An Underwater Wireless Optical Communication Method and Device for Integrated Multi-User Crosstalk Cancellation

Abstract

The present invention relates to the field of underwater wireless optical communication technology, and discloses a method and device for underwater wireless optical communication with integrated multi-user crosstalk cancellation, which can simultaneously eliminate inter-symbol interference, modulation non-linear distortion and multi-user channel interference, thereby improving the performance of the underwater wireless optical communication system with spatial multiplexing and enhancing the transmission rate of the underwater wireless optical communication system. The method includes the following steps: data processing at the transmitting end: generating multiple independent modulation signals, and outputting multiple signals after modulating binary data and inserting training sequences; signal conversion and driving: the multiple signals after digital-to-analog conversion are optimized in power by an electrical amplifier and an attenuator, and a direct current is superimposed by a biasing device to drive an array-type LED to work; optical transmission: the light output by multiple LEDs is expanded by respective corresponding convex lenses and then enters the underwater channel for transmission; receiving and preliminary processing: the light beam at the receiving end is converged by a convex lens and then detected by an array of photodetectors, and the converted multiple electrical signals are synchronously sampled and analyzed.

Description

Technical Field

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

[0002] In recent years, the rapidly developing technologies such as autonomous underwater vehicles (AUVs), remotely operated underwater vehicles (ROVs), and undersea observatory networks have provided technical support and guarantee for ocean monitoring and exploration. With the continuous increase in the number of these underwater platforms, the amount of data to be transmitted has increased sharply, 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, strong confidentiality, etc., and can support high-speed data transmission over distances of dozens to hundreds of meters. In existing underwater wireless optical communication systems, multiplexing technologies mainly adopt wavelength division multiplexing, spatial multiplexing, and time division multiplexing. In a spatial multiplexing system, there are not only channel crosstalks in its own link among multiple users, such as inter-symbol interference caused by bandwidth limitation, modulation nonlinear distortion caused by the non-ideality of optoelectronic devices, etc., but also interference of data streams among multi-user channels. Therefore, being able to simultaneously (integrally) cancel the inter-symbol interference caused by bandwidth limitation, the modulation nonlinear distortion of the system, and the interference among multi-user channels is of great significance for improving the performance of the spatial multiplexing system and enhancing the transmission rate of the existing underwater wireless optical communication system. Summary of the Invention

[0003] Aiming at the deficiencies in the prior art, the present invention provides an underwater wireless optical communication method and device for integrated multi-user crosstalk cancellation, which simultaneously cancels inter-symbol interference, modulation nonlinear distortion, and interference among multi-user channels, thereby improving the performance of the spatial multiplexing underwater wireless optical communication system and enhancing the transmission rate of the underwater wireless optical communication system.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] An underwater wireless optical communication method for integrated multi-user crosstalk cancellation includes the following steps:

[0006] Data processing at the transmitting end: generating multiple independent modulation signals, and outputting multiple signals after modulating binary data and inserting training sequences;

[0007] Signal conversion and driving: the multiple signals after digital-to-analog conversion are optimized in power by an electrical amplifier and an attenuator, and a direct current is superimposed by a biasing device to drive an array-type LED to work;

[0008] Optical transmission: the light output by multiple LEDs enters the underwater channel for transmission after being expanded by respective corresponding convex lenses;

[0009] Receiving and Preliminary Processing: The received beam at the receiving end is focused by a convex lens and then detected by an optoelectronic detector array, and the converted multi-channel electrical signals are synchronously sampled and analyzed;

[0010] Multi-user Crosstalk Cancellation and Signal Recovery: The sampled signals are resampled, synchronized, subjected to integrated multi-user channel crosstalk cancellation, demodulated, and bit error rate analyzed.

[0011] 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.

[0012] Preferably, the multi-user crosstalk cancellation adopts an integrated multi-user channel crosstalk cancellation module including a decision feedback equalizer, and this module recovers the transmitted data through a specific algorithm, where the i-th equalized signal is expressed as:

[0013]

[0014] 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 non-linear channel respectively; is the non-linear term pruning factor, , selecting an appropriate can effectively reduce the complexity of the non-linear equalizer; the coefficient represents the influence of the j-th channel on the i-th channel, is the memory length of the interference channel; is the tap coefficient of the decision feedback equalizer, and its memory length is; represents the symbol after decision.

