Optical CDMA; Optical Parallel Interference Cancellation Using the Lowest Threshold Value

Multiple Access Interference (MAI) is the major reason for the system degradation in the Optical Code Division Multiple Access (OCDMA). MAI increases with the number of simultaneous users, resulting in deterioration in the performance and limits the maximum number of simultaneous users. Optical Hard Limiter (OHL) is known to improve the performance of the conventional OCDMA system. However, in the present of other sources of noise, the improvement is not considerable. Moreover, the need for dynamic threshold value in the conventional OCDMA receiver to recover the data is very demanding requirement particularly in the high speed LANs. To overcome these limitations, some studies have been conducted on the Optical Parallel Interference Cancellation (OPIC) through this paper. OHL is placed in front of the receiver side to mitigate the effect of MAI. The study focuses on the lowest threshold value i.e. Th=1. The results are compared to the conventional OCDMA and it shows that, OHL is effective to reduce the power of MAI and a better performance can be obtained by selecting the smallest threshold value.

The performance of 2D wavelength/time optical code division multiple access (OCDMA) system is adversely affected by the presence of noise at its physical layer. It is present in the form of Multiple Access Interference (MAI) and beat noise in OCDMA systems and degrades its performance. In this paper an attempt has been made to determine as well as to mitigate the effect of noise using either Optical Hard Limiter (OHL) or Coherent detection technique for a system employing prime sequence permutations over time spreading optical orthogonal codes (OOCs). Investigations reveal that performance of system is severely affected by noise and it can be improved by using coherent detection as well as hard limiter. Specifically for this PC/OOC coding technique, it has been reported in the results that coherent detection for reducing the noise outperforms the use of optical hard limiter.

We compared the theoretical bit-error-rate (BER) and throughput performance limits of 2-D time-wavelength and coherent time-spreading optical code division multiple access (OCDMA) communication systems. The results show that the BER performance of the coherent time spreading OCDMA scheme is much superior to 2-D time wavelength scheme in the multiple access interference (MAI) noise limited case without considering beat noise, and the beat noise affects the system performance seriously and appears as a dominant source of noise for the two kinds of OCDMA systems. Nevertheless, the 2-D time wavelength scheme has better tolerance to beat noise than coherent time spreading OCDMA scheme, and the superiority is more apparent with the increasing of the code length N. While the coherent time spreading scheme has higher peak throughput, and it supports a higher throughput than the 2-D time wavelength scheme at higher offered loads.

Optical CDMA systems have received much attention in fiber optic networks where the high-speed, the huge band width, the secure and immune communication, asynchronous and simultaneous access for multiple users on the same channel. Those features nominate strongly Optical CDMA for future optical multimedia networks. However, multiple access interference (MAI), which is originated from other simultaneous users, severely limits the capacity of the system. In this paper, an efficient transceiver architecture has been proposed using MAI cancellation to improve the performance of the existence simple transceiver without MAI cancellation. The strategy of the proposed transceiver is based on an estimation and cancellation of MAI in Optical CDMA system with employing a new spreading code named double padded modified prime code (DPMPC) and an efficient pulse-position modulation (PPM) scheme. In addition, for further improvement of the bit-error rate (BER) performance for the proposed transceiver Manchester coding (source coding) is used in signaling the transmitted data. The MAI estimation is achieved by pre-reserving one of optical spreading code sequences at the receiver based on the correlation property of the DPMPC. The proposed receiver estimates the interference and cancels it out from the received signal after the photo-detection process. The performance of the proposed transceiver architecture and its improvement will be compared with the performance of simple transceiver without MAI cancellation. The performance of various codes like modified prime code (MPC), new modified prime code (NMPC) are applied and compared with the proposed DPMPC to demonstrate its potential. An upper bound on the BER for the proposed system is derived and compared with a lower bound on the BER from the system without cancellation. The simulated computer results reveal that the performance, in terms of the BER, of the proposed system is significance improved compared with that of the system without cancellation.

A detailed analysis of the scalability of two-dimensional optical codes is presented and two network deployment architectures for optical code division multiple access (OCDMA) are discussed. We present the architecture and code design for a highly scalable, 2.5 Gb/s per user OCDMA system. The system is scalable to 100 potential and more than 10 simultaneous users, each with BER of less than 10-9. The system architecture uses fast wavelength-hopping, time-spreading codes. Unlike phase sensitive coherent OCDMA systems, this architecture utilizes standard on-off-keyed optical pulses allocated in the time and wavelength domains. This incoherent OCDMA approach is compatible with existing WDM optical networks and utilizes off-the-shelf components. We discuss a novel optical subsystems design for encoders and decoders that enable the realization of a highly scalable incoherent OCDMA system with rapid reconfigurability. We demonstrate the operation of 4 simultaneous users operating at OC-48 (~2.5 Gbit/s) with a power penalty of <;0.5dB and the reduction of multiple-access interference using ultra-fast all-optical sampling with newly proposed TOAD-based OCDMA receiver.

