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).     

Optimum threshold detection in real-time scalable high-speedmulti-wavelength optical code-division multiple-access LANs

We examine the properties and applications of a general class of multi-wavelength optical code-division multiple access codes in high-speed optical local area networks. We demonstrate that multiple pulse per row codes with optimum threshold detection admit maximization of the number of simultaneous users and spectral efficiency. The code design problem is also greatly simplified when the optimum threshold detection is employed. Based on our results, we propose a simple and low-cost receiver to enable true real-time network optimization     

Optimizing spectral efficiency in multiwavelength optical CDMA system

Prime codes are excellent candidates for use in multiwavelength optical code-division multiple-access (O-CDMA) systems. We show that in an O-CDMA system using two-dimensional single-pulse-per-row codes, a single choice of the number of wavelength channels can. accommodate different numbers of users with maximal spectral efficiency. The optimum single-user-detection spectral efficiency of the system can be reached using AND detection. A fixed-hardware network can readily be adapted in response to changes in the number of users and traffic load.     

A New Approach to Achieve High Spectral Efficiency in Wavelength-Time OCDMA Network Transmission

We design a new wavelength-time optical code-division multiple-access (OCDMA) modulation scheme that does not use spreading sequences for information transmission, i.e., the spreading length is N=1. The proposed transmitter sends (error-control) coded data directly through the optical channel and exploits a probabilistic method to reduce the amount of multiuser interference. Simulation results show that by using turbo codes, Reed-Solomon codes, and soft-decision demodulation, the proposed OCDMA scheme can support hundreds of active users at target bit-error rate =10^-9. Furthermore, the achieved spectral efficiency of 0.740 bits per channel use is almost twice as large as the best previous OCDMA results     

Comparative Study of Multiencoding Schemes for OCDM Using a Single Multiport Optical Encoder/Decoder

We analyse the performance of multicode shift keying modulation in an optical code-division multiplexing network scenario and demonstrate the effectiveness of using a single multiport optical encoder/decoder as a source coding element. We assign a set of codes to each user, and numerically evaluate the system performances, in terms of bit-error rate and spectral efficiency     

Unipolar codes with ideal in-phase cross-correlation for spectral amplitude-coding optical CDMA systems

Unipolar codes with ideal in phase cross-correlation are important in spectral amplitude-coding optical code-division multiple-access (CDMA) systems since these codes eliminate multiuser interference and also suppress the effect of phase-induced intensity noise. However, very little research work has been done on such codes although codes with ideal cross-correlation have been studied for many years. In the paper by Zhou et al.(see Electron. Lett., vol.36, p.728-29, 2000), such a code has been introduced without a clear construction method. In this paper, we firstly review this old code, and then construct two new codes with ideal in-phase cross-correlation in algebraic ways. Both of the proposed new codes are obtained by modifying former codes with ideal cross-correlation. It has been shown that the system performance can be improved significantly by using codes with ideal in-phase cross-correlation instead of the Hadamard code. These codes can also be used in synchronous optical CDMA systems for multiuser interference cancellation.     

Noncoherent spectral optical CDMA system using 1-D subtracted square codes of all transmitters in one optical line terminal

We propose a family of one-dimensional subtracted square codes in the spectral amplitude coding optical code division multiple access system. The proposed codes perform the subtraction and multiplication operations to give one-to-one mappings function, which produces the code sequences of 1-D subtracted square codes. The proposed structure uses one optical line terminal to produce all of the transmitters. This proposed system overcomes the interference from other simultaneous users, known as multiuser interference, and the cross-correlations suppress the phase-induced intensity noise. In numerical simulations using the proposed 1-D subtracted square codes, we show that 83 simultaneous users can be supported at a bit error rate of \(10^{-9}\). This number of simultaneous users in the proposed system using the 1-D subtracted square codes is superior to that in the other systems using the 1-D M sequence codes, 1-D RSQC codes, and 1-D ESP codes. The proposed system using the 1-D subtracted square codes achieves a data transmission rate of 3.2 Gbps.     

Spectral amplitude-coding optical CDMA system using Mach-Zehnder Interferometers

In this paper, we propose a family of newly constructed codes to suppress the phase-induced intensity noise (PIIN) in spectral amplitude-coding (SAC) optical code division multiple access (OCDMA) systems. These new codes are derived from modified prime codes and their cross-correlation is not larger than one. We also present a novel SAC-OCDMA system employing the new codes together with Mach-Zehnder interferometers to eliminate the multi-user interference (MUI). Compared with the systems employing modified quadratic congruence codes (MQC codes), numerical results verify that our proposed system can more effectively suppress the PIIN and eliminate MUI. Hence, the number of simultaneously users and total transmission rate increases significantly.     

