Performance Of Optical Code Division Multiple Access System Research Articles

Performance Analysis of New 2D Spatial OCDMA Encoding based on HG Modes in Multicore Fiber

This paper presents a pioneering 2D spatial Optical Code-Division Multiple Access (OCDMA) encoding system that exploits Mode Division Multiplexing (MDM) and Multicore Fiber (MCF) technologies. This innovative approach utilizes two spatial dimensions to enhance the performance and security of OCDMA systems. In the first dimension, we employ Hermite-Gaussian modes (HG00, HG01, HG11) to modulate each user's signal individually. This unique approach offers a robust means of data transmission while ensuring minimal interference among users. The second-dimension leverages MCF encoding, introducing two incoherent OCDMA codes: the Zero Cross Correlation (ZCC) code (λc=0) and the ZFD code (λc=1). These codes are thoughtfully designed and simulated, taking into account their cross-correlation properties to guarantee minimal interference and heightened data security. To assess the efficiency of this novel OCDMA encoding system, we implemented simulations with three active users using the Opti system software. At the transmitter end, each user's signal is modulated individually by their designated HG mode (HG00, HG01, HG11), resulting in separate channels. Subsequently, at the multicore fiber, each user's data is encoded with a unique code-word, and they are directed through specific core groups, ensuring data isolation and integrity. In this paper, the BER and eye pattern are examined with respect to different parameters such as data rate and distance. At a distance of 5 km and data rate of 10 Gbit/s, a BER value around 10-70 is achieved.

Performance Analysis of New 2D Spatial OCDMA Encoding based on HG Modes in Multicore Fiber

This paper presents a pioneering 2D spatial Optical Code-Division Multiple Access (OCDMA) encoding system that exploits Mode Division Multiplexing (MDM) and Multicore Fiber (MCF) technologies. This innovative approach utilizes two spatial dimensions to enhance the performance and security of OCDMA systems. In the first dimension, we employ Hermite-Gaussian modes (HG00, HG01, HG11) to modulate each user's signal individually. This unique approach offers a robust means of data transmission while ensuring minimal interference among users. The second-dimension leverages MCF encoding, introducing two incoherent OCDMA codes: the Zero Cross Correlation (ZCC) code (λc=0) and the ZFD code (λc=1). These codes are thoughtfully designed and simulated, taking into account their cross-correlation properties to guarantee minimal interference and heightened data security. To assess the efficiency of this novel OCDMA encoding system, we implemented simulations with three active users using the Opti system software. At the transmitter end, each user's signal is modulated individually by their designated HG mode (HG00, HG01, HG11), resulting in separate channels. Subsequently, at the multicore fiber, each user's data is encoded with a unique code-word, and they are directed through specific core groups, ensuring data isolation and integrity. In this paper, the BER and eye pattern are examined with respect to different parameters such as data rate and distance. At a distance of 5 km and data rate of 10 Gbit/s, a BER value around 10-70 is achieved.

Impact of systematically constructed nonorthogonal code shift keying for optical code division multiple access

It is desirable to provide Optical Code Division Multiple Access (OCDMA) systems for practical use in optical wireless communication application systems. Because the data transmission efficiency of the conventional OCDMA system is relatively low, one of the issues encountered with the OCDMA system is increasing the data transmission efficiency. This study proposes the nonorthogonal CSK system in order to clarify the performance improvement of the proposed system on the OCDMA system. Our proposed nonorthogonal CSK system systematically constructs nonorthogonal codes. This paper analyzes the system performances of the proposed system considering the scintillation, background noise, and multiple access interferences to evaluate the fundamental performance of the proposed system. The numerical results show that the proposed system outperforms the conventional OCDMA systems. Our obtained results that the systematically constructed nonorthogonal code is effective for enhancing OCDMA system performance is a useful finding for future research approaches.

Cardinality Enhancement of SAC-OCDMA Systems Using New Diagonal Double Weight Code

Optical code division multiple access (OCDMA) provides another dimension to multiple access systems, in which each user is assigned a unique code. This allows each subscriber to simultaneously access the medium without any contention. However, simultaneous access of multiple users introduce multiple access interference (MAI) which primarily deteriorates the performance of OCDMA systems. This paper proposes a new code called diagonal double weight (DDW) code to elevate the performance and cardinality of spectral amplitude coding (SAC) OCDMA systems. Performance of our proposed code is evaluated using comprehensive analytical analysis followed by simulation analysis. Examination of bit error rate shows that DDW code along with single photodiode detection technique provides efficient performance, with added benefits of simplified design, large cardinality and ease of implementation.

