Space laser communication device

Abstract

The invention discloses a space laser communication device, and relates to the technical field of laser communication. The system comprises a protocol stack module, an Aurora Ethernet data forwarding module, a ground monitoring instruction issuing module, an RS422 serial port transceiving module, an LVDS link state reporting module, a laser link channel monitoring module, a self-adaptive rate switching module, a rate gear identification module, a sending channel and a receiving channel. The sending channel comprises a first CRC verification module, a PN code filling module, an LDPC coding module, an interleaving module and a first GTX serial-parallel conversion module. The receiving channel comprises a second CRC verification module, a PN code deletion module, an LDPC decoding module, a de-interleaving module and a second GTX serial-parallel conversion module. According to the invention, an anti-turbulence effect can be achieved in a digital domain, so that high rate and low error code of data transmission are ensured; on the premise of ensuring the transmission rate, the reliability is improved, and the performance of the optical system is improved.

Description

Technical Field

[0001] The present invention relates to the field of laser communication technology, and in particular to a space laser communication device. Background Art

[0002] With the development of the information age, the amount of information transmission is growing exponentially. Traditional microwave communication systems can no longer meet the needs of users, and space laser communication systems have attracted widespread attention for their higher capacity, larger bandwidth, and faster communication rate. Space laser communication technology combines the advantages of optical fiber communication and microwave communication. It does not require the laying of optical fibers, avoiding the problem of spectrum limitation. At the same time, this technology does not require approval and can be used directly, which has obvious advantages.

[0003] Space laser communication technology has the advantages of strong anti-interference ability, high security, high communication rate, fast transmission speed, convenient band selection and large information capacity. Its characteristics are small system size, light weight, low power consumption, simple construction, flexibility and maneuverability. It has great strategic needs and application value.

[0004] Space laser communication technology is an ideal choice for solving the "last kilometer" problem of information transmission due to its high bandwidth and fast transmission characteristics. Especially in 5G micro-base station transmission, its advantages are more obvious, providing technical support for the coverage and optimization of 5G networks. In addition, space laser communication technology is also used in satellite Internet, road traffic safety and other fields, and can also be used as an emergency communication solution for emergencies.

[0005] However, space laser communication is susceptible to atmospheric turbulence effects. Atmospheric turbulence effects refer to the state of fluid motion caused by irregular changes in temperature and density in the atmosphere, which will affect the propagation of light waves and cause the quality of the beam to deteriorate. On the surface of the earth, hot air rises and cold air sinks, forming air convection, resulting in irregular changes in temperature and density at various points in the atmosphere. This change varies with altitude and wind speed. When the change is more drastic, turbulence is formed. The refractive index of the atmosphere depends on density, so the refractive index of the atmosphere also changes irregularly with space and time. Atmospheric turbulence is mainly manifested as intensity fluctuations, phase fluctuations, and direction fluctuations in the propagation of the light beam. These effects will seriously affect the quality of the light beam, resulting in intensity flickering within the beam cross section, bending and drifting of the beam (directional jitter), beam dispersion distortion, and spatial coherence degradation. In laser communication systems, atmospheric turbulence will cause signal quality to deteriorate and increase the bit error rate, thereby affecting the reliability and stability of communication. In addition, atmospheric turbulence will also affect the quality of optical imaging, resulting in image blur and geometric distortion, which to a certain extent limits the application of optical technology in various fields. Summary of the invention

[0006] In view of this, the present invention proposes a space laser communication device. The present invention can play an anti-turbulence role in the digital domain to ensure high data transmission rate and low bit error; improve reliability while ensuring the transmission rate, and improve the performance of the optical system.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A space laser communication device, comprising a protocol stack module, an Aurora Ethernet data forwarding module, a sending channel and a receiving channel;

[0009] The sending channel includes a first CRC check module, a PN code filling module, an LDPC encoding module, an interleaving module and a first GTX serial-to-parallel conversion module; the receiving channel includes a second CRC check module, a PN code deletion module, an LDPC decoding module, a deinterleaving module and a second GTX serial-to-parallel conversion module;

[0010] The protocol stack module is used to configure the IP address and Mac address of its own space laser communication device. In addition, during the transmission process, the protocol stack module filters the Ethernet data packets transmitted by the connected hardware platform according to the Ethernet frame type, next packet header, port number, source Mac address, destination Mac address, source IP address and destination IP address, and transmits the Ethernet data packets that meet the requirements to the Aurora Ethernet data forwarding module;

[0011] During the receiving process, the protocol stack module receives the Ethernet data packet transmitted by the Aurora Ethernet data forwarding module, compares the IP address field of the Ethernet frame with the real-time IP address information of the connected hardware platform, finds the corresponding Mac address and replaces it with the destination Mac address field of the Ethernet frame; and performs CRC check on the Ethernet frame: calculates the header checksum field of the IP datagram, the UDP checksum field and the frame check sequence field of the Ethernet frame, and adds the calculation result to the Ethernet frame and sends it to the connected hardware platform;

[0012] During the sending process, the Aurora Ethernet data forwarding module is used to receive the Ethernet data packets transmitted by the protocol stack module, perform byte splicing on the Ethernet data packets, and transmit them to the sending channel; during the receiving process, the Aurora Ethernet data forwarding module is used to perform byte disassembly on the Ethernet data packets transmitted by the receiving channel, and transmit them to the protocol stack module;

[0013] In the sending channel, the first CRC check module receives the Ethernet data packet transmitted by the Aurora Ethernet data forwarding module, calculates the CRC check code, adds the CRC check code to the end of the Ethernet frame, and then transmits it to the PN code filling module;

[0014] The PN code filling module receives the Ethernet data packet transmitted by the first CRC check module, expands the Ethernet data packet to the fixed length required by the LDPC encoding module using the PN code, and then transmits it to the LDPC encoding module;

