CN117498940B - Method and device for transmitting multi-system phase coding real-time data in space optical communication - Google Patents
Method and device for transmitting multi-system phase coding real-time data in space optical communication Download PDFInfo
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Abstract
本发明公开了一种空间光通信中多进制相位编码实时数据传输方法和装置。本发明中，在发射端对终端产生的视频信号进行编码压缩并将压缩后的视频信号发送给发射端FPGA主控模块，码型切换模块根据大气信道环境时变特性对通信链路的调制参数进行实时优化，获得优化调制参数，压缩后的视频信号和根据优化调制参数设定的伪随机序列数据流通过光电相位调制器进行发送；在接收端中信号接收模块将接收到的信号发送给接收端FPGA主控模块，对接收到的信号进行数字信号处理后发送给上位机显示。本发明解决了传统无线光通信系统中实时性不强且码型速率单一的问题，在实时数据处理和传输方面具有显著的优势，并为无线光通信技术的进一步发展提供了新的思路。
The present invention discloses a multi-level phase-coded real-time data transmission method and device in space optical communication. In the present invention, the video signal generated by the terminal is encoded and compressed at the transmitting end, and the compressed video signal is sent to the transmitting end FPGA main control module, the code switching module optimizes the modulation parameters of the communication link in real time according to the time-varying characteristics of the atmospheric channel environment, obtains the optimized modulation parameters, and the compressed video signal and the pseudo-random sequence data stream set according to the optimized modulation parameters are sent through the photoelectric phase modulator; the signal receiving module at the receiving end sends the received signal to the receiving end FPGA main control module, performs digital signal processing on the received signal, and sends it to the host computer for display. The present invention solves the problem of low real-time performance and single code rate in traditional wireless optical communication systems, has significant advantages in real-time data processing and transmission, and provides new ideas for the further development of wireless optical communication technology.
Description
Technical Field
The invention relates to a real-time data transmission method and device for space optical communication in the field of free space optical communication, in particular to a real-time data transmission method and device for multi-system phase coding in space optical communication.
Background
Free space optical communication is a wireless communication technology in which data transmission is performed in free space by using laser as a carrier. The laser has the characteristics of concentrated energy, small divergence angle and the like, and the laser has the advantages of large frequency bandwidth, strong anti-interference capability, difficult information theft and the like when used as a carrier wave, can avoid the limitation of wiring and physical connection, can be used for high-speed and reliable data transmission scenes, and is one of important directions of the development of wireless communication technology in the future.
With the increase of data volume, the demands of people for communication are continuously increased, and coherent optical communication has the characteristics of high detection sensitivity, high transmission rate, high spectrum utilization rate and the like, so that the coherent optical communication is paid attention to.
In a coherent optical communication system, multi-level phase coding is an important means for coping with increasing data demands and improving transmission efficiency, and it uses carrier signals of different phase states to represent digital information, and common MPSK modulation includes Binary Phase Shift Keying (BPSK), quaternary Phase Shift Keying (QPSK), and octal phase shift keying (8 PSK).
The modulation and demodulation research of the multi-system phase coding in the traditional space optical communication is mostly offline processing, can not make quick response to real-time scenes, has limited generality, and is difficult to be flexibly applied to an actual coherent optical communication system with higher requirements on real-time performance.
Real-time processing can process real-time data transmitted to the system at any time and synchronously output results, but has high requirements on computing resources. The FPGA has a large number of logic units, is programmable, has strong parallel processing capability and low delay, and can be applied to high-speed data processing and communication.
Disclosure of Invention
In order to solve the problems and the demands in the background technology, the invention provides a method and a device for carrying out real-time data transmission in space optical communication, which are used for carrying out real-time digital signal processing through an FPGA (field programmable gate array) and carrying out different multi-system phase code switching according to channel conditions, so as to realize multi-system coherent code transmission of real-time data and switching of different code types, solve the problems of instantaneity in a space optical communication system and link stability under severe atmospheric channel conditions, and more intuitively reflect the transmission quality of the communication system.
