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CN114374433A - Laser line width tolerance determining method for atmosphere channel QAM communication system - Google Patents

Laser line width tolerance determining method for atmosphere channel QAM communication system Download PDF

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CN114374433A
CN114374433A CN202210053002.1A CN202210053002A CN114374433A CN 114374433 A CN114374433 A CN 114374433A CN 202210053002 A CN202210053002 A CN 202210053002A CN 114374433 A CN114374433 A CN 114374433A
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CN114374433B (en
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李密
傅万旺
郭优
王祎思
张越行
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Nanjing University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
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    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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    • H04B10/503—Laser transmitters
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    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
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Abstract

本发明公开了一种面向大气信道QAM通信系统的激光器线宽容限确定方法，为了在设计空间相干激光通信系统时满足系统的性能需求，我们需要在系统设计时严格控制好激光器的线宽，获取满足系统设计误码率要求的线宽容限参数；空间相干激光通信系统存在着复杂多变的大气信道，我们需要获取当前的大气信道信息，才能更准确地确定满足系统误码率的激光器线宽容限。本发明通过两次将数据和模型结合，可以较为准确的获得当前大气信道下QAM通信系统的激光器线宽容限。

Figure 202210053002

The invention discloses a method for determining the laser line width tolerance for an atmospheric channel QAM communication system. In order to meet the performance requirements of the system when designing a space coherent laser communication system, we need to strictly control the line width of the laser during system design, and obtain The line tolerance parameter that meets the system design bit error rate requirements; the spatial coherent laser communication system has complex and changeable atmospheric channels, and we need to obtain the current atmospheric channel information to more accurately determine the laser line tolerance that meets the system bit error rate. limit. The invention can obtain the laser line width tolerance of the QAM communication system under the current atmospheric channel more accurately by combining the data and the model twice.

Figure 202210053002

Description

面向大气信道QAM通信系统的激光器线宽容限确定方法Determination method of laser line width tolerance for atmospheric channel QAM communication system

技术领域technical field

本发明涉及技术领域，具体而言涉及一种面向大气信道QAM通信系统的激光器线宽容限确定方法。The present invention relates to the technical field, in particular to a method for determining the line width tolerance of a laser for an atmospheric channel QAM communication system.

背景技术Background technique

空间激光通信相较于微波通信，具有高通信速率、高带宽、高保密性能、免频谱许可证、低功耗、小体积等优势，成为众多研究者和研究机构的研究热点。此外，相较于地面光纤通信，空间激光通信不仅可以免去铺设光纤、从而更加节约成本，而且也因为不受光纤信道束缚，从而有了更多可能。相较于传统的强度调制/直接检测的空间激光通信系统，空间相干激光通信系统不仅能够提升带宽，带来通信速率的提升，并且能有效的抑制自由空间信道的背景噪声和系统的热噪声，是使得收机的灵敏度有效提升。Compared with microwave communication, space laser communication has the advantages of high communication rate, high bandwidth, high security performance, free spectrum license, low power consumption, small size, etc., and has become a research hotspot of many researchers and research institutions. In addition, compared with terrestrial optical fiber communication, space laser communication not only saves costs by eliminating the need to lay optical fibers, but also has more possibilities because it is not bound by fiber channels. Compared with the traditional intensity modulation/direct detection space laser communication system, the space coherent laser communication system can not only increase the bandwidth, bring about the improvement of the communication rate, but also effectively suppress the background noise of the free space channel and the thermal noise of the system, It is to effectively improve the sensitivity of the receiver.

虽然空间相干激光通信由于引入了相位调制带来了性能上的提升，但也正因为由于引入了相位调制从而使得空间相干激光通信系统对强度和相位都十分敏感。影响空间相干激光性能的因素主要有两个，一个是激光器的线宽，另一个是大气环境。一方面，激光器由于线宽的存在会引起激光器输出激光相位的不稳定，从而给系统带来相位噪声，引起空间相干激光通信系统性能的恶化。因此在设计空间相干激光通信系统时，必须严格控制好激光器的线宽。Although spatial coherent laser communication has improved performance due to the introduction of phase modulation, it is also precisely because of the introduction of phase modulation that spatial coherent laser communication systems are very sensitive to both intensity and phase. There are two main factors that affect the performance of spatially coherent lasers, one is the linewidth of the laser, and the other is the atmospheric environment. On the one hand, the existence of the linewidth of the laser will cause the instability of the laser output laser phase, which will bring phase noise to the system and cause the deterioration of the performance of the spatial coherent laser communication system. Therefore, when designing a space coherent laser communication system, the linewidth of the laser must be strictly controlled.

另一方面，空间相干激光通信系统一般都会包含一个较长距离甚至是超长距离的大气信道，大气信道不仅会影响接收端光信号强度的分布，也会带来接收端光信号相位的波动，后者对于系统性能的影响更大。大气信道十分复杂并且多变，对于不同地区不同高度的大气环境相差较大，同一地区早晚和夏冬的大气环境也不尽相同。因此对于空间相干激光通信系统中，必须获取当时的大气信道信息，才能更好地确定满足系统误码率的激光器线宽容限。On the other hand, the spatial coherent laser communication system generally includes a long-distance or even ultra-long-distance atmospheric channel. The atmospheric channel will not only affect the distribution of the optical signal intensity at the receiving end, but also bring about the fluctuation of the optical signal phase at the receiving end. The latter has a greater impact on system performance. The atmospheric channel is very complex and changeable. The atmospheric environment at different heights in different regions is quite different, and the atmospheric environment in the same region is also different in the morning and evening and in summer and winter. Therefore, in the space coherent laser communication system, the atmospheric channel information at that time must be obtained, in order to better determine the laser line width tolerance that satisfies the system bit error rate.

综上所述，为了在设计空间相干激光通信系统时满足系统的性能需求，需要在系统设计时严格控制好激光器的线宽，获取满足系统设计误码率要求的线宽容限参数；空间相干激光通信系统存在着复杂多变的大气信道，需要获取当前的大气信道信息，才能更准确地确定满足系统误码率的激光器线宽容限。In summary, in order to meet the performance requirements of the system when designing a spatially coherent laser communication system, it is necessary to strictly control the linewidth of the laser during system design, and obtain linewidth tolerance parameters that meet the requirements of the system design bit error rate; spatially coherent laser There are complex and changeable atmospheric channels in the communication system, and it is necessary to obtain the current atmospheric channel information in order to more accurately determine the laser line width tolerance that meets the system bit error rate.

激光器线宽容限地重要性以及大气信道地复杂性和多变性不言而喻。为了完成QAM通信系统设计需求，需要更准确地确定空间相干激光通信系统的线宽容限参数。由于空间相干激光通信系统存在着大气信道，因此获得当前大气信道的具体模型参数成为了重点，而大气信道地复杂性和多变性带来了实验测量大气信道的难度以及纯模型计算大气参数的不准确性，给准确地确定空间相干激光通信系统的线宽容限参数带来了难度。The importance of laser line width tolerances and the complexity and variability of atmospheric channels are self-evident. In order to complete the design requirements of QAM communication system, it is necessary to more accurately determine the line width tolerance parameters of the spatial coherent laser communication system. Due to the existence of atmospheric channels in the space coherent laser communication system, obtaining the specific model parameters of the current atmospheric channels has become the focus. The complexity and variability of the atmospheric channels bring the difficulty of experimental measurement of atmospheric channels and the inconsistency of pure model calculation of atmospheric parameters. The accuracy makes it difficult to accurately determine the line width tolerance parameters of the spatial coherent laser communication system.

现有的大气信道下QAM调制系统的误码率性能不仅会受到大气信道的影响，而且也会受到激光器线宽的影响，而一般在考虑空间相关激光通信系统的激光器线宽容限时，并不能很精确的获得线宽容限信息。The bit error rate performance of the existing QAM modulation system under the atmospheric channel is not only affected by the atmospheric channel, but also by the laser linewidth. Generally, when considering the laser linewidth tolerance of the space-correlated laser communication system, it is not very effective. Accurately obtain line width tolerance information.

