Sixteen-channel transmitting circuit for orbital angular momentum underwater acoustic communication system

Abstract

The present invention relates to a sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system, comprising an FPGA core board, which is used to respond to an amplitude adjustment command of a host computer, generate an orbital angular momentum multiplexing modulation waveform transmitted by each channel according to received data and convert it into a digital modulation waveform; a sixteen-channel DA module, which is used to convert the digital modulation waveform into an analog modulation waveform; a sixteen-channel amplitude modulation circuit, which is used to adjust the amplitude of the analog modulation waveform and amplify the waveform according to a control signal; and a sixteen-channel power amplifier circuit, which is used to form a driving waveform after power amplification of the waveform-amplified transmitting waveform to drive a transducer array. The present invention realizes the generation of an orbital angular momentum multiplexing modulation waveform that can be used to drive an underwater acoustic transducer according to transmission data, realizes the adjustment of the amplitude of the output waveform of each channel, and provides a solution for an orbital angular momentum underwater acoustic communication system.

Description

Technical Field

[0001] The invention relates to the technical field of underwater acoustic communication, and in particular to a sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system. Background Art

[0002] The ocean contains a large amount of resources, and the exploration and development of the ocean cannot be separated from the support of high-speed underwater communication technology. Since electromagnetic waves and light waves attenuate very quickly in water, they cannot be used for long-distance underwater communication scenarios. At present, sound waves are still the mainstream method for underwater wireless communication.

[0003] In order to achieve high-speed underwater acoustic communication, orbital angular momentum (OAM) has become a research hotspot in the field of underwater acoustic communication as a new spatial modulation method. At present, the methods for generating acoustic orbital angular momentum are mainly divided into two categories: passive method and active method. Among them, the array antenna method is the mainstream method because of its mature theory and can generate OAM waves of multiple modes. However, most of them use large laboratory equipment to generate the excitation signal of the array antenna. The large laboratory equipment is large in size and high in cost, and cannot be used in actual underwater acoustic communication systems. Summary of the invention

[0004] In view of the above problems, the present invention proposes a sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system, which realizes the generation of an orbital angular momentum multiplexing modulation waveform according to transmission data and the adjustment of the amplitude of the output waveform of each channel.

[0005] The present invention is achieved through the following technical solutions:

[0006] Sixteen-channel transmitting circuit for orbital angular momentum underwater acoustic communication system, including:

[0007] The FPGA core board is used to respond to the amplitude adjustment command of the host computer, generate the orbital angular momentum multiplexing modulation waveform emitted by each channel according to the received data, and convert it into a digital modulation waveform;

[0008] Sixteen-channel DA module, used to convert the digital modulation waveform output by the FPGA core board into an analog modulation waveform;

[0009] The sixteen-channel amplitude modulation board is used to adjust the amplitude of the analog modulation waveform output by the sixteen-channel DA module and amplify the waveform according to the control signal;

[0010] The sixteen-channel power amplifier circuit is used to power-amplify the waveform-amplified transmission waveform output by the sixteen-channel amplitude modulation circuit to form a driving waveform to drive the transducer array.

[0011] The FPGA core board loads the received transmission data onto eight OAM modes to generate a modulated waveform transmitted by each channel; by pre-storing waveform data and window function data of different OAM modes corresponding to each channel in the FPGA, summing, averaging, and multiplying the waveform data in the storage area according to the data to be sent, the modulated waveform data is obtained;

[0012] pass Calculate the excitation signal X required to be applied to each transducer array element jm ,

[0013] According to the data sent, vortex acoustic wave coupling with different topological charges is selected.

