Method for reducing single beam alignment sensitivity in free space optical fiber network through maximum combination ratio

Abstract

The invention is applicable to the technical field of wireless and optical fiber hybrid networks, and provides a method for reducing single-beam alignment sensitivity in a free space optical fiber network with a maximum merging ratio, which comprises the following steps of: 1, loading a signal into a transmitter after resampling so as to generate a scalar or vector optical signal for spatial dimension multiplexing; 2, the optical signal is coupled into a transmission optical fiber for transmission, and after optical fiber transmission, the signal is emitted to a free space from an optical transceiver through a lens; in a free space, the signal is influenced by atmospheric conditions and turbulence, propagates with different propagation characteristics, and is focused again and guided into the optical fiber. The method for reducing the single beam alignment sensitivity in the free space optical fiber network with the maximum combination ratio is high in communication speed, high in reliability and suitable for FSO / optical fiber hybrid transmission system architectures of various optical fibers and modulation formats.

Description

Technical Field

[0001] The invention belongs to the technical field of wireless and optical fiber hybrid networks, and in particular to a method for alleviating the sensitivity of single light beam alignment in a free space optical fiber network by a maximum combining ratio. Background Art

[0002] In a hybrid network of free-space optical (FSO) and fiber-optic (Fiber) communications, the alignment sensitivity of single-beam transmission is one of the main bottlenecks that limit system performance and stability. The alignment requirements for the beam are very high, and a slight deviation may cause severe signal attenuation or even communication interruption due to factors such as equipment vibration, thermal expansion, wind disturbance or terrain changes. In addition, the beam is significantly affected by atmospheric turbulence, scattering and refraction during long-distance transmission, which exacerbates the instability of the signal.

[0003] Traditional methods usually alleviate the symptomatic problem by improving hardware accuracy or using a larger receiving surface, but these methods are difficult to balance system complexity and cost. Summary of the invention

[0004] The present invention provides a method for alleviating the sensitivity of single-beam alignment in a free-space optical fiber network with a maximum combining ratio, aiming to solve the problem that the above-mentioned background technology proposes to alleviate the symptomatic problem by improving hardware accuracy or adopting a larger receiving surface, but it is difficult to take into account both system complexity and cost.

[0005] To solve the above problems, the present invention is implemented as follows: a method for alleviating the single beam alignment sensitivity in a free space optical fiber network with a maximum combining ratio, comprising the following steps:

[0006] Step 1:

[0007] After resampling, the signal is loaded into the transmitter to generate a scalar or vector optical signal with spatial dimension multiplexing;

[0008] Step 2:

[0009] The optical signal is coupled into the transmission fiber for transmission. After a certain distance of fiber transmission, the signal is emitted from the optical terminal to free space through the lens.

[0010] In free space, the signal is affected by atmospheric conditions and turbulence, propagating with different propagation characteristics, and after traveling a certain distance, the signal is focused again and guided into the optical fiber;

[0011] Step 3:

[0012] After receiving the signal, the receiving end performs mode demultiplexing and polarization demultiplexing, and then performs coherent detection on the polarization demultiplexed signal to convert the optical signal into a baseband electrical signal and capture the final baseband electrical signal;

[0013] Step 4:

[0014] The baseband electrical signal passes through the DSP at the receiving end to obtain multiple signals, which are then combined using the maximum combining ratio algorithm to obtain the original signal after transmission.

[0015] Preferably, the scalar or vector signal generated by the transmitter in step 1 transmits the same scalar or vector optical signal in different optical fiber transmission space dimensions.

[0016] Preferably, the transmission optical fiber described in step 2 is compatible with one of single-core multi-mode, multi-core single-mode or multi-core multi-mode light.

[0017] Preferably, the original transmission signal described in step 4 includes an OOK signal, a PAM signal or a probability-shaped QAM signal.

[0018] Compared with the related art, the method for alleviating the single beam alignment sensitivity in a free space optical fiber network with the maximum combining ratio provided by the present invention has the following beneficial effects:

[0019] Compared with the existing technology, the maximum merging ratio method provided by this scheme to reduce the sensitivity of single beam alignment in free space fiber networks is compared with the existing technology. By merging the signals from multiple beam paths at the receiving end and dynamically adjusting the weights to maximize the signal-to-noise ratio, the system's anti-interference ability and transmission efficiency are significantly improved. Combined with the transmission method of multi-mode beams or multi-beam paths, the maximum merging ratio method can effectively reduce the dependence on single beam alignment, which is especially suitable for communication scenarios in dynamic or complex environments. This technology not only optimizes link performance, but also enhances the system's adaptability under harsh environmental conditions, showing strong practical application potential.

