Multi-format compatible space laser communication receiving device and method

Abstract

A multi-format compatible space laser communication receiving device and method belongs to the field of free space optical communication technology. In order to solve the problem of high complexity and high maintenance cost of the existing system, and facing the problem of poor applicability of dynamic channel characteristics in the space laser communication system, the signal source of the device is connected to the IQ modulator through a radio frequency line, the C-band tunable laser is connected to the IQ modulator through an optical fiber, the IQ modulator is connected to the power amplifier, the power amplifier is connected to the transmitting antenna through an optical fiber, the transmitting antenna and the receiving antenna are wirelessly transmitted, the receiving antenna is connected to the optical fiber coupler through an optical fiber, the optical fiber coupler is respectively connected to the preamplifier and the optical power module through an optical fiber, the preamplifier, the photodetector, and the analog-to-digital converter are connected in turn through optical fibers, the analog-to-digital converter and the FPGA are connected with an radio frequency line, and the optical power module and the temperature pulsator are respectively connected to the FPGA through a USB data line. While meeting the requirements of multi-format compatible reception and high speed, the requirements for system hardware are reduced, the cost is low and the reliability is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of free space optical communication, and in particular relates to a multi-format compatible space laser communication receiving device and method. Background Art

[0002] Free space optical communication has the advantages of high speed, good confidentiality and light weight, and is an important part of the future wireless communication field. At present, long-distance and high-speed space laser communication mostly adopts high-sensitivity coherent communication system, which can demodulate various advanced modulation formats. Considering the compatibility of future communication networks, multi-format compatible receivers have been rapidly developed.

[0003] Multi-format compatible receivers are mainly composed of optical mixers, balanced detectors, local oscillator lasers, etc. The hardware is complex, the cost is high and the reliability is poor. They are not applicable in some light and small and dynamic channel scenarios. To this end, a direct detection method based on the Kramers-Kronig algorithm is proposed to achieve multi-format compatible reception. At the same time, considering the dynamic channels (turbulence, absorption and scattering) in the space laser communication system, a hybrid adaptive equalization method based on the received light intensity jitter and turbulence test is proposed. This method improves the communication signal distortion under the change of turbulence intensity and improves the anti-turbulence performance.

[0004] See Zhao He's master's thesis "Research on Multi-Modulation Format Compatible High-Speed ​​Laser Modulation Transmission Technology", which uses dual IQ modulators at the transmitter and coherent detection at the receiver, and is compatible with receiving multiple communication formats; the receiver consists of two optical mixers, four balanced detectors, and two local oscillator lasers. The device can effectively be compatible with multiple communication formats for transmission and can be compatible with receiving multiple communication formats at the same time. It has high speed and high applicability. However, this solution increases the complexity of the system and has high maintenance costs, and does not take into account the dynamic channel (turbulence, etc.) problems in space laser communication systems.

[0005] In addition, traditional receivers based on the Kramers-Kronig algorithm can demodulate the phase modulation format through direct detection, but receivers based on the Kramers-Kronig algorithm do not achieve multi-format compatible reception. In addition, traditional receivers are oriented to optical fiber communication applications, and have poor applicability to dynamic channel characteristics (turbulence, etc.) in space laser communication systems. Summary of the invention

[0006] The present invention solves the problems of high complexity and high maintenance cost of existing systems and poor applicability of dynamic channel characteristics in space laser communication systems, and proposes an adaptive equalization multi-format compatible space laser communication receiving device and method based on the Kramers-Kronig algorithm.

