An active backscatter 4QAM modulation device supporting long-distance transmission

Abstract

The present invention belongs to the field of wireless communication technology, and provides an active backscatter 4QAM modulation device supporting long-distance transmission, so as to solve the problem that the transmission distance of the traditional Backscatter 4QAM modulation device is too short. The present invention includes: an antenna, a directional coupling module, a switch modulation module, a control module, and four modulation branches. The switch modulation module is composed of a first single-pole four-throw switch and a second single-pole four-throw switch. The modulation branch is composed of a circulator, an amplifier and a load. The switch modulation module selects one of the four modulation branches to work under the control of the control module. The present invention adopts a dual-switch modulation mode suitable for the Backscatter communication system, which effectively realizes the modulation of the 4QAM signal; and, the active amplification method is used to increase the transmission distance and realize effective control, and the application scenario is more flexible; at the same time, compared with the modulation device using a directional antenna, the present invention can further improve the communication distance while realizing omnidirectional radiation.

Description

Technical Field

[0001] The invention belongs to the technical field of wireless communications, and in particular relates to an active backscattering 4QAM modulation device supporting long-distance transmission. Background Art

[0002] Modulation is an indispensable and important part of wireless communication systems. Compared with traditional modulation technologies in wireless communication systems, backscatter modulation has been widely used due to its advantages such as simple modulation equipment and low power consumption, especially in RFID technology applications. Wireless communication systems based on Backscatter technology have also received widespread attention. Such communication systems can realize passive tags and are one of the important technologies for the future smart Internet of Things.

[0003] Backscatter modulation is achieved by changing the terminal impedance of the antenna. When the antenna end is connected to different impedances, signal reflection will occur, and the intensity and phase of the reflected signal will change based on the different impedances. This change can be used to achieve signal modulation, and the modulated reflected signal will be transmitted on the same antenna. It can be seen that Backscatter modulation technology uses different reflection coefficients obtained when the antenna is connected to different loads to achieve signal modulation. Compared with traditional digital modulation, the complexity of implementation is greatly reduced, the equipment requirements are simpler, and the power consumption can be greatly reduced. It has great advantages in the application of the Internet of Things.

[0004] At present, the use of QAM modulation can make the Backscatter communication system have a faster transmission rate than 2ASK modulation, thereby improving bandwidth utilization. The most commonly used QAM modulation is 4QAM. However, the Backscatter communication system also has some problems, the most important of which is that the transmission distance is too short (the transmission distance is usually less than 100m), and long-distance transmission cannot be achieved, which greatly limits its application; therefore, how to improve the transmission distance of Backscatter modulation technology has become an important topic in today's Backscatter research. For example, the patent document with publication number CN 113542183 discloses a device for passively improving the transmission distance of backscatter 4QAM modulation, in which a directional antenna is used to increase the tag gain, thereby increasing the transmission distance; although the directional antenna increases the system gain, it also limits the radiation direction of the reflected signal, making it impossible to achieve omnidirectional communication, and two antennas are required to achieve it. Summary of the invention

[0005] The purpose of the present invention is to provide an active backscatter 4QAM modulation device supporting long-distance transmission, so as to solve the problem that the transmission distance of the traditional Backscatter 4QAM modulation device is too short; the present invention adopts an active structure and works together with dual switches to ensure that the Backscatter 4QAM has a good modulation effect while improving and controlling the transmission distance.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] An active backscatter 4QAM modulation device supporting long-distance transmission includes: an antenna, a directional coupling module, a switch modulation module, a control module, and four modulation branches; the characteristics are:

[0008] The switch modulation module is composed of a first single-pole four-throw switch and a second single-pole four-throw switch, wherein the first single-pole four-throw switch is composed of a moving port RFc1 and fixed ports RFs11, RFs12, RFs13, and RFs14, and the second single-pole four-throw switch is composed of a moving port RFc2 and fixed ports RFs21, RFs22, RFs23, and RFs24;

[0009] The modulation branch is composed of a circulator, an amplifier and a load. The circulator port 1 in the i-th modulation branch is connected to the fixed port RFs2i of the second single-pole four-throw switch, the port 2 is connected to the load, the port 3 is connected to the input end of the amplifier, and the output end of the amplifier is connected to the fixed end RFs1i of the first single-pole four-throw switch, i=1,2,3,4; the loads in the four modulation branches are Zc1, Zc2, Zc3, and Zc4 respectively;

[0010] The antenna is connected to the moving port RFc1 of the first single-pole four-throw switch and the moving port RFc2 of the second single-pole four-throw switch through a directional coupling module. The directional coupling module transmits the received signal to the moving port RFc2 of the second single-pole four-throw switch, and couples the modulated signal from the moving port RFc1 of the first single-pole four-throw switch to the antenna.

