Average Capacity of Optical Wireless Communication Systems Over Atmospheric Turbulence Channels

The optical wireless communication systems are rapidly gaining popularity as effective means of transferring data at high rates over short distances. These systems facilitate rapidly deployable, lightweight, high-capacity communication without licensing fees and tariffs. On the other hand, the performance of this new technology depends strongly on the atmospheric conditions and the parameters of the link such as the length and the operation wavelength. In this work, we extract closed form mathematical expression for the evaluation of the average (ergodic) capacity of such a system, using the log-normal and gamma-gamma distribution, in order to model the atmospheric turbulence conditions and we study the influence of the above parameters on it.     

无线光中继通信在弱湍流时的性能估计方法

对数正态信道是描述弱湍流条件下无线光通信衰落的有力数学工具.然而精确的对数正态信道性能表达式带有无法化简的多重积分,难以揭示信道参数和性能的联系,不利于性能估计.针对该问题,Wilkinson和Fenton近似被广泛应用于对数正态信道的性能分析,但Wilkinson和Fenton近似的应用范围却缺乏标准,这导致了系统设...     

Optical Communication Using Subcarrier PSK Intensity Modulation Through Atmospheric Turbulence Channels

This paper studies optical communications using subcarrier phase shift keying (PSK) intensity modulation through atmospheric turbulence channels. The bit error rate (BER) is derived for optical communication systems employing either on/off key (OOK) or subcarrier PSK intensity modulation. It is shown that at BER = 10^-6 and a scintillation level of sigma = 0.1, an optical communication system employing subcarrier BPSK is 3 dB better than a comparable system using fixed-threshold OOK. When sigma = 0.2, an optical communication system employing subcarrier BPSK achieves a BER = 10^-6 at SNR = 13.7 dB, while the BER of a comparable system employing OOK can never be less than 10^-4. Convolutional codes are discussed for optical communication through atmospheric turbulence channels. Interleaving is employed to overcome memory effect in atmospheric turbulence channels. An upper bound on BER is derived for optical communication systems employing convolutional codes and subcarrier BPSK modulation.     

基于Turbo码的大气无线光通信系统特性分析

提出并分析了基于Turbo码的大气无线光通信系统 ,针对大气无线光通信中的各种衰减和噪声分别进行了分析 ,通过仿真得出了特性曲线。比较了基于Turbo码的大气无线光通信系统与未编码大气无线光通信系统 ,发现Turbo码技术能够很好地补偿和克服各种衰减和噪声 ,提高了系统的抗干扰能力 ,使系统的性能得到了很大的提高。     

无线相干光通信空间分集接收合并技术

空间分集接收能补偿大气湍流造成的信道衰落。在给出相干检测分集接收的系统模型和晴朗大气信道模型的基础上,考虑子孔径间信号相关性,分析了等增益合并分集和最大比合并分集的误码率性能,并就中断概率与选择分集进行了比较。分析结果表明,空间分集接收能够明显改善相干光通信系统的性能,并且接收信号间的空间相关性越小分集接收的性能越好,其中最大比合并分集性能相对其他两种合并方式优势明显,选择分集性能最差,但它与等增益合并分集的差距不大,同时选择分集实现相对容易,在工程应用中要综合考虑实现的难易程度和性能。     

大气湍流对近地无线光通信链路影响的研究

大气湍流是影响大气无线光通信系统性能的主要因素之一,其影响主要表现为光通信系统中接收端接收的光强存在闪烁效应。本文将这种闪烁效应看作是光通信系统传输的乘性噪声,对光通信系统的传输性能进行了仿真和分析并与采用Turbo码编码的系统进行了比较。仿真结果表明,Turbo码是用来抑制大气湍流影响的一种有效的编码方式。     

BER Performance of FSO Links over Strong Atmospheric Turbulence Channels with Pointing Errors

In this letter, we investigate the error rate performance of free-space optical (FSO) links over strong turbulence fading channels together with misalignment (pointing error) effects. First, we present a novel closed-form expression for the distribution of a stochastic FSO channel model which takes into account both atmospheric turbulence-induced fading and misalignment-induced fading. Then, we evaluate the average bit-error rate in closed form of a FSO system operating in this channel environment, assuming intensity modulation/direct detection with on-off keying. Numerical examples are further provided to collaborate on the derived analytical expressions.     

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...     

大气无线光信道下基于光子计数的迭代译码性能

为了克服大气无线光信道中光强闪烁带来的长突发错误,本文提出了一种基于光子计数的迭代译码方案,并分析基于大气无线光信道下的译码性能.仿真结果表明,本方案不仅提高了系统的抗突发错误性能,并且与传统的信道交织+级连码方案相比,具有不引入信道交织时延和易于硬件实现的优点.     

Gamma-Gamma湍流中副载波大气光通信系统的性能分析

基于Gamma-Gamma光强闪烁分布大气湍流信道,在各种强度的湍流特性下而非仅限于弱湍流的分析背景,对采用数字副载波相移键控(PSK)强度调制技术的大气激光通信系统的差错性能进行研究与分析.选取一定发散角与接收孔径参数值,分别在不同闪烁强度与接收系统噪声下对系统的比特误码率(BER)进行了仿真,并以线性分组编码为例对系统的性能改进进行了仿真与讨论.     

Selection Transmit Diversity for FSO Links Over Strong Atmospheric Turbulence Channels

In this letter, transmit laser selection for multiple-input–single-output free-space optical communication systems with intensity modulation and direct detection over strong atmospheric turbulence channels is analyzed. Assuming channel side information at the transmitter and receiver, a transmit diversity technique based on the selection of the optical path with a greater value of scintillation has shown to be able to extract full diversity as well as providing better performance compared to other alternatives recently proposed such as orthogonal space–time block codes and repetition codes. Simulation results are further demonstrated to confirm the analytical results obtained for a diversity order of two.      

