Adaptive atmospheric channel coherent laser communication diversity receiving system and method

Abstract

The application relates to the technical field of atmospheric laser communication, and discloses a coherent laser communication diversity receiving system and method for self-adapting to an atmospheric channel, which comprises N optical amplifiers, N 90-degree optical mixers, N phase error modules, a phase error selection module, an optical phase-locked loop, a residual phase noise compensation module and a coherent combining module. Each 90-degree optical mixer is used to receive one-way signal light; the output end of the i-way optical amplifier, the i-way 90-degree optical mixer, the i-way phase error module, the phase error selection module, the optical phase-locked loop and the input end of the i-way optical amplifier are sequentially connected; and the i-way optical amplifier, the i-way 90-degree optical mixer, the i-way phase error module, the residual phase noise compensation module and the coherent combining module are sequentially connected. The application solves the problems of low stability of optical phase-locked coherent laser communication in an atmospheric channel and poor robustness of diversity receiving in the prior art.

Description

Technical Field

[0001] This invention relates to the field of atmospheric laser communication technology, specifically to a coherent laser communication diversity receiving system and method for adaptive atmospheric channels. Background Technology

[0002] Laser communication boasts advantages such as high communication speed, strong anti-interference capability, no need for spectrum application, and high confidentiality, making it a promising field for applications in satellite communication, stratospheric communication, 5G / 6G communication, integrated laser-RF communication, and near-ground building communication. Unlike the relatively ideal low-Earth orbit channels and space environment of satellite communication, laser signals transmitted through atmospheric channels are affected by atmospheric turbulence, atmospheric scattering and absorption, clouds, and fog, resulting in random fading and attenuation of the optical signal. Channel attenuation can be overcome by increasing the transmitted optical power and the receiver sensitivity. However, the random fading and fluctuations caused by atmospheric turbulence can reach approximately 10-40 dB, easily leading to link interruptions and reducing the reliability of laser communication transmission in atmospheric channels.

[0003] Generally speaking, although atmospheric channels exhibit significant fluctuations, their channel correlation is weaker and more advantageous than that of wireless and microwave communications. Taking a typical near-ground atmospheric channel (a 1km link under moderate turbulence) as an example, the coherence length of the atmospheric channel is approximately 5-10cm, meaning that different paths in the atmospheric channel exhibit independent, uncorrelated, and low crosstalk characteristics. Therefore, receivers can employ multiple receiving antennas to achieve diversity reception, thereby suppressing the influence of atmospheric turbulence and further improving the reliability of atmospheric laser communication. Consequently, single-transmitter-multiple-receiver diversity reception systems have been widely studied in atmospheric laser communication due to their simple structure and mature signal combining algorithms.

[0004] In recent years, laser communication based on coherent systems has been extensively studied and verified in long-distance atmospheric laser communication. Theoretical research [1] (N. Perlot. Turbulence-induced fading probability in coherent optical communication through the atmosphere. Applied Optics, 2007, 46(29).) discusses the feasibility of atmospheric coherent laser communication (BPSK signal) under small aperture reception. Theoretical research [2] (Jing Sun, Puming Huang, Zhoushi Yao, Jingzhong Guo. Adaptive digital combination for coherent free space optical communications with spatial diversity reception. Optics Communications. 2019, 44.) simulates the diversity reception performance of atmospheric coherent laser communication, but the digital coherent technology used has disadvantages such as weak resistance to frequency differences and high power consumption. The existing technology [3] (Zhu Zunzhen, Zhou Haijun, Xie Weilin, Qin Jie, Dong Yi. 10-Gb / s homodyne receiver based on Costas loop with enhanced dynamic performance. IEEE International Conference on Optical Communications and Networks (ICOCN), 2017.) uses optical phase-locked loop technology to realize zero-difference coherent reception of BPSK signals and can compensate for the large frequency difference (40GHz range) between the signal light and the local oscillator light in real time. However, it does not consider the influence of atmospheric channels or how to apply it to diversity reception systems.Experimental studies [4] (Robert Lange, Berry Smutny, Bernhard Wandernoth, Reinhard Czichy, Dirk Giggenbach. 142 km, 5.625 Gbps Free-space optical link based on homodyne BPSK modulation. processof SPIE, 2006, 6105.) have confirmed the feasibility of long-distance coherent laser communication in atmospheric channels. However, observations show significant fluctuations in optical power (20-40 dB), instability of optical phase-locking, and sudden interruptions in the laser communication link under atmospheric channels. Therefore, improving the stability of optical phase-locking and the robustness of diversity reception in coherent laser communication under atmospheric channels is particularly urgent and is a problem that needs to be solved in long-distance atmospheric laser communication. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a coherent laser communication diversity reception system and method with adaptive atmospheric channels, which solves the problems of low stability of optical phase-locking and poor robustness of diversity reception in existing technologies.