[0011] The control module provides control signals to the first single-pole four-throw switch and the second single-pole four-throw switch, so that one of the four modulation branches can be selected to work.

[0012] Furthermore, the directional coupling module adopts a directional coupler or a circulator.

[0013] Furthermore, the active backscatter 4QAM modulation device has four specific modulation states:

[0014] The first switch modulation state: the RFs11 port of the first single-pole four-throw switch is connected, the RFs21 port of the second single-pole four-throw switch is connected, and the first modulation branch is working;

[0015] Second switch modulation state: the RFs12 port of the first single-pole four-throw switch is connected, the RFs22 port of the second single-pole four-throw switch is connected, and the second modulation branch is working;

[0016] The third switch modulation state: the RFs13 port of the first single-pole four-throw switch is connected, the RFs23 port of the second single-pole four-throw switch is connected, and the third modulation branch is working;

[0017] The fourth switch modulation state: the RFs14 port of the first single-pole four-throw switch is connected, the RFs24 port of the second single-pole four-throw switch is connected, and the fourth modulation branch is working.

[0018] Furthermore, the first single-pole four-throw switch and the second single-pole four-throw switch are controlled by the same set of control signals.

[0019] Furthermore, the antenna is used to receive a carrier signal of a Backscatter communication system and radiate an amplified 4QAM signal into space.

[0020] It should be noted that: the directional coupling module on the main line of the present invention can adopt a circulator or a directional coupler, and both methods require excellent isolation to the third port; the circulator (or directional coupler) couples the amplified modulated signal to the antenna for transmission, thereby realizing active Backscatter communication; through the switch modulation module (the first single-pole four-throw switch and the second single-pole four-throw switch), one of the modulation branches where the loads Zc1, Zc2, Zc3, and Zc4 are located is synchronously selected to complete 4QAM modulation; in addition, the antenna is used to receive the carrier signal of the Backscatter communication system and radiate the amplified 4QAM signal into space, and a directional antenna or an omnidirectional antenna can be selected according to the specific application scenario.

[0021] Based on the above technical solution, the beneficial effects of the present invention are:

[0022] The present invention adopts a dual-switch synchronous modulation mode, and effectively realizes the modulation of 4QAM signals in a single antenna by introducing a loop and an amplifier into a traditional Backscatter modulation device; compared with the traditional Backscatter communication mode or the directional antenna Backscatter modulation scheme introduced in the publication number CN 113542183, the present invention has the following advantages:

[0023] 1) The introduction of active amplifiers greatly improves the transmission distance of Backscatter 4QAM modulation compared with passive modulation schemes, making it possible for Backscatter to be used in longer-distance communications. In addition, the device proposed in the present invention can control the transmission distance of the system by selecting a suitable amplifier, and the application scenario is more flexible.

[0024] 2) Compared with the Backscatter 4QAM modulation scheme using directional antennas (such as the Backscatter modulation scheme with publication number CN 113542183), the present invention reduces the number of antennas by using a tag architecture including an amplifier loop, and can achieve omnidirectional communication;

[0025] 3) The present invention adopts a loop to replace the reflective structure of the traditional Backscatter, but retains the same transceiver form as the traditional Backscatter device (i.e., single antenna transceiver) on the outside. It has the potential to be applied in scenarios where backscatter transmission of environmental signals is required, providing a feasible solution for the 5G Internet of Things. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the Backscatter 4QAM modulation principle.

[0027] Figure 2 Backscatter 4QAM modulation constellation diagram.

[0028] Figure 3 It is a schematic diagram of the structure of the active backscattering 4QAM modulation device supporting long-distance transmission in the present invention.

[0029] Figure 4 This is a test circuit diagram of an active backscatter 4QAM modulation device supporting long-distance transmission in an embodiment of the present invention.

[0030] Figure 5 The figure is a simulation comparison diagram of the received power of the embodiment of the present invention and the traditional Backscatter 4QAM communication system.

