Active frequency shift backscattering 2ASK modulation device

Abstract

The invention discloses an active frequency shift backscattering 2ASK modulation device, which comprises a receiving and transmitting common antenna, a signal directional transmission isolation module, a switch amplification modulation circuit and a control module, the control module is used for generating a 2ASK modulation signal and a frequency shift signal, the 2ASK modulation signal is output to a modulation signal input end of the line switching unit through a first control signal output end of the control module, and the frequency shift signal is output to a frequency shift signal input end of the line switching unit through a second control signal output end of the control module; under the action of two paths of signals output by the control module, the switch amplification modulation circuit modulates carrier signals received by the antenna, ASK signal modulation and frequency shifting are carried out firstly, useless frequency is filtered out through the filter, and the signals are amplified through the low-power-consumption amplifier and then transmitted to the antenna to be transmitted through the circulator. According to the method, the problem of self-interference of a traditional Backscatter ASK communication system during high-sensitivity receiving at the AP end is solved, and the good receiving effect of the AP end is guaranteed.

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 indispensable and important part of wireless communication systems. Compared with traditional modulation technologies in wireless communication systems, backscatter modulation has many advantages such as simple modulation equipment and low power consumption, and has been widely used, especially in RFID technology applications. Wireless communication systems based on backscatter technology have also received widespread attention. One of the benefits of this communication system is that it can realize passive tags, which is one of the important technologies for the future smart Internet of Things.

[0003] The backscatter wireless communication system includes a reader and a wireless access point (AP). The AP uses different reflection coefficients when the antenna is connected to different loads to achieve signal modulation. This is achieved by changing the impedance of the antenna. When the antenna is connected to different impedances, the reflected signal strength and phase will change. This change can be used to achieve signal modulation and realize signal transmission and reception on the same antenna. Backscatter communication is often based on binary amplitude keying modulation 2ASK, which transmits binary data by changing the amplitude of the carrier. The amplitude of the carrier changes with the change of the binary signal.

[0004] Compared with traditional digital modulation, Backscatter technology has greatly reduced complexity, simpler equipment requirements, and greatly reduced power consumption. However, in the scenario where the transmission and reception share the same antenna, there is a self-interference problem on the AP side. The signal transmission and reception on the AP side exist at the same time, which introduces a greater problem to the high-sensitivity reception on the AP side. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a backscatter 2ASK modulation device for achieving high-sensitivity reception of a common antenna through 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 shift 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 shift signal input terminal, a non-output reflection signal terminal, a filtering amplification unit and a backscatter 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 end of the line switching unit through the first control signal output end of the control module, and the frequency shift signal is output to the frequency shift signal input end of the line switching unit through the second control signal output end 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 non-output reflection signal terminal, and controls the modulated signal input terminal to be connected to the frequency shift signal input terminal or to the non-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 end to be connected with the modulation signal input end, controls the modulated signal input end to be connected with the frequency shift signal input end, and 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. After the 2ASK modulated signal completes the frequency shift 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 the useless frequency components introduced during the line switching and signal modulation process, and compensate for the introduced loss, and generate a frequency-shifted backscattered 2ASK modulated signal to the backscattered signal output end, and finally radiates to 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 beneficial effect of the present invention is that two sets of different signals from the control module are used to control the line connection mode of the switch amplification modulation line, and under the condition of ensuring that the Backscatter 2ASK modulation has a good modulation effect and can be transmitted over a certain distance, the 2ASK signal backscattered by the device and the AP carrier frequency offset can be effectively achieved, and the interference of the carrier signal on the AP end is improved to a certain extent, and the performance of high-sensitivity reception on the AP end is improved. The device architecture adopted by the present invention can be applied to high-sensitivity reception on the AP end of the backscatter wireless communication system in a common antenna scenario. 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 2It is a time domain waveform test diagram of the active frequency shifting Backscatter 2ASK modulation module of the embodiment;

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

[0015] The signal directional transmission isolation module can usually select a power divider, a circulator or a coupler. The embodiment selects a three-port circulator. 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 control signals from the control module to realize the separate control of the single-pole double-throw switch 1 and the single-pole double-throw switch 2, thereby realizing the modulation and frequency shifting of the signal. The filtering and amplifying 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 transmission and reception, a three-port circulator, a switch amplifier modulation circuit and a control module; the switch amplifier modulation circuit includes a single-pole double-throw switch 1, a single-pole double-throw switch 2, a non-output reflection signal terminal, a low-power amplifier 1, a filter and a low-power amplifier 2. A grounded matching load is used as the non-output reflection signal terminal. The switch amplifier modulation circuit also includes a carrier signal input terminal, a modulation signal input terminal, a modulated signal input terminal, a frequency shift signal input terminal and a backscatter signal output terminal.