[0020] In summary, the method of the present invention for alleviating the single beam alignment sensitivity in a free space optical fiber network with maximum combining ratio has fast communication speed and high reliability, and is applicable to FSO / optical fiber hybrid transmission system architectures of various optical fibers and modulation formats. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a diagram of the FSO / fiber hybrid transmission system architecture based on the maximum combining ratio algorithm proposed in the present invention. DETAILED DESCRIPTION

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field of this application; the terms used in the specification of the application are only for the purpose of describing specific embodiments and are not intended to limit the application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0023] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0024] The embodiment of the present invention provides a method for alleviating the single beam alignment sensitivity in a free space optical fiber network with a maximum combining ratio, comprising the following steps:

[0025] Step 1:

[0026] After resampling, the signal is loaded into the transmitter to generate a scalar or vector optical signal with spatial dimension multiplexing;

[0027] Step 2:

[0028] The optical signal is coupled into the transmission fiber for transmission. After a certain distance of fiber transmission, the signal is emitted from the optical terminal to free space through the lens.

[0029] In free space, the signal is affected by atmospheric conditions and turbulence, propagating with different propagation characteristics, and after traveling a certain distance, the signal is focused again and guided into the optical fiber;

[0030] Step 3:

[0031] After receiving the signal, the receiving end performs mode demultiplexing and polarization demultiplexing, and then performs coherent detection on the polarization demultiplexed signal to convert the optical signal into a baseband electrical signal and capture the final baseband electrical signal;

[0032] Step 4:

[0033] The baseband electrical signal passes through the DSP at the receiving end to obtain multiple signals, which are then combined using the maximum combining ratio algorithm to obtain the original signal after transmission.

[0034] In this embodiment, after the original signal is resampled, it is loaded into an arbitrary waveform generator and a polarization multiplexed scalar optical signal or a vector optical signal is generated in a modulation and polarization multiplexing module; finally, a multi-channel mode multiplexing is performed through a mode multiplexer.

[0035] Subsequently, the mode multiplexed signal is coupled into the multimode optical fiber for transmission. After a certain distance of optical fiber transmission, the signal is emitted from the optical terminal to the free space through a lens; after propagating in different propagation ranges in the FSO channel according to weather conditions and atmospheric turbulence, the signal is focused again and guided into the optical fiber. After reaching the receiving end, the transmission signal is mode demultiplexed and polarization demultiplexed, and the demultiplexed optical signal is coherently detected to achieve optoelectronic signal conversion and capture the generated baseband electrical signal. The received signal is processed by the DSP at the receiving end to obtain a multi-channel signal. Then, the maximum combining ratio algorithm is used to combine these multi-channel signals, and finally the bit error rate and signal-to-noise ratio of the combined signal are calculated to evaluate the performance of the scheme; it basically maintains the original signal quality, the constellation diagram has obvious convergence, and the signal quality has been significantly improved;

[0036] By multiplexing the spatial dimension, the transmission capacity and efficiency of the optical fiber network can be improved. At the same time, since the same signal is transmitted, it is helpful for subsequent signal merging and processing. Free space propagation increases the flexibility and coverage of the optical fiber network. Although it is affected by atmospheric conditions and turbulence, the subsequent signal processing steps can compensate for these effects.

[0037] This solution is applicable to a variety of FSO / optical fiber communication systems and has good universality. For example, in a multimode fiber-FSO transmission system, the electrical signal is converted from electrical to optical in the I / Q modulator, and the IQ signal is divided into two orthogonal single polarization signals through a polarization beam splitter. After passing through a section of polarization-maintaining fiber, the signal is combined into a polarization multiplexing signal through a polarization combiner. The mode multiplexing signal is coupled into the optical fiber for transmission, and then propagated in the FSO channel with different propagation ranges according to weather conditions and atmospheric turbulence.

[0038] The mode multiplexing signal is coupled into the optical fiber for transmission, and then propagated in different propagation ranges in the FSO channel according to weather conditions and atmospheric turbulence; after passing through the mode demultiplexer and polarization beam splitter and coherent reception in the coherent receiver, it is sampled and the sampled data is subjected to digital signal processing and maximum combining ratio algorithm at the receiving end. Among them, the core algorithm, the maximum combining ratio algorithm, is used to combine the multi-path equalized signals based on the maximum combining ratio principle, and its operation expression is shown in formula (1):

[0039] y MRC =w H y

[0040]

[0041] Formula (1) is the function expression of the maximum merging ratio algorithm;

[0042] In formula (1), w is the weight factor vector, y MRCis the output signal after the maximum merging ratio algorithm is combined, (·) H represents the transposed conjugate, y represents the input signal of the maximum merging ratio algorithm, and h i It is the diagonal element of the transmission matrix. Since the transmitted data is the same, the transmission matrix can be merged into a diagonal matrix. Its diagonal elements can cover all the linear degradation effects of the channel on the transmission signal during the optical fiber transmission process. T represents transpose, and n represents the diagonal element h of the transmission matrix. i The original transmitted symbols are restored through the maximum combining ratio algorithm to evaluate the performance improvement of the system.

