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。     

基于非线性光纤环镜的OCDMA全光码字转换方法

提出了一种利用非线性光纤环镜(NOLND实现二维全光码字转换方法,设计了基于NOLM的码字转换方案,并进行了系统性能仿真分析.研究结果表明:该方法能够成功实现系统的数据传输;采用这种码字转换方法,系统误码率性能远远高于没有进行码字转换的系统性能.     

Random assignment/transmitter-oriented code scheme for centralizedDS/SSMA packet radio networks

We address an issue of channel sharing among users by using a random assignment/transmitter-oriented (RA/T) code scheme which permits the contention mode only in the transmission of a header while avoiding collision during the data packet transmission. Once the header is successfully received, the data packet is ready for reception by switching to one of the programmable matched-filters. But the reception may be blocked due to a limited number of matched-filters so that this effect is taken into account in our analysis. We also consider an acknowledgment scheme to notify whether the header is correctly detected and the data packet can be processed continuously, which aims at reducing the interference caused by unwanted data transmission. For a realistic analysis, we integrate the detection performance at the physical level with the channel activity at the link level through a Markov chain model. It is shown that compared to classical code-division multiple-access (CDMA) systems, a reduction in the receiver complexity of a half is allowed by choosing a proper number of RA/T codes without losing the performance quality in view of the normalized throughput     

Random access protocols for high-speed interprocessor communicationbased on an optical passive star topology

A multiple-instruction multiple-data (MIMD) distributed memory parallel computer system environment is considered. Media access control protocols that maintain good performance with high capacity optical channels are investigated. Three examples of star-coupled structures are introduced, one of which exhibits optical self-routing. Self-routing single-step optically interconnected communication structures can be designed through the incorporation of agile laser diode sources and wavelength tunable optical filters in a wavelength-division multiple-access environment. Intermediary latencies typical of MIMD distributed memory systems are eliminated. The degree and diameter of the resulting structures are dramatically reduced, and the complexity of the communication subsystem is reduced since intermediate buffering and routing of packets are eliminated     

Performance analysis of a new random access protocol for OCDMA networks

A New random access protocol for OC-DMA networks is proposed in this paper. Employing a new mathematical model, namely the processor-sharing system, steady-state throughput ratio and average delay of OCDMA networks are calculated. The results reveal that our protocol outperforms other existing protocols. Meanwhile, we investigate the performance of OCDMA networks by altering the code parameters, i.e., length and weight, and the maximum number of active users in the system, corresponding results are indeed consistent with the practical situation. In addition, the analysis is simplified compared with the conventional Markov chain model. Thus the processor-sharing system is truly applicable to model OCDMA networks. Supported by National Natural Science Foundation of China (NSFC), No. 60472035.     

多维地址码对OCDMA系统性能的影响

讨论了一维/二维二次素数码、光正交码的构造过程、相关性、容量等特性,分析了它们对光码分多址(OCDMA)系统误码性能和用户容量的影响.为得到不同码字与不同维数码字对OCDMA系统的误码率影响程度,仿真比较了一维、二维二次素数码和一维、二维光正交码之间的误码率与同步用户数的关系以及二维素数码与二维光正交码的误码率与同步用...     

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.     

Construction and performance research on variable-length codes for multirate OCDMA multimedia networks

A new kind of variable-length codes with good correlation properties for the multirate asynchronous optical code divi- sion multiple access （OCDMA） multimedia networks is proposed, called non-repetition interval （NRI） codes. The NRI codes can be constructed by structuring the interval-sets with no repetition, and the code length depends on the number of users and the code weight. According to the structural characteristics of NRI codes, the formula of bit error rate （BER） is derived. Compared with other variable-length codes, the NRI codes have lower BER. A multirate OCDMA multimedia simulation system is designed and built, the longer codes are assigned to the users who need slow speed, while the shorter codes are assigned to the users who need high speed. It can be obtained by analyzing the eye diagram that the user with slower speed has lower BER, and the conclusion is the same as the actual demand in multimedia data transport.     

