斜程大气激光通信系统误码率分析
发布时间：2018-08-26 15:08
【摘要】：近年来,自由空间光通信(FSO,Free Space Optical Communication)的研究开始复苏。相较于射频通信,FSO具有带宽大,无需频谱认证,组网速度快,功耗低,通信设备尺寸小,安全性高,以及保密性好的优点。但是,FSO通信链路处于大气层中,传输光束会不可避免地受到大气分子及大气中粒子的吸收和散射衰减。同时还会面临一个很大的问题——大气湍流,大气湍流会引起大气折射率的随机变化,会产生光束扩展,光束漂移和光强闪烁等影响,其中光强闪烁的影响最为显著。光强闪烁会导致光束质量严重下降,接收端误码率增大,极大的影响了FSO通信系统的稳定性和可靠性,严重制约了FSO技术的发展。所以定量的对光强闪烁系数进行研究,对于优化通信系统传输速率和传输容量是十分必要的。本文首先在弱湍流情形下,基于三层高度谱,分析了平面波和球面波在斜程FSO链路中的闪烁系数。与传统的Kolmogorov谱相比,采用三层高度谱进行描述的湍流产生的闪烁效应更加严重。在对数正态(LogNormal,LN)信道衰落中分析了通信系统的误码率性能,量化分析了不同天顶角和光波波长对弱湍流信道激光通信的影响。在该研究的基础上,进一步推导了弱湍流中高斯波的闪烁系数表达式,利用LN信道衰落下误码率的表达式分析了不同情形下的误码率。量化分析了上行链路及下行链路中有限的光束半径对闪烁系数及误码率的影响,得到了下行链路误码率不随束腰半径变化,上行链路存在一个最优束腰半径可以使得误码率最小的结论。在上述研究的基础上又分析了在斜程大气激光通信系统中,基于三层高度湍流谱,采用扩展Rytov理论推导了忽略内尺度和外尺度效应的上行链路和下行链路的光强闪烁系数模型,该模型适用于湍流由弱到强的所有区域。文中分析了三层高度谱的幂律指数,近地湍流强度,波长,天顶角等因素对光强闪烁系数的影响。数值结果表明,闪烁系数随幂律指数和波长增大而减小,随天顶角增大而增大,在天顶角接近70°时,闪烁系数达到最大值而后又开始下降。文中还推导了采用OOK和M-PPM调制方式下,通信系统误码率的闭合表达式。分析了对不同湍流情形误码率,并得到了误码率随天顶角,波长等因素的变化趋势。根据分析结果可知,在实际系统中,考虑可能的湍流环境,设定可以通信的天顶角范围,通过选用较长波长进行通信,可以有效抑制光强波动。本文研究时在不同海拔高度用不同的幂指数值进行连续计算,与以往分析不同幂率取值情况不同,更加贴近实际斜程通信系统。
[Abstract]:In recent years, the research of free space optical communication (FSO,Free Space Optical Communication) has begun to recover. Compared with RF communication, FSO has the advantages of large bandwidth, no spectrum authentication, fast networking speed, low power consumption, small size of communication equipment, high security, and good confidentiality. However, because the FSO communication link is in the atmosphere, the propagation beam will inevitably be absorbed and attenuated by the atmospheric molecules and particles in the atmosphere. At the same time, there is also a big problem of atmospheric turbulence. Atmospheric turbulence will cause random changes of atmospheric refractive index, which will produce the effects of beam expansion, beam drift and intensity scintillation, among which the effect of intensity scintillation is the most significant. The light intensity flicker will lead to the serious deterioration of beam quality and the increase of bit error rate (BER) at the receiver, which greatly affects the stability and reliability of FSO communication system, and seriously restricts the development of FSO technology. So it is necessary to study the light intensity scintillation coefficient in order to optimize the transmission rate and capacity of communication system. In this paper, the scintillation coefficients of plane wave and spherical wave in oblique FSO link are analyzed based on the three-layer height spectrum in the case of weak turbulence. Compared with the traditional Kolmogorov spectra, the scintillation effect of the turbulence described by the three-layer height spectrum is more serious. The bit error rate (BER) performance of the communication system is analyzed in logarithmic normal (LogNormal,LN) channel fading, and the effects of different zenith angles and wavelength of light wave on the weak turbulence channel laser communication are quantitatively analyzed. On the basis of this study, the expression of the scintillation coefficient of Gaussian waves in weak turbulence is further derived, and the BER in different cases is analyzed by using the expression of BER in LN channel fading. The influence of limited beam radius in uplink and downlink on scintillation coefficient and bit error rate (BER) is analyzed quantitatively. It is concluded that the BER does not vary with the beam waist radius in downlink. There is an optimal beam waist radius for uplink to minimize the bit error rate (BER). On the basis of the above research, the model of intensity scintillation coefficient of uplink and downlink is derived by using the extended Rytov theory based on the three layer high turbulence spectrum in the oblique atmospheric laser communication system. The model is applicable to all regions where turbulence is weak to strong. In this paper, the influence of the power law exponent of three-layer height spectrum, the intensity of near-Earth turbulence, the wavelength and the zenith angle on the scintillation coefficient of light intensity is analyzed. The numerical results show that the scintillation coefficient decreases with the increase of power law exponent and wavelength, and increases with the increase of zenith angle. When the zenith angle is close to 70 掳, the scintillation coefficient reaches the maximum value and then begins to decrease. The closed expression of bit error rate (BER) of communication system using OOK and M-PPM modulation is also derived. The error rate of different turbulence is analyzed, and the change trend of error rate with zenith angle, wavelength and other factors is obtained. According to the analysis results, in the actual system, considering the possible turbulence environment, setting the range of zenith angle that can communicate, and selecting the longer wavelength to communicate, the fluctuation of light intensity can be effectively suppressed. In this paper, different power exponents are used for continuous calculation at different altitudes, which is different from the previous analysis of different power rates, which is closer to the actual slant range communication system.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.1
