A QAM modulation wireless communication method and system based on IM3

Abstract

The present invention provides a QAM modulation wireless communication method and system based on IM3. The wireless communication system includes a transmitting end and a receiving end. The transmitting end includes a transmitting signal source and a transmitting antenna connected in sequence. The receiving end includes a receiving antenna, a diode rectifier module, an IM3 modulator, a DC filter and a load. The IM3 modulator includes two branches connected in parallel between the signal transmission path and the ground line; an adjustable capacitor is provided on the first branch. An adjustable resistor is provided on the second branch. The present invention uses IM3 signals for communication, realizes zero energy consumption of wireless energy collaborative information transmission, reduces energy loss and prolongs system life, and is suitable for a variety of application environments. The present invention adopts a rectifier circuit with a single diode structure, and the IM3 signal used for transmission is generated by the diode itself, and does not require an additional oscillation circuit to generate it.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communications, and in particular relates to an IM3-based QAM modulation wireless communication method and system. Background Art

[0002] Radio frequency wireless power transfer (RF WPT) technology has attracted considerable attention for its potential to address energy shortages in future communication networks, particularly those in the Internet of Things (IoT). This technology's core advantage lies in its ability to extract energy from ambient RF signals to power power-constrained network nodes. RF signals are unique in their ability to transmit not only information but also energy, offering a new energy solution for wireless devices. As society's demands for communication technology continue to increase, the need for improved spectrum efficiency and energy efficiency (EE) is also growing. To meet these demands, a range of efficient wireless communication network technologies have emerged, including multi-antenna communication networks, device-to-device (D2D) communication networks, and bidirectional relay networks. The development of these technologies not only improves data transmission efficiency but also enables efficient energy utilization.

[0003] Backscatter communication is a wireless communication technology that allows devices to transmit information by reflecting existing wireless signals, without requiring their own transmitters. This technology can significantly reduce device energy consumption because it eliminates the need for active signal transmission. Combining RF wireless energy transmission with these efficient wireless communication technologies can form a new type of highly efficient wireless power communication network. This network can not only significantly extend the lifespan of network devices and reduce the frequency of battery replacements, but also improve overall system performance without increasing additional energy consumption. This is particularly important in scenarios such as the Internet of Things, which require a large number of low-power devices, as these devices often require frequent battery replacements or power supply connections.

[0004] Backscatter communication typically uses harmonics or intermodulation signals generated by the rectifier itself at the RF WPT receiver as data carriers. Third-order intermodulation signals are parasitic signals generated when two or more signals are mixed in a linear system due to nonlinear factors (in rectifier circuits, this factor is often the nonlinear characteristics of the diode itself), causing the second harmonic of one signal to mix with the fundamental frequency of another signal. Third-order intermodulation signals have a wide range of applications. In radar and other high-frequency systems, third-order intermodulation signals are widely used to improve system accuracy and stability. In radar systems, the use of third-order intermodulation signals helps enhance radar detection capabilities and anti-interference capabilities, enabling radar to accurately identify and track targets in complex environments. In high-frequency systems, third-order intermodulation signals also play an important role, helping to optimize system performance and improve signal transmission efficiency. Third-order intermodulation signals also have applications in wireless communications. While second-order intermodulation is more common in wireless communications, third-order intermodulation can also be useful in certain situations, such as improving signal transmission efficiency and anti-interference capabilities.

[0005] QAM (Quadrature Amplitude Modulation) is a modulation technique widely used in digital communications. It transmits digital data by simultaneously varying the amplitude and phase of the signal, achieving highly efficient data transmission within limited spectrum resources. The basic principle of QAM modulation is to divide digital data into multiple bit groups and map each bit group to a specific signal point. These signal points lie on a complex plane, with the real axis representing the signal amplitude and the imaginary axis representing the signal phase. By varying the signal phase and amplitude, different digital information can be represented. The QAM modulation process consists of two key steps: symbol mapping and complex modulation. In the symbol mapping stage, digital data is mapped to QAM symbol points on the complex plane. For example, in 16-QAM, there are 16 different symbol points, each representing a specific digital combination. In the complex modulation stage, each symbol point is amplitude- and phase-modulated to produce the corresponding QAM signal. QAM modulation technology has a wide range of applications in the communications field, including cable modems, digital television, digital audio broadcasting, and wireless communication systems such as Wi-Fi and LTE. It uses the amplitude and phase of a signal to transmit information, enabling more data to be transmitted within limited spectrum resources. Therefore, it is widely used in the modulation and demodulation processes of digital communication systems. As the modulation order increases, QAM signal complexity and data transmission rate increase, but it also increases susceptibility to noise and interference. Broadly speaking, QAM modulation maps the data signal onto multiple distinct vector states that are easily distinguishable.