[0007] The technical solution of the present invention to solve the technical problem is:

[0008] A multi-format compatible space laser communication receiving device, the device comprising a signal source, a C-band tunable laser, an IQ modulator, a power amplifier, a transmitting antenna, a receiving antenna, a fiber coupler, a preamplifier, a photodetector, an analog-to-digital converter, an optical power module, a temperature pulsator and an FPGA;

[0009] The signal source is connected to the IQ modulator via a radio frequency line, the C-band tunable laser is connected to the IQ modulator via an optical fiber, the IQ modulator is connected to the power amplifier, the power amplifier is connected to the transmitting antenna via an optical fiber, the transmitting antenna is wirelessly transmitted with the receiving antenna, the receiving antenna is connected to the optical fiber coupler via an optical fiber, the optical fiber coupler is respectively connected to the preamplifier and the optical power module via an optical fiber, the preamplifier, the photodetector, and the analog-to-digital converter are connected in sequence via optical fibers, the analog-to-digital converter is connected to the FPGA via a radio frequency line, and the optical power module and the temperature pulsator are respectively connected to the FPGA via a USB data line.

[0010] A single-sideband electrical signal is generated and emitted by a signal source, and is loaded onto an optical signal generated by a C-band tunable laser through an IQ modulator. At the same time, the bias operating point of the IQ modulator is adjusted to adjust the optical signal to a single-sideband optical signal. After the power is amplified by a power amplifier, the single-sideband optical signal is transmitted to a transmitting antenna. The transmitting antenna transmits the single-sideband optical signal, which is received by a receiving antenna through an atmospheric channel. The receiving antenna transmits the received single-sideband optical signal to a fiber coupler. The fiber coupler is divided into two transmission paths. The first optical signal is amplified by a preamplifier. The amplified single-sideband optical signal is accessed to a demodulator and restored by an optical fiber to a photodetector, and the optical signal is converted into an electrical signal. The analog signal is then converted into a digital signal through an analog-to-digital converter, and then the signal is transmitted to an FPGA for signal recovery. The second optical signal is connected to an FPGA through an optical power module to calculate the flicker index of the received light intensity jitter and feed it back to the FPGA in real time. The temperature pulsator feeds back the atmospheric refractive index structure constant to the FPGA in real time. The FPGA assigns weights to the light intensity jitter and the atmospheric refractive index structure constant and performs adaptive equalization.

[0011] The optical fiber coupler divides the input optical signal into two output optical signals at a ratio of 1:99.

[0012] The preamplifier is a gain-adjustable erbium-doped fiber amplifier.

[0013] A communication receiving method of a multi-format compatible space laser communication receiving device, the method comprising the following steps:

[0014] Step 1, transmitting a multi-format single sideband optical signal;

[0015] The signal source 1 generates and transmits a multi-format single-sideband electrical signal, which is loaded onto a 1550nm single-sideband optical signal generated by a C-band tunable laser 2 through an IQ modulator 3, and then enters a power amplifier 4 to amplify the power of the single-sideband optical signal. The amplified single-sideband optical signal enters a transmitting antenna 5 for transmission;

[0016] At the same time, the bias point of the IQ modulator 3 is switched, and when the bias point is adjusted to an orthogonal bias point, single-sideband optical modulation of each signal is performed.

[0017] Step 2, receiving the single sideband optical signal and processing the signal into an electrical signal;

[0018] After the single-sideband optical signal emitted from the IQ modulator 3 is transmitted to the receiving antenna 6 by the transmitting antenna 5, it is divided into two optical signals by the optical fiber coupler 7. The power of the first optical signal is amplified by the preamplifier 8. The amplified single-sideband optical signal is connected to the demodulation recovery of the photodetector 9 through the optical fiber, and the optical signal is converted into an electrical signal. Then, the analog signal is converted into a digital signal by the analog-to-digital converter, and the digital signal is transmitted to the FPGA13 for signal recovery. The second optical signal is connected to the FPGA13 through the optical power module 11 to calculate the flicker index of the received light intensity jitter and feed it back to the FPGA13 in real time. The temperature pulsator 12 feeds back the atmospheric refractive index structure constant to the FPGA13 in real time. The FPGA13 assigns weights to the light intensity jitter and the atmospheric refractive index structure constant and performs adaptive equalization.