[0031] Figure 6 It is a time domain simulation comparison diagram of the received signal of the embodiment of the present invention and the traditional Backscatter 4QAM communication system. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0033] This embodiment provides an active backscatter 4QAM modulation device supporting long-distance transmission, and its structure is as follows: Figure 3 As shown, it includes: an antenna, a directional coupling module, a switch modulation module, a control module, and first to fourth modulation branches; wherein the switch modulation module is composed of a first single-pole four-throw switch and a second single-pole four-throw switch, the first modulation branch is composed of a first circulator, a first amplifier and a first load Zc1, the second modulation branch is composed of a second circulator, a second amplifier and a second load Zc2, the third modulation branch is composed of a third circulator, a third amplifier and a third load Zc3, and the fourth modulation branch is composed of a fourth circulator, a fourth amplifier and a fourth load Zc4;

[0034] The switch modulation module is used to receive the control signal provided by the control module and modulate the carrier, wherein the first single-pole four-throw switch is composed of a moving port RFc1 and fixed ports RFs11, RFs12, RFs13, and RFs14, and the second single-pole four-throw switch is composed of a moving port RFc2 and fixed ports RFs21, RFs22, RFs23, and RFs24;

[0035] The antenna is connected to the moving port RFc1 of the first single-pole four-throw switch and the moving port RFc2 of the second single-pole four-throw switch through a directional coupling module, and the receiving signal received by the antenna is coupled to the moving port RFc2 of the second single-pole four-throw switch through a directional coupler, and the signal of the RFc1 port is coupled to the antenna; the directional coupling module adopts a directional coupler or a fifth circulator;

[0036] In each modulation branch, port 1 of the circulator is connected to the fixed port of the second single-pole four-throw switch, port 2 of the circulator is connected to the load, port 3 of the circulator is connected to the input of the amplifier, and the output of the amplifier is connected to the fixed end of the first single-pole four-throw switch; taking the first modulation branch as an example, port 1 of the first circulator is connected to the fixed port RFs21 of the second single-pole four-throw switch, port 2 of the first circulator is connected to the load Zc1, port 3 of the first circulator is connected to the input of the first amplifier, and the output of the first amplifier is connected to the fixed end RFs11 of the first single-pole four-throw switch, and the signal flows from the RFs21 port to the load Zc1, and from the load Zc1 to the input of the first amplifier;

[0037] The control module provides a control signal to the first single-pole four-throw switch and the second single-pole four-throw switch at the same time, and the control signal is the modulation signal of the user.

[0038] Based on the active backscatter 4QAM modulation device supporting long-distance transmission, the test circuit in this embodiment is as follows: Figure 4 As shown, the signal source (carrier source) sends a carrier signal to the device, which is received by the antenna. The received signal passes through the fifth circulator on the main line and is transmitted from the 1 port of the fifth circulator to the second single-pole four-throw switch from the active port RFc2;

[0039] The first single-pole four-throw switch and the second single-pole four-throw switch are linked to implement modulation under the control of the control module (user), specifically there are the following four situations:

[0040] The first switch modulation state, that is, the RFs11 port of the first single-pole four-throw switch is turned on, and the RFs21 port of the second single-pole four-throw switch is turned on; at this time, the carrier signal received by the antenna is transmitted to the RFs21 port through the fifth circulator (or directional coupler), and then transmitted to the load Zc1 through the first circulator on the branch and reflected, with a reflection coefficient of Г1. The reflected signal is transmitted to the first amplifier through the first circulator, and the amplified reflected signal is coupled to the antenna by the fifth circulator (or directional coupler) through the RFs11 port of the first single-pole four-throw switch and transmitted;

[0041] The second switch modulation state, that is: the RFs12 port of the first single-pole four-throw switch is turned on, and the RFs22 port of the second single-pole four-throw switch is turned on; at this time, the carrier signal received by the antenna is transmitted to the RFs22 port through the fifth circulator (or directional coupler), and then transmitted to the load Zc2 through the second circulator on the branch and reflected, with a reflection coefficient of Γ2. The reflected signal is transmitted to the second amplifier through the second circulator, and the amplified reflected signal is coupled to the antenna by the fifth circulator (or directional coupler) through the RFs12 port of the first single-pole four-throw switch and transmitted;

