Underwater wireless optical communication method and device for integrated multi-user crosstalk elimination

Abstract

The invention relates to the technical field of underwater wireless optical communication, and discloses an integrated multi-user crosstalk elimination underwater wireless optical communication method and device, which can eliminate inter-symbol crosstalk, modulate nonlinear distortion and multi-user inter-channel interference at the same time so as to improve the performance of a spatial multiplexing underwater wireless optical communication system. The method improves the transmission rate of an underwater wireless optical communication system, and comprises the following steps: transmitting end data processing: generating a plurality of paths of independent modulation signals, modulating binary data, inserting a training sequence, and outputting a plurality of paths of signals; signal conversion and driving: the multi-path signals after digital-to-analog conversion are subjected to power optimization through an electric amplifier and an attenuator and direct current superposition through a bias device to drive an array type LED to work; light transmission: the output light of the plurality of LEDs is expanded by respective corresponding convex lenses and then enters an underwater channel for transmission; receiving and primary processing: light beams at a receiving end are converged by a convex lens and then detected by a photoelectric detector array, and converted multi-path electric signals are synchronously sampled and analyzed;

Description

Technical Field

[0001] The present invention relates to the technical field of underwater wireless optical communication, and in particular to an underwater wireless optical communication method and device for integrated multi-user crosstalk elimination. Background Art

[0002] In recent years, the rapid development of autonomous underwater vehicles (AUVs), remotely controlled underwater robots (ROVs), and seabed observation networks has provided technical support and guarantee for ocean monitoring and exploration. With the increasing number of these underwater platforms, the amount of data required to be transmitted has also increased dramatically, and the demand for high-speed underwater communication has become increasingly urgent. Compared with traditional underwater acoustic communication and underwater radio frequency communication, underwater wireless optical communication technology has the advantages of large bandwidth, high energy efficiency, and strong confidentiality, and can support high-speed data transmission over a distance of tens to hundreds of meters. In existing underwater wireless optical communication systems, multiplexing technologies mainly use wavelength division multiplexing, space multiplexing, and time division multiplexing. In the space multiplexing system, there is not only channel crosstalk in the link itself between multiple users, such as inter-code crosstalk caused by bandwidth limitation, modulation nonlinear distortion caused by the non-ideality of optoelectronic devices, but also interference between data streams of multiple user channels. Therefore, being able to simultaneously (integratedly) eliminate the inter-code crosstalk caused by bandwidth limitation, the modulation nonlinear distortion of the system, and the interference between multiple user channels is of great significance for improving the performance of the space multiplexing system and increasing the transmission rate of the existing underwater wireless optical communication system. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides an underwater wireless optical communication method and device for eliminating multi-user crosstalk in an integrated manner, which simultaneously eliminates inter-code crosstalk, modulation nonlinear distortion and interference between multi-user channels, thereby improving the performance of the underwater wireless optical communication system with spatial multiplexing and increasing the transmission rate of the underwater wireless optical communication system.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions: An underwater wireless optical communication method for integrated multi-user crosstalk elimination comprises the following steps: Data processing at the transmitting end: Generate multiple independent modulation signals, modulate the binary data and insert the training sequence to output multiple signals; Signal conversion and driving: After the digital-to-analog conversion, the multi-channel signals are optimized through the power amplifier and attenuator, and the bias device superimposes the DC to drive the array LED to work; Light transmission: The output lights of multiple LEDs are expanded by their corresponding convex lenses and then transmitted through underwater channels; Receiving and preliminary processing: The light beam at the receiving end is converged by a convex lens and detected by a photodetector array, and the converted multi-channel electrical signals are synchronously sampled and analyzed; Multi-user crosstalk cancellation and signal recovery: resampling, synchronization, all-in-one multi-user channel crosstalk cancellation, demodulation and bit error rate analysis of the sampled signal.

[0005] Preferably, the modulation method of the binary data covers single carrier or multi-carrier, and the modulation format adopts low-order or high-order modulation.

