A frequency modulated continuous wave based near range backscatter communication system and method

Abstract

The application provides a near distance backscattering communication method based on frequency modulation continuous wave, and relates to the technical field of wireless communication; the method comprises the following steps: a stimulating signal is cyclically sent by a frequency modulation continuous wave signal source; a backscattering tag receives an incident signal from the frequency modulation continuous wave signal source, modulates the amplitude of the incident signal, and sends a reflected signal to a receiver; the receiver receives a received signal, which comprises the reflected signal and a straight-chain signal sent by the frequency modulation continuous wave signal source; the receiver demodulates the backscattering signal, and dynamically adjusts the modulation mode of the backscattering tag and the transmission power of the frequency modulation continuous wave signal source; the application has the beneficial effect that the frequency modulation continuous wave is amplitude-modulated, and a near distance high-rate backscattering communication method is realized.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and more specifically, to a short-range backscatter communication system and method based on frequency-modulated continuous wave. Background Technology

[0002] While existing RFID technology can achieve passive communication, its drawbacks are significant: low communication speed and short communication distance. Existing IoT communication technologies such as WiFi, Bluetooth, and NB-IoT can achieve high-speed, long-distance communication, but IoT nodes consume extremely high power and cannot operate stably for extended periods. Existing environmental reverse communication technologies, while utilizing environmental signals as a signal source, suffer from unstable environmental signals, making them unreliable communication methods.

[0003] Backscatter communication is a type of IoT communication technology. Its biggest advantage is its extremely low power consumption, which allows devices to communicate with each other even when their functionality is limited, making it very suitable for use in IoT application scenarios where batteries cannot be replaced. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a short-range backscatter communication system and method based on frequency-modulated continuous wave, and proposes a method for amplitude modulation of frequency-modulated continuous wave to achieve high-speed short-range backscatter communication.

[0005] The technical solution adopted by this invention to solve its technical problem is: a short-range backscatter communication method based on frequency-modulated continuous wave, the improvement of which is that the method includes the following steps:

[0006] Excitation signals are cyclically transmitted using a frequency-modulated continuous wave signal source;

[0007] The backscatter tag receives the incident signal from the frequency-modulated continuous wave signal source, modulates the amplitude of the incident signal, and sends the reflected signal to the receiver.

[0008] The receiver receives the backscattered signal, which includes the reflected signal and the direct-link signal transmitted by the frequency-modulated continuous wave (FM-CW) signal source. The receiver demodulates the backscattered signal and dynamically adjusts the modulation mode of the backscattered tag through the downlink feedback link from the receiver to the backscattered tag. The transmit power of the FM-CW signal source is dynamically adjusted through the control link from the receiver to the FM-CW signal source.

[0009] Furthermore, the path through which the frequency-modulated continuous wave signal source sends the incident signal to the backscatter tag is called path g, the path through which the backscatter tag sends the reflected signal to the receiver is called path b, and the path through which the frequency-modulated continuous wave signal source sends the direct-link signal to the receiver is called path f.

[0010] The backscattering tag modulates the amplitude of the incident signal, including:

[0011] The frequency-modulated continuous wave (FM continuous wave) signal source transmits a signal s(t), which is a spread spectrum signal with a linearly increasing frequency. Its frequency is expressed as: f(t) = f0 + kt; where f0 is the initial frequency of the FM continuous wave. The phase of the FM continuous wave signal is then:

[0012]

[0013] The frequency-modulated continuous wave signal s(t) is represented as:

[0014]

[0015] The frequency modulated continuous wave signal source has a transmission power of P. t Then the received signal that reaches the receiver via path g is:

[0016]

[0017] Among them, L f It is the free space propagation loss of path f, measured in dB, L. f The calculation method is as follows:

[0018] L = 32.45 + 20logD + 20logf;

[0019] The received signal at the receiving end after the reflected signal travels through reflection paths g and b is represented as:

[0020]

[0021] Where m(t) is the tag's reflected baseband signal, which is either an OOK signal or a 4ASK signal; L g ,L b It is the path loss of reflection paths g and b, θ g θ b The phase difference is caused by the propagation delay;

[0022] The received signal at the receiver end is represented as:

[0023] y(t) = sf(t) + sb(t) + n(t);

[0024] Among them, s f (t) is a direct-chain signal, s b (t) is the tag reflection signal, and n(t) is Gaussian white noise with a mean of 0 and a variance of σ. 2 It follows a normal distribution.

