Optical CDMA System Research Articles

Reduction of the fiber dispersion effects on MAI for long span high-speed OCDMA networks using Diagonal Eigenvalue Unity (DEU) code

In this paper, we study the performance of optical code-division multiple access (OCDMA) systems using Diagonal Eigenvalue Unity (DEU) code under various link parameters. DEU code was constructed based on Jordan block matrix with simple algebraic ways. Four sets of DEU code based on the code weight W and number of users N for the combination (even, even), (even, odd), (odd, odd) and (odd, even) are constructed. This combination gives a DEU more flexibility in code weight selection and free cardinality. The impact of the fiber dispersion effects on the multiple access interference (MAI) is reported using a commercial optical systems simulator Virtual Photonic Instrument (VPI™) version 7.1. The DEU code is characterized mathematically with reported codes which use similar techniques. We analyzed and optimized the data rate, fiber length, and channel spacing in order to reduce the BER without the need to deploy dispersion compensating devices. The performance and optimization of DEU code in OCDMA system are reported. We have demonstrated that, for a high data rate (higher than 2.5Gb/s), even if dispersion compensated devices are not deployed, the BER can be significantly improved when the DEU code desired parameters are selected. We have shown that when compensation dispersion devices are not deployed in the system, there is a tradeoff between the limited dispersion effects and the MAI.

Hybrid analog/digital wavelength-time optical CDMA systems in radio-over-fiber transmissions

This study presents a hybrid analog/digital (A/D) mechanism of two-dimensional (2-D) structure of wavelength-hopping and time-spreading coding optical code-division multiple-access (OCDMA) system f...

Performance Analysis of SAC-OCDMA Systems Adopting Overlapping PPM Schemes

A fertile technique, for increasing single-user throughput while keeping a constraint on the light pulsewidth, is proposed for spectral-amplitude-coding optical code-division multiple-access (SAC-OCDMA) systems. In this technique, two-level <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary overlapping pulse-position modulation ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -OPPM) scheme is adopted and each user is assigned two orthogonal code sequences to represent these two levels. The code sequences are selected from a minimum cross-correlation code set. The bit error rate (BER) of the proposed system is derived, taking into account the effects of phase-induced intensity noise, shot noise, and thermal noise in addition to the multiple-access interference. The BER performance of this system is compared to other systems adopting <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -PPM and OOK schemes under same pulsewidth constraints. Our results reveal that, while keeping the BER well below a prescribed threshold, the proposed <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -OPPM SAC-OCDMA system achieves higher transmission rate as compared to both <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -PPM and OOK SAC-OCDMA systems under same constraints. Specifically the transmission rate of a single user of the proposed system can be increased by about 34.44% as compared to traditional systems.

작은 입력신호를 위한 Two-Dimensional Symmetric Balance Incomplete Block Design Code

작은 입력신호의 spectral-amplitude-code(SAC) optical code-division multiple-access (OCDMA) 시스템에는 nonideal symmetric balance incomplete block design(BIBD) code의 사용이 효율적이나 충분한 사용자를 수용하지 못하는 단점이 있다. 이를 극복하기 위하여 본 논문에서는 ideal BIBD code를 공간 코드로 사용하고 nonideal code를 파장 코드로 사용하는 two-dimensional(2-D) BIBD code를 제안한다. 사용자 수에 따른 bit error-rate(BER) 분석을 통하여 제안하는 2-D BIBD code가 1-D BIBD code에 비하여 최대사용자 수를 현저하게 증가시킬 수 있음을 알 수 있다.

Performance Analysis of Equal-Energy Two-Level OCDMA System Using Generalized Optical Orthogonal Codes

In this paper, we analyze and obtain performance of a multilevel Optical Code Division Multiple Access (OCDMA) system with Variable-Weight Optical Orthogonal Codes (VW-OOCs) under the same-bit-energy assumption. The exact error-probability of this system is derived for the Generalized VW-OOCs (codes with arbitrary cross-correlation) which is necessary for the optimum design of multilevel OCDMA systems. We show that the bit power has an important role on determining the performance of codes with different weights. Furthermore, the results reveal that the performance of low-weight codes depends on the weight of the low-weight codes and the code-weight ratio of two classes. Moreover, our exact analytical model has resulted in more accurate performance analysis than the upper bound in <citerefgrp xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><citeref refid="ref12"/></citerefgrp> . We have found that the accuracy of the upper bound decreases when the number of simultaneously transmitting high-weight codes increases.

