光码分多址多比特传输系统性能分析

:多比特传输是光码分多址通信的一种方案。本文对光码分多址多比特传输系统的误码性能进行了理论分析和计算机数字仿真。在系统中存在光电检测器散粒噪声、暗电流噪声、背景光、热噪声的情况下 ,分别对无光硬件限幅器和引入一个光硬件限幅器的多比特传输系统进行讨论 ,得出相应的误比特率表达式 ,该表达式明确、具体。分析结果表明 ,当接收功率较大时 ,多比特传输系统的误码性能优于相应的单比特传输系统。     

基于跳频扩时光正交码的光码分多址系统性能分析

提出了一种基于光正交码（OOC）的跳频方案，与OOC系统相比，采用该跳频码字的光码分多址（OCDMA）系统的可容纳用户数目得到了极大提高，并且多用户干扰（MAI）大大降低，从而系统整体性能得到提高。同时提出了使用该跳频码的多比特传输光码分多址系统方案，该方案利用了跳频码字数目的充裕性，使得系统传输速率成倍提高。     

A semiclassical analysis of optical code division multiple access

A model noncoherent, optical, asynchronous, CDMA system is described. The error rate for a single-user matched-filter receiver that is valid for arbitrary photomultipliers and signature sequence sets, adheres to the semiclassical model of light, and does not depend on approximations for large user groups, strong received optical fields, or chip synchronism is analyzed. The exact minimum probability of error and optimal threshold are compared to those obtained with user-synchronism and multiple-access interference (MAI) distribution approximations. For the special case of unity-gain photodetectors and prime sequences, it is shown that the approximation of chip synchronism yields a weak upper bound on the exact error rate. It is demonstrated that the approximations of perfect optical-to-electrical conversion and Gaussian-distributed MAI yield a poor approximation to the minimum error rate and an underestimate of the optimal threshold. Arbitrarily tight bounds are developed on the error rate for unequal energies per bit. In the case when the signal energies coincide, these bounding expressions are considerably easier to compute than the exact error rate     

Chip-level detection in optical code division multiple access

A new detector for optical code-division multiple-access (CDMA) communication systems is proposed. This detector is called the chip-level receiver. Both ON-OFF keying (OOK) and pulse-position modulation (PPM) schemes, that utilize this receiver, are investigated in this paper. For OOK, an exact bit error rate is evaluated taking into account the effect of both multiple-user interference and receiver shot noise. An upper bound on the bit error probability for pulse-position modulation (PPM)-CDMA system is derived under the above considerations. The effect of both dark current and thermal noises is neglected in our analysis. Performance comparisons between chip-level, correlation, and optimum receivers are also presented. Both correlation receivers with and without an optical hardlimiter are considered. Our results demonstrate that significant improvement in the performance is gained when using the chip-level receiver in place of the correlation one. Moreover the performance of the chip-level receiver is asymptotically close to the optimum one. Nevertheless, the complexity of this receiver is independent of the number of users, and therefore, much more practical than the optimum receiver     

Performance evaluation of coherent optical code division multiple access

A coherent optical CDMA network employing Gold sequences for the spreading and despreading operations is analysed in terms of the signal to noise ratio penalty as a function of the number of simultaneous users incurred to maintain a given value of the bit error rate. The binary PSK and OOK modulation schemes are considered. Exact results in the presence of noise and interfering signals (interferers) are obtained.<>     

Performance evaluation of optical code division multiple access systems

In this paper, a new mechanism of faster routing known as message priority and fast routing (MPFR) mechanism in optical code division multiple access (OCDMA) is proposed for optimization of routing performance and to provide effective data transfer. In this proposed work, we have reduced the size of the header bits which are used in MPFR mechanism. In proposed algorithm, with accordance to packet header, the message size is being increased and priority bit is being added which leads to faster data transfer rate and effective data transfer in OCDMA. The transmitter sent the 2D codes to the MPFR which is then added priority bit. If the cover bit in any codes is enabling then the code is considered to be a priority packet and its superior bit then the code is considered to be routing. A modern novel approach which reduces the overhead for fast data transfer is proposed on name of MPFR. Thus the routing can be faster and the codes to be sent are being priorities and send. Thus the OCDMA can now become much faster to be used in critical areas. MPFR protocol, which prioritizes the code with high priority and also it reduces the header processing time of the codes with increase in message size. The prioritization of the code helped to process the particular code first and then rest of the codes and with increase in message size, help to reduce the transmission and processing time of the packet header.     

一种新有用于光码分多址的光相关器

本文提出了一种新的用于光码分多址系统的光相关器,并对光同步和异步系统给出了误比特率公式。数值仿真结果表明,无论是异步还是同步系统,这种光相关器的误比特率性能都优于传统光相关器的性能。     

光码分多址相位编/解码器

介绍了几种基于相干光的光码分多址(OCDMA)相位编/解码器.分别给出了采用空间光调制器(SLM)、平面光波导(PLC)、超结构光纤布喇格光栅(SSFBG)技术的OCDMA编/解码器的工作原理及最新研究进展,并分析了它们的特点.基于SSFBG的编/解码器在产生超长光学码方面是最好的;平面光波导编/解码器由于可实现单片集成,也是一种很有前途的器件.     