[0025] Furthermore, the receiver eliminates the direct-link signal and demodulates the backscattered signal using a demodulation algorithm, which includes:

[0026] S201. Mix the received signal with the local synchronization carrier, wherein the received signal includes the reflected signal and the direct link signal; downconvert the superimposed signal of the direct link signal and the reflected signal, that is, convert the frequency band signal into a baseband signal;

[0027] S202. Envelope detection is performed on the superimposed signal of the reflected signal and the direct-chain signal to eliminate direct-chain interference and obtain the amplitude modulation information of the reflected signal.

[0028] S203. During the envelope detection process, the direct-chain signal will introduce a DC component. By averaging the signal and subtracting the average from the signal after envelope detection, only the reflected signal is present in the obtained signal.

[0029] S204. Preamble synchronization: After synchronization, extract the effective data portion of the backscattered baseband signal.

[0030] S205. Accumulate the symbol energy of the sampled backscattered baseband signal, calculate the energy of each number of bits, and perform energy detection based on the energy of the received signal.

[0031] S206. Using the judgment threshold calculated by the preamble, perform bit decision based on the bit energy obtained from the reflected signal to recover the symbol information of the reflected signal.

[0032] Furthermore, in step S204, the preamble is a 13-bit Barker code sequence.

[0033] Furthermore, the receiver demodulates the backscattered signal and, through the downlink feedback link from the receiver to the tag, dynamically adjusts the modulation scheme of the backscattered tag. This is the adaptive modulation method of the backscattered tag based on information feedback from the receiver. This adaptive modulation method includes:

[0034] After demodulation, the receiver feeds back the channel quality index (CQI) of the received signal from the downlink to the backscatter tag based on the CRC error rate.

[0035] The backscatter tag selects the appropriate modulation scheme based on the value of the Channel Quality Index (CQI).

[0036] Furthermore, the modulation method includes a high-order amplitude modulation method and a low-order amplitude modulation method.

[0037] Furthermore, the adaptive modulation method also includes downlink design, and the downlink design includes:

[0038] Frequency selection: The downlink uses the ultra-high frequency band;

[0039] Modulation method: The downlink uses binary amplitude modulation demodulation;

[0040] The downlink data frame format includes a preamble, tag identifier, operation command, channel quality index (CQI), and checksum. The preamble uses a 13-bit Barker code sequence. The tag identifier is used to identify a specific, unique tag. The operation command consists of 8 bits and is used to indicate the operation corresponding to the tag. The channel quality index (CQI) consists of 4 bits and is used for feedback control of tag adaptive modulation. The checksum performs cyclic redundancy check coding on all data except the preamble to ensure the reliability of information transmission.

[0041] Furthermore, the adaptive modulation method includes the following steps:

[0042] S301, the backscatter tag actively sends data packets to the receiver using a low-order amplitude modulation method;

[0043] S302. If no response is received from the receiver, retransmit after a random delay of time T;

[0044] S303. If a response is received from the receiver and the CQI field of the response frame is greater than the CQI_GOOD threshold, the backscatter tag will adjust the modulation mode to a higher-order amplitude modulation mode; if a response is received from the receiver and the CQI field is less than the CQI_WORST threshold, the backscatter tag will request to increase the transmit power of the frequency modulated continuous wave signal source.

[0045] S304. If the maximum transmission power of the frequency modulated continuous wave signal source has been reached, then the adaptive modulation method ends.

[0046] Furthermore, at the receiver end, the adaptive modulation method further includes the following steps:

[0047] S305. The default initial value of the CQI field of each backscatter tag response frame is CQI_WORST. Every time the receiver receives a data packet from a certain backscatter tag and the cyclic redundancy check of the data packet is correct, the CQI value of the tag is incremented by 1.

[0048] S306. If the receiver receives a data packet from the tag, but the cyclic redundancy check of the data packet is incorrect, the CQI value of the tag's response frame is directly reduced to CQI_WORST.

[0049] S307. When the receiver receives an FM continuous wave signal source from a backscatter tag and increases its transmission power, it will send a corresponding control command to the FM continuous wave signal source through the control channel.

[0050] The present invention also provides a short-range backscatter communication system based on frequency-modulated continuous wave, the improvement of which is that it includes a frequency-modulated continuous wave signal source, a backscatter tag, and a receiver;

[0051] The frequency-modulated continuous wave signal source cyclically sends excitation signals;

[0052] The backscatter tag modulates the amplitude of the incident signal and sends the reflected signal to the receiver;

[0053] The receiver receives signals, including reflected signals and linear signals transmitted by a frequency-modulated continuous wave signal source; the receiver demodulates the backscattered signal and dynamically adjusts the modulation mode of the backscattered tag, dynamically adjusting the transmission power of the frequency-modulated continuous wave signal source.