LDPC-Coded MIMO Optical Communication Over the Atmospheric Turbulence Channel

In this paper, coded multiple-input-multiple-output (MIMO) communication schemes for data transmission over the optical atmospheric turbulence channels are studied. Two strategies are proposed and compared. The first is based on repetition coding, and the second on space-time (ST) coding. Both approaches employ low-density parity-check (LDPC) codes. The LDPC codes are designed using the concept of pairwise balanced design (PBD), balanced incomplete block design (BIBBD), and block-circulant (array) codes. To improve the spectral efficiency, we employ a bit-interleaved (BI) LDPC-coded modulation based on the pulse amplitude modulation (PAM). A better bit error rate (BER) performance is achieved by the iteration of extrinsic information between a demapper and LDPC decoder. The simulations show that the LDPC-coded MIMO schemes can operate under a strong atmospheric turbulence and at the same time provide excellent coding gains compared with the transmission of uncoded data. To verify the efficiency of the proposed coding schemes, achievable information rates are computed when the turbulence is modeled by a gamma-gamma distribution.     

BER Performance of FSO Communication System with Differential Signaling over Correlated Atmospheric Turbulence Fading

Free space optical(FSO) communication system with differential signaling possesses the advantage of requiring no channel state information and avoiding computational load or link throughput reduction compared to the systems with conventional receivers. In this work, we investigate bit error rate(BER) performance of this system over partially and fully correlated atmospheric turbulence fading. In order to conduct the above analysis, we obtain a probability density functions(PDF) of the channel fading on the differential signals and derive our instantaneous BER using differential signaling scheme. Based on these results, we develop two closed-form mathematical expressions for the average BER under fully correlated and partially correlated fading in the convergent infinite series confirmed by Cauchy’s ratio test. The accuracy of the derived BER expressions is demonstrated by the Monte Carlo simulations, and the analyses for the effects of the system parameters on the BER performance are provided.     

大气湍流信道中激光通信群延迟特性研究

选用数学模型模拟了激光大气通信系统中大气湍流信道的群延迟特性,并进行了数值计算,结果表明:大气湍流信道带来的群延迟失真很小,在激光大气通信中可以不予考虑。     

A New Approach for Performance Evaluation of TCP over Interference-Limited Wireless Channels over Interference Wireless Channels

A new metric for performance evaluation of transport control protocol(TCP) overwireless channels based on the interference-limited characteristics of code division multipleaddress(CDMA) system is proposed.According to the new metric,the performance of TCP over CDMAcorrelated channel for different protocol parameters and different versions is investigated.The resultsshow that appropriate selection of protocol parameters and packet error rate(PER) operation point canimprove significantly the capacity of packet-switched CDMA-based network.     

TCP在无线衰落信道下的性能研究

本文在分析无线TCP原理的基础之上,讨论了各种提高无线链路TCP性能的方法,并对其优缺点进行了分析和总结.最后给出无线环境下TCP改进的基本原则,并初步探讨了进一步改进的方向.     

无线光通信调制方式性能分析

无线光通信的调制方式有多种,但缺少综合系统的分析。在详细地分析了脉冲位置调制（PPM）、数字脉冲间隔调制（DPIM）和双头脉冲间隔调制（DH—PIM）等调制方式符号结构的基础上,比较了各种凋制方式的平均发射功率和带宽效率,并在给定模型下分析了误时隙率。通过分析得出DPIM和DH—PIM更具有优势,更适合于未来无线光通信系统。     

湍流大气中激光通信系统接收光功率的优化研究

以部分相干高斯-谢尔模型(GSM)光束为例,对湍流引起的漂移方差和扩展角进行模拟,综合考虑由光束漂移引起的瞄准误差和光束扩展引起的接收光功率密度的整体下降,对激光通信链路中接收端光功率进行数值计算和分析,找出激光通信系统中最佳发射光束的参数。研究结果表明,湍流大气中激光通信系统最佳发射光束的参数与光束的束腰半径、空间相干长度、波长、传播距离和湍流强度有关。部分相干GSM光束接收端光功率随着波长、光束束腰、空间相干长度和传输距离的变化存在一最优值。     

基于LDPC码和MIMO的无线光通信系统性能

针对大气湍流严重影响无线光通信系统性能的问题,研究了基于低密度奇偶校验(LDPC)码和多输入多输出(MIMO)无线光通信系统性能,给出了基于LDPC码的空时编码MIMO(ST MIMO)和重复编码MIMO(rep MIMO)系统的解码算法,最后在对数正态模型和K分布模型下进行了仿真分析。仿真结果表明rep MIMO系统性能优于ST MIMO和单输入单输出(SISO)系统,ST MIMO在强湍流情况下性能明显优于SISO系统,基于LDPC码的ST MIMO和rep MIMO能取得10 dB以上的编码增益,并且编码增益随着湍流强度的增大而增加,基于LDPC码和rep MIMO的无线光通信系统差错性能更加优异,可以有效提高系统抗干扰能力。     

Performance of STBC-OFDM Systems over Spatial Correlated Fading Channels

1　Introduction　Recently ,MultipleInputandMultipleOutput(MIMO)wirelesssystemsusingmulti elementan tennadiversityatboththetransmitterandthere ceiverhasdrawnconsiderableattention[1～3] .InMI MOsystems,space timecodingcouldbeemployedtoimprovelinkreliability ,suchasSpace TimeBlockCoding (STBC)whichhasaverysimplede codingmethodandfulldiversityachieved[4～7] .WhenSTBCisusedoverwidebandchannels,theOrthogonalFrequencyDivisionMultiplex (OFDM )techniquecanbeusedtogethertoeffectivelycombatf…