[0014]

[0015] Calculate the excitation signal required to be applied to each transducer array element after coupling;

[0016] Utilizing X jw =X j *W performs windowing on the excitation signal applied to each transducer array element to obtain the final modulation waveform X required to be emitted by each array element jw ;

[0017] Where A is the acoustic amplitude, f is the acoustic frequency, t is the time, m is the topological charge, n is the number of transducers, j is the transducer number in clockwise order, i is an imaginary number, which is the mathematical symbol for the exponential expression of the cosine signal, Z is the number of topological charges for coupling, l1 is the first topological charge, l Z is the Zth topological charge, W is the window function, and the Hanning window function is taken.

[0018] Among them, the conversion bit number of the sixteen-channel DA module is greater than or equal to 10 bits, the conversion rate is greater than or equal to less than 100MHz, the maximum conversion rate is 125MHz, and the output current is 0-20mA.

[0019] Among them, the sixteen-channel amplitude modulation board is connected to the single-chip microcomputer, and the single-chip microcomputer is used to send the amplitude adjustment command to the sixteen-channel amplitude board. The sixteen-channel amplitude modulation circuit on the sixteen-channel amplitude board converts the current signal output by the sixteen-channel DA module into a voltage signal through the operational amplifier U1, the digital potentiometer U2 and the operational amplifier U. The control signal input by the single-chip microcomputer is used to control the digital potentiometer to achieve an output waveform amplitude adjustable between 0-5V and a minimum adjustment accuracy of 19.5mV.

[0020] Wherein, the sixteen-channel amplitude modulation circuit includes an operational amplifier U1, a digital potentiometer U2 and an operational amplifier U, the output end of the operational amplifier U1 is connected to the PA end of the digital potentiometer U2 through a capacitor C2, the PB end of the digital potentiometer U2 is connected to a 0.3V DC signal, VDD is connected to a 3.3V voltage, and the PA end is connected to the voltage signal output by the transport amplifier U1, and the output voltage amplitude is adjusted by adjusting the position of the middle tap of the digital potentiometer U2; the adjustment of the middle tap position is achieved by the single-chip microcomputer by controlling the three pins SDI, SCK, and CS; the PW end of the digital potentiometer U2 is adjusted to connect to the positive input end of the operational amplifier U3 through a resistor R2, the negative input end of the operational amplifier U3 is connected to the VSS end of the digital potentiometer U2 through a resistor R3, and the VSS end of the digital potentiometer U2 is grounded, the negative input end of the operational amplifier U3 is connected to the output end of the operational amplifier through a resistor R4, and the output end of the operational amplifier outputs the amplitude modulated signal.

[0021] Among them, the FPGA core board is connected to the single-chip microcomputer, receives the FPGA core board control instructions, and sends amplitude adjustment commands to the sixteen-channel amplitude adjustment circuit according to the FPGA core board control instructions to adjust the amplitude of the output waveform of each channel.

[0022] The sixteen-channel power amplifier circuit includes two cascaded power amplifiers and a boost transformer for achieving impedance matching between the transducer array and the subsequent power operational amplifier. The two power operational amplifiers are cascaded to amplify the power of the transmission waveform, and the output waveform voltage is further amplified by the boost transformer to form a driving waveform. The turns ratio of the boost transformer is determined by the resistance of the transducer array and the output impedance of the subsequent power operational amplifier.

[0023] The gain-bandwidth product of the two cascaded power operational amplifiers is greater than or equal to 1 MHz, and the maximum output current of the subsequent power operational amplifier is greater than or equal to 4A.

[0024] The host computer sends the data or amplitude adjustment command to be sent to the FPGA core board through serial communication.

[0025] The present invention realizes a highly integrated sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system, realizes the generation of a modulation waveform, and realizes the adjustment of the amplitude of the output waveform of each channel. The overall volume is smaller and the cost is lower. The circuit can be used in actual underwater acoustic communication systems and provides a hardware solution for other orbital angular momentum underwater acoustic communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a structural block diagram of a sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system.

[0027] Figure 2 The present invention is a block diagram of the FPGA program structure of the FPGA core board of the sixteen-channel transmitting circuit for the orbital angular momentum underwater acoustic communication system.

