用遗传算法构造光正交码

提出了一种利用遗传算法构造任意码长、码重、自相关限、互相关限光正交码(GA-OOC)的方法,设计了新的码字矩阵;分析了基于GA-OOC的光CDMA系统的误码率性能。仿真结果表明:该算法具有构造算法简单、易于编程实现的特点;与基于PC,EPC,QC和BIBD-OOC的光码分多址系统相比,GA-OOC的光码分多址系统具有更好的误码率性能。GA-OOC有望用于构造二维光地址码。     

基于最大值判决及光硬限幅器的光码分多址并行干扰抑制系统

针对光码分多址（OCDMA）的多用户干扰问题,提出一种引入光硬限幅器、基于最大值判决的光码分多址并行干扰抑制系统.该系统在发送端对比特“0”和比特“1”分别使用一个地址码和它的移位变形进行映射,以避免发送比特“0”时无光脉冲通过的问题,实现并行干扰抑制;在接收端光电检测器前引入一个光硬限幅器,判决电路采用最大值判决,以避免门限判决所引起的误判,进一步减小多用户干扰.阐述了其工作原理,系统采用光正交码作为地址码,PIN光电检测器,分析推导了系统的误码率表达式,进而对新型系统的多用户干扰抑制作用进行误码性能仿真.仿真结果表明,当信号光子到达率为25时,新型系统比常规系统的误码性能改善10个数量级以上,比常规并行干扰抑制系统改善2个数量级以上.     

光谱幅度编码OCDMA系统研究

针对单极性码在光码分多址系统应用中存在正交性和用户容纳能力较差的缺点，对采用双极性地址码的光谱幅度编码系统中接收端采用差分检测的方案进行了研究。讨论了用于差分频谱幅度编码方案中的地址码应满足的条件，对OOK和双极性编码系统方案，在考虑散弹噪声和热噪声的条件下，分析了误码率性能。通过数值计算，比较了“1”和“0”都发信号的系统和只有“1”发信号的系统性能。比较结果表明，双极性地址码方案可提高系统性能；另外，提高光功率还可改善系统性能。     

适用于同步光码分多址通信系统的同步光码及其全光可调编/解码器

异步光码分多址通信系统,要求用户地址码具有好的循环自相关和互相关特性,因此,系统中的用户数受到很大的限制;而对同步光码分多址通信系统,只要求光地址码是非循环相关意义下的准正交,从而可实现较大的用户数,因此具有广阔的应用前景.实现同步光码分多址的关键之一是同步光码的设计和可调光编/解码器的实现.本文介绍了同步光码的构造方法,给出了同步光码的构造过程,分析了码的容量,提出了全光可调同步光码编/解码器的实现方法.     

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。     

基于最大似然准则的多波长OCDMA接收机的最佳判决门限研究

采用最大似然准则,研究了多波长光码分多址接收机的最佳判决门限值.通过检测信道的光信号能量,接收端估计出信道的并发用户数,并通过最大似然准则得到了最佳判决门限值与并发用户数、码字参量的变化关系.当并发用户数超过一定值后,最佳判决门限值将随并发用户数量变化,相应地改变接收机的判决门限值.根据最佳判决门限值,得到了多波长光码分多址系统误码率与并发用户数的关系.理论分析和模拟结果表明,采用最大似然准则得到的最佳判决门限值,MW OCDMA系统的误码率将明显降低.     

多噪声背景下光码分多址多用户干扰的抑制

针对光码分多址(OCDMA)的多用户干扰问题, 研究采用APD光电检测器的系统中存在多种噪声情况下, 基于最大值判决的光码分多址并行干扰抑制方法的多用户干扰抑制效果。阐述了其工作原理, 即在发送端对比特“0”和比特“1”分别使用一个地址码和它的移位变形进行映射, 以避免发送比特“0”时无光脉冲通过, 实现并行干扰抑制; 接收端判决电路采用最大值判决, 以避免门限判决所引起的误判, 进一步减小多用户干扰。系统采用光正交码作为地址码, 分析推导了系统的误码率表达式。根据所得的误码率表达式, 进行了数值仿真并与其他多用户干扰抑制方法进行比较。仿真结果表明, 本方法对多用户干扰的抑制作用与系统用户数和码重有关; 与引入双硬限幅器方法、多比特传输方法的多用户干扰抑制作用相比, 抑制效果要优于多比特传输的方法; 当接收功率较低时, 该方法优于引入双硬限幅器的方法, 因此可以有效的抑制多用户干扰。     

多噪音背景下引入光硬限幅器及并行干扰抑制器的光码分多址系统

为了抑制光码分多址中的多址干扰及多噪音,提出了一种引入光硬限幅器及基于最大值判决的并行干扰抑制器的光码分多址系统.在系统中存在APD噪音及热噪音的情况下,研究了系统对多址干扰的抑制作用.系统采用光正交码作为地址码,APD作为光电检测器,分析推导了系统的误码率表达式.根据所得的误码率表达式,进行了数值仿真,比较了该方法与其他方法的多址干扰抑制效果.研究结果表明:与现有其他有效方法(单比特引入一个光硬限幅器、单比特引入两个光硬限幅器、多比特传输、多比特引入光硬限幅器、基于最大值判决的并行干扰抑制器等)相比,本系统对多址干扰的抑制作用优于并行干扰抑制器、多比特传输、多比特引入光硬限幅器方法;当接收功率较低时,该系统优于引入双光硬限幅器的方法,因此可以有效的抑制多址干扰及多噪音.     

