基于OptiSystem软件的OCDMA系统仿真

分析了采用光素数地址码的异步OCDMA系统设计原理,阐述了OptiSystem软件针对光系统的强大仿真功能。在设计原理的基础上,采用光纤延时线编码技术给出了基于OptiSystem的异步OCDMA系统仿真模型,得出仿真结果并进行了分析,验证了系统设计的正确性和设计方案的可行性。     

A synchronous fiber-optic CDMA system using adaptive opticalhardlimiter

In this paper, we propose a new synchronous fiber-optic code-division multiple-access (CDMA) system using adaptive optical hardlimiter and modified prime sequence code. At the receiver, the energy in one bit duration is estimated and used to adjust the threshold value of the adaptive optical hardlimiter which is placed after the optical correlator. The bit error probability of the system is analyzed with the consideration of thermal noise, shot noise, and dark current noise of the photodetector. The results show that this system can support a larger number of simultaneous users than other systems also using modified prime sequence code under the same bit error probability constraint     

2-D optical CDMA networks using MWPM, double hard limiters and modified carrier-hopping prime sequences

This paper presents a two-dimensional optical code division multiple access (2-D-OCDMA) scheme using multiwavelength pulse modulation (MWPM), double optical hard limiters (DHL), and modified carrier-hopping prime sequences (MCHP) to increase the achievable system capacity. Design criteria to reduce multiaccess interference (MAI) are established and indicate that suitable signature sequences for 2-D-OCDMA/MWPM must have good cross-correlation property in terms of both time shift and wavelength shift. Performance analysis of 2-D-OCDMA/MWPM/DHL systems in the presence of MAI and photo detector shot noise is developed. Simulation and analytical results are in very good agreement and indicate that the proposed 2-D-OCDMA/MWPM/DHL systems using MCHP sequences can offer a much larger capacity than others, suitable for applications in broadband fiber-optic access networks.     

A 10 Gb/s optical code division multiplexing using 8-chip opticalbipolar code and coherent detection

bOptical code division multiplexing (OCDM) using optical bipolar code and coherent detection is a new multiplexing method for future fiber-optic communication networks. Some optical bipolar codes, which are described by the combination of phase of optical chip pulses, with a repetition frequency 10 GHz are generated experimentally. Temporal matched filtering for the 10 Gb/s OCDM is demonstrated using optical encoder and decoder, and their fundamental properties are investigated. Effect of interference code is shown experimentally and discussed. The novel coherent detection system with autocorrelation sidelobe suppression using balanced detector and local light source is proposed. The pseudocoherent detection is demonstrated experimentally by using a clock pulse. Advantageous properties of the coherent detection are shown. The fundamental functions to realize the gigabit rate OCDM system is revealed     

Spread spectrum fiber-optic local area network using optical processing

Spread spectrum code division multiple access (CDMA) allows asynchronous multiple access to a local area network (LAN) with no waiting. The additional bandwidth required by spread spectrum can be accommodated by using a fiber-optic channel and incoherent optical signal processing. New CDMA sequences are designed specifically for optical processing. It is shown that increasing the number of chips per bit, by using optical processing, allows an increase in capacity of a CDMA LAN. An experiment is performed demonstrating the performance of an optical CDMA LAN, operating at 100 Mbd with three users.     

Synchronous fiber-optic CDMA using hard-limiter and BCH codes

In this paper, synchronons code division multiple access (S/CDMA) for fiber-optic local area networks is considered. The performance of the fiber-optic S/CDMA network with negligible thermal and shot noises is interference limited. Here we derive the bit error rate of the S/CDMA system as a function of code length and number of active users, and the performance characteristics are also discussed. Furthermore, we analyze the performance of the fiber-optic S/CDMA system with an ideal optical hard-limiter, and the error probability with error control coding is also derived. In addition, the optimization between the S/CDMA and BCH codes of a constant bandwidth system is presented. The results show that by using an ideal hard-limiter in conjunction with BCH codes in this system, the influence of interference arising from other users can be greatly reduced, and the number of active users can also be increased significantly     

Trellis-coded asynchronous optical CDMA systems

Since optical code division multiple access (CDMA) is an interference-limited system, we propose a system employing trellis-coded scheme and double optical hardlimiters (TC-DHLs) to alleviate the adverse impact of multiple access interference. For asynchronous transmission, optical orthogonal code (OOC) is utilized as signature sequence. System performance is evaluated under the chip synchronous case among different users, and thermal noise, avalanche photodiode (APD) noise, and interference are taken into consideration. Numerical results show that our proposed scheme can further reduce the error floor up to several orders over systems that using only double optical hardlimiters     

