Optical CDMA System Research Articles

Comparison of novel coding techniques for a fixed wavelength hopping SAC-OCDMA

The optical code division multiple access (OCDMA), the most advanced multiple access technology in optical communication has become significant and gaining popularity because of its asynchronous access capability, faster speed, efficiency, security and unlimited bandwidth. Many codes are developed in spectral amplitude coding optical code division multiple access (SAC-OCDMA) with zero or minimum cross-correlation properties to reduce the multiple access interference (MAI) and Phase Induced Intensity Noise (PIIN). This paper compares two novel SAC-OCDMA codes in terms of their performances such as bit error rate (BER), number of active users that is accommodated with minimum cross-correlation property, high data rate that is achievable and the minimum power that the OCDMA system supports to achieve a minimum BER value. One of the proposed novel codes referred in this work as modified random diagonal code (MRDC) possesses cross-correlation between zero to one and the second novel code referred in this work as modified new zero cross-correlation code (MNZCC) possesses cross-correlation zero to further minimize the multiple access interference, which are found to be more scalable compared to the other existing SAC-OCDMA codes. In this work, the proposed MRDC and MNZCC codes are implemented in an optical system using the optisystem version-12 software for the SAC-OCDMA scheme. Simulation results depict that the OCDMA system based on the proposed novel MNZCC code exhibits better performance compared to the MRDC code and former existing SAC-OCDMA codes. The proposed MNZCC code accommodates maximum number of simultaneous users with higher data rate transmission, lower BER and longer traveling distance without any signal quality degradation as compared to the former existing SAC-OCDMA codes.

A Review on Successive Interference Cancellation-Based Optical PPM-CDMA Signaling

AbstractThis paper presents a comprehensive review of successive interference cancellation (SIC) scheme using pulse position modulation (PPM) for optical code division multiple access (OCDMA) systems. SIC scheme focuses on high-intensity signal, which will be selected after all users were detected, and then it will be subtracted from the overall received signal, hence, generating a new received signal. This process continues till all users eliminated one by one have been detected. It is shown that the random location of the sequences due to PPM encoding can reduce the probability of concentrated buildup of the pulse overlap in any one-slot time, and support SIC to easily remove the effect of the strongest signal at each stage of the cancellation process. The system bit error rate (BER) performance with modified quadratic congruence (MQC) codes used as signature sequence has been investigated. A detailed theoretical analysis of proposed system taking into account the impact of imperfect interference cancellation, the loss produced from the splitting during encoding and decoding, the channel loss and multiple access interference is presented. Results show that under average effective power constraint optical CDMA system using SIC scheme with

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.

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.

Optical CDMA system using duobinary signaling scheme and LDPC code

In this paper, the duobinary signaling scheme and LDPC code are employed for enhancing the performance in time-spreading wavelength-hopping optical CDMA system. As the multiple access interference and beat noise will bring about serious adverse impact on system performance, using duobinary signaling scheme is a preferable manner to alleviate such channel impairments. In our proposed system, the duobinary signaling scheme is predicated upon EWO, which applies the orthogonality of carrier-hopping prime code. Once the channel condition is further improved, the utilization of LDPC code would be more powerful and can make tremendous progress in performance. Our proposed scheme is compact and simple; also it can allow more simultaneous users accommodated in the network. Therefore, it is a promising way to be the platform for broadband optical access network.

Gigabit Ethernet signal transmission using asynchronous optical code division multiple access.

We propose and experimentally demonstrate a novel architecture for interfacing and transmitting a Gigabit Ethernet (GbE) signal using asynchronous incoherent optical code division multiple access (OCDMA). This is the first such asynchronous incoherent OCDMA system carrying GbE data being demonstrated to be working among multi-users where each user is operating with an independent clock/data rate and is granted random access to the network. Three major components, the GbE interface, the OCDMA transmitter, and the OCDMA receiver are discussed in detail. The performance of the system is studied and characterized through measuring eye diagrams, bit-error rate and packet loss rate in real-time file transfer. Our Letter also addresses the near-far problem and realizes asynchronous transmission and detection of signal.

Design and Analysis of Self-Healing Dual-Ring Spectral Amplitude Coding Optical Code Division Multiple Access System

Conventional tree-based optical code division multiple access (OCDMA) systems do not provide any protection between optical line terminal and optical network units. This makes the entire OCDMA system significantly vulnerable to failures. This paper proposes a novel dual-ring spectral amplitude coding (SAC) OCDMA system, which consists of a single ring at the feeder level and two semi-rings at the distribution level. Analysis shows that the proposed system immediately detects and restores the flow of affected traffic and ensures survivability of the entire network. Moreover, comparison of the proposed system with exiting protection schemes shows that the proposed dual-ring SAC-OCDMA system provides desirable availability, 99.9995%, with minimum expenditure through simple architecture and simultaneous protection against failures at both feeder and distribution rings.