[0006] The technical solution adopted by the present invention to solve the above problems is: An adaptive atmospheric channel coherent laser communication diversity receiving system includes N optical amplifiers, N 90° optical mixers, N phase error modules, a phase error selection module, an optical phase-locked loop, a residual phase noise compensation module, and a coherent merging module. Each 90° optical mixer is used to receive one channel of signal light. The output of the i-th optical amplifier, the i-th 90° optical mixer, the i-th phase error module, the phase error selection module, the optical phase-locked loop, and the input of the i-th optical amplifier are connected in sequence. The i-th optical amplifier, the i-th 90° optical mixer, the i-th phase error module, the residual phase noise compensation module, and the coherent merging module are connected in sequence. Wherein, 1≤i≤N and i is an integer, N≥2 and N is an integer.

[0007] As a preferred technical solution, the phase error module includes two balanced detectors and a frequency and phase detector. The two balanced detectors are referred to as the first balanced detector and the second balanced detector, respectively. The first balanced detector and the second balanced detector are each connected to a 90° optical mixer. The first balanced detector, the frequency and phase detector, and the second balanced detector are connected in sequence.

[0008] As a preferred technical solution, the phase error module also includes a first low-pass filter connected to the frequency and phase detector.

[0009] As a preferred technical solution, the phase error selection module includes a channel selector connected to a first low-pass filter.

[0010] As a preferred technical solution, the phase error selection module also includes a second low-pass filter connected to the channel selector.

[0011] As a preferred technical solution, the residual phase noise compensation module includes N data selectors, N third low-pass filters, one fan-out, and N-1 phase difference compensation modules. The first data selector is connected to the first low-pass filter, the first data selector, the first third low-pass filter, and the fan-out are connected in sequence, the i-th data selector, the i-th third low-pass filter, and the i-th phase difference compensation module are connected in sequence, and the fan-out is connected to the i-th phase difference compensation module; where i≥2.

[0012] As a preferred technical solution, the coherent combining module includes a maximum signal-to-noise ratio (MSNR) combiner, which is used for the diversity combining of the digital signals output by each phase difference compensation module.

[0013] As a preferred technical solution, it also includes a matched filter, a residual phase noise compensation module, a matched filter, and a maximum signal-to-noise ratio combiner connected in sequence.

[0014] As a preferred technical solution, it also includes a channel estimator, a residual phase noise compensation module, a channel estimator, a matched filter, and a maximum signal-to-noise ratio combiner connected in sequence.

[0015] A method for coherent laser communication diversity reception with an adaptive atmospheric channel, employing the aforementioned coherent laser communication diversity reception system with an adaptive atmospheric channel, includes the following steps: S1, based on the slow-changing characteristics of the atmospheric channel, performs frame processing on the transmitted baseband data and pilot data; S2 receives the signal light, coherently mixes the signal light of each branch with the local oscillator light on a 90° optical mixer, converts it into two data streams with phase error and phase error through the phase error module, then feeds the phase error into the phase error selection module to control the optical phase-locked loop, and feeds the two data streams into the residual phase noise compensation module for processing and generating a digital signal; S3, the digital signals generated by each branch are respectively connected to the coherent merging module for processing and output, realizing diversity reception of atmospheric coherent laser communication.