Performance Analysis of Dual Unipolar/Bipolar Spectral Code in Optical CDMA Systems

This study analyzes and calculates dual unipolar and bipolar coded configurations of spectral-amplitude-coding opticalcode division multiple access (SAC-OCDMA) systems by using simulation methods. The important feature of theSAC-OCDMA systems is that multiple access interference (MAI) can be eliminated by code sequences of a fixed inphasecross-correlation value. This property can be effectively canceled multiple access interference by using balancedetection schemes. This study uses Walsh-Hadamard codes as signature codes for the unipolar and bipolar schemes.The coder and decoder structures are based on optical filters of fiber Bragg gratings (FBGs). The simulation results ofunipolar/bipolar coding structures are first presented by commercial simulation obtained using OptiSystem software.The simulation results show that the bit error rate (BER) through use of the bipolar coding method is superior to theunipolar scheme, especially when the received effect power is large. When the system needs good performance totransmit multimedia data, we can use bipolar scheme in the network. If the users only transmit voice data, the unipolarmethod can be employed. The eye diagram also shows that the bipolar encoding structure exhibits a wider openingthan the unipolar encoding structure. The flexible implementation of codewords assigns and integratable hardwaredesigns for the scheme with FBGs to realize dual coding OCDMA system is proposed.

Design and Analysis of Generalized Diversity Optical CDMA Systems

In our recently proposed diversity O-CDMA scheme, every user transmitted multiple copies of its optical codeword per data bit of one in order to improve code performance. Our analysis assumed that users were “chip-synchronized” among their transmissions, and the copies of each user's codeword were allocated at different chip (or time-slot) positions, per bit duration, in order to maintain “copy independency” for good code performance. However, copy independency is hard to achieve, especially in short code length. In addition, it is known that code performance can be improved if all simultaneous users are assumed to transmit chip-asynchronously. In this paper, we combine the realistic effects of user asynchronism and copy dependency in the analysis of our diversity O-CDMA scheme and formulate a new, generalized, more accurate performance model. Furthermore, the improvement in copy dependency and code performance due to the use of finer “granularity” in the chip positions allowed for the copies of each user's codeword are studied with the support of computer simulation.

Impact of polarization mode dispersion on the performance of optical CDMA transmission system

The impact of fiber polarization mode dispersion (PMD) on the bit error rate (BER) performance of a direct sequence optical code-division multiple-access system is analyzed by the split-step Fourier method based on the coupled nonlinear Schrödinger equation, the three-dimensional Poincare sphere theory and the Jones matrix method. When the incident pulse's width is bigness than the chip duration, which causes spreading and overlapping of chips and degrades system performance due to increased interchip interference and reduced received optical power conduce cannot decoding or error decoding. When the incident pulse's width is less than the chip duration, good encoding/decoding performance can be achieved.

Cardinality enhancement of spectral/spatial modified double weight code optical code division multi-access system by PIIN suppression

A new two-dimensional (2-D) optical code division multiple access (OCDMA) scheme to increase the achievable system capacity is proposed. The code exhibits good cross-correlation property time and wavelength shift. Performances are analyzed on code size and correlation properties affecting two important system parameters, bit error rate (BER) as a function of cardinality generated and optical power transmission requirement. The proposed system can effectively suppress phase-induced intensity noise (PIIN) and has multi-access interference (MAI) cancellation property. Results in a good agreement indicate that 2-D modified double weight (MDW) offers 163.7% and 336.2% larger cardinality compare to 2-D perfect difference code (PDC) and 2-D modified quadratic congruence (MQC) code. By increasing spatial code (N) and keeps similar code length system performance can be further optimized. 2-D MDW (M=45, N=18) accommodates 252.2% and 18.3% cardinality increment and low effective transmitted power (Psr) at −17.9dBm, compare to 2-D MDW (M=247, N=3) and (M=84, N=9) at 10−9 BER error floor. The architecture of the spectral/spatial MDW OCDMA system with property of MAI cancellation is presented.

