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...     

基于修正素数码的双OHL同步OCDMA性能分析

基于单硬限幅器(OHL)的同步光码分多址 (OCDMA) 系统不能完全消除信道串扰,引入了双OHL结构来优化系统传输性能.文章给出地址码的码重、光谱强度、用户数与误码率及同异步系统归一化吞吐量间的关系,结果表明:在用户数与地址码重相差较大的情况下,双OHL同步OCDMA系统误码率下降明显且比异步系统的归一化吞吐量大.     

二维同步OCDMA光编码器设计与研究

文章以"同步修正素数码"为基础,利用互相垂直的两组线偏振光构造了适用于同步光码分多址(OCDMA)系统的二维光正交地址码.通过分析码字的自相关和互相关特性,确定了其选码原则.在此基础上,设计了适用于同步OCDMA系统的二维光编码器.仿真结果表明,与一维同步OCDMA系统相比,二维同步光正交地址码具有更优良的接收性能,并解决了器件在实际使用过程中可能出现的功率非线性叠加问题.     

无线OCDMA中扩频编码的研究

分析和比较了无线光码分多址(OCDMA)中一维扩频编码和二维扩频编码的原理、码字容量、误码率等性能及其差异。得出二维扩频编码相对于一维扩频编码而言,通信系统的码字容量、系统的传输速率得到大大的提高;同时通过适当选择码长和码重,系统满足1×10-9的误码率要求,并发用户数可以高达200以上。     

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。     

BCH码对自由空间OCDMA系统性能的改善

基于自由空间的信道特性,提出用BCH信道编码来改善自由空间OCDMA系统性能.考虑系统中存在多用户干扰、背景光噪声以及APD接收机噪声的情况下,分析了基于多波长二维光正交码的同步OCDMA系统BCH编码前后的误码率公式,并对采用不同BCH码的系统误码率性能进行了计算机仿真.仿真结果表明,BCH码在降低系统编解码器的复杂度的同时能够有效地增加系统同时容纳的用户数,有效地降低系统对接收光功率的要求.     

OCDMA中的正交码和素数码的误码率分析

OCDMA是一种用于光通信的扩频通信技术,具有大用户容量,随机异步接入、保密性好等特点.能充分发挥光纤的高速率、宽带宽的特性.本文介绍了光码分多址(OCDMA)系统中的六种重要地址码的误码性能,包括一维和二维光正交码(OOC)、一维和二维素数码(PC)、变重和变长光正交码.并对它们的误码性能进行了比较分析.     

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...     

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).     

多维码OCDMA通信系统的研究

提出了OCDMA系统中所使用的多维码的概念并对其性能进行了分析．重点介绍了光素数码、二维光正交码、二维素数码及三维码．     

基于改进LSOOC的SAC-OCDMA通信系统性能分析

提出了一种基于改进的latin方阵光正交码(MLSOOC)、适合光谱幅度编码(SAC)光码分多址(OCDMA)系统的地址码构造方法,码字间有理想的互相关,容量达到了SAC的上限.分析了SAC编解码的原理、光纤Bragg光栅(FBGs)谱幅编解码的工作过程及在考虑相位引起的强度噪声(PIIN)、热噪声和散弹噪声情况下的系统信噪比(SNR)和误码率(BER).结果表明:在光源和信道理想条件下,多址干扰(MAI)可以消除;在考虑噪声的情况下,可以有效抑制PIIN减小BER;在满足一定BER下,系统承载的同步上路用户多容量比用Hadamard码大大增加.     

Multiuser receiver scheme for full‐rate space–time coded CDMA system with imperfect estimation

By introducing a full‐rate space–time coding (STC) scheme, a synchronous CDMA (code division multiple access) system with full‐rate STC is given, and the corresponding uplink performance is investigated in Rayleigh fading channel with imperfect estimation. Considering that existing STC‐CDMA system has high decoding complexity, low‐complexity multiuser receiver schemes are developed for perfect and imperfect estimations, respectively. The schemes can make full use of the complex orthogonality of STC to reduce the high decoding complexity of the existing scheme, and have linear decoding complexity compared with the existing scheme with exponential decoding complexity. Moreover, the proposed schemes can achieve almost the same performance as the existing scheme. Compared with full‐diversity STC‐CDMA, the given full‐rate STC‐CDMA can achieve full data rate, low complexity, and partial diversity, and form efficient spatial interleaving. Thus, the concatenation of channel coding can effectively compensate for the performance loss due to partial diversity. Simulation results show that the full‐rate STC‐CDMA has lower bit error rate (BER) than full‐diversity STC‐CDMA systems under the same system throughput and concatenation of channel code. Moreover, the system BER with imperfect estimation are worse than that with perfect estimation due to the estimation error, which implies that the developed multiuser receiver schemes are valid and reasonable. Copyright © 2010 John Wiley & Sons, Ltd.     