[0054] The beneficial effects of this invention are: by introducing tag adaptive adjustment technology, this invention can significantly improve the performance and reliability of the backscatter communication system, enhance the system's adaptability and robustness, reduce power consumption, and improve the system's capacity and efficiency. Attached Figure Description

[0055] Figure 1 The present invention provides a system structure diagram of a short-range backscatter communication system based on frequency-modulated continuous wave.

[0056] Figure 2 This is a schematic diagram of the frequency-modulated continuous wave signal source transmitting a continuous frequency-modulated wave in this invention.

[0057] Figure 3 This is a schematic diagram of the real part waveform, imaginary part waveform, and envelope of the received signal at the receiver end in this invention.

[0058] Figure 4 This is a schematic diagram of the demodulation algorithm of the receiver in this invention.

[0059] Figure 5 This is a schematic diagram of the internal structure of the radio frequency switch in this invention.

[0060] Figure 6 This is a schematic diagram of a two-port network in this invention.

[0061] Figure 7 This is a schematic diagram of the Smith chart design impedance in this invention.

[0062] Figure 8 This is a schematic diagram of the digital logic control module in this invention.

[0063] Figure 9 This is a schematic diagram of the adaptive modulation method in this invention.

[0064] Figure 10 This is a schematic diagram of the bit error rate curve of tag OOK modulation in this invention. Detailed Implementation

[0065] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0066] The following will clearly and completely describe the concept, specific structure, and technical effects of the present invention in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Furthermore, all connections / linkages involved in the patent do not simply refer to direct contact between components, but rather to the ability to form a better connection structure by adding or reducing connecting accessories according to specific implementation conditions. The various technical features in this invention can be combined interactively without contradicting each other.

[0067] This invention provides a short-range backscatter communication method based on frequency-modulated continuous wave, combined with... Figure 1 As shown, the method includes the following steps:

[0068] S10. Excitation signals are cyclically transmitted using a frequency-modulated continuous wave signal source, referencing... Figure 2 The diagram shown is a schematic of a frequency modulation continuous wave signal source transmitting a continuous frequency modulation wave.

[0069] S20. The backscatter tag receives the incident signal from the frequency-modulated continuous wave signal source, modulates the amplitude of the incident signal, and sends the reflected signal to the receiver; the amplitude modulation methods of the backscatter tag are OOK and 4ASK.

[0070] Combination Figure 1 As shown, in this embodiment, the path from which the frequency-modulated continuous wave signal source sends the incident signal to the backscatter tag is called path g, the path from which the backscatter tag sends the reflected signal to the receiver is called path b, and the path from which the frequency-modulated continuous wave signal source sends the direct-link signal to the receiver is called path f. The backscatter tag performs amplitude modulation on the incident signal, specifically including the following steps:

[0071] The frequency-modulated continuous wave (FM continuous wave) signal source transmits a signal s(t), which is a spread spectrum signal with a linearly increasing frequency. Its frequency is expressed as: f(t) = f0 + kt; where f0 is the initial frequency of the FM continuous wave. The phase of the FM continuous wave signal is then:

[0072]

[0073] The frequency-modulated continuous wave signal s(t) is represented as:

[0074]

[0075] The frequency modulated continuous wave signal source has a transmission power of P. t Then the received signal that reaches the receiver via path g is:

[0076]

[0077] Among them, L f It is the free space propagation loss of path f, measured in dB, L. f The calculation method is as follows:

[0078] L = 32.45 + 20logD + 20logf;

[0079] The received signal at the receiving end after the reflected signal travels through reflection paths g and b is represented as:

[0080]

[0081] Where m(t) is the tag's reflected baseband signal, which is either an OOK signal or a 4ASK signal; L g ,L b It is the path loss of reflection paths g and b, θ g θ b The phase difference is caused by the propagation delay;

[0082] The received signal at the receiver end is represented as:

[0083] y(t) = sf(t) + sb(t) + n(t);

[0084] Among them, s f (t) is a direct-chain signal, s b (t) is the tag reflection signal, and n(t) is Gaussian white noise with a mean of 0 and a variance of σ. 2 It follows a normal distribution.

[0085] In this embodiment, the real part waveform, imaginary part waveform, and envelope of y(t) are as follows: Figure 3 As shown.

[0086] S30. The receiver receives the signal, which includes the reflected signal and the direct-link signal transmitted by the frequency-modulated continuous wave signal source. The receiver demodulates the backscattered signal and, through the downlink feedback link from the receiver to the backscattered tag, dynamically adjusts the modulation mode of the backscattered tag. Through the control link from the receiver to the frequency-modulated continuous wave signal source, the transmit power of the frequency-modulated continuous wave signal source is dynamically adjusted.

