2D Optical Code Division Multiple Access Research Articles

Design and performance analysis of modified two dimensional Golomb code for optical code division multiple access networks

In this work, a two dimensional (2D) wavelength/time code is developed. The 64 bit 2D code is constructed by a technique based on folding of Golomb rulers referred in this work as modified Golomb code (2D MGC) and the proposed 2D code is generated using Java 8.1 software. The performance of the proposed 2D MGC is evaluated in terms of bit error rate (BER), received signal power, and time domain analysis of multiple users. In this experiment, it is found that the BER increases with multiple numbers of simultaneous users due to multiple access interference. The proposed 2D code yields better network performance in terms of BER compared to that of different existing 2D OCDMA codes. In this work, mathematical analysis is also carried out to prove that the proposed 64 bit code is optimal satisfying auto and cross correlation properties. Furthermore, the complexity analysis of the proposed 64 bit optical code division multiple access (OCDMA) code is analysed. The OCDMA model is validated using the optisystem software.

Comparative study of 2D‐OCDMA‐WDM system performance in 40‐Gb/s PON context

In this study, a optical passive networks system-based 2D-optical code division multiple access (OCDMA) wavelength division multiplexing (WDM) is proposed. For the uplink, 2D-prime hop system (PHS) codes and 2D-HC are employed. Nonetheless, a WDM scheme is used for the downlink. The system is firstly analysed and the performances are then provided in terms of signal-to-noise ratio (SNR) bit error rate (BER), Q-factor and optical power budget as function of optical received power. The authors show that the proposed system can reach 40 Gb/s with a good BER value <10 − 10 when a vertical-cavity surface-emitting laser and an APD receiver are deployed in the optical network unit and optical line terminal, respectively. Moreover, it is shown that bit rate can be increased up to 150 Gb/s using 2D-HC codes for the uplink. Finally, power budget for 524 network subscribers is achieved showing a long PON distance up to 41 Km with a maximum throughput equal to 285.1 Gb/s/Km using an emitted average power equal to 15 dBm.

Performance of 1‐D and 2‐D OCDMA systems in presence of atmospheric turbulence and various weather conditions

In this study, the authors compare the performance of one-dimensional (1D) and two-dimensional (2D) optical code division multiple access (OCDMA) systems in presence of turbulence and various weather conditions. Lognormal fading model is used for analysis of weak turbulence and gamma–gamma model for moderate and strong turbulence. It is observed that presence of moderate and strong turbulence may lead to a complete link failure in 2D OCDMA system depending upon the number of users and turbulence level. The various weather conditions considered are very clear air, light fog and thick fog. The results show that the performance degradation due to thick fog is more than the light fog and very clear air in all turbulence regimes.

Design and Performance Analysis of 2D OCDMA System with Polarization States

AbstractThis paper focuses on increasing the number of subscribers in optical code-division multiple access (OCDMA) system by using one of the features of light signal that it can be propagated in two polarization states. The performance of two-dimensional (2D) OCDMA system based on wavelength-time coding scheme by adding polarization state is investigated at varying data rates from 1 GHz to 6 GHz and for various modulation formats. It is reported that with increase in data rate of system, the performance of the system deteriorates due to polarization mode dispersion. Non-return to-zero (RZ), return to-zero (RZ), carrier suppressed return-to-zero (CSRZ) and differential phase shift keying (DPSK) modulation formats are simulated for a single user system with polarization. Investigations reveal that differential phase shift keying (DPSK) modulation format suits best to the proposed system and exhibit the potential to improve the flexibility of system for more number of users. The investigations are reported in terms of Q-factor, BER, received optical power (ROP) and eye diagrams.

The effects of power control on the optical CDMA random access protocol

In this work, the performance of the hybrid system that combines the distributed power control algorithm (DPCA) with the random access protocol as a novel and simple scheme of achieving a high performance in decentralized optical code division multiple access (OCDMA) networks has been investigated. The multiple access interference (MAI) and the near–far problem effects have been considered. The DPCA’s advantage lies in its characteristics being effectively implemented to each node, since only local parameters are necessary. The principal results have shown that the network throughput and delay are strongly affected by the near–far problem and the DPCA works to solve this problem. Hence, the introduction of a certain level of the power control to the random access temporally coded (1D) or the time-wavelength coded (2D) OCDMA networks has demonstrated profitability of the throughput increase and the delay reduction. As a consequence, the proposed system configuration with the DPCA using a very low number of iterations has resulted in a better throughput and simultaneously in a delay decrease when compared to the system without power control mechanisms.

Emerging OCDMA communication systems and data networks [Invited

Feature Issue on Optical Code Division Multiple AccessI present an in-depth review of the trends and the directions taken by researchers worldwide in optical code-division multiple-access (OCDMA) systems. I highlight those trends and features that I believe are essential to the successful introduction of various OCDMA techniques in communication systems and data networks in the near future. In particular I begin by giving a comprehensive review of the construction of optical orthogonal codes (OOCs). Specifically I discuss the recently developed algorithms that are based on matrix algebra, which simplify and enhance the efficiencies of algorithms in OOC generation. In communication systems studies I first focus on and discuss various OCDMA techniques, such as incoherent and coherent OCDMA. A comprehensive discussion takes place on all important aspects of each OCDMA technique. In particular, I elaborate on enabling technologies that are needed prior to full scale consideration of OCDMA in communication systems. For incoherent OCDMA the technique is categorized into two distinguished techniques, namely, 1D and 2D OCDMA. For each technique I discuss the various receiver structures proposed to date. In particular I discuss a recently introduced powerful receiver structure based on optical AND logic gate elements. Based on this receiver structure I conclude that in many practical applications, OOCs with a cross-correlation value λ equal to 2 or 3, which have a much larger cardinality compared to OOCs with λ=1, perform much better. Many fundamental issues, including architectural consideration of multiple amplifiers, various acquisition algorithms, and advanced signaling methods, such as pulse position modulation, are discussed. For coherent OCDMA or spectrally encoded ultrashort light pulse OCDMA, I begin by having an in-depth discussion on the key and enabling technologies that are essential in the successful implementation of this very important and extremely powerful technique. In particular on the encoder-decoder side I present discussions on various key device technologies such as virtually imaged pulsed array, fiber Bragg gratings, and arrayed waveguide gratings. On the receiver side I elaborate on various nonlinear detection schemes used in such OCDMA networks. I will present an analytical framework on the above nonlinear detection schemes and discuss their pros and cons. I extend the discussion to various data networks. In particular I will discuss applications such as wireless OCDMA LAN, free-space OCDMA, fiber-to-the-home, and other code-division-multiple-access-based packet communication networks using label addressing and processing techniques to indicate the directions and the applications for which OCDMA systems are considered. It is believed that in the not so distant future OCDMA, once fully developed and matured, will be an inseparable part of advanced optical communication systems and networks, due to its various desirable features and functionalities.

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.