Frame structure and space optical communication method and system

Abstract

The invention belongs to the technical field of space laser communication, and discloses a frame structure and a space optical communication method and system. The frame structure provided by the invention comprises a synchronization sequence and a data sequence, the synchronization sequence comprises a lead code and a frame start character, and the data sequence comprises a control signaling, an information bit and a frame check sequence; the lead code is embedded into the beacon light, and the frame start character and the data sequence are embedded into the signal light. The method comprises the following steps: determining a channel state at a transmitting end according to monitoring information, further determining a transmission control parameter, modulating a beacon laser to generate a lead code in combination with a control time sequence, modulating a signal laser to generate a data frame except the lead code, forming a complete optical signal based on the control time sequence, and transmitting the optical signal; an optical signal is separated into beacon light and signal light at a receiving end, a lead code is detected through an electric signal output by a beacon light detector, and a frame start character and an information bit are detected through an electric signal output by a signal light detector. According to the invention, the communication system can work stably in a turbulent environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of space laser communication, and more particularly relates to a frame structure, a space optical communication method and system. BACKGROUND

[0002] The space laser communication system is an optical communication system taking laser light wave as a carrier and taking atmosphere as a transmission medium. The space laser communication has the advantages of large communication capacity, high-speed transmission and strong confidentiality. In the space optical communication, the atmospheric turbulence is an important factor affecting the communication quality. The atmospheric turbulence not only causes light intensity flicker, but also causes burst error.

[0003] The data transmission and reception is in units of frames. The error of the synchronization signal in the frame structure will cause the complete loss of the entire data frame. The interference such as atmospheric turbulence easily causes the difficulty in identifying the synchronization signal, and further causes the problems of packet loss or communication interruption. How to ensure that the communication system can stably work in the turbulence environment is a problem to be solved in the field. SUMMARY

[0004] The purpose of the application is to provide a frame structure, a space optical communication method and system, so that the communication system can stably work in the turbulence environment.

[0005] In a first aspect, the application provides a frame structure, comprising: a synchronization sequence and a data sequence; the synchronization sequence comprises a preamble and a frame start symbol, and the data sequence comprises control signaling, information bits and a frame check sequence; the preamble is embedded into beacon light, and the frame start symbol and the data sequence are embedded into signal light.

[0006] Preferably, the preamble is obtained by modulating a beacon laser according to transmission control parameters and control timing; The transmission control parameters are determined based on a channel state, and the transmission control parameters comprise data transmission information, data frame length and symbol rate; The total sequence length of the preamble is adaptively adjusted under different channel states; the total sequence length of the preamble is changed by changing the repetition number of the same pulse, different pulse combinations under different channel states are formed, and different pulse combinations correspond to different data frame lengths and symbol rates.

[0007] Preferably, the channel state is determined according to monitoring information, and the monitoring information comprises the power of the beacon light, the power of the signal light and the atmospheric refractive index structure constant.

[0008] Preferably, the data frame except the preamble is obtained by modulating a signal laser according to the transmission control parameters and the control timing.

[0009] In a second aspect, the application provides a space optical communication method, comprising: At the transmitting end, a channel monitoring unit determines a channel state according to monitoring information; a first control unit determines a transmission control parameter according to the channel state, and modulates a beacon laser to generate a preamble and modulates a signal laser to generate a data frame except the preamble, the data frame except the preamble including a frame start symbol, a control signaling, information bits and a frame check sequence, and the control timing is used to form a complete optical signal; a transmitting unit transmits the optical signal; At the receiving end, a receiving unit receives the optical signal and separates the optical signal into beacon light and signal light; a beacon light detector converts the beacon light into a first electrical signal, and a signal light detector converts the signal light into a second electrical signal; a second control unit detects the preamble through the first electrical signal and detects the frame start symbol and the information bits through the second electrical signal.

[0010] Preferably, the monitoring information includes the power of the beacon light, the power of the signal light and the atmospheric refractive index structure constant.

[0011] Preferably, the transmission control parameter includes data transmission information, data frame length and symbol rate.

[0012] Preferably, the total length of the sequence of the preamble is adaptively adjusted under different channel states; the total length of the sequence of the preamble is changed by changing the repetition number of the same pulse, different pulse combinations are formed under different channel states, and different pulse combinations correspond to different data frame lengths and symbol rates.

