同步跳频素数码及其在OCDMA系统中的应用

从跳频素数码的构造方法出发,为同步混合直扩/跳频光码分多址(DS/FH-OCDMA)系统构造了一种新的扩频码一同步跳频素数码,并给出了构造方法和构造实例.在此基础上,运用阵列波导光栅作为编解码器设计了一种同步DS/FH-OCDMA系统的实现方案,并对该系统进行了详细的性能分析.结果表明,基于同步跳频素数码的同步Ds/FH-OCDMA系统具有用户容量大和误码率低等方面的优点.     

频域跳频/时间扩频混合光CDMA编码及其编解码器结构

本文提出了一种新的频域跳频、时间扩频混合光CDMA编码方案,并提出了其编、解码器结构.这种新的编码方案利用(L,ω,1)-光正交码（OOC）为频域跳频模式,以素数码（Prime Code）为时间扩频模式,我们称之为Prime/OOC 码.该码具有良好的自相关、互相关性能和大的容量,更为重要的是,该混合码的编、解码器可以通过多布喇格光纤光栅来实现.相对于时间扩频码分多址系统的编、解码器,这种编、解码器更简单,容易变址和集成.     

基于二次全等跳频码的跳频光码分多址系统

从跳频光码分多址(FH-OCDMA)系统的扩频特征出发,推导出具有良好相关性能的扩频码所能达到的最大码容量,再利用二次全等理论为跳频光码分多址系统构造出一种具有最大码容量的扩频码——二次全等跳频码(QCHC),并给出了构造实例。在此基础上,运用光纤布拉格光栅序列作为编解码器设计了一种跳频光码分多址系统的实现方案,并对该系统的性能进行了详细的分析。结果表明,采用二次全等跳频码的跳频光码分多址系统具有设计简单、用户容量大和误码率低等方面的优点。     

从素数码到级联素数码

研究级联素数码与素数码的关系，得出级联素数码是由素数码序列时移、频移后级联得到的构造思想，并得出具体时移规律和频移规律。这一结论对于研究素数码在其他有限扩域GF（W），n〉2上的扩展具有启发意义。此外，根据素数码时移与频移等价的性质，得出得到具有理想汉明相关特性的跳频序列组的分组规律，即同一分组中，所有序列对应的时移步长对相同，为选择具有理想汉明相关特性的跳频序列组提供了理论依据。最后列出基于上述结论的仿真模型。     

用于光码分多址系统中的跳频地址码研究

研究了光正交码,EQC码和素数码与频率相结合构成的单跳频及多跳频二维地址码,并对它们的容量与采用波分复用系统时的容量进行了比较,得到了比采用跳频地址码容量更大的结论。     

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。     

频域跳频／时间扩频混合光CDMA编码及礤编解码器结构

本文提出了一种新的频域跳频、时间扩频混合光CDMA编码方案,并提出了其编、解码器结构。这种新的编码方案利用（L,w,1)-光正交码（OOC）为频域跳频模式,以素数码（Prime Code)为时间扩频模式,我们称之为Prine/OOC码。该码具有良好的自相关、互相关性能和大的容量,更为重要的是,该混合码的编、解码器可以通过多布喇格光纤光栅来实现。相对于时间扩频码分多址系统的编、解码器、这种编、解码器更简单,容易变址和集成。     

跳频扩时混合光纤CDMA系统的研究

本文从素数码的随机特性出发,得出加入跳频图案可以改善素数码的自互相关系,引入了跳／扩时（ＦＨ／ＴＨ）混合光纤ＣＤＭＡ的概念;给出了一种可灵活变址、无需延迟线网络的编解码方案,分析了ＦＨ／ＴＨ系统的网络性能,得出跳频图案的引入可以提高分组成功解码概率,从而改善了网络特性。     

一种基于光纤布拉格光栅的新型多址干扰消除方案

在强度调制、直接探测的光码分多址(CDMA)通信系统中,为了有效克服并发用户数之间的多址干扰,提高系统的通信性能,根据组信息,针对由光正交码(OOC)和修正素数码(MPC)构成的扩时/跳频地址码MPC/OOC,提出一种基于光纤布拉格光栅(FBG)的多址干扰消除方案,并详细分析了采用这种多址干扰消除方案的光CDMA通信系统的性能。结果表明,这种基于光纤布拉格光栅的多址干扰消除方案,可以很好地消除光CDMA通信系统中的多址干扰,提高系统的用户数和误码率性能。     

布拉格光栅间距限制速率对光码分多址系统特性的影响

在全光接入技术中，光码分多址(OCDMA)以其抗干扰性强、保密性好以及用户接人灵活等优点，成为当前研究热点。光码分多址技术中的关键技术之一是地址码的编解码，一维编码方案有素数码，光正交码等，采用了波长和时间的二维编码主要有素数跳频码，二维光正交码等。采用二维编码的光码分多址可以大大增加系统用户容量，更适合于高性能、多用户、接人灵活的全光接入网。     

Performance analysis of modified prime-hop codes for OCDMA systems with multiuser detectors