发明内容SUMMARY OF THE INVENTION

本发明针对现有技术中的不足，提供一种面向大气信道QAM通信系统的激光器线宽容限确定方法，能够考虑大气信道地复杂性和多变性，更准确地确定空间相干激光通信系统的线宽容限参数。Aiming at the deficiencies in the prior art, the present invention provides a laser line tolerance determination method for an atmospheric channel QAM communication system, which can more accurately determine the line tolerance of a space coherent laser communication system considering the complexity and variability of the atmospheric channel. limited parameters.

为实现上述目的，本发明采用以下技术方案：To achieve the above object, the present invention adopts the following technical solutions:

本发明实施例提出了一种面向大气信道QAM通信系统的激光器线宽容限确定方法，所述激光器线宽容限确定方法包括以下步骤：An embodiment of the present invention provides a method for determining a laser line width tolerance for an atmospheric channel QAM communication system, and the method for determining the laser line width tolerance includes the following steps:

S1，采用自由空间的光学跟瞄子系统完成发射端与接收端的瞄准工作，令信号光发射系统发出功率恒定的信号光，在接收端采用光强传感器接收光信号，得到不同光信号强度的时间分布，计算出接收端的平均光信号强度；S1, the free space optical tracking and aiming subsystem is used to complete the aiming work of the transmitting end and the receiving end, so that the signal light transmitting system emits signal light with constant power, and the light intensity sensor is used at the receiving end to receive the light signal, and the time of different light signal intensities is obtained. distribution, and calculate the average optical signal strength at the receiving end;

S2，将步骤S1得到的接收端的不同光信号强度的时间分布转换为接收端的光信号强度概率分布，得到接收端光信号强度概率分布数据；S2, converting the time distribution of different optical signal intensities at the receiving end obtained in step S1 into the probability distribution of the optical signal intensity at the receiving end, to obtain the probability distribution data of the optical signal intensity at the receiving end;

S3，构建接收端光信号强度的概率密度模型，将步骤S1计算得到的接收端的平均光信号强度代入接收端光信号强度的概率密度模型，通过改变大气湍流闪烁方差，得到不同大气湍流闪烁下接收光信号强度的概率密度曲线；再计算步骤S2得到的接收端光信号强度概率分布数据与不同大气湍流闪烁下接收光信号强度的概率密度曲线的相关系数，选择相关系数最大的曲线，得到接收面光信号强度的概率密度模型的大气湍流闪烁方差

Figure BDA0003473531460000021
S3, constructing a probability density model of the optical signal intensity at the receiving end, substituting the average optical signal intensity at the receiving end calculated in step S1 into the probability density model of the optical signal intensity at the receiving end, and by changing the variance of atmospheric turbulence scintillation to obtain reception under different atmospheric turbulence scintillation The probability density curve of the optical signal intensity; then calculate the correlation coefficient between the probability distribution data of the receiving end optical signal intensity obtained in step S2 and the probability density curve of the received optical signal intensity under different atmospheric turbulence scintillation, and select the curve with the largest correlation coefficient to obtain the receiving surface. Atmospheric Turbulence Scintillation Variance for Probability Density Models of Optical Signal Intensity
Figure BDA0003473531460000021

S4，在接收端选择一个确定好功率和线宽的激光器搭建好QAM通信系统接收端，改变接收端接收到的光信号的强度，通过数字信号处理模块得到大气信道下QAM通信系统的不同接收光信号强度的误码率信息；S4, select a laser with determined power and line width at the receiving end to build the receiving end of the QAM communication system, change the intensity of the optical signal received by the receiving end, and obtain different received light of the QAM communication system under the atmospheric channel through the digital signal processing module bit error rate information of signal strength;

S5，构建面向大气信道含有激光器线宽容限的QAM通信系统的误码率模型：S5, construct the bit error rate model of the QAM communication system oriented to the atmospheric channel with the laser line width tolerance:

Figure BDA0003473531460000022
Figure BDA0003473531460000022

式中，

Figure BDA0003473531460000023
为没有大气湍流影响下的含有激光器线宽容限的QAM误码率模型，I为接收光信号强度，
Figure BDA0003473531460000024
为接收光信号相位，Δvt为发射端窄线宽激光器线宽，Δvr为接收端本振激光器线宽，P(I)为大气湍流影响下接收端不同光信号强度I的概率密度，
Figure BDA0003473531460000025
为大气湍流影响下接收端光信号相位
Figure BDA0003473531460000026
分布概率密度；In the formula,
Figure BDA0003473531460000023
is the QAM bit error rate model with laser line width tolerance without the influence of atmospheric turbulence, I is the received optical signal intensity,
Figure BDA0003473531460000024
is the phase of the received optical signal, Δv t is the linewidth of the laser with narrow linewidth at the transmitting end, Δv r is the linewidth of the local oscillator laser at the receiving end, P(I) is the probability density of different optical signal intensities I at the receiving end under the influence of atmospheric turbulence,
Figure BDA0003473531460000025
is the phase of the optical signal at the receiving end under the influence of atmospheric turbulence
Figure BDA0003473531460000026
distribution probability density;

P(I)的计算模型如下：The calculation model of P(I) is as follows:

Figure BDA0003473531460000027
Figure BDA0003473531460000027

式中，<I>为接收端光信号平均光信号强度，

Figure BDA0003473531460000028
为大气湍流闪烁方差；In the formula, <I> is the average optical signal intensity of the optical signal at the receiving end,
Figure BDA0003473531460000028
is the atmospheric turbulence scintillation variance;

Figure BDA0003473531460000029
的计算模型如下：
Figure BDA0003473531460000029
The calculation model is as follows:

Figure BDA00034735314600000210
Figure BDA00034735314600000210

式中，

Figure BDA0003473531460000031
为大气湍流引起的接收光信号相位波动方差；In the formula,
Figure BDA0003473531460000031
is the phase fluctuation variance of the received optical signal caused by atmospheric turbulence;

改变接收端光信号强度，得到大气对接收端光信号相位波动影响下误码率随接收光信号强度变化的曲线，计算步骤S4中得到的不同接收光信号强度的误码率数据与误码率随接收光信号强度变化的曲线的相关系数，选择相关系数最大的曲线，得到大气湍流引起的接收光信号相位波动方差

Figure BDA0003473531460000032
Change the optical signal intensity at the receiving end to obtain a curve of the bit error rate changing with the intensity of the received optical signal under the influence of the atmosphere on the phase fluctuation of the optical signal at the receiving end, and calculate the bit error rate data and bit error rate of different received optical signal intensities obtained in step S4 The correlation coefficient of the curve that changes with the intensity of the received optical signal, select the curve with the largest correlation coefficient, and obtain the phase fluctuation variance of the received optical signal caused by atmospheric turbulence
Figure BDA0003473531460000032

S6，根据步骤S3得到的大气湍流闪烁方差

Figure BDA0003473531460000033
和步骤S5得到的大气湍流引起的接收光信号相位波动方差
Figure BDA0003473531460000034
建立当前大气信道下含线宽容限变量的QAM通信系统误码率模型：S6, according to the atmospheric turbulence scintillation variance obtained in step S3
Figure BDA0003473531460000033
and the variance of the phase fluctuation of the received optical signal caused by atmospheric turbulence obtained in step S5
Figure BDA0003473531460000034
Establish the bit error rate model of the QAM communication system with line and tolerance tolerance variables under the current atmospheric channel:

Figure BDA0003473531460000035
Figure BDA0003473531460000035

S7，根据步骤S6得到的当前大气信道下含线宽容限变量的QAM通信系统误码率模型，按照目标QAM通信系统的误码率要求指标，确定当前大气信道状况下QAM所用激光器的线宽容限。S7, according to the QAM communication system bit error rate model containing the line tolerance variable under the current atmospheric channel obtained in step S6, according to the bit error rate requirement index of the target QAM communication system, determine the line tolerance of the laser used for QAM under the current atmospheric channel condition .