[0019] Step 3, recovering and adaptively equalizing and demodulating the incoherent signal;

[0020] First, the complete signal is restored based on the Kramers-Kronig algorithm; then, the signal is demodulated in an incoherent manner and then in a coherent manner; Figure 2 As shown;

[0021] The incoherent demodulation method is as follows: the optical power module 11 is used to obtain the received light intensity jitter in real time, and the temperature pulsator 12 is used to obtain the atmospheric refractive index structure constant in real time. Value; FPGA13 uses RLS algorithm for adaptive equalization based on the results of received light intensity jitter and turbulence test; after adaptive equalization, threshold judgment, bit synchronization and bit error rate calculation, non-coherent demodulation is completed;

[0022] The specific contents of adaptive equalization are as follows: Adaptive equalization based on the received light intensity jitter and turbulence test RLS algorithm, real-time update of the forgetting factor, in this way can better adapt to changes in the turbulent environment:

[0023] (one);

[0024] in, represents the cost function, which is used to minimize the weighted sum of squared errors, is a time series, represents the error signal, is the expected output, is the filter coefficient vector, is the input signal, It is the forgetting factor;

[0025] The forgetting factor update formula is as follows:

[0026] (two);

[0027] in, is the update forgetting factor, is the initial value, is the light intensity jitter flicker index, and is the update weight;

[0028] If the signal is demodulated by the non-coherent demodulation method and the bit error rate meets the requirements, OOK demodulation is completed. If the bit error rate is greater than 0.1, the coherent demodulation method is directly entered (step 4), and then the PSK demodulation process is entered in turn.

[0029] Step 4, recovering and adaptively equalizing and demodulating the coherent signal;

[0030] The signal is sequentially subjected to clock recovery, constant modulus equalization, frequency offset estimation, and phase recovery to obtain a pre-decision signal. The signal is subjected to the same adaptive equalization as step 3, and then bit synchronization and bit error rate calculation are performed to complete demodulation.

[0031] Step 5, determine the communication status and restart the demodulation system;

[0032] If demodulation is still not completed in step 4 (the bit error rate is still greater than 0.1), it is determined that the current channel environment is poor and error-free transmission cannot be achieved. The current modulation format is defaulted to PSK, and step 3 is re-entered after waiting for a while.

[0033] The beneficial effects of the present invention are:

[0034] The main functions realized by the present invention are: modulation and demodulation of multi-format signals based on Kramers-Kronig algorithm; hybrid adaptive equalization based on received light intensity jitter and turbulence test.

[0035] 1) Compared with the multi-format signal demodulation of traditional coherent detection, the demodulation structure and algorithm based on the Kramers-Kronig algorithm completes multi-format signal demodulation without format recognition, saving hardware logic resources and system power consumption. At the same time, it reduces the hardware such as local oscillator laser, balanced detector, optical mixer, etc., reduces the requirements for system hardware, has low cost and high reliability.

[0036] 2) The hybrid adaptive equalization method based on the received light intensity jitter and turbulence test of the present invention can effectively improve the communication signal distortion under the change of turbulence intensity, thereby facilitating the judgment of multiple formats and improving the communication error performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of the multi-format compatible space laser communication receiving device of the present invention.

[0038] Figure 2 This is a flow chart of the demodulation algorithm described in the present invention. DETAILED DESCRIPTION

[0039] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0040] like Figure 1 As shown, a multi-format compatible space laser communication receiving device includes a signal source 1, a C-band tunable laser 2, an IQ modulator 3, a power amplifier 4, a transmitting antenna 5, a receiving antenna 6, a fiber coupler 7, a preamplifier 8, a photodetector 9, an analog-to-digital converter 10, an optical power module 11, a temperature pulsator 12 and an FPGA 13;