[0006] like Figure 1The figure shows a schematic diagram of a rectifier using harmonics for backscatter communication. The second harmonic 2f0 and third harmonic 3f0, generated by the rectifier's inherent nonlinearity, are used as carrier waves. A reconfigurable filter, constructed using a DGS (Digital Gaussian Sequencing System), amplitude modulates the uplink and downlink communication data. An external voltage bias is used to create two distinct states, representing data "0" and data "1," respectively. This technical solution has the following disadvantages: the second and third harmonics used have a significant spectral difference from the fundamental frequency, requiring the design of antennas for multiple frequency bands, increasing system complexity. The modulation method is ASK, which can only transmit binary digits (1) per unit time, resulting in a slow transmission rate.

[0007] like Figure 2 The figure shows a rectifier circuit that performs QAM modulation on backscattered signals. This QAM modulation is achieved by designing M microstrip line short-circuit stubs, introducing different matching circuits. This shifts the rectifier circuit's impedance to M different positions on the Smith diagram. Since the different impedances set at the receiving end reflect the received RF signal to varying degrees, the transmitting end can implement QAM modulation by detecting the amplitude and phase of the reflected signal. This technical solution has the following disadvantages: QAM modulation is achieved by varying the matching impedance, and changes in matching can affect the normal rectifier's operating efficiency. Summary of the Invention

[0008] The object of the present invention is to provide a QAM modulation wireless communication method and system based on IM3.

[0009] In a first aspect, the present invention provides a QAM modulation wireless communication method based on IM3, wherein the wireless communication system used includes a transmitter and a receiver. The transmitter includes a transmitting signal source and a transmitting antenna connected in sequence. The receiving end includes a receiving antenna, a diode rectifier module, an IM3 modulator, a DC filter, and a load. The IM3 modulator includes two branches connected in parallel between the signal transmission path and the ground line; the first branch is provided with an adjustable capacitor C T The second branch is equipped with an adjustable resistor R T .

[0010] The IM3-based QAM modulation wireless communication method comprises the following steps:

[0011] The transmitting end transmits a dual-frequency AC excitation signal; the receiving antenna receives the dual-frequency AC excitation signal.

[0012] The diode rectifier module generates a third-order intermodulation signal IM3 under the excitation of the dual-frequency AC excitation signal.

[0013] Adjust the adjustable capacitor C according to the uplink information that the receiving end needs to send. T and adjustable resistor RT , so that the vector state of the third-order intermodulation signal IM3 matches the uplink information.

[0014] The receiving end sends an uplink signal corresponding to the third-order intermodulation signal IM3 through backscattering. The transmitting end receives the uplink signal and demodulates it to obtain the uplink information.

[0015] Preferably, the two frequencies ω1 and ω2 of the dual-frequency AC excitation signal transmitted by the transmitting end meet the following condition: 0.01ω1≤|ω1-ω2|≤Bw; wherein Bw is the bandwidth of the transmitting antenna.

[0016] Preferably, the vector state of the third-order intermodulation signal IM3 includes two dimensions: amplitude and phase; any two different uplink signals differ in at least one dimension.

[0017] Preferably, the number of vector states of the third-order intermodulation signal IM3 is greater than or equal to 4, preferably 4-QAM, 8-QAM, and 16-QAM modulation modes.

[0018] Preferably, the third-order intermodulation signal IM3 has eight vector states. The eight vector states are divided into two groups. The four vector states in the same group are sequentially 90° out of phase with each other. The amplitude ranges corresponding to the vector states in different groups do not overlap and differ by at least 10 dBm.

