An active frequency-shifted backscatter 2ASK modulation device

Abstract

The present invention discloses an active frequency-shifted backscatter 2ASK modulation device, comprising a common antenna for transmission and reception, a signal directional transmission isolation module, a switch amplifying modulation circuit, and a control module; the control module is used to generate a 2ASK modulation signal and a frequency-shifted signal, the 2ASK modulation signal being output to the modulation signal input of a circuit switching unit via a first control signal output terminal of the control module, and the frequency-shifted signal being output to the frequency-shifted signal input of the circuit switching unit via a second control signal output terminal of the control module; under the action of the two signals output by the control module, the switch amplifying modulation circuit modulates the carrier signal received by the antenna, first performing ASK signal modulation, performing frequency shifting, then filtering out useless frequencies through a filter, and then amplifying the signal through a low-power amplifier and transmitting it to the antenna for transmission through a circulator. The present invention overcomes the self-interference problem of traditional Backscatter ASK communication systems during high-sensitivity reception at the AP end, ensuring good reception at the AP end.

Description

Technical Field

[0001] The present invention relates to wireless communication technology, and in particular to active backscatter modulation technology. Background Art

[0002] Modulation is an essential component of wireless communication systems. Compared to traditional modulation techniques, backscatter modulation offers numerous advantages, such as simple modulation equipment and low power consumption, making it widely used, particularly in RFID applications. Wireless communication systems based on backscatter technology are also attracting considerable attention. One benefit of this technology is its ability to implement passive tags, making it a key technology for the future intelligent Internet of Things.

[0003] A backscatter wireless communication system consists of a reader / writer and a wireless access point (AP). The AP modulates the signal by varying the reflection coefficient obtained when the antenna is connected to different loads. This is achieved by changing the antenna's impedance. When the antenna is connected to different impedances, the reflected signal strength and phase change. This variation allows for signal modulation, enabling signal transmission and reception on the same antenna. Backscatter communication is often based on binary amplitude-shifted keying (2ASK), which transmits binary data by varying the carrier amplitude. The carrier amplitude varies with the binary signal.

[0004] Compared to traditional digital modulation, backscatter technology significantly reduces implementation complexity, requires simpler equipment, and significantly reduces power consumption. However, in scenarios where both transmit and receive signals share a common antenna, the AP experiences self-interference. Simultaneous signal transmission and reception at the AP pose significant challenges to high-sensitivity reception. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a backscatter 2ASK modulation device which realizes high-sensitivity reception of a common antenna by frequency shifting in order to overcome the backscatter self-interference problem.

[0006] The technical solution adopted by the present invention to solve the above technical problems is an active frequency-shifted backscatter 2ASK modulation device, including a common antenna for transmission and reception, a signal directional transmission isolation module, a switch amplification modulation circuit and a control module; the switch amplification modulation circuit includes a circuit switching unit, a carrier signal input terminal, a modulation signal input terminal, a modulated signal input terminal, a frequency-shifted signal input terminal, a non-output reflection signal terminal, a filtering and amplification unit and a backscattered signal output terminal;

[0007] The control module is used to generate a 2ASK modulation signal and a frequency shift signal, the 2ASK modulation signal is output to the modulation signal input terminal of the line switching unit through the first control signal output terminal of the control module, and the frequency shift signal is output to the frequency shift signal input terminal of the line switching unit through the second control signal output terminal of the control module;

[0008] The antenna is respectively connected to the carrier signal input terminal and the backscatter signal output terminal through the signal directional transmission isolation module, the modulation signal input terminal is connected to the modulated signal input terminal, the frequency shift signal input terminal is connected to the input terminal of the filter amplifier unit, and the output terminal of the filter amplifier unit is connected to the backscatter signal output terminal; the line switching unit controls the carrier signal input terminal to be connected to the modulation signal input terminal or to the no-output reflection signal terminal, and controls the modulated signal input terminal to be connected to the frequency shift signal input terminal or to the no-output reflection signal terminal.

[0009] The specific working principle of the device is as follows: when the 2ASK modulation signal is 1, the line switching unit controls the carrier signal input terminal to be connected to the modulation signal input terminal, and controls the modulated signal input terminal to be connected to the frequency shift signal input terminal. The carrier from the antenna and the 2ASK modulation signal from the control module are modulated to generate a 2ASK modulated signal to the modulated signal input terminal. After the 2ASK modulated signal completes frequency shifting through the frequency shift signal from the control module, it passes through the filtering and amplifying unit. The filtering and amplifying unit is used to filter out useless frequency components introduced during the line switching and signal modulation process, compensate for the introduced loss, and generate a frequency-shifted backscattered 2ASK modulated signal to the backscattered signal output terminal, which is finally radiated into space through the antenna.

