孔径接收对强海洋湍流DPSK调制的水下光通信系统误码率影响研究

水下光通信（underwater wireless optical communication,UWOC）系统具有宽带宽、高保密等优点,适用于水下通信。然而,水下吸收、散射和湍流效应影响了光束传输,限制了系统在长距离方面的应用。本文探讨了差分相移键控（differential phase-shift-keying, DPSK）调制和孔径接收对在Gamma-Gamma强湍流信道中传输的UWOC系统误码率（bit error rate,BER）的影响。基于Whittaker函数,推导出了系统采用DPSK调制高斯光束在强湍流中传输的BER解析式。仿真观察了系统调制方式、孔径接收直径、传输距离以及四种海洋参数对BER性能的影响。结果表明,采用DPSK和较大尺寸的孔径直径接收可以有效地提高BER性能。同时,系统在均方温度耗散率和温度和盐度波动对海洋湍流贡献的比值较小、动力粘度较大,湍流动能耗散率较大或较小的短距离海洋湍流环境中可以获得较好的通信性能。      

MIMO水下无线光通信系统性能解析研究

为了消除海洋湍流引起的信号衰落和衰减,在基 于BPSK调制的水下无线光通信(underwater wireless optical communication,UWOC)系统中引入了MIMO(multi-input multi-outpu t)技术。在 假设海洋湍流模型为log-normal分布基础上,得出了球面波光束在弱海洋湍流传输的闪烁 指数计算公 式。借助于Gauss-Hermite正交积分近似公式,推导了UWOC系统分别采用SISO(single-in put single-output)、SIMO(single-input multi-output)、MIMO三种技术,且接收端 采用等增益合并法时, 系统误码率(bit error rate,BER)的解析公式。应用此解析公式,数值仿真观察了系统 误码率在不同 的信噪比下受三种海洋参数(即均方温度耗散率,单位质量液体中的湍流动能耗散率,温度 和盐度波 动的相对强度)以及系统通信距离的影响。仿真结果表明,UWOC系统采用MIMO技术,在较小 的 均方温度耗散率、较小的温度和盐度波动的相对强度、较大的湍流动能耗散率的海洋中,以 及通过较 短的通信链路都可以得到更优的误码率性能。     

水下光通信系统在非Kolmogorov湍流中的传输特性

湍流效应是限制水下无线光通信(underwater wireless optical communication,UWOC)系统性能的关键因素之一。在强海洋非Kolmogorov湍流中,首先以平面波和球面波为光源,研究了采用孔径接收的差分相移键控(differential phase-shift-keying,DPSK)调制的UWOC系统性能。接着,基于Gamma-Gamma信道模型,利用Whittaker函数推导出了平均误码率(average bit error rate,ABER)的解析表达式。最后研究了不同光束形状、调制方式、孔径尺寸以及非Kolmogorov湍流参数即内尺寸和幂率对ABER的影响规律。结果表明,UWOC系统采用球面波传输、DPSK调制在比较小的内尺寸和较大的幂率湍流下传输经孔径接收可以提升ABER性能。     

Gamma Gamma强海洋湍流和瞄准误差下水下无线光通信系统的性能研究

采用外差式差分相移键控(Differential phase-shift keying,DPSK)调制的水下无线光通信(Underwater wireless optical communication,UWOC)系统经过Gamma Gamma强海洋湍流信道传输,当接收端与发送端之间存在瞄准误差并采用孔径接收方式时,分析了湍流效应和瞄准误差对接收光强的抖动影响,推导了UWOC系统的平均误码率(Bit error rate,BER)和中断概率(Outage probability,OP)的解析表达式。数值模拟研究了不同的瞄准误差、束宽、接收孔径和海洋湍流参数对平均BER和OP性能的影响。结果表明,在相同的束宽和信道环境下,瞄准误差越大,系统性能越差;光束束宽与孔径半径之比越大,接收孔径直径越大,系统性能越好;另外,选择较小的温度和盐度波动对海洋湍流贡献的比值ω和均方温度耗散率χT,以及较大的湍流动能耗散率ε和动力粘度u的海洋湍流环境也有利于获得较好的系统性能。     

