IM3-based QAM (Quadrature Amplitude Modulation) wireless communication method and system

Abstract

The invention provides a QAM (Quadrature Amplitude Modulation) wireless communication method and system based on IM3. The wireless communication system comprises a transmitting end and a receiving end. The transmitting end comprises a transmitting signal source and a transmitting antenna which are connected in sequence. The receiving end comprises a receiving antenna, a diode rectification module, an IM3 modulator, a direct current filter and a load. The IM3 modulator comprises two branches connected in parallel between a signal transmission path and a ground wire; and an adjustable capacitor is arranged on the first branch. And an adjustable resistor is arranged on the second branch. According to the invention, the IM3 signal is used for communication, the zero energy consumption of wireless energy cooperative information transmission is realized, the energy loss is reduced, the service life of the system is prolonged, and the system is suitable for various application environments. According to the invention, the rectification circuit with a single diode structure is adopted, and IM3 signals for transmission are generated by the diode itself and do not need to be generated by an additional oscillation circuit.

Description

Technical Field

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

[0002] Radio frequency wireless power transfer (RF WPT) technology has attracted much attention due to its potential in solving the energy shortage problem in future communication networks, especially Internet of Things (IoT) networks. The core advantage of this technology is the ability to extract energy from RF signals in the surrounding environment to power network nodes with limited power. The uniqueness of RF signals is that they can not only transmit information but also energy, which provides a new energy solution for wireless devices. As society's requirements for communication technology continue to increase, the demand for spectrum efficiency and energy efficiency (EE) is also growing. In order to meet these needs, a series of efficient wireless communication network technologies have emerged, including multi-antenna communication networks, device-to-device (D2D) communication networks, and two-way relay networks. The development of these technologies not only improves the efficiency of data transmission, but also makes it possible to use energy efficiently.

[0003] Backscatter communication is a wireless communication technology that allows devices to transmit information by reflecting existing wireless signals without the need for their own transmitters. This technology can significantly reduce the energy consumption of devices because it does not require active signal transmission. Combining RF wireless energy transmission technology with these efficient wireless communication technologies can form a new type of efficient wireless power supply communication network. This network can not only significantly extend the service life of network equipment and reduce the frequency of battery replacement, but also improve the overall performance of the system without increasing additional energy consumption. This is especially important in scenarios such as the Internet of Things that require a large number of low-power devices, because these devices are often difficult to frequently replace batteries or connect to a power source.

[0004] Backscatter communication usually uses the harmonic or intermodulation signal generated by the rectifier itself at the receiving end of the RF WPT as the carrier of the data. Among them, the third-order intermodulation signal is a parasitic signal generated when two or more signals are in a linear system, and the second harmonic of a signal is mixed with the fundamental frequency of another signal due to the presence of nonlinear factors (in the rectifier circuit, this factor is usually the nonlinear characteristics of the diode itself). Third-order intermodulation signals are widely used in many fields. In radar and other high-frequency systems, third-order intermodulation signals are widely used to improve the accuracy and stability of the system. In radar systems, the application of third-order intermodulation signals helps to improve the detection capability and anti-interference capability of radar, 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. In addition, third-order intermodulation signals also have their applications in the field of wireless communications. Although second-order intermodulation is more common in wireless communication systems, third-order intermodulation can also play its role in certain specific situations, such as improving signal transmission efficiency and anti-interference capability.

[0005] QAM (Quadrature Amplitude Modulation) is a modulation technology widely used in digital communications. It transmits digital data by changing the amplitude and phase of the signal at the same time, thereby achieving 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 are located on a complex plane, the real axis represents the amplitude of the signal, and the imaginary axis represents the phase of the signal. By changing the phase and amplitude of the signal, different digital information can be represented. The QAM modulation process includes 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, for 16-QAM, there are 16 different symbol points, each symbol point represents a specific digital combination, and in the complex modulation stage, each symbol point generates a corresponding QAM signal through amplitude and phase modulation. QAM modulation technology has a wide range of applications in the field of communications, 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 the signal to transmit information, and can transmit more data within limited spectrum resources. Therefore, it is widely used in the modulation and demodulation process in digital communication systems. As the modulation order increases, the complexity and data transmission rate of the QAM signal will also increase, but it will also be more susceptible to noise and interference. In a broad sense, QAM modulation is to map the data signal to multiple different vector states, and these vector states are easy to distinguish.