[0019] In a second aspect, the present invention provides an IM3-based QAM modulation wireless communication system, comprising a transmitter and a receiver. The transmitter comprises a transmitting signal source and a transmitting antenna connected in sequence. The receiving terminal comprises a receiving antenna, a diode rectifier module, an IM3 modulator, a DC filter, and a load connected in sequence. The IM3 modulator comprises two branches connected in parallel between the signal transmission path and the ground line; the first branch is provided with an adjustable capacitor C T The second branch is equipped with an adjustable resistor R T .

[0020] The receiving antenna receives the dual-frequency AC excitation signal from the transmitting end; the diode rectifier module converts the dual-frequency AC excitation signal into a DC signal and generates a third-order intermodulation signal IM3; the vector state of the third-order intermodulation signal IM3 changes with the adjustable capacitor C T and adjustable resistor R T The different vector states of the third-order intermodulation signal IM3 correspond to different uplink information at the receiving end. The receiving antenna automatically sends the frequency ω IM3 =2ω1-ω2 uplink signal; the transmitting end demodulates the uplink signal to obtain the uplink information, thereby realizing backscatter communication from the receiving end to the transmitting end.

[0021] Preferably, the adjustable resistor R TThere is a DC blocking capacitor C in series on the branch. M .

[0022] Preferably, the diode rectifier module includes a rectifier diode D connected in series between the signal transmission path and the ground line, an inductor L1 , and a capacitor C1 connected in parallel across the rectifier diode D.

[0023] Preferably, the DC filter adopts an LC filter structure. An isolation capacitor C is provided between the receiving antenna and the diode rectifier module. block .

[0024] Preferably, the adjustable capacitor C T , The second branch is equipped with an adjustable resistor R T A variable capacitance conversion array and a variable resistance conversion array are used respectively.

[0025] The present invention has the following beneficial effects:

[0026] 1. Zero energy consumption of wireless energy cooperative information transmission: The present invention uses IM3 signals for communication, achieving zero energy consumption of wireless energy cooperative information transmission, reducing energy loss and extending system life, and is suitable for a variety of application environments.

[0027] 2. Wide range of applications: The communication system proposed in the present invention can realize multi-base QAM modulation, such as 4-QAM, 8-QAM, 16-QAM, etc., through different settings of component parameters. The modulation mode can be adjusted according to specific needs to broaden the application scenarios of the system; therefore, the modulation mode can be flexibly set, and high-base QAM modulation can be realized in application scenarios requiring high speed. Compared with traditional ASK, FSK and other modulation modes that can only transmit 1 binary bit at a time, it has a great rate improvement; in systems that do not require high speed, the settings can be simplified, the system operating costs can be reduced, and the application scope is greatly expanded.

[0028] 3. Reduced circuit complexity: The present invention adopts a rectifier circuit with a single diode structure. The transmission signal used is generated by the diode itself and does not require an additional oscillation circuit. In addition, the modulation of the IM3 signal in the present invention is achieved through a simple filter structure, and data detection and information transmission do not require additional detection circuits and modulation circuits, so the circuit complexity is low.

[0029] 4. Cost reduction: Since the present invention uses IM3 signals as communication signals, which are relatively close to baseband signals, the WPT system's transceiver antenna design only requires a smaller bandwidth to achieve multiplexing. At the same time, flexible component parameter settings also reduce system construction costs.

[0030] 5. Improved system reliability and stability: Due to the design of the present invention, the unit circuits required by the system are simplified, the connection failure points between the unit circuits are reduced, and the reliability and stability of the entire system are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of a conventional harmonic backscatter rectifier;

[0032] Figure 2 Schematic diagram of a conventional M-QAM passive backscatter communication array;

[0033] Figure 3 This is a schematic diagram of the system workflow of Example 1 of the present invention;

[0034] Figure 4 This is a constellation diagram of the 8-QAM modulation method used in Example 1 of the present invention;

[0035] Figure 5 Schematic diagram of the mixing process of the third-order intermodulation signal IM3 in Example 1 of the present invention

