OCDMA System Research Articles

An Approach for Increasing User Capacity of OCDMA System Based on Vernier Effect

A structure of serially coupled dumbbell microring resonator (SCDMRR) is proposed based on Vernier effects to obtain wider free spectral range (FSR), and a new kind of two-dimensional optical en/decoder is designed taking advantage of the SCDMRR. Numerical simulations are done to analyze reflection spectrum of the SCDMRR and test performance of the proposed en/decoder according to the coupled mode theory. In addition, the coupling coefficients of both ring-bus and ring-ring are optimized to suppress the spurious mode. Furthermore, a comparison is performed between the en/decoder based on SCDMRRs and the en/decoder using ordinarily coupled identical three-order-ring resonators (OCITRR). The results show that the FSR is 13 nm for SCDMRR with the ring radius of 40–30–40 μm, which is about four to five times larger than that of OCITRR. Such FSR will contain more column numbers of parallel-coupled MRR and the code cardinality generated by the proposed device is 3.43E17. For the SCDMRR-based en/decoder, the peak to wing ratio (P/W) of autocorrelation signal and peak power ratio (P/C) between the auto-/cross-correlations are 6.39 and 8.71, which have risen by approximately 33% and 8% against that of en/decoder based on OCITRR, respectively.

Variable-Weight Optical Code Division Multiple Access System using Different Detection Schemes

In this paper a Variable Weight OCDMA (VWOCDMA) system using KS code with Direct Decoding (DD), Complementary Subtraction (CS) and AND subtraction detections is proposed. System performance is analyzed using mathematical approximation and software simulation. In mathematical analysis, the effects of Phase-Induced Intensity Noise, shot noise and thermal noise are taken into account. Bit Error Rate of different users is plotted as a function of received optical power per chip with varying the bit rates and number of active users. It has been shown that for different bit rates and number of users, system using DD has better performance than the system applying CS and AND detection. Using DD scheme, the number of active users are 100 while this value is 27 and 25 in case of using CS and AND detection, respectively, when the received optical power per chip is –10 dBm.

Understanding of FWM Behavior in 2-D Time-Spreading Wavelength-Hopping OCDMA Systems

Understanding of FWM Behavior in 2-D Time-Spreading Wavelength-Hopping OCDMA Systems

Generalized optical code construction for enhanced and Modified Double Weight like codes without mapping for SAC–OCDMA systems

Abstract Double Weight (DW) code family is one of the coding schemes proposed for Spectral Amplitude Coding–Optical Code Division Multiple Access (SAC–OCDMA) systems. Modified Double Weight (MDW) code for even weights and Enhanced Double Weight (EDW) code for odd weights are two algorithms extending the use of DW code for SAC–OCDMA systems. The above mentioned codes use mapping technique to provide codes for higher number of users. A new generalized algorithm to construct EDW and MDW like codes without mapping for any weight greater than 2 is proposed. A single code construction algorithm gives same length increment, Bit Error Rate ( BER ) calculation and other properties for all weights greater than 2. Algorithm first constructs a generalized basic matrix which is repeated in a different way to produce the codes for all users (different from mapping). The generalized code is analysed for BER using balanced detection and direct detection techniques.

Simulation and Analysis of Optimum Golomb Ruler Based 2D Codes for OCDMA System

The need for high speed communications networks has led the research communities and industry to develop reliable, scalable transatlantic and transpacific fiber-optic communication links. In this paper the optimum Golomb ruler based 2D OCDMA codes has been demonstrated. An OCDMA system based on the discussed 2D codes is designed and simulated on Optisystem. The encoder and decoder structure of OCDMA system have been designed using filter and time delays. Further the performance is analysed for various parameter such as bit rate, number of users, BER (Bit Error Rate), quality factor, eye diagram and signal diagram. The system is analyzed for up to 18 users at 1 Gbps and 1.25 Gbps bit rate.

An Inclusive Comparison in LAN Environment between Conventional and Hybrid Methods for Spectral Amplitude Coding Optical CDMA Systems

In this paper, performance analysis of conventional spectral amplitude coding (CSAC) with hybrid (HSAC) for OCDMA system is investigated in local area network (LAN) environment. The CSAC is built based on arithmetic sequence with simple algebraic ways. The HSAC technique is used in which spectral amplitude coding (SAC) combined with wavelength division multiplexing (WDM) to effectively reduce multiple access interference (MAI) and mitigate the influence of phase induced intensity noise (PIIN) arising in photodetecting process. The main idea is to construct the code sequences in SAC domain then repeat it diagonally in the wavelength domain as groups which maintains the same cardinality of a given code weight. Results show that HSAC outperforms CSAC when the number of active users is high due to its better correlation properties. It has been shown that the HSAC can suppress intensity noise effectively and improve the bandwidth utilization significantly up to 4.2 nm.