[0006] Preferably, the multi-user crosstalk elimination adopts an integrated multi-user channel crosstalk elimination module including a decision feedback equalizer, which recovers the transmitted data through a specific algorithm, wherein the signal after equalization of the i-th channel It is expressed as:

[0007] represents the i-th signal received after transmission through the channel; and are the coefficients and memory length of the linear channel, respectively; and are the coefficients and memory length of the nonlinear channel respectively; is the nonlinear term pruning factor, , select the appropriate Can effectively reduce the complexity of nonlinear equalizer; coefficient represents the influence of channel j on channel i, is the memory length of the interference channel; is the tap coefficient of the decision feedback equalizer, and its memory length is; Indicates the symbol after the judgment.

[0008] Preferably, the matrix form of the multi-user crosstalk elimination formula is: ; in, represents the transpose operation, and the specific expressions of other signal vectors are as follows: .

[0009] Preferably, a training sequence is used to accelerate the convergence speed of multi-user crosstalk coefficient estimation, and the specific steps are as follows: Step 1: Set the count value; Step 2: Get the observation vector: ; Step 3: Update the error vector: ,in, is a known training sequence inserted by the transmitter, The initial value of is 0; Step 4: Calculate the gain vector: , The initial value of is the identity matrix, and the correlation matrix is ​​updated: ; Step 5: Update the coefficient vector: , the counter is incremented by 1, and it is determined whether the set count value has been reached. If not, it returns to step 2; Step 6: Equalize the multi-user crosstalk, so that the equalized signal is: .

[0010] An apparatus for an underwater wireless optical communication method for eliminating multi-user crosstalk in an integrated manner, comprising: An optical transmitter, the optical transmitter comprising a transmitter data processing module, a digital-to-analog converter, an electric amplifier, an attenuator, a bias device, an LED and a lens connected in sequence, the digital-to-analog converter outputs multiple independent radio frequency signals, each signal is processed by the electric amplifier, the attenuator, the bias device, the LED and the lens, the bias device superimposes direct current, and the electric amplifier, the attenuator, the bias device, the LED and the lens are all arrays; An optical receiving end, the optical receiving end includes a lens, a photodetector, an analog-to-digital converter, and a receiving end data processing module connected in sequence, the photodetector is an array, and the receiving end data processing module includes an integrated multi-user channel crosstalk elimination module; The underwater channel is located between the optical transmitter and the optical receiver.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The receiving end can eliminate the inter-code interference and system modulation nonlinear distortion caused by bandwidth limitation by adopting decision feedback nonlinear channel equalization, and at the same time eliminate the interference between multi-user channels by modeling. It can improve the performance of spatial multiplexing system, increase transmission capacity and distance, reduce the bit error rate under different water qualities, improve reliability and transmission efficiency, perform well in terms of system delay and energy efficiency, have good adaptability to different scenarios, and have reasonable design of equipment selection, algorithm complexity and resource requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0013] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0014] Figure 2 It is a specific flow chart of the present invention.

[0015] Figure 3Here is a comparison chart of performance in tap water.

[0016] Figure 4 This is a performance comparison chart in clean seawater.

[0017] Figure 5 It is a performance comparison chart in coastal seawater. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to the accompanying drawings.

[0019] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art can think of other obvious variations. The basic principles of the present invention defined in the following description can be used for other embodiments, variations, improvements, equivalents, and other technical solutions that do not deviate from the spirit and scope of the present invention.

[0020] Those skilled in the art should understand that, in the disclosure of the present invention, the directions or positions indicated by the terms "longitudinal", "lateral", "up", "down", "left", "right", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the directions or positional relationships shown in the accompanying drawings, which are only simplified descriptions for the convenience of describing the present invention, and do not indicate or imply that the device or component referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, the above terms should not be understood as limitations on the present invention.

[0021] It is to be understood that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the element may be multiple, and the term "one" should not be understood as a limitation on the quantity.

[0022] Example: See also Figure 1-5 , an underwater wireless optical communication method and device for integrated multi-user crosstalk elimination, the device comprising: The optical transmitter includes a transmitter data processing module, a digital-to-analog converter, an electric amplifier, an attenuator, a bias device, an LED and a lens connected in sequence, the digital-to-analog converter outputs multiple independent radio frequency signals, each signal is processed by the electric amplifier, the attenuator, the bias device, the LED and the lens, the bias device superimposes direct current, and the electric amplifier, the attenuator, the bias device, the LED and the lens are all arrays; The optical receiving end includes a lens, a photodetector, an analog-to-digital converter, and a receiving end data processing module which are connected in sequence. The photodetector is an array, and the receiving end data processing module includes an integrated multi-user channel crosstalk elimination module; The underwater channel is located between the optical transmitter and the optical receiver.