[0043] In a further preferred embodiment of the present invention, the scalar or vector signal generated by the transmitter in step 1 transmits the same scalar or vector optical signal in different optical fiber transmission space dimensions.

[0044] In this embodiment, by multiplexing the same signal in different optical fiber transmission space dimensions, the transmission capacity of the optical fiber network is effectively improved, which helps to meet the growing demand for data transmission.

[0045] Since the signal is transmitted in multiple spatial dimensions, even if there is a problem with the beam alignment in one or several dimensions, the signals in other dimensions can still be received and processed, which greatly reduces the impact of single beam alignment sensitivity on system performance.

[0046] In a further preferred embodiment of the present invention, the transmission optical fiber described in step 2 is compatible with one of single-core multi-mode, multi-core single-mode or multi-core multi-mode light.

[0047] In this embodiment, a design compatible with multiple optical fiber types is used so that the system can adapt to different application scenarios and network requirements. For example, the use of multi-core optical fiber can significantly increase the transmission capacity, especially in applications requiring high bandwidth. The use of multi-mode optical fiber can tolerate a certain modal dispersion, while single-mode optical fiber has lower attenuation and higher bandwidth potential. The combination of the two can give full play to their respective advantages in different scenarios and adapt to different application scenarios and network requirements. At the same time, it can also improve anti-interference ability and recovery quality, thereby further reducing the impact of single-beam alignment sensitivity on system performance.

[0048] In a further preferred embodiment of the present invention, the original transmission signal described in step 4 includes an OOK signal, a PAM signal or a probability shaped QAM signal.

[0049] In this embodiment, in the receiving end DSP system, after combining the multi-channel received signals through the maximum combining ratio algorithm, the restored original transmission signal can be an OOK (on-off keying) signal, a PAM (pulse amplitude modulation) signal or a probability shaping QAM (quadrature amplitude modulation) signal. These signal types are selected according to the actual application scenario and transmission requirements.

[0050] OOK signals are simple and easy to implement, and are suitable for scenarios with low bandwidth requirements; PAM signals can provide higher spectrum efficiency and are suitable for scenarios that need to transmit more information; Probability Shaped QAM signals can improve transmission capacity and energy efficiency without increasing bandwidth by optimizing the probability distribution of signals, and are particularly suitable for scenarios with high requirements for energy efficiency and transmission capacity.

[0051] In summary, compared with related technologies, this solution has fast communication speed and high reliability, and is suitable for FSO / fiber hybrid transmission system architecture with various optical fibers and modulation formats.

[0052] In the several embodiments provided in this application, it should be understood that the disclosed device can be implemented in other ways.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the scope of protection of the invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on these embodiments, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in this field can still combine, add, delete or make other adjustments to the features in the various embodiments of the present invention according to the circumstances without conflict, without making creative work, so as to obtain different other technical solutions that do not deviate from the concept of the present invention in essence, and these technical solutions also belong to the scope of protection of the present invention.

Claims

1. A method for alleviating single beam alignment sensitivity in a free space optical fiber network with maximum combining ratio, characterized in that: The steps include: Step 1: After resampling, the signal is loaded into the transmitter to generate a scalar or vector optical signal with spatial dimension multiplexing; Step 2: The optical signal is coupled into the transmission fiber for transmission. After being transmitted through the fiber, the signal is emitted from the optical terminal into free space through a lens; In free space, the signal is affected by atmospheric conditions and turbulence, propagating with different propagation characteristics, and the signal is focused again and guided into the optical fiber; Step 3: After receiving the signal, the receiving end performs mode demultiplexing and polarization demultiplexing, and then performs coherent detection on the polarization demultiplexed signal to convert the optical signal into a baseband electrical signal and capture the final baseband electrical signal; Step 4: The baseband electrical signal passes through the DSP at the receiving end to obtain multiple signals, which are then combined using the maximum combining ratio algorithm to obtain the original signal after transmission.

2. The method of claim 1 for alleviating single beam alignment sensitivity in a free space optical fiber network with maximum combining ratio, characterized in that: The scalar or vector signal generated by the transmitter described in step 1 transmits the same scalar or vector optical signal in different optical fiber transmission space dimensions.

3. The method of claim 1 for alleviating single beam alignment sensitivity in a free space optical fiber network with maximum combining ratio, characterized in that: The transmission optical fiber described in step 2 is compatible with one of single-core multi-mode, multi-core single-mode or multi-core multi-mode light.

4. The method of claim 1 for alleviating single beam alignment sensitivity in a free space optical fiber network with maximum combining ratio, characterized in that: The original transmission signal described in step 4 includes an OOK signal, a PAM signal or a probability-shaped QAM signal.

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