[0036] Figure 6 The basic working principle diagram of the IM3 modulator provided by Example 1 of the present invention

[0037] Figure 7 This is an equivalent model diagram of the diode rectifier module in Example 1 of the present invention;

[0038] Figure 8 Spectrum distribution diagram of the signal at the receiving end under dual-frequency excitation in Example 1 of the present invention;

[0039] Figure 9 Schematic diagram of the current direction of the receiving end during the second frequency mixing process in Example 1 of the present invention;

[0040] Figure 10 1 is a diagram showing the calculation results of the third-order intermodulation signal IM3 in Example 1 of the present invention (wherein (a) is a schematic diagram showing the amplitudes of the components of the third-order intermodulation signal IM3; and (b) is a schematic diagram showing the vector superposition of the components of the third-order intermodulation signal IM3);

[0041] Figure 11 Schematic diagram of the circuit structure of the IM3 modulator in Example 1 of the present invention.

[0042] Figure 12 This is a schematic diagram of the overall circuit of the receiving end in Example 1 of the present invention;

[0043] Figure 13 1 is a vector coordinate diagram of the third-order intermodulation signal IM3 under different states in Example 1 of the present invention.

[0044] Figure 14Schematic diagram of a variable capacitance conversion array and a variable resistance conversion array used as examples in Example 1 of the present invention. DETAILED DESCRIPTION

[0045] The present invention will be further described below with reference to the accompanying drawings.

[0046] Example 1

[0047] A QAM modulation wireless communication system based on IM3 is used to achieve multi-bit data upload through backscatter communication. The key terms and abbreviations involved in this embodiment are explained as follows:

[0048] IM3: the Third-order Intermodulation (third-order intermodulation signal); WPT: Wireless Power Transfer (wireless power transmission); RF: Radio Frequency (radio frequency); QAM: Quadrature Amplitude Modulation (quadrature amplitude modulation); IoT: Internet of Things (Internet of Things); EE: Energy Efficient; D2D: Device to Device (device-to-device); DGS: Defected Ground Structure).

[0049] like Figure 3 As shown, this embodiment provides an IM3-based QAM modulation wireless communication system, including a transmitter and a receiver. The transmitter includes a transmission signal source (Base Station) and a transmission antenna (Tx) connected in sequence. The receiver includes a receiving antenna (Rx), a diode rectifier module (Rectifier), an IM3 modulator (IM3 Modulator), a DC filter (DC-Pass), and a load (DC-Load) connected in sequence.

[0050] The working process of the QAM modulation wireless communication system is as follows Figure 3 shown. Figure 3 The red path in the upper half is the system's energy transmission channel. The transmitting signal source (Base Station) generates dual-frequency AC excitation (frequencies ω1 and ω2), which is then emitted by the transmitting antenna (Tx). The receiving antenna (Rx) acquires the energy signal and converts the AC signal into a DC signal through the diode rectifier module (Rectifier). At the same time, the nonlinear characteristics of the diode generate a third-order intermodulation signal IM3. The frequency of the third-order intermodulation signal IM3 is ω. IM3=2ω1-ω2. Due to the presence of the DC-pass, only DC energy is transferred to the load, completing the wireless energy transmission process. Frequencies ω1 and ω2 satisfy the following condition: 0.01ω1≤|ω1-ω2|≤Bw; where Bw is the bandwidth of the transmitting antenna.

[0051] Figure 3 The blue path in the lower part is the data transmission channel of the system. IM3 =2ω1-ω2 is not far from the excitation signals ω1 and ω2, so we can use the antenna of the same frequency band to transmit the signal ω IM3 In this embodiment, by detecting ω IM3 The vector coordinates of the signal ω are used for uplink information transmission. IM3 It is generated spontaneously by the nonlinear characteristics of the rectifier during operation, and does not require additional oscillation circuits or other signal generation units. For example, if you want to use 8-QAM modulation, you can distinguish them by setting 8 different IM3 vector signal states, such as Figure 4 As shown, the eight vector states have their own amplitudes and phases, and any two signals differ in at least one dimension, which can effectively reduce the bit error rate of data transmission.