We present packet switching applications based on extended spectral-amplitude-coding (SAC) labels in generalized multi-protocol label switching (GMPLS) networks. The proposed approach combines the advantages of wavelength-division multiplexing (WDM) and optical code-division multiple access (OCDMA). The extended SAC labels preserve the orthogonal property to avoid the effect of multiple access interference (MAI) shown at the decoder. We investigate the node architecture of label generation/recognition based on arrayed waveguide grating (AWG). Combining cyclic-shifted maximal length sequence (MLS) codes with the wavelength routed property of AWG simplifies the node structure. The simulation results show that the proposed labels achieve good performances against receiver noise due to the low average cross-correlation values. Under a given bit-error-rate (BER), the switching efficiency of the extended SAC labels outperforms the previous OCDMA schemes, as the network nodes are capable of processing a large number of labels simultaneously.

Optical Code Division Multiple Access (OCDMA) has been proposed as an attractive alternative for access networks due to its advantages over current Wavelength Division Multiplexing (WDM) and Optical Time Division Multiplexing (OTDM), such as asynchronous transmission, fair division of bandwidth and quality of service control [1]. However, OCDMA systems suffer from the phenomenon of Multiple Access Interference (MAI) which is generated by other channels transmitting over the same fibre as the desired data signal. This MAI noise reduces system performance and increases proportionally with the number of channels in the system.

Optical code division multiple access (OCDMA) systems, intensively investigated these last years, are known to suffer from multiple access interference (MAI). In addition, the photodetection process leads to beatings between the desired user information and the interferer ones, strongly degrading the system performance. To simplify the performance analysis, noise statistic is generally approximated by a Gaussian distribution which is not very accurate regarding to optical considerations. In this paper, by considering beat noise along with MAI, we develop a more precise analysis of the probability density function of the decision variable as a mixture of chi-square distributions. To investigate beat noise impact, the theoretical error probability expression is then determined. The results permit obtaining the conditions required to reach the optimal performance in beat noise corrupted OCDMA systems.

In this paper we study the performance of source matching technique for an optical code division multiple access (OCDMA) system in the presence of source coherence effects and square law detection process. We use a binary-asymmetric channel (BAC) model for an OCDMA system employing an all-optical passive correlator receiver. Source coherence effects lead to relative-intensity-noise (RIN) and phase-induced-intensity-noise (PIIN), which are included in our analysis. Previous studies only considered multiple access interference (MAI) noise, resulting in a Z-channel (where errors only occur for the transmission of data bit zero) model, and neglected RIN and PIIN. The presence of RIN and PIIN leads to errors occurring for both transmitted data bits one and zero, thus a BAC model. We show that source matching gain depends on the normalized source coherence time, defined as the ratio of the optical source coherence time to the bit duration. Our analysis shows that, while MAI limited analysis predicts that increasing the number of users increases the source matching gain, when taking into account RIN and PIIN, source matching gain is both bit rate and source type dependent, and tends to zero for very high numbers of users.

Chromatic and temperature induced dispersion can both severely affect incoherent high data rate communications in optical fibre. This is certainly also true for incoherent optical code division multiple access (OCDMA) systems with multi-wavelength picosecond code carriers. Here, even a relatively small deviation from a fully dispersion compensated transmission link can strongly impact the overall system performance, the number of simultaneous users, and the system cardinality due to the recovered OCDMA auto-correlation being strongly distorted, time-skewed, and having its full width at half maximum (FWHM) value changed. It is therefore imperative to have a simple tunable means for controlling fibre chromatic or temperature induced dispersion with high sub-picosecond accuracy. To help address this issue, we have investigated experimentally and by simulations the use of a semiconductor optical amplifier (SOA) for its ability to control the chirp of the passing optical signal (OCDMA codes) and to exploit the SOA ability for dispersion management of a fibre link in an incoherent OCDMA system. Our investigation is done using a 19.5 km long fibre transmission link that is exposed to different temperatures (20 °C and 50 °C) using an environmental chamber. By placing the SOA on a transmission site and using it to manipulate the code carrier’s chirp via SOA bias adjustments, we have shown that this approach can successfully control the overall fibre link dispersion, and it can also mitigate the impact on the received OCDMA auto-correlation and its FWHM. The experimental data obtained are in a very good agreement with our simulation results.