[0010] When the 2ASK modulation signal is 0, the line switching unit controls the carrier signal input terminal and the modulated signal input terminal to be connected to the no-output reflected signal terminal.

[0011] The present invention has the beneficial effect of using two different sets of signals from a control module to control the connection mode of the switch amplifier modulation circuit. While ensuring good modulation effect and transmission distance of Backscatter 2ASK modulation, it can effectively achieve frequency offset between the 2ASK signal backscattered by the device and the AP carrier, thereby reducing interference with the carrier signal on the AP end to a certain extent and improving the performance of high-sensitivity reception on the AP end. The device architecture adopted by the present invention can be applied to high-sensitivity reception on the AP end of backscatter wireless communication systems in shared antenna scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of an active frequency shifting Backscatter 2ASK modulation module according to an embodiment;

[0013] Figure 2This is a time domain waveform test diagram of the active frequency shifting Backscatter 2ASK modulation module of the embodiment;

[0014] Figure 3 This is a spectrum test diagram of the active frequency shifting Backscatter 2ASK modulation module in the embodiment. DETAILED DESCRIPTION

[0015] The signal directional transmission isolation module can generally be a power splitter, circulator, or coupler. A three-port circulator is selected in this embodiment. The line switching unit is composed of a single-pole double-throw switch 1 and a single-pole double-throw switch 2. The line switching unit receives two different sets of control signals from the control module to achieve separate control of the single-pole double-throw switch 1 and the single-pole double-throw switch 2, thereby achieving signal modulation and frequency shifting. The filtering and amplification unit includes a low-power amplifier 1, a filter BPF, and a low-power amplifier 2 connected in sequence.

[0016] like Figure 1 As shown, the active backscatter 2ASK modulation device includes a common antenna for both transmission and reception, a three-port circulator, a switching amplifier modulation circuit, and a control module. The switching amplifier modulation circuit includes single-pole double-throw switch 1, single-pole double-throw switch 2, a non-output reflection signal terminal, low-power amplifier 1, a filter, and low-power amplifier 2. A grounded matching load serves as the non-output reflection signal terminal. The switching amplifier modulation circuit also includes a carrier signal input, a modulation signal input, a modulated signal input, a frequency-shifted signal input, and a backscatter signal output.

[0017] The control module is used to generate two control signals, control signal 1 and control signal 2. Control signal 1 is a user modulation signal, that is, a 2ASK modulation signal, which is used to control the single-pole double-throw switch 1 to realize the ASK modulation function. Control signal 2 is a square wave signal of a certain frequency, that is, a frequency shift signal, which is used to control the switching of the moving end of the single-pole double-throw switch 2 to realize the frequency shifting function. The control signal 1 output end of the control module is connected to the modulation signal input end of the line switching unit, and the control signal output end 2 is connected to the frequency shift signal input end of the line switching unit. The switch amplification modulation circuit is used to receive the control signal provided by the control module to complete the modulation carrier and frequency shift, and then perform power amplification.

[0018] The antenna is connected to the antenna through port 1 of a three-port circulator, port 2 of the circulator is connected to the carrier signal input end of a switching amplifier modulation circuit serving as a backscatter signal output end, and port 3 of the circulator is connected to the backscatter signal output end.

[0019] The single-pole double-throw switch 1 consists of three ports, namely a fixed terminal RFc1 and two movable terminals 11 and 12; the single-pole double-throw switch 2 consists of three ports, namely a fixed terminal RFc2 and two movable terminals 21 and 22.

[0020] The fixed terminal of single-pole double-throw switch 1 is the carrier signal input terminal, one movable terminal 11 of single-pole double-throw switch 1 is the modulation signal input terminal, and the other movable terminal 12 is connected to the no-output reflection signal terminal. Single-pole double-throw switch 1 controls the carrier signal input terminal to be connected to the modulation signal input terminal or the no-output reflection signal terminal. The movable terminal 11 of single-pole double-throw switch 1 is connected to the fixed terminal of single-pole double-throw switch 2. The fixed terminal of single-pole double-throw switch 2 is the modulated signal input terminal, one movable terminal 21 of single-pole double-throw switch 2 is the frequency-shifted signal input terminal, and the other movable terminal 22 is connected to the no-output reflection signal terminal. Single-pole double-throw switch 2 controls the modulated signal input terminal to be connected to the frequency-shifted signal input terminal or the no-output reflection signal terminal. The movable terminal 21 of single-pole double-throw switch 2 is connected to the input terminal of low-power amplifier 1. The output terminal of low-power amplifier 1 is connected to the filter input terminal, the filter output terminal is connected to the input terminal of low-power amplifier 2, and the output terminal of low-power amplifier 2 is connected to the backscattered signal output terminal.