[0041] The signal source 1 is connected to the IQ modulator 3 via a radio frequency line, the C-band tunable laser 2 is connected to the IQ modulator 3 via an optical fiber, the IQ modulator 3 is connected to the power amplifier 4, the power amplifier 4 is connected to the transmitting antenna 5 via an optical fiber, the transmitting antenna 5 is wirelessly transmitted with the receiving antenna 6, the receiving antenna 6 is connected to the optical fiber coupler 7 via an optical fiber, the optical fiber coupler 7 is respectively connected to the preamplifier 8 and the optical power module 11 via an optical fiber, the preamplifier 8, the photodetector 9, and the analog-to-digital converter 10 are connected in sequence via optical fibers, the analog-to-digital converter 10 is connected to the FPGA 13 via a radio frequency line, and the optical power module 11 and the temperature pulsator 12 are respectively connected to the FPGA 13 via a USB data line.

[0042] The signal source 1 generates and transmits multi-format single-sideband electrical signals based on an FPGA high-speed board.

[0043] The C-band tunable laser 2 is used to generate signal light with a narrow line width and stable wavelength in the 1550nm band.

[0044] The optical fiber coupler 7 splits the input optical signal into two output optical signals at a ratio of 1:99.

[0045] The preamplifier 8 is a gain-adjustable erbium-doped fiber amplifier, which is used to amplify the signal light power received by the receiving end.

[0046] A single sideband electrical signal is generated and emitted by a signal source 1, and is loaded onto an optical signal generated by a C-band tunable laser 2 through an IQ modulator 3. At the same time, the bias operating point of the IQ modulator 3 is adjusted to adjust the optical signal to a single sideband optical signal. After the power is amplified by a power amplifier 4, the single sideband optical signal is transmitted to a transmitting antenna 5. The transmitting antenna 5 transmits the single sideband optical signal, which is received by a receiving antenna 6 through an atmospheric channel. The receiving antenna 6 transmits the received single sideband optical signal to a fiber coupler 7. The optical fiber coupler 7 is divided into two transmission paths. The first optical signal is amplified by the preamplifier 8. The amplified single-sideband optical signal is accessed through the optical fiber to the demodulation recovery of the photodetector 9, and the optical signal is converted into an electrical signal. The analog signal is then converted into a digital signal through the analog-to-digital converter 10, and the signal is transmitted to the FPGA13 for signal recovery; the second optical signal is connected to the FPGA13 through the optical power module 11 to calculate the flicker index of the received light intensity jitter and feed it back to the FPGA13 in real time. The temperature pulsator 12 feeds back the atmospheric refractive index structure constant to the FPGA13 in real time. The FPGA13 assigns weights to the light intensity jitter and the atmospheric refractive index structure constant and performs adaptive equalization.

[0047] A multi-format compatible space laser communication receiving method, the method comprising the following steps:

[0048] Step 1, transmitting a multi-format single sideband optical signal;

[0049] The signal source 1 generates and transmits a multi-format single-sideband electrical signal, which is loaded onto a 1550nm single-sideband optical signal generated by a C-band tunable laser 2 through an IQ modulator 3, and then enters a power amplifier 4 to amplify the power of the single-sideband optical signal. The amplified single-sideband optical signal enters a transmitting antenna 5 for transmission;

[0050] At the same time, the bias point of the IQ modulator 3 is switched, and when the bias point is adjusted to an orthogonal bias point, single-sideband optical modulation of each signal is performed.

