各向异性海洋湍流DHPIM无线光通信性能分析

Performance of Double-headed Pulse Interval Modulated Wireless Optical Communication System in Anisotropic Ocean Turbulence

水下无线光通信系统易受由折射率波动起伏引起的海洋湍流的影响,造成光强闪烁、光束漂移、光束扩展和波前畸变等效应,从而使光信号产生衰落,导致通信质量降低及通信性能恶化。利用扩展的惠更斯-菲涅耳原理和渐近Rytov理论分别导出有限尺寸探测器的平均接收光功率和辐照度通量方差,研究了Gamma-Gamma湍流信道模型下双头脉冲间隔调制的高斯光束在各向异性海洋湍流中的误包率性能。分析了在不同的各向异性海洋湍流下,海洋湍流参数(温度方差耗散率、湍流动能耗散率、温度与盐度波动对功率谱贡献大小的比值)、比特分辨率、比特传输速率、光电探测器的响应度以及链路距离对误包率的影响,为降低双头脉冲间隔调制下高斯光束的误包率性能提供了理论依据。

The ocean is abundant in chemical and power resources,it is the space for human survival and development. Underwater Wireless Communication (UWC) technology realizes the wireless transmission of ocean exploration information,and has received extensive attention from researchers in recent years.Currently,radio frequency communication technology and acoustic communication technology are two comparatively mature technologies in seawater communications,in which the problems conceal. In the radio frequency communication,the large volume of transceiver,the high cost and energy consumption,and the rapidly attenuated radio wave underwater would make it impossible to achieve long-distance transmission and high-speed underwater communication. As for the acoustic communication technology,its large-size equipment,high power consumption,low transmission rate,limited available bandwidth,and severe multipath effects during transmission,would cause speed limits of the data transmission and the increase in bit error rate. With the advantages of no electromagnetic radiation,fast speed,strong mobility,good safety, high bandwidth and green environmental protection, the underwater wireless optical communication has become a new choice for underwater sensor data transmission and acquisition of marine monitoring information,thus playing a paramount role in the detection in underwater environments and development of marine resources. Specifically,the lower loss of blue-green light caused by seawater absorption and scattering can help to reach the underwater transmission rate as Gbit/s. Therefore,bluegreen light is used to carry information to realize long-distance underwater transmission. However,as the light beam propagating in seawater,not only will it be affected by the attenuation effect of the absorption and scattering of the seawater impurities,but also easily affected by ocean turbulence caused by fluctuations in refractive index. Ocean turbulence will lead to a series of problems,including light intensity flicker,beam drift,beam expansion,wavefront distortion and other effects,turning to the consequence of the optical signal fading,degrading the communication quality and deteriorating its performance. In previous studies,turbulence was regarded as isotropic,in which the vortex structure (that is,the spatial frequency of turbulence) was symmetric in different directions,and isotropic turbulence was a simple and idealized model. The ocean turbulence occurring naturally is often anisotropic. Ocean turbulence is composed of eddy structures with different sizes and frequencies (that is, eddy structures are asymmetric in different directions). Therefore,this paper considers the asymmetry of ocean vortex motion (that is,the case where the horizontal scale of the vortex is much larger than the vertical scale),as well as uses ocean turbulence parameters and anisotropy factors to express the equivalent structural parameters of ocean turbulence,applying the equivalent structural parameters of ocean turbulence expressed by ocean turbulence parameters and anisotropy factors,the extended Huygens-Fresnel principle and the asymptotic Rytov theory are also used to derive the average received optical power and radiation of a finite-size detector. Meanwhile,the paper also conducts research on the degree of flux variance,and the packet error rate performance of the double-headed pulse interval modulated Gaussian beam in anisotropic ocean turbulence under the GammaGamma turbulence channel model. DHPIM has its built-in symbol synchronization and slot synchronization functions. Compared with PPM and DPIM,DHPIM has shorter symbol length,higher transmission rate,larger transmission capacity, higher bandwidth requirements and better ability to resist multipath dispersion. In the simulation analysis of ocean turbulence parameters (temperature variance dissipation rate,turbulence energy consumption) under different anisotropic ocean turbulence Spread rate,the ratio of the contribution of temperature and salinity fluctuations to the power spectrum),bit resolution and transmission rate,photodetector responsivity and the impact of link distance on the packet error rate,the results come out and indicate that:no matter what kind of ocean turbulence parameters,the performance of the wireless optical communication system is all proportional to the anisotropy factors in the x-direction and y-direction. For different anisotropy factors,when the temperature variance dissipation rate χTdecreases,the ratio of temperature and salinity contribution to the power spectrum ω decreases,or the turbulent energy dissipation rate εincreases,the intensity of ocean turbulence can be weakened,and the system decreases accordingly. For the same bit error rate level in the isotropic ocean turbulence,the wireless optical communication system in the anisotropic ocean turbulence can achieve a longer transmission distance. Simultaneously,approaches such as reducing the bit rate,increasing the responsivity of the photodetector,applying a smaller modulation order while appropriately using a larger diameter aperture to receive the average signal fluctuations,would resist the impact of ocean turbulence and reduce the system′s packet error rate effectively. This study provides a certain reference value for improving the performance of underwater wireless optical communication systems in an anisotropic ocean turbulent environment.