Fiber Non-linear Effects in Multiple-wavelengths Optical CDMA Systems

Multi-wavelength Optical Code Division Multiple Access (OCDMA) systems suffer from fiber impairments including non-linear effects (NLE), especially when the number of wavelengths and input power level increase. In this paper, a review of NLE, including self-phase modulation, cross-phase modulation, four wave mixing (FWM), stimulated Brillouin scattering and stimulated Raman scattering on the system performance of OCDMA systems is presented. As some of the non-linearities may have correlated effects on the performance of the system, the relations between these effects are also investigated. Bit error rate results reveal that the most important unwanted effect was caused by FWM.

A Study of Modified Prime Codes Optical CDMA for Wired-Wireless System

In this study, we propose optical code-division multiple-access (OCDMA) network for the radio-over-fiber (RoF) transmissions. The network encoder/decoders (codecs) are structured on the basis of arrayed-waveguide-grating (AWG) routers coded with modified prime codes (MPCs). Performances are numerically evaluated with the effect of phase-induced-intensity-noise (PIIN). It showed that the new code families with lower cross correlation can suppress the intensity noise and cancel out the multiple-access interference (MAI) in balanced detection process effectively and hence improve the system performance. By the proposed MPC-coded OCDMA ROF network codecs, each network requires only two AWG routers to accomplish spectral coding of radio base station (RBS) and decoding of control station (CS), thus, resulting in a simpler and lower cost system. It is possible to accomplish interference- and crosstalk-free optical CDMA system for RoF transmissions.

Simulative Investigation on Spectral Efficiency of Unipolar Codes based OCDMA System using Importance Sampling Technique

This paper analyses the spectral efficiency of Optical Code Division Multiple Access (OCDMA) system using Importance Sampling (IS) technique. We consider three configurations of OCDMA system namely Direct Sequence (DS), Spectral Amplitude Coding (SAC) and Fast Frequency Hopping (FFH) that exploits the Fiber Bragg Gratings (FBG) based encoder/decoder. We evaluate the spectral efficiency of the considered system by taking into consideration the effect of different families of unipolar codes for both coherent and incoherent sources. The results show that the spectral efficiency of OCDMA system with coherent source is higher than the incoherent case. We demonstrate also that DS-OCDMA outperforms both others in terms of spectral efficiency in all conditions.

Performance Analysis of Spectral Amplitude Coding Based OCDMA System with Gain and Splitter Mismatch

This paper presents the practical analysis of the optical code-division multiple-access (O-CDMA) systems based on perfect difference codes. The work carried out use SNR criterion to select the optimal value of avalanche photodiodes (APD) gain and shows how the mismatch in the splitters and gains of the APD used in the transmitters and receivers of network can degrade the BER performance of the system. The investigations also reveal that higher APD gains are not suitable for such systems even at higher powers. The system performance, with consideration of shot noise, thermal noise, bulk and surface leakage currents is also investigated.

A Novel Scheme of Fast-frequency Hopping Optical CDMA System with No-hit-zone Sequence

In traditional fast frequency-hopping OCDMA (FFH-OCDMA) system, beat noise and multiple-access interference are the main performance limitations, and complicated power control must be employed to eliminate the near-far effect. In this paper, a novel scheme of FFH-OCDMA with no-hit-zone sequence is proposed, which is named NHZ FFH-OCDMA. In NHZ FFH-OCDMA, the synchronization among users can be controlled within permissible time delay, and the code cross-correlation for different users equals zero. Therefore, near-far effect can be eliminated. Furthermore, beat noise and multiple-access interference also can be removed. Simulation of eight simultaneous users with dada rate 100 Mbit/s is demonstrated, where the fiber link consists of 50 km single-mode fiber, plus 5 km dispersion compensating fiber. Simulation results show that the near-far problem of NHZ FFH-OCDMA can be eliminated, and complicated power control can be removed. Therefore, this scheme is a good candidate for optical access network.

