OCDMA系统二维RS地址码的设计方案及性能分析

首次在有限伽罗瓦域GF(7)上以本原元3构造出RS地址序列码.在一维RS素数码的基础上,给出基于二素数的二维RS矩阵码(2D-RSC)的设计方案.系统地研究了2D-RSC的OCDMA系统总体性能：分析了2D-RSC码字的相关性;导出了系统的最大用户容量;研究了2D-RSC系统以多址干扰为主的误码性能.结果表明：2D-RSC系统性能较之一维RS码有明显的改进. 特别是在大信息量传输时,采用两个较大的素数,基于2D-RSC的OCDMA系统的总体性能远优于一维素数码.     

基于2D-OOC的OCDMA系统的地址码结构研究

提出了二维光正交码(2D-OOC)设计方案,围绕光码分多址(OCDMA)技术实用化的两个主要指标-最大并发用户数和系统误码率的改进和提高,系统地研究了基于2D-OOC的OCDMA的性能,分析了2D-OOC码字的相关性,导出了系统的最大用户容量,详细研究了2D-OOC系统以多址干扰为主的系统误码率.研究表明:较之一维时域扩频码或一维谱域扩频码,2D-OOC系统性能大大提高,在大信息量传输时,适当选择码长和码重,系统总容量可高达Tbits/s量级,性能优于基于1D-OOC的OWDM和OCDMA混合系统.     

基于2D-OOC的OCDMA系统的地址码结构研究

提出了二维光正交码 (2D OOC)设计方案 ,围绕光码分多址 (OCDMA)技术实用化的两个主要指标—最大并发用户数和系统误码率的改进和提高 ,系统地研究了基于 2D OOC的OCDMA的性能 ,分析了 2D OOC码字的相关性 ,导出了系统的最大用户容量 ,详细研究了 2D OOC系统以多址干扰为主的系统误码率 .研究表明 :较之一维时域扩频码或一维谱域扩频码 ,2D OOC系统性能大大提高 ,在大信息量传输时 ,适当选择码长和码重 ,系统总容量可高达Tbits/s量级 ,性能优于基于 1D OOC的OWDM和OCDMA混合系统 .     

新型多速率光码分多址实现方案的研究

提出了一种新颖的多速率光码分多址系统的实现方案,使得光码分多址系统能够同时传输不同速率的用户信号。对系统的误码性能进行了理论分析,并讨论了在系统中加入硬件限幅器以提高系统性能的可能性。以同时传输两种不同速率信号为例,将系统与变码长光码分多址系统的误码性能进行了仿真和比较。分析表明,随着速率的增加,虽然地址码字的性能有一定下降,但其整体性能仍优于变码长的多速率的光码分多址系统。最后,设计了相应的实验,验证了码字的性能和实现多速率光码分多址系统的可能性。     

基于RS码及网格编码调制技术的60 GHz OFDM-RoF系统

分析了60 GHz正交频分复用技术光纤无线通信系统中的子载波互拍及频率选择性衰落.提出利用里德-所罗门码级联网格编码调制技术结合符号交织来降低两者对系统性能的不良影响.采用符号交织来分散正交频分复用中子载波上的误码,然后通过高码率的里德-所罗门码级联实用的网格编码调制技术来纠正比特错误.仿真结果表明:经过符号交织后,误码在子载波上的分布变得较均匀,有利于纠错|2.5 Gb/s正交频分复用信号采用RS-PTCM-64QAM方案比采用未编码的16QAM调制提高了5 dB左右的接收机灵敏度.     

Turbo码对快跳频光码分多址系统性能的改善

在考虑多用户干扰、色散效应和差拍噪声的情况下,分析了Turbo码对二进制脉冲位置调制(BPPM)的快跳频光码分多址(FFH OCDMA)系统性能的影响.在均匀交织器的情况下,用Turbo码的条件重量枚举函数得到了该系统的误码率的上界.数值模拟表明,Turbo码对FFH OCDMA系统的误码率性能有明显的改善,并且随着用户数的提高,Turbo码对误码率的改善程度也随之提高.也就是说,在一定的误码率性能要求下,Turbo编码的FFH OCDMA系统增加了同时使用的用户数.     

