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

Abstract

The present invention provides a backscatter communication synchronization and control method based on an environmental cellular OFDM signal, and relates to the technical field of wireless communication; the method comprises the following steps: S10, sending an environmental cellular OFDM signal through a transmitting end, the environmental cellular OFDM signal carrying synchronization and control information; S20, a backscatter tag obtains synchronization and control information from the environmental cellular OFDM signal, including: the backscatter tag converts the environmental cellular OFDM signal into a digital pulse signal by 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; the beneficial effects of the present invention are: it is applicable to environmental cellular OFDM signals of any bandwidth, and reliable synchronization and control are achieved without relying on additional excitation signals.

Description

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 environmental cellular OFDM signals. Background Art

[0002] The new generation of mobile communications (5G / 6G), smart car networking, mobile medical care, smart home, industrial control, environmental monitoring and other applications are driving the large-scale expansion of the Internet of Things. Trillions of sensor devices will be connected to the network to realize the true intelligent connection of all things. However, with the rapid growth of the number of IoT devices, the power consumption and cost issues brought about by classic wireless communication technologies need to be solved urgently. In recent years, backscatter technology has become an effective solution for low-power and low-cost IoT technology, but most backscatter systems require the deployment of additional excitation sources, which increases the deployment cost of low-power IoT devices. Backscatter communication systems based on environmental cellular signals can easily achieve low-power, low-cost, and wide-coverage IoT connections due to the ubiquitous nature of cellular signals.

[0003] In the process of reflecting the ambient cellular signal, in order to ensure that the CP (cyclic prefix) part is consistent with the copied part and no useful information is modulated onto the CP (otherwise it will be deleted by the receiver), the tag needs to be roughly synchronized first. In general cellular networks, the synchronization of the receiving end is completed by correlating the received signal, and such complexity is unbearable for low-power tags. In addition, although a large number of existing backscatter systems have given tags powerful uplink capabilities, there is a lack of sufficient research on the control of tags. Summary of the invention

[0004] 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.

[0005] 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 comprises the following steps:

[0006] S10, sending an ambient cellular OFDM signal through a transmitting end, where the ambient cellular OFDM signal carries synchronization and control information;

[0007] S20, backscatter tag obtains synchronization and control information from the ambient cellular OFDM signal, including:

[0008] The backscatter tag converts the ambient cellular OFDM signal into a digital pulse signal using an envelope detection circuit;

[0009] The backscatter tag establishes synchronization with the transmitting end by detecting the rising edge of the digital pulse signal;

[0010] The backscatter tag identifies the control information of the transmitting end by detecting the multiple pulse widths of the digital pulse signal.

[0011] Further, step S10 includes the following steps:

[0012] S101, the transmitting end increases the PSS signal for synchronization with the backscatter tag, and the PSS signal is a main synchronization signal;

[0013] S102, the sending end generates a corresponding control sequence according to the tag to be controlled;

[0014] S103: The transmitting end maps the bit information corresponding to the control sequence to the relative size of the power of the SSS signal.

[0015] Furthermore, the control sequence is a PN pseudo-random sequence, and the SSS signal is a secondary synchronization signal.

[0016] 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.

[0017] 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.

[0018] Further, in step S103, in LTE, the PSS signal and the SSS signal exist in two consecutive OFDM symbols;

[0019] 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.

[0020] Further, 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 which are electrically connected in sequence;

[0021] The backscatter tag converts the ambient cellular OFDM signal into a digital pulse signal using an envelope detection circuit, including:

[0022] 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 of other frequency bands are suppressed;

[0023] S202, the received ambient cellular OFDM signal passes through an envelope detection circuit to obtain a signal envelope, and then a baseband amplifier circuit improves the signal-to-noise ratio;

[0024] 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.

[0025] Further, in step S20, the backscatter tag establishes synchronization with the transmitting end by detecting the rising edge of the digital pulse signal, including:

[0026] 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 prevents the backscatter tag information from being modulated into the CP part of the ambient cellular OFDM signal.

[0027] Further, in step S20, the backscatter tag identifies the control information of the transmitter by detecting multiple pulse widths of the digital pulse signal, including:

[0028] S204, the backscatter tag collects pulse widths of multiple digital pulse signals and calculates the average to obtain a decision threshold;

[0029] S205, judging the pulse width of the digital pulse signal as 0 or 1, and storing the result;

[0030] S206, each time a control bit is collected, the backscatter tag updates the stored multiple bits using a shift register; these bit data will be 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 value threshold to determine whether the current backscatter tag is a target backscatter tag controlled by the transmitter, and the start time of backscattering is determined by the peak point of the correlation calculation;

[0031] S207: If the current backscatter tag is the target backscatter tag controlled by the transmitter, backscattering will begin. At this time, the previous backscatter tag ends backscattering, thus completing the control of the backscatter communication process of the backscatter tag by the transmitter.