[0087] In this embodiment, the receiver eliminates the direct-link signal and demodulates the backscattered signal using a demodulation algorithm, referring to... Figure 4 As shown, the demodulation algorithm includes:

[0088] S201. Mix the received signal with the local synchronization carrier, wherein the received signal includes the reflected signal and the direct link signal; downconvert the superimposed signal of the direct link signal and the reflected signal, that is, convert the frequency band signal into a baseband signal;

[0089] S202. Envelope detection is performed on the superimposed signal of the reflected signal and the direct-chain signal to eliminate direct-chain interference and obtain the amplitude modulation information of the reflected signal.

[0090] S203. During the envelope detection process, the direct-chain signal will introduce a DC component. By averaging the signal and subtracting the average from the signal after envelope detection, only the reflected signal is present in the obtained signal.

[0091] S204, preamble synchronization, to obtain backscattered baseband signal;

[0092] In step S204, the preamble is a 13-bit Barker code sequence; Barker codes have good autocorrelation properties, and their autocorrelation function is shown below:

[0093]

[0094] The autocorrelation function has a maximum output n only when the Barker code sequences overlap, where n is the length of the Barker code sequence. In other cases, the output is 0 or ±1. Therefore, using a 13-bit Barker code can minimize the risk of preamble correlation errors.

[0095] S205. Accumulate the symbol energy of the sampled backscattered baseband signal, calculate the energy of each number of bits, and perform energy detection based on the energy of the received signal.

[0096] S206. Using the judgment threshold calculated by the preamble, perform bit decision based on the bit energy obtained from the reflected signal to recover the symbol information of the reflected signal.

[0097] In the above embodiments, for the design of backscattering tags, the present invention also proposes a design method for amplitude-modulated backscattering tags, including the following:

[0098] Backscatter tags are the most numerous devices in a backscatter communication system. Their primary function is to modulate the excitation signal by backscattering. While a backscatter communication system typically has only one signal source and receiver, it can contain hundreds of tags. Therefore, designing simple, reliable, and low-cost backscatter tags is one of the core tasks in constructing a backscatter communication system. This embodiment primarily describes the backscatter tag design of this system, including the design of impedance tags and the digital logic control module.

[0099] Taking OOK amplitude modulation of a tag as an example, impedance matching and mismatch are crucial concepts in the impedance modulation module. The tag is a passive system that only modulates the frequency-modulated continuous wave in the environment via backscattering. Therefore, the antenna in the impedance modulation module acts as a signal source, and the signal source and load resistor form a two-port network. Impedance matching includes two aspects: first, the conjugate matching between the signal source and the transmission line; and second, the matching between the load and the transmission line. Let the characteristic impedance of the antenna be Z0, and the load impedance be Z... l When the antenna and load impedances are matched, i.e., Z0 = Z l At this time, the reflection coefficient |Γ tag When |Γ = 0, the incident signal is completely absorbed by the antenna, resulting in only the incident wave and no reflected wave. This state is called a traveling wave in radio frequency theory. When the incident wave is completely reflected by the load terminal, the reflected wave has the same amplitude but opposite direction to the incident wave, and the reflection coefficient |Γ| is 0. tag When |=1, the antenna and load are completely mismatched, which is called a pure standing wave (VSW) state in radio frequency theory. There are four situations in which a pure VSW can be formed: short circuit at the terminal, open circuit at the terminal, pure capacitive reactance, and pure inductive reactance of the load.

[0100] The tag in this embodiment uses amplitude modulation, requiring the tag impedance to switch between matched and mismatched states. In the matched state, the incident signal is completely absorbed by the tag, indicating that the tag transmits a bit "0". In the completely mismatched state, the incident signal is completely reflected by the tag, indicating that the tag transmits a bit "1". This achieves the switching between the two impedance states.

[0101] For applications requiring a single-pole double-throw (SPDT) RF switch, the ADG901 or ADG902 from Analog Devices (ADI) can be used to simplify circuit design. Their internal structure is as follows: Figure 5As shown. The ADG901 is an absorptive RF switch with an internal 50-ohm impedance matching resistor. By default, it completely absorbs incident waves. Using the ADG901 requires an antenna connected to the RF2 port. The RF1 port can be grounded, short-circuited, or used as a purely reactive load. The RF switch is controlled via the CTRL interface signal. The ADG902 is a reflective RF switch with an internal short-circuit load. By default, it completely reflects incident waves. Using the ADG902 requires an antenna connected to the RF2 port. An impedance matching resistor can be connected to the RF1 port. The RF switch is controlled via the CTRL interface signal.

[0102] This design uses the ADG902 reflective RF switch. The ADG902's supply voltage is V. DD The voltage is 1.65-2.75V. When using an external 3.3V power supply, it is necessary to perform voltage division. The CTRL port uses CMOS / LVTTL control level, and the maximum control voltage cannot exceed V. DD The maximum closing time t of the ADG902 switch. on =6ns, maximum switch off time t off =9.5ns, and the calculated switching frequency supported by the switch is 105MHz.