Realization of OSW/AWG-based bipolar wavelength–time optical CDMA for wired–wireless transmissions

This study proposes a novel radio-over-fiber (RoF) system using two-dimensional (2-D) optical code-division multiple-access (OCDMA) scheme using pseudorandom (PN) codes for the time-spreading and wavelength-hopping (t-spreading/λ-hopping) codes. The 2-D system is implemented using optical switches (OSWs) and arrayed-waveguide grating (AWG) routers. By constructing 2-D codes using bipolar PN codes rather than unipolar codes provides a significant increase in the maximum permissible number of active radio base stations (RBSs). In general, the phase-induced intensity noise (PIIN) generated at high optical intensities significantly degrades the performance of a conventional multi-wavelength scheme. However, the OSW-based time-spreading method employed in the current 2-D OCDMA scheme effectively suppresses the PIIN effect. Additionally, multiple-access interference (MAI) is suppressed by the use of a wavelength/time balanced detector structure in the network receivers. The numerical evaluation results demonstrate that under PIIN- and MAI-limited conditions, the proposed system outperforms a conventional multi-wavelength OCDMA scheme by using the spectral spreading scheme to suppress beating noise. Especially, the t-spreading encoder/decoder (codec) groups share the same wavelength codec and the overall complexity is reduced and system network becomes more compact.     

改进型多元QC-LDPC码的构造及其在PDM-CO-OFDM系统中的应用

位长度相同的多元LDPC(NB-LDPC)码优于相应的二 元LDPC(B-LDPC)码,但是它的实现复杂度相对较高。为了降低NB- LDPC码的实现复杂度,提高系统的编码增益,利用置换多项式的方法对一般多元准循 环LDPC(NB-QC-LDPC)码进行改进,并将改进后的NB-QC-LDPC码应用于基于偏振复用的 相干光正交频分复用(PDM-CO-OFDM)系统中,详细研究了其传输性能。仿真结果表明:基于GF(4) QC-LDPC 编码的系统性能 明显优于相应的B-QC-LDPC编码的系统性能,而且基于改进型GF(4) QC-LDPC编码的 系统与 一般GF(4) QC-LDPC编码的系统相比,其误码性能可改善0.65dB, 频谱效率提高了2.16bit/s/Hz,抑制信道色散能力和运转复杂度也 均得到了改善。     

Performance Analysis of 2-D Optical Codes with Arbitrary Cross-Correlation Values under the Chip-Asynchronous Assumption

In this letter, the performance of two-dimensional (2-D) optical codes in incoherent optical code-division multiple-access systems is analyzed without the traditional pessimistic chip-synchronous assumption. We apply a combinatorial method for a more accurate analysis, which can be generalized to 2-D optical codes with arbitrary maximum cross-correlation values. As numerical examples, the performances of 2-D optical codes with the maximum cross-correlation values of one and two are compared under the chip-synchronous and chip-asynchronous assumptions     

Design and performance analysis of wavelength/time (W/T) matrix codes for optical CDMA

Two-dimensional (2-D) codes for optical CDMA (OCDMA) are increasingly important because the code set size (cardinality) of such codes is large and the codes have good spectral efficiency, especially when compared to linear or direct sequence codes. As an example, the 2-D codes described in this paper (that use intensity modulation and direct detection, IM/DD) have a cardinality of 32, and their spectral efficiency is /spl sim/0.5 bit/s/Hz when a guard-time is used to avoid intersymbol interference. The cardinality is readily increased to 64-80, using the techniques described in the paper. The next best 2-D codes of comparable cardinality that use IM/DD tend to have a lower spectral efficiency (going like 1/K, where K is the cardinality) because they do not support multiple entries per row or per column of the code matrix. To improve on the spectral efficiency of the codes described in this paper, bipolar codes must be considered. Two-dimensional codes or matrices can be generated from pseudoorthogonal (PSO) sequences by means of simple quasigraphical operations. Important results of this construction are that both the cardinality and the spectral efficiency or information spectral density of the set of matrices is higher than that of the generating set of sequences. The matrices can be interpreted (implemented) as space/time (S/T) or wavelength/time (W/T) matrix codes for OCDMA applications. The resultant matrix codes are robust, have high information spectral density, and are effective wavelength multipliers. This paper describes the design and construction of the matrices; analyzes their performance from a communications viewpoint; describes their use as codes for the asynchronous, concurrent communication of multiple users; and analyzes the bit error rate performance based on capturing and modeling a typical network topology and performing a numerical modeling of the system.     