[0042] The third switch modulation state, that is, the RFs13 port of the first single-pole four-throw switch is turned on, and the RFs23 port of the second single-pole four-throw switch is turned on; at this time, the carrier signal received by the antenna is transmitted to the RFs23 port through the fifth circulator (or directional coupler), and then transmitted to the load Zc3 through the third circulator on the branch and reflected, with a reflection coefficient of Γ3. The reflected signal is transmitted to the third amplifier through the third circulator, and the amplified reflected signal is coupled to the antenna by the fifth circulator (or directional coupler) through the RFs13 port of the first single-pole four-throw switch and transmitted;

[0043] The fourth switch modulation state, that is, the RFs14 port of the first single-pole four-throw switch is turned on, and the RFs24 port of the second single-pole four-throw switch is turned on; at this time, the carrier signal received by the antenna is transmitted to the RFs24 port through the fifth circulator (or directional coupler), and then transmitted to the load Zc4 through the fourth circulator on the branch and reflected, and the reflection coefficient is Γ4. The reflected signal is transmitted to the fourth amplifier through the fourth circulator, and the amplified reflected signal is coupled to the antenna by the fifth circulator (or directional coupler) through the RFs14 port of the first single-pole four-throw switch and transmitted;

[0044] The signal transmitted by the antenna is received by the receiver, and a series of operations such as demodulation are performed to complete the reception of the baseband signal.

[0045] In the above Backscatter 4QAM modulation process, it is assumed that the carrier signal (taking a single tone as an example) received by the antenna is A0cos(2πf c t+θ), the signal s(t) transmitted by the antenna in the device of the present invention can be expressed as:

[0046] s(t)=A·cos(2πf c t+θ+θ n )

[0047] Where A is the amplitude of the transmitted signal, which is related to the carrier amplitude, control signal amplitude, amplifier gain, circulator loss and other actual circuit losses; f c is the carrier frequency, θ is the carrier phase, θ n (n=1,2,3,4) is the load connected to Z c1 , Z c2 , Z c3 , Z c4 The signal phase changes caused by the reflection coefficient in the first, second, third and fourth switch modulation states (i.e., the first, second, third and fourth switch modulation states), and it can be seen that the transmitted signal is a 4QAM signal.

[0048] The following briefly analyzes the link budget of the conventional Backscatter communication system and compares it with the link budget when the present invention is adopted:

[0049] The principle of traditional Backscatter4QAM modulation is as follows Figure 1 As shown, the Backscatter4QAM modulation constellation diagram is as follows Figure 2 As shown; For the convenience of analysis, the two points with the smallest Euclidean distance in the constellation diagram are used to measure the Backscatter power when performing link budgeting;

[0050] Remember a =R a +jX a is the complex impedance of the antenna, where R a is the resistance value, X a Reactance value, denoted by four different load impedances as Z c1 , Z c2 , Z c3 , Z c4 , and the corresponding load reflection coefficients are Γ1=1∠45°, Γ2=1∠-45°, Γ3=1∠-135°, Γ4=1∠135°; when the tag antenna gain is G, the differential Backscatter power is used to characterize the power of the scattered signal:

[0051]

[0052] It can be considered as the power radiated by the antenna driven by the difference between the complex currents I1 and I2;

[0053] in, V0 is the antenna voltage caused by the incident wave;

[0054] When the power density of the incident wave is S, V0 can be given by the following formula:

[0055]

[0056] The differential radar cross section (DifferentialRCS) is:

[0057]

[0058] Then the signal power received by the traditional passive Backscatter 4QAM receiver is:

[0059]

[0060] Among them, P t is the carrier power, G t is the carrier source transmitting antenna gain, λ is the system operating wavelength, and d is the distance from the carrier source to the Backscatter tag;

[0061] The following is an analysis of the link budget of the system when the present invention is adopted, assuming that the carrier power P t , carrier source transmitting antenna gain G t , system operating wavelength λ, distance d from carrier source to Backscatter tag, tag antenna gain G and load impedance Z c1 , Z c2 , Z c3 , Z c4 In addition, for the convenience of analysis, it is assumed that the circulator and the circuit are connected ideally, that is, the attenuation is 0; then the differential scattered power is:

[0062]

[0063] in, G a is the power gain of the first amplifier and the second amplifier;

[0064] The differential radar cross section is:

[0065]

[0066] At this time, the power received by the receiver is:

[0067]

[0068] According to the expression of Δσ and Δσ′: Δσ′=G a Δσ, combined with the source end transmission power: P s =P t G t , the link loss of the traditional Backscatter single-station mode is obtained as:

[0069]

[0070] The link loss when adopting the present invention is:

[0071]

[0072] It can be seen that when the present invention is adopted, the signal loss of the Backscatter system is smaller, it can support a longer transmission distance, and it can be adjusted according to the amplifier gain G a to adjust.