[0015] Preferably, the matrix form of the multi-user crosstalk cancellation formula is:

[0016] ;

[0017] wherein, represents the transpose operation, and the specific expressions of other signal vectors are as follows:

[0018] .

[0019] Preferably, training sequences are used to accelerate the convergence rate of multi-user crosstalk coefficient estimation, and the specific steps are as follows:

[0020] Step 1: Set the counting value;

[0021] Step 2: Obtain the observation vector:

[0022] ;

[0023] Step 3: Update the error vector: , where is a known training sequence inserted by the transmitting end, has an initial value of 0;

[0024] Step 4: Calculate the gain vector: , has an initial value of the identity matrix, and update the relevant matrix: ;

[0025] Step 5: Update the coefficient vector: , increment the counter by 1, and determine whether the set count value is reached. If not, return to Step 2;

[0026] Step 6: Equalize multi-user crosstalk to obtain the equalized signal as: .

[0027] Device for an integrated multi-user crosstalk cancellation underwater wireless optical communication method, comprising:

[0028] An optical transmitting end, the optical transmitting end includes a transmitting end data processing module, a digital-to-analog converter, an electrical amplifier, an attenuator, a bias unit, an LED, and a lens connected in sequence. The digital-to-analog converter outputs multiple independent radio frequency signals, and each signal is processed by the electrical amplifier, attenuator, bias unit, LED, and lens. The bias unit superimposes direct current, and the electrical amplifier, attenuator, bias unit, LED, and lens are all arrays;

[0029] 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 cancellation module;

[0030] An underwater channel, located between the optical transmitting end and the optical receiving end.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The receiving end can eliminate inter-symbol interference caused by bandwidth limitation and modulation nonlinear distortion of the system by adopting decision feedback non-linear channel equalization. At the same time, it models and eliminates interference between multi-user channels, which is beneficial to improving the performance of the spatial multiplexing system, increasing the transmission capacity and distance, reducing the bit error rate under different water qualities, improving the reliability and transmission efficiency, performing well in terms of system latency, energy efficiency, etc., having good adaptability to different scenarios, and having reasonable device selection and algorithm complexity and resource requirements design. Description of the Drawings

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the accompanying drawings required in the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0034] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0035] Figure 2 It is a specific flowchart of the present invention.

[0036] Figure 3 It is a performance comparison diagram in tap water.

[0037] Figure 4 It is a performance comparison diagram in clean seawater.

[0038] Figure 5 It is a performance comparison diagram in coastal seawater. Specific embodiments

[0039] The following further describes the present invention in detail with reference to the accompanying drawings.

[0040] 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 in the following description are only examples, and those skilled in the art can think of other obvious deformations. The basic principles defined in the following description can be used in other implementation schemes, deformation schemes, improvement schemes, equivalent schemes, and other technical schemes without departing from the spirit and scope of the present invention.

[0041] Those skilled in the art should understand that in the disclosure of the present invention, the terms "longitudinal", "lateral", "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or position based on the orientation or position relationship shown in the accompanying drawings. It is only for the convenience of simplifying the description of the present invention, rather than indicating or implying that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting the present invention.

[0042] It can 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 can be one, and in other embodiments, the number of the element can be multiple. The term "one" should not be construed as limiting the quantity.

[0043] Embodiment:

[0044] Please refer to Figures 1-5, an underwater wireless optical communication method and device for integrated multi-user crosstalk cancellation, the device comprising:

[0045] An optical transmitter, which includes a transmitter data processing module, a digital-to-analog converter, an electrical amplifier, an attenuator, a bias unit, an LED, and a lens connected in sequence. The digital-to-analog converter outputs multiple independent radio frequency signals, and each signal is processed by the electrical amplifier, the attenuator, the bias unit, the LED, and the lens. The bias unit superimposes direct current, and the electrical amplifier, the attenuator, the bias unit, the LED, and the lens are all arrays;

[0046] An optical receiver, which includes a lens, a photodetector, an analog-to-digital converter, and a receiver data processing module connected in sequence. The photodetector is an array, and the receiver data processing module includes an integrated multi-user channel crosstalk cancellation module;

[0047] An underwater channel, located between the optical transmitter and the optical receiver.