[0013] Preferably, the first control unit includes a tracking module, a communication module and a timing control module; the timing control module is used to generate the control timing; the tracking module is used to modulate the beacon laser according to the transmission control parameter and the control timing; and the communication module is used to modulate the signal laser according to the transmission control parameter and the control timing.

[0014] In a third aspect, the present application provides a spatial optical communication system, comprising: a transmitting end and a receiving end; the transmitting end comprising a channel monitoring unit, a first control unit, a beacon laser, a signal laser and a transmitting unit; the receiving end comprising a receiving unit, a beacon light detector, a signal light detector and a second control unit; the spatial optical communication system is used to execute the steps in the spatial optical communication method provided by the second aspect of the present application.

[0015] One or more technical solutions provided in the present application have at least the following technical effects or advantages: (1) The present application takes the modulated beacon light pulse sequence as a preamble (i.e. as a synchronization signal), since the beacon light is emitted by a pulse laser with a very high instantaneous power, and the beacon light at the receiving end does not need to be coupled into an optical fiber, without coupling loss, so the receiving power is much larger than the signal light power, therefore the frame structure provided by the present application is beneficial to identifying the synchronization signal, and improves the anti-interference ability of the spatial optical communication. In addition, the sensitivity of the beacon light detector is higher, which can greatly improve the detection rate and the anti-interference ability of frame synchronization. The frame structure provided by the present application and the spatial optical communication scheme provided on the basis of the frame structure can ensure that the communication system can still work stably in a turbulent environment.

[0016] (2) The present application also combines channel state monitoring to adaptively adjust the total time length of the preamble sequence under different channel states, i.e. the present application can also dynamically optimize the preamble based on the channel state, taking into account efficiency and reliability, and this adaptive transmission scheme is simple to implement and has good resistance effect on burst interference. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A schematic diagram of a spatial optical communication method provided for embodiment 2 of the present application. DETAILED DESCRIPTION

[0018] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the drawings in the specification and specific embodiments.

[0019] Embodiment 1: Embodiment 1 provides a frame structure, comprising: a synchronization sequence and a data sequence; the synchronization sequence comprises a preamble and a frame start symbol, and the data sequence comprises control signaling, information bits and a frame check sequence; the preamble is embedded into beacon light, and the frame start symbol and the data sequence are both embedded into signal light.

[0020] Wherein, the preamble is obtained by modulating a beacon laser according to a transmission control parameter and a control timing.

[0021] The data frame except the preamble, i.e. the frame start symbol, the control signaling, the information bits and the frame check sequence, are obtained by modulating a signal laser according to the transmission control parameter and the control timing.

[0022] Specifically, the channel state is determined according to monitoring information, and the monitoring information includes the power of the beacon light, the power of the signal light, the atmospheric refractive index structure constant, etc. The transmission control parameter is determined based on the channel state, and the transmission control parameter includes data transmission information, data frame length and symbol rate.

[0023] Adaptively adjust the total length of the preamble sequence under different channel states; the total length of the preamble sequence is changed by changing the repetition number of the same pulse, forming different pulse combinations under different channel states, and different pulse combinations correspond to different data frame lengths and symbol rates.

[0024] That is, the application transmits channel states and working modes by beacon light pulse combinations, controls data transmission or non-transmission, and changes data frame length and communication rate.

[0025] Embodiment 1 uses modulated beacon light as a preamble to identify the start of a data frame, and signal light is mainly used to transmit information bits. No frame synchronization preamble is transmitted, and the receiving end in the corresponding application identifies the preamble through beacon light detection.

[0026] In summary, the application uses a modulated beacon light pulse sequence as a preamble (i.e., as a synchronization signal). Since the beacon light is emitted by a pulse laser with a very high instantaneous power, and the beacon light at the receiving end does not need to be coupled into an optical fiber, there is no coupling loss, so the received power is much greater than the signal light power. Therefore, the frame structure provided by the application is beneficial to improving the anti-interference ability of spatial optical communication. In addition, the beacon light can use a unique detection method, and the probe has higher sensitivity, which can greatly improve the detection rate and the anti-interference ability of frame synchronization. Moreover, the application also combines channel state monitoring to adaptively adjust the total length of the preamble sequence under different channel states. That is, the application can also dynamically optimize the preamble based on the channel state, taking into account efficiency and reliability. This adaptive transmission scheme is simple to implement and has good resistance to burst interference, which is beneficial to ensuring the stable operation of the communication system in a turbulent environment.