基于Turbo码的无线光通信副载波误码性能分析

介绍了湍流信道条件下光强闪烁的对数正态分布模型,结合大气信道特点,在不同光强闪烁效应下,对比分析了几种未编码大气激光通信副载波系统的误码性能。采用Turbo码性能限分析了基于Turbo编码的无线光通信副载波调制系统误码性能,并对Turbo编码前后系统误比特性能进行了对比。仿真结果表明,二进制相移键控(BPSK)误码性能优于其它几种副载波调制,同时Turbo码技术在较强光强闪烁指数下能够获得较大的编码增益,可以有效地提高系统的抗干扰能力。     

基于成像光通信的时间-空间扩频混合光码分多址编码方案

为了在成像光通信中充分利用时间和空间两种频带资源,以成像光通信为基础,提出一种利用二维光正交Pattern码结合时域扩频实现光码分多址(OCDMA)编码的新方案。分析在该方案中存在的多址干扰噪声,并给出了噪声的概率密度函数,然后讨论由多址噪声引起的误码率与判决门限、用户数、码长积和码重积之间的关系。在相同的码容量下与时域扩频光码分多址编码和空间扩频光码分多址编码方案相比,该方案能降低对相关器件性能(时域码片数量和空间像素规模)的要求,而且还可获得更小的误码率。最后给出编码解码的光学实现方案。     

基于低密度奇偶校验码的MPPM比特符号映射及系统性能研究

建立了基于低密度奇偶校验(LDPC)码和多脉冲位置调制(MPPM)的无线光通信系统模型,给出了相应系统模型下的解码算法,研究了(m,2)MPPM的比特符号映射方式,提出了用改进的遗传算法(GA)搜索的优化映射方法,最后在大气湍流信道下进行了仿真。仿真结果表明基于LDPC码和MPPM的无线光通信系统性能明显优于未编码的MPPM系统,结合LDPC码和多光束发射技术可以提高系统抗强大气湍流影响的能力;通过GA优化的映射方法在不增加系统复杂性的情况下能进一步提高系统的纠错性能,可以获得更大的编码增益。     

基于围长为8的QC-LDPC编码调制的高速相干光传输系统(英文)

针对常规LDPC码结构性差,编译码复杂度高,且存在差错平台效应的缺点.本文采用了一种改进的基于Tanner图的搜索算法,来构造具有准循环结构的校验矩阵.和未经过编码的调制方案相比,本文所提方案不仅没有表现出差错平台效应,而且带来了显著的编码增益,同时降低了实现复杂度.针对系统纠错性能和数据吞吐量之间的矛盾,提出了QC-LDPC编码与MQAM调制相结合的自适应编码调制系统方案,仿真结果表明,该方案在保证系统误码率性能的同时,能够提供最大化的数据吞吐量.     

大气湍流光PPM通信系统中LDPC码的置信传播译码

对大气弱湍流光PPM通信系统中LDPC码的BP 解码算法进行了研究,提出了相应系统模型下的解码算法.通过理论分析和大量计算机仿真,结果表明:采用LDPC的大气弱湍流光PPM通信系统比未编码的大气弱湍流光PPM通信系统的性能好,但是系统的BER性能随着PPM的时隙数的增加而增大.     

高效纠错编码技术在无线光通信中的性能分析

在介绍无线光通信信道及系统模型的基础上,推导了无线光通信未编码系统和RS编码系统在已知信道边信息条件下的平均误码率,从接收光功率和对数振幅起伏方差方面对RS码编码系统和Turbo编码系统的性能进行比较.仿真结果表明,采用编码方案可以有效地改善大气湍流对通信链路性能的恶化,Turbo码编码方案比RS码编码方案能更好地抗大气湍流干扰.     

Application of Turbo codes in optical OFDM multimode fiber communication system

In this paper, Turbo Code is proposed in optical OFDM multimode fiber communication system in order to decrease the bit error rate (BER) of the system, which is mainly affected by the deep nulls of the magnitude response of multimode fiber in the high frequency region (above 3 dB). A simulation system in SIMULINK is established. Based on the system, the BER of the system with Turbo Code is compare to the systems with another two typical coding schemes including convolutional code (CC) and serially concatenated code (SCC) which uses a concatenation of convolutional and RS codes when transmitting 10 Gbps data over various length multimode fibers. Different transmitting rate is also considered. The results show that Turbo coded system has a lower BER than the other two systems and the Turbo coded system can transmit 10 Gbps data to the distance of 300 m with BER below 1e−6.     

A novel encoder/decoder design scheme utilizing differential detection in OCDMA systems

In this paper, we report the use of differential detection in optical code-division multiple access (OCDMA) systems which use encoders and decoders based on unbalanced codes and utilize bipolar modulation/differential detection to demonstrate a significant improvement in system performance. Differential detection has been reported earlier also requiring a large number of one-chips in the code for (balanced codes) or with unbalanced codes with very long temporal dimensions requiring a large number of delay elements (either the delay lines in the ladder-type structures or the gratings in the multiple fiber gratings) making the encoder/decoder structures. We use single pulse per row codes to design our system and carry out the simulations for showing the results. The improved BER performance is achieved that can be traded for increasing the number of codes. Using optical simulation tool, the OCDMA system has been simulated for four users. The results of this system utilizing differential detection and another system that uses the same coding scheme but employing direct detection, for the same number of interfering users, are shown for comparison. The BER and the power penalty plots are shown for the two systems. Also, it is shown that performance degradation occurs due to the linear and non-linear effects of the fiber medium. The BER worsens more rapidly with link length for direct detection case, whereas for differential detection with an initial improvement of 8 dB, the increase in BER is insignificantly small for a link length of 500 km.     

