synchronization and control information from the ambient cellular OFDM signal, wherein step S20 comprises: the backscatter tag using an envelope detection circuit to convert the ambient cellular OFDM signal into a digital pulse signal; the backscatter tag establishing synchronization with the sending end by means of performing detection on a rising edge of the digital pulse signal; and the backscatter tag identifying control information of the sending end by means of measuring multiple pulse widths of the digital pulse signal. The method realizes reliable synchronization and control without relying on an additional excitation signal.

Description

A method for synchronization and control of backscatter communication based on ambient cellular OFDM signals Technical Field

[0001] The present invention relates to the field of wireless communication technology, and more particularly to a backscatter communication synchronization and control method based on an environmental cellular OFDM signal. Background Art

[0002] Next-generation mobile communications (5G / 6G), applications such as smart car connectivity, mobile healthcare, smart homes, industrial control, and environmental monitoring are driving the massive expansion of the Internet of Things (IoT). Trillions of sensor devices will be connected to the network, enabling a truly intelligent interconnected world. However, with the rapid growth in the number of IoT devices, the power consumption and cost challenges presented by traditional wireless communication technologies need to be addressed. In recent years, backscatter technology has emerged as an effective solution for low-power, low-cost IoT technology. However, most backscatter systems require the deployment of additional excitation sources, increasing the cost of deploying low-power IoT devices. Backscatter communication systems based on ambient cellular signals, leveraging the ubiquitous nature of cellular signals, facilitate low-power, low-cost, and wide-coverage IoT connectivity.

[0003] When reflecting ambient cellular signals, tags must first undergo coarse synchronization to ensure that the CP (cyclic prefix) portion is consistent with the replicated portion and that no useful information is modulated onto the CP (otherwise it would be deleted by the receiver). In typical cellular networks, synchronization at the receiver is accomplished by correlating the received signal, a complexity prohibitive for low-power tags. Furthermore, while many existing backscatter systems provide tags with powerful uplink capabilities, tag control is understudied.

[0004] Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a backscatter communication synchronization and control method based on environmental cellular OFDM signals.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a backscatter communication synchronization and control method based on environmental cellular OFDM signals, the improvement of which is that the method includes the following steps:

[0007] S10, sending an ambient cellular OFDM signal through the transmitting end, where the ambient cellular OFDM signal carries synchronization and control information;

[0008] S20, backscatter tag obtains synchronization and control information from the ambient cellular OFDM signal, including:

[0009] The backscatter tag converts the ambient cellular OFDM signal into a digital pulse signal using an envelope detection circuit;

[0010] The backscatter tag establishes synchronization with the transmitting end by detecting the rising edge of the digital pulse signal;

[0011] The backscatter tag identifies the control information of the transmitting end by detecting multiple pulse widths of the digital pulse signal.

[0012] Furthermore, step S10 includes the following steps:

[0013] S101, the transmitting end increases the PSS signal for synchronization with the backscatter tag, the PSS signal being a primary synchronization signal;

[0014] S102: The sending end generates a corresponding control sequence according to the tag to be controlled;

[0015] S103: The transmitting end maps the bit information corresponding to the control sequence to the relative size of the power of the SSS signal.

[0016] Furthermore, the control sequence is a PN pseudo-random sequence, and the SSS signal is a secondary synchronization signal.

[0017] Furthermore, in step S101, the transmitting end increases the transmission power of the PSS signal of the ambient cellular OFDM signal by several dB, so that the OFDM symbol power where the PSS signal is located is larger and the rising edge can be detected by the backscatter tag in an envelope detection manner.

[0018] Furthermore, in step S102, the transmitting end uses a control sequence of appropriate length to distinguish different backscatter tags according to the number of backscatter tags that need to be controlled.

[0019] Furthermore, in step S103, in LTE, the PSS signal and the SSS signal exist in two consecutive OFDM symbols;

[0020] In 5G NR, the PSS signal and SSS signal exist in the same SSB block, which are two closer OFDM symbols. The SSB block is a synchronization signal and a physical broadcast channel block.