进一步地，所述QAM通信系统包括发射端和接收端；Further, the QAM communication system includes a transmitter and a receiver;

所述发射端包括窄线宽激光器、QAM调制器、掺铒光纤放大器、发射系统；The transmitting end includes a narrow linewidth laser, a QAM modulator, an erbium-doped fiber amplifier, and a transmitting system;

所述接收端包括接收系统、光强传感器、光衰减器、确定功率和线宽的激光器、耦合器、平衡探测器、数字信号处理模块；所述接收系统分别连接光衰减器和光强传感器，所述数字信号处理模块包括解调模块和误码率计算模块。The receiving end includes a receiving system, a light intensity sensor, an optical attenuator, a laser for determining power and line width, a coupler, a balanced detector, and a digital signal processing module; the receiving system is respectively connected to the optical attenuator and the light intensity sensor, The digital signal processing module includes a demodulation module and a bit error rate calculation module.

进一步地，步骤S1中，计算出接收端的平均光信号强度的过程包括以下子步骤：Further, in step S1, the process of calculating the average optical signal strength of the receiving end includes the following sub-steps:

设接收端接收到的随时间变化的光信号强度为Ire(t)，统计得到接收端不同光信号强度的时间分布TI；Let the time-varying optical signal intensity received by the receiving end be I re (t), and statistically obtain the time distribution T I of different optical signal intensities at the receiving end;

根据下述公式计算得到接收端平均光信号强度<I>为：According to the following formula, the average optical signal intensity <I> of the receiving end is calculated as:

Figure BDA0003473531460000036
Figure BDA0003473531460000036

式中，T为接收端接收光信号的总时间。In the formula, T is the total time for the receiving end to receive the optical signal.

进一步地，步骤S2中，得到接收端光信号强度概率分布数据的过程包括以下子步骤：Further, in step S2, the process of obtaining the probability distribution data of the optical signal intensity at the receiving end includes the following sub-steps:

根据接收端不同光信号强度时间分布TI，通过接收端光信号强度的概率密度P(I)积分为1的特点，采用下述公式计算得到接收端光信号强度概率为：According to the time distribution TI of different optical signal strengths at the receiving end, and through the feature that the probability density P( I ) of the receiving end optical signal strength is integral to 1, the following formula is used to calculate the receiving end optical signal strength probability:

Figure BDA0003473531460000037
Figure BDA0003473531460000037

进一步地，步骤S3中，得到接收面光信号强度的概率密度模型的大气湍流闪烁方差

Figure BDA0003473531460000038
的过程包括以下步骤：Further, in step S3, the atmospheric turbulence scintillation variance of the probability density model of the optical signal intensity of the receiving surface is obtained
Figure BDA0003473531460000038
The process includes the following steps:

S31，将步骤S1得到的接收端平均光信号强度<I>代入到P(I)的计算模型中，通过改变大气湍流闪烁方差

Figure BDA0003473531460000039
参数，得到不同大气湍流闪烁方差
Figure BDA00034735314600000310
下的P(I)曲线；S31: Substitute the average optical signal intensity <I> of the receiving end obtained in step S1 into the calculation model of P(I), by changing the variance of atmospheric turbulence scintillation
Figure BDA0003473531460000039
parameters to get different atmospheric turbulence scintillation variances
Figure BDA00034735314600000310
P(I) curve below;

S32，根据下述公式计算步骤S2得到的接收端光信号强度概率分布数据PT(I)与不同大气湍流闪烁方差

Figure BDA0003473531460000041
下的P(I)曲线的相关系数：S32, calculate the probability distribution data P T (I) of the optical signal intensity at the receiving end obtained in step S2 and the variance of different atmospheric turbulence scintillation according to the following formula
Figure BDA0003473531460000041
The correlation coefficient of the P(I) curve below:

Figure BDA0003473531460000042
Figure BDA0003473531460000042

式中Cov(PT(I)，P(I))表示PT(I)和P(I)的协方差，var(PT(I))和var(P(I))分别表示PT(I)和P(I)的方差；where Cov(P T (I), P(I)) represents the covariance of P T (I) and P(I), var(P T (I)) and var(P(I)) represent P T respectively The variance of (I) and P(I);

S33，根据相关系数r(PT(I)，P(I))的结果，选择相关系数最大的P(I)曲线，得到当前大气湍流闪烁方差

Figure BDA0003473531460000043
参数的值，得到当前大气湍流下的P(I)计算模型的全部信息。S33, according to the result of the correlation coefficient r(P T (I), P(I)), select the P(I) curve with the largest correlation coefficient to obtain the current atmospheric turbulence scintillation variance
Figure BDA0003473531460000043
The value of the parameter can get all the information of the P(I) calculation model under the current atmospheric turbulence.

进一步地，步骤S4中，设接收光信号强度为：Further, in step S4, set the received optical signal strength as:

Iα(t)＝αIre(t)I α (t)=αI re (t)

式中，α为光衰减器的衰减系数，其取值范围为0～1，通过数字信号处理模块得到不同Iα(t)下的误码率

Figure BDA0003473531460000044
In the formula, α is the attenuation coefficient of the optical attenuator, and its value ranges from 0 to 1. The bit error rate under different I α (t) is obtained through the digital signal processing module.
Figure BDA0003473531460000044

进一步地，步骤S5中，得到大气湍流引起的接收光信号相位波动方差

Figure BDA0003473531460000045
的过程包括以下步骤：Further, in step S5, the phase fluctuation variance of the received optical signal caused by atmospheric turbulence is obtained
Figure BDA0003473531460000045
The process includes the following steps:

S51，将步骤S3得到的当前大气湍流下的P(I)代入面向大气信道含有激光器线宽容限的QAM通信系统的误码率模型BERQAM，通过改变接收光信号强度和相位波动方差

Figure BDA0003473531460000046
参数，得到不同相位波动方差下随接收光信号强度的BERQAM曲线；S51, Substitute the P(I) under the current atmospheric turbulence obtained in step S3 into the bit error rate model BER QAM of the QAM communication system facing the atmospheric channel with the laser line tolerance tolerance, by changing the received optical signal intensity and phase fluctuation variance
Figure BDA0003473531460000046
parameters to obtain the BER QAM curve with the received optical signal intensity under different phase fluctuation variances;

S52，根据下述公式计算步骤S4得到的不同接收光信号强度的

Figure BDA0003473531460000047
信息与不同相位波动方差下随接收光信号强度的BERQAM曲线的相关系数：S52, calculate the difference between the different received optical signal intensities obtained in step S4 according to the following formula
Figure BDA0003473531460000047
Correlation coefficient of information and BER QAM curve with received optical signal strength under different phase fluctuation variances:

Figure BDA0003473531460000048
Figure BDA0003473531460000048

式中，

Figure BDA0003473531460000049
表示
Figure BDA00034735314600000410
和BERQAM的协方差，
Figure BDA00034735314600000411
和var(BERQAM)分布表示
Figure BDA00034735314600000412
和BERQAM的方差；In the formula,
Figure BDA0003473531460000049
express
Figure BDA00034735314600000410
and the covariance of BER QAM ,
Figure BDA00034735314600000411
and var(BER QAM ) distribution representation
Figure BDA00034735314600000412
and variance of BER QAM ;

S53，根据相关系数

Figure BDA00034735314600000413
的结果，选择相关系数最大的BERQAM模型，得到当前大气湍流引起的接收光信号相位波动方差
Figure BDA00034735314600000414
S53, according to the correlation coefficient
Figure BDA00034735314600000413
The BER QAM model with the largest correlation coefficient is selected to obtain the phase fluctuation variance of the received optical signal caused by the current atmospheric turbulence
Figure BDA00034735314600000414

进一步地，步骤S7中，确定当前大气信道状况下QAM所用激光器的线宽容限的过程包括以下子步骤：Further, in step S7, the process of determining the line width tolerance of the laser used in the QAM under the current atmospheric channel condition includes the following sub-steps:

根据步骤S6得到的面向大气信道含有确定的当前大气湍流下闪烁方差和接收光信号相位波动方差的BERQAM模型，得到不同通信系统BER的本振激光器最大线宽，即线宽容限，根据面向大气QAM通信系统设计的误码率要求，确定当前大气下的线宽容限。According to the BERQAM model of the atmosphere-oriented channel obtained in step S6, which contains the determined scintillation variance under the current atmospheric turbulence and the phase fluctuation variance of the received optical signal, the maximum linewidth of the local oscillator laser of the BER of different communication systems, that is, the line width tolerance, is obtained. According to the atmosphere-oriented QAM The bit error rate requirement for communication system design determines the line tolerance limit in the current atmosphere.