[0016] Compared with the prior art, the present invention has the following advantages: (1) This invention can be applied to atmospheric laser communication, laser-RF integrated communication, satellite laser communication, stratospheric laser communication and other scenarios, making full use of the diversity gain of laser communication, thereby improving the reliability of atmospheric laser communication; (2) In this invention, only one optical phase-locked loop is needed to compensate for the large frequency difference (GHz level) in coherent laser communication, and the output local oscillator light is allocated for coherent demodulation of other branch signal light, avoiding the use of multiple optical phase-locked loops, which greatly reduces the complexity of the coherent laser communication diversity receiving system.

[0017] (3) In this invention, the phase error information of the feedback optical phase-locked loop is not provided by a fixed branch, but by the phase error selection module monitoring the status of each branch and outputting the branch with the highest signal-to-noise ratio, thus avoiding problems such as optical phase-locking failure and instability caused by deep channel fading (10-40dB).

[0018] (4) In this invention, the residual phase difference compensation of each branch does not take the demodulated data of a certain fixed branch as a reference, but selects the branch data with the largest signal-to-noise ratio as the phase reference in the residual phase noise compensation module, thereby avoiding the influence of additional phase noise introduced by the fixed branch optical phase lock under the atmospheric channel, thus improving the robustness of diversity reception.

[0019] (5) In this invention, the coherent combining module uses channel estimation, matched filtering, maximum signal-to-noise ratio combining and other technologies to achieve coherent combining of multiple signals, and has strong environmental adaptability.

[0020] (6) The present invention can adapt diversity reception under different atmospheric channel (weak-medium-strong atmospheric turbulence) conditions by flexibly adjusting the number of pilots in the transmitted data frame.

[0021] (7) The present invention is transparent to the modulation format of the signal and is compatible with coherent diversity reception of modulation formats such as on-off keying (OOK), binary phase keying modulation (BPSK), differential phase shift keying (DPSK), and quadrature phase shift keying (QPSK).

[0022] (8) The present invention adopts a hybrid analog coherent reception (optical phase-locked loop to achieve zero-difference coherence) and digital combining technology (residual phase noise compensation and coherent combining), which greatly reduces the system power consumption of coherent lasers compared with pure digital phase-locked loops, and is easy to promote to multi-channel (N>4) coherent diversity reception systems. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a coherent laser communication diversity receiving system with adaptive atmospheric channels. Figure 2 This is a schematic diagram of the phase error module. Figure 3A schematic diagram of the phase error selection module; Figure 4 This is a schematic diagram of the residual phase noise compensation module; Figure 5 This is a schematic diagram of the coherent merging module.

[0024] The labels and their corresponding names in the attached diagram are as follows: 1. Optical amplifier; 2. 90° optical mixer; 3. Phase error module; 4. Phase error selection module; 5. Optical phase-locked loop; 6. Residual phase noise compensation module; 7. Coherent combining module; 31. Balanced detector; 32. Frequency and phase discriminator; 33. First low-pass filter; 41. Channel selector; 42. Second low-pass filter; 61. Data selector; 62. Third low-pass filter; 63. Fan-out; 64. Phase difference compensation module; 71. Channel estimator; 72. Matched filter; 73. Maximum signal-to-noise ratio combiner; 311. First balanced detector; 312. Second balanced detector. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0026] Example 1 like Figures 1 to 5 As shown, the purpose of this invention is to improve the stability of coherent laser communication in atmospheric channels, and a coherent laser communication diversity receiving system adapted to atmospheric channels is proposed. The system has three key features: First, it uses only one optical phase-locked loop (PLL) to compensate for the large frequency difference encountered in coherent laser communication, and outputs this local oscillator light for zero-difference coherent demodulation of each branch, thus avoiding the need for a separate PLL for each branch. Second, the phase error information of the PLL is not provided by a fixed branch, but is provided by a phase error selection module that monitors the status of each branch in real time and outputs the branch with the highest signal-to-noise ratio (SNR), thus avoiding PLL failure and instability caused by atmospheric channels. Third, the residual phase difference compensation of each branch does not use the demodulated data of a fixed branch as a reference, but instead selects the data of the branch with the highest SNR in the residual phase noise compensation module as the phase reference to compensate for the phase difference of other branches, thereby improving the robustness of diversity reception. Because it only requires one optical phase-locked loop, a highly reliable phase error selection module, a highly robust residual phase noise compensation module, and a multi-channel signal synchronization and merging algorithm, the reliability of atmospheric coherent laser communication is improved.