Construction and performance analysis of variable-weight optical orthogonal codes for asynchronous OCDMA systems

A construction scheme of variable-weight optical orthogonal codes （VW-OOCs） for asynchronous optical code division multiple access （OCDMA） system is proposed. According to the actual situation, the code family can be obtained by programming in Matlab with the given code weight and corresponding capacity. The formula of bit error rate （BER） is derived by taking account of the effects of shot noise, avalanche photodiode （APD） bulk, thermal noise and surface leakage currents. The OCDMA system with the VW-OOCs is designed and improved. The study shows that the VW-OOCs have excellent performance of BER. Despite of coming from the same code family or not, the codes with larger weight have lower BER compared with the other codes in the same conditions. By taking simulation, the conclusion is consistent with the analysis of BER in theory. And the ideal eye diagrams are obtained by the optical hard limiter.     

基于AWG二维编解码的OCDMA多用户分插复用

提出了一种新型的光码多分址(OCDMA)多用户分插复用器(ADM),所设计的ADM是基于阵列波导光栅(AWG)和二维时域/频域编码技术,可以从网络中同时取下多个码的数据而不影响剩余的码字信道,并且可以同时向网络中添加多个本地数据.设计的编解码器利用了Prime/OOC等具有特定规律的二维时域/频域扩展的码字,可以利用较少的AWG达到海量用户的编解码,系统集成度高.对所提出的ADM进行系统仿真,可以实现从4用户的网络中同时添加和取下2用户的功能,结果显示达到了所需的功能要求.     

Photonic access node using optical code-based label processing andits applications to optical data networking

An ultrahigh-speed photonic access node using optical code-based photonic add-drop multiplexing (PADM) and its novel applications to optical data networking are proposed. PADM processes a photonic label of packet, which is mapped onto an optical code, and adds-drops the packet from or to the node, or bypasses the node. PADM is distinct from conventional wavelength ADM (WADM) in that it can handle traffic on a packet-by-packet basis. In the application of PADM to optical data networking, pseudo-time division multiple access (TDMA) and rate-controlled asynchronous access are proposed. The analyses and their numerical simulations of the performances are presented. The simulation results demonstrate low packet-loss probability. Their optical implementations are also demonstrated, in which exploit parallel photonic label processing shows the applicability of proposed optical data networking in an ultrahigh-speed regime     

Code for spectral amplitude coding optical CDMA systems

A new code structure for spectral amplitude coding optical code division multiple access (CDMA) is proposed and analysed. It is shown that such codes can effectively suppress the intensity noise and in turn increase the number of active users and improve the bit error rate performance     

双向时分复用光纤时间传递链路噪声分析

研究分析了双向时分复用(BTDM)光纤时间传递链路 的主要噪声及产生机理,建立了基于BTDM光纤时间传递 的链路噪声模型。仿真分析了激光器强度噪声、光放大器增益与个数、接收机带宽等对BTDM 光纤时间传 递接收信噪比(SNR)的影响。结果表明,BTDM光纤时间传递 接收SNR在光放大器达到最优增益时最大,且最 大SNR随光放大器个数的增加而增加并趋于稳定;相同长度光纤链路,光放大器个数越多 ,在一定范围 内,激光器相对强度噪声对BTDM光纤时间传递链路接收SNR 影响更大,接收机带宽对BTDM光纤时 间传递接收信号抖动的影响越小;BTDM光纤时间传递接收SNR随定时信号前 光持续时间的增加而减小,并趋于WDM方案的SNR。     

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).     

Real-time multimedia broadcasting via direct-detection fiber-opticsynchronous CDMA networks

A new coding architecture for M-ary fiber-optic synchronous code division multiple access (CDMA) network is proposed to provide real-time multimedia broadcasting. In contrast with variable bit rate (VBR) transmission, the constant bit rate (CBR; i.e. isochronous) transport is more preferable in view of the networking simplicity. We apply a bit-stuffed unipolar m-sequence and maximum a posteriori (MAP) receiver in the proposed network. The system performance is determined by the following parameters: (1) number of simultaneous access broadcasting hosts K, (2) received laser power, (3) input bit rate, and (4) the dimension of M. Furthermore, the adverse impact (thermal noise, APD noise) in the photodetection process is carefully analyzed. Numerical results reveals that for the binary case, the aggregate capacity can achieve 10.2 Gbps     