本发明通过将模型和数据相结合的方式计算出大气信道对空间相干激光通信的影响参数，这一方面降低了模型与实际环境偏离太多而导致的导致准确度下降风险，又避免了通过复杂且难度很大的实验来获得大气信道的信息，并且模型和数据结合过程分两步进行，增加了模型准确性。然后得到当前大气湍流闪烁方差和接收光信号相位波动方差下的QAM通信系统的误码率模型，最后根据QAM通信系统设计指标，即可得到当前大气信道下QAM通信系统的线宽容限。The present invention calculates the influence parameters of the atmospheric channel on the space coherent laser communication by combining the model and the data, which reduces the risk of accuracy degradation caused by too much deviation between the model and the actual environment, and avoids the complexity of And very difficult experiments to obtain the information of the atmospheric channel, and the model and data combination process is carried out in two steps, which increases the accuracy of the model. Then, the bit error rate model of the QAM communication system under the current atmospheric turbulence scintillation variance and the received optical signal phase fluctuation variance is obtained. Finally, according to the design index of the QAM communication system, the line width tolerance of the QAM communication system under the current atmospheric channel can be obtained.

本发明的有益效果是：The beneficial effects of the present invention are:

第一，本发明提出的面向大气信道QAM通信系统的激光器线宽容限确定方法，在确定面向大气QAM通信系统的线宽容限参数时，考虑了大气信道的影响；由于大气环境复杂且多变，很难做到通过实验获得大气信道的细节信息，现有的方法大部分都是通过模型来分析，而本方法将模型和实测数据相结合，既避免了模型与实际环境偏离太多导致准确度下降，又避免了通过复杂且难度很大的实验来获得大气信道的信息。First, the method for determining the line width tolerance of a laser for the atmospheric channel QAM communication system proposed by the present invention takes the influence of the atmospheric channel into consideration when determining the line width tolerance parameters of the atmospheric channel QAM communication system; due to the complex and changeable atmospheric environment, It is difficult to obtain the detailed information of the atmospheric channel through experiments. Most of the existing methods are analyzed through models, and this method combines the model and the measured data, which avoids too much deviation between the model and the actual environment, which leads to accuracy. decrease, and avoid complicated and difficult experiments to obtain atmospheric channel information.

第二，本发明提出的面向大气信道QAM通信系统的激光器线宽容限确定方法，在将模型和数据相结合得到大气信道信息的过程中，并不是通过一次结合从而得到所有信息，而是分步骤两次得到，这样不仅可以降低数据和模型结合的难度，也能提升模型的准确度。Second, the method for determining the laser line width tolerance for the atmospheric channel QAM communication system proposed by the present invention, in the process of combining the model and the data to obtain the atmospheric channel information, not all the information is obtained through one combination, but is divided into steps Obtained twice, this can not only reduce the difficulty of combining data and model, but also improve the accuracy of the model.

第三，本发明提出的面向大气信道QAM通信系统的激光器线宽容限确定方法，可以通过QAM通信系统简单改造完成，实现成本也比较低廉。Thirdly, the method for determining the laser line width tolerance for the atmospheric channel QAM communication system proposed by the present invention can be completed by simple modification of the QAM communication system, and the implementation cost is relatively low.

附图说明Description of drawings

图1是本发明实施例的发射端与接收端系统结构图。FIG. 1 is a system structure diagram of a transmitter and a receiver according to an embodiment of the present invention.

图2是接收端信号光强度概率密度散点示意图。FIG. 2 is a schematic diagram of the scatter of the signal light intensity probability density at the receiving end.

图3是不同大气湍流方差下的接收端光信号强度概率密度分布曲线。Figure 3 is the probability density distribution curve of the optical signal intensity at the receiving end under different atmospheric turbulence variances.

图4是QAM通信系统在不同接收光信号强度下的误码率散点示意图。FIG. 4 is a schematic diagram of the scatter of the bit error rate of the QAM communication system under different received optical signal strengths.

图5是QAM通信系统在不同大气湍流引起接收光信号相位波动方差下和接收光信号强度下的误码率曲线。Figure 5 is the bit error rate curve of the QAM communication system under different atmospheric turbulence-induced phase fluctuation variances of the received optical signal and the received optical signal strength.

图6是面向大气的QAM通信系统不同通信指标BER下的线宽容限图。Fig. 6 is the line width tolerance diagram under different communication index BER of the QAM communication system facing the atmosphere.

图7是本发明实施例的面向大气信道QAM通信系统的激光器线宽容限确定方法流程图。FIG. 7 is a flowchart of a method for determining a laser line width tolerance for an atmospheric channel QAM communication system according to an embodiment of the present invention.

具体实施方式Detailed ways

现在结合附图对本发明作进一步详细的说明。The present invention will now be described in further detail with reference to the accompanying drawings.

需要注意的是，发明中所引用的如“上”、“下”、“左”、“右”、“前”、“后”等的用语，亦仅为便于叙述的明了，而非用以限定本发明可实施的范围，其相对关系的改变或调整，在无实质变更技术内容下，当亦视为本发明可实施的范畴。It should be noted that the terms such as "up", "down", "left", "right", "front", "rear", etc. quoted in the invention are only for the convenience of description and clarity, and are not used for Limiting the applicable scope of the present invention, the change or adjustment of the relative relationship shall be regarded as the applicable scope of the present invention without substantially changing the technical content.

图7是本发明实施例的面向大气信道QAM通信系统的激光器线宽容限确定方法流程图。该激光器线宽容限确定方法包括以下步骤：FIG. 7 is a flowchart of a method for determining a laser line width tolerance for an atmospheric channel QAM communication system according to an embodiment of the present invention. The laser line width tolerance determination method includes the following steps:

S1，采用自由空间的光学跟瞄子系统完成发射端与接收端的瞄准工作，令信号光发射系统发出功率恒定的信号光，在接收端采用光强传感器接收光信号，得到不同光信号强度的时间分布，计算出接收端的平均光信号强。S1, the free space optical tracking and aiming subsystem is used to complete the aiming work of the transmitting end and the receiving end, so that the signal light transmitting system emits signal light with constant power, and the light intensity sensor is used at the receiving end to receive the light signal, and the time of different light signal intensities is obtained. distribution, and calculate the average optical signal strength at the receiving end.

示例性地，步骤S1的具体过程如下：信号光功率恒定，考虑到大气湍流的影响，接收端光信号强度会随时间变化，假设接收端接收到的随时间变化的光信号强度为Ire(t)，则可以统计得到接收端不同光信号强度的时间分布TI；以及得到接收端平均光信号强度<I>为：Exemplarily, the specific process of step S1 is as follows: the signal optical power is constant, taking into account the influence of atmospheric turbulence, the optical signal intensity at the receiving end will vary with time, and it is assumed that the optical signal intensity received by the receiving end that varies with time is I re ( t), then the time distribution TI of different optical signal intensities at the receiving end can be obtained statistically; and the average optical signal intensity < I > of the receiving end is obtained as:

Figure BDA0003473531460000061
Figure BDA0003473531460000061

式中，T为接收端接收光信号的总时间。In the formula, T is the total time for the receiving end to receive the optical signal.

S2，将步骤S1得到的接收端的不同光信号强度的时间分布转换为接收端的光信号强度概率分布，得到接收端光信号强度概率分布数据。S2: Convert the time distributions of different optical signal intensities at the receiving end obtained in step S1 into probability distributions of optical signal strengths at the receiving end to obtain data on the probability distribution of optical signal strengths at the receiving end.