[0027] An adaptive atmospheric channel coherent laser communication diversity receiving system is disclosed. The system consists of five parts: an optical coherent receiving branch, an optical phase-locked loop, a phase error selection module, a residual phase noise compensation module, and a coherent merging module.

[0028] Furthermore, the optical coherent receiving branch consists of an optical amplifier, a 90° optical mixer, and a phase error module. The output port of the optical amplifier is connected to the local oscillator input port of the 90° optical mixer, and the output port of the 90° optical mixer is connected to the input port of the phase error module.

[0029] Furthermore, the connection relationship between the optical coherent receiving branch and other modules is as follows: one output port of the phase error module of each branch is connected to the input port of the phase error selection module and the other is connected to the input port of the residual phase noise compensation module. The output port of the phase error selection module is connected to the input port of the optical phase-locked loop. The output port of the optical phase-locked loop (local oscillator) is connected to the input port of the optical amplifier. The output terminal (digital signal) of the residual phase noise compensation module is connected to the coherent merging module, outputting the digital signal for diversity reception, thereby realizing diversity reception of coherent laser communication.

[0030] The optical field scalars of signal light 1, signal light 2, ..., signal light N-1 and signal light N are respectively: ; ; ; ; The frequencies of the signal light are all 100. The optical powers are respectively , , , The light phases are respectively , , , Due to the influence of atmospheric channels, all optical signals experienced slow-varying, independent random channel fading, while the optical phases experienced slow-varying, independent phase distortion and fluctuations.

[0031] The optical field scalar of the local oscillator output from the optical phase-locked loop is: ; Among them, the optical power is The light phase is .

[0032] The signal light from each branch is coherently mixed with the local oscillator light. Assuming that the phase difference signal-to-noise ratio of the branch corresponding to signal light 1 is highest within a certain time period, the phase error selection module outputs the phase error of signal light 1 and feeds it back to the optical phase-locked loop (PLL). Therefore, the PLL ensures that the frequency and phase of the local oscillator light are consistent with those of signal light 1, i.e.: ; At this point, the phase error module demodulates the digital baseband signal corresponding to signal light 1, and the local oscillator light output from the optical phase-locked loop is split and used for coherent detection of signal light 2, ..., signal light N-1 and signal light N. Correspondingly, the photocurrent signal output by the phase error module of each branch (taking the in-phase I path as an example) is... ; ; ; in, To balance the detector's responsivity, , , These are the phase shifts generated between the local oscillator light and signal light 2, signal light N-1, and signal light N after passing through optical fiber, optical amplifier, and 90° optical mixer.

[0033] The present invention provides a coherent laser communication diversity reception method for adaptive atmospheric channels, the method comprising the following steps: Step 1: Based on the slow-changing characteristics of the atmospheric channel, the transmitted baseband data and pilot data are framed.

[0034] Step 2: Receive signal light For example, the signal light of this branch The local oscillator light is coherently mixed with the optical signal on a 90° optical mixer. The signal is then converted into I / Q channel data with phase error by the phase error module and the phase error itself. The phase error is then fed into the phase error selection module to control the optical phase-locked loop. The I / Q channel data is fed into the residual phase noise compensation module for low-pass filtering, phase noise compensation and other processing, and a stable digital signal is generated.

[0035] Step 3: The digital signals generated by each branch are respectively connected to the coherent combining module, and channel estimation and matched filtering of each signal are performed based on the pilot of each frame of data. Finally, the digital signals are combined and output through the maximum signal-to-noise ratio, thereby realizing diversity reception of atmospheric coherent laser communication.

[0036] Compared with the prior art, the advantages of the present invention are as follows: (1) This invention can be applied to atmospheric laser communication, laser-RF integrated communication, satellite laser communication, stratospheric laser communication and other scenarios, making full use of the diversity gain of laser communication, thereby improving the reliability of atmospheric laser communication; (2) In this invention, only one optical phase-locked loop is needed to compensate for the large frequency difference (GHz level) in coherent laser communication, and the output local oscillator light is allocated for coherent demodulation of other branch signal light, avoiding the use of multiple optical phase-locked loops, which greatly reduces the complexity of the coherent laser communication diversity receiving system.