Novel secure and bandwidth efficient optical code division multiplexed system for future access networks

Abstract In this paper, a spectrally coded optical code division multiple access (OCDMA) system using a hybrid modulation scheme has been investigated. The idea is to propose an effective approach for simultaneous improvement of the system capacity and security. Data formats, NRZ (non-return to zero), DQPSK (differential quadrature phase shift keying), and PoISk (polarisation shift keying) are used to get the orthogonal modulated signal. It is observed that the proposed hybrid modulation provides efficient utilisation of bandwidth, increases the data capacity and enhances the data confidentiality over existing OCDMA systems. Further, the proposed system performance is compared with the current state-of-the-art OCDMA schemes.

Performance Analysis of DPSK-OCDMA System for Optical Access Network

AbstractIn this research, the performance of optical code division multiple access (OCDMA) using differential phase shift keying (DPSK) has been compared with OCDMA On-Off Keying (OOK). This comparison took place in terms of bit error rate (BER) and receiver power where two bit rates (155 Mbps and 622 Mbps) have been used for this analysis. Using of OptiSystem 7.0 simulation, comparing eye diagram and optical spectrum alongside with BER and Rx power. It is found that OCDMA-DPSK performs better in comparison to OCDMA-OOK. The performance analysis also provides parameter for designing and development of an OCDMA system for optical access network using DPSK.

Design of a Hybrid Multirate Asynchronous O-CDMA System: Performance, Spectral Efficiency, and Throughput Analyses

The multiple-code (MC) and multicode-keying (MK) schemes were recently proposed to support multirate multimedia services in asynchronous optical code-division multiple-access (O-CDMA) systems. A user in the MC scheme simultaneously conveys multiple codewords to represent the transmission of multiple data bits of 1. While the MK scheme only transmits one codeword at a time, each codeword represents a symbol (of multiple data bits of 0 and 1). In this paper, a hybrid multirate asynchronous O-CDMA system model that comprises the conventional single-rate scheme and these two multirate schemes is studied. The bit error probability (BEP), spectral efficiency (SE), and throughput of the proposed hybrid systemare formulated. The conditions and combinations of simultaneous users from these three schemes that can optimize the system’s BEP, SE, and throughput are investigated. Finally, the new analytical models are validated with numerical examples and computer simulations.

Performance Analysis of Heterodyne-Detected OCDMA Systems Using PolSK Modulation over a Free-Space Optical Turbulence Channel

This paper presents a novel model of heterodyne-detected optical code-division multiple-access (OCDMA) systems employing polarization shift keying (PolSK) modulation over a free-space optical (FSO) turbulence channel. In this article, a new transceiver configuration and detailed analytical model for the proposed system are provided and discussed, taking into consideration the potential of heterodyne detection on mitigating the impact of turbulence-induced irradiance fluctuation on the performance of the proposed system under the gamma-gamma turbulence channel. Furthermore, we derived the closed-form expressions for the system error probability and outage probability, respectively. We determine the advantages of the proposed modeling by performing a comparison with a direct detection scheme obtained from an evaluation of link performance under the same environment conditions. The presented work also shows the most significant impact factor that degrades the performance of the proposed system and indicates that the proposed approach offers an optimum link performance compared to conventional cases.

New Tree-Structured Optical Codes for Incoherent Optical-CDMA Applications

Optical codes with large cardinality and tree structure of multiple levels of subsets of codewords for adjustable performance and cardinality have recently been studied. These codes support contemporary applications, such as a scalable, multihop, multilevel network architecture with rapid code-switching/dropping and multicode-keying encryption for improving physical-layer confidentiality in optical code-division multiple-access systems and networks. In this paper, to further enlarge such code collection, two new families of optical codes are constructed from the rich families of cyclic maximal-distance-separable (MDS) codes. The code performances are algebraically analyzed using both the distance and weight distributions of the MDS codes and validated with computer simulation.

Secured relay‐assisted atmospheric optical code‐division multiple‐access systems over turbulence channels

The authors propose a relay-assisted atmospheric optical code-division multiple-access (AO/CDMA) system for secured, multiuser optical communications. Chip detect-and-forward (CDF) scheme is used at relay nodes so that the complex multiuser decoding process can be avoided. The proposed system performance, in terms of bit-error rate (BER) and transmission confidentiality, is analysed over atmospheric turbulence channel taking into account channel loss due to atmospheric attenuation and beam divergence. Multiple-access interference and background noise are also included in the analysis. In addition, a quantitative analysis of data confidentiality is further examined in the study. The numerical results show that the relay transmission is an efficient solution to improve the system performance. Thanks to this solution, AO/CDMA systems can achieve low BER, long distance, and a large number of users. Moreover, high confidentiality can be attained by properly configuring system parameters, such as limiting the transmitted power and/or reducing the signal beam width.

Generation of spectral-encoded signals in noncoherent optical communication systems based on acousto-optic multiwavelength filters

New acousto-optical (AO) methods and devices necessary for the creation of noncoherent optical code division multiple access (O-CDMA) systems are considered. Based on an AO multiwavelength filter, an original device generating spectral-encoded signals for O-CDMA systems with optimum WDM has been created and studied. It is shown that modern AO technology is capable of surmounting difficulties that previously hindered the transition of optical communication systems to CDMA data transmission.