本文编号：2205254
[Abstract]:In recent years, the research of free space optical communication (FSO,Free Space Optical Communication) has begun to recover. Compared with RF communication, FSO has the advantages of large bandwidth, no spectrum authentication, fast networking speed, low power consumption, small size of communication equipment, high security, and good confidentiality. However, because the FSO communication link is in the atmosphere, the propagation beam will inevitably be absorbed and attenuated by the atmospheric molecules and particles in the atmosphere. At the same time, there is also a big problem of atmospheric turbulence. Atmospheric turbulence will cause random changes of atmospheric refractive index, which will produce the effects of beam expansion, beam drift and intensity scintillation, among which the effect of intensity scintillation is the most significant. The light intensity flicker will lead to the serious deterioration of beam quality and the increase of bit error rate (BER) at the receiver, which greatly affects the stability and reliability of FSO communication system, and seriously restricts the development of FSO technology. So it is necessary to study the light intensity scintillation coefficient in order to optimize the transmission rate and capacity of communication system. In this paper, the scintillation coefficients of plane wave and spherical wave in oblique FSO link are analyzed based on the three-layer height spectrum in the case of weak turbulence. Compared with the traditional Kolmogorov spectra, the scintillation effect of the turbulence described by the three-layer height spectrum is more serious. The bit error rate (BER) performance of the communication system is analyzed in logarithmic normal (LogNormal,LN) channel fading, and the effects of different zenith angles and wavelength of light wave on the weak turbulence channel laser communication are quantitatively analyzed. On the basis of this study, the expression of the scintillation coefficient of Gaussian waves in weak turbulence is further derived, and the BER in different cases is analyzed by using the expression of BER in LN channel fading. The influence of limited beam radius in uplink and downlink on scintillation coefficient and bit error rate (BER) is analyzed quantitatively. It is concluded that the BER does not vary with the beam waist radius in downlink. There is an optimal beam waist radius for uplink to minimize the bit error rate (BER). On the basis of the above research, the model of intensity scintillation coefficient of uplink and downlink is derived by using the extended Rytov theory based on the three layer high turbulence spectrum in the oblique atmospheric laser communication system. The model is applicable to all regions where turbulence is weak to strong. In this paper, the influence of the power law exponent of three-layer height spectrum, the intensity of near-Earth turbulence, the wavelength and the zenith angle on the scintillation coefficient of light intensity is analyzed. The numerical results show that the scintillation coefficient decreases with the increase of power law exponent and wavelength, and increases with the increase of zenith angle. When the zenith angle is close to 70 掳, the scintillation coefficient reaches the maximum value and then begins to decrease. The closed expression of bit error rate (BER) of communication system using OOK and M-PPM modulation is also derived. The error rate of different turbulence is analyzed, and the change trend of error rate with zenith angle, wavelength and other factors is obtained. According to the analysis results, in the actual system, considering the possible turbulence environment, setting the range of zenith angle that can communicate, and selecting the longer wavelength to communicate, the fluctuation of light intensity can be effectively suppressed. In this paper, different power exponents are used for continuous calculation at different altitudes, which is different from the previous analysis of different power rates, which is closer to the actual slant range communication system.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.1
【参考文献】
相关博士学位论文 前1条
1 易湘;大气激光通信中光强闪烁及其抑制技术的研究[D];西安电子科技大学;2013年
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