[0032] Furthermore, in step S205, a shift register is used to store multiple groups of pulse widths of the digital pulse signal.

[0033] 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 to be solved urgently in the current backscatter communication technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention is a flowchart of a backscatter communication synchronization and control method based on environmental cellular OFDM signals.

[0035] Figure 2 It is a schematic diagram of a system model of a backscatter communication synchronization and control method based on environmental cellular OFDM signals in the present invention.

[0036] Figure 3 The present invention is a flow chart of the synchronization and control steps of backscatter communication based on environmental cellular OFDM signals.

[0037] Figure 4 The figure is a structural diagram of an envelope detection circuit of a backscatter tag in the present invention.

[0038] Figure 5 This is a schematic diagram of a backscatter tag control process in the present invention.

[0039] Figure 6 This is the simulation result of the PN sequence correlation performance used in the present invention.

[0040] Figure 7 The results are performance tests of a backscatter communication control method based on environmental cellular OFDM signals in the present invention.

[0041] Figure 8 The performance test results of a backscatter communication synchronization method based on environmental cellular OFDM signals in the present invention are shown in FIG. DETAILED DESCRIPTION

[0042] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0043] 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 technicians in this field without creative work are all 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 formation of a better connection structure by adding or reducing connection accessories according to the specific implementation situation. The various technical features in the invention can be combined interchangeably without conflicting with each other.

[0044] Example 1

[0045] Reference Figure 1 As shown, the present invention provides a backscatter communication synchronization and control method based on environmental cellular OFDM signals. Figure 2 The method of the present invention is implemented on a backscatter communication synchronization and control system based on an environmental cellular OFDM signal. The system consists of a transmitter, a backscatter tag, and a receiver, wherein the transmitter is Figure 2 The backscatter tag is the base station shown in Figure 2 The transmitter will send a downlink ambient cellular OFDM signal in a certain frequency band to communicate with the receiver to form a direct link. At the same time, the ambient 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 communication of the backscatter tag.

[0046] In this embodiment, the present invention provides a backscatter communication synchronization and control method based on an environmental cellular OFDM signal, the method comprising steps S10-S20:

[0047] S10. Send an ambient cellular OFDM signal through a transmitting end. The ambient cellular OFDM signal carries synchronization and control information.

[0048] Step S10 includes steps S101-S103:

[0049] 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;

[0050] In step S101, the transmitting end increases the transmission power of the PSS signal of the LTE signal by several dB, so that the OFDM symbol power where the PSS signal is located is relatively large, and the rising edge can be detected by the backscatter tag in the form of 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 once every 5ms;

[0051] 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, but it should be noted that this embodiment only takes the PN pseudo-random sequence as an example for description, and the use of other replaceable 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;

[0052] 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, and the SSB block is a synchronization signal and a physical broadcast channel block.

[0053] S20, the backscatter tag obtains synchronization and control information from the environmental cellular OFDM signal, including: the backscatter tag uses an envelope detection circuit to convert the environmental cellular OFDM signal into a digital pulse signal; 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.

[0054] 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.

[0055] In this embodiment, the backscatter tag converts the ambient cellular OFDM signal into a digital pulse signal using an envelope detection circuit, including:

[0056] 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 of other frequency bands are suppressed;

[0057] S202, the received ambient cellular OFDM signal passes through an envelope detection circuit to obtain a signal envelope, and then a baseband amplifier circuit improves the signal-to-noise ratio;

[0058] 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.

[0059] Further, 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, establishes time synchronization with the transmitting end, and avoids the backscatter tag information being modulated into the CP part of the environmental cellular OFDM signal.

[0060] 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:

[0061] S204, the backscatter tag collects pulse widths of multiple digital pulse signals and calculates the average to obtain a decision threshold;

[0062] 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;

[0063] S206, each time a control bit is collected, the backscatter tag updates the stored multiple bits using a shift register; these bit data will be 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 value threshold to determine whether the current backscatter tag is a target backscatter tag controlled by the transmitter, and the start time of backscattering is determined by the peak point of the correlation calculation;

[0064] S207: If the current backscatter tag is the target backscatter tag controlled by the transmitter, backscattering will begin. At this time, the previous backscatter tag ends backscattering, thus completing the control of the backscatter communication process of the backscatter tag by the transmitter.

[0065] Based on this, the present invention provides a backscatter communication synchronization and control method based on environmental cellular OFDM signals, which is applicable to environmental cellular OFDM signals of any bandwidth. When the power and frequency band of the environmental cellular OFDM signal received by the backscatter tag match it, the synchronization between the backscatter tag and the transmitter within a range of 12 meters and the control of the backscatter tag by the transmitter can be achieved. 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 in the current backscatter technology.