The technical scheme of the invention is as follows:
1. Multi-system phase coding real-time data transmission method in space optical communication
1) The method comprises the steps that in a transmitting end, video signals generated by a terminal are encoded and compressed, the compressed video signals are sent to a transmitting end FPGA main control module, the transmitting end FPGA main control module optimizes modulation parameters of a communication link in real time according to time-varying characteristics of an atmosphere channel environment to obtain optimized modulation parameters, a pseudo-random sequence data stream is set according to the optimized modulation parameters, and the compressed video signals and the pseudo-random sequence data stream are sent through a photoelectric phase modulator;
2) And in the receiving end, the signal receiving module sends the received signal to the receiving end FPGA main control module, and the receiving end FPGA main control module processes the digital signal of the received signal and sends the processed signal to the upper computer.
In the step 1), an FSO error rate is obtained by calculation according to time-varying characteristics of an atmosphere channel environment in a transmitting end FPGA main control module, when the FSO error rate is lower than a preset threshold lower limit, the order of a code pattern is improved on the basis of keeping the signal rate, and if the order of the code pattern cannot be improved, the signal rate is improved;
when the FSO error rate is higher than the upper limit of the preset threshold, the order of the code pattern is reduced on the basis of maintaining the signal rate, if the order of the code pattern cannot be reduced, the signal rate is reduced, and the other modulation parameters are unchanged.
In the step 2), the signal receiving module comprises an EDFA and a coherent receiver, and the optical signals of the transmitting end are sequentially transmitted to the receiving end FPGA main control module through the EDFA and the coherent receiver.
In the step 2), the receiving end FPGA main control module sequentially performs sampling clock recovery, channel equalization, carrier frequency offset estimation and compensation and carrier phase recovery on the received signals and then sends the signals to the upper computer.
2. Multi-system phase coding real-time data transmission device in space optical communication
The device comprises a transmitting end and a receiving end, wherein the transmitting end comprises a video encoder, a transmitting end FPGA main control module, a laser and a photoelectric phase modulator, the receiving end comprises an EDFA, a tunable laser, a coherent receiver, a receiving end FPGA main control module and an upper computer, the video encoder encodes and compresses data of a terminal and sends compressed data streams to the transmitting end FPGA main control module, the transmitting end FPGA main control module optimizes modulation parameters of a communication link in real time according to time-varying characteristics of an atmosphere channel environment to obtain optimized modulation parameters, then a pseudorandom sequence data stream is set according to the optimized modulation parameters, the laser is connected with the photoelectric phase modulator, the compressed video signals and the pseudorandom sequence data stream are sent through the photoelectric phase modulator, the tunable laser is connected with the coherent receiver, the receiving end sends received signals to the receiving end FPGA main control module through the EDFA and the coherent receiver, and the receiving end FPGA main control module carries out digital signal processing on the received signals and sends the signals to the upper computer.
The transmitting end FPGA main control module comprises a code pattern switching module, wherein the code pattern switching module calculates and obtains an FSO error rate according to the time-varying characteristic of the atmosphere channel environment, when the FSO error rate is lower than a preset threshold lower limit, the order of the code pattern is improved on the basis of keeping the signal rate, and if the order of the code pattern cannot be improved, the signal rate is improved;
when the FSO error rate is higher than the upper limit of the preset threshold, the order of the code pattern is reduced on the basis of maintaining the signal rate, if the order of the code pattern cannot be reduced, the signal rate is reduced, and the other modulation parameters are unchanged.
And the receiving end FPGA main control module sequentially performs sampling clock recovery, channel equalization, carrier frequency offset estimation and compensation and carrier phase recovery on the received signals and then sends the signals to the upper computer.