[0015] The LDPC encoding module receives the Ethernet data packet transmitted by the PN code filling module, adds redundancy to the Ethernet data packet according to the LDPC code, and transmits it to the interleaving module;

[0016] The interleaving module is provided with an interleaving matrix, which writes data in row order for the Ethernet data packets transmitted by the LDPC encoding module, and outputs the data in column order to the first GTX serial-to-parallel conversion module;

[0017] The first GTX serial-to-parallel conversion module converts the parallel data output by the interleaving module into serial data, and transmits it to the optical antenna for transmission;

[0018] In the receiving channel, the second GTX serial-to-parallel conversion module receives serial data transmitted by the optical antenna, converts the serial data into parallel data, and transmits the parallel data to the deinterleaving module;

[0019] The deinterleaving module is provided with a deinterleaving matrix, which writes data in column order for the parallel data transmitted by the second GTX serial-to-parallel conversion module, and outputs the data to the LDPC decoding module in row order; the deinterleaving matrix is ​​the same size as the interleaving matrix;

[0020] The LDPC decoding module receives the data transmitted by the deinterleaving module, removes redundancy in the Ethernet data packet according to the LDPC code, and transmits it to the PN code removal module;

[0021] The PN code deletion module receives the data transmitted by the LDPC decoding module, deletes the PN code in the data, restores the Ethernet data packet, and transmits it to the second CRC check module;

[0022] The second CRC check module receives the Ethernet data packet transmitted by the PN code deletion module, extracts the CRC check code in the Ethernet data packet for verification, and transmits the Ethernet data packet to the Aurora Ethernet data forwarding module when the CRC check is correct.

[0023] Furthermore, it also includes an LVDS link status reporting module, a laser link channel monitoring module, an adaptive rate switching module and a rate gear identification module;

[0024] The laser link channel monitoring module counts the Ethernet data packets output by the second CRC check module, and obtains the link establishment time, communication rate, rate gear and bit error rate of the link in real time; transmits the link establishment time, communication rate, rate gear and bit error rate to the LVDS link status reporting module, and transmits the bit error rate to the adaptive rate switching module;

[0025] The LVDS link status reporting module receives the link establishment time, communication rate, rate gear and bit error rate transmitted by the laser link channel monitoring module, and transmits them to the connected hardware platform through the protocol stack module for reporting;

[0026] The adaptive rate switching module is provided with a plurality of gear thresholds, and corresponding leading structures are provided for different gears; the adaptive rate switching module receives the bit error rate transmitted by the laser link channel monitoring module, compares the bit error rate with the plurality of gear thresholds, obtains the corresponding gear information and transmits it to the PN code filling module and the LDPC encoding module; and adds the leading structure corresponding to the latest gear information to the data frame header output by the interleaving module;

[0027] The PN code filling module performs corresponding PN code filling on the Ethernet data packet transmitted by the first CRC check module according to the gear information transmitted by the adaptive rate switching module; wherein the length of the Ethernet data packet output by the PN code filling module to the LDPC encoding module is fixed, and the higher the gear, the greater the number of double bytes occupied by the service information in each Ethernet data packet;

[0028] The LDPC encoding module adds corresponding redundancy to the Ethernet data packet transmitted by the PN code filling module in combination with the LDPC code according to the gear information transmitted by the adaptive rate switching module. The higher the gear, the higher the code rate of the LDPC encoding module. The code rate of the LDPC encoding module is: the result obtained by dividing the number of double bytes occupied by the business information in the Ethernet data packet output from the PN code filling module to the LDPC encoding module by the number of double bytes of the Ethernet data packet.

[0029] The rate gear identification module parses the data frame header output by the second GTX serial-to-parallel conversion module to obtain the gear information of the data output by the second GTX serial-to-parallel conversion module, and transmits the gear information to the PN code deletion module and the LDPC decoding module;

[0030] The LDPC decoding module deletes the corresponding redundancy in the output data of the deinterleaving module according to the gear information transmitted by the rate gear identification module and in combination with the LDPC code, and transmits it to the PN code deletion module; the higher the gear, the higher the code rate of the LDPC decoding module, and the corresponding relationship between the code rate and the gear of the LDPC decoding module is consistent with the corresponding relationship between the code rate and the gear of the LDPC encoding module;

[0031] The PN code deletion module deletes the PN code in the data transmitted by the LDPC decoding module according to the gear information transmitted by the rate gear identification module, and transmits it to the second CRC check module; wherein, in the PN code deletion module, for different gears, the number of double bytes occupied by the business information in each Ethernet data packet is consistent with the PN code filling module.

[0032] Furthermore, it also includes a ground monitoring command sending module and an RS422 serial port transceiver module;

[0033] The ground monitoring instruction issuing module receives control information transmitted by the hardware platform via the protocol stack module, and drives the optical antenna according to the control information, wherein the control information includes piezoelectric, tracking and scanning control information of the optical antenna;

[0034] The RS422 serial port transceiver module receives the time synchronization information transmitted by the hardware platform via the protocol stack module, and transmits the time synchronization information to the optical antenna for time synchronization.

[0035] Due to the adoption of the above technical solution, the beneficial effects of the present invention compared with the prior art are:

[0036] 1. The present invention realizes the anti-turbulence effect in space laser communication through the design of interleaving and deinterleaving and LDPC encoding and decoding, ensures high data transmission rate and low bit error, and improves the performance of the optical system.

[0037] 2. The present invention supports adaptive rate switching. To ensure communication quality, three communication rates are designed according to the distance of communication. A higher communication rate is used when the distance is short and a lower communication rate is used when the distance is long, thereby improving reliability while ensuring the transmission rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the overall structure of a space laser communication device in an embodiment of the present invention.