[0006] like Figure 1The figure shows a schematic diagram of a rectifier using harmonics for backscatter communication. The second harmonic 2f0 and the third harmonic 3f0 generated by the nonlinearity of the rectifier itself are used as carriers. The reconfigurable filter formed by DGS is used to modulate the amplitude of the up and down communication data. The external voltage bias DGS is used to form two different states to represent data "0" and data "1". This technical solution has the following disadvantages: the second harmonic and the third harmonic used have a considerable spectrum difference with the fundamental frequency, and antennas with multiple frequency bands need to be designed, which increases the complexity of the system. The modulation method is ASK modulation, which can only transmit 1 as a binary number per unit time, and the transmission rate is slow.

[0007] like Figure 2 The figure shows a rectifier circuit that performs QAM modulation on the backscattered signal. The method for implementing QAM modulation is to design M types of microstrip line short-circuit branches, that is, to introduce different matching circuits, so as to move the impedance of the rectifier circuit to M different positions on the Smith diagram. Since the receiving end sets different impedances, the received RF signal can be reflected to different 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 implemented by changing different matching impedances, because changes in matching conditions will affect the normal working efficiency of the rectifier. 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 in the method 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 a signal transmission path and a ground line; an adjustable capacitor C is provided on the first branch. 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] According to the uplink information that the receiving end needs to send, adjust the adjustable capacitor C 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 out 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 emitted by the transmitting end satisfy 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 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 in sequence; the amplitude ranges corresponding to the vector states in different groups do not overlap and differ by more than 10 dBm.

[0019] In a second aspect, the present invention provides a QAM modulation wireless communication system based on IM3, which 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 connected in sequence. 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 .

[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 the backscatter communication from the receiving end to the transmitting end.

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

[0022] Preferably, the diode rectifier module comprises 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 at both ends of 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 utilizes IM3 signals for communication, realizes zero energy consumption of wireless energy cooperative information transmission, reduces energy loss and prolongs 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, which has a great rate improvement compared to traditional ASK, FSK and other modulation modes that can only transmit 1 binary bit at a time; 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, and the transmission signal used is generated by the diode itself, without the need for an additional oscillation circuit; and 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, and the circuit complexity is low.

[0029] 4. Cost reduction: Since the present invention adopts IM3 signal as the communication signal, the signal is relatively close to the baseband signal. The design of the transceiver antenna of the WPT system only requires a smaller bandwidth to achieve multiplexing. At the same time, the flexible component parameter setting also reduces the system construction cost.

[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 is a constellation diagram of the 8-QAM modulation method used in Embodiment 1 of the present invention;

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

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

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

[0038] Figure 8 : is a spectrum distribution diagram of a signal at a receiving end under dual-frequency excitation in Embodiment 1 of the present invention;

[0039] Fig. 9 A schematic diagram of the current direction of the receiving end during the second frequency mixing process in Embodiment 1 of the present invention;

[0040] Fig.10 1 is a diagram showing the calculation results of the third-order intermodulation signal IM3 in Embodiment 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 form of the components of the third-order intermodulation signal IM3);

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

[0042] Fig.12 is an overall circuit schematic diagram of the receiving end in Embodiment 1 of the present invention;

[0043] Fig.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] Fig.14Schematic diagram of a variable capacitance conversion array and a variable resistance conversion array used as examples in Embodiment 1 of the present invention. DETAILED DESCRIPTION

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

[0046] Example 1

[0047] A QAM modulation wireless communication system based on IM3 is used to upload multi-bit data through backscatter communication. The key terms 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 (between devices); DGS: Defected Ground Structure (defective ground structure).

[0049] like Figure 3 As shown, the present embodiment provides a QAM modulation wireless communication system based on IM3, including a transmitter and a receiver. The transmitter includes a transmitting signal source (Base Station) and a transmitting antenna (Tx) connected in sequence. The receiving end 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 part is the energy transmission channel of the system; the transmitting signal source (Base Station) generates dual-frequency AC excitation (frequencies are ω1 and ω2) and then it is sent out by the transmitting antenna (Tx); the receiving antenna (Rx) obtains the energy signal and converts the AC signal into a DC signal through the diode rectifier module (Rectifier). At the same time, due to the nonlinear characteristics of the diode, a third-order intermodulation signal IM3 is generated; the frequency of the third-order intermodulation signal IM3 is ω IM3=2ω1-ω2, and then due to the existence of the DC filter (DC-Pass), only DC energy is loaded onto the load, completing the wireless energy transmission process. Frequencies ω1 and ω2 satisfy the following conditions: 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 spontaneously generated by the nonlinear characteristics of the rectifier when it is working, and does not require additional signal generating units such as oscillation circuits. For example, if you want to adopt the 8-QAM modulation method, 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) according to the different data signals. 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 IM3 generated by the direct mixing process → By performing vector superposition, the rectifier output ω can be modulated 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] Among them, 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 another 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 1. In direct mixing, the third-order intermodulation signal ω IM3Directly generated by the cubic term in equation (3); in the up-mixing and down-mixing process, the dual-frequency excitation signal is first generated by the square term in equation (3) after the first mixing to generate the difference frequency signal ω Δ =ω2-ω1 and the second harmonic 2ω1, and then mixed with the original ω1 or ω2 for the second time, and the signal ω is generated by the square term in equation (3) IM3 , the following analyzes the three components 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: Up-mixing process

[0070] from Figure 5 It can be seen that the up-mixing process has two steps. In the first step, 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 Mixing with the original excitation ω1, the diode junction voltage at this time is expressed as formula (6). Fig. 9 As shown, since the difference frequency current and the excitation signal are in 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 condition.