[0021] Furthermore, in step S20, the envelope detection circuit includes an impedance matching circuit, an envelope detection circuit, a baseband amplifier circuit, a filter circuit, and a comparator electrically connected in sequence;

[0022] The backscatter tag converts the ambient cellular OFDM signal into a digital pulse signal using an envelope detection circuit, including:

[0023] S201, after the ambient cellular OFDM signal passes through the impedance matching circuit, only the ambient cellular OFDM signal carrying the synchronization information frequency band is received, and the ambient signals in other frequency bands are suppressed;

[0024] S202, the received ambient cellular OFDM signal passes through the envelope detection circuit to obtain the signal envelope, and then the baseband amplifier circuit improves the signal-to-noise ratio;

[0025] S203: The backscatter tag uses a filter circuit and a comparator to convert the synchronization information into a digital pulse signal that can be read by a tag control module.

[0026] Furthermore, in step S20, the backscatter tag establishes synchronization with the transmitting end by detecting the rising edge of the digital pulse signal, including:

[0027] By capturing the rising edge of the digital pulse signal, the backscatter tag determines the occurrence time of the PSS signal and establishes time synchronization with the transmitter, thereby preventing the backscatter tag information from being modulated into the CP part of the ambient cellular OFDM signal.

[0028] Furthermore, in step S20, the backscatter tag identifies the control information of the transmitter by detecting multiple pulse widths of the digital pulse signal, including:

[0029] S204, the backscatter tag collects pulse widths of multiple digital pulse signals and calculates the average to obtain a decision threshold;

[0030] S205, judging the pulse width of the digital pulse signal as 0 or 1, and storing the result;

[0031] S206: Each time a control bit is collected, the backscatter tag updates the stored multiple bits using a shift register; these bit data are used by the backscatter tag to perform a correlation calculation with its own corresponding PN sequence, and the peak value of the calculation result is compared with a preset threshold to determine whether the current backscatter tag is the target backscatter tag controlled by the transmitter, and the start time of backscattering is determined by the peak point of the correlation calculation;

[0032] S207: If the current backscatter tag is the target backscatter tag controlled by the transmitter, it will start backscattering. At this time, the previous backscatter tag ends backscattering, thus completing the transmitter's control over the backscatter communication process of the backscatter tag.

[0033] Furthermore, in step S205, a shift register is used to store multiple groups of pulse widths of the digital pulse signal.

[0034] The beneficial effects of the present invention are: a backscatter communication synchronization and control method based on environmental cellular OFDM signals is applicable to environmental cellular OFDM signals of any bandwidth; the present invention does not rely on additional excitation signals to achieve reliable synchronization and control, which is a problem that needs to be solved urgently in current backscatter communication technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a flow chart of a backscatter communication synchronization and control method based on an ambient cellular OFDM signal according to the present invention.

[0036] FIG2 is a schematic diagram of a system model of a backscatter communication synchronization and control method based on an ambient cellular OFDM signal in the present invention.

[0037] FIG3 is a flow chart of synchronization and control steps of backscatter communication based on environmental cellular OFDM signals in the present invention.

[0038] FIG4 is a structural diagram of an envelope detection circuit of a backscatter tag in the present invention.

[0039] FIG5 is a schematic diagram of a backscatter tag control process in the present invention.

[0040] FIG6 is a simulation result of the PN sequence correlation performance used in the present invention.

[0041] FIG7 shows the performance test results of a backscatter communication control method based on an environmental cellular OFDM signal in the present invention.

[0042] FIG8 shows the performance test results of a backscatter communication synchronization method based on an environmental cellular OFDM signal in the present invention. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to the accompanying drawings and examples.

[0044] The following will clearly and completely describe the concept, specific structure and technical effects of the present invention in combination with the embodiments and drawings, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. In addition, all the connection / connection relationships involved in the patent do not refer to the direct connection of components, but refer to the fact that a better connection structure can be formed by adding or reducing connection accessories according to the specific implementation situation. The various technical features in the invention can be combined interactively without conflicting with each other.