[0103] When routing on a PCB, it's necessary to design impedance matching between the microstrip line's characteristic impedance (Z0) and the antenna impedance (50Ω). Impedance matching between the load and the microstrip line also needs to be designed. The formula for calculating the characteristic impedance (Z0) of a microstrip line is as follows:

[0104]

[0105] Where, ε r t is the dielectric constant of the insulating material; h is the dielectric thickness between the microstrip line and the ground; w is the width of the microstrip line; and t is the thickness of the microstrip line.

[0106] Furthermore, when designing impedance matching, it is also necessary to consider the S11 and S22 parameters of the RF switch ADG902, namely the scattering parameters. For a two-port network, the S11 parameter refers to the voltage reflection coefficient of port 1 when port 2 is connected to a matched load; similarly, S22 refers to the voltage reflection coefficient of port 2 when port 1 is connected to a matched load.

[0107]

[0108] Among them, such as Figure 6 As shown, the incident voltage at port 1 is a1, the reflected voltage at port 1 is b1, the incident voltage at port 2 is a2, and the reflected voltage at port 2 is b2.

[0109] The impedance load of an RF switch can be designed using the Smith chart or electromagnetic simulation software HFSS. This embodiment uses the Smith chart method for impedance design. The S-parameter model of the ADG902 RF switch is imported into the Smith chart, and impedance matching is achieved using a matching network design on the transmission line. The matching network design method involves connecting resistors, capacitors, and inductors in series on the transmission line. For example... Figure 7 As shown in (a), the impedance matching design of the ADG902 RF switch can be achieved by using a parallel resistor of 1.1kΩ and a series inductor of 2.2nH. Figure 7 As shown in (b), the ADG902 RF switch can be designed with a completely mismatched impedance by using a parallel inductor of 183nH.

[0110] The digital logic control module is the core of tag control, responsible for controlling the entire tag's information acquisition, processing, and modulation. In existing backscatter communication system tag designs, the digital logic control module typically uses a microcontroller or FPGA (Field Programmable Gate Array) solution.

[0111] The digital control module in the label of this embodiment consists of a Xilinx FPGA and is developed using the hardware description language (Verilog HDL). An FPGA is used as the digital logic control module because it can easily and quickly achieve precise timing control, which is a necessary condition for controlling impedance for backscatter modulation.

[0112] The logical structure of the digital logic control module is as follows: Figure 8 As shown, the system consists of a phase-locked loop (PLL) module, a control module, a modulation module, and a sensor interface module. The PLL module uses a digital PLL IP core design. The control module is responsible for overall control and scheduling, primarily handling downlink signal reception, sensor drive control, backscatter data frame generation, and control of the modulation module. The modulation module connects to an external RF switch, which, based on data from the control module, transforms the data information into impedance and modulates it onto the ambient RF signal.

[0113] The sensor interface module uses an IIC (Inter-Integrated Circuit) interface, a half-duplex synchronous serial bus, to communicate with external sensors and acquire sensor data. When transmitting data between the sensor interface module and the external sensor, the sensor interface module first performs addressing. After addressing, the sensor structure module sends read / write register commands. Upon receiving these commands, the sensor reads the corresponding register data and sends it back to the sensor interface module. The sensor interface module responds with a low-level signal, ending the communication.

[0114] In the above embodiments, the receiver demodulates the backscattered signal and dynamically adjusts the modulation scheme of the backscatter tag, i.e., the backscatter tag uses an adaptive modulation method based on information feedback from the receiver. In this embodiment, the adaptive modulation method includes: after demodulation, the receiver feeds back the channel quality index (CQI) of the received signal from the downlink to the backscatter tag based on the CRC error rate; the backscatter tag selects the appropriate modulation scheme based on the value of the CQI. When the channel quality is good, a higher-order amplitude modulation (4ASK) scheme is used; when the channel quality is poor, a lower-order amplitude modulation (OOK) scheme is used. Simultaneously, the reliability of the uplink can be improved by requesting the receiver to increase the transmit power of the frequency-modulated continuous wave signal source.

[0115] The design of the downlink feedback link is the core of the adaptive modulation method for backscatter tags based on information feedback from the receiver. In this embodiment, a request-response mechanism is adopted, where the reader initiates a request, and the backscatter tag responds with corresponding data according to the reader's request command. The adaptive modulation method also includes the design of the downlink, which includes:

[0116] Frequency selection: The downlink uses the ultra-high frequency band (UHF, 300-3000MHz); the ultra-high frequency band is moderate in terms of transmission distance and data rate, and supports the tag's backscatter modulation method.