Theoretical Studies of Ultrashort Light Pulse Spectrally-Phase-Encoded OCDMA System Using Power-Cubic Optical Nonlinear Preprocessor

In this paper, a spectral-phase-encoded ultrashort light pulse optical code division multiple access (SPE-OCDMA) system employing a novel nonlinear power-cubic optical preprocessor at its receiver's front end is theoretically investigated. The system's mathematical model and the statistical distribution of the decision variable $Y$ , prior to the decision module of the receiver, are discussed. The first three moments of the random decision variable $Y$ are obtained in the context of the above OCDMA system and subsequently used in an appropriate Log-Pearson type 3 (LP3) distribution to represent the random decision variable $Y$ . Multiple access interference (MAI) and amplified spontaneous emission (ASE) noises are taken into account to obtain the bit error rate of the system. Furthermore, the effects of shot and thermal noises are also included in the system performance modeling. In this context, performance comparison of the system based on power-cubic preprocessor and systems employing power-quadratic nonlinear optical thresholders, such as second harmonic generation crystals, are discussed. Finally, through numerical calculations under various conditions, we show the superiority of power-cubic systems, especially in high power regime where MAI is the dominant noise.

Performance Comparison of Various Coding & Detection Schemes in OCDMA System

Performance Comparison of Various Coding & Detection Schemes in OCDMA System

Analysis of the Performance of a PAM/PPM/OOK System Operating with OCDMA, under Nonlinear Optical Effects in Optical Fiber Propagation

AbstractIn this article, we present a numerical simulation study of encoding, decoding and propagation performance of short optical pulses and words with modulations OOK, PAM and PPM in OCDMA systems (Optical Code Division Multiple Access). The encoding and decoding of short pulses are obtained through fiber Bragg grating(FBG – FBG optical) devices, where the codes are inserted through discrete jumps in the optical phase (±

Development of SAC–OCDMA in FSO with multi-wavelength laser source

We propose and demonstrate a free space optical network, based on spectral amplitude coding optical code division multiple access (SAC–OCDMA) with a multi-wavelength laser source. A detailed theoretical analysis that represents the characteristics of SAC–OCDMA system was developed. In addition to the impact of turbulence, influences of several system noises such as optical beat interference (OBI), relative intensity noise, and receiver noises, have been studied. From the numerical results, it was found that the influence of OBI is more dominant, especially at higher received power. Two different codes, namely, modified quadratic congruence and modified double weight, are then compared with the latter which provides better performance. A transmission distance of 2.6km with 10 users and an 8cm aperture diameter is advisable whenever the turbulence is moderate. These results can be improved when a beam divergence smaller than 1mrad is utilized.

Mathematical Analysis of Different Noises for 3D Perfect Difference Codes based OCDMA System

Mathematical Analysis of Different Noises for 3D Perfect Difference Codes based OCDMA System

Development of OCDMA system based on Flexible Cross Correlation (FCC) code with OFDM modulation

The performance of the OCDMA systems is governed by numerous quantitative parameters such as the data rate, simultaneous number of users, the powers of transmitter and receiver, and the type of codes. This paper analyzes the performance of the OCDMA system using OFDM technique to enhance the channel data rate, to save power and increase the number of user of OSCDMA systems compared with previous hybrid subcarrier multiplexing/optical spectrum code division multiplexing (SCM/OSCDM) system. The average received signal to noise ratio (SNR) with the nonlinearity of subcarriers is derived. The theoretical results have been evaluated based on BER and number of users as well as amount of power saved. The proposed system gave better performance and save around −6dBm of the power as well as increase the number of users twice compare to SCM/OCDMA system. In addition it is robust against interference and much more spectrally efficient than SCM/OCDMA system. The system was designed based on Flexible Cross Correlation (FCC) code which is easier construction, less complexity of encoder/decoder design and flexible in-phase cross-correlation for uncomplicated to implement using Fiber Bragg Gratings (FBGs) for the OCDMA systems for any number of users and weights. The OCDMA–FCC_OFDM improves the number of users (cardinality) 108% compare to SCM/ODCMA–FCC system.

Improving OCDMA System via Combination of OFDM/OCDMA Techniques

This paper proposes a single sideband orthogonal frequency division multiplexing (SSB-OFDM) incorporated with spectral amplitude coding (SAC) optical code division multiple accesses (SAC-OCDMA). This scheme is a new technique designed to enhance overall OCDMA system performance. The system indicates good result in terms of higher transmission data rates and long distance according to conventional OCDMA system. Moreover, the results show that the presented system gives good performance based on constellation diagram distance and BER. The transceiver bit error rate (BER) for SSB improved by 10-10 compared to double side band for distances up to 50 km at 10 Gbps.

