光码分多址系统中Gold序列标签的研究

研究了基于Gold序列的地址码的生成,对其相关性、频谱效率进行分析,并且与光正交码、素数码的性能进行比较。分析结果表明：Gold序列是一种自相关和互相关性能比较好的码字,并且具有较大的码字容量,在相同参数下具有较小的误码率,较大的码字容量和较大的频谱效率,是OCDMA（光码分多址）系统地址码较好的选择。     

一种新的光CDMA编码方案

本文以光正交码（OOC）为基础,提出了一种新的光CDMA编码方案。这种新的方案充分利用了已有的成熟的OOC编码技术,可以灵活方便地构造出光正交跳频以及光正交时间/频率组合码。这种新的地址码具有良好的自相关、互相关性能、较大的容量和良好的系统性能,还可以灵活地和现有的光天源器件相匹配。     

时域相位OCDMA码序列的优化

研究时域相位光码分多址的地址码优化技术。为获取自相关和互相关性能好的码字,对双极性码进行优化,给出了双极性码的优化方案,以及优化结果,为时域相位OCDMA系统提供了优化的地址码序列。     

二维同步OCDMA光编码器设计与研究

文章以"同步修正素数码"为基础,利用互相垂直的两组线偏振光构造了适用于同步光码分多址(OCDMA)系统的二维光正交地址码.通过分析码字的自相关和互相关特性,确定了其选码原则.在此基础上,设计了适用于同步OCDMA系统的二维光编码器.仿真结果表明,与一维同步OCDMA系统相比,二维同步光正交地址码具有更优良的接收性能,并解决了器件在实际使用过程中可能出现的功率非线性叠加问题.     

二维光码分多址的地址码及干扰估计接收机

阐述了自相关旁瓣为0，互相关值小于等于1的二维光正交码(2D-OOC)的新构造方法及非同步频域跳频时域扩频二维光码分多址(2D-OCDMA)系统中的干扰估计接收机模型。二维光正交码的新构造方法以两个单极性码分别作为频域跳频模式和时域扩频模式。用作频域跳频模式的地址码是自相关旁瓣及互相关值小于等于1的一维光正交码(1D-OOC)，用作时域扩频模式的地址码其码长为素数或码长与码中任意两个非零码元的位置差值互质。将一个没有分配给任何用户并且和接收用户地址码正交的地址码用作干扰估计码来得到多用户干扰(MUI)估计值，从而得到最佳的判决门限。系统误码率(BER)的分析显示干扰估计接收机系统的性能要优于传统的接收机系统。     

MPC/OOC二维地址码的构造及性能分析

基于光正交跳频码构造原理,用改进素数码作为时域扩频模式,光正交码为频域跳频模式,构造了适用于光码分多址(OCDMA)系统的MPC／OOC二维地址码。和现有二维地址码相比,该MPC／OOC二维组合码容量更大,通过有规律地分组,每组内码字具有良好的自相关和互相关性能,同时每组内具有较大的码容量。     

地址码互相关特性对光码分多址系统性能的影响研究

基于Wyner窃听信道模型,建立了光码分多址系 统(OCDMA)的窃听信道模型,并利用“信道容量”和“安全泄露因子”作为指标来定量地 评估系统的传输性能和安全性。基于此 ,本文分析了地址码的互相关特性对OCDMA系统性能的影响。结果表明:地址码的互相关特 性对OCDMA系统性能有着重要的影响,采用互相关性更好的地址码能够提高系统的传输性能 和安全性;增加 地址码的码字长度以及使用二维地址码或者双极性地址码都有利于改善系统的传输性能和安全性。     

OCDMA中光地址码的资源利用性能

光地址码直接影响到光码分多址网络的整体性能。在简单介绍几种典型 的单、多维光地址码的基础上,从基于码集大小和系统同时通信用户数的两个不同的系统业务特性出发,分析、比较了它们的资源利用性能,探讨了单、多维光地址码在系统升级中的应用。     