[0066] Example 2

[0067] Combination Figure 1 , Figure 2 As shown, the present invention provides a backscatter communication synchronization and control method based on environmental cellular OFDM signals. Figure 2 The method of the present invention is implemented on a backscatter communication synchronization and control system based on an environmental cellular OFDM signal. The system consists of a transmitter, a backscatter tag, and a receiver, wherein the transmitter is Figure 2 The backscatter tag is the base station shown in Figure 2 The transmitter will send a downlink ambient cellular OFDM signal in a certain frequency band to communicate with the receiver, forming a direct link.

[0068] At the same time, the ambient 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 communication of the backscatter tag. 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, the rising edge of the synchronization signal can be used to achieve coarse synchronization, avoid information being modulated into the CP part of the ambient OFDM signal, and effectively backscatter information to the ambient cellular OFDM signal.

[0069] In order to facilitate the description of a backscatter communication synchronization and control method based on an environmental cellular OFDM signal provided by the present invention, in this embodiment, the environmental cellular OFDM signal sent in step S10 adopts an LTE OFDM signal; however, it should be noted that other environmental cellular OFDM signals can use the same principle to synchronize and control backscatter communications.

[0070] Combination Figure 3 As shown, it is a flow chart of the synchronization and control steps of backscatter communication based on environmental cellular OFDM signals in the present invention. Specifically, it includes steps S10-S20:

[0071] S10. Send an ambient cellular OFDM signal through a transmitting end. The ambient cellular OFDM signal carries synchronization and control information.

[0072] Step S10 includes steps S101-S103:

[0073] 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;

[0074] In step S101, the transmitting end increases the transmission power of the PSS signal of the LTE signal by several dB, so that the OFDM symbol power where the PSS signal is located is relatively large, and the rising edge can be detected by the backscatter tag in the form of 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 once every 5ms;

[0075] S102, the transmitting end generates a corresponding control sequence according to the label to be controlled; wherein, the control sequence should have good autocorrelation and cross-correlation characteristics. In the present embodiment, the control sequence is a PN pseudo-random sequence, but it should be noted that the present embodiment only takes the PN pseudo-random sequence as an example for explanation, and the use of other replaceable 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 a suitable length to distinguish different backscatter labels according to the number of backscatter labels to be controlled; in the present embodiment, the transmitting end uses a 31-bit m-sequence as the PN pseudo-random sequence for controlling the backscatter label, and different backscatter labels are distinguished by using different m-sequences;

[0076] 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.

[0077] In this embodiment, the PN pseudo-random sequence generated by the feedback coefficient 37 is a sequence of length 31, 0000101011101100011111001101001, which includes 16 bits 1 and 15 bits 0; the above sequence will be mapped in 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 mapping bit 1 will be widened compared with bit 0; these pulse width changes caused by the relative size of the 31 SSS signal powers carry the transmitter's control information on the backscatter tag.

[0078] S20, the backscatter tag obtains synchronization and control information from the environmental cellular OFDM signal, including: the backscatter tag uses an envelope detection circuit to convert the environmental cellular OFDM signal into a digital pulse signal; 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.

[0079] In step S20, refer to Figure 4 As shown, the envelope detection circuit includes an impedance matching circuit, an envelope detection circuit, a baseband amplifier circuit, a filter circuit and a comparator which are electrically connected in sequence. In this embodiment, the backscatter tag uses the envelope detection circuit to convert the ambient cellular OFDM signal into a digital pulse signal, including:

[0080] 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 of other frequency bands are suppressed;

[0081] S202, the received ambient cellular OFDM signal passes through an envelope detection circuit to obtain a signal envelope, and then a baseband amplifier circuit improves the signal-to-noise ratio;

[0082] 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.

[0083] 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 to prevent the backscatter tag information from being modulated into the CP part of the ambient cellular OFDM signal. Figure 3 As shown, the digital pulse signal output by the envelope detection circuit not only contains synchronization information, but also the change of its pulse width carries the control information of the transmitter on the backscatter tag.

[0084] Furthermore, the backscatter tag identifies the control information of the transmitter by detecting multiple pulse widths of the digital pulse signal, including:

[0085] S204, the backscatter tag collects pulse widths of multiple digital pulse signals and calculates the average to obtain a decision threshold;

[0086] 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;

[0087] S206, each time a control bit is collected, the backscatter tag updates the stored multiple bits using a shift register; these bit data will be 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 value threshold to determine whether the current backscatter tag is a target backscatter tag controlled by the transmitter, and the start time of backscattering is determined by the peak point of the correlation calculation;

[0088] S207: If the current backscatter tag is the target backscatter tag controlled by the transmitter, backscattering will begin. At this time, the previous backscatter tag ends backscattering, thus completing the control of the backscatter communication process of the backscatter tag by the transmitter.