示例性地，步骤S2的具体过程如下：Exemplarily, the specific process of step S2 is as follows:

根据步骤一得到的接收端不同光信号强度时间分布TI，通过接收端光信号强度的概率密度P(I)积分为1的特点，可以得到接收端不同光信号强度概率为：According to the time distribution TI of different optical signal intensities at the receiving end obtained in step 1 , and through the feature that the probability density P(I) of the optical signal intensity at the receiving end is integral to 1, the probability of different optical signal intensities at the receiving end can be obtained as:

Figure BDA0003473531460000062
Figure BDA0003473531460000062

由此得到接收端不同光信号强度概率PT(I)。Thereby, the probability P T (I) of different optical signal strengths at the receiving end is obtained.

S3，构建接收端光信号强度的概率密度模型，将步骤S1计算得到的接收端的平均光信号强度代入接收端光信号强度的概率密度模型，通过改变大气湍流闪烁方差，得到不同大气湍流闪烁下接收光信号强度的概率密度曲线；再计算步骤S2得到的接收端光信号强度概率分布数据与不同大气湍流闪烁下接收光信号强度的概率密度曲线的相关系数，选择相关系数最大的曲线，得到接收面光信号强度的概率密度模型的大气湍流闪烁方差

Figure BDA0003473531460000063
S3, constructing a probability density model of the optical signal intensity at the receiving end, substituting the average optical signal intensity at the receiving end calculated in step S1 into the probability density model of the optical signal intensity at the receiving end, and by changing the variance of atmospheric turbulence scintillation to obtain reception under different atmospheric turbulence scintillation The probability density curve of the optical signal intensity; then calculate the correlation coefficient between the probability distribution data of the receiving end optical signal intensity obtained in step S2 and the probability density curve of the received optical signal intensity under different atmospheric turbulence scintillation, and select the curve with the largest correlation coefficient to obtain the receiving surface. Atmospheric Turbulence Scintillation Variance for Probability Density Models of Optical Signal Intensity
Figure BDA0003473531460000063

示例性地，步骤S3的具体过程如下：将步骤S1得到的接收端平均光信号强度<I>代入到P(I)计算模型中，由此得到的P(I)计算模型只剩下了一个未知参数，即大气湍流闪烁方差

Figure BDA0003473531460000064
通过改变大气湍流闪烁方差
Figure BDA0003473531460000065
参数，得到不同大气湍流闪烁方差
Figure BDA0003473531460000066
下的P(I)曲线，然后计算步骤s2得到的接收端光信号强度概率分布数据PT(I)与上述曲线的相关系数，PT(I)和P(I)的相关系数计算公式如下：Exemplarily, the specific process of step S3 is as follows: the average optical signal intensity <I> of the receiving end obtained in step S1 is substituted into the P(I) calculation model, and only one P(I) calculation model obtained thereby remains. The unknown parameter, the atmospheric turbulence scintillation variance
Figure BDA0003473531460000064
By changing atmospheric turbulence scintillation variance
Figure BDA0003473531460000065
parameters to get different atmospheric turbulence scintillation variances
Figure BDA0003473531460000066
P(I) curve below, then calculate the correlation coefficient between the receiving end optical signal intensity probability distribution data P T (I) obtained in step s2 and the above curve, the correlation coefficient calculation formula of P T (I) and P (I) is as follows :

Figure BDA0003473531460000067
Figure BDA0003473531460000067

式中Cov(PT(I)，P(I))表示PT(I)和P(I)的协方差，var(PT(I))和var(P(I))分别表示PT(I)和P(I)的方差，根据相关系数r(PT(I)，P(I))的结果，选择相关系数最大的P(I)曲线，得到当前大气湍流闪烁方差

Figure BDA0003473531460000068
参数的值，由此得到当前大气湍流下的P(I)计算模型的全部信息。where Cov(P T (I), P(I)) represents the covariance of P T (I) and P(I), var(P T (I)) and var(P(I)) represent P T respectively (I) and P(I) variance, according to the result of the correlation coefficient r(P T (I), P(I)), select the P(I) curve with the largest correlation coefficient, and obtain the current atmospheric turbulence scintillation variance
Figure BDA0003473531460000068
The value of the parameter is obtained, thereby obtaining all the information of the P(I) calculation model under the current atmospheric turbulence.

S4，在接收端选择一个确定好功率和线宽的激光器搭建好QAM通信系统接收端，改变接收端接收到的光信号的强度，通过数字信号处理模块得到大气信道下QAM通信系统的不同接收光信号强度的误码率信息。S4, select a laser with determined power and line width at the receiving end to build the receiving end of the QAM communication system, change the intensity of the optical signal received by the receiving end, and obtain different received light of the QAM communication system under the atmospheric channel through the digital signal processing module Bit error rate information for signal strength.

示例性地，步骤S4的具体过程如下：在接收端改变光衰减器，从而改变接收端接收光信号的强度，此时接收光信号强度如下：Exemplarily, the specific process of step S4 is as follows: the optical attenuator is changed at the receiving end, thereby changing the intensity of the received optical signal at the receiving end, and the received optical signal intensity is as follows:

Iα(t)＝αIre(t) (4)I α (t)=αI re (t) (4)

式中，α为光衰减器的衰减系数，其取值范围为0～1，通过数字信号处理模块得到不同Iα(t)下的误码率

Figure BDA0003473531460000071
In the formula, α is the attenuation coefficient of the optical attenuator, and its value ranges from 0 to 1. The bit error rate under different I α (t) is obtained through the digital signal processing module.
Figure BDA0003473531460000071

S5，构建面向大气信道含有激光器线宽容限的QAM通信系统的误码率模型：S5, construct the bit error rate model of the QAM communication system oriented to the atmospheric channel with the laser line width tolerance:

Figure BDA0003473531460000072
Figure BDA0003473531460000072

式中，

Figure BDA0003473531460000073
为没有大气湍流影响下的含有激光器线宽容限的QAM误码率模型，I为接收光信号强度，
Figure BDA0003473531460000074
为接收光信号相位，Δvt为发射端窄线宽激光器线宽，Δvr为接收端本振激光器线宽，P(I)为大气湍流影响下接收端不同光信号强度I的概率密度，
Figure BDA0003473531460000075
为大气湍流影响下接收端光信号相位
Figure BDA0003473531460000076
分布概率密度。In the formula,
Figure BDA0003473531460000073
is the QAM bit error rate model with laser line width tolerance without the influence of atmospheric turbulence, I is the received optical signal intensity,
Figure BDA0003473531460000074
is the phase of the received optical signal, Δv t is the linewidth of the laser with narrow linewidth at the transmitting end, Δv r is the linewidth of the local oscillator laser at the receiving end, P(I) is the probability density of different optical signal intensities I at the receiving end under the influence of atmospheric turbulence,
Figure BDA0003473531460000075
is the phase of the optical signal at the receiving end under the influence of atmospheric turbulence
Figure BDA0003473531460000076
Distribution probability density.

P(I)的计算模型如下：The calculation model of P(I) is as follows:

Figure BDA0003473531460000077
Figure BDA0003473531460000077

式中，<I>为接收端光信号平均光信号强度，

Figure BDA0003473531460000078
为大气湍流闪烁方差。In the formula, <I> is the average optical signal intensity of the optical signal at the receiving end,
Figure BDA0003473531460000078
is the atmospheric turbulence scintillation variance.

Figure BDA0003473531460000079
的计算模型如下：
Figure BDA0003473531460000079
The calculation model is as follows:

Figure BDA00034735314600000710
Figure BDA00034735314600000710

式中，

Figure BDA00034735314600000711
为大气湍流引起的接收光信号相位波动方差。In the formula,
Figure BDA00034735314600000711
is the variance of the phase fluctuation of the received optical signal caused by atmospheric turbulence.