[0028] Figure 3 It is a structural diagram of the sixteen-channel DA module of the present invention.

[0029] Figure 4 The figure is a structural diagram of the amplitude adjustment circuit of the sixteen-channel amplitude modulation board of the present invention.

[0030] Figure 5 This is a structural diagram of a sixteen-channel power amplifier circuit of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] See also Figure 1-5 As shown, the sixteen-channel transmitting circuit for the orbital angular momentum underwater acoustic communication system of the present invention comprises:

[0033] The FPGA core board is used to respond to the amplitude adjustment command of the host computer (PC), generate the orbital angular momentum multiplexing modulation waveform emitted by each channel according to the received data and convert it into a digital modulation waveform;

[0034] Sixteen-channel DA module, used to convert the digital modulation waveform output by the FPGA core board into an analog modulation waveform;

[0035] The sixteen-channel amplitude modulation board is used to adjust the amplitude of the analog modulation waveform output by the sixteen-channel DA module and amplify the waveform according to the control signal;

[0036] The sixteen-channel power amplifier circuit is used to power-amplify the waveform-amplified transmission waveform output by the sixteen-channel amplitude modulation circuit to form a driving waveform to drive the transducer array.

[0037] Among them, FPGA communicates with the host computer and the single-chip microcomputer through the UART serial communication module, receives data and commands from the host computer, sends control commands to the single-chip microcomputer, and stores the data stream received through the UART serial communication module in the corresponding storage area after processing. The program structure of the FPGA waveform modulation of the embodiment of the present invention is as follows Figure 2 As shown, the storage area is a ROM storage area, including ROM storage area 1 and ROM storage area 2.

[0038] Taking a typical uniform circular transducer array composed of sixteen transducers as an example, if we want to generate a vortex sound wave with a topological charge of m, the excitation signal that needs to be applied to each transducer element is:

[0039]

[0040] Among them, A is the sound wave amplitude, f is the sound wave frequency, t is time, m is the topological charge, n is the number of transducers (here 16), i is an imaginary number, which is the mathematical symbol used to express the cosine signal exponentially, and j is the transducer number in clockwise order, where j = 0, 1, 2, ..., n-1.

[0041] Through the above formula, the excitation signal of each transducer corresponding to different topological charges can be calculated. After calculating each excitation signal in advance, it is stored in the OAM mode in the ROM storage area 1 of the FPGA. Since there are 8 OAM modes and 16 transmitting transducers, the excitation signal of each transducer corresponding to different OAM modes is different, so there are 8 columns and 16 rows in total. In order to suppress the sidelobe interference of the modulated waveform, the window function data is stored in the ROM storage area 2 for windowing the modulated waveform.

[0042] According to the transmitted data, vortex acoustic waves with different topological charges are selected for coupling. After coupling, the excitation signal required to be applied to each transducer array element is:

[0043]

[0044] Among them, Z is the number of coupled topological charges, l1 is the first topological charge, l Z is the Zth topological charge.

[0045] The excitation signal applied to each transducer array element is windowed to obtain the modulation waveform required to be emitted by each array element:

[0046] X jw =X j *W

[0047] Where W is the window function, here we take the Hanning window function. After the above steps, we finally get the modulation waveform X required to be transmitted by each array element. jw , considering the subsequent steps, it is quantized into ten-bit binary data here.

[0048] The circuit structure diagram of the sixteen-channel DA module of the present invention is as follows Figure 3As shown, the modulation waveform output by the FPGA core board is a digital waveform, which cannot be directly used for transducer (array) driving. It needs to be converted into an analog waveform through a 16-channel DA module before the subsequent steps can be carried out. The FPGA core board outputs the obtained modulation waveform data and conversion clock to the 16-channel DA module, and the 16-channel DA module outputs an analog waveform with a current range of 0-20mA according to the received data.