[0027] Based on the frame structure provided in Embodiment 1, the application also provides a corresponding spatial optical communication method and spatial optical communication system, which are described below in Embodiment 2 and Embodiment 3, respectively.

[0028] Embodiment 2: Embodiment 2 provides a spatial optical communication method, as shown in Figure 1 , comprising: At the transmitting end, a channel monitoring unit is used to determine the channel state according to monitoring information; a first control unit is used to determine transmission control parameters according to the channel state, and a beacon laser is used to generate a preamble in combination with a control timing, a signal laser is used to generate a data frame excluding the preamble, the data frame excluding the preamble includes a frame start symbol, control signaling, information bits, and a frame check sequence, and a complete optical signal is formed based on the control timing; and a transmitting unit is used to transmit the optical signal. At the receiving end, the optical signal is received by a receiving unit and separated into beacon light and signal light; the beacon light is converted into a first electrical signal by a beacon light detector, and the signal light is converted into a second electrical signal by a signal light detector; a second control unit detects the preamble through the first electrical signal and detects the frame start symbol and information bits through the second electrical signal.

[0029] In the present application, the preamble is followed by a frame start symbol, control signaling, information bits and a frame check sequence. The transmitting end outputs a beacon modulation signal (containing the preamble) and an information signal (containing the frame start symbol, control signaling, information bits and frame check sequence), and the beacon modulation signal and the information signal together constitute a frame signal. The receiving end detects the frame synchronization signal (i.e. the preamble) through the electrical signal output by the beacon light detector, and after detecting a complete frame synchronization signal, detects the frame start symbol and information bits from the signal light until a complete frame is received.

[0030] The monitoring information includes the power of the beacon light, the power of the signal light and the atmospheric refractive index structure constant.

[0031] The transmission control parameters include data transmission information, data frame length and symbol rate.

[0032] The total length of the sequence of the preamble is adaptively adjusted under different channel states; the total length of the sequence of the preamble is changed by changing the repetition number of the same pulse, forming different pulse combinations under different channel states, and different pulse combinations correspond to different data frame lengths and symbol rates.

[0033] For example, the channel states include excellent, good, medium, poor and the like; when the channel state is poor, no information is transmitted; when the channel state is excellent, the data frame length and symbol rate > when the channel state is good, the data frame length and symbol rate > when the channel state is medium, the data frame length and symbol rate.

[0034] The following examples are given in conjunction with the parameters.

[0035] For example, when the power of the signal light or the beacon light is lower than the sensitivity of the corresponding detector, and the atmospheric refractive index structure constant indicates medium or strong turbulence, the channel state is poor; Under the condition that the power of the signal light or the beacon light is higher than the sensitivity of the corresponding detector, if the average power of the signal light exceeds 1 / 3 of the system design power redundancy, and the atmospheric refractive index structure constant indicates medium or weak turbulence, the channel state is medium; Under the condition that the power of the signal light or the beacon light is higher than the sensitivity of the corresponding detector, if the average power of the signal light exceeds 1 / 2 of the system design power redundancy, and the atmospheric refractive index structure constant indicates weak turbulence, the channel state is good; When the power of the signal light or beacon light is higher than the corresponding detector sensitivity, if the average power of the signal light exceeds 2 / 3 of the system design power redundancy, and the atmospheric refractive index structure constant indicates weak turbulence, the channel state is excellent.

[0036] For example, according to the channel state, whether to send a signal, the data frame length and the data transmission rate are determined, and the following design can be used: When the channel state is poor, no signal is sent, and communication is stopped; When the channel state is medium, the frame data length is L, and the symbol rate is r; When the channel state is good, the frame data length is 2L, and the symbol rate is 2r; When the channel state is excellent, the frame data length is 4L, and the symbol rate is 4r.

[0037] That is, the present application can control the data to be sent or not to be sent according to the channel state, and the corresponding data frame length and data transmission rate, so as to ensure orderly work under strong interference.

[0038] For example, the coding scheme is: When the channel state is poor, the corresponding code is 0; When the channel state is medium, the corresponding code is 111; When the channel state is good, the corresponding code is 11; When the channel state is excellent, the corresponding code is 1.