海洋湍流下波长分集无线光通信系统性能分析

由于海水的吸收、散射衰减以及海洋湍流效应会引起水下无线光通信（Underwater wireless optical communication,UWOC）系统接收端光信号的闪烁,导致UWOC系统传输性能下降。基于Gamma-gamma分布的海洋湍流信道模型,根据海洋湍流参数和各向异性因子表示的等效结构参数,推导出波长分集UWOC系统中断概率（Outage probability,OP）与平均误码率（Bit error rate,BER）封闭表达式。研究分析随着各向异性因子的增加,具有不同波长分集阶的水下无线光通信系统中断概率与平均误码率的变化,比较接收端使用最佳组合（Optimal combining,OC）与等增益组合（Equal gain combining,EGC）技术的水下无线光通信系统平均误码率,并仿真不同海洋湍流参数、传输距离对波长分集UWOC系统性能的影响。数值结果表明,随着各向异性因子的增加,海洋湍流对水下无线光通信系统产生的影响逐渐减弱,使用波长分集技术的UWOC系统比无波长分集技术的UWOC系统中断概率与平均误码率明显改善。     

孔径接收下各向异性海洋湍流UWOC系统误码分析

为了研究孔径接收对各向异性海洋湍流条件下水下无线光通信(UWOC)系统误比特率的影响, 系统采用高斯光束传输, 接收端通过孔径接收, 在脉冲位置调制方式下通过各向异性海洋湍流信道。引入各向异性海洋湍流结构常数, 通过对闪烁的形成原理和各向异性海洋湍流条件下闪烁系数的分析, 数值模拟得到了在不同接收孔径和各向异性因子下, 海洋湍流参量、传输距离、雪崩光电二极管(APD)平均增益和调制阶数对系统误比特率的影响。结果表明, 相同各向异性因子和海洋湍流参量下, 大孔径接收能有效提升系统误比特率性能; 相同孔径直径和海洋湍流参量下, 各向异性因子越大, 系统通信性能越好; 均方温度耗散率、温度和盐度对海洋功率谱变化贡献的比值较小, 湍流动能耗散率、动力粘度较大以及传输距离越短, 系统误码性能越好; APD增益为100或150时, 系统通信性能最佳; 调制阶数M=8时, 系统通信性能最佳, M>64时, 系统误比特率变化程度几乎饱和。该研究为UWOC系统平台搭建和性能估计提供了参考。     

各向异性海洋湍流对外差式DPSK无线光通信系统的性能研究

应用广义的惠更斯-菲涅耳原理及改进的Rytov方法,采用基于Gamma-Gamma光强概率分布的海洋湍流信道模型,得到了中断概率解析式.并在此基础上对各向异性海洋湍流高斯光束外差式差分相移键控(DPSK)调制的中断概率性能进行了研究.仿真分析了不同的各向异性海洋湍流下各种海洋湍流参数(温度与盐度波动对功率谱变化贡献之比、单位质量流体动能耗散率、均方温度耗散率)、传输距离、DPSK调制的数据传输速率对中断概率的影响.为降低高斯光束DPSK调制下的中断概率、提高通信质量及可靠性提供了理论依据.     

水下无线光通信系统一般测试方法

水下无线光通信(UWOC)是一种新兴的高速水下通信技术,因其拥有传输带宽高、抗电磁干扰能力强、功耗低和体积小等优点,在学术界和工业界逐渐引起广泛关注。尽管光作为信息载体在水下传输时存在较大衰减,但其传输距离仍然可达百米级别,足以满足传感器数据传输的距离要求。然而,目前UWOC技术仍处于早期发展阶段,大部分UWOC系统的实验仅在实验室水箱开展,且性能测试方法各不相同,缺乏统一的性能测试模型和方法。为更客观地评估UWOC系统的性能,文章尝试提出UWOC系统的一般测试方法,建立测试模型,并总结系统评价指标,以促进UWOC技术的发展。     

水下无线光通信中MIMO技术研究现状

水下无线光通信(UWOC)具有大容量和高速率等优势,然而受水下复杂环境和光学器件带宽的影响,实际通信范围和传输速率受到制约。多输入多输出(MIMO)技术将空间单流数据转换为多流数据并行传输,可以扩展UWOC的通信距离,缓解水下吸收、散射效应和湍流引起的通信性能下降,因而受到广泛关注。基于此,文章围绕UWOC中的MIMO技术,分析和总结了MIMO-UWOC的信道模型、研究现状、实验装置与原型以及发展趋势与展望。     

湍流大气中传输光波的波相位结构解析函数

在湍流大气对传输光波调制的双尺度湍涡(大尺度湍涡和小尺度湍涡)近似下,研究了用于计算描述湍流大气中传输光波相干长度变化的核心函数(互相干函数)的关键因子波结构函数(WSF),通过建立包含不同尺度湍流因子的折射率起伏谱密度函数,导出了可以用于精确理论分析平面波与球面波在湍流大气中传播时所产生的诸如到达角起伏和相干性变化等效应的波相位结构函数的精确解析式,同时给出了便于数值计算的近似误差在2%范围以内的波相位结构函数的精确渐近表达式。     

