Construction and performance analysis of 2-D variable-length variable-weight optical orthogonal codes

In this paper, a new generation algorithm of a two-dimensional variable-length and variable-weight optical orthogonal codes (2-D VLVWOOCs) is proposed. By analysis of the BER performance for the corresponding optical code division multiple access (OCDMA) system, it is shown that the users with different codewords have significant differences in performance. Users with heavier-weight address matrices always outperform those with lighter-weight address matrices, and shorter-length and longer-length matrices support high bit-rate and low bit-rate in OCDMA applications, respectively. Therefore, heavier-weight shorter-length matrices can accommodate high bit-rate and high-quality of services (QoS) (e.g., real-time video), and lighter-weight longer-length matrices can achieve low bit-rate and low-QoS (e.g., voice). The system performance becomes worse as the users concentrate on one type of service. Especially, a surge of the number of users with shorter-length matrices has particularly impact on system performance. Thus, the 2-D VLVWOOCs can be used to provide many different types of services with different rate-levels and different levels of QoS, and simultaneously make better use of bandwidth resources in optical networks.

OCDMA系统中新型正交码的设计及性能研究

为了得到性能较为良好的正交码,采用没有重复数字的全间隔集,进行了地址码的设计和系统仿真验证,设计出的正交码具有理想的相关性和灵活的码字容量。分析整个系统,在考虑各种噪声和多址干扰的影响下,推导出正交码的误比特率公式。自行设计并搭建了采用光纤延时线作为编解码器的异步光码多分址系统。结果表明,该正交码能够适应更多用户的需求,通过误比特率公式计算和系统仿真得到的结果都较为理想,此研究对需要大容量的光码多分址系统的进一步发展具有一定的帮助。     

OCDMA在光接入网中的应用方案

文章对光接入网（OAN）中光码分多址（OCDMA）方式进行了研究分析，并进行了计算机模拟，结果表明，在OAN中引入OCDMA技术，不需网络同步，在下行方向有很好的安全性，用户和业务可随机接入，可构成灵活的通用接入网传输平台。     

A new family of three-dimensional codes for optical CDMA systems with differential detection

Two-dimensional codes for OCDMA have been shown to be more versatile compared to the one-dimensional codes for their good spectral efficiency as well as better BER performance. The two-dimensional (2-D) codes also benefit from the reduction of the wavelength/time-like property over the one-dimensional (1-D) codes. The three-dimensional (3-D) codes are important as these produce a larger code set. In this paper, we present a new family of 3-D single-pulse per plane codes for differential detection (SPDD) for OCDMA systems (based on the 1-D golomb ruler sequences), which achieve good code cardinality and a very high BER performance. The improved BER performance is obtained by using two codes to encode ‘1’ and ‘0’ bits in the encoder and differential detection in the receiver. The comparison of 3-D SPDD with some of the best reported 2-D/3-D codes, shows that the 3-D SPDD codes perform significantly better than the others. A larger number of simultaneous users is supported at 1e-9 compared to the earlier proposed 2-D/3-D orthogonal codes.     

一种二维光码分多址系统编解码的新方法

提出一种实现二维光码分多址系统编解码的方法.阐述编解码的原理和电光晶体的基本性质,用电光晶体构造编解码器的关键部件电光偏转器和电光开关,对系统的每个部分进行分析,用具体的地址码进行模拟.结果表明,该方法能有效实现二维光码分多址系统的编解码,并且方法简单、控制灵活、系统升级方便,能够在全光网络通信中发挥重要作用.

Abstract：

A new encoder-decoder scheme of 2-D OCDMA (Optical Code Division Multiple Access) system is proposed.The principles of encoding-decoding and the characteristics of electro-optic crystals are discussed.The key components,electro-optic deflector and switch,were manufactured by electro-optic crystals and each part of this system was analyzed respectively.A simulation was made with 2-D OOC (optical orthogonal code),and the results showed the effectiveness of this technique in realizing encoder-decoder.This system would play an important role in all-optical telecommunications with its simple scheme,flexible control and convenient upgrade.     

光码分多址多用户系统实验及性能分析

报道采用光码分多分址(OCDMA)技术实现了3用户通信的实验,传输速率为2.5 Gchip/s,传输距离为20 km.给出了OCDMA系统基本参数设计方法,搭建并实现了OCDMA实验,通过设计实验系统与得到的实验结果作了详细的分析,结果表明,我们成功实现了3用户传输2.5 Gchip/s的OCDMA通信实验,并验证了多用户干扰是OCDMA系统下降的主要噪声源.     