The invention provides a real-time data transmission scheme aiming at space laser communication multi-system phase coding based on an FPGA development board, and solves the problem of weak real-time performance in the traditional wireless optical communication system. This solution has significant advantages in real-time data processing and transmission and provides a new solution for further developments in wireless optical communication technology.
The beneficial effects of the invention are as follows:
the invention provides a scheme of real-time data transmission based on the FPGA by utilizing the parallel processing capability and low delay characteristic of the FPGA, and a logic circuit in the FPGA immediately responds and processes the data in real time, so that the method can be applied to fields with higher real-time requirements and can more intuitively reflect the performance of a communication system.
The invention also uses the programmability of the FPGA to switch the multi-system phase codes according to different channel conditions. This means that the present invention can dynamically select an optimal coding scheme according to the real-time channel quality, thereby further improving the reliability and efficiency of data transmission. This flexibility enables the solution of the present invention to adapt to optical communication needs in different environments and provide better performance.
Drawings
Fig. 1 is a schematic diagram of a real-time optical communication system.
Fig. 2 is a schematic diagram of a transmitting end FPGA master control module.
Fig. 3 is a schematic diagram of a pattern switching module.
Fig. 4 is a schematic diagram of a receiving-end FPGA master control module.
Detailed Description
The following describes the embodiment of the present invention with reference to the drawings.
Fig. 1 is a schematic diagram of a real-time optical communication system. The method comprises the following steps:
1) In the transmitting end, video signals generated by the PC end are encoded and compressed, the compressed video signals are sent to the FPGA main control module of the transmitting end, data between the encoder and the FPGA are sent in a network mode, the adopted network protocol is UDP, the development board main control module firstly analyzes the UDP protocol, and then the data are sent in an electric signal mode through the external DAC module. The code pattern switching module in the FPGA main control module of the transmitting end optimizes the modulation parameters of the communication link in real time according to the time-varying characteristic of the atmosphere channel environment to obtain optimized modulation parameters, wherein the modulation parameters of the communication link comprise code patterns and speed, stable and reliable information transmission is realized among nodes of the laser communication link, a pseudo-random sequence data stream is set according to the optimized modulation parameters, and compressed video signals and the pseudo-random sequence data stream are transmitted through the photoelectric phase modulator;
the video signal of the PC end is used for compressing the digital video signal, the size of the video data is reduced by reducing redundancy and unnecessary information of the video data, and higher efficiency is provided in the transmission and storage process. The coding format, code rate and resolution of the video coder can be adjusted, and the coded data stream is output to a main control FPGA development board of the transmitting end in the form of network TS stream. The selected development board chip model is Xilinx Artix series, the cost is lower, the use scene is wider, the development board resources are sufficient and the development board chip contains rich interfaces, and the design requirement can be met. The real-time data analyzed by the UDP protocol or the signal generated by the code type switching module is transmitted through the DA module, and the UDP protocol is selected because the UDP protocol does not need to establish connection before transmitting the data or maintain the connection state after transmitting the data, and the data can be transmitted more quickly, so that the UDP protocol is widely used in real-time audio and video streaming. And outputting a radio frequency signal through an SMA interface, loading the radio frequency signal on two arms of an IQ phase modulator, and modulating the radio frequency signal on 1550nm optical signals output by a laser. The electrical signal after development of the board is photoelectrically converted by an IQ phase modulator, and the electrical signal is modulated onto an optical signal, in conventional binary coding, each symbol can only carry one bit of information, and in multilevel coding, one symbol can represent more bits. The QPSK modulation used in the invention has 0 degree, 90 degree, 180 degree and 270 degree, each symbol can transmit two bits of information, and the capacity of the channel for transmitting data is multiplied. The optical signal loaded with data is diverged from the optical fiber to the space by the collimating mirror, and the signal damage caused by the atmospheric turbulence is simulated by the rotating phase screen. The code type switching module determines the selected modulation order and data rate according to the turbulence intensity, the data rate is switched between 5Gbps,10Gbps and 20Gbps, when the modulation order selects the second-order BPSK modulation, the pseudo-random sequence only needs to be sent in a single channel, one arm of the phase modulator is driven to modulate, when the modulation order selects the fourth-order QPSK modulation, the pseudo-random sequence is split into two channels by odd-even bits, two arms of the modulator are driven, and different modulation rates and formats are subjected to parameter modification in a receiving end program.