[0052] In some embodiments, any two different vector states are different in two dimensions, thereby further improving the reliability of data transmission.

[0053] In the rectifier, the signal ω IM3 There are three ways to generate Figure 5 As shown. By calculation, the IM3 generated by down-mixing ↓ The power is small, that is, ω IM3 Contributed by direct mixing and up-mixing. Figure 6 As shown, the working mode of the IM3 modulator in this embodiment is to adjust the differential frequency (ω Δ =ω2-ω1) under the embedded impedance Z n (ω Δ ) to control the IM3 generated by the up-mixing process ↑ The amplitude and phase of the IM3 generated by the direct mixing process → Perform vector superposition to modulate the rectifier output ω IM3 The amplitude and phase of the QAM modulation are controlled to complete the setting of various vector states.

[0054] (1) IM3 modulator design

[0055] First, in order to analyze the third-order intermodulation signal IM3 generated by the nonlinear characteristics of the diode, the equivalent circuit model of the Schottky diode is as follows: Figure 7As shown; the diode equivalent model includes the RF source V equivalent to the receiving antenna g 、R g , truncated capacitance C block , the junction capacitance of the diode C j , junction resistance R j , as well as the choke inductor RF Choke and the DC load R L When a dual-frequency signal is input, the voltage at the nodes across the diode is V j It can be expressed by formula (1):

[0056] V j =Acos(ω1t)+Bcos(ω2t) Formula (1)

[0057] Wherein, ω1 and ω2 are the angular frequencies of the two excitation signals; A and B are the effective values ​​of the two excitation signals respectively.

[0058] The intermodulation frequency components generated by the two excitation signals after the rectifier are as follows: Figure 8 As shown, the third-order intermodulation signals include 2ω1-ω2 and 2ω2-ω1. In order to simplify the analysis, only 2ω1-ω2 is considered in the following analysis, and the analysis principle of the other third-order intermodulation signal 2ω2-ω1 is the same and will not be repeated.

[0059] From the diode equivalent model, we know that the junction current of the diode is determined by the resistance current I Rj and current capacitance I Cj Composition, expressed as formula (2):

[0060]

[0061] Since the intermodulation signal is generated by the nonlinear characteristics of the diode, the junction current I j Using Taylor's formula to expand to the third order when the diode bias voltage is 0, we can get:

[0062]

[0063] Among them, I s is the diode reverse saturation current, C j0 is the zero-bias junction capacitance, φ is the junction potential, M is the gradient coefficient constant, α = q / nTk, q is the unit charge, n is the emission factor, k is the Boltzmann constant, and T is the Kelvin temperature.

[0064] For the third-order intermodulation signal ω generated by diode mixing IM3 ,consider Figure 5 There are three processes shown in Figure 2. In direct mixing, the third-order intermodulation signal ω IM3Directly generated by the cubic term in formula (3); in the process of up-mixing and down-mixing, the dual-frequency excitation signal is first generated by the square term in formula (3) to generate the difference frequency signal ω after the first mixing. Δ =ω2-ω1 and the second harmonic 2ω1, and then respectively mixed with the original ω1 or ω2 for the second time, and the signal ω is generated by the square term in formula (3) IM3 , the following three components are analyzed one by one.

[0065] A: Direct mixing process

[0066] In direct mixing, the IM3 signal is directly generated by the cubic term of equation (3). Substituting equation (1) into the cubic term of equation (3), the IM3 signal component in the direct mixing process can be obtained as follows:

[0067]

[0068] Where j represents a phase difference of 90°, ω IM3 =2ω1-ω2.

[0069] B: Upmixing process

[0070] from Figure 5 It can be seen that the up-mixing process has two steps. In the first step, by substituting equation (1) into the square term of equation (3), we can get the current I(ω) at the difference frequency. Δ ),

[0071]

[0072] where ω Δ =ω2-ω1.

[0073] In the second step, the difference frequency signal ω Δ Mixed with the original excitation ω1, the diode junction voltage at this time is expressed as formula (6). Figure 9 As shown in the figure, since the difference frequency current and the excitation signal have opposite directions during the mixing process, there is a negative sign before the difference frequency current in the formula.