Investigating wavelength allocation and suitable modulation format for 2-d wavelength/time and 3-d wavelength/time/space codes in order to enhance system performance

In this paper the design, implementation and performance analysis of 2-dimensional and 3-dimensional wavelength/time/space codes in OCDMA system have been presented using folding of Golomb rulers. It is shown that BER increases with increase in number of active users when number of decoder’s increases on receiver side. Further, the optical encoding/decoding for 90 km length of fiber without amplification has been reported with good quality factor (Q) with 32 users while maintaining bit-error rate (BER) < 1e-11 for the correctly decoded signal. The comparison of 3-D single pulse differential detection (SPDD) with designed 2-D wavelength-time (W/T) matrix codes shows that the 3-D SPDD codes perform significantly better.

English

In this paper, a third dimension i.e. space is added in earlier proposed Wavelength/Time Multiple Pulses per Row (W/T MPR) codes. An OCDMA system is designed using the 3D W/T/S MPR codes by using zero transmission length of the system. The performance of this system is analyzed at different data rates. The simulation has been carried out on OPTSIM.

Utilization of balanced detection with optical hard-limiters in T/W OCDMA system

In this paper, we utilize optical hard-limiters to further enhance the system performance in balanced detection T/W optical CDMA system. In T/W optical CDMA systems, it had been investigated that the balanced detection scheme is not superior to the OOK scheme because of the adverse impact of beat noise. The employment of optical hard-limiter is an effective way to alleviate the deteriorating effect of beat noise. The carrier-hopping prime code is utilized as signature sequences whose out of phase autocorrelation is zero and the cross-correlation is at most one. Due to the orthogonality of signature sequence, the correlator of shifted version of carrier-hopping prime code is utilized in the receiver. The numerical results reveal that our proposed scheme can greatly reduce the error floor; also it is superior to that using OOK scheme with optical hard-limiter. Most important of all, our proposed scheme has fixed and optimum thresholds which do not vary with system parameters; and this will lead to dynamic estimation of optimal thresholds unnecessary in the receiver.

Enhancing the Performance of Coherent Sources SAC OCDMA Networks via Spatial Multiplexing

The beating of two or more lasers that have the same or a finite difference in the central frequencies, is the main source of noise in spectral amplitude coding optical code division multiple access (SAC OCDMA) systems. In this paper we adopt a spatial multiplexing (SM) scheme for SAC OCDMA systems to mitigate this beat noise. The results show that for different code weights and different data rates SM SAC can support a larger number of users than the conventional SAC for all different laser source configurations. However, SM SAC requires a more complex system than the conventional SAC, and almost twice as much optical component.

Constructions for (2×n,{2,2},1)-2D optical orthogonal codes

Optical orthogonal codes (OOCs) have been designed for OCDMA system. Most researches on 2D OOCs have concentrated on the codes with one-pulse per wavelength (OPPW) or at most one-pulse per wavelength (AM-OPPW). However, the OPPW or AM-OPPW 2D OOCs are so sparse that reduce the bandwidth utilization, so the more pulses per wavelength cases should be used. A family of two-dimensional optical orthogonal code (2×n,4,1)-2D OOCs with two-pulses per wavelength is proposed in this paper. A tight upper bound on the maximum possible code size and some direct constructions of almost optimal (2×n,{2,2},1)-2D OOCs with n=q,2q,3q,4q, where q is an odd prime, are given.

Implementation and performance analysis of three dimensional (3D) space/wavelength/time single pulse per plane codes with direct detection

In this paper, we present space/wavelength/time single pulse per plane (SPP) codes with direct detection (SPPDD) and implemented it as two dimensional codes by using W2T scheme. We analyze these codes by varying the number of space channels (S) and keeping other two dimensions, wavelength (W) and time (T) constant and report that it gives better results when (W>S). It is found that the space channels S=2 and S=3 provide better BER rate than other space channels and also analyze these 3D codes by using different data modulation formats. It is found that OCDMA system with NRZ data modulation format performs better than RZ.

A Novel Multi User Interference Cancellation Scheme for Synchronous OCDMA Networks

In this paper we have proposed a novel multi-user interference (MUI) cancellation scheme for OCDMA systems employing prime code families. We have also discussed in detail the feasibility and implementation of this novel scheme. In addition, the performance analysis of a few prime code families are evaluated experimentally using this newly proposed MUI cancellation scheme. The results reveal that the proposed scheme is easy to implement and totally removes the MUI effect.