The method comprises the steps that a code pattern switching module of a transmitting end FPGA main control module calculates and obtains an FSO error rate according to time-varying characteristics of an atmosphere channel environment, when the FSO error rate is lower than a preset threshold lower limit, the order of the code pattern is improved on the basis of keeping the signal rate, and if the order of the code pattern cannot be improved, namely the code pattern is optimal, the signal rate is improved;
when the FSO error rate is higher than the upper limit of the preset threshold, the order of the code pattern is reduced on the basis of maintaining the signal rate, if the order of the code pattern cannot be reduced, namely the code pattern is the lowest, the signal rate is reduced, and other modulation parameters are unchanged.
The code type switching module in fig. 2 switches the phase shift keying signals of different orders in real time according to different channel conditions, and fully considers the transmission capacity and the link quality. High-rate and multi-system phase modulation is adopted when the atmospheric channel condition is good, and low-rate and low-system phase modulation is adopted when the channel condition is bad. And (3) defining a counter through the FPGA, and generating one or two paths of pseudo-random sequences with different rates to realize the conversion of the electric signals.
Fig. 3 is a schematic diagram of a pattern switching module. Assuming that the initial transmission signal is a BPSK signal of 5Gbps, the upper and lower limits of the tolerance bit error rate threshold of the spatial optical communication link are set according to the channel condition. If the real-time FSO error rate is below the threshold lower limit, which indicates that the channel condition is good at this time, an attempt may be made to switch patterns and rates. For convenience, the signal rate is not changed, two paths of electric signals are generated, two paths of IQ modulators are driven simultaneously, so that QPSK signals of 5Gbps can be obtained, and if the error rate is still lower than the lower threshold value, the signal rate is switched to a higher signal rate.
Similarly, when the calculated bit error rate is higher than the upper threshold, the rate needs to be reduced and the bit error rate is switched to a lower-order code pattern, so that the bit error rate is always stable within the threshold range. When the bit error rate is between the upper and lower thresholds, the rate and pattern are maintained.
2) And the signal receiving module in the receiving end sends the received signal to the receiving end FPGA main control module, and the receiving end FPGA main control module processes the digital signal of the received signal and sends the processed signal to the upper computer.
The signal receiving module comprises an erbium-doped fiber amplifier (EDFA) and a coherent receiver, and the optical signals of the transmitting end are sequentially transmitted to the receiving end FPGA main control module through the EDFA and the coherent receiver. And outputting an I path signal and a Q path signal under a certain polarization state, amplifying by AGC, and inputting the amplified signals into a receiving end FPGA main control module through an AD acquisition module. The coherent receiver mixes the local oscillation light and the signal light, improves the receiving sensitivity and completes the photoelectric signal conversion.
As shown in fig. 4, fig. 4 is a main structure of the receiving end FPGA main control module, and mainly includes a digital signal processing, DDR storage and HDMI display module. The DSP section includes several steps of signal preprocessing, clock recovery, channel equalization, and phase estimation. The receiving end FPGA main control module sequentially performs sampling clock recovery, channel equalization, carrier frequency offset estimation and compensation and carrier phase recovery on the received signals and then sends the signals to the upper computer.
The signal preprocessing refers to normalization, de-shifting and orthogonalization of signals. De-skew refers to compensating for the bias in the sampling instants of the I and Q paths, and orthogonalization is the step of recovering the quadrature signal by causing amplitude and phase mismatch through the modulator and mixer.