Investigation of 2D-WH/TS OCDMA Code Stability in Systems with SOA-Based Device

This paper investigates for the first time how the implementation of semiconductor optical amplifier (SOA)-based devices in photonic networks can negatively impact the integrity of two-dimensional wavelength-hopping time-spreading (2D-WH/TS) optical code-division multiple access (OCDMA) codes based on multi-wavelength picosecond code carriers. It is demonstrated and confirmed by simulations that the influence of an SOA under driving currents of 50 mA to 250 mA causes a 0.08 to 0.8 nm multi-wavelength picosecond code carriers’ wavelength redshift. The results obtained are then used to calculate the degradation of OCDMA system performance in terms of the probability of error Pe and the decrease in the number of simultaneous users. It is shown that, when the SOA-induced 0.8 nm code carriers redshift becomes equal to the code carries wavelength channel spacing, the (8,53)-OCDMA system performs only as a (7,53)-OCDMA system, and the number of simultaneous users drops from 14 to 10 or 84 to 74 with the forward error correction (FEC) Pe of 10−9, respectively. The impact of the 0.8 nm redshift is then shown on a (4,53)-OCDMA system, where it causes a drop in the number of simultaneous users from 4 to 3 or 37 to 24 with the FEC Pe of 10−9, respectively.

BER performance of OCDMA system based on optimised 2D PhC passive encoder

This study introduces an accurate design and optimisation of a passive optical code division multiple access (OCDMA) network encoder using the coupled cavity waveguide (CCW) as an optical delay line. Such CCW has the capability of providing more time delay with minimum encoder size. The proposed design and analysis are based on the two-dimensional (2D) photonic crystal (PhC) structure. Additionally, two different 2D-PhC structures are studied, in which a silicon material with an effective refractive index of 3.487 is used. The first structure is a silicon bar in air background, whereas the second one is air holes in a silicon substrate. Furthermore, the behaviour of the proposed 2D-PhC structures is studied over the wavelength, ranging from 1300 to 1600 nm. Since the structure geometry is simple with a clear operating principle, it is sufficient to use in the photonic integrated circuits. Moreover, the performance analysis of such design is investigated in terms of the bit error rate (BER) calculations. Finally, the results showed that a 21% BER performance enhancement was achieved using the optimised silicon bars in air background encoder model and this model can be utilised for the multimedia applications in the OCDMA networks.

Performance analysis of a new OCFHC/QCC vis‐a‐vis synchronous PC/OOC code using photon count approach

In this study, the performance of one-coincidence frequency hopping code/quadratic congruence code (OCFHC/QCC) has been analysed and compared with an existing code. The error probabilities of an eight-user optical code division multiple access (OCDMA) system are 4.7934 × 10 − 9 and 5.9497 × 10 − 10 for the synchronous prime code/optical orthogonal code (PC/OOC) and OCFHC/QCC, respectively, at the received power level −15 dBm and data rate 1 Gbps. The improvement in the performance is of the order of 10 − 1 which becomes better if the received power level increases beyond −15 dBm. In addition, the effect of variation in code weight, code length and number of wavelengths of the OCFHC/QCC code on the performance of the OCDMA system is also studied. OCFHC/QCC has a simple design methodology, flexibility in choosing the number of wavelengths, large cardinality and superior performance than the synchronous PC/OOC. Furthermore, the performance of the OCFHC/QCC is also analysed in the atmospheric channel. Based on the analysis, it is concluded that this code should be preferred for local area network, multicode keying, and wireless optical communication.

The effect of total noise on two-dimension OCDMA codes

In this research, we evaluate the performance of total noise effect on two dimension (2-D) optical code-division multiple access (OCDMA) performance systems using 2-D Modified Double Weight MDW under various link parameters. The impact of the multi-access interference (MAI) and other noise effect on the system performance. The 2-D MDW is compared mathematically with other codes which use similar techniques. We analyzed and optimized the data rate and effective receive power. The performance and optimization of MDW code in OCDMA system are reported, the bit error rate (BER) can be significantly improved when the 2-D MDW code desired parameters are selected especially the cross correlation properties. It reduces the MAI in the system compensate BER and phase-induced intensity noise (PIIN) in incoherent OCDMA The analysis permits a thorough understanding of PIIN, shot and thermal noises impact on 2-D MDW OCDMA system performance. PIIN is the main noise factor in the OCDMA network.

Performance enhancement of OCDMA systems for LAN consideration

In this study, the performance of optical code-division-multiple-access (OCDMA) systems using 2D optical codes, taking into account an optical channel in local area network context is investigated. The authors demonstrate that one can enhance the 3-dB multi-mode fibre baseband bandwidth up to 4 GHz by exciting only two mode groups with the optimal axial launching. It has been demonstrated, that the OCDMA system performance can achieve a very low bit-error-rates in the range of −9 dBm. Furthermore, a large number of simultaneous users can be supported. In the authors’ treatment, the effect of both multiple access interference and modal dispersion are considered. Nonetheless, an OCDMA successive interference cancellation receiver is used to foster a better system performance.

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.

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.

Effect of Variations in Environmental Temperature on 2D-WH/TS OCDMA Code Performance

Extensive research has been carried out on the performance investigation of two-dimensional wavelength hopping/time spreading optical code division multiple access (OCDMA) codes, which are based on picosecond multiwavelength pulses under the influence of temperature variations resulting from changing environmental conditions. Equations have been derived to theoretically evaluate the extent to which such temperature changes will degrade the overall OCDMA system performance. To mitigate these negative effects on the OCDMA system, several steps have been introduced to improve the code robustness. System design improvements have then been investigated. We also found they would help to improve the spectral efficiency.