[0021] When the 2ASK modulation signal is 1, the fixed end of the single-pole double-throw switch 1 is connected to its moving end 11, and the fixed port of the single-pole double-throw switch 2 is connected to its fixed end 21. The carrier from the antenna and the 2ASK modulation signal from the control module are modulated to generate a 2ASK modulated signal to the modulated signal input end. The 2ASK modulated signal is frequency-shifted by the frequency shift signal from the control module and then filtered and amplified by two low-power amplifiers and filters in the on state to form a frequency-shifted backscattered 2ASK modulated signal to the backscattered signal output end, and finally radiated into space through the antenna.

[0022] When the 2ASK modulated signal is 0, the fixed end of the single-pole double-throw switch 1 is connected to its movable end 12, and the fixed end of the single-pole double-throw switch 2 is connected to its movable end 22. The movable end 12 and the movable end 22 are respectively connected to matching loads. The low-power amplifier is in the disconnected state. The carrier signal received by the antenna is absorbed by the matching load, and the antenna has no signal output.

[0023] In the embodiment, the state of the single-pole double-throw switch 1 in the device is changed by the control signal 1 output by the control module, thereby effectively realizing the modulation of the 2ASK signal; the state of the single-pole double-throw switch 2 in the device is changed by the control signal 2 output by the control module, thereby effectively realizing the frequency shift of the 2ASK signal, and other useless frequency components introduced by the switching of the single-pole double-throw switch 2 are filtered out by the filter, thereby ensuring that the frequency output by the switch amplification modulation module is clean; a low-power amplifier module is added, on the one hand, to compensate for the loss introduced by the switch switching modulation process and the filter, and on the other hand, to isolate the signal transmitted in the reverse direction of the circulator to prevent it from entering the switch to participate in the modulation and introducing other useless frequency components.

[0024] Optionally, in addition to being connected to a matching load serving as a non-output reflection signal terminal, ports 12 and 22 of the single-pole double-throw switch 1 and the single-pole double-throw switch 2 may also be connected to other non-output reflection signal output terminals.

[0025] Optionally, the antenna is used to receive the carrier signal of the Backscatter wireless communication system and radiate the frequency-shifted 2ASK modulated signal into space. A directional antenna or an omnidirectional antenna can be selected according to the specific application scenario.

[0026] The specific steps of using the present invention to perform Backscatter 2ASK communication are described below:

[0027] Step 1

[0028] As a carrier source, it sends a carrier signal to the AP end, which is received by the antenna. The signal flows through the circulator. Due to its directional transmission characteristics and port isolation, most of the signal energy will be transmitted to the RFc1 port.

[0029] Step 2

[0030] The control module (user) starts to implement modulation. Let’s assume that the control signal

[0031]

[0032] When the control signal c1(t) = 0, SPDT switch 1 connects to the matching load. At this time, the carrier signal received by the antenna will be absorbed by the matching load. SPDT switch 2 is grounded through the matching load, and no signal passes through. Therefore, no signal is transmitted to the antenna through the circulator. That is, the antenna transmits the '0' signal in 2ASK.

[0033] When the control signal c1(t) = 1, the SPDT switch 1 is connected to the signal path, that is, connected to the SPDT switch RFs21 terminal, and another control signal c2(t) is used to control the SPDT switch 2, which is generally at a frequency of f c2 square wave;

[0034]

[0035] When the control signal c2(t) = 0, the SPDT switch 2 is connected to the matching load, and the signal transmitted from the SPDT switch 1 will be absorbed; when the control signal c2(t) = 1, the SPDT switch 2 is connected to the signal path, and the ASK signal from the SPDT switch 1 is re-modulated. The main purpose is to use c2(t) to control the opening and closing of the SPDT switch 2 to achieve ±f c2 frequency offset.

[0036] The ASK modulated signal after frequency shifting is filtered out of useless sidebands by the back-end filter, and then passes through a low-power amplifier to compensate for the losses in the modulation and filtering processes, so that the backscattered signal can be transmitted over a certain distance.

[0037] The amplified signal is transmitted through the circulator to the antenna, which transmits the '1' signal in 2ASK.

[0038] Step 3

[0039] The signal transmitted by the antenna is received by the receiver on the carrier source side, and after a series of operations such as demodulation, the baseband signal is received.

[0040] Assume that the carrier signal received by the antenna (taking a single tone as an example) is A0cos(2πf c t+θ). In the above process, the signal s(t) transmitted by the antenna can be expressed as:

[0041] s(t)=A·c1(t)·cos(2π(f c t±f c2 )t+θ+ξ)

[0042] Where A is the transmit signal amplitude, which is related to the control signal amplitude, circulator losses, and other actual circuit losses. ξ is the phase change caused by reflection and circuit transmission. The expression shows that the transmit signal is a 2ASK signal modulated by the control signal. The envelope characteristics of this modulated signal are consistent with the modulation waveform input by the control module.