SAC OCDMA系统FOC地址码设计及性能研究

设计了一种新的适合同步光谱幅度编码光码分变址(Spectral-amplitude coding optical code division multiple access,SAC OCDMA)系统的地址码,能够使多址干扰产生的误码率为0.且该地址码的互相关限为1,在给定码重和用户数的情况下能够得到较小码长,便于系统的编解码。利用OptiSys 7.0设计出仿真系统,分析比较用波分复用器和光纤光栅作为编解码器适用的不同系统,在考虑散弹噪声、相位引起的强度噪声(PIIN)和热噪声的情况下,根据该地址码的特点分析整个编解码系统的信噪比和误码率,并与现有的SAC地址码性能进行比较.结果表明:选用该地址码的SAC OCDMA系统得到的眼图更为理想,在系统误码率、编解码实现,及系统性能上都有了很大的提高。     

用改进的模拟退火算法构造光正交码

提出了一种利用模拟退火算法构造任意码长、任意码重(n,w,1)光正交码(SA-OOC)的方法.此方法由三个步骤组成:根据自相关特性筛选可能的码字;去除重复的码字;利用模拟退火算法根据互相关特性组合出一个符合条件的码组.仿真结果表明:该算法具有简单、易于实现的特点;与使用素数码(PC)、扩展的素数码(EPC)、二次同余码(QC)的系统相比,以SA-OOC作为地址码的系统具有更好的误码率特性.SA-OOC有望用于二维光地址码的构造.     

Comparison of novel coding techniques for a fixed wavelength hopping SAC-OCDMA

The optical code division multiple access (OCDMA), the most advanced multiple access technology in optical communication has become significant and gaining popularity because of its asynchronous access capability, faster speed, efficiency, security and unlimited bandwidth. Many codes are developed in spectral amplitude coding optical code division multiple access (SAC-OCDMA) with zero or minimum cross-correlation properties to reduce the multiple access interference (MAI) and Phase Induced Intensity Noise (PIIN). This paper compares two novel SAC-OCDMA codes in terms of their performances such as bit error rate (BER), number of active users that is accommodated with minimum cross-correlation property, high data rate that is achievable and the minimum power that the OCDMA system supports to achieve a minimum BER value. One of the proposed novel codes referred in this work as modified random diagonal code (MRDC) possesses cross-correlation between zero to one and the second novel code referred in this work as modified new zero cross-correlation code (MNZCC) possesses cross-correlation zero to further minimize the multiple access interference, which are found to be more scalable compared to the other existing SAC-OCDMA codes. In this work, the proposed MRDC and MNZCC codes are implemented in an optical system using the optisystem version-12 software for the SAC-OCDMA scheme. Simulation results depict that the OCDMA system based on the proposed novel MNZCC code exhibits better performance compared to the MRDC code and former existing SAC-OCDMA codes. The proposed MNZCC code accommodates maximum number of simultaneous users with higher data rate transmission, lower BER and longer traveling distance without any signal quality degradation as compared to the former existing SAC-OCDMA codes.     

Optical orthogonal codes with nonideal cross correlation

For optical code division multiple access (OCDMA) networks, many optical orthogonal codes (OOCs) with ideal auto- and cross-correlation properties had been studied widely. In this paper, we relax the cross-correlation constraint slightly and propose a new code family based on perfect difference codes. Given the same code weight and code length, the size of new codes may increase 10 times more than that of ideal OOCs. Although the maximum cross correlation of new codes is larger than one, the cross correlation is less than or equal to one, for the most part. Consequently, the performance of new codes approaches that of ideal OOCs. Numerical results show that the performance of proposed codes was almost the same as that of conventional OOCs under the same code length and code weight     

Unipolar codes with ideal in-phase cross-correlation for spectral amplitude-coding optical CDMA systems

Unipolar codes with ideal in phase cross-correlation are important in spectral amplitude-coding optical code-division multiple-access (CDMA) systems since these codes eliminate multiuser interference and also suppress the effect of phase-induced intensity noise. However, very little research work has been done on such codes although codes with ideal cross-correlation have been studied for many years. In the paper by Zhou et al.(see Electron. Lett., vol.36, p.728-29, 2000), such a code has been introduced without a clear construction method. In this paper, we firstly review this old code, and then construct two new codes with ideal in-phase cross-correlation in algebraic ways. Both of the proposed new codes are obtained by modifying former codes with ideal cross-correlation. It has been shown that the system performance can be improved significantly by using codes with ideal in-phase cross-correlation instead of the Hadamard code. These codes can also be used in synchronous optical CDMA systems for multiuser interference cancellation.     