[0048] The method steps are as follows:

[0049] Transmitter data processing: The transmitter data processing module is responsible for modulating multiple channels of original binary data, which can adopt single-carrier (such as on-off keying, pulse amplitude modulation, quadrature amplitude phase modulation) or multi-carrier (such as orthogonal frequency division multiplexing) methods, and the modulation format can be low-order or high-order. After modulation, a training sequence is inserted and multiple channels of signals are output;

[0050] Signal conversion and driving: The multiple channels of signals after digital-to-analog conversion are first input into the electrical amplifier. The electrical amplifier adopts an amplifier circuit with adjustable gain. According to the signal strength and transmission requirements, the signal is amplified to an appropriate power range to ensure the effectiveness of the signal in subsequent transmission; then it passes through the attenuator. The attenuator is based on a precision resistor network or other attenuation technologies to optimize the power of the amplified signal to meet the power requirements of underwater channel transmission, avoiding non-linear distortion caused by too high signal power or the receiver being unable to accurately detect due to too low signal power; finally, direct current is superimposed through the bias unit. The bias unit adopts a high-precision direct current bias circuit to provide an appropriate direct current bias voltage for the signal, ensuring that the array-type LED works at the best operating point and driving the array-type LED to work. The array-type LED adopts a special packaging structure and optical design to improve the light emission efficiency and directivity;

[0051] Optical transmission: The light output by multiple LEDs is expanded by corresponding convex lenses respectively. The convex lenses are designed according to the principle of optical refraction, and their focal lengths and radii of curvature are optimized to effectively expand the optical signal, reduce the divergence of the optical signal during underwater transmission, and improve the transmission efficiency and distance of the optical signal. The expanded optical signal enters the underwater channel for transmission. During the transmission process, the characteristics of the underwater channel, such as the absorption, scattering, and turbulence of water on the optical signal, are fully considered. These effects are reduced through the preprocessing of the optical signal (such as beam expansion) and the signal processing at the subsequent receiving end (such as multi-user crosstalk cancellation, etc.) to ensure the accurate and stable transmission of the optical signal.

[0052] Receiving and preliminary processing: The light beam at the receiving end is converged by a convex lens, which is matched with the beam-expanding convex lens at the sending end. According to the principle of optical imaging, the divergent optical 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 optical signal. The multiplexed electrical signals after detection are synchronously sampled and analyzed by a synchronous sampling circuit. The synchronous sampling circuit is based on a high-precision clock source and a sample-and-hold circuit to ensure the time synchronization of each signal 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.

[0053] Multi-user crosstalk cancellation and signal recovery: The sampled signal is resampled. The resampling process is based on digital signal processing algorithms. According to the spectral characteristics of the signal and the sampling theorem, an 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 uses a synchronization algorithm based on a training sequence or a pilot signal to ensure the accurate alignment of each signal in time and frequency. Next, crosstalk cancellation is performed through an integrated multi-user channel crosstalk cancellation module. This module uses advanced signal processing technologies, such as algorithms based on adaptive filtering and decision feedback equalization, to effectively suppress multi-user interference. After crosstalk cancellation, demodulation is performed. The demodulation process selects the corresponding demodulation algorithm according to the modulation method used at the sending end, such as coherent demodulation or non-coherent demodulation, to accurately recover the original binary data. Finally, bit error rate analysis is performed. By calculating the difference between the received data and the original transmitted data, the performance of the communication system is evaluated. The results of the bit error rate analysis are used to feedback and adjust the parameters of the communication system, such as the modulation method and power control, to optimize the system performance.

[0054] To more clearly illustrate the actual application process of the present invention, an embodiment with a typical scenario of 2 LEDs transmitting data and 2 photodetectors receiving data is used for illustration:

[0055] First, multiple channels of original binary data are modulated. After adding training sequences respectively, the transmitting - end data - processing module generates transmitted signals (taking 4 - PAM as an example). Then, multiple independent electrical signals are generated through a digital - to - analog converter (AWG, Tektronix 7122C). After the power of multiple electrical signals is optimized by electrical amplifiers and attenuators respectively, a DC bias is added through a biaser, and each drives an LED of the same model to work within the linear range. The emitted light from multiple LEDs is expanded and mixed by lenses and then incident on a 5 - meter - long underwater channel. At the receiving end, the light beam converged by the lens is converted into an electrical signal by an avalanche photodiode (Hamamatsu, 12702 - 11). Multiple electrical signals are sampled by an analog - to - digital converter (Tektronix, DSA72004C) and then sent to the receiving - end data - processing module. The receiving - end data - processing module resamples, synchronizes, eliminates the integrated multi - user channel crosstalk, demodulates the received signal to recover the binary data, and calculates the bit - error rate.