[0039] Figure 2 Schematic diagram of the command forwarding relationship between ground monitoring, board card and optical antenna in an embodiment of the present invention.

[0040] Figure 3 The figure is a schematic diagram of a writing and reading process of a 4×5 group deinterleaver in an embodiment of the present invention.

[0041] Figure 4 Schematic diagram of transmitting end interleaving in an embodiment of the present invention.

[0042] Figure 5 Schematic diagram of deinterleaving at a receiving end in an embodiment of the present invention.

[0043] Figure 6 It is a statistical diagram of error correction performance at different bit rates in an embodiment of the present invention.

[0044] Figure 7 Schematic diagram of the cross-correlation rate gear identification process in an embodiment of the present invention.

[0045] Figure 8 Schematic diagram of the peak amplitude of the cross-correlation rate gear recognition in an embodiment of the present invention. DETAILED DESCRIPTION

[0046] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0047] A space laser communication device, such as Figure 1 As shown, it includes a protocol stack module, an Aurora Ethernet data forwarding module, a sending channel and a receiving channel;

[0048] The sending channel includes a first CRC check module, a PN code filling module, an LDPC encoding module, an interleaving module and a first GTX serial-to-parallel conversion module; the receiving channel includes a second CRC check module, a PN code deletion module, an LDPC decoding module, a deinterleaving module and a second GTX serial-to-parallel conversion module;

[0049] like Figure 2 As shown, the protocol stack module is used to configure the IP address and Mac address of its own space laser communication device. In addition, during the sending process, the protocol stack module filters the Ethernet data packets transmitted by the connected hardware platform according to the Ethernet frame type, next packet header, port number, source Mac address, destination Mac address, source IP address and destination IP address, and transmits the Ethernet data packets that meet the requirements to the Aurora Ethernet data forwarding module;

[0050] During the receiving process, the protocol stack module receives the Ethernet data packet transmitted by the Aurora Ethernet data forwarding module, compares the IP address field of the Ethernet frame with the real-time IP address information of the connected hardware platform, finds the corresponding Mac address and replaces it with the destination Mac address field of the Ethernet frame; and performs CRC check on the Ethernet frame: calculates the header checksum field of the IP datagram, the UDP checksum field and the frame check sequence field of the Ethernet frame, and adds the calculation result to the Ethernet frame and sends it to the connected hardware platform;

[0051] During the sending process, the Aurora Ethernet data forwarding module is used to receive the Ethernet data packets transmitted by the protocol stack module, perform byte splicing on the Ethernet data packets, and transmit them to the sending channel; during the receiving process, the Aurora Ethernet data forwarding module is used to perform byte disassembly on the Ethernet data packets transmitted by the receiving channel, and transmit them to the protocol stack module;

[0052] In the sending channel, the first CRC check module receives the Ethernet data packet transmitted by the Aurora Ethernet data forwarding module, calculates the CRC check code, adds the CRC check code to the end of the Ethernet frame, and then transmits it to the PN code filling module;

[0053] The PN code filling module receives the Ethernet data packet transmitted by the first CRC check module, expands the Ethernet data packet to the fixed length required by the LDPC encoding module using the PN code, and then transmits it to the LDPC encoding module;

[0054] The LDPC encoding module receives the Ethernet data packet transmitted by the PN code filling module, adds redundancy to the Ethernet data packet according to the LDPC code, and transmits it to the interleaving module;

[0055] like Figure 4 As shown, the interleaving module is provided with an interleaving matrix, which writes data in row order for the Ethernet data packets transmitted by the LDPC encoding module, and outputs the data in column order to the first GTX serial-to-parallel conversion module;

[0056] The first GTX serial-to-parallel conversion module converts the parallel data output by the interleaving module into serial data, and transmits it to the optical antenna for transmission;

[0057] In the receiving channel, the second GTX serial-to-parallel conversion module receives serial data transmitted by the optical antenna, converts the serial data into parallel data, and transmits the parallel data to the deinterleaving module;

[0058] like Figure 3 , Figure 5 As shown, the deinterleaving module is provided with a deinterleaving matrix, which writes data in column order for the parallel data transmitted by the second GTX serial-to-parallel conversion module, and outputs the data to the LDPC decoding module in row order; the deinterleaving matrix is ​​the same size as the interleaving matrix;

[0059] The LDPC decoding module receives the data transmitted by the deinterleaving module, removes redundancy in the Ethernet data packet according to the LDPC code, and transmits it to the PN code removal module;

[0060] The PN code deletion module receives the data transmitted by the LDPC decoding module, deletes the PN code in the data, restores the Ethernet data packet, and transmits it to the second CRC check module;

[0061] The second CRC check module receives the Ethernet data packet transmitted by the PN code deletion module, extracts the CRC check code in the Ethernet data packet for verification, and transmits the Ethernet data packet to the Aurora Ethernet data forwarding module when the CRC check is correct.

[0062] Furthermore, if Figure 1 As shown, it also includes an LVDS link status reporting module, a laser link channel monitoring module, an adaptive rate switching module and a rate gear identification module;

[0063] The laser link channel monitoring module counts the Ethernet data packets output by the second CRC check module, and obtains the link establishment time, communication rate, rate gear and bit error rate of the link in real time; transmits the link establishment time, communication rate, rate gear and bit error rate to the LVDS link status reporting module, and transmits the bit error rate to the adaptive rate switching module;

[0064] The LVDS link status reporting module receives the link establishment time, communication rate, rate gear and bit error rate transmitted by the laser link channel monitoring module, and transmits them to the connected hardware platform through the protocol stack module for reporting;

[0065] The adaptive rate switching module is provided with a plurality of gear thresholds, and corresponding leading structures are provided for different gears; the adaptive rate switching module receives the bit error rate transmitted by the laser link channel monitoring module, compares the bit error rate with the plurality of gear thresholds, obtains the corresponding gear information and transmits it to the PN code filling module and the LDPC encoding module; and adds the leading structure corresponding to the latest gear information to the data frame header output by the interleaving module;