[0023] The method steps are: Data processing at the transmitter: The data processing module at the transmitter is responsible for modulating the multi-channel original binary data. It can adopt single carrier (such as on-off keying, pulse amplitude modulation, orthogonal amplitude phase modulation) or multi-carrier (such as orthogonal frequency division multiplexing). The modulation format can be low-order or high-order. After modulation, the training sequence is inserted to output multi-channel signals. Signal conversion and drive: After the digital-to-analog conversion, the multi-channel signals are first input into the electrical amplifier. The electrical amplifier uses an amplifier circuit with adjustable gain to amplify the signal to a suitable power range according to the signal strength and transmission requirements to ensure the effectiveness of the signal in subsequent transmission; then it passes through the attenuator. The attenuator optimizes the power of the amplified signal based on a precision resistor network or other attenuation technology to make it meet the power requirements of underwater channel transmission, avoiding nonlinear distortion caused by excessive signal power or inability to accurately detect the receiving end caused by too low signal power; finally, direct current is superimposed through the bias device. The bias device uses a high-precision DC bias circuit to provide a suitable DC bias voltage for the signal, ensuring that the array LED works at the optimal working point and driving the array LED to work. The array LED uses a special packaging structure and optical design to improve the light emission efficiency and directionality; Optical transmission: The output lights of multiple LEDs are expanded by their corresponding convex lenses. The convex lenses are designed according to the principle of optical refraction. Their focal length and radius of curvature are optimized to achieve effective expansion of optical signals, reduce the divergence of optical signals during underwater transmission, and improve the transmission efficiency and distance of optical signals. The expanded optical signals enter the underwater channel for transmission. During the transmission process, the characteristics of the underwater channel, such as the influence of water absorption, scattering, turbulence, etc. on the optical signals, are fully considered. These influences are reduced through pre-processing of the optical signals (such as beam expansion) and subsequent signal processing at the receiving end (such as multi-user crosstalk elimination), ensuring that the optical signals can be transmitted accurately and stably. Receiving and preliminary processing: The light beam at the receiving end is converged by a convex lens, which matches the parameters of the beam expansion convex lens at the transmitting end. According to the principle of optical imaging, the divergent light signal is converged onto the photodetector array. The photodetector array uses highly sensitive photodetection elements, such as PIN photodiodes or APD avalanche photodiodes, to efficiently detect the light signal. After detection, the converted multi-channel electrical signals are synchronously sampled and analyzed through a synchronous sampling circuit. The synchronous sampling circuit is based on a high-precision clock source and a sample-and-hold circuit to ensure that each signal is synchronized in time for subsequent accurate processing. The sampling frequency is set according to the signal bandwidth and the requirements of the communication system to obtain sufficient signal information. Multi-user crosstalk elimination and signal recovery: The sampled signal is resampled. The resampling process is based on the digital signal processing algorithm. According to the spectral characteristics of the signal and the sampling theorem, the appropriate resampling rate and interpolation algorithm are selected to improve the sampling accuracy of the signal. Then a synchronization operation is performed. The synchronization operation adopts a synchronization algorithm based on a training sequence or a pilot signal to ensure that each signal is accurately aligned in time and frequency. Then, the crosstalk is eliminated through the integrated multi-user channel crosstalk elimination module. The module adopts advanced signal processing techniques, such as algorithms based on adaptive filtering and decision feedback equalization, to effectively suppress multi-user interference. After the crosstalk is eliminated, demodulation is performed. The demodulation process selects the corresponding demodulation algorithm according to the modulation method adopted by the transmitter, such as coherent demodulation or incoherent demodulation, to accurately restore the original binary data. Finally, a bit error rate analysis is performed to evaluate the performance of the communication system by calculating the difference between the received data and the original transmitted data. The bit error rate analysis results are used to feedback and adjust the parameters of the communication system, such as modulation method, power control, etc., to optimize the system performance.