[0056] Specifically, taking the case of 2 LEDs transmitting data and 2 photodetectors receiving data as an example, the first - path and second - path signals after using the integrated multi - user crosstalk cancellation and can be respectively expressed as:

[0057] ;

[0058] where, and respectively represent the first - path and second - path channel signals received after passing through the channel; and are respectively the coefficient and memory length of the linear channel of the i - th channel; and are respectively the coefficient and memory length of the non - linear channel of the i - th channel; is the non - linear term trimming factor, , by selecting an appropriate the complexity of the non - linear equalizer can be effectively reduced; the coefficient represents the influence of the second channel on the first channel, and the coefficient represents the influence of the first channel on the second channel, is the memory length of the interference channel; is the tap coefficient of the decision - feedback equalizer, and its memory length is . and respectively represent the symbols after decision for the first channel and the second channel.

[0059] Furthermore, the matrix form of the multi - user crosstalk cancellation method adopted by the first user can be expressed as:

[0060] ;

[0061] Among them, represents the transpose operation, and the specific expressions of other signal vectors are as follows:

[0062] ;

[0063] Preferably, a training sequence is used to accelerate the convergence rate of multi-user crosstalk coefficient estimation. Specifically, the specific steps of the integrated multi-user crosstalk estimation and cancellation method are as follows:

[0064] Step S110: Set the counting value;

[0065] Step S120: Obtain the observation vector:

[0066] ;

[0067] Step S130: Update the error vector: , where is the known training sequence inserted by the transmitter, has an initial value of 0;

[0068] Step S140: Calculate the gain vector: , has an initial value of the identity matrix and updates the correlation matrix: ;

[0069] Step S150: Update the coefficient vector: , increment the counter by 1, and determine whether the set counting value has been reached. If not, return to step S120;

[0070] Step S160: Equalize multi-user crosstalk, and the equalized signal is: .

[0071] Experimental data and comparative analysis:

[0072] Figure 3Taking the 2 transmitters and 2 receivers spatial multiplexing underwater wireless optical communication system in tap water as an example, when using 4 - Pulse Amplitude Modulation (4 - PAM), the comparison diagrams of bit error rate versus transmission rate and bit error rate versus received optical power for the traditional method and the integrated multi - user crosstalk cancellation method disclosed in the embodiments of the present invention are shown. It can be seen from the figure that after adopting the integrated multi - user crosstalk cancellation method, the bit error rates of the two signals are significantly improved. In the low - transmission - rate region, the bit error rate of the traditional method is relatively high, while 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 upward trend of the bit error rate of the method of the present invention is relatively gentle and always 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 relatively low received optical power, indicating that it has a higher utilization efficiency of optical signals and stronger anti - interference ability.

[0073] Figure 4 and Figure 5 are respectively the comparison diagrams of bit error rate versus transmission rate and bit error rate versus received optical power for the traditional method and the integrated multi - user crosstalk cancellation method disclosed in the embodiments of the present invention, taking the 2 transmitters and 2 receivers spatial multiplexing underwater wireless optical communication system as an example in clean seawater and turbid seawater. Similarly, it can be seen that in clean seawater, the bit error rate of the method of the present invention at high transmission rates is significantly lower than that of the traditional method, and when the received optical power changes, the stability of the bit error rate is better; 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 increase of the bit error rate and maintain relatively good communication performance. This fully proves that the method of the present invention can effectively improve the system performance under different water quality conditions and adapt to complex underwater communication environments.

[0074] Those skilled in the art should understand that the embodiments of the present invention described above and shown in the drawings are only examples and do not limit the present invention. The object 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. Without departing from the said principles, the embodiments of the present invention can have any deformation or modification.

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, integrated multi-user channel crosstalk cancellation, demodulation and bit error rate analysis of the sampled signal; The modulation method of the binary data includes single carrier or multi-carrier, and the modulation format adopts low-order or high-order modulation; 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, , 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; A symbol indicating the post-judgment period; 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: ； 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: .

2. A device for implementing the underwater wireless optical communication method for eliminating multi-user crosstalk as described in claim 1, 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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