On the performance of an indicator-based stall avoidance mechanism for high-speed downlink packet access systems

The stall of delivering medium access control (MAC) layer data to the upper layer is a serious problem when a negative acknowledgement (NACK) control signal becomes an acknowledgement (ACK) signal, especially for a high-speed mobile terminal during handoff. Stall avoidance mechanisms aim to reduce such the transmission delay and keep in-sequence delivery of the MAC layer data to the upper layer. Recently, for providing high-speed downlink packet access (HSDPA) in the wideband code-division multiple access system, an indicator-based stall avoidance (ISA) mechanism was proposed to remove the nonrecoverable gap in the received out-of-sequence packets. In this paper, we derive the closed-form expression for the gap-processing time of the ISA mechanism when applying the multiprocess stop-and-wait (SAW) hybrid automatic repeat request (HARQ) mechanism. The derived analytical formulas can be used to understand performance tradeoffs between the gap-processing time and throughput in terms of various numbers of users and parallel processes when implementing the multiprocess SAW HARQ mechanism in the HSDPA system.     

A new family of space/wavelength/time spread three-dimensionaloptical code for OCDMA networks

A new family of space/wavelength/time spread three-dimensional (3-D) optical codes for optical code-division multiple-access (OCDMA) networks has been proposed. Two types of 3-D codes have been constructed: 3-D codes with single pulse per plane and 3-D codes with multiple pulses per plane. Both codes are based on the prime sequence algorithm and have shown improved performance compared to the previously proposed two-dimensional (2-D) prime code. Effective implementation of the 3-D code has also been proposed. In order to eliminate the requirement of fiber ribbons and multiple star couplers in space/wavelength/time spread 3-D code based optical networks, a wavelength²/time scheme has been suggested, in which the periodic property of an arrayed waveguide grating (AWG) is used. It has been shown that the system performance can be maximized for given resources with a proper choice of the wavelength²/time scheme. Due to the improved performance of the 3-D code and the effective architecture of the wavelength²/time scheme, the feasibility of the OCDMA network is much enhanced     

基于光纤布拉格步进啁啾光栅的OCDMA频域编/解码器的探索

依据频域编码的理论,分析和论证了基于光纤布拉格步进啁啾光纤光栅的 OCDMA 频域编/解码器的原理。通过对地址码做一映射变换,在步进啁啾光纤光栅上以相移的方式嵌入相应的多址码,实现了基于步进啁啾光纤光栅的光码分复用频域相位编/解码;文章给出了编/解码器的等效模型;对该编/解码器的仿真结果得到了很好的相关输出,证明了这种编/解码方法的可行性;并对影响基于此编解码器系统性能的参数进行了分析。     

MaxDiv: an optimal randomized spectrum access with maximum diversity scheme for cognitive radio networks

Cognitive radio network (CRN) is an emerging technology that can increase the utilization of spectrum underutilized by primary users (PUs). In the literature, most exiting investigations on CRNs have focused on how secondary users (SUs) can coexist harmlessly with the PUs. Despite the importance of such a coexistence issue, it is also crucial to investigate the coexistence of SUs because (i) the PUs usually rarely use the licensed spectrum and (ii) the advantages of CRN will significantly increase the number of SUs in the future. To address this challenging issue, we propose, in this paper, an optimal randomized spectrum access scheme, whose main ideas include the following: (i) an SU shares its sensing results with neighboring SUs and (ii) with the regional sensing results, an SU will access available channels with a non‐uniform probability distribution. We first formulate a multichannel optimal randomized multiple access (MC‐ORMA) problem that aims to maximize the throughput of the CRN; we then develop efficient distributed algorithms to solve the MC‐ORMA problem; we derive the closed‐form value of collision probability for each SU; and finally, we conduct extensive numerical experiments and compare our theoretical analysis with simulation results to demonstrate the advantages of our scheme. Copyright © 2011 John Wiley & Sons, Ltd.     