[0066] The PN code filling module performs corresponding PN code filling on the Ethernet data packet transmitted by the first CRC check module according to the gear information transmitted by the adaptive rate switching module; wherein the length of the Ethernet data packet output by the PN code filling module to the LDPC encoding module is fixed, and the higher the gear, the greater the number of double bytes occupied by the service information in each Ethernet data packet;

[0067] The LDPC encoding module adds corresponding redundancy to the Ethernet data packet transmitted by the PN code filling module in combination with the LDPC code according to the gear information transmitted by the adaptive rate switching module. The higher the gear, the higher the code rate of the LDPC encoding module. The code rate of the LDPC encoding module is: the result obtained by dividing the number of double bytes occupied by the business information in the Ethernet data packet output from the PN code filling module to the LDPC encoding module by the number of double bytes of the Ethernet data packet.

[0068] The rate gear identification module parses the data frame header output by the second GTX serial-to-parallel conversion module to obtain the gear information of the data output by the second GTX serial-to-parallel conversion module, and transmits the gear information to the PN code deletion module and the LDPC decoding module;

[0069] The LDPC decoding module deletes the corresponding redundancy in the output data of the deinterleaving module according to the gear information transmitted by the rate gear identification module and in combination with the LDPC code, and transmits it to the PN code deletion module; the higher the gear, the higher the code rate of the LDPC decoding module, and the corresponding relationship between the code rate and the gear of the LDPC decoding module is consistent with the corresponding relationship between the code rate and the gear of the LDPC encoding module;

[0070] The PN code deletion module deletes the PN code in the data transmitted by the LDPC decoding module according to the gear information transmitted by the rate gear identification module, and transmits it to the second CRC check module; wherein, in the PN code deletion module, for different gears, the number of double bytes occupied by the business information in each Ethernet data packet is consistent with the PN code filling module.

[0071] Furthermore, if Figure 1 As shown, it also includes a ground monitoring command sending module and an RS422 serial port transceiver module;

[0072] The ground monitoring instruction issuing module receives control information transmitted by the hardware platform via the protocol stack module, and drives the optical antenna according to the control information, wherein the control information includes piezoelectric, tracking and scanning control information of the optical antenna;

[0073] The RS422 serial port transceiver module receives the time synchronization information transmitted by the hardware platform via the protocol stack module, and transmits the time synchronization information to the optical antenna for time synchronization.

[0074] Specifically, the key technologies used in the present invention are as follows:

[0075] 1) Error correction coding technology. Error correction coding technology adds some additional redundant information to the original information, so that the receiver can detect and correct errors after receiving the signal. It is widely used in wireless communications, satellite communications, digital television and other fields. Common error correction codes include Hamming codes, Reed-Solomon codes, convolutional codes, etc. Among these codes, LDPC is the error correction code with higher reliability and error correction efficiency. LDPC code is a linear code that is widely used in many wireless communication standards, such as Wi-Fi, DVB-S2, 5G, etc. The use of LDPC error correction coding can correct the errors caused by atmospheric turbulence to a certain extent.

[0076] 2) Interleaving technology. Interleaving technology is used to distribute the transmitted information bits in the time domain or frequency domain or both. The interleaver shuffles the code elements within the range of several packet lengths or several constraint lengths so that the burst errors of the channel can be spread in time, so that the decoder can treat them as random errors. Interleaving will inevitably introduce delay in the system because the order of the received bits is different from the order of the bits sent by the transmitting source. This delay is determined by the interleaving depth.

[0077] 3) Adaptive rate switching technology: Adaptive rate switching technology aims to constantly sense the communication quality of the channel, thereby adjusting the data transmission rate of the transmitter and increasing the LDPC coding rate in exchange for higher reliability.

[0078] 4) Protocol stack technology. The TCP / IP protocol stack is the sum of a series of network protocols and is the core framework of network communication. The TCP / IP protocol adopts a 4-layer structure, namely the application layer, transport layer, network layer and link layer. The ground network works at the application layer, the FPGA works at the link layer, and the device works at the physical layer. In order to realize the control of the device by the ground network and obtain the information of the device in real time, the FPGA is required as a relay to complete the forwarding of instructions and the reporting of status. The present invention defines the protocol stack function at the PL end and realizes the network access of the device.

[0079] 5) Cross-link data fusion technology. In response to different channel conditions, the system can adaptively switch RF and laser channels to maximize communication quality.

[0080] like Figure 1 As shown, the board models used in this embodiment are XIKINX Z-7 (XC7Z045) and V-7 (XC7VX690T), which have functions such as address resolution, protocol conversion, label switching, serial / parallel and parallel / serial conversion, and realize high-speed transmission and reception of data packets. The XIKINX Z-7 (XC7Z045) board is used to implement the protocol stack module, the ground monitoring command sending module, the Aurora Ethernet data forwarding module and the LVDS link status reporting module; the protocol stack module is connected to the host PC A, and the V-7 (XC7VX690T) board is used to implement the RS422 serial port transceiver module, the first CRC check module, the PN code filling module, the LDPC encoding module, the interleaving module and the first GTX serial-to-parallel conversion module, the second CRC check module, the PN code deletion module, the LDPC decoding module, the deinterleaving module, the second GTX serial-to-parallel conversion module, the laser link channel monitoring module, the adaptive rate switching module and the rate gear recognition module;

[0081] Each board includes a JTAG interface module, a crystal oscillator, a FLASH module, an SFP transceiver module, a high-speed serial-to-parallel conversion module, a LVDS module, a serial port driver module, a data storage module and an FPGA chip.

[0082] The JTAG interface module is mainly used to download programs and burn fixed bit files.