[0045] Example 1

[0046] With reference to FIG1 , the present invention provides a method for synchronizing and controlling backscatter communications based on environmental cellular OFDM signals. As described in conjunction with FIG2 , the method of the present invention is implemented on a backscatter communication synchronization and control system based on environmental cellular OFDM signals, the system consisting of a transmitter, a backscatter tag, and a receiver, wherein the transmitter is the base station shown in FIG2 , and the backscatter tag is the tag in FIG2 . The transmitter will send a downlink environmental cellular OFDM signal in a certain frequency band to communicate with the receiver, forming a direct link. At the same time, the environmental cellular OFDM signal will also wake up the backscatter tag, provide it with continuous synchronization and control signals, and serve as a carrier to support low-power backscatter communications of the backscatter tag.

[0047] In this embodiment, the present invention provides a method for synchronizing and controlling backscatter communication based on an ambient cellular OFDM signal, the method comprising steps S10-S20:

[0048] S10. Send an ambient cellular OFDM signal through the transmitting end. The ambient cellular OFDM signal carries synchronization and control information.

[0049] Step S10 includes steps S101-S103:

[0050] S101: The transmitting end increases the PSS signal for synchronization with the backscatter tag. The PSS signal is a primary synchronization signal. In this embodiment, the SSS signal is a secondary synchronization signal.

[0051] In step S101, the transmitting end increases the transmission power of the PSS signal of the LTE signal by several dB, so that the power of the OFDM symbol where the PSS signal is located is large and the rising edge can be detected by the backscatter tag by envelope detection. Since the PSS signal in LTE has a period of 5ms, the backscatter tag can establish synchronization with the ambient cellular OFDM signal every 5ms.

[0052] S102: The transmitting end generates a corresponding control sequence based on the tags to be controlled. The control sequence should have good autocorrelation and cross-correlation characteristics. In this embodiment, the control sequence is a PN pseudo-random sequence. However, it should be noted that this embodiment only uses the PN pseudo-random sequence as an example for illustration, and the use of other alternative control sequences is still considered to be within the scope of the present invention. Furthermore, in step S102, the transmitting end uses a PN pseudo-random sequence of appropriate length to distinguish different backscatter tags based on the number of backscatter tags to be controlled.

[0053] S103. The transmitting end maps the bit information corresponding to the control sequence to the relative size of the power of the SSS signal. In this embodiment, in LTE, the PSS signal and the SSS signal exist in two consecutive OFDM symbols. In another embodiment, in 5G NR, the PSS signal and the SSS signal exist in the same SSB block, which are two closer OFDM symbols. The SSB block is a synchronization signal and a physical broadcast channel block.

[0054] S20, the backscatter tag obtains synchronization and control information from the ambient cellular OFDM signal, including: the backscatter tag uses an envelope detection circuit to convert the ambient cellular OFDM signal into a digital pulse signal; the backscatter tag establishes synchronization with the transmitter by detecting the rising edge of the digital pulse signal; the backscatter tag identifies the control information of the transmitter by detecting multiple pulse widths of the digital pulse signal.

[0055] In step S20, the envelope detection circuit includes an impedance matching circuit, an envelope detection circuit, a baseband amplifier circuit, a filter circuit, and a comparator that are electrically connected in sequence.

[0056] In this embodiment, the backscatter tag converts the ambient cellular OFDM signal into a digital pulse signal using an envelope detection circuit, including:

[0057] S201: After the ambient cellular OFDM signal passes through the impedance matching circuit, only the ambient cellular OFDM signal carrying the synchronization information frequency band is received, and the ambient cellular OFDM signals in other frequency bands are suppressed;

[0058] S202, the received ambient cellular OFDM signal passes through the envelope detection circuit to obtain the signal envelope, and then the baseband amplifier circuit improves the signal-to-noise ratio;

[0059] S203: The backscatter tag uses a filter circuit and a comparator to convert the synchronization information into a digital pulse signal that can be read by a tag control module.

[0060] Furthermore, in step S20, the backscatter tag establishes synchronization with the transmitter by detecting the rising edge of the digital pulse signal, including: by capturing the rising edge of the digital pulse signal, the backscatter tag determines the occurrence time of the PSS signal, establishes time synchronization with the transmitter, and avoids the backscatter tag information being modulated into the CP part of the ambient cellular OFDM signal.