基于三种调制模式下的turbo码光无线通信系统分析

从分析大气对光无线通信系统的影响出发,研究了大气信道特性,建立了大气信道信噪比和能见度的关系.为降低系统误码率,提出了基于OOK、BPSK、BPPM三种调制模式的turbo码的编码方案,推导出三种不同方案对应的turbo码迭代MAP算法.应用建立的信噪比关系,分析和计算了基于三种不同方案的系统的误码率.结果表明,基于BPSK的turbo码系统比OOK和BPPM系统的信噪比降低约3dB,且在高的信噪比情况下,BPSK系统能显著降低系统的误码率.因此,基于BPSK的turbo码方案较适合光无线通信系统.     

The Effects of Polarization and Non-Linearity on the Performance of WDM System with Optical Cross-Connects

The performance of a wavelength division multiplexing (WDM) system with optical cross-connects (OXCs) and in the presence of polarization and nonlinear effects was analyzed. We determined the effect of PMD and PDL; nonlinearity such as XPM, SPM, and FWM; and CD on the system performance. We found that the system outage probability is highest at DGD threshold for the respective maximum eye closure (EC). We showed that the allowable DGD depends on the time slot for one bit T, which is the inverse of the network bit rate. Wider T is more immune to large PMD with the EC still maintained at the same level since DGD/T is unchanged. Our analysis also indicated that as DGD increases, BER increases. The BER also increases with increase in PDL and further increases with the presence of XPM, SPM, FWM, and CD.     

Reflections from polished single mode fiber ends

Abstract

The performance of a wavelength division multiplexing (WDM) system with optical cross-connects (OXCs) and in the presence of polarization and nonlinear effects was analyzed. We determined the effect of PMD and PDL; nonlinearity such as XPM, SPM, and FWM; and CD on the system performance. We found that the system outage probability is highest at DGD threshold for the respective maximum eye closure (EC). We showed that the allowable DGD depends on the time slot for one bit T, which is the inverse of the network bit rate. Wider T is more immune to large PMD with the EC still maintained at the same level since DGD/T is unchanged. Our analysis also indicated that as DGD increases, BER increases. The BER also increases with increase in PDL and further increases with the presence of XPM, SPM, FWM, and CD.     

New design of spectral amplitude coding in OCDMA with zero cross-correlation

A zero cross-correlation (ZCC) code is proposed to reduce the impact of system impairment and multiple access interference (MAI) in spectral amplitude coding optical code division multiple access (SAC-OCDMA) system. Bit-error-rate (BER) performance is derived taking into account the effect of some noises. The key to an effective OCDMA system is the choice of efficient address codes with good or almost zero correlation properties for encoding the source. The use of ZCC code can eradicate phase induced intensity noise (PIIN) which will contribute to better BER. Thus, we demonstrate, theoretically, the performance of optical ZCC code. It is shown that optical ZCC code can accommodate more users simultaneously for the typical error rate of optical communication system of 10⁻⁹. The result indicates that the established system not only preserves the capability of suppressing MAI, but also improves bit-error-rate performance as compared to the conventional coders.     

Performance evaluation of Fi-Wi network based on SCM–optical code division multiple access architecture

This paper investigates the performance of a spectral amplitude coding (SAC)–OCDMA system design utilizing subcarrier multiplexing techniques for use in the popular fiber-wireless (Fi-Wi) technology. Zero cross correlation code is employed because of its ability to eliminate phase induced intensity noise (PIIN) and the simplicity of using a direct detection technique at the receiving end. The performances are evaluated theoretically to derive the signal-to-noise ratio and results are presented in terms of bit error rates (BER). Results are analyzed to investigate the effect of code weight and variable data rates on the system performance. To validate the results, simulative analysis is also done using Optisys version 6.0. We demonstrated that the ZCC code performed better compared to other code for a BER floor of 10⁻⁹ with larger cardinality of subscribers. Results obviously indicate that system performance can be improved with larger code weight. In addition, the choice of lower bit rate is observed to perform better and more suitable for application in this hybrid Fi-Wi network.