[0043] The test results are as follows Figure 2 、 Figure 3As shown, the Backscatter 2ASK modulation device described in the present invention can complete Backscatter 2ASK signal modulation and perform frequency shifting. Compared with the traditional Backscatter 2ASK modulation device, the present device can offset the backscattered return signal and the carrier signal at the AP end. The common antenna reception at the AP end can realize simultaneous transmission and reception. The AP end uses a filter to suppress the self-interference signal, ensuring the high sensitivity reception of the AP.

[0044] In summary, this invention proposes a device for extending the transmission distance of active frequency-shifted Backscatter 2ASK modulation. Compared to traditional Backscatter 2ASK communication modes, this device can achieve high-sensitivity reception in scenarios where AP transmits and receives data on the same antenna. This invention, to some extent, addresses the carrier self-interference issue in Backscatter communication systems and provides a new approach to Backscatter communication of ambient signals.

Claims

1. An active frequency-shifted backscatter 2ASK modulation device, characterized in that: It includes a common antenna for transmission and reception, a signal directional transmission isolation module, a switch amplification modulation circuit and a control module; the switch amplification modulation circuit includes a circuit switching unit, a carrier signal input terminal, a modulation signal input terminal, a modulated signal input terminal, a frequency shift signal input terminal, a non-output reflection signal terminal, a filtering and amplification unit and a backscattered signal output terminal; The control module is used to generate a 2ASK modulation signal and a frequency shift signal, the 2ASK modulation signal is output to the modulation signal input terminal of the line switching unit through the first control signal output terminal of the control module, and the frequency shift signal is output to the frequency shift signal input terminal of the line switching unit through the second control signal output terminal of the control module; The antenna is connected to the carrier signal input terminal and the backscatter signal output terminal through the signal directional transmission isolation module, the modulation signal input terminal is connected to the modulated signal input terminal, the frequency shift signal input terminal is connected to the input terminal of the filter amplifier unit, and the output terminal of the filter amplifier unit is connected to the backscatter signal output terminal; the line switching unit controls the carrier signal input terminal to be connected to the modulation signal input terminal or to the no-output reflection signal terminal, and controls the modulated signal input terminal to be connected to the frequency shift signal input terminal or to the no-output reflection signal terminal.

2. The device according to claim 1, characterized in that When the 2ASK modulation signal is 1, the line switching unit controls the carrier signal input terminal to be connected to the modulation signal input terminal, and controls the modulated signal input terminal to be connected to the frequency shift signal input terminal. The carrier from the antenna and the 2ASK modulation signal from the control module are modulated to generate a 2ASK modulated signal to the modulated signal input terminal. The 2ASK modulated signal is frequency-shifted by the frequency shift signal from the control module, and then passes through the filtering and amplifying unit to form a frequency-shifted backscattered 2ASK modulated signal to the backscattered signal output terminal, and finally radiated into space through the antenna. When the 2ASK modulation signal is 0, the line switching unit controls the carrier signal input terminal and the modulated signal input terminal to be connected to the no-output reflected signal terminal.

3. The device according to claim 2, characterized in that The filtering and amplifying unit is used to filter out useless frequency components introduced during line switching and signal modulation, and to compensate for the introduced losses.

4. The device according to claim 1, wherein The signal directional transmission isolation module is a power divider or a circulator.

5. The device according to claim 1, wherein: The signal directional transmission isolation module is a three-port circulator; port 1 of the three-port circulator is connected to the antenna, port 2 is connected to the carrier signal input end of the switch amplification modulation circuit, and port 3 is connected to the backscatter signal output end.

6. The device according to claim 1, wherein: The line switching unit is composed of a first single-pole double-throw switch and a second single-pole double-throw switch; The fixed end of the first single-pole double-throw switch is a carrier signal input end, one movable end of the first single-pole double-throw switch is a modulation signal input end, and the other movable end is connected to a non-output reflection signal terminal; The fixed end of the second single-pole double-throw switch is the modulated signal input end, one movable end of the second single-pole double-throw switch is the frequency shift signal input end, and the other two movable ends are connected to the no-output reflection signal terminal.

7. The device according to claim 1, wherein: The filtering and amplifying unit includes a first low-power amplifier, a filter, and a second low-power amplifier connected in sequence.

8. The device according to claim 1, wherein: The antenna is a directional antenna or an omnidirectional antenna.

9. The device according to claim 1, wherein: No output reflection signal The output terminal is a matched load connected to ground.

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