[0061] Furthermore, in step S20, the backscatter tag identifies the control information of the transmitter by detecting multiple pulse widths of the digital pulse signal, including:

[0062] S204, the backscatter tag collects pulse widths of multiple digital pulse signals and calculates the average to obtain a decision threshold;

[0063] S205, judging the pulse width of the digital pulse signal as 0 or 1, and storing the judgment result; in this embodiment, a shift register is used to store the pulse width of the digital pulse signal and the judgment result;

[0064] S206: Each time a control bit is collected, the backscatter tag updates the stored multiple bits using a shift register; these bit data are used by the backscatter tag to perform a correlation calculation with its corresponding PN pseudo-random sequence, and the peak value of the calculation result is compared with a preset threshold to determine whether the current backscatter tag is the target backscatter tag controlled by the transmitter, and the start time of backscattering is determined by the peak point of the correlation calculation;

[0065] S207: If the current backscatter tag is the target backscatter tag controlled by the transmitter, it will start backscattering. At this time, the previous backscatter tag ends backscattering, thus completing the transmitter's control over the backscatter communication process of the backscatter tag.

[0066] Based on this, the present invention provides a method for synchronizing and controlling backscatter communications based on ambient cellular OFDM signals, applicable to ambient cellular OFDM signals of any bandwidth. When the power and frequency band of the ambient cellular OFDM signal received by the backscatter tag match those of the surrounding cellular OFDM signal, synchronization between the backscatter tag and the transmitter and control of the backscatter tag by the transmitter within a range of 12 meters are achieved. This method achieves reliable synchronization and control without relying on additional excitation signals, a pressing issue in current backscatter technology.

[0067] Example 2

[0068] As shown in Figures 1 and 2, the present invention provides a method for synchronizing and controlling backscatter communications based on ambient cellular OFDM signals. As shown in Figure 2, the method is implemented in a system for synchronizing and controlling backscatter communications based on ambient cellular OFDM signals. The system comprises a transmitter, a backscatter tag, and a receiver. The transmitter is the base station shown in Figure 2, and the backscatter tag is the tag in Figure 2. The transmitter transmits downlink ambient cellular OFDM signals in a certain frequency band to communicate with the receiver, forming a direct link.

[0069] At the same time, the ambient cellular OFDM signal also wakes up the backscatter tag, providing it with continuous synchronization and control signals. It also serves as a carrier to support low-power backscatter communication. The backscatter tag uses envelope detection to obtain control and synchronization signals from the ambient cellular OFDM signal. When the target backscatter tag is activated, it uses the rising edge of the synchronization signal to achieve coarse synchronization, preventing information from being modulated into the CP portion of the ambient OFDM signal and effectively backscattering information onto the ambient cellular OFDM signal.

[0070] To facilitate description of a backscatter communication synchronization and control method based on an ambient cellular OFDM signal provided by the present invention, in this embodiment, the ambient cellular OFDM signal sent in step S10 adopts an LTE OFDM signal; however, it should be noted that other ambient cellular OFDM signals can adopt the same principle for synchronization and control of backscatter communication.

[0071] FIG3 shows a flow chart of the synchronization and control steps of backscatter communication based on the environmental cellular OFDM signal in the present invention. Specifically, it includes steps S10-S20:

[0072] S10. Send an ambient cellular OFDM signal through the transmitting end. The ambient cellular OFDM signal carries synchronization and control information.

[0073] Step S10 includes steps S101-S103:

[0074] S101: The transmitting end increases the PSS signal for synchronization with the backscatter tag. The PSS signal is a primary synchronization signal. In this embodiment, the SSS signal is a secondary synchronization signal.

[0075] In step S101, the transmitting end increases the transmission power of the PSS signal of the LTE signal by several dB, so that the power of the OFDM symbol where the PSS signal is located is large and the rising edge can be detected by the backscatter tag by envelope detection. Since the PSS signal in LTE has a period of 5ms, the backscatter tag can establish synchronization with the ambient cellular OFDM signal every 5ms.