In high-speed data transmission, the clock of the receiving end may deviate from the clock of the transmitting end, so that data is not synchronous, and clock recovery eliminates the deviation by sampling the received data and adjusting the clock frequency phase, so that the receiving end can accurately analyze the data. Clock recovery is performed based on a phase-locked loop PLL, and the phase relationship between the received data and the local clock is compared to dynamically adjust the own clock frequency and phase to keep the same.
The polarization state in the optical fiber channel changes randomly along with the transmission process, and the self-adaptive channel equalization after passing through the coherent receiver can compensate the change of the polarization state. The CMA constant modulus algorithm is adopted, is insensitive to carrier phase, and eliminates intersymbol interference of signals and de-polarization multiplexing by estimating channels.
The VVPE algorithm is adopted as carrier phase estimation, which is also called M-th phase estimation, and the front and back conjugate of the received signal are multiplied to obtain a phase difference, so that the phase damage caused by the line width of the laser is removed, then the M-th power is carried out on the M-PSK encoded signal, the influence of the signal modulation phase is removed, and the phase deviation correction is completed.
Considering the size of data, DDR3 memory on a development board is needed, which is a common memory at present and can be applied to the requirements of large memory, high bandwidth and low delay. The DDR3 control module is used for driving the off-chip memory, and the DDR3 complex read-write operation is packaged into a FIFO-like user interface, so that the use is simplified.
The digital signal processed signal needs to be restored to its original form for comparison. The HDMI display module encodes the pixel data into a video signal format conforming to HDMI protocol standard, and drives an HDMI chip on the development board to convert the encoded signal into an HDMI signal which can be received by the display, and then outputs the HDMI signal to the upper computer for display through a corresponding interface.
The invention realizes the real-time demodulation of the multi-system phase coding signal in the coherent optical communication through the FPGA digital signal processing algorithm, designs the code pattern conversion module to better consider the transmission quality and the capacity, meets the requirement of high speed in the coherent optical communication system, and has stronger practicability.
The multi-system phase coding real-time data transmission device in space optical communication mainly comprises a transmitting end, a receiving end and an intermediate analog atmosphere channel, wherein the transmitting end comprises a video encoder, a transmitting end FPGA main control module, a laser and a photoelectric phase modulator, the intermediate analog atmosphere channel is generated by a rotary phase plate method, special materials are smeared on the plate to generate random phases, the phase plate is arranged to rotate at different rotating speeds to simulate atmospheric turbulence, the receiving end comprises an EDFA, a tunable laser, a coherent receiver, a receiving end FPGA main control module and an upper computer, the video encoder encodes and compresses data of a terminal and sends compressed data streams to the transmitting end FPGA main control module, the transmitting end FPGA main control module optimizes modulation parameters of a communication link in real time according to the time-varying characteristics of the environment of the atmosphere channel, obtains optimized modulation parameters, sets pseudo-random sequence data streams according to the optimized modulation parameters, the laser is connected with the photoelectric phase modulation, compressed video signals and the pseudo-random sequence data streams are transmitted from the optical fibers through the photoelectric phase modulator, are coupled to the atmosphere through a collimating mirror, the optical fibers are collimated and coupled to the receiving end in space, and then transmitted back to the coherent receiver through the receiving end, and the receiving end is connected with the receiving end of the FPGA main control module, and the receiving end receives signals are transmitted to the coherent receiver through the FPGA.
The invention provides a real-time data transmission scheme aiming at space laser communication multi-system phase coding based on an FPGA development board, and solves the problem of weak real-time performance in the traditional wireless optical communication system. This solution has significant advantages in real-time data processing and transmission and provides a new solution for further developments in wireless optical communication technology.
The foregoing is merely illustrative of the embodiments of the present application, and the present application is not limited thereto, and any minor variations or substitutions within the technical scope of the present application as claimed by those skilled in the art should be included in the scope of the present application.
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