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。     

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.     

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.     

光码分多址系统中光学相关接收机判决阈值的分析

介绍了光码分多址系统中常用地址码（一维扩时码、二维码和三维码）的特点，并对它们各自的互相关均值和方差进行了理论分析。基于非相干光码分多址系统中光学相关接收机的基本原理，结合不同的用户地址码，对系统误码率性能进行了分析，得到了接收机最佳判决阈值与地址码基本特性参数和系统同时用户数间的关系。最后，给出了数值仿真结果。结果表明，对于采用特定地址码的光码分多址系统，只有选择合适的接收机判决阈值，系统的误码率性能才能达到最佳。研究结果对光码分多址系统中接收机判决阈值的选取具有一定的参考作用。     

A New Algorithm for Development of Dynamic Cyclic Shift Code for Spectral Amplitude Coding Optical Code Division Multiple Access Systems

Abstract

This article presents a new code—the dynamic cyclic shift code—for spectral amplitude coding–optical code division multiple access systems. One of the important properties of the dynamic cyclic shift code is that the number of users can be increased without increasing the weight value. System performance was evaluated by using both theoretical analysis as well as the simulation experiment. The analysis results show that the proposed dynamic cyclic shift code can support more users in spectral amplitude coding–optical code division multiple access systems compared to spectral amplitude coding–optical code division multiple access codes. It was ascertained by performance evaluation that the dynamic cyclic shift code possesses ideal properties for use in spectral amplitude coding–optical code division multiple access systems.     

Performance improvement of spectral amplitude coding-optical code division multiple access systems using NAND detection with enhanced double weight code

The bit-error rate (BER) performance of the spectral amplitude coding-optical code division multiple access (SACOCDMA) system has been investigated by using NAND subtraction detection technique with enhanced double weight (EDW) code. The EDW code is the enhanced version of double weight (DW) code family where the code weight is any odd number and greater than one with ideal cross-correlation. In order to evaluate the performance of the system, we used mathematical analysis extensively along with the simulation experiment. The evaluation results obtained using the NAND subtraction detection technique was compared with those obtained using the complementary detection technique for the same number of active users. The comparison results revealed that the BER performance of the system using NAND subtraction detection technique has greatly been improved as compared to the complementary technique.     

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.     

Design and implementation of 2-dimensional wavelength/time codes for OCDMA

In this paper, two-dimensional (2D) wavelength/time codes are designed and implemented. The 2D codes are constructed by a technique based on folding of Golomb rulers. The performance evaluation of OCDMA system based on wavelength/time code has been analyzed by measuring the values of bit error rates and eye diagrams for different number of active users. It is shown that eye opening decreases and BER increases with increase in number of active users. It is also shown that BER further increases with increase in number of active users when number of decoders increases on receiver side. Hence, it is concluded that multiple access interference (MAI) is the dominant source of BER and there is graceful degradation in system performance when number of simultaneously active users increases. The received optical power is also measured at different transmission distance. It has been observed that received optical power decreases with increase in length of fiber due to attenuation.     

An efficient MAI cancellation technique in Optical CDMA

Optical code division multiple access (OCDMA) is a promising operational system for future backhaul optical networks especially for switching and optical signal multiplexing. However, OCDMA operation is restricted by multiple access interference (MAI) due to the asynchronous nature of transmission. In this study, we discuss an efficient MAI technique for OCDMA systems that depends not only on using hybrid frequency shift keying (FSK) modulation but also on employing the double padded modified prime code (DPMPC) as a signature sequence. MAI cancellation is performed by subtracting a reference signal from the received signal of the desired user. The simulation results show that the performance of the FSK-OCDMA technique is superior to the performance of the PPM-OCDMA technique. Furthermore, the obtained results illustrate that the FSK-OCDMA technique is able to accommodate a large number of simultaneous active users with low error-rate.     

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.     

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.     

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。     

Improvement of the bit error rate of a non-coherent OCDMA system for FTTH network applications

In this paper, an optical code division multiple access (OCDMA) system was analysed to improve the bit error rate (BER) performance at 10 Gbps. The improvements to this system were based on a modified double weight code and a NAND subtraction technique and aimed to support the large number of active users in the fibre-to-the-home network. The system performance was investigated through extensive theoretical and numerical simulation analyses. The theoretical and simulation results revealed that the new detection technique exhibits improved BER performance compared to conventional techniques, such as complimentary subtraction techniques. The system performance was characterised by the signal-to-noise ratio, the bit error rate (BER), and various transmit powers ( $P_{sr} - 10$  dBm). The results show that the proposed system, which is based on a new detection technique, can achieve the optimal BER with a high number of users and maintains the error floor transmission rate $(\le 10^{-9})$ .     

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.     

Improvement of physical-layer security and reliability in coherent time-spreading OCDMA wiretap channel

Optical code division multiple access (OCDMA) can enhance the physical-layer security performance of optical fiber communication systems. In asynchronous coherent time-spreading OCDMA employing m sequence and Gold code, the reliability, capacity and physical-layer security of the system will degrade due to multiple access interference and beat noise. In order to enhance the physical-layer security and reliability of coherent OCDMA systems, a quasi-synchronous coherent time-spreading OCDMA wiretap channel is proposed in this paper. The influences of the extraction location, the extraction ratio, the number of active users on the physical-layer security are analyzed quantitatively. System performances are characterized by bit error rate, secrecy capacity as well as security leakage factor. The numerical results prove that the proposed scheme can improve the physical-layer security and reliability simultaneously.     

A divided spectrum balanced detection technique for intensity noise reduction in SAC OCDMA systems

In this paper we propose a simple divided spectrum balanced detection (DSBD) for spectral amplitude coding (SAC) optical code division multiple access (OCDMA) systems. SAC OCDMA systems are limited by phase induced intensity noise (PIIN), which is a signal dependent source of noise. Our proposed technique reduces the PIIN by dividing the spectrum of the signal into two or more, and detecting each spectrum by a different photodiode. The DSBD scheme reduces the detected optical power at photodetection, thus resulting in a higher mitigation of the PIIN. Theoretical results show that DSBD demonstrate noticeable improvement over traditional balanced detection technique, for example an up to 33% increase in the number of active users can be achieved, and at least 1 × 10⁻³ b/s Hz increase in the spectral efficiency is obtained. However, the SDBD is more complex and append more constrains on system components.     

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 .     

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.     

A new family of two-dimensional triple-codeweight asymmetric optical orthogonal code for OCDMA networks

A new generation algorithm of two-dimensional triple-codeweight asymmetric optical orthogonal codes for optical code division multiple access （OCDMA） networks is proposed. The code cardinality is obtained and the error-probability performance for corresponding OCDMA system is analyzed. The codes with two constraints （i.e., auto- and cross-correlation properties） being unequal are taken into account. On the premise of fixed system resources, the code of the error-probability performance, it is shown cardinality can be significantly improved. By analysis that the codes with different parameters have different performances. Therefore, this type of codes can be applied to support diverse quality of service （QoS） and satisfy the quality requirement of different multimedia or distinct users, and simultaneously make the better use of bandwidth resources in oDtical networks.