A New Family of 2-D Codes for Fiber-Optic CDMA Systems With and Without the Chip-Synchronous Assumption

In this paper, we propose a new family of wavelength-time codes, which are based on one-dimensional optical orthogonal codes (1-D OOCs) of cross-correlation functions of at most two. By relaxing the maximum cross-correlation values to two, the new 2-D codes provide larger code cardinality for accommodating more subscribers and support heavier code weight for better code performance. It is known that the traditional chip-synchronous assumption used in the analyses of optical codes gives a pessimistic performance upper bound, while the newer chip-asynchronous assumption offers a more accurate analysis. The performance of the new 2-D codes is here analyzed under both assumptions for comparison. Under certain conditions, our results show that the new wavelength-time codes outperform our recently reported multiple-wavelength OOCs and 2-D codes, which were based on 1-D OOCs of cross-correlation functions of at most one and two, respectively.      

Design and analysis of three-dimensional OCDMA code families

A new code design algorithm for application in three-dimensional (3D) optical code division multiple access (OCDMA) for asynchronous optical fiber communication is proposed. 3D refers to space-wavelength-time codes. The performance analysis of the proposed algorithm in 3D multiple pulses per plane (MPP) codes is shown. This design ensures a maximum cross-correlation of ‘1’ between any two codes. The performance metrics that have been investigated are the bit error rate due to multiple access interference (MAI) for different values of the number of simultaneous users and, cardinality for different values of temporal length.     

Punctured PN codes

It is shown that the maximum absolute value of cross-correlation between two pseudorandom noise (PN) sequences can be reduced by deleting those dimensions of the code that contribute to high correlations. The cross-correlation of optimum punctured PN codes to length 1023 is numerically computed.     

Construction and performance analysis of variable weight zero cross correlation Latin square code for spectral amplitude coding OCDMA systems

The selection of appropriate codes for an optical code division multiple access (OCDMA) network, which determines the maximum number of users and bit error rate (BER) supported by the system, is crucial. This study proposed a variable weight zero cross-correlation Latin square (VW-ZLS) code for spectral amplitude coding (SAC)-OCDMA systems, which offers high autocorrelation and zero cross-correlation, while providing differentiated quality of service (QoS) features. Using direct detection (DD) technology, the data rate of the proposed VW-ZLS code reached 4.8 Gbit/s under the condition that BER does not exceed 10-9. This was 0.5 Gbit/s higher than that of zero cross-correlation magic square variable weight optical orthogonal code (ZMS-VWOOC) with the same cross-correlation characteristics. Further, simulation results showed that in SAC-OCDMA system, the VW-ZLS code was better than ZMS-VWOOC and exhibited excellent performance.     

异步OCDMA系统地址码相关值分布算法的研究

在码集中任意取两个不同码字,从其码字之间的“1”的位置之差的移位下必发生“1”的碰撞出发,给出了一维地址码互相关值分布的算法,并用此方法分析了几种典型一维码的相关值分布,且在此基础上验证了文中前面部分关于用概率分析法给出的求平均互相关值的式子,在一维地址码分析的基础上给出了对称二维码的互相关值分布的算法。     

混沌二相码的性能分析

混沌二相码由于其抗干扰能力和低截获性能,适宜作为雷达信号。Logistic序列是常见的用于产生二相码的混沌序列,其自相关函数旁瓣较低,但是带内功率谱波动较大、互相关函数峰值较高。针对这一问题,选取混沌特性较好的四种混沌序列产生二相码,从多个方面进行分析比较。仿真结果表明,利用Chebyshev映射得到的混沌调相信号在保持自相关函数旁瓣较低的条件下,可以获得更平坦的带内功率谱和更好的互相关性能。     

Multiple-wavelength optical orthogonal codes under prime-sequence permutations for optical CDMA

A new family of two-dimensional (2-D) wavelength-hopping time-spreading codes, which employs wavelength hopping algebraically under prime-sequence permutations on top of time-spreading optical orthogonal codes, is studied and analyzed. Different from other 2-D codes, our new codes allow the number of wavelengths and code length to be chosen independently and, at the same time, the code cardinality is a quadratic function of the number of wavelengths without sacrificing the maximum cross-correlation value (i.e., still at most one). They are particularly suitable for high bit-rate optical code-division multiple-access systems with broadband mode-locked lasers, in which the number of time slots is very limited, and system capacity can only be grown by increasing the number of wavelengths, rather than code length. Finally, a novel wavelength-aware detector for wavelength-hopping time-spreading codes is discussed and shown to provide improved code performance.