[0073] Based on the above theoretical analysis, the simulation comparison of the received power of this embodiment and the traditional Backscatter 4QAM communication system is shown in the figure below: Figure 5 As shown in FIG. 1 , the time domain simulation comparison of the received signal of the present embodiment and the traditional Backscatter 4QAM communication system is shown in FIG. Figure 6 As shown; the simulation results show that the present invention can complete Backscatter 4QAM signal modulation. Compared with the traditional Backscatter 4QAM modulation device, under the same other conditions, the modulated signal obtained by the present invention can be transmitted farther and the signal quality received at the same distance is better.

[0074] In summary, the present invention proposes an active backscatter 4QAM modulation device supporting long-distance transmission. Compared with the traditional Backscatter 4QAM communication mode, the receiving power is increased to the original G a times, achieving the purpose of increasing and controlling the transmission distance; and to a certain extent, making up for the shortcoming of the Backscatter communication system's insufficient transmission distance, and providing a new idea for the Backscatter communication of environmental signals.

[0075] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. An active backscatter 4QAM modulation device supporting long-distance transmission, comprising: Antenna, directional coupling module, switch modulation module, control module, and four modulation branches; characterized in that: The switch modulation module is composed of a first single-pole four-throw switch and a second single-pole four-throw switch, wherein the first single-pole four-throw switch is composed of a moving port RFc1 and fixed ports RFs11, RFs12, RFs13, and RFs14, and the second single-pole four-throw switch is composed of a moving port RFc2 and fixed ports RFs21, RFs22, RFs23, and RFs24; The modulation branch is composed of a circulator, an amplifier and a load. The circulator port 1 in the i-th modulation branch is connected to the fixed port RFs2i of the second single-pole four-throw switch, the port 2 is connected to the load, the port 3 is connected to the input end of the amplifier, and the output end of the amplifier is connected to the fixed end RFs1i of the first single-pole four-throw switch, i=1,2,3,4; the loads in the four modulation branches are Zc1, Zc2, Zc3, and Zc4 respectively; The antenna is connected to the moving port RFc1 of the first single-pole four-throw switch and the moving port RFc2 of the second single-pole four-throw switch through a directional coupling module. The directional coupling module transmits the received signal to the moving port RFc2 of the second single-pole four-throw switch, and couples the modulated signal from the moving port RFc1 of the first single-pole four-throw switch to the antenna. The control module provides control signals to the first single-pole four-throw switch and the second single-pole four-throw switch, so that one of the four modulation branches can be selected to work.

2. The active backscatter 4QAM modulation device supporting long-distance transmission according to claim 1, characterized in that: The directional coupling module adopts a directional coupler or a circulator.

3. The active backscatter 4QAM modulation device supporting long-distance transmission according to claim 1, characterized in that: The active backscatter 4QAM modulation device has four specific modulation states: The first switch modulation state: the RFs11 port of the first single-pole four-throw switch is connected, the RFs21 port of the second single-pole four-throw switch is connected, and the first modulation branch is working; Second switch modulation state: the RFs12 port of the first single-pole four-throw switch is connected, the RFs22 port of the second single-pole four-throw switch is connected, and the second modulation branch is working; The third switch modulation state: the RFs13 port of the first single-pole four-throw switch is connected, the RFs23 port of the second single-pole four-throw switch is connected, and the third modulation branch is working; The fourth switch modulation state: the RFs14 port of the first single-pole four-throw switch is connected, the RFs24 port of the second single-pole four-throw switch is connected, and the fourth modulation branch is working.

4. The active backscatter 4QAM modulation device supporting long-distance transmission according to claim 1, characterized in that: The first single-pole four-throw switch and the second single-pole four-throw switch are controlled by the same set of control signals.

5. The active backscatter 4QAM modulation device supporting long-distance transmission according to claim 1, characterized in that: The antenna is used to receive the carrier signal of the Backscatter communication system and radiate the amplified 4QAM signal into space.

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