[0051] Step 2, receiving the single sideband optical signal and processing the signal into an electrical signal;

[0052] After the single-sideband optical signal emitted from the IQ modulator 3 is transmitted to the receiving antenna 6 by the transmitting antenna 5, it is divided into two optical signals by the optical fiber coupler 7. The power of the first optical signal is amplified by the preamplifier 8. The amplified single-sideband optical signal is connected to the demodulation recovery of the photodetector 9 through the optical fiber, and the optical signal is converted into an electrical signal. Then, the analog signal is converted into a digital signal by the analog-to-digital converter, and the digital signal is transmitted to the FPGA13 for signal recovery. The second optical signal is connected to the FPGA13 through the optical power module 11 to calculate the flicker index of the received light intensity jitter and feed it back to the FPGA13 in real time. The temperature pulsator 12 feeds back the atmospheric refractive index structure constant to the FPGA13 in real time. The FPGA13 assigns weights to the light intensity jitter and the atmospheric refractive index structure constant and performs adaptive equalization.

[0053] Step 3, recovering and adaptively equalizing and demodulating the incoherent signal;

[0054] First, the complete signal is restored based on the Kramers-Kronig algorithm; then, the signal is demodulated in an incoherent manner and then in a coherent manner; Figure 2 As shown;

[0055] The incoherent demodulation method is as follows: the optical power module 11 is used to obtain the received light intensity jitter in real time, and the temperature pulsator 12 is used to obtain the atmospheric refractive index structure constant in real time. Value; FPGA13 uses RLS algorithm for adaptive equalization based on the results of received light intensity jitter and turbulence test; after adaptive equalization, threshold judgment, bit synchronization and bit error rate calculation, non-coherent demodulation is completed;

[0056] The specific contents of adaptive equalization are as follows: Adaptive equalization based on the received light intensity jitter and turbulence test RLS algorithm, real-time update of the forgetting factor, in this way can better adapt to changes in the turbulent environment:

[0057] (one);

[0058] in, represents the cost function, which is used to minimize the weighted sum of squared errors, is a time series, represents the error signal, is the expected output, is the filter coefficient vector, is the input signal, It is the forgetting factor;

[0059] The forgetting factor update formula is as follows:

[0060] (two);

[0061] in, is the update forgetting factor, is the initial value, is the light intensity jitter flicker index, and is the update weight;

[0062] If the signal is demodulated by the non-coherent demodulation method and the bit error rate meets the requirements, OOK demodulation is completed. If the bit error rate is greater than 0.1, the coherent demodulation method is directly entered (step 4), and then the PSK demodulation process is entered in turn.

[0063] Step 4, recovering and adaptively equalizing and demodulating the coherent signal;

[0064] The signal is sequentially subjected to clock recovery, constant modulus equalization, frequency offset estimation, and phase recovery to obtain a pre-decision signal. The signal is subjected to the same adaptive equalization as step 3, and then bit synchronization and bit error rate calculation are performed to complete demodulation.

[0065] Step 5, determine the communication status and restart the demodulation system;

[0066] If demodulation is still not completed in step 4 (the bit error rate is still greater than 0.1), it is determined that the current channel environment is poor and error-free transmission cannot be achieved. The current modulation format is defaulted to PSK, and step 3 is re-entered after waiting for a while.