Code-based all optical routing using two-level coding

Code-based all optical routing employing a two-level-coding scheme is proposed. The first level of coding is employed to establish connections between users within a local area network; a second level of coding provides routing/interconnectivity between networks. The limitations due to physical-layer impairments, such as relative intensity noise (RIN) of the optical source, the signal-dependent shot noise, optical beat interference (OBI), and thermal noise at the receiver, which are some of the fundamental issues in the design of practical optical code division multiple access (CDMA) systems, are analyzed for the two-level scheme. The throughput in terms of "packets/time slot" offered by the scheme is also compared with that of the wavelength division multiple access (WDMA) system. The system capacity in WDMA is limited by the number of available wavelengths; optical CDMA, on the other hand, has many codes (user addresses), but the throughput is limited by multiple user interference, OBI, and RIN. System designs that overcome these effects and thereby improve the throughput are suggested.     

Statistical analysis of fiber-optic CDMA communication systems. II. Incorporating multiple optical amplifiers

For pt. I see ibid., vol.20, no.8, p.1304-16 (2002). In this paper, we study and elaborate on the architectural consideration of using multiple optical amplifiers in an all-optical fiber-optic code-division multiple-access (FO-CDMA) network. Our study and considerations are based on obtaining the statistical characteristic functions for photon-counts of a string of output pulses that constitutes the address code in a FO-CDMA network. Optical orthogonal codes (OOCs) with minimum auto-and cross correlation are employed as the address or signature sequence codes. Our analysis is based on chip-synchronous interference only, which provides an upper bound on the system performance. Shot noise, thermal noise, and extinction ratio are considered in this analysis. Bit error rate (BER) results are obtained using two methods, namely, saddle-point and Gaussian approximations. From our BER analysis, we develop some insight into the optimum distribution of optical amplifiers and their corresponding gain setting parameter. Moreover, the effects of source power, code weight, number of users, bit rate, and amplified spontaneous emission noise are investigated.     

Optical orthogonal code-division multiple-access system .I. APDnoise and thermal noise

In an optical multiple-access system, overall system throughput efficiency add significant implementation cost-reduction would be achieved if many users could access a common optical channel at any time without control among users. Recently one such scheme, an optical orthogonal code division multiple-access system (OOCDMA), was introduced by Salehi et al. (1982) for the case of no noise. In this paper, some extensions of that work are presented, including the effects of avalanche photodiode (APD) noise and thermal noise as well as interference for the OOCDMA direct-detection receiver. Since it has been shown that an optical hard-limiter before the receiver correlator can reduce the interference effect for the OOCDMA system in the absence of noise, the hard-limiter role in the presence of thermal and APD noise is also examined     

光码分多址多比特传输系统性能分析

:多比特传输是光码分多址通信的一种方案。本文对光码分多址多比特传输系统的误码性能进行了理论分析和计算机数字仿真。在系统中存在光电检测器散粒噪声、暗电流噪声、背景光、热噪声的情况下 ,分别对无光硬件限幅器和引入一个光硬件限幅器的多比特传输系统进行讨论 ,得出相应的误比特率表达式 ,该表达式明确、具体。分析结果表明 ,当接收功率较大时 ,多比特传输系统的误码性能优于相应的单比特传输系统。     

Design and analysis of a dynamic code division multiple access communication system based on tunable optical filter

A dynamic optical code division multiple access (DOCDMA) communication system is proposed for high-bandwidth communication systems. An implementation of the system is proposed based on a fast tunable optical filter (TOF) in each encoder and decoder. This technique actively modulates the central wavelength of a TOF according to a functional code at the transmitter during the bit period before the transmission of the data. The system is modeled and analyzed taking into account multiple access interference (MAI), thermal noise, and phase-induced intensity noise (PIIN). The performance of this system is compared to that of a spectral amplitude coding system that uses either a Hadamard code or a modified quadratic congruence (MQC) code. The results show that the proposed DOCDMA system reduces the PIIN effect on the performance of the system and improves the bit error rate (BER) performance at a large number of users. Furthermore, it is found that when the effective power is large enough, the MAI becomes the main factor that limits system performance, whereas when the effective power is relatively low, both thermal noise and PIIN become the main limiting factors with thermal noise having the main influence.     

一种新的光码分多址技术

提出了一种新的、实现光ＣＤＭＡ的方案。它采用平衡发射和接收技术同时使用Ｍａｃｈ－Ｚｅｈｎｄｅｒ干涉链来进行地址编码。该ＣＤＭＡ系统接近波分复用的性能,但是也面临一些有待解决的问题,例如多用户时的谱干扰,散弹噪声等。而本系统可以在非相干调制光系统中得到地址码的真正正交,从而改善系统的性能。