[0076] S102: The transmitting end generates a corresponding control sequence according to the tag to be controlled; wherein the control sequence should have good autocorrelation and cross-correlation characteristics. In this embodiment, the control sequence is a PN pseudo-random sequence. However, it should be noted that this embodiment only uses the PN pseudo-random sequence as an example for description, and the use of other alternative control sequences is still considered to be within the scope of the present invention. Further, in step S102, the transmitting end uses a PN pseudo-random sequence of appropriate length to distinguish different backscatter tags according to the number of backscatter tags to be controlled. In this embodiment, the transmitting end uses a 31-bit m-sequence as the PN pseudo-random sequence for controlling the backscatter tags, and different backscatter tags are distinguished by using different m-sequences.

[0077] S103. The transmitting end maps the bit information corresponding to the control sequence to the relative magnitude of the power of the SSS signal. In this embodiment, in LTE, the PSS signal and the SSS signal exist in two consecutive OFDM symbols.

[0078] In this embodiment, the PN pseudo-random sequence generated by the feedback coefficient 37 is a sequence of length 31, 0000101011101100011111001101001, which contains 16 bits 1 and 15 bits 0; the above sequence will be mapped into 31 SSS signals; for bit 0, the SSS signal power remains unchanged compared with the general LTE system; for bit 1, the SSS signal power will be increased by several dB by the transmitter; and because the PSS and SSS signals in the LTE signal exist in two consecutive OFDM symbols, in the LTE signal envelope transmitted by the transmitter, the pulse width corresponding to the area mapped to bit 1 will be wider than that of bit 0; these pulse width changes caused by the relative sizes of the 31 SSS signal powers carry the transmitter's control information on the backscatter tag.

[0079] S20, the backscatter tag obtains synchronization and control information from the ambient cellular OFDM signal, including: the backscatter tag uses an envelope detection circuit to convert the ambient cellular OFDM signal into a digital pulse signal; the backscatter tag establishes synchronization with the transmitter by detecting the rising edge of the digital pulse signal; the backscatter tag identifies the control information of the transmitter by detecting multiple pulse widths of the digital pulse signal.

[0080] In step S20, as shown in FIG4 , the envelope detection circuit includes an impedance matching circuit, an envelope detection circuit, a baseband amplifier circuit, a filter circuit, and a comparator electrically connected in sequence. In this embodiment, the backscatter tag converts the ambient cellular OFDM signal into a digital pulse signal using the envelope detection circuit, including:

[0081] S201: After the ambient cellular OFDM signal passes through the impedance matching circuit, only the ambient cellular OFDM signal carrying the synchronization information frequency band is received, and the ambient cellular OFDM signals in other frequency bands are suppressed;

[0082] S202, the received ambient cellular OFDM signal passes through the envelope detection circuit to obtain the signal envelope, and then the baseband amplifier circuit improves the signal-to-noise ratio;

[0083] S203: The backscatter tag uses a filter circuit and a comparator to convert the synchronization information into a digital pulse signal that can be read by a tag control module.

[0084] Furthermore, in step S20, the backscatter tag establishes synchronization with the transmitter by detecting the rising edge of the digital pulse signal, including: by capturing the rising edge of the digital pulse signal, the backscatter tag determines the occurrence time of the PSS signal and establishes time synchronization with the transmitter, thereby preventing the backscatter tag information from being modulated into the CP portion of the ambient cellular OFDM signal. In step S20, as shown in Figure 3, the digital pulse signal output by the envelope detection circuit not only contains synchronization information, but also carries control information from the transmitter on the backscatter tag due to changes in its pulse width.

[0085] Furthermore, the backscatter tag identifies the control information of the transmitter by detecting multiple pulse widths of the digital pulse signal, including:

[0086] S204, the backscatter tag collects pulse widths of multiple digital pulse signals and calculates the average to obtain a decision threshold;

[0087] S205, judging the pulse width of the digital pulse signal as 0 or 1, and storing the judgment result; in this embodiment, a shift register is used to store the pulse width of the digital pulse signal and the judgment result;

[0088] S206: Each time a control bit is collected, the backscatter tag updates the stored multiple bits using a shift register; these bit data are used by the backscatter tag to perform a correlation calculation with its own corresponding PN sequence, and the peak value of the calculation result is compared with a preset threshold to determine whether the current backscatter tag is the target backscatter tag controlled by the transmitter, and the start time of backscattering is determined by the peak point of the correlation calculation;

[0089] S207: If the current backscatter tag is the target backscatter tag controlled by the transmitter, it will start backscattering. At this time, the previous backscatter tag ends backscattering, thus completing the transmitter's control over the backscatter communication process of the backscatter tag.