[0083] The V7 board uses a 25M crystal oscillator as the system clock, and the Z7 board uses a 33.3M crystal oscillator as the system clock. The 25M clock of the V7 is multiplied by 125M and 200M, which are used as the reference clock of the high-speed transceiver MGT and the system clock of the baseband algorithm respectively, while the 50M clock of the Z7 is used to multiply the reference clocks of 125M and 150M for use by the Gigabit IP core and SSD storage module.

[0084] The FLASH module is used to store programs and register configurations of the programmable clock chip. When the board is powered on, the program stored in the FLASH is burned into the FPGA chip and the programmable clock chip is configured to achieve synchronous output of the reference clock.

[0085] The SFP optical module is a hot-swappable small package module. It is an interface device that converts electrical signals into optical signals, realizing photoelectric conversion. The transmission rates of the SFP optical module are 100M and 1G, and the SFP+ optical module is an enhanced version of the SFP optical module with a transmission rate of 10G. The SFP transceiver module of the XIKINX KINTEX-7 board has a total of four Ethernet interfaces (LAN interface) for data communication with the hardware platform or host. Two of the interfaces use SFP electrical port optical modules to receive Gigabit Ethernet data, and two interfaces use SFP+ optical port optical modules to receive 10G Ethernet data. The received Ethernet data is sent to the FPGA chip through four G-bit transceivers (GTX).

[0086] In order to improve the transmission bandwidth, serial communication is used between different boards for high-speed data transmission. The high-speed serial-to-parallel conversion module uses MGT (G-bit transceiver) data transmission link to realize the serial-to-parallel conversion function. In Virtex7, MGT is called GTX / GTH / GTZ. The maximum line rate of GTX is 12.5Gb / s, the maximum line rate of GTH is 13.1Gb / s, and the maximum line rate of GTZ is 28.05Gb / s.

[0087] LVDS module, LVDS is a low voltage differential signal technology interface, it transmits data through differential on two PCB traces or balanced cables, the rate can reach several hundred Mb / s, it has the advantages of high transmission rate, strong anti-interference ability, low power consumption, etc., it is very suitable for high-speed bidirectional data transmission system.

[0088] The serial port driver module uses 2 RS422 (control and debug interface) to realize serial port communication with the FPGA chip to send clock synchronization information.

[0089] The data storage module uses DDR3 chip (model MT41J256M16HA-125) with advantages of low power consumption and heat generation, higher operating frequency, and good versatility. It is suitable for large-capacity data storage under high transmission rates of 1000 or 10000. For larger capacity data storage, onboard SSD is used.

[0090] 1. Protocol stack module

[0091] In this embodiment, the protocol stack module is mainly used to connect to the switch and receive and forward different types of Ethernet data packets. At the sending end, the Ethernet data packets sent by the PC need to be filtered, and only the data packets that meet the requirements can be sent to the Aurora Ethernet data forwarding module. The filtering content mainly includes the Ethernet frame type, the next packet header, the port number, the MAC address, the source IP address, and the destination IP address. And configure the IP address and Mac address of the board as follows Figure 2 As shown, Ethernet data packets are sent to and from the hardware platform or host to obtain the real-time address information of the connected device and implement the address resolution function. At the receiving end, the Ethernet frame IP address field obtained by the Aurora Ethernet data forwarding module is compared with the real-time IP address information of the connected device, and the corresponding Mac address is found and replaced with the destination Mac address field of the Ethernet frame, and the Ethernet frame is subjected to CRC check module: the header checksum field of the IP datagram, the UDP checksum field and the frame check sequence (FCS) field of the Ethernet frame are calculated according to the datagram, and added to the data frame. The calculation method is as follows:

[0092] ① IP datagram header checksum, only checks the datagram header, not the data part. First, divide the IP datagram header into a sequence of many 16-bit words, and set the checksum field to 0. Use the inverse arithmetic operation to add all 16-bit words. The inverse of the sum is the IP datagram header checksum.

[0093] ②UDP checksum, UDP checksum verification content includes 12 bytes pseudo header (including 4 bytes source IP address, 4 bytes destination IP address, 1 byte 0, 1 byte protocol, 2 bytes UDP datagram length), 2 bytes source port, 2 bytes destination port, 2 bytes UDP datagram length, 2 bytes UDP checksum (filled with 0 when calculating), and the data part of the UDP datagram. The UDP checksum verifies both the header and the data, while the IP datagram header checksum only verifies the IP datagram header.

[0094] ③ There are three verification methods for FCS. The first method is to calculate the CRC32 check code bit by bit. The second method is to use a non-flipped lookup table for fast calculation and calculate the CRC32 check code by byte. The third method is to use a flipped lookup table for fast calculation and calculate the CRC check code by byte. The present invention uses the first method to calculate the value of FCS. First, a CRC generator polynomial G(x) is selected, the transmitted data is shifted left by k bits, and 0 is added to the right side (where k is the highest power of the generator polynomial). Then, the data after shifting and 0-filling is used to perform a modulo-2 division (actually an XOR operation) on G(x). The remainder obtained is the CRC check code of the data.

[0095] After verification is completed, it is sent to the connected hardware platform or host.

[0096] 2. Aurora Ethernet data forwarding module

[0097] The Aurora Ethernet data forwarding module is used to receive Ethernet data sent by the protocol stack module, and forward it to the CRC check module of the V7 board for processing after processing. In this embodiment, Aurora 64 / 66B encoding is used, which is a high-performance, low-power serial communication method with good clock recovery capability. It can effectively reduce the clock jitter and clock offset problems in serial communication and is commonly used in high-speed data transmission, optical fiber communication and other fields. Since the Ethernet data packet is 8 bits, it is necessary to splice 8 bytes into a 64-bit byte for transmission. When receiving, the 64-bit byte is disassembled into 8 bytes and transmitted to the protocol stack module.