MSE tracking performance of DS/SS code tracking scheme using an FIRadaptive filter

The authors investigate the mean-square error (MSE) tracking performance of a DS/SS code tracking system based on an adaptive filtering technique proposed earlier. The ability of this scheme to track a fast linearly changing delay and delay changing in a random walk model is presented. It is shown that the proposed scheme outperforms the maximum likelihood estimator (MLE) by ~4 dB. Also, the MSE results indicate that a filter with small number of taps is recommended during tracking. This supports the conclusions made previously which was based on the mean hold in time performance of the system     

二维地址码对OCDMA系统误码率性能的研究

介绍了二维二次素数码、二维光正交码及二维Rs地址码的构造,讨论了它们对OCDMA系统误码性能和用户容量的影响.通过仿真分析了二维地址码的用户容量与码长、码重的关系,以及误码率随同步用户数、判决门限的变化曲线.结果表明,对于二维OCDMA系统,在判决门限一定的条件下,同步用户数越大,系统的误码率越低;系统同步用户容量随着...     

On the establishment of an access VPN in broadband access networks

Many corporate networks use the Internet as a cost-effective substitute for expensive leased lines and long-distance telephone calls, for allowing their users to have on-demand connectivity into their intranets through ad hoc tunnels, a concept known as access VPN. Establishing an access VPN in a broadband access network is very often a difficult networking challenge that requires several tunnels to be established between the various involved entities. This is especially the case in an open broadband access network where the association between a host and its ISP is not known to the network in advance. This article discusses several schemes for establishing an access VPN in a broadband access network, and explains the need for the various tunnels in each scheme.     

一种基于主动网络技术的改善无线链路上TCP性能的方案

针对TCP在无线环境中性能下降问题,本文提出一种基于主动网络技术的方案,来改善无线链路上的TCP性能.通过网络仿真,证明这种方案具有更高的性能和更多的优点.     

紫外光通信信道参数对Turbo码的影响

在紫外光通信中采用了纠错性能优异的Turbo码,用gamma-gamma湍流模型仿真信道中的大气湍流,考虑紫外光通信常用的P P M(脉冲位置调制)方式以及湍流的影响,在紫外信道中,分析了在相同的条件下折射率结构常数和波长等因素的变化给Turbo码性能带来的影响。仿真结果表明：在相同的条件下,折射率结构常数越小,波长越长,Turbo码的性能越好,该结论可为实际实现提供理论参考。     

Resource allocation scheme for orthogonal frequency division multiple access networks based on cooperative game theory

Cooperative game theory can be applied to orthogonal frequency division multiple access (OFDMA) networks for fair resource allocation. In this work, we consider a comprehensive cross‐layer framework including physical and medium access control layer requirements. We apply two cooperative games, nontransferable utility (NTU) game and transferable utility (TU) game, to provide fairness in OFDMA networks. In NTU game, fairness is achieved by defining appropriate objective function, whereas in TU game, fairness is provided by forming the appropriate network structure. For NTU game, we analyze the Nash bargaining solution as a solution of NTU game taking into account channel state information and queue state information. In a TU game, we show that coalition among subcarriers to jointly provide rate requirements leads to better performance in terms of power consumption. The subcarrier's payoff is determined according to the amount of payoff which that subcarrier brings to the coalition by its participation. We show that although NTU and TU games are modeled as rate adaptive and margin adaptive problems, respectively, both solutions provide a fair distribution of resources with minimum fairness index of 0.8. Copyright © 2012 John Wiley & Sons, Ltd.     

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) technol...     

A note on optimal input control policy for an Aloha access scheme

Input control policies had been proposed previously (e.g. in Lam and Kleinrock, 1975; and Fayolle et al., 1977) to improve the delay-throughput performance of Aloha access schemes. Through simulation results, Lam and Kleinrock observed that the optimal control policies were in general of control limit type. The authors discuss input control policies for one such Aloha access scheme and prove analytically that the optimal policy is indeed of the control limit type. The optimal policy is found to be extremely simple for the access scheme discussed. This policy is to accept the newly arrived packet if the present system state is either zero or one, and to reject the packet otherwise