[0024] In order to more clearly illustrate the practical application process of the present invention, a typical embodiment in which two LEDs send data and two photoelectric detectors receive data is used for illustration: First, multiple channels of original binary data are modulated, and after adding training sequences, the data processing module at the transmitting end generates a transmission signal (taking 4-PAM as an example), and then generates multiple independent electrical signals through a digital-to-analog converter (AWG, Tektronix7122C). After the power of the multiple electrical signals is optimized by the electrical amplifier and attenuator, the DC is superimposed by the bias device, and each drives the same type of LED to work within the linear range. The multiple beams of LED output light are mixed by the lens and then incident on the 5-meter-long underwater channel. At the receiving end, the light beams converged by the lens are converted into electrical signals by an avalanche photodiode (Hamamatsu, 12702-11). The multiple electrical signals are sampled by the analog-to-digital converter (Tektronix, DSA72004C) and sent to the receiving end data processing module. The receiving end data processing module resamples, synchronizes, eliminates crosstalk of the integrated multi-user channel, and demodulates the received signal to restore the binary data, and calculates the bit error rate.

[0025] Specifically, taking 2 LEDs sending data and 2 photodetectors receiving data as an example, the 1st and 2nd signal paths after the integrated multi-user crosstalk elimination are used. and They can be expressed as: ; in, and They respectively represent the first and second channel signals received after being transmitted through the channel; and are the coefficients and memory length of the linear channel of the i-th channel respectively; and are the coefficients and memory length of the nonlinear channel of the i-th channel respectively; is the nonlinear term pruning factor, , select the appropriate Can effectively reduce the complexity of nonlinear equalizer; coefficient Indicates the influence of the second channel on the first channel, the coefficient Indicates the influence of channel 1 on channel 2, is the memory length of the interference channel; is the tap coefficient of the decision feedback equalizer, and its memory length is . and They represent the symbols after judgment of the 1st and 2nd channels respectively.

[0026] Furthermore, the matrix form of the multi-user crosstalk elimination method used by the first user can be expressed as: ; in, represents the transpose operation, and the specific expressions of other signal vectors are as follows: ; Preferably, a training sequence is used to accelerate the convergence speed of multi-user crosstalk coefficient estimation. In particular, the specific steps of using an integrated multi-user crosstalk estimation and elimination method are as follows: Step S110: setting the count value; Step S120: Obtain observation vector: ; Step S130: Update the error vector: ,in, is a known training sequence inserted by the transmitter, The initial value of is 0; Step S140: Calculate the gain vector: , The initial value of is the identity matrix, and the correlation matrix is ​​updated: ; Step S150: Update coefficient vector: , the counter is incremented by 1, and it is determined whether the set count value has been reached. If not, the process returns to step S120; Step S160: Equalize multi-user crosstalk, and obtain the equalized signal: .

[0027] Experimental data and comparative analysis: Figure 3 In tap water, taking a 2-transmit 2-receive spatial multiplexing underwater wireless optical communication system as an example, when using 4-order pulse amplitude modulation (4-PAM), the bit error rate and transmission rate, bit error rate and received optical power comparison diagram of the traditional method and the integrated multi-user crosstalk elimination method disclosed in the embodiment of the present invention are used. It can be seen from the figure that after adopting the integrated multi-user crosstalk elimination method, the bit error rate of the two signals is significantly improved. In the low transmission rate area, the bit error rate of the traditional method is high, and the method of the present invention can reduce the bit error rate by more than one order of magnitude; as the transmission rate increases, the bit error rate of the method of the present invention rises more slowly and remains at a low level, indicating that the method of the present invention has good performance at different transmission rates. In terms of received optical power, the method of the present invention can still maintain a low bit error rate at a lower received optical power, indicating that it has a higher utilization efficiency of optical signals and a stronger anti-interference ability.

[0028] Figure 4 and Figure 5 The following are comparison diagrams of the bit error rate and transmission rate, and the bit error rate and received optical power of the traditional method and the integrated multi-user crosstalk elimination method disclosed in the embodiment of the present invention, respectively, in clean seawater and turbid seawater, taking a 2-transmit 2-receive spatial multiplexing underwater wireless optical communication system as an example. It can also be seen that in clean seawater, the bit error rate of the method of the present invention at a high transmission rate is significantly lower than that of the traditional method, and the stability of the bit error rate is better when the received optical power changes; in turbid seawater, due to the more serious scattering and absorption of optical signals by the water body, the bit error rate of the traditional method rises sharply, while the method of the present invention can still effectively suppress the growth of the bit error rate and maintain relatively good communication performance. This fully proves that the method of the present invention can effectively improve system performance under different water quality conditions and adapt to complex underwater communication environments.