[0049] The structure diagram of the sixteen-channel amplitude adjustment circuit on the sixteen-channel amplitude modulation board of the present invention is as follows Figure 4 As shown, it includes an operational amplifier U1, a capacitor C1, a digital potentiometer U2 and an operational amplifier U3; the positive phase input terminal of the operational amplifier U1 is grounded through a resistor R1 and the negative phase input terminal is connected to the output terminal, the output terminal of the operational amplifier U1 is connected to the PA terminal of the digital potentiometer U2 through a capacitor C2, the PB terminal of the digital potentiometer U2 is connected to a 0.3V DC signal, VDD is connected to a 3.3V voltage, and the PA terminal is connected to the voltage signal output by the transport amplifier U1, and the output voltage amplitude is adjusted by adjusting the position of the middle tap. The adjustment of the middle tap position is achieved by the single-chip microcomputer by controlling the three pins SDI, SCK, and CS to obtain an output voltage signal, wherein the PW terminal is connected to the positive phase input terminal of the operational amplifier U3 through a resistor R2, the negative phase input terminal of the operational amplifier U3 is connected to the VSS terminal of the digital potentiometer U2 through a resistor R3, and the VSS terminal of the digital potentiometer U2 is grounded, the negative phase input terminal of the operational amplifier U3 is connected to the output terminal of the operational amplifier through a resistor R4, and the output terminal of the operational amplifier outputs the amplitude modulated signal.

[0050] The sixteen-channel amplitude adjustment circuit adjusts the amplitude of the output waveform of each channel according to the amplitude adjustment command sent by the microcontroller. The single-chip microcomputer controls the amplitude adjustment circuit to adjust the amplitude of the output waveform of each channel according to the amplitude adjustment command sent by the FPGA.

[0051] Specifically, by adjusting the resistance value of the digital potentiometer of each channel and cooperating with the operational amplifier, the output voltage can be adjusted in the range of 0-5V, and the minimum adjustment accuracy is 19.5mV.

[0052] Assuming that the current signal output by DA conversion is I, it is converted into a voltage signal through resistor R1:

[0053] U1=I*R1

[0054] Operational amplifier U1 is a voltage follower, which plays a role of buffer isolation. Capacitor C1 is a DC blocking capacitor, which isolates the DC component in the output signal. One end of the digital potentiometer U2 is connected to a 0.3V DC signal, and the other end is connected to the voltage signal output by U1. The output voltage amplitude is adjusted by adjusting the position of the middle tap. The adjustment of the middle tap position is achieved by the microcontroller by controlling the three pins SDI, SCK, and CS to obtain the output voltage signal:

[0055] U2=U1*Adj+0.3

[0056] Where Adj is the adjustment amplitude of the digital potentiometer, 0≤Adj≤1. The operational amplifier U3 constitutes an amplifier circuit to amplify the adjusted signal and finally obtain an amplitude modulated output:

[0057]

[0058] The structure diagram of the sixteen-channel power amplifier circuit of the embodiment of the present invention is as follows Figure 5 As shown, it includes a pre-amplifier U4 and a post-amplifier U5. The negative phase input of the pre-amplifier U4 is between series-connected resistors R5 and R6, grounded through the resistor R5, and connected to the output end of the pre-amplifier U4 through the resistor R6. The negative phase input of the pre-amplifier U4 is grounded through a resistor R7, and receives an amplitude modulated output signal through a capacitor C2. Its output end is connected to the positive phase input end of the post-amplifier U5 through a capacitor C3. The positive phase input end of the post-amplifier U5 is grounded through a resistor R10. The negative phase input end of the post-amplifier U5 is grounded through a resistor R8, and is connected to the output end of the post-amplifier U5 through a resistor R9. The output end of the post-amplifier U5 is connected to a +24V voltage through a diode D1, connected to a -24V voltage through a diode D2, and connected to the input end of the input side coil of the step-up transformer T1 through a capacitor C4. The output end of the output side coil of the step-up transformer T1 outputs a power amplified signal. The other end of the input side coil of the step-up transformer T1 and the other end of the output side coil are grounded, and the output end of the output side coil is grounded through a resistor R11.