[0098] 3. LVDS link status reporting module

[0099] The main purpose of the LVDS link status reporting module is to report the link establishment time, rate gear, communication rate, and bit error rate information counted by the laser link channel monitoring module to the host computer through the LVDS signal line in a timely manner.

[0100] 4. Ground monitoring command issuing module

[0101] When the host computer receives the status reported by the link status reporting module, it drives the physical layer device according to the actual situation. The command code sent by the host computer is directly forwarded to the optical antenna by the ground monitoring command sending module. The command forwarding relationship between ground monitoring-board-optical antenna is shown in the figure below. Figure 2 shown.

[0102] 5. CRC check module

[0103] In this embodiment, the CRC check module at the transmitting end is used to receive the data frame from the Aurora Ethernet data forwarding module, calculate and obtain a 16-bit CRC check code to add to the end of the frame, and the CRC check module at the receiving end is used to receive the data frame from the PN code filling module and determine the correctness of the frame.

[0104] 6. PN code filling module and PN code deletion module

[0105] The data after verification by the CRC verification module is sent to the PN code filling module. The PN code (Pseudo-Noise Code) is a coding sequence with a similar white noise autocorrelation property. The most well-known is the maximum length shift register sequence (m sequence), which is generated by a linear feedback shift register. The PN code has good anti-interference ability, can effectively resist the influence of noise and interference signals, ensure communication quality, has a high data transmission speed and coding efficiency, can transmit a large amount of data in a short time, and its randomness and pseudo-randomness make it widely used in the field of covert communication, effectively protect the communication content, and improve communication security. In this embodiment, since the length of the Ethernet data packet is random, at the transmitting end, the PN code is used to expand the fixed input length of the LDPC encoding module for data packets of different lengths: wherein, the fixed input length of the LDPC encoding module is 4050 double bytes, and there are 1014 double bytes of business information in the 4050 double bytes corresponding to the 0th gear, 2700 double bytes of business information in the 4050 double bytes corresponding to the 1st gear, and 3650 double bytes of business information in the 4050 double bytes corresponding to the 2nd gear. At the receiving end, the PN code removal module is used to remove the PN code added by the sending end and restore the Ethernet data packet.

[0106] 7. LDPC encoding and decoding module

[0107] LDPC encoding and decoding plays an important role in communication systems, and is mainly used to improve the reliability and accuracy of data transmission. LDPC (Low Density Parity Check Code) is a linear block code whose core feature is that its check matrix is ​​sparse, that is, the number of non-zero elements in the matrix is ​​relatively small. This feature makes the LDPC code perform well in error correction performance, close to the Shannon limit, that is, when the channel capacity is close, it can minimize the bit error rate and ensure the reliability of data transmission. In addition, the description and implementation of LDPC codes are relatively simple, which is convenient for theoretical analysis and research. The decoding process is simple and supports parallel operations. These characteristics make it very suitable for hardware implementation and widely used in various communication systems. In this embodiment, the LDPC encoding and decoding module is designed with three code rates: 1 / 4, 2 / 3, and 9 / 10, which correspond to three communication rates: 50Mbps, 300Mbps, and 1Gbps respectively. The error correction performance statistics under different code rates are as follows: Figure 6 shown.

[0108] 8. Interleaving module and deinterleaving module

[0109] The interleaving module receives the data sent by the LDPC encoding module and further processes the data. The interleaving module uses group interleaving for a frame of data. The group interleaver is described by a matrix. The input bits are written in row order and read out in column order. De-interleaving is the opposite of interleaving, that is, restoring the bits to their original order. Take 4×5 group interleaving as an example. Figure 3 As shown in FIG. 1 , the number of bits in a packet is called the interleaving depth. The greater the interleaving depth, the greater the discreteness and the stronger the ability to resist burst errors. However, the corresponding interleaving coding processing time is also longer. For the case of more data, the transmitting end interleaving structure in this embodiment is as follows: Figure 4 As shown in the figure, it is a matrix with M rows and N columns. In actual applications, due to the fluctuation of channel quality, data packets are easily affected by atmospheric turbulence and produce bit errors. At the receiving end, due to the change of reading and writing order, continuous random bit errors are dispersed into each discrete coding block, and then sent to the LDPC decoding module to correct the bit errors to a certain extent. Figure 5 shown.

[0110] 9. GTX serial-to-parallel conversion module

[0111] It is used to receive parallel data after LDPC encoding and interleaving, convert it into serial data and send it to the optical antenna, or receive serial data sent by other optical antennas and convert it into parallel data and send it to the deinterleaving and LDPC decoding module to achieve high-speed data transmission. In this embodiment, GTX converts 16-bit parallel data into serial data through 8b / 10b encoding and decoding function, and forwards it between different nodes. The data transmission and reception are all performed at the data link layer. The GTX high-speed serial transceiver uses clock recovery technology (CDR) to synchronize the clocks at both ends of the transmitter and receiver. In addition, in order to align the serial-to-parallel conversion byte boundary at the receiving end, the transmitting end needs to send comma regularly. The 16-bit wide data is divided into 8 bits high and low, and the control character consists of two bytes of D code and K code (frame header: K28.2 / K27.7, frame tail: K29.7 / K30.7, synchronization character: D5.6 / K28.5, synchronization response character: D12.1 / K28.5, idle character: D10.2 / K28.5). The system is in a state of out-of-step when it is powered on. In order to establish synchronization, the transmitter will send a 1ms synchronization character, and then the transmitter will start to send data frames, and synchronization characters need to be sent at the beginning and end of the frame to maintain the synchronization state of the link. When the system is in a synchronous state, the receiver continuously detects the control signals RKLSB and RKMSB, determines the data type according to the status of RKLSB and RKMSB, discards the frame header, frame tail and synchronization characters, latches the data that is really needed, and finally detects the frame header. The interleaved coded data frame is converted into serial data through 8b / 10b encoding through the GTX serial-to-parallel conversion module and transmitted through the RF or laser physical channel.