OCDMA系统中2-D码和3-D码

光码分多址(OCDMA)技术主要应用在接入网中。设计大容量的地址码是该技术实用化的前提。本文在构造2 D素数码的基础上提出了一种用于OCDMA系统的空域/频域/时域3 D地址码。这种码基于素数序列运算。理论分析和数学计算结果表明，3 D码比2 D码的容量更大，系统带宽效率更高，误码率(BER)更低，表现出的性能更好。     

多噪音背景下引入光硬限幅器及并行干扰抑制器的光码分多址系统

为了抑制光码分多址中的多址干扰及多噪音,提出了一种引入光硬限幅器及基于最大值判决的并行干扰抑制器的光码分多址系统.在系统中存在APD噪音及热噪音的情况下,研究了系统对多址干扰的抑制作用.系统采用光正交码作为地址码,APD作为光电检测器,分析推导了系统的误码率表达式.根据所得的误码率表达式,进行了数值仿真,比较了该方法与其他方法的多址干扰抑制效果.研究结果表明:与现有其他有效方法(单比特引入一个光硬限幅器、单比特引入两个光硬限幅器、多比特传输、多比特引入光硬限幅器、基于最大值判决的并行干扰抑制器等)相比,本系统对多址干扰的抑制作用优于并行干扰抑制器、多比特传输、多比特引入光硬限幅器方法|当接收功率较低时,该系统优于引入双光硬限幅器的方法,因此可以有效的抑制多址干扰及多噪音.     

Multiple access interference cancellation in Manchester-coded synchronous optical PPM-CDMA network

A new interference cancellation technique for direct-detection optical code- division multiple-access (OCDMA) network employing pulse-position modulation (PPM) is proposed in this paper. The multiple access interference (MAI) estimation is achieved by pre-reserving one of optical spreading code sequences at the receiver based on the correlation property of padded modified prime codes (PMPC). The estimated interference is then cancelled out after photo-detection process. Additionally, the transmitted signal is Manchester-coded to further improve the system performance. Based on this proposed interference canceller in a shot-noise limited regime, we have obtained an expression for the upper bound of the bit-error probability (BEP) taking into account effects of both MAI and shot-noise. This BEP is compared with that of a PPM-OCDMA without cancellation. Finally, the receiver structure of the proposed optical network unit (ONU) is fairly simple to compare with the conventional cancellation schemes.     

Design and performance analysis of various one dimensional codes using different data formats for OCDMA system

In this paper, the design, implementation and performance analysis of various one dimensional codes in an OCDMA system for different data formats is presented. A number of different codes are used with optical CDMA to improve its error performance. Here, three such codes, optical orthogonal codes (OOC), Walsh Hadamard codes and zero cross-correlation (ZCC) codes have been compared using different data formats, NRZ raised cosine, NRZ rectangular, RZ raised cosine and RZ rectangular. It is found that NRZ raised cosine has the best system performance for all the codes used. After that, the three codes have been compared in terms of the BER, eye diagrams and received optical power using NRZ raised cosine modulation format. It is analyzed that ZCC codes have zero cross-correlation property. The simulation results revealed that ZCC codes can provide a better BER compared to the OOC and Walsh Hadamard codes and it is most suitable to be employed in the OCDMA systems.     

一种新的大容量的二维光正交码

构造了一种扩展的双曲线性同余码(EHLC)并分析了其码字性能.用该码作为时间扩频伪随机序列和以素数码(PC)作为波长跳频伪随机序列,再构成一种新的二维光正交码EHLC/PC.然后分析了EHLC/PC码字的性能,并与EQC/PC作了比较.相比之下,前者的互相关性能略有下降,但码字容量大大增加.因此,EHLC/PC适合于用户数较多的OCDMA系统.     

A novel 2D-OCDMA system with dynamic optimum decision threshold by estimating the number of active users

A novel two dimensional optical code division multiple access (2D-OCDMA) system with dynamic optimum decision threshold by estimating the number of active users is proposed. The bit-error rates (BER) of the system is analyzed. By using one wavelength as the estimator of the number of active users, which is not assigned to any address code, the number of active users can be obtained. The dynamic optimum decision threshold can be obtained according to the multiple user interference (MUI), which can be obtained by cross-correlation characteristics between address codes and the number of active users.     

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.     

Novel family of prime codes for synchronous optical CDMA

In this paper we have proposed a novel prime spreading sequence family hereby referred to as “new-Modified Prime Code (n-MPC)” for direct-detection synchronous optical code-division multiple-access (OCDMA) networks. The new code has been applied to Overlapping Pulse-Position Modulation (OPPM) CDMA system and the performance of system is evaluated. In addition, we have analyzed the system throughput and also introduced a new interference cancellation technique which significantly improves the bit error probability (BEP) of OPPM-OCDMA systems.