[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 shift 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 switch amplification modulation circuit 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 end of the single-pole double-throw switch 1 is the carrier signal input end, a movable end 11 of the single-pole double-throw switch 1 is the modulation signal input end, and the other movable end 12 is connected to the non-output reflection signal terminal. The single-pole double-throw switch 1 controls the carrier signal input end to be connected to the modulation signal input end or to the non-output reflection signal terminal; the movable end 11 of the single-pole double-throw switch 1 is connected to the fixed end of the single-pole double-throw switch 2; the fixed end of the single-pole double-throw switch 2 is the modulated signal input end, a movable end 21 of the single-pole double-throw switch 2 is the frequency shift signal input end, and the other movable end 22 is connected to the non-output reflection signal terminal, and the single-pole double-throw switch 2 controls the modulated signal input end to be connected to the frequency shift signal input end or to the non-output reflection signal terminal. The movable end 21 of the single-pole double-throw switch 2 is connected to the input end of the low-power amplifier 1, the output end of the low-power amplifier 1 is connected to the filter input end, the filter output end is connected to the input end of the low-power amplifier 2, and the output end of the low-power amplifier 2 is connected to the backscattering signal output end.

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

[0023] The embodiment changes the state of the single-pole double-throw switch 1 in the device through the control signal 1 output by the control module, thereby effectively realizing the modulation of the 2ASK signal; changes the state of the single-pole double-throw switch 2 in the device through the control signal 2 output by the control module, thereby effectively realizing the frequency shift of the 2ASK signal, and filters out some other useless frequency components introduced when the single-pole double-throw switch 2 is switched, 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 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 2ASK modulated signal after frequency shifting into space, and 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, the SPDT switch 1 is connected to the matching load, and the carrier signal received by the antenna will be absorbed by the matching load; the SPDT switch 2 is grounded through the matching load, and no signal passes through, so 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 end, and another control signal c2(t) is used to control the SPDT switch 2, generally with 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, mainly by using 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 with useless sidebands through the back-end filter, and then compensated for the losses in the modulation and filtering process through a low-power amplifier, so that the backscattered signal can be transmitted over a certain distance.

[0037] The amplified signal is transmitted to the antenna through the circulator. That is, the antenna 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 reception of the baseband signal is completed.

[0040] Assume that the carrier signal (taking a single tone as an example) received by the antenna 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 amplitude of the transmitted signal, which is related to the amplitude of the control signal, the circulator loss and other actual circuit losses, and ξ is the phase change caused by reflection and circuit transmission. From the expression, it can be seen that the transmitted signal is a 2ASK signal modulated by the control signal, and the envelope characteristics of the 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 device can offset the backscattered return signal and the carrier signal of the AP end, and 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, the present invention proposes a device for active frequency shifting Backscatter 2ASK modulation transmission distance, which can achieve high-sensitivity reception in the AP transmission and reception common antenna scenario compared with the traditional Backscatter 2ASK communication mode. The present invention makes up for the carrier self-interference problem of the Backscatter communication system to a certain extent, and provides a new idea for the Backscatter communication of environmental 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 amplification unit and a backscattering 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 end of the line switching unit through the first control signal output end of the control module, and the frequency shift signal is output to the frequency shift signal input end of the line switching unit through the second control signal output end 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 non-output reflection signal terminal, and controls the modulated signal input terminal to be connected to the frequency shift signal input terminal or to the non-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, controls the modulated signal input terminal to be connected to the frequency shift signal input terminal, and 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 radiates to 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 filter amplifier 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, characterized in that: The signal directional transmission isolation module is a power divider or a circulator.

5. The device according to claim 1, characterized in that: 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, characterized in that: 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 moving end of the second single-pole double-throw switch is the frequency shift signal input end, and the other two moving ends are connected to the non-output reflection signal terminal.

7. The device according to claim 1, characterized in that: 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, characterized in that: The antenna is a directional antenna or an omnidirectional antenna.

9. The device according to claim 1, characterized in that: No output reflection signal output terminal is a grounded matched load.

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