[0074] V j,↑ =Acos(ω1t)-I(ω Δ )×Z n (ω Δ ) Formula (6)

[0075] where Z n (ω Δ ) is the load impedance under difference frequency conditions.

[0076] Substituting Equation (6) into the square term of Equation (3), the IM3 signal component generated during the up-mixing process is expressed as Equation (7):

[0077]

[0078] C: Down-mixing process

[0079] The down-mixing process is similar to the up-mixing process, so the IM3 signal component generated in the down-mixing process can be quickly obtained as formula (8),

[0080]

[0081] Therefore, the IM3 signal generated during the rectification process is the sum of three components, as shown in equation (9):

[0082] I IM3 =I IM3,→ +I IM3,↑ +I IM3,↓ Formula (9)

[0083] Finally, if Figure 7 As shown, the secondary radiation IM3 signal for data communication (i.e. the uplink signal backscattered by the receiving end) passes through the rectifier circuit source impedance R g The third-order intermodulation voltage after is:

[0084] V IM3 =I IM3 ×R g Formula (10)

[0085] According to the above analysis, the IM3 calculation results are as follows: Figure 10 The parameters used in the calculation process are shown in Table 1. Figure 10 In part (a), as the differential frequency embeds the impedance Z n (ω Δ ) changes, the amplitudes of the various components and the synthesized IM3 signal show different changes. Among them, the red and blue curves represent the components IM3 generated by direct mixing, respectively. → and the down-mixing component IM3 ↓ This is because what changes is the embedded impedance at the differential frequency, which has nothing to do with the generation of these two components, and it can be seen that IM3 ↓ The green curve represents the IM3 component generated by up-mixing. ↑ With Z n (ω Δ )The real part increases gradually. During the calculation process, we keep Z n (ω Δ ) remains unchanged and is fixed at +1000. → Remain unchanged while IM3 ↑Gradually increasing, the superposition of these two components results in different Z n (ω Δ ) can obtain IM3 signals of different amplitudes (represented as black curves in the figure), thereby realizing amplitude modulation.

[0086] Figure 10 Part (b) is the vector form of each component in polar coordinates. It can be seen from the figure that as Z n (ω Δ ) changes due to IM3 → and IM3 ↑ The vector superposition effect can change the amplitude and phase of the total IM3 signal, so the Z n (ω Δ ) value, the IM3 signal used for data communication is set to 8 vector states with different amplitudes and phases, thereby meeting the coding requirements of QAM modulation.

[0087] Table 1 Calculation parameters

[0088] parameter Diode model HSMS286B <![CDATA[Reverse saturation current C j0 > 0.18pF <![CDATA[Zero-bias junction capacitance I s > 50nA Gradient coefficient constant M 0.5 Junction potential Φ 0.65 Unit charge q 1.6021892*10^-19C Emission factor n 1.08 Kelvin temperature T 298.15K Boltzmann constant k 1.380649*10^23J / K

[0089] Through the above analysis, Figure 11 This is the structure diagram of the IM3 modulator proposed in this embodiment. It includes a fixed inductor L2, an adjustable capacitor C T and adjustable resistor R T , and a capacitor C for DC isolation M According to the knowledge of filters, L2 and C T A low-pass filter can be formed, and the cutoff frequency ω0 of the filter is:

[0090]

[0091] In this embodiment, the cut-off frequency of the low-pass filter is set near the differential frequency, that is, ω0≈ω Δ Therefore, by adjusting the capacitor C T With resistor R T , can achieve the differential frequency embedded impedance Z n (ω Δ ) changes, and then set different IM3 signal vector states to achieve QAM modulation. In addition, since the IM3 modulator is designed as a low-pass filter structure, all signals with frequencies higher than its cutoff frequency can be blocked, including the fundamental frequencies ω1, ω2, the second harmonics 2ω1, 2ω2, the intermodulation signal 2ω1-ω2 and other harmonics and intermodulation components, thereby further suppressing the intensity of the down-mixing component and enhancing the intensity of the reflected IM3 signal, thereby improving the reliability of data transmission. In practice, the adjustable capacitor C T and adjustable resistor RT It can be realized by using fixed-value capacitors and resistor arrays, or it can be constructed by using voltage-controlled varactor tubes and adjustable potentiometers.