改变接收端光信号强度，得到大气对接收端光信号相位波动影响下误码率随接收光信号强度变化的曲线，计算步骤S4中得到的不同接收光信号强度的误码率数据与误码率随接收光信号强度变化的曲线的相关系数，选择相关系数最大的曲线，得到大气湍流引起的接收光信号相位波动方差

Figure BDA00034735314600000712
Change the optical signal intensity at the receiving end to obtain a curve of the bit error rate changing with the intensity of the received optical signal under the influence of the atmosphere on the phase fluctuation of the optical signal at the receiving end, and calculate the bit error rate data and bit error rate of different received optical signal intensities obtained in step S4 The correlation coefficient of the curve that changes with the intensity of the received optical signal, select the curve with the largest correlation coefficient, and obtain the phase fluctuation variance of the received optical signal caused by atmospheric turbulence
Figure BDA00034735314600000712

示例性地，步骤S5的具体方法如下：将步骤S3得到的当前大气湍流下的P(I)代入到面向大气信道含有激光器线宽容限的QAM通信系统的误码率模型BERQAM中，由此得到的BERQAM模型只剩下了一个未知参数，即大气湍流引起的接收光信号相位波动方差

Figure BDA00034735314600000713
通过改变接收光信号强度和相位波动方差
Figure BDA00034735314600000714
参数，得到不同相位波动方差下随接收光信号强度的BERQAM曲线，计算步骤四得到的不同接收光信号强度的
Figure BDA00034735314600000715
信息与上述曲线的相关系数，
Figure BDA0003473531460000081
和BERQAM的相关系数计算公式如下：Exemplarily, the specific method of step S5 is as follows: Substitute the P(I) under the current atmospheric turbulence obtained in step S3 into the bit error rate model BER QAM of the QAM communication system oriented to the atmospheric channel containing the laser line tolerance tolerance, thereby The obtained BER QAM model has only one unknown parameter left, which is the variance of the phase fluctuation of the received optical signal caused by atmospheric turbulence
Figure BDA00034735314600000713
By changing the received optical signal strength and phase fluctuation variance
Figure BDA00034735314600000714
parameters, obtain the BER QAM curve with the received optical signal intensity under different phase fluctuation variances, and calculate the difference between the different received optical signal intensities obtained in step 4.
Figure BDA00034735314600000715
The correlation coefficient of the information with the above curve,
Figure BDA0003473531460000081
The calculation formula of the correlation coefficient with BER QAM is as follows:

Figure BDA0003473531460000082
Figure BDA0003473531460000082

式中，

Figure BDA0003473531460000083
表示
Figure BDA0003473531460000084
和BERQAM的协方差，
Figure BDA0003473531460000085
和var(BERQAM)分布表示
Figure BDA0003473531460000086
和BERQAM的方差，根据相关系数
Figure BDA0003473531460000087
的结果，选择相关系数最大的BERQAM模型，即可得到当前大气湍流引起的接收光信号相位波动方差
Figure BDA0003473531460000088
参数。In the formula,
Figure BDA0003473531460000083
express
Figure BDA0003473531460000084
and the covariance of BER QAM ,
Figure BDA0003473531460000085
and var(BER QAM ) distribution representation
Figure BDA0003473531460000086
and BER QAM variance, according to the correlation coefficient
Figure BDA0003473531460000087
By selecting the BER QAM model with the largest correlation coefficient, the phase fluctuation variance of the received optical signal caused by the current atmospheric turbulence can be obtained.
Figure BDA0003473531460000088
parameter.

S6，根据步骤S3得到的大气湍流闪烁方差

Figure BDA0003473531460000089
和步骤S5得到的大气湍流引起的接收光信号相位波动方差
Figure BDA00034735314600000810
建立当前大气信道下含线宽容限变量的QAM通信系统误码率模型：S6, according to the atmospheric turbulence scintillation variance obtained in step S3
Figure BDA0003473531460000089
and the variance of the phase fluctuation of the received optical signal caused by atmospheric turbulence obtained in step S5
Figure BDA00034735314600000810
Establish the bit error rate model of the QAM communication system with line and tolerance tolerance variables under the current atmospheric channel:

Figure BDA00034735314600000811
Figure BDA00034735314600000811

S7，根据步骤S6得到的当前大气信道下含线宽容限变量的QAM通信系统误码率模型，按照目标QAM通信系统的误码率要求指标，确定当前大气信道状况下QAM所用激光器的线宽容限。S7, according to the QAM communication system bit error rate model containing the line tolerance variable under the current atmospheric channel obtained in step S6, according to the bit error rate requirement index of the target QAM communication system, determine the line tolerance of the laser used for QAM under the current atmospheric channel condition .

示例性地，步骤S7的具体方法如下：根据步骤S6得到的面向大气信道含有确定的当前大气湍流下闪烁方差和接收光信号相位波动方差的BERQAM模型，得到不同通信系统BER的本振激光器最大线宽，即线宽容限，根据面向大气QAM通信系统设计的误码率要求，即可确定当前大气下的线宽容限。Exemplarily, the specific method of step S7 is as follows: According to the BER QAM model of the atmospheric channel obtained in step S6 containing the scintillation variance and the phase fluctuation variance of the received optical signal under the determined current atmospheric turbulence, it is obtained that the maximum BER of the local oscillator laser in different communication systems is obtained. The line width, that is, the line tolerance limit, can be determined according to the bit error rate requirements for the design of the atmospheric QAM communication system.

图1是本发明实施例的发射端与接收端系统结构图。参见图1，本实施例的QAM通信系统包括发射端和接收端。发射端由窄线宽激光器、QAM调制器、掺铒光纤放大器、发射系统等组成，接收端由接收系统、光强传感器、光衰减器、确定功率和线宽的激光器、耦合器、平衡探测器、数字信号处理模块等组成。发射端用于信号的调制和发射。电信号经过驱动放大器进入到QAM调制器的射频输入端，调制由窄线宽激光器产生的进入到QAM调制器的激光，得到电信号调制的光信号，QAM调制器的出射光信号经由掺铒光纤放大器放大之后，进入到发射系统进行发射，发射系统将调制好的光信号发射进入大气信道。接收端主要用于光信号的接收和解调。经过大气信道的光信号被接收端的接收系统接收之后，可以进入到光强传感器测量光信号强度，也可以经过光衰减器之后进入到3dB耦合器与接收端的本振激光器进行光的相干混频，混频之后的光信号进入到平衡探测器，将光信号转换成电信号并消去高频部分，然后进入到数字信号处理模块。FIG. 1 is a system structure diagram of a transmitter and a receiver according to an embodiment of the present invention. Referring to FIG. 1 , the QAM communication system of this embodiment includes a transmitter and a receiver. The transmitting end is composed of narrow linewidth laser, QAM modulator, erbium-doped fiber amplifier, transmitting system, etc. The receiving end is composed of receiving system, light intensity sensor, optical attenuator, laser for determining power and linewidth, coupler, balanced detector , digital signal processing module, etc. The transmitter is used for signal modulation and transmission. The electrical signal enters the RF input end of the QAM modulator through the drive amplifier, modulates the laser generated by the narrow linewidth laser and enters the QAM modulator to obtain the optical signal modulated by the electrical signal, and the output optical signal of the QAM modulator passes through the erbium-doped fiber After the amplifier is amplified, it enters the transmitting system for transmission, and the transmitting system transmits the modulated optical signal into the atmospheric channel. The receiving end is mainly used for receiving and demodulating optical signals. After the optical signal passing through the atmospheric channel is received by the receiving system at the receiving end, it can enter the light intensity sensor to measure the intensity of the optical signal, or after passing through the optical attenuator, enter the 3dB coupler and perform coherent mixing with the local oscillator laser at the receiving end. The mixed optical signal enters the balanced detector, converts the optical signal into an electrical signal and eliminates the high-frequency part, and then enters the digital signal processing module.