基于时域/频域OCDMA系统的一种新型二维变码重光正交码构造

构造了一种适用于光码分多址(OCDMA)系统的新型二维变码重光正交码(2D-VWOOC),用于满足不同用户及业务对服务质量(QoS)的不同要求,以两两正交拉丁方阵序列(MOLS)为波长跳频序列,以一维严格变码重光正交码(1D-SVWOOC)为扩时序列。分析了该码字在不同参数(码长、码重及波长数)下的码字性能;在相同条件下与其他二维变码重光正交码进行对比,该码字码容量较大,误码率相对其他码字低9～17个数量级。在Optisystem仿真中,当系统传输速率为16 Gbits/s时,码重为4比码重为2的用户误码率低2个数量级,能获得清晰端正的眼图。     

一种基于素数码和单重合序列的二维光正交码

以素数码(PC)作为时间扩频伪随机序列,以单重合序列(OCS)作为波长跳频伪随机序列,构造了一种新的二维光正交码(OOC)PC/OCS,并分析了码字的互相关性能.与素数跳频码PC/PC相比,PC/OCS的波长数并不局限于素数,可以是任意整数,不仅构造灵活,而且可充分利用多波长光码分多址(MW OCDMA)系统的有效波长数.当系统的有效波长数为大于某个素数的整数时,PC/OCS不仅码字容量大于PC/PC,而且互相关性能也有所改善,降低了MW OCDMA系统的误码率(BER).     

OCDMA系统中一种新的多倍长光垂直码

提出了一种新的容量大、相关性好的多倍长、多波长二维光正交码（2D MW-OOC），基于多倍长一维光正交码（1DOOC）构造了MW-OOC。对同时使用具有2种码长的MW-OOC的光码分多址（OCD-MA）系统性能分析表明，使用该MW-OOC的系统性能良好，明显好于同样码长下的多倍长1-DOOC；使用短码序列的信号误码率性能好于使用长码序列信号的误码率性能。这些特征能充分发挥OCDMA系统大容量的技术优势，满足将来大容量多媒体OcDMA网络系统对同时传输的不同信号所需传输质量不同的需求。     

双硬限幅器二维异步OCDMA系统的性能分析

在二维异步光码分多址(OCDMA)系统中,考虑光接收机存在多种噪声源干扰和用户之间存在的多址干扰(MAI),使用了具有双硬限幅器(OHL)的光接收机来优化系统传输性能.文章数值分析了阈值、用户数和入射光功率等对系统误码率的影响.结果表明:双OHL二维异步OCDMA系统的误码率相对于单OHL系统和无OHL系统明显下降,基本消除了MAI.     

OCDMA系统中二维变重光正交码的设计及性能分析

以单重合序列作为波长跳频序列,严格变重光正交码作为时间扩频序列,构造一种新的跳频/扩时二维变重光正交码。对所构造二维码的自相关和互相关性能进行了详细地分析,得出互相关均值的表达式,并对该二维地址码的多址干扰误码率进行了仿真比较和理论分析。结果表明,确定严格变重光正交码的参数和单重合序列的长度,增加波长数会增加码字容量并会降低系统的误码率;确定单重合序列的参数和严格变重光正交码的码重和码字个数,增加码长将降低系统的误码率。     

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。     

基于光码柱面的二维地址码相关性分析和码字容量研究

在谱域和时域同时编码的二维OCDMA系统是增加系统容量的主要方案.在一维光码盘和光码环的基础上,设计出直观描述二维λ-t地址码的几何装置-二维光码柱面,直观便捷地描述二维码字结构,给出基于光码柱面的二维码码字相关性分析方法.并根据光码柱面,建立了在光码集本身导出二维码码字容量的分析理论.所得结果与直接引用电通信中的Johnson界得出的结果一致.因此,二维光码柱面给二维的相关性分析和码字容量研究提供了便捷有效的工具.     