采用光硬限幅器和RS码的多波长OCDMA性能分析

提出了一种采用多个光硬限幅器和RS信道编码的多波长光码多分址（MW OCDMA）系统,理论分析了其误码率和（BER）和归一化吞吐量性能.结果表明,采用光硬限幅器的MW OCDMA系统BER性能将明显改善,进一步采用RS信道编码后,MW OCDMA系统BER性能将大大改善.另一方面,采用光硬限幅器的MW OCDMA系统的归一化吞吐量明显提高,特别是归一化吞吐量峰值提高了约1倍,但进一步采用RS信道编码后,MW OCDMA系统的归一化吞吐量并没有提高,在系统负载量不是很大的情况下还略有下降.     

大气二维光PPM CDMA通信系统

提出了采用脉冲相位调制(PPM)和采用纠错能力极强的Turbo码进行信道编码的大气信道二维光码分多址(OCDMA)系统,考虑存在多用户干扰、大气闪烁、背景光噪声以及APD接收机噪声等问题,研究了信道编码前后系统误码率性能.对M=4的PPM OCDMA系统的误码率性能研究表明,在光强闪烁的对数方差小于0.1时,能够实现大气OCDMA通信;在采用Turbo编码后,系统性能明显改善,和只采用多用户干扰检测技术的系统方案比较,采用Turbo编码可更有效改善系统性能.     

A performance analysis of optical overlapping PPM-CDMAcommunication systems

Direct-detection optical code-division multiple-access (CDMA) systems employing overlapping pulse-position modulation (OPPM) schemes are proposed. Both upper and lower hounds on the bit error rate (BER) are derived taking into account the effect of both multiple-user interference and receiver shot noise. The photodiodes' dark currents are neglected since their effect is minor. The throughput limitation of this system is evaluated as well. Performance characteristics are then compared to optical CDMA systems employing traditional ON-OFF keying (OOK) and pulse-position modulation (PPM) schemes. It is shown that under fixed data rate and chip time, OPPM-CDMA system superperforms both traditional systems. Moreover, it is shown that the throughput limitation of OPPM-CDMA is almost 6.7 times greater than that of OOK-CDMA     

二维大气无线光码分多址通信系统

在无线光通信系统中采用光码分多址(OCDMA)技术,可以充分利用其丰富带宽,提高系统性能。考虑背景光噪声、探测器噪声、多用户干扰和大气闪烁等影响因素,给出了二维无线光码分多址(2D-WOCDMA)系统模型,在该模型中采用了脉冲位置调制(PPM)和光纤布拉格光栅(FBG)编解码器。通过数值分析,详细讨论了该无线光通信系统的性能。结果表明,大气闪烁是影响二维无线光码分多址通信系统性能的重要因素,当其对数方差较大时,系统难以实现通信,需要采用诸如多用户检测、信道编码及阵列接收等技术提高系统的性能;二维无线光码分多址通信系统适合采用1550 nm波段;该通信系统还受背景光、雪崩光电二极管(APD)增益和调制消光比等因素的影响。     

Combinatorial BER analysis of synchronous optical CDMA with primesequences

A previous BER analysis (see ibid., vol.39, no.11, p.1625, 1991) is based on a Gaussian approximation. We derive a combinatorial BER analysis and an improved Gaussian approximation for synchronous optical code-division multiple-access (S/CDMA) with prime codes. This analysis is shown to be in good agreement with the Gaussian approximation as well as with simulation results     

BER analysis of coherent optical CDMA communication systems with transfer function matrix

We analyze the bit error rate (BER) of coherent optical code-division multiple-access (CDMA) communication systems with a transfer function matrix (TFM). The coherent optical CDMA is a promising system for an access network due to its advantages of asynchronous transmission, information security, multiple-access capability. TFM is defined as the Fourier transform of the impulse response of an optical fiber, which interconnects each CDMA system. TFM has parameters such as the state of polarization (SOP), phase difference, power distribution between two orthogonal modes over an optical frequency range. We first analyze the statistic of a received signal via an optical fiber with TFM, and then apply the statistic to the BER analysis. The analytical results show that BER increases with the bandwidth of a signal, and that selecting a proper center frequency leads to the BER reduction.     

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.     

Throughput Analysis of Adaptive Modulated STS-based CDMA System Over Multipath Fading Channel

The throughput enhancement of Space-Time Spreading (STS)-based Code Division Multiple Access (CDMA) system is investigated in this paper. Adaptive Modulation is utilized to improve the data throughput of the system in multipath Rayleigh fading channel. In this contribution, an analytical approach is proposed to compute a new expression for the Bit Error Rate (BER) performance and the output Signal-to-Interference-and-Noise Ratio (SINR) of the RAKE receiver-assisted STS-based CDMA system for QAM data, considering multipath and multiuser interferences. The other contribution of the paper is deriving a new closed form expression for computing the throughput enhancement and the BER performance of the adaptive modulated STS-based CDMA system over multipath fading channel. Simulation and analytical results demonstrate that using adaptive modulation method in this system improves the average throughput by keeping the BER performance at a target level. The novel expressions presented in this paper bring out the facility of evaluation of the proposed system with no need to more calculations and simulations.