[0090] Based on this, the present invention provides a method for synchronizing and controlling backscatter communications based on ambient cellular OFDM signals, applicable to ambient cellular OFDM signals of any bandwidth. When the power and frequency band of the ambient cellular OFDM signal received by the backscatter tag match those of the surrounding cellular OFDM signal, synchronization between the backscatter tag and the transmitter and control of the backscatter tag by the transmitter within a range of 12 meters are achieved. This method achieves reliable synchronization and control without relying on additional excitation signals, a pressing issue in current backscatter technology.

[0091] Based on the above embodiments, the present invention also provides simulation results and a verification platform to verify the performance of the above embodiments.

[0092] First, simulations were conducted to verify the performance of the proposed backscatter communication control method based on ambient cellular OFDM signals. Two PN sequences, PN1: 0000101011101100011111001101001, and PN2: 0000110101001000101111101100111, were used. The simulations tested the correlation performance of the backscatter tag using PN1 with no bit errors and after an 8-bit bit error, respectively, when the transmitter transmitted only PN1 (autocorrelation); when PN1 and PN2 were alternately transmitted (correlation with a varying PN sequence); and when only PN1 was transmitted (cross-correlation). In Figures 6(a) to (d), the backscatter tag correlation peaks correspond to a 15-bit shift, regardless of the 8-bit bit error or the varying PN sequence, indicating that the backscatter tag can recognize the PN1 control information sent by the transmitter. In Figures 6(e) and (f), even with 8 bit errors, the cross-correlation performance of the backscatter tag is still excellent, and the correlation results are much lower than the correlation peaks in Figures 6(a) to (d). The backscatter tag can distinguish non-PN1 control information sent by the transmitter.

[0093] Next, the performance of the proposed backscatter communication synchronization and control method based on ambient cellular OFDM signals was verified on a verification platform. In step S10, the transmitter was implemented using an NI USRP2952R, with a carrier frequency of 845 MHz and an average power of 15 dBm. The addition of synchronization and control information improved the peak-to-average power ratio of the ambient cellular OFDM signal by 3.5 dB. The ambient cellular OFDM signal was a 5M LTE signal. In step S20, the backscatter tag consisted of the envelope detection circuit shown in Figure 4 and a ZYNQ 7020 FPGA. The control and synchronization performance of the backscatter tag, with a distance between the transmitter and the backscatter tag of 4 to 12 meters, is shown in Figures 7 and 8, respectively. The error rate shown in Figure 7 represents the probability that the backscatter tag fails to perform backscatter at the correct time.

[0094] Based on this, the present invention proposes a method for synchronizing and controlling backscatter communications based on ambient cellular OFDM signals, applicable to ambient cellular OFDM signals of any bandwidth. When the power and frequency band of the ambient cellular OFDM signal received by the backscatter tag match those of the ambient cellular OFDM signal, synchronization between the backscatter tag and the transmitter, as well as control of the backscatter tag by the transmitter, can be achieved within a 12-meter range. The core advantage of this method is that it achieves reliable synchronization and control without relying on additional excitation signals, a pressing issue in current backscatter technology.

[0095] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for synchronizing and controlling backscatter communication based on ambient cellular OFDM signals, characterized in that: The method comprises the following steps: S10, sending an ambient cellular OFDM signal through the transmitting end, where the ambient cellular OFDM signal carries synchronization and control information; S20, backscatter tag obtains synchronization and control information from the ambient cellular OFDM signal, including: The backscatter tag converts the ambient cellular OFDM signal into a digital pulse signal using an envelope detection circuit; The backscatter tag establishes synchronization with the transmitting end by detecting the rising edge of the digital pulse signal; The backscatter tag identifies the control information of the transmitting end by detecting multiple pulse widths of the digital pulse signal.