码分多址系统中多用户检测算法的性能分析

多用户检测算法是码分多址系统中解决多址干扰的关键技术之一，近年来人们对此做了许多研究。现分析了几种典型的多用户检测算法的特性，给出了它们的性能特点。     

光码分多址系统中二维QCC码的误码性能分析

对基于一维二次同余码构成的QCC/QCC跳频扩时码和QCC/OOC跳频扩时码进行了详细的码字性能分析.通过计算不同情况下码字的碰撞次数,得出了互相关均值,并对这两种二维QCC码进行了误码率的仿真比较和理论分析,数值模拟表明,当码字长度确定时,QCC/OOC码的码字性能较QCC/QCC码更加优良,码字容量更大,但对跳频码片的要求较高.当码字容量确定时,较大p值的QCC/QCC码的码字性能更加优良,但码字长度相对较长.     

Effect of imperfect power control on cellular code division multiple access system

An analytical model is developed to evaluate the performance of a cellular direct-sequence code division multiple access (DS CDMA) system with a perfect as well as an imperfect power control scheme and without power control considering the near-far effect. The effect of the three schemes on the performance is compared.<>     

Direct-sequence code division multiple access: From radio communications to optical networks

A direct sequence optical code division multiple access technique is investigated. This paper introduces, first, the principles definitions of Code Division Multiple Access in radio communications. After that, the performances of Optical Code Division Multiple Access are evaluated in association with a realistic amplified optical channel model. To determine the performances obtained by this combination, different detection methods are investigated in an OpticalCDMA system. Threshold and multi-user detections are developed in association with Optical Orthogonal Codes:ooc and Prime Sequences:ps, specially designed to be adapted to fiber optic channel.     

Novel encryption technique for security enhancement in optical code division multiple access

Photonic Network Communications - In this paper, a novel two dimensional (2D) wavelength/time (W/T) optical code division multiple access (OCDMA) code with zero cross-correlation property to...     

可调谐光纤F-P线性滤波器的设计与分析

光纤滤波器在光纤通信和光纤传感领域发挥着重要的作用。本文基于光学薄膜干涉理论设计了一种用于光纤传感的可调谐F-P线性滤波器,该滤波器由两端面相对的入射光纤与出射光纤构成,两光纤端端面分别镀有反射光纤薄膜。该F-P干涉腔改善了传统F-P腔的透射率响应特性,有助于提高滤波器的线性度和线性范围。本文采用光学薄膜干涉矩阵分析法对该滤波器的透射率响应关系进行了计算与分析,并得出该FP滤波器的结构参数。设计结果表明,这种新型线性滤波器具有线性度好、线性范围宽和线性区间可调的优点。     

基于LDPC码的相干光通信QNSC系统方案

针对光网络物理层安全通信问题,提出了基于低密度奇偶校验(LDPC)码的相干通信量子噪声流加密(QNSC)系统方案,将码率为9/10的LDPC码和离散傅里叶变换正交频分复用(DFT-0FDM)技术应用在系统方案中,最后对该方案进行了实验验证.实验结果表明:经过传输跨距为40 km、80 km,120 km和160 km的...     

多维码OCDMA通信系统的研究

提出了OCDMA系统中所使用的多维码的概念并对其性能进行了分析．重点介绍了光素数码、二维光正交码、二维素数码及三维码．     

Welch bound analysis on generic code division multiple access codes with interference free windows

Code-division multiple access (CDMA) technology has been applied to many wireless communication systems. CDMA system suffers from both multiple access interference (MAI) and inter-symbol interference (ISI) over a multipath channel. To suppress MAI and ISI, this paper proposes the spreading codes with interference free windows. In particular, we will develop several upper bounds on the efficiency of generalized spreading codes (for both unitary and complementary codes) in terms of the width of their interference free windows.     

基于Turbo码的无线相干光通信系统性能研究

为了提高无线光通信系统的性能,提出并分析了基于Turbo码的无线相干光通信系统。对无线光通信系统中的衰减和噪声进行了分析,并通过Matlab仿真得出了特性曲线。借助系统的误码率,通过对比基于Turbo码的BPSK调制的无线相干光通信系统与BPSK调制的无线非相干光通信系统和未编码无线光通信系统性能,得到无线相干光通信系统借助Turbo编码技术,可以提高系统的抗干扰能力,节省发射光功率,提高了系统性能。     

Performance of a quasi synchronous code division multiple access signal interfered by FM-television

This paper presents the results obtained in computer simulations and laboratory measurements of interference caused by FM-TV signals to band limited quasi synchronous code division multiple access (BLQS-CDMA) signals. Certain parameters, such as frequency spacing between wanted and interfering carriers and type of modulating TV signal (75 per cent saturated colour bar or saturated red field), were varied during the measurements and simulations, in order to study their influence on the amount of interference suffered by the BLQS-CDMA signal. Computer simulations were validated by hardware measurements, in order to have available an in-house software tool for future analyses. Protection ratio (PR) masks have been obtained and show that BLQS-CDMA is well adapted to a VSAT network operating in an FM-TV interference environment. © 1997 John Wiley & Sons, Ltd.