[0117] The downlink uses binary amplitude modulation demodulation. Because the tag uses a semi-active design, envelope detector diodes are used for detection in order to save demodulation power consumption in the downlink as much as possible.

[0118] The downlink data frame format includes a preamble, tag identifier, operation command, channel quality index (CQI), and checksum. The preamble uses a 13-bit Barker code sequence. The tag identifier is used to identify a specific, unique tag. The operation command consists of 8 bits and is used to indicate the operation corresponding to the tag. The channel quality index (CQI) consists of 4 bits and is used for feedback control of tag adaptive modulation. The checksum performs cyclic redundancy check coding on all data except the preamble to ensure the reliability of information transmission.

[0119] Reference Figure 9 As shown, the adaptive modulation method includes the following steps:

[0120] S301, the backscatter tag actively sends data packets to the receiver using a low-order amplitude modulation method;

[0121] S302. If no response is received from the receiver, retransmit after a random delay of time T;

[0122] S303. If a response is received from the receiver and the CQI field of the response frame is greater than the CQI_GOOD threshold, the backscatter tag will adjust the modulation mode to a higher-order amplitude modulation mode; if a response is received from the receiver and the CQI field is less than the CQI_WORST threshold, the backscatter tag will request to increase the transmit power of the frequency modulated continuous wave signal source.

[0123] S304. If the maximum transmission power of the frequency modulated continuous wave signal source has been reached, then the adaptive modulation method ends.

[0124] In addition, at the receiver end, the adaptive modulation method further includes the following steps:

[0125] S305. The default initial value of the CQI field of each backscatter tag response frame is CQI_WORST. Every time the receiver receives a data packet from a certain backscatter tag and the cyclic redundancy check of the data packet is correct, the CQI value of the tag is incremented by 1.

[0126] S306. If the receiver receives a data packet from the tag, but the cyclic redundancy check of the data packet is incorrect, the CQI value of the tag's response frame is directly reduced to CQI_WORST.

[0127] S307. When the receiver receives an FM continuous wave signal source from a backscatter tag and increases its transmission power, it will send a corresponding control command to the FM continuous wave signal source through the control channel.

[0128] The present invention also provides a short-range backscatter communication system based on frequency-modulated continuous wave (FM-CVT), comprising an FM-CVT signal source, a backscatter tag, and a receiver; the FM-CVT signal source cyclically transmits an excitation signal; the backscatter tag modulates the amplitude of the incident signal and transmits the reflected signal to the receiver; the receiver receives the received signal, which includes the reflected signal and the direct-link signal transmitted by the FM-CVT signal source; the receiver demodulates the backscatter signal and dynamically adjusts the modulation of the backscatter tag, thereby dynamically adjusting the transmission power of the FM-CVT signal source.

[0129] A specific embodiment of the frequency-modulated continuous wave (FM-CVT) based short-range backscatter communication system of the present invention is provided. In this embodiment, the FM-CVT-based short-range backscatter communication system mainly consists of three parts: an FM-CVT signal source, a backscatter tag, and a receiver. The FM-CVT signal source cyclically transmits an FM-CVT signal with a fixed bandwidth of 500 kHz and a fixed period of 0.256 ms; the backscatter tag is responsible for the backscatter modulation transmission of the data to be transmitted, and the backscatter tag adopts amplitude modulation; the receiver is responsible for receiving and demodulating the tag's reflected signal.

[0130] The verification platform system consists of three parts: an FM continuous wave signal source, a backscatter tag, and an NI USRP2952R. The system operates at 440MHz, so the backscatter tag's structure comprises an impedance board and an FPGA control board. The FM continuous wave signal source transmits an excitation signal with a transmit power of 20dBm. The experimental parameters of the verification platform are as follows: FM continuous wave signal source frequency 440MHz, receiver sampling rate 10M / s, signal source transmit power 20dBm, and distance between the signal source and the receiver 5m.