基于超连续谱的光阈值器的实验研究

光阈值器件能够抑制光码分多址(OCDMA)系统中多址干扰(MAI)噪声,增加用户数量。基于超连续谱(SC)的光阈值器件,对偏振态不敏感,而且结构简单,易于实现。为克服放大器放大倍数和高非线性光纤(HNLF)长度对SC阈值实验研究的限制,本文提出通过改变输入脉冲占空比来改变峰值功率的方法。在通信波长为1 550nm的OCDMA系统中,基于SC的阈值时,最佳阈值脉冲峰值功率为6.195W,所需带通滤波器中心波长为1 558nm,带宽为5nm。     

光正交码构造算法的研究

介绍了代数同余算法和遗传算法在光码分多址系统中的应用,研究了使用这些算法构造光正交码的特性,分析了它们的优缺点.     

Design and analysis of synchronous dynamic frequency hopping code division multiple access communication system

An optical dynamic frequency hopping code division multiple access communication system is proposed. In this system, an electrically controlled tunable optical filter (TOF) is used to encode the modulated broadband light source. The code depends on the function set to the controller. Two-dimensional code, named functional code, is also proposed based of shifted sine function. The function defines the dynamic coding pattern of the central wavelength of the transmitted narrowband optical signal. Thus, the system will allow for an easy reconfiguration of the transmitter without the need for sophisticated encoder. At the receiver, a synchronized TOF with the same function is used as a decoder. The system is modeled and analyzed taking into account the multiple access interference, phase induced intensity noise, and thermal noise. The performance of this system is shown to be better compared with a fast frequency hopping system and a spectral amplitude coding system that uses either a Hadamard code, a modified quadratic congruence code (MQC), or a modified frequency hopping code (MFH).     

OCDMA系统二维QPC地址码的设计和性能研究

通过对光纤信道波长片和时间片的重新组合,提出了一种新的适用于二维OCDMA系统的素数码(2D-QPC)的结构方案;给出了具体的码字设计步骤和过程;运用有限域理论,分析了码字的相关特性.在此基础上,根据"撞击法'研究2D-QPC应用于同步OCDMA系统时的用户容量和误码性能.结果表明:较之一维QPC,2D-QPC的相关特性有了很大的改进,最大自相关旁瓣由1降为0,最大互相关由2降为1;2D-QPC在系统容量上也有很大提高,在相同带宽,传输速率相同的情况下,比一维QPC的系统容量增加p 1倍.     

Comparison of coded orthogonal frequency division multiplexing and multicarrier code division multiple access systems for power line communications

Orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC‐CDMA) systems are comparatively evaluated for power line communications (PLC) in a frequency‐selective fading environment with additive coloured Gaussian noise which is used to model the actual in‐home power line channel. OFDM serves as a benchmark in order to measure the performance of various MC‐CDMA systems, since multicarrier modulation systems are considered the best candidate for this kind of channel. Both single‐user and multi‐user cases are taken into account, making use of the appropriate combiner schemes to take full advantage of each case. System efficiency is enhanced by the application of different coding techniques, a fact which shows that powerful coding can make the difference under such a hostile medium. The impact of block interleaving is investigated, while the simulation examines how different modulation schemes fair under the imposed channel conditions as well. The performance of the system is assessed by the commonly used bit error rate vs signal‐to‐noise ratio diagrams and there is also a comparison regarding throughput efficiency among all the tested systems. As stated in Section 4, a promising PLC application is attained. Copyright © 2004 John Wiley & Sons, Ltd.     

Performance analysis of dynamic channel allocation based on the greedy approach for orthogonal frequency‐division multiple access downlink systems

This paper presents a performance analysis of dynamic channel allocation (DCA) based on the greedy approach (GA) for orthogonal frequency‐division multiple access downlink systems over Rayleigh fading channels. The GA‐based DCA achieves its performance improvement using multiuser diversity. We analyze the statistics of the number of allocable users that represents the multiuser diversity order at each allocation process. The derived statistics are then used to analyze the performance of GA‐based DCA. The analysis results show that the number of subcarriers allocated to each user must be equal to achieve the maximum system performance based on outage probability and data throughput. Copyright © 2011 John Wiley & Sons, Ltd.     

基于光纤光栅和二维编码的OCDMA分插复用

对基于布托格光纤光栅（FBG）和二维时域／频域编码技术的光码分多址（OCDMA）系统进行深入的研究，提出了一种新型的应用二维叫时域／频域编码技术的OCDMA码分插复用器（ADM）单元。设计的ADM单元基于FBG的编解码器结构性价比高，可以简单地从网络巾取下相应码的数据同时向网络中添加本地数据。最后，把所提出的ADM单元应用于高速OCDMA系统进行模拟仿真，性能良好。