A new architecture for Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) system based on two Dimensional Multi Diagonal (2D-MD) codes named 2D-MD SAC-OCDMA and utilizing a laser optical source is proposed for Long-Reach Passive Optical Network (LR-PON). In this work, a computer simulator tool is used, for the first time, as a SAC-OCDMA simulation set-up utilizing the unique combination of a coherent laser array and 2D-MD codes. In addition, the system performance is addressed numerically by taking into account Multiple Access Interference (MAI), optical coherent source noise, first, second and third order fiber dispersion, nonlinear effects and photo-detector noise. Simulation results indicate that for a single user (i.e., without considering MAI), the system can operate at a maximum bit rate of 55 Gb/s over 250 km of Single Mode Fiber (SMF), with a Bit Error Rate (BER) below 10−9 (Q-limit = 15.5 dB), when only first order fiber dispersion is considered. However, including the effects of second and third order fiber dispersion as frequency domain parameters, results in a reduction of the maximum bit rate to 40 Gb/s, while maintaining a Q-factor above the Q-limit under the same transmission distance. Furthermore, we demonstrate that the proposed architecture extends the SMF transmission reach up to 600 km and 480 km, when considering linear and nonlinear effects, respectively. Finally, we show that our proposed 2D-MD SAC-OCDMA system outperforms existing solutions presented in the literature for LR-PON configuration, in terms of both aggregate bit rate and transmission reach.

This manuscript deals with analysis of Spectral Amplitude Coding Optical Code Division Multiple Access (SACOCDMA) system. The major noise source in optical CDMA is co-channel interference from other users known as multiple access interference (MAI). The system performance in terms of bit error rate (BER) degrades as a result of increased MAI. It is perceived that number of users and type of codes used for optical system directly decide the performance of system. MAI can be restricted by efficient designing of optical codes and implementing them with unique architecture to accommodate more number of users. Hence, it is a necessity to design a technique like spectral direct detection (SDD) technique with modified double weight code, which can provide better cardinality and good correlation property.

Many multiple access techniques have been proposed and demonstrated to provide flexible solutions for FTTH network configurations. The performance of this system suffers because of the correlation properties that contribute to a high level of Multiple Access Interference (MAI), low system capacity (users), and lower transmission rate. In this paper, we have proposed Optical CDMA (OCDMA) as a configuration solution for FTTH networks to improve the performance of this type of network. Full Text: PDF References. Z. Mateusz, M. Mariusz, On cost of the uniformity in FTTH network design, Conference on Transparent Optical Networks (2017), 87-90 CrossRef CEDRIC F. LAM, Passive Optical Networks- Principles and Practice, first ed., British Library, USA, 2007. DirectLink M.K. Abdullah, W.T. P'ng, P.W. Lau, E.R. Tee, FTTH access network protection using a switch, Asia Pacific Conference on Communications (APCC), 3(2003) 1219–1222. CrossRef J. Ronnakorn, S. Napat, L. Somkiat, Design and implement of GPON-FTTH network for residential condominium, Conference on Computer Science and Software Engineering, (2017), 333-339. CrossRef M. BOUREGAA, M. CHIKH-BLED, Comparative Study of Optical Unipolar Codes for Incoherent DS-OCDMA system, International Journal of Hybrid Information Technology, 6 (2013) 225-236. CrossRef M. BOUREGAA, M. CHIKH-BLED, The performance of a DS-OCDMA system using Orthogonal Optical Codes (OOC), European Scientific Journal, 9 (2013), 322-335 CrossRef M. Iwase, Y. Ishikawa, T. Komatsu, J. Kasahara, N. Hattori, M. Miura, N. Nakamura, K. Odaka, Optical transceiver modules for gigabit Ethernet PON FTTH systems, Furukawa Review, 28 (2005) 8-10. DirectLink

This 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 &amp; Sons, Ltd.

Iterative or Turbo decoding of parallel concatenated binary error control codes in Binary Phase Shift Keyed (BPSK) Communication System corrupted by both Additive White Gaussian Noise (AWGN) and oscillator phase noise is discussed. As an example of application of the discussed theory, iterative decoding technique of Parallel Concatenated block Codes (PCBC) is applied to a coherent Optical Code Division Multiple Access (OCDMA) network in the presence of Multiple Access Interference (MAI), detector shot noise and laser phase noise. Remarkable improvement in performance resulting from the use of turbo decoding in the OCDMA network is also discussed.