[0131] An amplitude modulation method for frequency-modulated continuous wave (FM-Continuous Wave) utilizes the characteristic that FM-Continuous Wave is a constant envelope signal. First, a signal source cyclically transmits FM-Continuous Wave signals with a fixed bandwidth and fixed period. A tag synchronizes with the FM-Continuous Wave. After synchronization, an RF switch uses baseband data to switch between matched and mismatched impedances on the tag at a rate of 5 Mbps, achieving absorption and reflection of the FM-Continuous Wave. This causes the reflected signal to exhibit high and low level changes in its envelope amplitude, thus achieving amplitude modulation on the FM-Continuous Wave. (See attached diagram.) Figure 3 As shown. The receiver demodulates the signal based on its envelope; the demodulation algorithm is shown in the attached figure. Figure 4 As shown, the main steps are as follows: First, carrier synchronization is performed on the radio frequency signal, shifting the baseband signal to zero frequency. Second, envelope detection is performed on the superimposed signal of the reflected signal and the direct-link signal to eliminate direct-link interference. Third, the DC component introduced by the envelope detection is removed, resulting in a signal containing only the reflected signal. Fourth, preamble synchronization is performed on the reflected signal by correlating the signal with the local preamble sequence. The preamble uses a Barker code sequence with good autocorrelation properties to complete the data frame synchronization of the reflected signal. Fifth, symbol energy is accumulated to calculate the energy of each data bit. Sixth, bit decision is performed based on the data bit energy to recover the reflected signal code data.

[0132] The verification platform operates with a fixed distance of 5m between the frequency modulated continuous wave signal source and the receiver, and the tag moves between the signal source and the receiver. Bit error rate (BER) curves are measured for the tag at different positions. The received BER curve of the verification platform at a reflected signal symbol rate of 5Mbps is shown below. Figure 10 As shown, the basic pattern is that the bit error rate (BER) is lower when the system is close to the signal source and receiver, but increases when it is positioned closer to them. At a close distance of 5 meters, the overall BER of the system is around 10%. -1 Up to 10 -2 between.

[0133] Based on this, this invention proposes a basic frequency-modulated continuous wave (FM-CVT) backscatter communication system and method. By deploying a dedicated signal source device, FM-CVT is transmitted as a stable and reliable excitation signal. For short-range, high-speed applications, an amplitude modulation method for FM-CVT is proposed to achieve short-range, high-speed backscatter communication. At the receiver, the constant envelope characteristic of FM-CVT is utilized to achieve envelope detection and demodulation of the reflected signal. Furthermore, the receiver uses CQI (Channel Quality Indication) feedback to dynamically adjust the tag's modulation scheme. Adaptive modulation technology can also dynamically adjust the signal source's transmission power according to system requirements, thereby reducing the power consumption of the backscatter communication system. Introducing tag adaptive adjustment technology can significantly improve the performance and reliability of the backscatter communication system, enhance its adaptability and robustness, reduce power consumption, and increase its capacity and efficiency.

[0134] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A short-range backscatter communication method based on frequency-modulated continuous wave, characterized in that, The method includes the following steps: Excitation signals are cyclically transmitted using a frequency-modulated continuous wave signal source; The backscatter tag receives the incident signal from the frequency-modulated continuous wave signal source, modulates the amplitude of the incident signal, and sends the reflected signal to the receiver. The receiver receives the backscattered signal, which includes the reflected signal and the direct-link signal transmitted by the frequency-modulated continuous wave (FM-CW) signal source. The receiver demodulates the backscattered signal and dynamically adjusts the modulation mode of the backscattered tag through the downlink feedback link from the receiver to the backscattered tag. The transmit power of the FM-CW signal source is dynamically adjusted through the control link from the receiver to the FM-CW signal source.

2. The short-range backscatter communication method based on frequency-modulated continuous wave according to claim 1, characterized in that, The path from which the frequency-modulated continuous wave signal source sends the incident signal to the backscatter tag is called path g; the path from which the backscatter tag sends the reflected signal to the receiver is called path b; and the path from which the frequency-modulated continuous wave signal source sends the direct-link signal to the receiver is called path f. The backscattering tag modulates the amplitude of the incident signal, including: The signal transmitted by the frequency modulated continuous wave signal source is , For a spread spectrum signal whose frequency increases linearly, its frequency is expressed as: ;in If the initial frequency is the frequency of the frequency-modulated continuous wave, then the phase of the frequency-modulated continuous wave signal is: ； Frequency Modulated Continuous Wave Signal Represented as: ； The transmit power of the frequency modulated continuous wave signal source is Then the received signal that reaches the receiver via path g is: ； in, It is the free space propagation loss of path f, measured in dB. The calculation method is as follows: ； The reflected signal passes through the reflection path and The received signal arriving at the receiving end is represented as: ； in, It is the reflectance of the label. It is the tag's reflected baseband signal, which is either an OOK signal or a 4ASK signal; It is the reflection path and Path loss, , The phase difference is caused by the propagation delay; The received signal at the receiver end is represented as: ； in, It is a straight-chain signal. It is a signal reflected from the tag. It is Gaussian white noise with a mean of 0 and a variance of . It follows a normal distribution.