[0037] (3) In this invention, the phase error information of the feedback optical phase-locked loop is not provided by a fixed branch, but by the phase error selection module monitoring the status of each branch and outputting the branch with the highest signal-to-noise ratio, thus avoiding problems such as optical phase-locking failure and instability caused by deep channel fading (10-40dB).

[0038] (4) In this invention, the residual phase difference compensation of each branch does not take the demodulated data of a certain fixed branch as a reference, but selects the branch data with the largest signal-to-noise ratio as the phase reference in the residual phase noise compensation module, thereby avoiding the influence of additional phase noise introduced by the fixed branch optical phase lock under the atmospheric channel, thus improving the robustness of diversity reception.

[0039] (5) In this invention, the coherent combining module uses channel estimation, matched filtering, maximum signal-to-noise ratio combining and other technologies to achieve coherent combining of multiple signals, and has strong environmental adaptability.

[0040] (6) The present invention can adapt diversity reception under different atmospheric channel (weak-medium-strong atmospheric turbulence) conditions by flexibly adjusting the number of pilots in the transmitted data frame.

[0041] (7) The present invention is transparent to the modulation format of the signal and is compatible with coherent diversity reception of modulation formats such as on-off keying (OOK), binary phase keying modulation (BPSK), differential phase shift keying (DPSK), and quadrature phase shift keying (QPSK).

[0042] (8) The present invention adopts a hybrid analog coherent reception (optical phase-locked loop to achieve zero-difference coherence) and digital combining technology (residual phase noise compensation and coherent combining), which greatly reduces the system power consumption of coherent lasers compared with pure digital phase-locked loops, and is easy to promote to multi-channel (N>4) coherent diversity reception systems.

[0043] Example 2 like Figures 1 to 5 As shown, as a further optimization of Embodiment 1, this embodiment also includes the following technical features based on Embodiment 1: See Figure 1As shown, this invention proposes a coherent laser communication diversity receiving system with an adaptive atmospheric channel. Its components include an optical amplifier 1, a 90° optical mixer 2, a phase error module 3, a phase error selection module 4, an optical phase-locked loop 5, a residual phase noise compensation module 6, and a coherent merging module 7. In this example, the laser wavelength is 1550nm, the modulation format is BPSK, the total length of each data frame is 2048 bits, the communication rate is 10Gbps, the output optical power of the optical amplifier 1 is 48mW, the 90° optical mixer 2 outputs I and Q optical signals, and the phase error module 3, phase error selection module 4, residual phase noise compensation module 6, and coherent merging module all support high-speed signal transmission of DC-10Gbps.

[0044] The phase error module 3 outputs phase error and I / Q channel data, mainly composed of a balanced detector 31 (including a first balanced detector 311 and a second balanced detector 312), a frequency and phase detector 32, and a first low-pass filter 33. The balanced detector 31 (with a bandwidth of 10 GHz) is located on both the I and Q channels and generates I / Q channel data. The frequency and phase detector 32 generates error information containing frequency and phase differences, which is then smoothed by the first low-pass filter 33 to generate phase error information.

[0045] The phase error selection module 4 mainly consists of a channel selector 41 and a second low-pass filter 42. Due to the random deep fading (10-40dB) of the atmospheric channel, a single branch signal light is easily interrupted, leading to instability in the single-branch optical phase-locked loop and deterioration of residual phase noise. Thanks to the coherent characteristics of the atmospheric channel, the probability of multiple signal lights simultaneously experiencing deep fading or interruption is very low. Therefore, in this module, the phase error of a fixed branch is not used. Instead, the phase error information of all branches is collected into the channel selector 41, and the signal-to-noise ratio of the phase error of each branch is monitored in real time. The phase error of the branch with the highest signal-to-noise ratio is selected through gating information S0 and S1, and then smoothed by the second low-pass filter 42 before being fed back to the optical phase-locked loop. For BPSK signals in the Gbps range, the atmospheric channel and phase error can be considered as slowly varying processes. Therefore, within a time interval on the order of milliseconds, the amplitude of the signal light power and phase error can be considered to remain almost constant, avoiding frequent selection and switching of the phase error signal. In this scheme, the channel selector uses high-speed AD / DA and FPGA to realize functions such as phase error signal acquisition, signal-to-noise ratio comparison, and phase error gating. It also compares the signal-to-noise ratio of the phase error of each branch every 5ms, thereby avoiding problems such as optical phase-locking failure and instability caused by atmospheric channels.