[0067] The implementation scheme described above can further change the wavelength, the number of carriers of different wavelengths, etc., and the implementation scheme only describes the preferred embodiments of the patent of the present invention, and does not limit the concept and scope of the patent of the present invention. Without departing from the design concept of the patent of the present invention, various changes and improvements made by professional and technical personnel in this field to the technical solution of the patent of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A multi-format compatible space laser communication receiving device, characterized in that: The device comprises a signal source (1), a C-band tunable laser (2), an IQ modulator (3), a power amplifier (4), a transmitting antenna (5), a receiving antenna (6), an optical fiber coupler (7), a preamplifier (8), a photodetector (9), an analog-to-digital converter (10), an optical power module (11), a temperature pulsator (12) and an FPGA (13); The signal source (1) is connected to the IQ modulator (3) via a radio frequency line, the C-band tunable laser (2) is connected to the IQ modulator (3) via an optical fiber, the IQ modulator (3) is connected to the power amplifier, the power amplifier (4) is connected to the transmitting antenna (5) via an optical fiber, the transmitting antenna (5) is wirelessly transmitted with the receiving antenna (6), the receiving antenna (6) is connected to the optical fiber coupler (7), the optical fiber coupler (7) is respectively connected to the preamplifier (8) and the optical power module (11) via an optical fiber, the preamplifier (8), the photodetector (9), and the analog-to-digital converter (10) are sequentially connected via optical fibers, the analog-to-digital converter (10) is connected to the FPGA (13) via a radio frequency line, and the optical power module (11) and the temperature pulsator (12) are respectively connected to the FPGA (13) via a USB data line; A single-sideband electrical signal is generated and emitted by a signal source (1), and is loaded onto an optical signal generated by a C-band tunable laser (2) through an IQ modulator (3). At the same time, the bias operating point of the IQ modulator (3) is adjusted to adjust the optical signal into a single-sideband optical signal. After the power is amplified by a power amplifier (4), the single-sideband optical signal is transmitted to a transmitting antenna (5). The transmitting antenna (5) transmits the single-sideband optical signal, which is received by a receiving antenna (6) through an atmospheric channel. The receiving antenna (6) transmits the received single-sideband optical signal to an optical fiber coupler (7); the optical fiber coupler (7) divides the signal into two transmission paths. The power of the first optical signal is amplified by a preamplifier (8). The amplified single-sideband optical signal is demodulated and restored by an optical fiber access photoelectric detector (9). The optical signal is converted into an electrical signal. The analog signal is converted into a digital signal by an analog-to-digital converter (10). The signal is then transmitted to an FPGA (13) for signal recovery. The second optical signal is connected to the FPGA (13) through the optical power module (11) to calculate the flicker index of the received light intensity jitter and feed it back to the FPGA (13) in real time, and the temperature pulsator (12) feeds back the atmospheric refractive index structure constant to the FPGA (13) in real time, and the FPGA (13) assigns weights to the light intensity jitter and the atmospheric refractive index structure constant and performs adaptive equalization; FPGA (13) recovers and adaptively equalizes and demodulates the incoherent signal: First, the complete signal is restored based on the Kramers-Kronig algorithm; then, the signal is demodulated in an incoherent manner and then in a coherent manner; The incoherent demodulation method is as follows: an optical power module (11) is used to obtain the received light intensity jitter in real time, and a temperature pulsator (12) is used to obtain the atmospheric refractive index structure constant in real time. Numerical value; FPGA (13) adopts RLS algorithm to perform adaptive equalization based on the results of received light intensity jitter and turbulence test; after adaptive equalization, threshold judgment, bit synchronization and bit error rate calculation, non-coherent demodulation is completed; The specific contents of adaptive equalization are as follows: Adaptive equalization based on the received light intensity jitter and turbulence test RLS algorithm, real-time update of the forgetting factor, in this way can better adapt to changes in the turbulent environment: Where J(n) represents the cost function, which is used to minimize the weighted error sum of squares, n is the time series, and e(i) = d i -ω T (i) χ(i) represents the error signal, d i is the desired output, ω(i) is the filter coefficient vector, χ(i) is the input signal, and δ is the forgetting factor; The forgetting factor update formula is as follows: Among them, δ i is the updated forgetting factor, C0 is the initial value, SI is the light intensity jitter flicker index, ω1 and ω2 are the updated weights; If the signal is demodulated by the non-coherent demodulation method and the bit error rate meets the conditions, OOK demodulation is completed. If the bit error rate is greater than 0.1, it directly enters the coherent demodulation method of the next step and enters the PSK demodulation process in turn.

2. The multi-format compatible space laser communication receiving device according to claim 1, characterized in that: The optical fiber coupler (7) splits the input optical signal into two output optical signals at a ratio of 1:

99.

3. The multi-format compatible space laser communication receiving device according to claim 1, characterized in that: The preamplifier (8) is a gain-adjustable erbium-doped fiber amplifier.