[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 used 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: Fig.10 The parameters used in the calculation process are shown in Table 1. Fig.10 In part (a), as the differential frequency embeds the impedance Z n (ω Δ ), the amplitude of each component and the synthesized IM3 signal show different changes. Among them, the red and blue curves represent the IM3 components generated by direct mixing. → and the down-mixed 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 component has a significantly smaller amplitude than other components and can therefore be ignored. The green curve represents the component IM3 generated by the 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 leads to different Z n (ω Δ ) can obtain IM3 signals of different amplitudes (represented as black curves in the figure), thereby realizing amplitude modulation.

[0086] Fig.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 that 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*10^23 J / K

[0089] Through the above analysis, Fig.11 This is the structure diagram of the IM3 modulator proposed in this embodiment. It includes a fixed value 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 , the embedded impedance Z at the differential frequency can be realized 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 base frequency ω1, ω2, the second harmonic 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 and adjustable potentiometer.

[0092] In some embodiments, Fig.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 provided with an adjustable capacitor C T The second branch has a capacitor C in series. M and adjustable resistor R T Capacitor C3 is connected between 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 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; the capacitor C3 and the 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 Fig.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: Fig.13As shown, the letters AH represent the eight states. The red dots represent the four states corresponding to the outer circle amplitude, and the blue squares represent the four states corresponding to the inner circle amplitude. 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, Fig.13 This roughly conforms to the form of the commonly used constellation diagram of 8-QAM. Therefore, these eight states can be encoded, corresponding to 3 binary numbers, 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 each state in the ADS simulation. 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. Fig.14 A schematic diagram of how to convert various capacitance and resistance values ​​in actual circuits is given, such as Fig.14 As shown, in C T With R T An 8-to-1 switch chip is used in the conversion array. The output end of the chip is connected to the corresponding position in the IM3 modulator, and the input end 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 Fig.12 According to the wiring requirements in the circuit, different data signals are input to control the switch to connect different capacitors and resistors to adjust the IM3 state. It is worth noting that Fig.14 The implementation diagram given is only a schematic diagram. If multiple capacitance values ​​or resistance values ​​are reused in the design, the required switch circuit can be simplified. For example, if the resistance values ​​given in Table 2 are used, a 4-to-1 switch can be used in the resistance selection array, which can effectively reduce the system complexity.

Claims

1. A QAM modulation wireless communication method based on IM3, wherein the wireless communication system used comprises a transmitting end and a receiving end; the transmitting end comprises a transmitting signal source and a transmitting antenna connected in sequence; the receiving end comprises 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 C T ; The second branch is equipped with an adjustable resistor R T ; 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; According to the uplink information of the receiving end, adjust the adjustable capacitor C T and adjustable resistor R T , so that the vector state of the third-order intermodulation signal IM3 matches the uplink information; The receiving end sends out an uplink signal corresponding to the third-order intermodulation signal IM3; and 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 two frequencies ω1 and ω2 of the dual-frequency AC excitation signal transmitted by the transmitting end satisfy the following condition: 0.01ω1≤|ω1-ω2|≤Bw; wherein Bw 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 in sequence; 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 C is provided on the first branch T ; The second branch is equipped with an adjustable resistor R T ; 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 C T and adjustable resistor R T changes with the change of; different vector states of the third-order intermodulation signal IM3 correspond to different uplink information of the receiving end.

7. The QAM modulation wireless communication system based on IM3 according to claim 6, characterized in that: The adjustable resistor R T The branch is connected in series with a DC blocking capacitor C M .

8. The IM3-based QAM modulation wireless communication system according to claim 6, characterized in that: The diode rectifier module includes a rectifier diode D, an inductor L1 connected in series, and a capacitor C1 connected at both ends of the rectifier diode D in parallel.

9. The IM3-based QAM modulation wireless communication system according to claim 1, characterized in that: The DC filter adopts an LC filter structure; an isolation capacitor C is provided between the receiving antenna and the diode rectifier module. block .

10. The wireless communication method based on IM3 QAM modulation according to claim 1, characterized in that: 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.

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