[0039] Correspondingly, under the driving of the timing control module, the beacon laser is demodulated based on the code to generate a preamble, and the following design can be used: When the channel state code is 0, no optical pulse is sent; When the channel state code is 111, the beacon laser continuously sends three pulses with a duration of T, that is, a sequence with a total duration of 3T is formed; When the channel state code is 11, the beacon laser continuously sends two pulses with a duration of T, forming a sequence with a total duration of 2T; When the channel state code is 1, the beacon laser sends a pulse with a duration of T.

[0040] In the above scheme, the working mode of the system is determined according to the channel state, when the channel is excellent, good, medium, respectively, 1, 2 or 3 continuous pulses are sent, respectively corresponding to different data frame lengths and symbol rates, when the channel state is poor, no beacon and information is sent, The application changes the total time length of the preamble sequence (corresponding to the energy) by changing the repetition number of the same pulse, and the principle of improving the anti-interference capability includes: (1) the longer sequence allows the receiving end to perform longer coherent or non-coherent integration. The receiving end performs correlation operation on the received signal and the locally known pulse template, the longer the integration time, the better the cumulative effect on the signal energy, and the stronger the noise suppression capability, so that the synchronization signal can be reliably detected under the condition of low signal-to-noise ratio. (2) The transmission of multiple pulses introduces time diversity and redundancy. Even if a pulse is lost due to instantaneous deep fading or burst interference, the subsequent pulse can still be correctly captured, greatly improving the robustness of synchronization.

[0041] In addition, the implementation complexity of the above scheme is low, and the scheme is relatively simple. The transmitting end only needs to control the pulse repetition number, and the receiving end can use a simple energy detector or integrator.

[0042] The application provides a self-adaptive modulation and coding scheme. When it is found that the channel state is poor and the interference is large, the application can dynamically switch to a longer preamble sequence, and vice versa, to use a shorter preamble to improve efficiency. The application dynamically optimizes based on the channel state, and takes into account efficiency and reliability. The application is simple to implement and has good resistance to burst interference.

[0043] The first control unit comprises a tracking module, a communication module and a timing control module; the timing control module serves as a control module for coordinating the operation of the tracking module and the communication module. The timing control module is configured to generate the control timing. The tracking module is configured to modulate the beacon laser according to the transmission control parameter and the control timing; and the communication module is configured to modulate the signal laser according to the transmission control parameter and the control timing.

[0044] The tracking module generates a fine tracking beacon modulation signal. After determining whether to send data, the data frame length and the symbol rate according to the channel state, the beacon laser is modulated based on an encoding scheme under the driving of the timing control module to generate a preamble. The communication module adds signaling and CRC check to the data according to the determined data frame length to form a data frame excluding the preamble. The signal laser is modulated by the data frame under the driving of the timing control module to generate a frame of data. Specifically, the frame start symbol, the signaling and the frame data are input to a sending buffer, and the input frame data is CRC encoded to obtain a frame check sequence which is sent to the sending buffer and connected to the frame data to finally form a complete optical data frame.

[0045] That is, the timing control module lets the beacon modulation signal and the data frame drive the corresponding laser modulators in a time sequence. Under the timing control, the laser generates beacon light and signal light, which form a frame of optical data.

[0046] Overall, at the transmitting end, the channel monitoring unit collects the power of the fine tracking beacon light, the power of the signal light, and the atmospheric refractive index structure constant in real time, evaluates the channel state, and divides the channel into excellent, good, medium, and poor types. The first control unit determines whether to send data, the data frame length, and the data transmission rate (i.e., the symbol rate) according to the channel state. Under the driving of the timing control module, the beacon laser is modulated to generate a preamble. Meanwhile, the first control unit adds control signaling and a frame check sequence (e.g., CRC check) to the data according to the determined data frame length to form a data frame excluding the preamble. Under the driving of the timing control module, the signal laser is modulated to generate a frame of data, thus forming a complete frame of optical data (i.e., obtaining a complete optical signal). Then, the optical data frame is transmitted through the transmitting unit.

[0047] The design of the frame structure used in embodiment 2 can greatly improve the detection rate and the anti-interference ability of frame synchronization. Moreover, the working mode of the space optical communication is determined according to the channel state. This adaptive transmission method further improves the anti-interference ability of the space optical communication.