[0092] In some embodiments, as Figure 12 As shown, an isolation capacitor C is provided between the receiving antenna (Rx) and the diode rectifier module (Rectifier). block The diode rectifier module (Rectifier) ​​includes a rectifier diode D, a capacitor C1 and an inductor L1. The IM3 modulator includes an inductor L2, an adjustable capacitor C T and adjustable resistor R T , and the DC blocking capacitor C M ; The DC filter (DC-Pass) includes capacitor C3 and inductor L3.

[0093] The specific circuit structure is: receiving antenna (Rx), isolation capacitor C block , inductor L2, and inductor L3 are connected in series between the receiving antenna (Rx) and the load. The series rectifier diode D and inductor L1 are connected to the isolation capacitor C block The connection point of inductor L2 and inductor L3 is connected to the ground line. Capacitor C1 is connected in parallel to both ends of rectifier diode D. There are two branches in parallel between the connection point of inductor L2 and inductor L3 and the ground line. The first branch is equipped with an adjustable capacitor C T The second branch is connected in series with capacitor C M and adjustable resistor R T . Capacitor C3 is connected to the isolation capacitor C block , between the connection point of the load and the ground.

[0094] Capacitor C1 and inductor L1 are used to match the impedance of the rectifier diode. The adjustable capacitor C in the IM3 modulator is T , adjustable resistor R T A variable capacitance switching array and a variable resistance switching array are respectively used; thus, different IM3 vector states are set by switching the switching array (SwitchArray); the capacitor C M As an adjustable resistor R T The isolation capacitor, when set to 0Ω, has no effect on the characteristics of the IM3 modulator. Capacitor C3 and inductor L3 form a DC filter to filter out the AC signal and load the DC signal to the DC load R L Above, the specific parameters of each component are Figure 12 Mark the lower left corner.

[0095] According to the 8-QAM constellation distribution, in the ADS simulation software, by adjusting C T and R T The positions of the IM3 vector signals of the 8 different vector states in the polar coordinate system are as follows: Figure 13As shown, the letters AH represent the eight states. The red dots represent the four states corresponding to the amplitude of the outer circle, and the blue squares represent the four states corresponding to the amplitude of the inner circle. The four states on the outer circle have a phase difference of more than 90° between each other, and the four states on the inner circle also meet this condition. Figure 4 contrast, Figure 13 This roughly conforms to the form of the commonly used constellation diagram of 8-QAM. Therefore, these eight states can be encoded into a 3-bit binary number to achieve 8-QAM modulation.

[0096] Table 2 Status codes and component parameter settings

[0097] <![CDATA[C T ]]> <![CDATA[R T ]]> A 000 30 1500 B 001 75 1500 C 010 115 1500 D 011 170 1500 E 100 85 700 F 101 100 800 G 110 105 700 H 111 105 600

[0098] Table 2 shows an encoding method and also shows the adjustable capacitor C set in the ADS simulation for each state. T With adjustable resistor R T , it can be seen that although 8 states are designed, C T or R T The value setting has a certain degree of reusability, which can simplify the number of components in the implementation and also simplify the system construction and maintenance costs. Figure 14 A schematic diagram of how to convert various capacitance and resistance values ​​in actual circuits is given, such as Figure 14 As shown, in C T With R T The conversion array uses an 8-to-1 switch chip. The output of the chip is connected to the corresponding position in the IM3 modulator, and the input is connected to the digital signal data bus to be transmitted. At the same time, the 8 selection pins are connected to a capacitor C of different values. T1 -C T8 or resistor R T1 -R T8 and ground the other end of each capacitor or resistor to satisfy Figure 12 According to the wiring requirements in the , by inputting different data signals to control the switch to connect different capacitors and resistors, the IM3 state can be adjusted. It is worth noting that Figure 14 The implementation diagram provided is merely a schematic. If multiple capacitor or resistor values ​​are reused in the design, the required switch circuitry can be simplified. For example, if the resistor values ​​given in Table 2 are used, a single 4-to-1 switch can be used in the resistor selection array, effectively reducing system complexity.