[0059] Among them, the 16-channel power amplifier circuit further amplifies the output waveform to improve the load capacity of the system. The first half of the power amplifier circuit realizes power amplification of the modulated waveform by cascading two power operational amplifiers. The two power operational amplifiers are cascaded to achieve a wider frequency response. The gain-bandwidth product of the two power operational amplifiers is not less than 1MHz, and the maximum output current of the rear power operational amplifier is not less than 4A. The modulated waveform after two-stage amplification is:

[0060]

[0061] Diode D1 and diode D2 are fast recovery rectifier diodes with a continuous current rating greater than or equal to 4A. They are used to prevent the load current from returning to the amplifier, causing the output voltage to exceed the power supply voltage and damage the power operational amplifier. Capacitor C4 is a DC blocking capacitor that isolates the DC component in the drive signal to prevent damage to the transformer caused by the DC component.

[0062] The second half of the 16-channel power amplifier circuit is a step-up transformer T1, which realizes the impedance matching between the transducer (array) and the subsequent power operational amplifier. Assume that the output impedance of the subsequent power operational amplifier is R O , the equivalent impedance of the transducer is R L , then the turns ratio T of the transformer should be:

[0063]

[0064] Among them, [] is the rounding function, and [x] represents the largest integer not exceeding x.

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system, characterized in that: Used to generate and transmit orbital angular momentum multiplexing modulation waveform according to transmission data, including: The FPGA core board is used to respond to the amplitude adjustment command of the host computer, generate the orbital angular momentum multiplexing modulation waveform emitted by each channel according to the received data, and convert it into a digital modulation waveform; Sixteen-channel DA module, used to convert the digital modulation waveform output by the FPGA core board into an analog modulation waveform; The sixteen-channel amplitude modulation board is used to adjust the amplitude of the analog modulation waveform output by the sixteen-channel DA module and amplify the waveform according to the control signal; The sixteen-channel power amplifier circuit is used to power amplify the waveform of the waveform amplified transmission waveform output by the sixteen-channel amplitude modulation circuit to form a driving waveform to drive the transducer array; the FPGA core board loads the received transmission data onto eight OAM modes to generate a modulated waveform emitted by each channel; by pre-storing the waveform data and window function data of different OAM modes corresponding to each channel in the FPGA, the waveform data in the storage area are summed, averaged, and multiplied according to the data to be sent, to obtain the modulated waveform data: pass Calculate the excitation signal required to be applied to each transducer element According to the data sent, vortex acoustic wave coupling with different topological charges is selected. Calculate the excitation signal required to be applied to each transducer array element after coupling; use The excitation signal applied to each transducer array element is windowed to obtain the modulation waveform required to be emitted by each array element. ; In the formula, is the sound wave amplitude, is the sound wave frequency, For time, is the topological charge number, is the number of transducers, are the transducer numbers in clockwise order, is an imaginary number, using the mathematical symbol for the exponential expression of the cosine signal. is the number of topological charges for coupling, is the first topological charge, is the Zth topological charge, is the window function, take the Hanning window function; The sixteen-channel power amplifier circuit includes two cascaded power amplifiers and a step-up transformer for achieving impedance matching between the transducer array and the subsequent power operational amplifier. The transmission waveform is power amplified by the two cascaded power operational amplifiers, and the output waveform voltage is further amplified by the step-up transformer to form a driving waveform; the turns ratio of the step-up transformer is determined by the resistance value of the transducer array and the output impedance of the subsequent power operational amplifier.

2. The sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system according to claim 1, characterized in that: The conversion bit number of the sixteen-channel DA module is greater than or equal to 10 bits, the conversion rate is greater than or equal to 100 MHz, the maximum conversion rate is 125 MHz, and the output current is 0-20 mA.