This article presents the performance analysis of modified prime-hop codes (MPHCs) proposed by Wen et al. for optical code division multiple access (OCDMA) systems with multiuser detectors. MPHCs have many advantages over prime-hop codes (PHCs), including low complexity of hardware implementation, low power loss and better performance. The systems using MPHCs would benefit from these advantages under a heavy traffic load. To enhance the performances of MPHCs, the multiuser detectors are utilized to mitigate the negative effect of multiple access interference (MAI) in this study. With a combinatorial approach, the performances of the systems using MPHCs and PHCs are analyzed and compared with one another. The factors to be considered in degrading the system performance include MAI, additive optical intensity noise, and the Poisson characteristics of the optical direct detection process. The numeric results indicate that the systems using MPHCs perform much better than those using PHCs, especially with multiuser detectors.     

Higher-order dispersion mitigation for spectrum-sliced FFH-OCDMA using adaptive prime-hop codes

The fast frequency hopping optical CDMA with prime-hop codes (PHCs) provides great flexibility and increases spectral efficiency in comparison with direct sequence methods. Applying the spectrum-sliced incoherent source will further reduce the system cost. However, the dispersion in such an incoherent system becomes a limiting factor to the bit error rate. A novel adaptive PHC scheme to such systems is proposed in this article. The main impact of the scheme is to reduce the power loss and the bit error rate (BER) degradation due to higher-order dispersion. The impact of inherit beat noise in spectrum slicing systems is also alleviated. Performance comparisons between the adaptive PHC and original PHC schemes indicate that the former is more suitable for use in the considered incoherent system, accommodating up to 17% more users for a given BER. The proposed adaptive method can be universally applied to mitigate dispersion effects in the similar 2D OCDMA systems.     

光码分多址系统中双极性码的应用研究

基带双极性光码分多址(OCDMA)系统，采用码的极性转换思想，实现在考虑信道非理想下的单极性信道中传输双极性码。研究了Gold序列，m序列在系统中的应用和传输信道对光码分多址系统性能的影响。仿真得到了双极性码在光码分多址系统的自相关和互相关特性。基于不同码字的光码分多址系统用户数与误码率的关系和基于非理想传输信道的系统性能影响曲线。结果表明，Gold序列和m序列适合双极性光码分多址系统，但Gold序列较m序列更适合应用到双极性光码分多址系统，当系统激活用户数为20，系统误码率分别达到了10^-9，10^-7，非理想传输信道对系统性能有较大的影响(恶化近20dB)，在系统研究中不可忽略。     

An OCDMA Scheme to Reduce Multiple Access Interference and Enhance Performance for Optical Subscriber Access Networks

We propose a new optical code division multiple access (OCDMA) scheme for reducing multiple access interference (MAI) and enhancing performance for optical subscriber access networks using modified pseudorandom noise (PN)‐coded fiber Bragg gratings with bipolar OCDMA decoders. Through the bipolar OCDMA decoder and the modified PN codes, MAI among users is effectively depressed. As the data are encoded either by a unipolar signature sequence of the modified PN code or its complement according to whether the data bit is 1 or 0, the bit error ratio (BER) can be more improved with the same signal to interference plus noise ratio over the conventional on‐off shift keying‐based OCDMA system. We prove by numerical analysis that the BER of the proposed bipolar OCDMA system is better than the conventional unipolar OCDMA system. We also analyze the spectral power distortion effects of the broadband light source.     

波分复用OCDMA系统的性能分析

分析了波分复用(WDM)光码分多址(OCDMA)系统的归一吞吐量性能。当同时用户数均匀分配到不同的波长时,得到了WDM OCDMA系统归一化吞吐量性能的上界;当同时用户数尽量分配到同一个波长时,得到了WDM OCDMA系统归一化吞吐量性能的下界。在所有用户均匀分配到不同波长信道的条件下,比较了WDM OCDMA与多波长(MW)OCDMA系统的归一化吞吐量性能。结果表明,当负载较小时,两者的性能基本相当;当负载较大时,WDM 0CDMA的性能优于MW OCDMA系统。同时,WDM OCDMA的归一化吞吐量峰值高于MW OCDMA系统的归一化吞吐量峰值。     

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.     

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。     

Construction of two-dimensional wavelength/time optical orthogonal codes using difference family

A new family of two-dimensional (2-D) wavelength/time optical orthogonal codes (OOCs) for asynchronous optical code division multiple access (OCDMA) systems is proposed. The construction scheme uses the difference family (DF), which is an assemblage of difference sets in the combinatorial theory. It is proven that the proposed codewords satisfy the correlation properties required for the asynchronous OCDMA systems. The code dimension of the proposed codes is more flexible than that of the conventional 2-D codewords. The performance of the system with the proposed codes is analyzed by using the Markov-chain method. Numerical results show that the bit error rate (BER) has a minimal value given the number of simultaneous users. It is also observed that the maximum number of simultaneous users of the system can be achieved by properly choosing both the code weight and cross correlation of the 2-D OOCs.