Claims

1. A wireless communication method based on IM3 QAM modulation, wherein the wireless communication system includes a transmitter and a receiver; the transmitter includes a transmitting signal source and a transmitting antenna connected in sequence; the receiving end includes a receiving antenna, a diode rectifier module, an IM3 modulator, a DC filter, and a load; characterized in that: The IM3 modulator comprises two branches connected in parallel; the first branch is provided with an adjustable capacitor ; The second branch is equipped with an adjustable resistor ; The IM3-based QAM modulation wireless communication method comprises the following steps: The transmitting end transmits a dual-frequency AC excitation signal; the receiving antenna receives the dual-frequency AC excitation signal; The diode rectifier module generates a third-order intermodulation signal IM3 under the excitation of the dual-frequency AC excitation signal; Adjust the adjustable capacitor according to the uplink information of the receiving end and adjustable resistors , so that the vector state of the third-order intermodulation signal IM3 matches the uplink information; The receiving end sends an uplink signal corresponding to the third-order intermodulation signal IM3; the transmitting end receives the uplink signal.

2. The QAM modulation wireless communication method based on IM3 according to claim 1, characterized in that: The transmitting end transmits two frequencies of the dual-frequency AC excitation signal 、 The following conditions are met: ;in, is the bandwidth of the transmitting antenna.

3. The QAM modulation wireless communication method based on IM3 according to claim 1, characterized in that: The vector state of the third-order intermodulation signal IM3 includes two dimensions: amplitude and phase; any two different uplink signals differ in at least one dimension.

4. The QAM modulation wireless communication method based on IM3 according to claim 1, characterized in that: The number of vector states of the third-order intermodulation signal IM3 is greater than or equal to four.

5. The QAM modulation wireless communication method based on IM3 according to claim 4, characterized in that: The number of vector states of the third-order intermodulation signal IM3 is equal to eight; the eight vector states are divided into two groups; the four vector states in the same group are 90° phase-different from each other; the amplitude ranges corresponding to the vector states in different groups do not overlap and differ by more than 10dBm.

6. A QAM modulation wireless communication system based on IM3, comprising a transmitting end and a receiving end; the transmitting end comprises a transmitting signal source and a transmitting antenna connected in sequence; characterized in that: The receiving end includes a receiving antenna, a diode rectifier module, an IM3 modulator, a DC filter and a load connected in sequence; the IM3 modulator includes two branches connected in parallel; an adjustable capacitor is provided on the first branch ; The second branch is equipped with an adjustable resistor ; The receiving antenna receives the dual-frequency AC excitation signal from the transmitting end; the diode rectifier module generates a third-order intermodulation signal IM3; the vector state of the third-order intermodulation signal IM3 changes with the adjustable capacitor and adjustable resistors Different vector states of the third-order intermodulation signal IM3 correspond to different uplink information of the receiving end; Adjust the adjustable capacitor according to the uplink information of the receiving end and adjustable resistors , so that the vector state of the third-order intermodulation signal IM3 matches the uplink information; the receiving end sends an uplink signal corresponding to the third-order intermodulation signal IM3; and the transmitting end receives the uplink signal.

7. The IM3-based QAM modulation wireless communication system according to claim 6, characterized in that: The adjustable resistor There is a DC blocking capacitor in series on the branch .

8. The IM3-based QAM modulation wireless communication system according to claim 6, characterized in that: The diode rectifier module includes rectifier diodes connected in series ,inductance , and the rectifier diode in parallel The capacitance across the .

9. The IM3-based QAM modulation wireless communication system according to claim 6, characterized in that: The DC filter adopts an LC filter structure; an isolation capacitor is provided between the receiving antenna and the diode rectifier module. .

10. The IM3-based QAM modulation wireless communication system according to claim 6, characterized in that: The adjustable capacitor , The second branch is equipped with an adjustable resistor A variable capacitance conversion array and a variable resistance conversion array are used respectively.

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