[0046] The optical phase-locked loop 5 employs optical phase-locking technology, ensuring that the frequency and phase of the output local oscillator light are identical to the signal light to be locked. It can also compensate for frequency differences present in coherent laser communication in real time and allocate the local oscillator light for coherent demodulation of other branch signal lights. The center wavelength of the local oscillator laser output by this optical phase-locked loop is 1550nm, with a tuning range up to 40GHz, covering the frequency difference range of laser communication. Since the acquisition time of the phase-locked loop is on the order of 3-10ms, to avoid frequent unlocking and locking processes, the phase error selection module 4 must employ techniques such as hold and delay comparison at the algorithm level to minimize frequent switching.

[0047] The residual phase noise compensation module 6 consists of a data selector 61, a third low-pass filter 62, a fan-out 63, and a phase difference compensation module 64. When the optical phase-locked loop (PLL) achieves optical phase locking with the signal light of a certain branch, although the frequency of the output local oscillator is the same as that of the signal light of other branches, the phase of each signal light exhibits a certain degree of randomness under atmospheric conditions. Furthermore, the allocated local oscillator light is introduced with additional random phase noise after passing through different optical amplifiers, 90° optical mixers, and fiber optic devices. Therefore, residual phase noise still exists between the other signal lights and the local oscillator light, and the demodulated digital signal exhibits significant random fluctuations, requiring secondary compensation. Generally, the PLL 5 can achieve zero-difference coherent demodulation of the signal light of a certain branch, meaning that the signal-to-noise ratio of the digital signal in that branch is maximized, and the residual phase noise is approximately 0. Using the gating information S0 and S1 output by the phase error selection module 4, the digital signal of the branch can be selected in the data selector 61 and then passed through the third low-pass filter 62 and fan-out 63 as a reference input to the phase difference compensation module 64 to compensate for the residual phase noise in the digital signals of other branches.

[0048] To reduce system complexity, the phase difference compensation module 64 of this invention employs classic phase noise compensation algorithms (maximum likelihood phase estimation, M-fold multiplication, etc.) to correct phase deviations in other branch digital signals, thereby achieving stable output of each digital signal. In this example, the bandwidth of the data selector 61, the third low-pass filter 62, and the fan-out 63 is 10 GHz, and the phase difference compensation module 64 uses a double multiplication, a digital domain phase-locked loop, and a soft-decision method.

[0049] The coherent combining module 7 comprises a channel estimator 71, a matched filter 72, and a maximum signal-to-noise ratio (MSNR) combiner 73. This module is used for the coherent combining of multiple baseband digital signals to achieve multi-channel signal synchronization and diversity reception in coherent laser communication. In the channel estimator 71, atmospheric channel estimation is performed using the pilot signals of each frame of data. The length of the pilot sequence is approximately 1 / 10 to 1 / 5 of the data length to balance high-precision atmospheric channel estimation with high-speed transmission requirements. Since the coherence time of the atmospheric channel is on the order of milliseconds while the communication rate is on the order of Gbps, high-precision atmospheric channel estimation can be achieved with an interval of 5 milliseconds. The matched filter 72 not only achieves the maximum MSNR output for each digital signal but also extracts time synchronization information to facilitate the maximum MSNR combiner 73 in achieving coherent combining of multiple signals, thereby achieving optimal diversity reception gain.

[0050] As described above, the present invention can be implemented well.