3. The short-range backscatter communication method based on frequency-modulated continuous wave according to claim 1, characterized in that, The receiver eliminates the direct-link signal and demodulates the backscattered signal using a demodulation algorithm, which includes: S201. Mix the received signal with the local synchronization carrier, wherein the received signal includes the reflected signal and the direct link signal; downconvert the superimposed signal of the direct link signal and the reflected signal, that is, convert the frequency band signal into a baseband signal; S202. Envelope detection is performed on the superimposed signal of the reflected signal and the direct-chain signal to eliminate direct-chain interference and obtain the amplitude modulation information of the reflected signal. S203. During the envelope detection process, the direct-chain signal will introduce a DC component. By averaging the signal and subtracting the average from the signal after envelope detection, only the reflected signal is present in the obtained signal. S204. Preamble synchronization: After synchronization, extract the effective data portion of the backscattered baseband signal. S205. Accumulate the symbol energy of the sampled backscattered baseband signal, calculate the energy of each number of bits, and perform energy detection based on the energy of the received signal. S206. Using the judgment threshold calculated by the preamble, perform bit decision based on the bit energy obtained from the reflected signal to recover the symbol information of the reflected signal.

4. The short-range backscatter communication method based on frequency-modulated continuous wave according to claim 3, characterized in that, In step S204, the preamble is a 13-bit Barker code sequence.

5. A short-range backscatter communication method based on frequency-modulated continuous wave according to claim 1, characterized in that, The receiver demodulates the backscattered signal and dynamically adjusts the modulation scheme of the backscattered tag, which is an adaptive modulation method based on the information feedback from the receiver. This adaptive modulation method includes: After demodulation, the receiver feeds back the channel quality index (CQI) of the received signal from the downlink to the backscatter tag based on the CRC error rate. The backscatter tag selects the appropriate modulation scheme based on the value of the Channel Quality Index (CQI).

6. A short-range backscatter communication method based on frequency-modulated continuous wave according to claim 5, characterized in that, The modulation methods include high-order amplitude modulation and low-order amplitude modulation.

7. A short-range backscatter communication method based on frequency-modulated continuous wave according to claim 5, characterized in that, The adaptive modulation method further includes downlink design, and the downlink design includes: Frequency selection: The downlink uses the ultra-high frequency band; Modulation method: The downlink uses binary amplitude modulation demodulation; The downlink data frame format includes a preamble, tag identifier, operation command, channel quality index (CQI), and checksum. The preamble uses a 13-bit Barker code sequence. The tag identifier is used to identify a specific, unique tag. The operation command consists of 8 bits and is used to indicate the operation corresponding to the tag. The channel quality index (CQI) consists of 4 bits and is used for feedback control of tag adaptive modulation. The checksum performs cyclic redundancy check coding on all data except the preamble to ensure the reliability of information transmission.

8. A short-range backscatter communication method based on frequency-modulated continuous wave according to claim 5, characterized in that, The adaptive modulation method includes the following steps: S301, the backscatter tag actively sends data packets to the receiver using a low-order amplitude modulation method; S302. If no response is received from the receiver, retransmit after a random delay of time T; S303. If a response is received from the receiver and the CQI field of the response frame is greater than the CQI_GOOD threshold, the backscatter tag will adjust the modulation mode to a higher-order amplitude modulation mode; if a response is received from the receiver and the CQI field is less than the CQI_WORST threshold, the backscatter tag will request to increase the transmit power of the frequency modulated continuous wave signal source. S304. If the maximum transmission power of the frequency modulated continuous wave signal source has been reached, then the adaptive modulation method ends.

9. A short-range backscatter communication method based on frequency-modulated continuous wave according to claim 8, characterized in that, At the receiver end, the adaptive modulation method further includes the following steps: S305. The default initial value of the CQI field of each backscatter tag response frame is CQI_WORST. Every time the receiver receives a data packet from a certain backscatter tag and the cyclic redundancy check of the data packet is correct, the CQI value of the tag is incremented by 1. S306. If the receiver receives a data packet from the tag, but the cyclic redundancy check of the data packet is incorrect, the CQI value of the tag's response frame is directly reduced to CQI_WORST. S307. When the receiver receives an FM continuous wave signal source from a backscatter tag and increases its transmission power, it will send a corresponding control command to the FM continuous wave signal source through the control channel.

10. A short-range backscatter communication system based on frequency-modulated continuous wave, characterized in that, This includes a frequency-modulated continuous wave signal source, a backscatter tag, and a receiver; The frequency-modulated continuous wave signal source cyclically sends excitation signals; The backscatter tag modulates the amplitude of the incident signal and sends the reflected signal to the receiver; The receiver receives signals, including reflected signals and linear signals transmitted by a frequency-modulated continuous wave signal source; the receiver demodulates the backscattered signal and dynamically adjusts the modulation mode of the backscattered tag, dynamically adjusting the transmission power of the frequency-modulated continuous wave signal source.

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