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.     

A new shared AWG-based OCDMA scheme implemented with time-spreading and wavelength-group-hopping embedded M-sequence code

This paper exploits the inherent cyclic and periodic free-spectral-range (FSR) properties of arrayed-waveguide grating (AWG) routers to construct a two-dimensional (2D) time-spreading and wavelength-group-hopping embedded M-sequence code for optical multiple-access networks. In the proposed codecs (encoder/decoder), a fine arrayed-waveguide grating (AWG) is used to generate an M-sequence code pattern, which is then spread in the wavelength domain by multiple coarse AWGs. The signals produced at the output ports of the coarse AWGs are then spread in the time domain using optical delay lines. The 2D code is evaluated in terms of its correlation, bit-error-rate (BER) and cardinality characteristics. It is shown that the TS/GH embedded M-sequence code yields a significant improvement in both the BER and cardinality performance of the optical multiple-access networks compared to that obtained using conventional prime-hop code (PHC), modified prime-hop code (MPHC), Barker and Walsh-based bipolar–bipolar sequence.     

基于光纤光栅编解码和修正素数跳频码的一种光码分多址系统方案研究

在素数跳频码（PHCs）的基础上，研究了修正素数跳频码（MPHCs）的构造方法和性能，提出了基于光纤布拉格光栅（FBG）编解码实现修正素数跳频码这种二维地址码的光码分多址（OCDMA）系统方案。并通过对素数跳频码和修正素数跳频码这两种码字误码性能的分析，得到以下结论：对于相同的素数P，当系统误码率（BER）B≤10^-9，P≥37时，修正素数跳频码所容纳的最大用户数大于素数跳频码；在光纤布拉格光栅阵列上修正素数跳频码所需要的编码光栅数相对素数跳频码减少（P一1）／2个，从而降低了光纤布拉格光栅阵列的制作难度。     

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.     

A new family of 2D wavelength/time codes with large cardinality for incoherent spectral amplitude coding OCDMA networks and analysis of its performance

A new family of two-dimensional wavelength/time codes (2D-W/T-MQC/MQCs) and its system structure of encoder/decoder are proposed, which is based on tunable optical fiber delay lines (TOFDLs) and fiber Bragg gratings (FBGs). Multiple-access interference (MAI) can fully be eliminated by using a wavelength/time balanced detector structure at the receivers. Furthermore, the performance of the system is also analyzed by taking into account the phase-induced intensity noise (PIIN), shot noise, and thermal noise. The simulation results reveal that the new code family possesses higher signal-to-noise ratio (SNR) and lower bit-error rate (BER) than the family of one-dimensional spectral amplitude coding modified quadratic congruence codes (1D-SAC-MQCs) and that of the two-dimensional wavelength/spatial M-matrices codes (2D-W/S-M-Matrices) so that a larger number of subscribers can be supported simultaneously. Additionally, the 2D-W/T-MQC/MQC system requires less signal power for each light source under the same error-free condition. As a result, the network based on the new code family will support more active users and utilize the frequency bandwidth more efficiently.     

New architecture for incoherent optical CDMA to achieve bipolarcapacity

A simple and efficient method for using bipolar codes in noncoherent optical code-division multiple access systems is proposed. The proposed system requires only incoherent optical delay lines and direct detection receivers. Practical architectures for the encoder/decoder are given. The Letter shows that combining Gold codes of period M=127 and Barker code of period K=4 into composite sequences of period N=508 allows 20 simultaneous active users for P_e=10 ^-9, while requiring only four nonprogrammable delay lines     

A non-coherent SAC-OCDMA system using extended quadratic congruence codes for two-code keying scheme in passive optical networks

In this paper, we propose a family of extended quadratic congruence codes for two-code keying (TCK) with the corresponding encoding/decoding architecture for passive optical networks (PONs) in spectral amplitude coding optical code division multiple access (OCDMA) systems. The proposed system can simultaneously eliminate multi-user interference (MUI) and further suppress phase-induced intensity noise (PIIN). We reduce the complexity of the encoding/decoding architecture of the optical line terminal reduced by exploiting arrayed waveguide gratings (AWGs) and the properties of the extended quadratic congruence codes (EQC codes). Moreover, we also design a deployment method to increase the number of simultaneous users. Our numerical results demonstrate that the proposed system outperforms the improved quadratic congruence codes (improved QC codes).     

Comparison of diverse optical CDMA codes using a normalized throughput metric

A new method of comparing optical CDMA codes of different families, sizes and weights is described. We outline why the traditional performance metric of bit-error rate versus number of simultaneous users is lacking and propose a new performance measure - the peak throughput normalized with respect to the size of the code. This new metric is used to show that optical-orthogonal codes (OOCs) with a weight of 4 perform best at low offered loads while OOCs with weight 5 should be used at higher offered loads. By applying the technique across different families of codes, we demonstrate that multi-wavelength OOCs (MWOOCs) perform better than both OOCs (by a factor of approximately 1.25) and asymmetric prime-hop codes (by a factor of approximately 3.5), over a wide range of offered loads.     

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.     