[0112] 10. Adaptive rate switching module

[0113] The adaptive rate switching module is controlled by the laser link channel monitoring module. When the communication quality of the channel changes dynamically, the laser link channel monitoring module counts the bit error rate information at the receiving end. When the bit error rate is higher than the set threshold, it indicates that the communication quality has seriously deteriorated. The adaptive rate switching module is controlled to adjust the data transmission rate of the transmitting end, adaptively switch to a low-speed bit rate, reduce the amount of data transmission, keep the packet length unchanged, and reduce the LDPC coding rate in exchange for higher reliability. When the channel quality improves, it adaptively switches to a high-speed bit rate and increases the LDPC coding rate. In addition, for the data packet after the coding interleaving is completed, different preamble structures are added according to the gear information and then sent to the optical antenna. Specifically, in this embodiment, there are 3 gears: 0, 1 and 2, corresponding to three communication rates: 50Mbps, 300Mbps, and 1Gbps.

[0114] 11. RS422 serial port transceiver module

[0115] The RS422 serial port transceiver module is used to receive clock synchronization information from the protocol stack module and forward it to the antenna. The RS422 interface is a commonly used asynchronous interface, which is used to receive clock synchronization information from the hardware platform or host and send it to the optical antenna. The transmission format of the RS422 interface in this embodiment is: start bit + 8 data bits + stop bit, and the check bit is not used. The serial port communication rate is 115.2Kbps and the communication distance is 15m.

[0116] 12. Speed ​​gear recognition module

[0117] The rate gear identification module receives data from the GTX serial-to-parallel conversion module. By judging the frame header, it can know the code rate and communication rate of the frame data, thereby adjusting the gear of the LDPC decoding module to decode the data packet. In this embodiment, the packet length after encoding is unified to 4050 double bytes, and the maximum number of double bytes input is: 1014 double bytes for gear 0, 2700 double bytes for gear 1, and 3650 double bytes for gear 2. The schematic diagram of cross-correlation rate gear identification is shown in Figure 7 , Figure 8 As shown, the preamble structure is known to both the transmitter and the receiver. The data is cross-correlated with the locally known preamble structure, and the amplitude peak is found by accumulating and summing after correlation calculation, thereby determining the end point of the preamble structure. Figure 7 Among them, PN1, PN2, ..., PNn are leading structures, and D1, D2, D3, ..., Dn are business information;

[0118] 13. Laser link channel monitoring module

[0119] The laser link channel monitoring module is used to count the data sent by the CRC check module at the receiving end to obtain the link establishment time, communication rate, rate gear and bit error rate of the link in real time. When the quality of the laser channel is seriously reduced or even the link is interrupted, the link status is reported in real time through the LVDS link status reporting module, and the coding rate of the sending end is switched to obtain a more stable communication effect. In this embodiment, the link establishment time statistics adopt a handshake method similar to the TCP protocol. After three handshakes, the time from receiving power to completing the handshake is counted; the communication rate is the actual information bandwidth received by the receiving end; the bit error rate is obtained by dividing the total number of bits sent by the sending end and the number of correct bits received by the receiving end; the rate gear is the communication rate selected at this time, 1Gbps, 300Mbps or 50Mbps.

[0120] Specifically, the technical indicators and effects of the space laser communication device of this embodiment are as follows:

[0121] 1) Power supply: 220V±22V, 50Hz±1Hz.

[0122] 2) Communication capabilities:

[0123] Different data transmission rates are used for different communication distances:

[0124] 1Gbps at 100km

[0125] 300 Mbps at 300 km

[0126] 50Mbps at 600km

[0127] 3) Communication bit error rate: ≤10 -6

[0128] 4) Capture tracking time: ≤30s

[0129] 3) Capture tracking probability: ≥95%

[0130] 6) Signal light working band: 1550nm

[0131] 7) Beacon light working band: 800nm.

[0132] In summary, the present invention proposes a space laser communication device that can play an anti-turbulence role in the digital domain to ensure high data transmission rate and low bit error, improve reliability and improve the performance of the optical system while ensuring the transmission rate.