Performance Improving of OCDMA System Using 2-D Optical Codes With Optical SIC Receiver

In this paper, we have studied the probability of error of optical code division multiple access (OCDMA) system using 2-D optical codes, namely prime hop and hybrid codes with a probability distribution approach. In order to increase the OCDMA system performance and increase the number of simultaneous users in the system, we have investigated the system when two different receivers are employed, namely, OCDMA serial interference cancellation (SIC) receivers and OCDMA correlation conventional receiver (CCR). Comparison in terms of OCDMA system's performance between these two receivers has been reported. In order to obtain the optimum OCDMA system's performance, we have studied several optical SIC receiver structures. Optimum choice of the number of stages in the SIC receiver and the threshold value on each stage has been reported.

Performance of OCDMA system with FEC based on interference statistical distribution analysis

AbstractThe optical code division multiple access (OCDMA) technique has been investigated for several years as a promising alternative to provide multiple access in high speed optical networks. However, due to the use of binary on off keying (OOK) modulation, an inherent main performance limitation is multiple access interference (MAI), following a specific distribution. In order to reduce errors induced by MAI, it is necessary to take into account this specific statistic when applying forward error correction (FEC) with soft decision decoding. In this paper, we analyse the MAI distribution in order to determine FEC soft decoding calculation rules. The study is performed for a low density parity check (LDPC) code scheme over an OCDMA system using two‐dimensional (2‐D) OCDMA spreading codes. The a priori information required for soft decoder initialisation is calculated according to the specific OCDMA channel statistic. The enhancement provided by the decoding algorithm adaptation confirms that it is important to take into account the specific MAI distribution as described in this paper. Finally, we show that, despite the loss of available data rate linked to the addition of redundancy, the data rates per user can significantly be increased thanks to this efficient error correction scheme. Copyright © 2009 John Wiley & Sons, Ltd.

Performance enhancement of perfect difference codes with spectral amplitude coding using sub‐optimal decision threshold

AbstractThis paper applies perfect difference code (PDC) to develop an optical code‐division multiple‐access (OCDMA) system with spectral amplitude coding (SAC). The differential receiver of the proposed systems exploits the cross‐correlation property of PDC to remove the multiple‐access interference (MAI) without reducing the power of the received signal. The threshold applied in the data decision process has a crucial influence on the bit error rate (BER). Hence, this study investigates the effects of several different decision rules. The numerical results show that the BERs of the synchronous OCDMA system using PDC proposed by Weng and Wu are 100 times and 17 times greater than those of the current system for code sizes of 183 and 307, respectively, under conditions of equal power budgets. To achieve the same BERs, the theoretical analysis reveals that the transmission power required by the Weng's system is around k/(k‐1) times greater than that of the current system, where k denotes the code weight of the signature code employed. Additionally, under conditions of reliable communication (i.e. BER ≤ 10−9), the capacity of the proposed system is almost one and half times greater than that of Weng's system. Regarding the data decision threshold, this study proposes a realisable sub‐optimal decision threshold as a replacement for the optimal decision threshold. The performance of the proposed system using this sub‐optimal threshold is found to be only marginally poorer than that obtained when the optimal decision threshold is employed. Therefore, the proposed sub‐optimal threshold provides a suitable means of improving the system performance of SAC OCDMA systems using signature codes with a fixed in‐phase cross‐correlation property. Copyright © 2007 John Wiley & Sons, Ltd.

On error-correction coding for CDMA PON

Optical-code-division multiple access (OCDMA) has been investigated as a multiple-access technique for a long time, but so far, it has not reached any practical success. We investigate the performance of low-complexity OCDMA systems with a realistic model of noise and interference; the main limitation of the system is beat noise. To improve the performance, we consider forward-error correction (FEC) and soft decoding using standard error-correcting codes. The achievable error rates are evaluated using simulations and show significant improvement when FEC is used. The results also show that frequency-hopping systems perform better than temporally coded systems when beat noise is taken into account.

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.

Performance analysis of an optical CDMA system with non-ideal optical hard-limiters

Abstract Performance analysis of an incoherent time spread on–off keying optical Code Division Multiple Access (O-CDMA) system with non-ideal optical hard-limiters is reported in this paper. For the first time we made an approximation of the properties of an implemented passive optical hard-limiter. It was named as a non-ideal optical hard-limiter and its non-ideal parameter was defined. Shortened optical orthogonal codes generated by an extended set technique achieved multiple accesses in the investigated O-CDMA system. Performance improvement of O-CDMA system for the cases of O-CDMA receiver without any, with one and with two optical hard-limiters is shown by simulation of the signal-to-interference ratio and the bit error probability. The influence of non-ideal properties of the optical hard-limiter upon the performance of O-CDMA system is studied.