[0029] Those skilled in the art should understand that the embodiments of the present invention described above and shown in the accompanying drawings are only examples and do not limit the present invention. The purpose of the present invention has been fully and effectively achieved. The functions and structural principles of the present invention have been demonstrated and explained in the embodiments, and the embodiments of the present invention may be deformed or modified in any way without departing from the principles.

Claims

1. An integrated underwater wireless optical communication method for multi-user crosstalk elimination, characterized in that: The following steps are involved: Data processing at the transmitting end: Generate multiple independent modulation signals, modulate the binary data and insert the training sequence to output multiple signals; Signal conversion and driving: After the digital-to-analog conversion, the multi-channel signals are optimized through the power amplifier and attenuator, and the bias device superimposes the DC to drive the array LED to work; Light transmission: The output lights of multiple LEDs are expanded by their corresponding convex lenses and then transmitted through underwater channels; Receiving and preliminary processing: The light beam at the receiving end is converged by a convex lens and detected by a photodetector array, and the converted multi-channel electrical signals are synchronously sampled and analyzed; Multi-user crosstalk cancellation and signal recovery: resampling, synchronization, all-in-one multi-user channel crosstalk cancellation, demodulation and bit error rate analysis of the sampled signal.

2. The underwater wireless optical communication method for eliminating multi-user crosstalk according to claim 1, characterized in that: The modulation method of the binary data includes single carrier or multi-carrier, and the modulation format adopts low-order or high-order modulation.

3. The underwater wireless optical communication method for eliminating multi-user crosstalk according to claim 1, characterized in that: The multi-user crosstalk elimination adopts an integrated multi-user channel crosstalk elimination module including a decision feedback equalizer, which recovers the transmitted data through a specific algorithm, wherein the signal after equalization of the i-th channel It is expressed as: ； represents the i-th signal received after transmission through the channel; and are the coefficients and memory length of the linear channel, respectively; and are the coefficients and memory length of the nonlinear channel respectively; is the nonlinear term pruning factor, Choose the right one Can effectively reduce the complexity of nonlinear equalizer; coefficient represents the influence of channel j on channel i, is the memory length of the interference channel; is the tap coefficient of the decision feedback equalizer, and its memory length is; The symbol after the judgment.

4. The underwater wireless optical communication method for eliminating multi-user crosstalk according to claim 3, characterized in that: The matrix form of the multi-user crosstalk elimination formula is: ； in, represents the transpose operation, and the specific expressions of other signal vectors are as follows: 。 5. The underwater wireless optical communication method for eliminating multi-user crosstalk according to claim 4, characterized in that: The training sequence is used to speed up the convergence of multi-user crosstalk coefficient estimation. The specific steps are as follows: Step 1: Set the count value; Step 2: Get the observation vector: ; Step 3: Update the error vector: ,in, is a known training sequence inserted by the transmitter, The initial value of is 0; Step 4: Calculate the gain vector: , The initial value of is the identity matrix, and the correlation matrix is ​​updated: ; Step 5: Update the coefficient vector: , the counter is incremented by 1, and it is determined whether the set count value has been reached. If not, it returns to step 2; Step 6: Equalize the multi-user crosstalk, so that the equalized signal is: .

6. A device for implementing the underwater wireless optical communication method for eliminating multi-user crosstalk as described in claims 1-5, characterized in that: include: An optical transmitter, the optical transmitter comprising a transmitter data processing module, a digital-to-analog converter, an electric amplifier, an attenuator, a bias device, an LED and a lens connected in sequence, the digital-to-analog converter outputs multiple independent radio frequency signals, each signal is processed by the electric amplifier, the attenuator, the bias device, the LED and the lens, the bias device superimposes direct current, and the electric amplifier, the attenuator, the bias device, the LED and the lens are all arrays; An optical receiving end, the optical receiving end includes a lens, a photodetector, an analog-to-digital converter, and a receiving end data processing module connected in sequence, the photodetector is an array, and the receiving end data processing module includes an integrated multi-user channel crosstalk elimination module; The underwater channel is located between the optical transmitter and the optical receiver.

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