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) has begun to revive. Compared with radio frequency communication, FSO has the advantages of wide bandwidth, no need for spectrum authentication, fast networking speed, low power consumption, small size of communication equipment, high security and good security. At the same time, it will also face a big problem - atmospheric turbulence, atmospheric turbulence will cause random changes in atmospheric refractive index, beam expansion, beam drift and intensity scintillation, among which intensity scintillation is the most significant. As a result, the beam quality is seriously degraded and the BER at the receiver is increased, which greatly affects the stability and reliability of the FSO communication system and seriously restricts the development of the FSO technology. Therefore, it is necessary to study the scintillation coefficient quantitatively to optimize the transmission rate and capacity of the communication system. Then, the scintillation coefficients of plane wave and spherical wave in slant-path FSO link are analyzed based on three-layer altitude spectrum. Compared with the traditional Kolmogorov spectrum, the scintillation effect caused by turbulence described by three-layer altitude spectrum is more serious. The influence of zenith angle and wavelength of light wave on laser communication in weak turbulent channel is studied. Based on this study, the expression of scintillation coefficient of Gaussian wave in weak turbulent channel is deduced. The BER under different conditions is analyzed by using the expression of BER under LN channel fading. The finite BER in uplink and downlink is quantitatively analyzed. The influence of beam radius on scintillation coefficient and bit error rate is studied. It is concluded that the BER of downlink does not change with beam waist radius, and there exists an optimal beam waist radius in uplink which can minimize the BER. Rytov's theory deduces an intensity scintillation coefficient model for both uplink and downlink links, which ignores the effects of internal and external scales. The model is suitable for all regions of turbulence from weak to strong. The effects of power law exponent of three-layer height spectrum, near-earth turbulence intensity, wavelength, zenith angle on the intensity scintillation coefficient are analyzed. It is shown that the scintillation coefficient decreases with the increase of power law exponent and wavelength, and increases with the zenith angle. When the zenith angle is close to 70 degrees, the scintillation coefficient reaches its maximum value and then begins to decrease. The closed-form expression of BER for communication systems with OOK and M-PPM modulation is derived. The BER for different turbulent conditions is analyzed and obtained. The variation trend of BER with zenith angle, wavelength and other factors is analyzed. According to the analysis results, considering the possible turbulence environment, the range of zenith angle which can be communicated can be set and the fluctuation of light intensity can be effectively suppressed by choosing a longer wavelength to communicate. The continuous calculation is different from the previous analysis of different power rates and is closer to the actual slant 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：2205253
[Abstract]:In recent years, the research of Free Space Optical Communication (FSO) has begun to revive. Compared with radio frequency communication, FSO has the advantages of wide bandwidth, no need for spectrum authentication, fast networking speed, low power consumption, small size of communication equipment, high security and good security. At the same time, it will also face a big problem - atmospheric turbulence, atmospheric turbulence will cause random changes in atmospheric refractive index, beam expansion, beam drift and intensity scintillation, among which intensity scintillation is the most significant. As a result, the beam quality is seriously degraded and the BER at the receiver is increased, which greatly affects the stability and reliability of the FSO communication system and seriously restricts the development of the FSO technology. Therefore, it is necessary to study the scintillation coefficient quantitatively to optimize the transmission rate and capacity of the communication system. Then, the scintillation coefficients of plane wave and spherical wave in slant-path FSO link are analyzed based on three-layer altitude spectrum. Compared with the traditional Kolmogorov spectrum, the scintillation effect caused by turbulence described by three-layer altitude spectrum is more serious. The influence of zenith angle and wavelength of light wave on laser communication in weak turbulent channel is studied. Based on this study, the expression of scintillation coefficient of Gaussian wave in weak turbulent channel is deduced. The BER under different conditions is analyzed by using the expression of BER under LN channel fading. The finite BER in uplink and downlink is quantitatively analyzed. The influence of beam radius on scintillation coefficient and bit error rate is studied. It is concluded that the BER of downlink does not change with beam waist radius, and there exists an optimal beam waist radius in uplink which can minimize the BER. Rytov's theory deduces an intensity scintillation coefficient model for both uplink and downlink links, which ignores the effects of internal and external scales. The model is suitable for all regions of turbulence from weak to strong. The effects of power law exponent of three-layer height spectrum, near-earth turbulence intensity, wavelength, zenith angle on the intensity scintillation coefficient are analyzed. It is shown that the scintillation coefficient decreases with the increase of power law exponent and wavelength, and increases with the zenith angle. When the zenith angle is close to 70 degrees, the scintillation coefficient reaches its maximum value and then begins to decrease. The closed-form expression of BER for communication systems with OOK and M-PPM modulation is derived. The BER for different turbulent conditions is analyzed and obtained. The variation trend of BER with zenith angle, wavelength and other factors is analyzed. According to the analysis results, considering the possible turbulence environment, the range of zenith angle which can be communicated can be set and the fluctuation of light intensity can be effectively suppressed by choosing a longer wavelength to communicate. The continuous calculation is different from the previous analysis of different power rates and is closer to the actual slant 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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