2. The method for synchronizing and controlling backscatter communication based on ambient cellular OFDM signals according to claim 1, wherein: Step S10 includes the following steps: S101, the transmitting end increases the PSS signal for synchronization with the backscatter tag, the PSS signal being a primary synchronization signal; S102: The sending end generates a corresponding control sequence according to the tag to be controlled; S103: The transmitting end maps the bit information corresponding to the control sequence to the relative size of the power of the SSS signal.

3. The method for synchronizing and controlling backscatter communication based on ambient cellular OFDM signals according to claim 2, wherein: The control sequence is a PN pseudo-random sequence, and the SSS signal is a secondary synchronization signal.

4. The method for synchronizing and controlling backscatter communication based on ambient cellular OFDM signals according to claim 2, wherein: In step S101, the transmitter increases the transmission power of the PSS signal of the ambient cellular OFDM signal by several dB, so that the OFDM symbol power of the PSS signal is larger and the rising edge can be detected by the backscatter tag in an envelope detection manner.

5. The method for synchronizing and controlling backscatter communication based on ambient cellular OFDM signals according to claim 2, wherein: In step S102, the transmitting end uses a control sequence of appropriate length to distinguish different backscatter tags according to the number of backscatter tags that need to be controlled.

6. The method for synchronizing and controlling backscatter communication based on ambient cellular OFDM signals according to claim 2, wherein: In step S103, in LTE, the PSS signal and the SSS signal exist in two consecutive OFDM symbols; In 5G NR, the PSS signal and SSS signal exist in the same SSB block, which are two closer OFDM symbols. The SSB block is a synchronization signal and a physical broadcast channel block.

7. The method for synchronizing and controlling backscatter communication based on ambient cellular OFDM signals according to claim 1, wherein: In step S20, the envelope detection circuit includes an impedance matching circuit, an envelope detection circuit, a baseband amplifier circuit, a filter circuit, and a comparator electrically connected in sequence; The backscatter tag converts the ambient cellular OFDM signal into a digital pulse signal using an envelope detection circuit, including: S201: After the ambient cellular OFDM signal passes through the impedance matching circuit, only the ambient cellular OFDM signal carrying the synchronization information frequency band is received, and the ambient signals in other frequency bands are suppressed; S202, the received ambient cellular OFDM signal passes through the envelope detection circuit to obtain the signal envelope, and then the baseband amplifier circuit improves the signal-to-noise ratio; S203: The backscatter tag uses a filter circuit and a comparator to convert the synchronization information into a digital pulse signal that can be read by a tag control module.

8. The method for synchronizing and controlling backscatter communication based on ambient cellular OFDM signals according to claim 7, wherein: In step S20, the backscatter tag establishes synchronization with the transmitting end by detecting the rising edge of the digital pulse signal, including: By capturing the rising edge of the digital pulse signal, the backscatter tag determines the occurrence time of the PSS signal and establishes time synchronization with the transmitter, thereby preventing the backscatter tag information from being modulated into the CP part of the ambient cellular OFDM signal.

9. The method for synchronizing and controlling backscatter communication based on ambient cellular OFDM signals according to claim 8, wherein: In step S20, the backscatter tag identifies the control information of the transmitter by detecting multiple pulse widths of the digital pulse signal, including: S204, the backscatter tag collects pulse widths of multiple digital pulse signals and calculates the average to obtain a decision threshold; S205, judging the pulse width of the digital pulse signal as 0 or 1, and storing the result; S206, each time a control bit is collected, the backscatter tag updates the stored multiple bits using the shift register; these bit data will be used by the backscatter tag to perform a correlation calculation with its own corresponding PN pseudo-random sequence, and the peak value of the calculation result will be compared with the preset value threshold to determine the current backscatter tag. Tag, whether it is the target backscatter tag controlled by the transmitting end, and the start time of backscattering is determined by the peak point of the relevant calculation; S207: If the current backscatter tag is the target backscatter tag controlled by the transmitter, it will start backscattering. At this time, the previous backscatter tag ends backscattering, thus completing the transmitter's control over the backscatter communication process of the backscatter tag.

10. The method for synchronizing and controlling backscatter communication based on ambient cellular OFDM signals according to claim 9, characterized in that: In step S205 , a shift register is used to store multiple groups of pulse widths of the digital pulse signal.

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