4. The communication receiving method of the multi-format compatible space laser communication receiving device according to claim 1, characterized in that: The method comprises the following steps: Step 1, transmitting a multi-format single sideband optical signal; A signal source (1) generates and transmits a multi-format single-sideband electrical signal, which is loaded onto a single-sideband optical signal generated by a C-band tunable laser (2) through an IQ modulator (3), and then enters a power amplifier (4) to amplify the power of the single-sideband optical signal. The amplified single-sideband optical signal enters a transmitting antenna (5) for transmission; At the same time, the bias point of the IQ modulator (3) is switched, and when the bias point is adjusted to an orthogonal bias point, single-sideband optical modulation of each signal is performed; Step 2, receiving the single sideband optical signal and processing the signal into an electrical signal; The single-sideband optical signal emitted from the IQ modulator (3) is transmitted to the receiving antenna (6) by the transmitting antenna (5), and then divided into two optical signals by the optical fiber coupler (7). The power of the first optical signal is amplified by the preamplifier (8). The amplified single-sideband optical signal is connected to the demodulation recovery of the photodetector (9) through the optical fiber, and the optical signal is converted into an electrical signal. The analog signal is then converted into a digital signal by the analog-to-digital converter, and the digital signal is transmitted to the FPGA (13) for signal recovery. The second optical signal is connected to the FPGA (13) through the optical power module (11) to calculate the flicker index of the received light intensity jitter and feed it back to the FPGA (13) in real time. The temperature pulsator (12) feeds back the atmospheric refractive index structure constant to the FPGA (13) in real time. The FPGA (13) assigns weights to the light intensity jitter and the atmospheric refractive index structure constant and performs adaptive equalization. Step 3, recovering and adaptively equalizing and demodulating the incoherent signal; First, the complete signal is restored based on the Kramers-Kronig algorithm; then, the signal is demodulated in an incoherent manner and then in a coherent manner; The incoherent demodulation method is as follows: an optical power module (11) is used to obtain the received light intensity jitter in real time, and a temperature pulsator (12) is used to obtain the atmospheric refractive index structure constant in real time. Numerical value; FPGA (13) adopts RLS algorithm to perform adaptive equalization based on the results of received light intensity jitter and turbulence test; after adaptive equalization, threshold judgment, bit synchronization and bit error rate calculation, non-coherent demodulation is completed; The specific contents of adaptive equalization are as follows: Adaptive equalization based on the received light intensity jitter and turbulence test RLS algorithm, real-time update of the forgetting factor, in this way can better adapt to changes in the turbulent environment: Where J(n) represents the cost function, which is used to minimize the weighted error sum of squares, n is the time series, and e(i) = d i -ω T (i) χ(i) represents the error signal, d i is the desired output, ω(i) is the filter coefficient vector, χ(i) is the input signal, and δ is the forgetting factor; The forgetting factor update formula is as follows: Among them, δ i is the updated forgetting factor, C0 is the initial value, SI is the light intensity jitter flicker index, ω1 and ω2 are the updated weights; If the signal is decoded by the non-coherent demodulation method and the bit error rate meets the conditions, OOK demodulation is completed. If the bit error rate is greater than 0.1, the next step of coherent demodulation is directly entered, and then the PSK demodulation process is entered in turn; Step 4, recovering and adaptively equalizing and demodulating the coherent signal; The signal is sequentially subjected to clock recovery, constant modulus equalization, frequency offset estimation, and phase recovery to obtain a pre-decision signal. The signal is subjected to the same adaptive equalization as step 3, and then bit synchronization and bit error rate calculation are performed to complete demodulation. Step 5, determine the communication status and restart the demodulation system; If demodulation is still not completed in step 4, that is, the bit error rate is still greater than 0.1, it is determined that the current channel environment is poor and error-free transmission cannot be achieved. The current modulation format is defaulted to PSK, and step 3 is re-entered after waiting for a while.

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