Optimal 2-D $(n\times m,3,2,1)$-optical Orthogonal Codes

Optical orthogonal codes are commonly used as signature codes for optical code-division multiple access systems. So far, research on 2-D optical orthogonal codes has mainly concentrated on the same autocorrelation and cross-correlation constraints. In this paper, we are concerned about optimal 2-D optical orthogonal codes with the autocorrelation λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> and the cross-correlation 1. Some combinatorial constructions for 2-D ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> × <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> ,λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> ,1) -optical orthogonal codes are presented. When <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> =3 and λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> =2, the exact number of codewords of an optimal 2-D ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> × <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> ,3,2,1)-optical orthogonal code is determined for any positive integers <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> ≡ 0,1,3,6,9,10 (mod 12) and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> ≡ 2(mod 4).

Reducing BER of spectral-amplitude coding optical code-division multiple-access systems by single photodiode detection technique

In this paper, we present a single photodiode detection (SPD) technique for spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems. The proposed technique eliminates both phase-induced intensity noise (PIIN) and multiple-access interference (MAI) in the optical domain. Analytical results show that for 35 simultaneous users transmitting at data rate of 622 Mbps, the bit-error rate (BER) = 1.4×10−28 for SPD technique is much better compared to 9.3×10−6 and 9.6×10−3 for the modified-AND as well as the AND detection techniques, respectively. Moreover, we verified the improved performance afforded by the proposed technique using data transmission simulations.

Analysis of the Performance of Optical Code-Division Multiple-Access System (OCDMA), Operating with Gold Codes under Nonlinear Effects

A numerical simulation study of the performance of encoding and decoding of short optical pulse in OCDMA (Optical Code Division Multiple Access) systems under non-linear optical effects is presented. The performance of encoding and decoding short pulses is obtained through use of device FBG (fiber Bragg grating) where the codes are inserted through discrete jumps in the optical phase (±π). The multiuser interference is also the object of the present study, where a figure of merit (interference figure) is used to quantify the interference in multiuser auto and cross correlation. We evaluate the dependence of the multiuser interference for the coupling constant of FBG. Finally, the interference inserted in the autocorrelation due to nonlinear effects generated in the nonlinear switching of the coded pulse in a dual core nonlinear directional coupler is examined, where temporal broadening of pulses decoded is observed.

A New Family of Optical Codes Based on Complementary Theory for OCDMA System

A new family of optical codes for Optical Code-division Multiple Access (OCDMA) systems, named as Optical Complementary Codes (OCCs), is proposed in this paper. The constructions of these codes consist of multiple sub-codes, and the codes have an auto-correlation interference constraint as 0 and a cross-correlation interference constraint as 1. Compared with conventional optical codes such as OPCs, OOCs and 2-D OOCs, the OCC has a shorter code length and higher code efficiency with better correlation property.

SOA/SPD-based incoherent SAC-OCDMA system at 9&lt;I&gt;×&lt;/I&gt;5Gbps

To boost the performance of spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems, the need for an effective solution to diminish phase-induced intensity noise (PIIN) is becoming progressively more crucial. In this letter, two PIIN suppression approaches: semiconductor optical amplifier (SOA)-based noise cleaning, and single photodiode detection (SPD) are employed. The performance of the hybrid SOA/SPD scheme is validated through simulation experiments. Our results show that SOA/SPD scheme remarkably improves the performance and increases the throughput of SAC-OCDMA system.

Performance Analysis of Optical Code Division Multiplex System

This paper presents the Pseudo-Orthogonal Code generator for Optical Code Division Multiple Access (OCDMA) system which helps to reduce the need of bandwidth expansion and improve spectral efficiency. In this paper we investigate the performance of multi-user OCDMA system to achieve data rate more than 1 Tbit/s.