[0051] All features disclosed in all embodiments of this specification, or steps in all methods or processes implied in the disclosure, may be combined and / or extended or replaced in any way, except for mutually exclusive features and / or steps.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Based on the technical essence of the present invention, any simple modifications, equivalent substitutions, and improvements made to the above embodiments within the spirit and principles of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A coherent laser communication diversity receiving system with adaptive atmospheric channels, characterized in that, It includes N optical amplifiers (1), N 90° optical mixers (2), N phase error modules (3), a phase error selection module (4), an optical phase-locked loop (5), a residual phase noise compensation module (6), and a coherent merging module (7). Each 90° optical mixer (2) is used to receive one signal light. The output of the i-th optical amplifier (1), the i-th 90° optical mixer (2), the i-th phase error module (3), the phase error selection module (4), the optical phase-locked loop (5), and the input of the i-th optical amplifier (1) are connected in sequence. The i-th optical amplifier (1), the i-th 90° optical mixer (2), the i-th phase error module (3), the residual phase noise compensation module (6), and the coherent merging module (7) are connected in sequence. Wherein, 1≤i≤N and i is an integer, N≥2 and N is an integer.

2. The coherent laser communication diversity receiving system with adaptive atmospheric channel according to claim 1, characterized in that, The phase error module (3) includes two balanced detectors (31) and a frequency and phase detector (32). The two balanced detectors (31) are respectively referred to as the first balanced detector (311) and the second balanced detector (312). The first balanced detector (311) and the second balanced detector (312) are respectively connected to a 90° optical mixer (2). The first balanced detector (311), the frequency and phase detector (32), and the second balanced detector (312) are connected in sequence.

3. The coherent laser communication diversity receiving system with adaptive atmospheric channel according to claim 2, characterized in that, The phase error module (3) also includes a first low-pass filter (33) connected to the frequency and phase detector (32).

4. The coherent laser communication diversity receiving system with adaptive atmospheric channel according to claim 3, characterized in that, The phase error selection module (4) includes a channel selector (41) connected to a first low-pass filter (33).

5. The coherent laser communication diversity receiving system with adaptive atmospheric channel according to claim 4, characterized in that, The phase error selection module (4) also includes a second low-pass filter (42) connected to the channel selector (41).

6. The coherent laser communication diversity receiving system with adaptive atmospheric channel according to claim 5, characterized in that, The residual phase noise compensation module (6) includes N data selectors (61), N third low-pass filters (62), one fan-out (63), and N-1 phase difference compensation modules (64). The first data selector (61) is connected to the first low-pass filter (33). The first data selector (61), the first third low-pass filter (62), and the fan-out (63) are connected in sequence. The i-th data selector (61), the i-th third low-pass filter (62), and the i-th phase difference compensation module (64) are connected in sequence. The fan-out (63) is connected to the i-th phase difference compensation module (64). Where i ≥ 2.

7. The coherent laser communication diversity receiving system with adaptive atmospheric channels according to claim 6, characterized in that, The coherent combining module (7) includes a maximum signal-to-noise ratio combiner (73), which is used for the combination of digital signals output by each phase difference compensation module (64).

8. The coherent laser communication diversity receiving system with adaptive atmospheric channel according to claim 7, characterized in that, It also includes a matched filter (72), a residual phase noise compensation module (6), a matched filter (72), and a maximum signal-to-noise ratio combiner (73) connected in sequence.

9. A coherent laser communication diversity receiving system with an adaptive atmospheric channel according to claim 8, characterized in that, It also includes a channel estimator (71), a residual phase noise compensation module (6), a channel estimator (71), a matched filter (72), and a maximum signal-to-noise ratio combiner (73) connected in sequence.

10. A method for coherent laser communication diversity reception in an adaptive atmospheric channel, characterized in that, The coherent laser communication diversity receiving system with an adaptive atmospheric channel as described in any one of claims 1 to 9 includes the following steps: S1, based on the slow-changing characteristics of the atmospheric channel, performs frame processing on the transmitted baseband data and pilot data; S2, receive signal light, coherently mix each branch signal light with the local oscillator light on a 90° optical mixer (2), convert it into two data with phase error and phase error through the phase error module (3), then feed the phase error into the phase error selection module (4) and then feed it back to control the optical phase-locked loop (5), and feed the two data into the residual phase noise compensation module (6) for processing and generate digital signals; S3, the digital signals generated by each branch are respectively connected to the coherent merging module (7) for processing and output, so as to realize the diversity reception of atmospheric coherent laser communication.

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