Hard-Limiting Performance Analysis of 2-D Optical Codes Under the Chip-Asynchronous Assumption

The traditional chip-synchronous assumption used in the analyses of optical codes in optical code-division multiple access gives a pessimistic performance upper bound, while a more realistic chip-asynchronous assumption gives a more accurate performance. It is also known that a hard-limiter can be placed at the front end of an optical decoder to reduce the effects of multiple-access interference and the near-far problem. In this paper, the "hard-limiting" performance of two-dimensional (2-D) optical codes is analyzed under the chip-asynchronous assumption. We apply a Markov-chain method for a more accurate analysis, which can be generalized to 2-D optical codes with arbitrary maximum cross-correlation values. The performance of 2-D optical codes with the hard-limiting and chip-asynchronous assumptions is also compared with the soft-limiting and chip- synchronous assumptions.     

Noncoherent spatial/spectral optical CDMA system with two-dimensional perfect difference codes

In this paper, the family of newly constructed codes, named 2-D perfect difference codes, is proposed to suppress the phase-induced intensity noise (PIIN) in noncoherent spatial/spectral optical code division multiple access (OCDMA) systems. A novel spatial/spectral transceiver structure employing the new codes to eliminate the multiuser interference (MUI) by using the MUI cancellation property of the new codes is also presented. Compared with the systems employing modified quadratic congruence codes (MQC codes) and maximal-area matrices codes (M-matrices codes), numerical results verify that our proposed system can more effectively suppress the PIIN and eliminate MUI. Hence, the number of simultaneous users and total transmission rate increase significantly.     

基于光码柱面的二维地址码相关性分析和码字容量研究

在谱域和时域同时编码的二维OCDMA系统是增加系统容量的主要方案.在一维光码盘和光码环的基础上,设计出直观描述二维λ-t地址码的几何装置-二维光码柱面,直观便捷地描述二维码字结构,给出基于光码柱面的二维码码字相关性分析方法.并根据光码柱面,建立了在光码集本身导出二维码码字容量的分析理论.所得结果与直接引用电通信中的Johnson界得出的结果一致.因此,二维光码柱面给二维的相关性分析和码字容量研究提供了便捷有效的工具.     

Optical spectral amplitude CDMA communication

We report the first demonstration of bipolar coding techniques in the optical spectral domain for incoherent optical code division multiple access (CDMA) communication. Based on the modulation and detection principles that we have developed, the power spectrum of an erbium-doped superfluorescent fiber source was encoded using bipolar codes and decoded using an optical bipolar correlator. A CDMA testbed consisting of two encoders and one decoder was implemented with bulk optics and free-space transmission. Our measurements verify the correlations between the bipolar codewords and demonstrate the rejection of multiple access interference     

Wavelength aware receiver for enhanced 2D OCDMA system performance

A novel receiver for two-dimensional (2D) optical code division multiple access (OCDMA) which utilises the wavelength information of the codes to provide enhanced performance than the regular receiver is presented. The performance improvement increases with the number of wavelengths. Maximal spectral efficiency is doubled, for carrier-hopping prime codes.     

AWG在谱域幅度编码光码分多址系统中的应用研究

分析了谱域幅度编码的光CDMA通信系统的特点及其对编解码器的要求,根据阵列波导光栅的复用和解复用功能,设计了用于该通信系统中的两种阵列波导光栅编解码器。基于修正素数码MQC码,考虑接收机的热噪声和散弹噪声,采用数值分析的方法,研究了谱域幅度编码的光CDMA系统的通信性能。分析结果表明,由于AWG编解码器可以提供足够多的波长数,基于AWG编解码器的谱域光CDMA通信系统具有很好的误码率性能,可以同时容纳更多的用户数。     

Design of Close-to-Capacity Constrained Codes for Multi-Level Optical Recording

We report a new method for designing (M,d, k) constrained codes for use in multi-level optical recording channels. The method allow us to design practical codes, which have simple encoder tables and decoders having fixed window length. The codes presented here for the d = 1 and d = 2 cases, achieve higher storage densities than previously reported codes, and come within 0.3 - 0.7% of capacity.     

Symbol-based turbo codes

We present a new turbo-coding method which parses the input block into n-bit symbols and interleaves on a symbol-by-symbol basis. This is used in conjunction with different modulation techniques to take advantage of tradeoffs between bit error rate performance, code-rate, spectral efficiency, and decoder complexity. The structure of the encoder and decoder of these codes, which We call symbol-based turbo codes, are outlined. The bit error rate performance of a few specific codes are examined. A discussion on decoder complexity is also included. Symbol-based turbo codes are good candidates for low delay transmission of speech and data in spread spectrum communication systems