水下复合信道对GMSK无线光通信系统性能的影响

The absorption and scattering of light in seawater channel cause signal attenuation, and the turbulence of seawater causes signal amplitude fluctuation, both of which will reduce the bit error rate (BER) performance of underwater wireless optical communication (UWOC) system. The effects of the two channel characteristics on the signal performance were considered comprehensively, and a method was proposed to equate the transmission distance and turbulence probability density function to the system signal-to-noise ratio (SNR) and turbulence noise, and then the signal attenuation and turbulence noise were combined into the signal waveform to establish the underwater composite channel signal transmission model. According to the experimental system parameters, the signal transmission waveforms of Gaussian minimum frequency shift keying (GMSK) modulation under composite channel were simulated, and the one-bit difference demodulation algorithm was used to compare the demodulated waveforms with the original waveform, and the influence relationships of composite channel on the system BER performance was analyzed. The simulation experiment results show that, compared with on-off keying modulation (OOK), pulse position modulation (PPM), GMSK system can obtain the SNR gain of 3.3 dB, 4.8 dB respectively only in the attenuation channel with seawater attenuation coefficient of 0.151 m?1. Under the composite channel, GMSK modulation performance is superior to OOK modulation and PPM modulation. When the water attenuation coefficient is 0.151 m?1, and turbulence intensity variance is smaller than 0.16, GMSK modulation system has no error rate limit, the system BER is decided by signal attenuation and turbulence noise and Gaussian noise together, GMSK modulation achieves SNR gain of 4.35 dB compared with PPM modulation. Furthermore, turbulence intensity variance is greater than 0.16, system BER arrives limit, which value is determined by the turbulence intensity, and the limit value of BER increases nonlinearly with the increase of turbulence intensity.     

Research on the system error performance of coherent orthogonal frequency division multiplexing system with M-distribution in satellite-to-ground laser communication

In order to alleviate the influence of atmospheric turbulence on the performance of satellite-to-ground laser communication system,based on the M-distribution atmospheric channel model,a multi-carrier coherent orthogonal frequency division multiplexing (OFDM) modulation system was proposed for uplink and downlink in the satellite-to-ground laser communication.The closed-form expression of bit error rate (BER) of coherent OFDM modulation system was derived.The relationship between the zenith angle,receiving aperture,signal-to-noise ratio (SNR),optimal beam divergence angle,and optimal transmission radius and the BER were studied under weak,and strong atmosphere turbulence,and compared with binary coherent differential phase shift keying (DPSK) modulation.Both the theory and the simulation results show that compared with coherent DPSK modulation,the bit error performance of the coherent OFDM modulation system in the satellite-to-ground laser communication system is better.     

SER performance investigation of UWOC system over composite EGG oceanic turbulence fading channel with BSF

In this work, the symbol error rate (SER) performance of a relay-assisted underwater wireless optical communication (UWOC) system has been investigated over the composite exponential-generalized gamma (EGG) distribution with the beam spread function (BSF) under two hard decision schemes of fixed decision threshold (FDT) and dynamic decision threshold (DDT). Specifically, the oceanic turbulence is assumed to follow the EGG distribution, and the impacts of absorption, scattering and misalignment loss are characterized by BSF. The cumulative distribution function (CDF) of this UWOC system is derived with the max-min criterion as the best path selection scheme. And with the help of Gauss-Laguerre quadrature function, the analytical SER expressions for these two threshold schemes are then achieved and validated by Monte Carlo (MC) simulation. Moreover, the SER performance is further studied under different temperature gradients, bubble levels (BLs) and water salinity over three water types, as well as the system structure parameters. Results show that the UWOC system with DDT scheme can efficiently overcome the error floor induced by FDT scheme and demonstrates better SER performance. Furthermore, the SER performance would be improved with lower BL, temperature gradients and water salinity as well as the concentration of dissolved particles. This work will benefit the design and research of relay-assisted UWOC system.     

基于极化码的无线光通信副载波误码性能分析

提出了一种基于极化码的无线光信道副载波调制方法,给出了极化编译码的具体算法过程,并将其应用于无线光通信系统。在不同大气湍流强度下,对系统的差错性能进行了仿真分析,其重对基于极化码的二相相移键控和四相相移键控两种调制方法的误码率进行了对比,结果表明,采用极化码的副载波二相相移键控调制系统的性能优于四相相移键控系统。最后,实验比较分析了极化编码前后副载波调制系统的误比特率,结果表明,在无线光通信大气湍流信道模型下,采用副载波极化码编码调制技术可使误码率性能改善一个量级。