由于实际的空间相干激光通信系统的搭建涉及诸多方面的内容，利用实际系统的测试数据来说明比较复杂，因此采取数值模拟示意的方式来说明本发明实施例所涉及的面向大气信道QAM通信系统的激光器线宽容限确定方法的效果，通过采用数值模拟的方式来说明本发明实施例所涉及的面向大气信道QAM通信系统的激光器线宽容限确定方法。出于通用性和便利性的考虑，本实施例使用地球同步卫星的QAM空间相干激光通信系统，轨道高度为36000km，通信系统采用正交振幅调制(QAM)方式。通信链路的主要参数设置如下：通信光波长为1550nm，速率为2.5Gbps，发射端激光器功率为30mW，掺铒光纤放大器放大倍数为30dB，接收器直径为0.1m。Since the construction of an actual spatial coherent laser communication system involves many aspects, it is more complicated to use the test data of the actual system to explain. Therefore, a numerical simulation is used to illustrate the method of the atmospheric channel-oriented QAM communication system involved in the embodiment of the present invention. The effect of the method for determining the laser line width tolerance, the method for determining the laser line width tolerance for the atmospheric channel QAM communication system involved in the embodiment of the present invention is described by using numerical simulation. For the consideration of versatility and convenience, this embodiment uses the QAM space coherent laser communication system of the geostationary satellite, the orbit height is 36000km, and the communication system adopts the quadrature amplitude modulation (QAM) method. The main parameters of the communication link are set as follows: the wavelength of the communication light is 1550nm, the rate is 2.5Gbps, the power of the laser at the transmitter is 30mW, the magnification of the erbium-doped fiber amplifier is 30dB, and the diameter of the receiver is 0.1m.

在自由空间的光学跟瞄子系统在完成发射端与接收端的瞄准工作后，接收端得到的光强分布情况，示意图如图2所示，将其转换为接收端光信号强度分布概率；然后本实施例实验模型模拟不同大气湍流闪烁方差下的P(I)曲线，可以得到如图3所示的曲线(为了直观展示，本实施例在此处画出0.02、0.08、0.14和0.20大大气湍流方差下的P(I)曲线)，计算接收端光信号强度概率分布数据与上述不同方差曲线的相关系数，本实施例得到在大气湍流方差为0.02、0.08、0.14和0.20下的相关系数分别为0.9969、0.9875、0.9840和0.9798，由此得到当前的大气湍流闪烁方差为0.02；After the optical tracking and aiming subsystem in free space completes the aiming work of the transmitting end and the receiving end, the light intensity distribution obtained by the receiving end, as shown in Figure 2, is converted into the probability of the light signal intensity distribution at the receiving end; then this The experimental model of the embodiment simulates the P(I) curve under different atmospheric turbulence scintillation variances, and the curve shown in Figure 3 can be obtained (for intuitive display, this embodiment draws 0.02, 0.08, 0.14 and 0.20 large atmospheric turbulence here. P(I) curve under the variance), calculate the correlation coefficient between the optical signal intensity probability distribution data at the receiving end and the above-mentioned different variance curves. 0.9969, 0.9875, 0.9840 and 0.9798, thus the current atmospheric turbulence scintillation variance is 0.02;

接下来本实施例通过改变不同接收光信号强度获得QAM通信系统在不同接收光信号强度下的误码率变化，示意图如图4所示，本实施例得到了随着接收光信号强度变化的QAM通信系统的误码率。然后改变BERQAM模型中接收端光信号强度，得到大气对接收端光信号相位波动影响下误码率随接收光信号强度变化的曲线，如图5所示，图5绘制了大气湍流引起接收光信号相位波动分别为1.26×10-4、2.52×10-4、5.02×10-4和10.02×10-4，然后计算图4中的不同接收光信号强度的误码率数据与上述曲线的相关系数，分别为0.9992、0.9990、0.9988和0.9979，选择相关系数最大的曲线，由此得到大气湍流引起的接收光信号的相位波动方差为1.26×10-4。本实施例此时已经得到了当前大气信道的大气湍流对接收光信号强度闪烁方差和大气湍流引起的接收光信号相位波动方差，那么本实施例就可以建立当前大气信道下含有线宽容限变量的QAM通信系统的误码率模型，得到不同通信误码率指标下的线宽容限要求，如图6所示。最后按照目标QAM通信系统的误码率要求指标，即可确定当前大气信道状况下QAM所用激光器的线宽容限。通过本发明实施例确定当前大气信道QAM通信系统的激光器线宽容限，由于采用了将模型和实测数据相结合，既避免了模型与实际环境偏离太多导致准确度下降，又避免了通过复杂且难度很大的实验来获得大气信道的信息；另外，本实施例在将模型和数据相结合得到大气信道信息的过程中，并不是通过一次结合从而得到所有信息，而是分步骤两次得到，这样不仅可以降低数据和模型结合的难度，也能提升模型的准确度。Next, in this embodiment, the change of the bit error rate of the QAM communication system under different received optical signal intensities is obtained by changing different received optical signal strengths. The schematic diagram is shown in FIG. The bit error rate of a communication system. Then change the optical signal intensity at the receiving end in the BER QAM model, and obtain the curve of the bit error rate changing with the intensity of the received optical signal under the influence of the atmosphere on the phase fluctuation of the optical signal at the receiving end, as shown in Figure 5. Figure 5 plots the received light caused by atmospheric turbulence. The signal phase fluctuations are 1.26×10 -4 , 2.52×10 -4 , 5.02×10 -4 and 10.02×10 -4 , and then calculate the correlation between the bit error rate data of different received optical signal strengths in Fig. 4 and the above curves The coefficients are 0.9992, 0.9990, 0.9988 and 0.9979 respectively, and the curve with the largest correlation coefficient is selected, and the variance of the phase fluctuation of the received optical signal caused by atmospheric turbulence is 1.26×10 -4 . In this embodiment, the variance of the received optical signal intensity scintillation caused by the atmospheric turbulence of the current atmospheric channel and the variance of the received optical signal phase fluctuation caused by atmospheric turbulence have been obtained. Then, in this embodiment, the current atmospheric channel can be established with a line tolerance variable. The bit error rate model of the QAM communication system obtains the line tolerance tolerance requirements under different communication bit error rate indicators, as shown in Figure 6. Finally, according to the bit error rate requirement index of the target QAM communication system, the line tolerance of the laser used in QAM under the current atmospheric channel conditions can be determined. The laser line width tolerance of the current atmospheric channel QAM communication system is determined by the embodiment of the present invention. Due to the combination of the model and the measured data, the accuracy of the model and the actual environment is avoided due to too much deviation, and it is also avoided. It is a very difficult experiment to obtain the information of the atmospheric channel; in addition, in the process of combining the model and the data to obtain the information of the atmospheric channel, all the information is not obtained by one combination, but is obtained in two steps. This not only reduces the difficulty of combining data and models, but also improves the accuracy of the model.

以上仅是本发明的优选实施方式，本发明的保护范围并不仅局限于上述实施例，凡属于本发明思路下的技术方案均属于本发明的保护范围。应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明原理前提下的若干改进和润饰，应视为本发明的保护范围。The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions that belong to the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims (8)