[0089] Based on this, the present invention provides a backscatter communication synchronization and control method based on environmental cellular OFDM signals, which is applicable to environmental cellular OFDM signals of any bandwidth. When the power and frequency band of the environmental cellular OFDM signal received by the backscatter tag match it, the synchronization between the backscatter tag and the transmitter within a range of 12 meters and the control of the backscatter tag by the transmitter can be achieved. 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 in the current backscatter technology.

[0090] Based on the above embodiments, the present invention also provides simulation results and a verification platform to verify the performance of the above embodiments.

[0091] Firstly, the performance of the proposed backscatter communication control method based on environmental cellular OFDM signals is verified through simulation, using two PN sequences, PN1: 0000101011101100011111001101001 and PN2: 0000110101001000101111101100111. The simulation tests the performance of the backscatter tag with no bit error or 8-bit bit error when the transmitter sends only PN1 (autocorrelation); when PN1 and PN2 are sent alternately (correlated with the changing PN sequence); and when only PN1 is sent (cross-correlation). Figure 6 In (a) to (d), regardless of the bit error of up to 8 bits or the PN sequence that changes back and forth, the backscatter tag correlation peak corresponds to an offset of 15, and the backscatter tag can identify the PN1 control information sent by the transmitter. Figure 6 In (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 Figure 6 The correlation peaks in (a) to (d) show that the backscatter tag can distinguish the non-PN1 control information sent by the transmitter.

[0092] Next, the performance of the proposed backscatter communication synchronization and control method based on the environmental cellular OFDM signal is verified in the verification platform. In step S10, the transmitter is implemented by NI USRP2952R, the carrier frequency is 845MHz, the average power is 15dBm, and the addition of synchronization and control information increases the peak-to-average power ratio of the environmental cellular OFDM signal by 3.5dB. The environmental cellular OFDM signal is a 5M LTE signal. In step S20, the backscatter tag is implemented by Figure 4 The envelope detection circuit and ZYNQ7020FPGA are shown in Figure 1. When the distance between the transmitter and the backscatter tag is 4 to 12 meters, the control and synchronization performance of the backscatter tag are as follows: Figure 7 , Figure 8 As shown. Among them, Figure 7 The error rate shown is the probability that a backscatter tag does not backscatter at the correct time.

[0093] Based on this, the backscatter communication synchronization and control method based on the environmental cellular OFDM signal of the present invention is applicable to environmental cellular OFDM signals of any bandwidth. When the power and frequency band of the environmental cellular OFDM signal received by the backscatter tag match it, the synchronization between the backscatter tag and the transmitter within a range of 12 meters and the control of the backscatter tag by the transmitter can be achieved. The core advantage of the present invention is that it does not rely on additional excitation signals to achieve reliable synchronization and control, which is a problem that needs to be solved in the current backscatter technology.

[0094] 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 synchronization and control of 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 a transmitting end, where the ambient cellular OFDM signal carries synchronization and control information; Step S10 includes the following steps: S101, the transmitting end increases the PSS signal for synchronization with the backscatter tag, and the PSS signal is a main 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; 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 the multiple pulse widths of the digital pulse signal; 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 which are 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 of other frequency bands are suppressed; S202, the received ambient cellular OFDM signal passes through an envelope detection circuit to obtain a signal envelope, and then a 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; 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, establishes time synchronization with the transmitting end, and prevents the backscatter tag information from being modulated into the CP part of the ambient cellular OFDM signal; 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 a shift register; these bit data will be 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 value threshold to determine whether the current backscatter tag is a target backscatter tag controlled by the transmitter, and the start time of backscattering is determined by the peak point of the correlation calculation; S207: If the current backscatter tag is the target backscatter tag controlled by the transmitter, backscattering will begin. At this time, the previous backscatter tag ends backscattering, thus completing the control of the backscatter communication process of the backscatter tag by the transmitter.

2. A method for synchronization and control of backscatter communication based on environmental cellular OFDM signals according to claim 1, characterized in that: The control sequence is a PN pseudo-random sequence, and the SSS signal is a secondary synchronization signal.

3. A method for synchronization and control of backscatter communication based on environmental cellular OFDM signals according to claim 1, characterized in that: 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.

4. A method for synchronization and control of backscatter communication based on ambient cellular OFDM signals according to claim 1, characterized in that: 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.

5. A method for synchronization and control of backscatter communication based on environmental cellular OFDM signals according to claim 1, characterized in that: 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 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.

6. A method for synchronization and control of backscatter communication based on ambient cellular OFDM signals according to claim 1, 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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