A novel OCDMA drop unit based on fiber gratings and 2D wavelength-time codes

Opticalcode divisionmultipleaccess(OCDMA)hasalwaysbeenofinterestbecauseofitsinherentabilityto supportasynchronousburstycommunications.Itwas pursuedforlocalareaandthenforaccessnetworkappli cations.However,toourknowledge,littlehasbeendoneontheAdd DropMultiplexer(ADM)usingtheOCD MAtechnologyuntilmostrecently.In[1],atwo dimen sionaltime wavelengthOCDMAcode dropunitbasedonwavelengthdivisionmultiplexersandaterahertzop ticalasymmetricdemultiplexerwasproposed.Bysimply addingacouplerandatu…     

Performance Analyses on Hybrid MQC/M-Sequence Coding Over Frequency/Spatial Optical CDMA System

A new two-dimensional frequency/spatial code for spectral-amplitude coding a optical code-division multiple-access system is proposed. The corresponding coder/decoder pairs are based on the tunable fiber-Bragg gratings cooperating with optical splitters/combiners, and multiple-access interference can be eliminated through the proposed decoding mechanism. For the performance analysis, the effects of phase-induced intensity noise, shot noise, and thermal noise are considered simultaneously. Bit-error rate (BER) performance is compared with that of the former system using M-matrix codes. It is shown that the system using these new code matrices not only maintains most advantages of the former one, but also allows larger number of active users under a given BER     

Pseudorandom Coding for Improved Antenna Range Measurements

The autocorrelation function for pseudorandom binary codes is such that these codes are ideal for suppressing unwanted reflections on antenna ranges. The method presented here depends on amplitude modulating the transmitted signal with a maximum-length linear recurring modulo-two sequence (PN code) and correlating it at the receiver with a delayed version of the code. In this way reflections whose path transit times are greater than 1 bit time from the direct path transmission time are reduced in amplitude by a factor inversely proportional to the length of the code word. Also presented is a simple means for generating the maximum-length shift-register codes using delay lines and mixers that makes this method especially practical for most antenna range applications.     

Performance comparison of proposed 3-d coherent spatial-phase-time coding/decoding with super structured fiber Bragg grating-based optical CDMA systems

In this paper, performance comparison in terms of bit error rate (BER) of proposed WDM compatible optical CDMA system incorporating 3-D spectral-phase-time encoding/decoding to a 7 chip-super-structured fiber Bragg grating (SSFBG)-based optical code division multiple access (OCDMA) system is investigated. Coding and decoding using binary [0, π] phase chips is demonstrated for six users at 5 Gb/s, and a single coded signal is separated with acceptable bit-error rate ≤10^?9. In our proposed optical CDMA system encoding and decoding is done by converting hadamard codes (used for conventional CDMA system) to phase codes. It is then compared with two optical pulse retiming and reshaping systems incorporating super structured fiber Bragg gratings (SSFBGs) as pulse shaping elements. Simulation results show that with all input bands having same sample rate, size data rates our proposed codes with even larger number of channels perform better in terms of eye opening & BER.     

采用光码分多址技术的高速计算机局域网

本文提出一种可行的适于高速计算机网络的光码分多址技术，该网络采用光正交码和光信号处理，以保证实时数据通信。提出的全光结构的快速可调光正交码编码器和解码器，可在光域中用电光开关和光延迟线实现，能支持超高速吞吐量且重构时间很短     

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.     

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     

A New Family of Wavelength-Time Optical CDMA Codes Utilizing Programmable Arrayed Waveguide Gratings

A two-dimensional, so-called wavelength-hopping time-spreading, optical code-division multiple-access coding scheme has recently been studied for supporting more subscribers and simultaneous users than conventional one-dimensional techniques. To further improve the numbers of subscribers and simultaneous users without sacrificing performance, a new code, which utilizes the unipolar version of bipolar codes (for wavelength hopping) and optical unipolar codes (for time spreading), is studied and analyzed in this paper. A programmable and integratable coding hardware based on arrayed waveguide gratings is designed for this coding scheme.     

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。     

Performance Evaluation of a Novel Converged Architecture for Digital-Video Transmission Over Optical Wireless Channels

A robust channel coding architecture for multigigabit-per-second digital-video transmission over the optical wireless channel is introduced and evaluated. The proposed scheme combines low-density parity-check coding with channel interleaving to improve the transmission over turbulent temporally correlated optical wireless channels while satisfying real-time video delay constraints. Frame error rates of the presented code design are evaluated via simulation for intensity-modulation/direct-detection optical wireless links in both lognormal- and Rayleigh-fading channels. Results indicate that the performance of the proposed system is effective across a large range of atmospheric turbulence strengths and achieves significant temporal diversity in moderately long (10 ms) temporal correlation times while satisfying a 0.3-s real-time delay constraint. Moreover, the proposed design is shown to outperform the Reed-Solomon codes prevalent in the legacy fiber and wireless digital-television distribution systems.     

基于超结构光纤光栅的新型OCDMA编解码方案

提出了一种基于超结构取样光纤光栅的光码多分址(OCDMA)编解码器.以修正Walsh码为例,研究了利用间隔光0.8 nm的超结构取样光纤光栅编解码器的实现方法,通过控制温度实现了基于超结构取样光纤光栅的OCDMA编解码器的变址.研究表明:采用该编解码器实现谱域编码,可以避免光纤光栅串联方案中多个光纤光栅接点引起的损耗,易通过应力或温度变化调节中心波长、尺寸小及调谐方便,有利于实用化.