3. The sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system according to claim 1, characterized in that: The sixteen-channel amplitude modulation board is connected to a single-chip microcomputer, and the single-chip microcomputer is used to send an amplitude adjustment command to the sixteen-channel amplitude board. The sixteen-channel amplitude modulation circuit on the sixteen-channel amplitude board converts the current signal output by the sixteen-channel DA module into a voltage signal through an operational amplifier U1, a digital potentiometer U2 and an operational amplifier U. The digital potentiometer is controlled by a control signal input by the single-chip microcomputer to achieve an output waveform amplitude adjustable between 0-5V and a minimum adjustment accuracy of 19.5mV.

4. The sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system according to claim 3, characterized in that: The sixteen-channel amplitude modulation circuit includes an operational amplifier U1, a digital potentiometer U2 and an operational amplifier U, wherein the output end of the operational amplifier U1 is connected to the PA end of the digital potentiometer U2 through a capacitor C2, the PB end of the digital potentiometer U2 is connected to a 0.3V DC signal, VDD is connected to a 3.3V voltage, and the PA end is connected to a voltage signal output by the transport amplifier U1, and the output voltage amplitude is adjusted by adjusting the position of the middle tap of the digital potentiometer U2; the adjustment of the middle tap position is achieved by the single-chip microcomputer by controlling the three pins SDI, SCK, and CS; the PW end of the digital potentiometer U2 is adjusted to be connected to the positive input end of the operational amplifier U3 through a resistor R2, the negative input end of the operational amplifier U3 is connected to the VSS end of the digital potentiometer U2 through a resistor R3, and the VSS end of the digital potentiometer U2 is grounded, the negative input end of the operational amplifier U3 is connected to the output end of the operational amplifier through a resistor R4, and the output end of the operational amplifier outputs an amplitude modulated signal.

5. The sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system according to claim 1, characterized in that: The FPGA core board is connected to the single-chip microcomputer, receives the FPGA core board control instructions, and sends amplitude adjustment commands to the sixteen-channel amplitude adjustment circuit according to the FPGA core board control instructions to adjust the amplitude of the output waveform of each channel.

6. The sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system according to claim 1, characterized in that: The gain-bandwidth product of the two cascaded power operational amplifiers is greater than or equal to 1 MHz, and the maximum output current of the subsequent power operational amplifier is greater than or equal to 4A.

7. The sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system according to claim 6, characterized in that: The two cascaded power amplifiers include a pre-stage amplifier U4 and a post-stage amplifier U5. The negative phase input of the pre-stage amplifier U4 is between series-connected resistors R5 and R6, is grounded through the resistor R5, and is connected to the output end of the pre-stage amplifier U4 through the resistor R6. The negative phase input of the pre-stage amplifier U4 is grounded through a resistor R7, and receives an amplitude modulation output signal through a capacitor C2. The output end of the pre-stage amplifier U4 is connected to the positive phase input end of the post-stage amplifier U5 through a capacitor C3. The positive phase input end of the post-stage amplifier U5 is grounded through a resistor R10. The negative phase input end of the post-stage amplifier U5 is grounded through a resistor R8, and is connected to the output end of the post-stage amplifier U5 through a resistor R9. The output end of the post-stage amplifier U5 is connected to a +24V voltage through a diode D1, to a -24V voltage through a diode D2, and to the input end of the input side coil of the boost transformer through a capacitor C4. The output end of the output side coil of the boost transformer outputs a power-amplified signal. The other end of the input side coil of the boost transformer and the other end of the output side coil are grounded, and the output end of the output side coil is grounded through a resistor R11.

8. The sixteen-channel transmitting circuit for an orbital angular momentum underwater acoustic communication system according to claim 1, characterized in that: The host computer sends the data to be sent or the amplitude adjustment command to the FPGA core board through serial communication.

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