[0133] Those skilled in the art will appreciate that the embodiments described are intended to help readers understand the principles of the present invention, and should be understood that the scope of protection of the present invention is not limited to the embodiments described. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A space laser communication device, characterized in that: It includes protocol stack module, Aurora Ethernet data forwarding module, sending channel and receiving channel; The sending channel includes a first CRC check module, a PN code filling module, an LDPC encoding module, an interleaving module and a first GTX serial-to-parallel conversion module; the receiving channel includes a second CRC check module, a PN code deletion module, an LDPC decoding module, a deinterleaving module and a second GTX serial-to-parallel conversion module; The protocol stack module is used to configure the IP address and Mac address of its own space laser communication device. In addition, during the transmission process, the protocol stack module filters the Ethernet data packets transmitted by the connected hardware platform according to the Ethernet frame type, next packet header, port number, source Mac address, destination Mac address, source IP address and destination IP address, and transmits the Ethernet data packets that meet the requirements to the Aurora Ethernet data forwarding module; During the receiving process, the protocol stack module receives the Ethernet data packet transmitted by the Aurora Ethernet data forwarding module, compares the IP address field of the Ethernet frame with the real-time IP address information of the connected hardware platform, finds the corresponding Mac address and replaces it with the destination Mac address field of the Ethernet frame; and performs CRC check on the Ethernet frame: calculates the header checksum field of the IP datagram, the UDP checksum field and the frame check sequence field of the Ethernet frame, and adds the calculation result to the Ethernet frame and sends it to the connected hardware platform; During the sending process, the Aurora Ethernet data forwarding module is used to receive the Ethernet data packets transmitted by the protocol stack module, perform byte splicing on the Ethernet data packets, and transmit them to the sending channel; during the receiving process, the Aurora Ethernet data forwarding module is used to perform byte disassembly on the Ethernet data packets transmitted by the receiving channel, and transmit them to the protocol stack module; In the sending channel, the first CRC check module receives the Ethernet data packet transmitted by the Aurora Ethernet data forwarding module, calculates the CRC check code, adds the CRC check code to the end of the Ethernet frame, and then transmits it to the PN code filling module; The PN code filling module receives the Ethernet data packet transmitted by the first CRC check module, expands the Ethernet data packet to the fixed length required by the LDPC encoding module using the PN code, and then transmits it to the LDPC encoding module; The LDPC encoding module receives the Ethernet data packet transmitted by the PN code filling module, adds redundancy to the Ethernet data packet according to the LDPC code, and transmits it to the interleaving module; The interleaving module is provided with an interleaving matrix, which writes data in row order for the Ethernet data packets transmitted by the LDPC encoding module, and outputs the data in column order to the first GTX serial-to-parallel conversion module; The first GTX serial-to-parallel conversion module converts the parallel data output by the interleaving module into serial data, and transmits it to the optical antenna for transmission; In the receiving channel, the second GTX serial-to-parallel conversion module receives serial data transmitted by the optical antenna, converts the serial data into parallel data, and transmits the parallel data to the deinterleaving module; The deinterleaving module is provided with a deinterleaving matrix, which writes data in column order for the parallel data transmitted by the second GTX serial-to-parallel conversion module, and outputs the data to the LDPC decoding module in row order; the deinterleaving matrix is ​​the same size as the interleaving matrix; The LDPC decoding module receives the data transmitted by the deinterleaving module, removes redundancy in the Ethernet data packet according to the LDPC code, and transmits it to the PN code removal module; The PN code deletion module receives the data transmitted by the LDPC decoding module, deletes the PN code in the data, restores the Ethernet data packet, and transmits it to the second CRC check module; The second CRC check module receives the Ethernet data packet transmitted by the PN code deletion module, extracts the CRC check code in the Ethernet data packet for verification, and transmits the Ethernet data packet to the Aurora Ethernet data forwarding module when the CRC check is correct.

2. A space laser communication device according to claim 1, characterized in that: It also includes an LVDS link status reporting module, a laser link channel monitoring module, an adaptive rate switching module and a rate gear identification module; The laser link channel monitoring module counts the Ethernet data packets output by the second CRC check module, and obtains the link establishment time, communication rate, rate gear and bit error rate of the link in real time; transmits the link establishment time, communication rate, rate gear and bit error rate to the LVDS link status reporting module, and transmits the bit error rate to the adaptive rate switching module; The LVDS link status reporting module receives the link establishment time, communication rate, rate gear and bit error rate transmitted by the laser link channel monitoring module, and transmits them to the connected hardware platform through the protocol stack module for reporting; The adaptive rate switching module is provided with a plurality of gear thresholds, and corresponding preamble structures are provided for different gears; the adaptive rate switching module receives the bit error rate transmitted by the laser link channel monitoring module, compares the bit error rate with the plurality of gear thresholds, obtains the corresponding gear information and transmits it to the PN code filling module and the LDPC encoding module; and adding the leading structure corresponding to the latest gear information to the data frame header output by the interleaving module; The PN code filling module performs corresponding PN code filling on the Ethernet data packet transmitted by the first CRC check module according to the gear information transmitted by the adaptive rate switching module; wherein the length of the Ethernet data packet output by the PN code filling module to the LDPC encoding module is fixed, and the higher the gear, the greater the number of double bytes occupied by the service information in each Ethernet data packet; The LDPC encoding module adds corresponding redundancy to the Ethernet data packet transmitted by the PN code filling module in combination with the LDPC code according to the gear information transmitted by the adaptive rate switching module. The higher the gear, the higher the code rate of the LDPC encoding module. The code rate of the LDPC encoding module is: the result obtained by dividing the number of double bytes occupied by the business information in the Ethernet data packet output from the PN code filling module to the LDPC encoding module by the number of double bytes of the Ethernet data packet. The rate gear identification module parses the data frame header output by the second GTX serial-to-parallel conversion module to obtain the gear information of the data output by the second GTX serial-to-parallel conversion module, and transmits the gear information to the PN code deletion module and the LDPC decoding module; The LDPC decoding module deletes the corresponding redundancy in the output data of the deinterleaving module according to the gear information transmitted by the rate gear identification module and in combination with the LDPC code, and transmits it to the PN code deletion module; the higher the gear, the higher the code rate of the LDPC decoding module, and the corresponding relationship between the code rate and the gear of the LDPC decoding module is consistent with the corresponding relationship between the code rate and the gear of the LDPC encoding module; The PN code deletion module deletes the PN code in the data transmitted by the LDPC decoding module according to the gear information transmitted by the rate gear identification module, and transmits it to the second CRC check module; wherein, in the PN code deletion module, for different gears, the number of double bytes occupied by the business information in each Ethernet data packet is consistent with the PN code filling module.

3. A space laser communication device according to claim 1 or 2, characterized in that: It also includes a ground monitoring command sending module and an RS422 serial port transceiver module; The ground monitoring instruction issuing module receives control information transmitted by the hardware platform via the protocol stack module, and drives the optical antenna according to the control information, wherein the control information includes piezoelectric, tracking and scanning control information of the optical antenna; The RS422 serial port transceiver module receives the time synchronization information transmitted by the hardware platform via the protocol stack module, and transmits the time synchronization information to the optical antenna for time synchronization.

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