1. A laser line width tolerance determining method facing an atmospheric channel QAM communication system is characterized by comprising the following steps:
s1, finishing the aiming work of the transmitting end and the receiving end by adopting an optical tracking subsystem of free space, enabling the signal light emitting system to emit signal light with constant power, receiving the light signals at the receiving end by adopting a light intensity sensor to obtain the time distribution of different light signal intensities, and calculating the average light signal intensity of the receiving end;
s2, converting the time distribution of different optical signal intensities of the receiving end obtained in the step S1 into optical signal intensity probability distribution of the receiving end to obtain optical signal intensity probability distribution data of the receiving end;
s3, constructing a probability density model of the intensity of the optical signal of the receiving end, substituting the average optical signal intensity of the receiving end calculated in the step S1 into the probability density model of the intensity of the optical signal of the receiving end, and obtaining a probability density curve of the intensity of the received optical signal under different atmospheric turbulence flashes by changing the flicker variance of the atmospheric turbulence; then calculating the correlation coefficient of the probability distribution data of the receiving end optical signal intensity obtained in the step S2 and the probability density curve of the receiving optical signal intensity under different atmospheric turbulence flickering, selecting the curve with the maximum correlation coefficient, and calculating the atmospheric turbulence flickering variance of the probability density model of the receiving surface optical signal intensity
Figure FDA00034735314500000111
S4, selecting a laser with determined power and line width at a receiving end to build a QAM communication system receiving end, changing the intensity of optical signals received by the receiving end, and obtaining the error rate information of different received optical signal intensities of the QAM communication system under the atmosphere channel through a digital signal processing module;
s5, constructing an error rate model of the QAM communication system which faces the atmospheric channel and contains the laser line width tolerance:
Figure FDA0003473531450000011
in the formula (I), the compound is shown in the specification,
Figure FDA0003473531450000012
is a QAM bit error rate model with laser line width tolerance under the condition of no atmospheric turbulence influence, I is received optical signal intensity,
Figure FDA0003473531450000013
to receive the phase of the optical signal, Δ vtFor narrow linewidth laser linewidth at the emitting end, Δ vrThe line width of the local oscillator laser at the receiving end, P (I) the probability density of different optical signal intensities I at the receiving end under the influence of atmospheric turbulence,
Figure FDA0003473531450000014
for receiving the optical signal phase under the influence of atmospheric turbulence
Figure FDA0003473531450000015
A distribution probability density;
the calculation model for P (I) is as follows:
Figure FDA0003473531450000016
in the formula (I), the compound is shown in the specification,<I>to average the optical signal strength of the optical signal at the receiving end,
Figure FDA0003473531450000017
is the atmospheric turbulence scintillation variance;
Figure FDA0003473531450000018
the calculation model of (2) is as follows:
Figure FDA0003473531450000019
in the formula (I), the compound is shown in the specification,
Figure FDA00034735314500000110
the phase fluctuation variance of the received optical signal caused by atmospheric turbulence;
changing the intensity of the optical signal at the receiving end to obtain a curve of the error rate changing with the intensity of the received optical signal under the influence of the atmospheric fluctuation on the phase of the optical signal at the receiving end, calculating the correlation coefficient of the error rate data of different intensities of the received optical signal obtained in the step S4 and the curve of the error rate changing with the intensity of the received optical signal, selecting the curve with the maximum correlation coefficient, and calculating to obtain the variance of the fluctuation of the phase of the received optical signal caused by the atmospheric turbulence
Figure FDA0003473531450000021
S6, according to the atmosphere turbulence flicker variance obtained in the step S3
Figure FDA0003473531450000022
And the variance of the phase fluctuation of the received optical signal caused by the atmospheric turbulence obtained in step S5
Figure FDA0003473531450000023
Establishing a QAM communication system error rate model containing a line width tolerance variable under a current atmospheric channel:
Figure FDA0003473531450000024
and S7, determining the line width tolerance of the laser used by the QAM under the current atmospheric channel condition according to the error rate requirement index of the target QAM communication system and the QAM communication system error rate model containing the line width tolerance variable under the current atmospheric channel obtained in the step S6.
2. The atmospheric-channel-oriented QAM communication system laser linewidth tolerance determination method of claim 1, wherein said QAM communication system comprises a transmitting end and a receiving end;
the transmitting end comprises a narrow linewidth laser, a QAM modulator, an erbium-doped fiber amplifier and a transmitting system;
the receiving end comprises a receiving system, a light intensity sensor, an optical attenuator, a laser for determining power and line width, a coupler, a balance detector and a digital signal processing module; the receiving system is respectively connected with the optical attenuator and the light intensity sensor, and the digital signal processing module comprises a demodulation module and a bit error rate calculation module.
3. The method for determining the line width tolerance of the laser of the air channel-oriented QAM communication system according to claim 1, wherein the step S1 of calculating the average optical signal strength at the receiving end comprises the following sub-steps:
setting the intensity of the optical signal received by the receiving end and changing along with the time as Ire(T), counting to obtain the time distribution T of different optical signal intensities of the receiving endI；
The average optical signal intensity (I) of the receiving end is calculated according to the following formula:
Figure FDA0003473531450000025
where T is the total time for the receiving end to receive the optical signal.
4. The method for determining the line width tolerance of the laser of the air channel-oriented QAM communication system according to claim 1, wherein the step S2 of obtaining the probability distribution data of the optical signal strength at the receiving end comprises the following sub-steps:
according to the intensity time distribution T of different optical signals at the receiving endIAccording to the characteristic that the integral of the probability density P (I) of the intensity of the optical signal at the receiving end is 1, the probability of the intensity of the optical signal at the receiving end is calculated by adopting the following formula:
Figure FDA0003473531450000026
5. the method for determining laser linewidth tolerance of an atmospheric channel QAM communication system as claimed in claim 1, wherein in step S3, obtaining atmospheric turbulence flicker variance of probability density model of receiving surface optical signal intensity
Figure FDA0003473531450000027
Comprises the following steps:
s31, averaging the intensity of the receiving end average optical signal obtained in the step S1<I>Substituting into the calculation model of P (I), and changing the scintillation variance of the atmospheric turbulence
Figure FDA0003473531450000028
Parameters to obtain different atmospheric turbulence scintillation variances
Figure FDA0003473531450000029
The P (I) curve below;
s32, calculating the probability distribution data P of the intensity of the receiving end optical signal obtained in the step S2 according to the following formulaT(I) Scintillation variance with different atmospheric turbulences
Figure FDA0003473531450000031
Correlation coefficient of the following p (i) curve:
Figure FDA0003473531450000032
wherein Cov (P)T(I) P (I) represents PT(I) And covariance of P (I), var (P)T(I) And var (P (I)) respectively represent PT(I) And variance of P (I);
s33, according to the correlation coefficient r (P)T(I) And the result of P (I)) selects the curve P (I) with the maximum correlation coefficient to obtain the current atmospheric turbulence scintillation variance
Figure FDA0003473531450000033
And obtaining all information of the P (I) calculation model under the current atmospheric turbulence by the parameter value.
6. The method for determining the line width tolerance of the laser of the air channel-oriented QAM communication system according to claim 5, wherein in step S4, the received optical signal strength is set as:
Iα(t)＝αIre(t)
in the formula, alpha is the attenuation coefficient of the optical attenuator, the value range of alpha is 0-1, and different I values are obtained through the digital signal processing moduleαBit error rate at (t)
Figure FDA00034735314500000314
7. The method for determining the line width tolerance of the laser of the atmosphere channel QAM communication system as claimed in claim 6, wherein in step S5, the variance of the phase fluctuation of the received optical signal caused by the atmospheric turbulence is obtained
Figure FDA0003473531450000034
Comprises the following steps:
s51, substituting the P (I) under the current atmospheric turbulence obtained in the step S3 into the bit error rate model BER of the QAM communication system which faces the atmospheric channel and contains the laser line width toleranceQAMBy varying the received optical signal strength and phase fluctuation variance
Figure FDA0003473531450000035
Obtaining the BER along with the intensity of the received optical signal under different phase fluctuation variancesQAMA curve;
s52, calculating the intensities of the received light signals obtained in step S4 according to the following formula
Figure FDA0003473531450000036
BER (bit error rate) along with received optical signal strength under information and different phase fluctuation variancesQAMCorrelation coefficient of the curve:
Figure FDA0003473531450000037
in the formula (I), the compound is shown in the specification,
Figure FDA0003473531450000038
to represent
Figure FDA0003473531450000039
And BERQAMThe covariance of (a) of (b),
Figure FDA00034735314500000310
and var (BER)QAM) Distribution representation
Figure FDA00034735314500000311
And BERQAMThe variance of (a);
s53, according to the correlation coefficient
Figure FDA00034735314500000312
As a result, the BER with the largest correlation coefficient is selectedQAMThe model obtains the phase fluctuation variance of the received optical signal caused by the current atmospheric turbulence
Figure FDA00034735314500000313
8. The method for determining the laser linewidth tolerance of an atmospheric channel QAM communication system as claimed in claim 1, wherein the step of determining the linewidth tolerance of the laser used for QAM under the current atmospheric channel condition in step S7 comprises the following sub-steps:
BER obtained from step S6 for which the atmosphere-oriented channel contains the flicker variance and the received-light-signal phase fluctuation variance under the determined current atmospheric turbulenceQAMAnd the model obtains the maximum line width of the local oscillator lasers of different communication system BERs, namely the line width tolerance, and determines the line width tolerance under the current atmosphere according to the bit error rate requirement designed for the atmosphere QAM communication system.
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孔英秀;柯熙政;杨媛;: "激光器线宽对空间相干光通信链路传输误码率研究", 激光与光电子学进展, no. 04 *
李会希: "高速高阶相干光通信系统中的损伤分析及补偿技术研究", 《硕士电子期刊》 *

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