[0048] Embodiment 3: Embodiment 3 provides a space optical communication system, which includes a transmitting end and a receiving end. The transmitting end includes a channel monitoring unit, a first control unit (i.e., a communication / following control unit of the transmitting end), a beacon laser, a signal laser, and a transmitting unit (e.g., optical devices including a fine tracking device and an optical antenna). The receiving end includes a receiving unit, a beacon light detector, a signal light detector, and a second control unit (i.e., a communication / following control unit of the receiving end). The space optical communication system is used to perform the steps in the space optical communication method of embodiment 2.

[0049] Since the functions of the units or devices in the space optical communication system provided in embodiment 3 correspond to the steps in the space optical communication method provided in embodiment 2, embodiment 3 can be understood by referring to embodiment 2, and thus no further description is provided herein.

[0050] Finally, it should be noted that the above detailed description is merely illustrative of the technical solutions of the present application and is not limiting, and although the present application has been described in detail with reference to the examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application, and all should be covered in the scope of the claims of the present application.

Claims

1. A frame structure, characterized in that, include: The system includes a synchronization sequence and a data sequence; the synchronization sequence includes a preamble and a start-of-frame symbol, and the data sequence includes control signaling, information bits, and a frame check sequence; the preamble is embedded in the beacon light, and the start-of-frame symbol and the data sequence are both embedded in the signal light.

2. The frame structure according to claim 1, characterized in that, The preamble is obtained by modulating the beacon laser according to the transmission control parameters and the control timing. The transmission control parameters are determined based on the channel state, and include whether data is being transmitted, as well as the data frame length and symbol rate. The total duration of the preamble sequence is adaptively adjusted under different channel conditions; the total duration of the preamble sequence is changed by changing the number of repetitions of the same pulse, forming different pulse combinations under different channel conditions, and different pulse combinations correspond to different data frame lengths and symbol rates.

3. The frame structure according to claim 2, characterized in that, The channel state is determined based on monitoring information, including the power of the beacon light, the power of the signal light, and the atmospheric refractive index structure constant.

4. The frame structure according to claim 2, characterized in that, Based on the transmission control parameters and the control timing modulation signal laser, a data frame excluding the preamble is obtained.

5. A space optical communication method, characterized in that, include: At the transmitting end, the channel monitoring unit determines the channel status based on monitoring information; The first control unit determines the transmission control parameters based on the channel state, and generates a preamble by modulating the beacon laser in combination with the control timing. The modulated signal laser generates a data frame excluding the preamble. The data frame excluding the preamble includes a frame start symbol, control signaling, information bits and a frame check sequence, and forms a complete optical signal based on the control timing. The transmitting unit transmits optical signals; At the receiving end, the receiving unit receives the optical signal and separates it into beacon light and signal light; The beacon light is converted into a first electrical signal using a beacon photodetector, and the signal light is converted into a second electrical signal using a signal photodetector. The second control unit detects the preamble using the first electrical signal and the start-of-frame character and information bits using the second electrical signal.

6. The space optical communication method according to claim 5, characterized in that, The monitoring information includes the power of the beacon light, the power of the signal light, and the atmospheric refractive index structure constant.

7. The space optical communication method according to claim 5, characterized in that, The transmission control parameters include whether data is being sent, as well as the data frame length and symbol rate.

8. The space optical communication method according to claim 7, characterized in that, The total duration of the preamble sequence is adaptively adjusted under different channel conditions; the total duration of the preamble sequence is changed by changing the number of repetitions of the same pulse, forming different pulse combinations under different channel conditions, and different pulse combinations correspond to different data frame lengths and symbol rates.

9. The space optical communication method according to claim 5, characterized in that, The first control unit includes a tracking module, a communication module, and a timing control module; the timing control module is used to generate the control timing sequence; the tracking module is used to modulate the beacon laser according to the transmission control parameters and the control timing sequence; the communication module is used to modulate the signal laser according to the transmission control parameters and the control timing sequence.

10. A space optical communication system, characterized in that, include: The system comprises a transmitter and a receiver; the transmitter includes a channel monitoring unit, a first control unit, a beacon laser, a signal laser, and a transmitter unit; the receiver includes a receiver unit, a beacon photodetector, a signal photodetector, and a second control unit; the space optical communication system is used to perform the steps in the space optical communication method as described in any one of claims 5 to 9.

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