Increasing the Capacity of SAC-OCDMA by Using OFDM Modulation

Optical CDMA (OCDMA) systems have received more attention because CDMA allows many users share the same transmission medium asynchronously and simultaneously with a high level of transmission security. In this paper, we describe the improved performance of the spectrum amplitude coding (SAC) OCDMA system using OFDM technique compare to SCM/SAC-OCDMA system. The theoretical results of proposed system shows that, the new SAC/OCDMA system with OFDM technique provides better performance compare to SCM/OCDMA system based on Random Diagonal Code (RD), the results evaluated based on BER, number of users and weight of code. Thus this system could be one promising solution to the symmetric high capacity access network with high spectral efficiency, reducing the required power and cost effective of broadband access network

Bounds and constructions for optimal [formula omitted]-OOCs

Let W={w1,w2,…,wr} be an ordering of a set of r integers greater than 1, Λa=(λa(1),λa(2),…,λa(r)) be an r-tuple of positive integers, λc be a positive integer, and Q=(q1,q2,…,qr) be an r-tuple of positive rational numbers whose sum is 1. In 1996, Yang introduced variable-weight optical orthogonal code ((n,W,Λa,λc,Q)-OOC) for multimedia optical CDMA systems with multiple quality of service (QoS) requirements. Some work had been done on the constructions of optimal (n,{3,4},Λa,1,Q)-OOCs with unequal auto- and cross-correlation constraints. In this paper, we focus our main attention on (n,{3,5},Λa,1,Q)-OOCs, where Λa∈{(1,2),(2,1),(2,2)}. Tight upper bounds on the maximum code size of an (n,{3,5},Λa,1,Q)-OOC are obtained, and infinite classes of optimal balanced (n,{3,5},Λa,1)-OOCs are constructed.

Statistical Modeling and Performance Characterization of Ultrashort Light Pulse Communication System Using Power-Cubic Optical Nonlinear Preprocessor

In this paper, we present an analytical approach in obtaining the probability density function (pdf) of the random decision variable Y, which is formed at the output of the power-cubic all-optical nonlinear preprocessor followed by the photodetector, with applications in ultrafast optical time-division multiplexing and optical code-division multiple-access systems. Our approach can be used to accurately evaluate the performance of ultrafast pulse detection in the presence of Gaussian noise. Through rigorous Monte Carlo simulation, the accuracy of the widely used Gaussian approximation of decision variable Y is refuted. However, in this paper, we show that the so-called log-Pearson type-3 (LP3) pdf is an excellent representation for the decision variable Y. Three distinguishable parameters of the LP3 pdf are obtained through an analytical derivation of three moments of the decision variable Y. Furthermore, toward a more realistic model, in addition to amplified spontaneous emission Gaussian noise, the effects of shot and thermal noises are also included. Finally, using the presented analytical approach, it is shown that the power-cubic preprocessor outperforms its quadratic counterparts, i.e., second-harmonic-generation and two-photon-absorption devices, in the high-power regime where shot and thermal noises can be neglected.

Design and Analysis of Asynchronous Incoherent Optical-CDMA Systems Using a New Code-Shifting Technique

In this paper, a novel code-shifting technique, which can be added atop asynchronous incoherent optical code-division multiple-access systems without complex modifications, is proposed and studied. The new technique divides the time-slot (or chips), in which the optical pulses of codewords are located, into $g$ equal-width sub-chips; every pulse is randomly and independently shifted to start at one of the $g$ sub-chips of its own chip, where $g > 1$ is a positive integer. The effects of this random $g$ -shift to the cross-correlation property and performance of asynchronous optical codes (of periodic cross-correlation functions of at most one) are formulated. Although it is found that the periodic cross-correlation functions are worsened to $3-2/g$ , our theoretical and computer-simulation results show an unconventional finding that code performance improves as $g$ increases.

Hybrid Analog/Digital Modulations Using Polarization Multiplexing OCDMA Scheme in Free Space Optics

With the development of the Internet, how to provide a high-speed and high-security comprehensive network has become urgent issue. In this project, we propose hybrid analog/digital transmissions format scheme which integrated optical code-division multiple-access (OCDMA) and polarization multiplexing technique in free space optics (FSO) transmission. Orthogonal frequency division multiplexing (OFDM) transmits as the analog format and (on-off keying) OOK transmits as digital format in the study, respectively. In the proposed hybrid OCDMA system, it has high-speed transmission, signal security and low cost...etc. we adopt quasi-orthogonal Walsh-Hadamard codes (WHC) that with fixed cross correlation value as the codeword for each base station. With the property, the multiple access interference (MAI) can be efficiently eliminated by using the balanced detection scheme at the receive end. The constellation and eye diagrams show that both OFDM signal as analog signal and OOK modulation as digital signal in the proposed hybrid OCDMA system perform good performance in FSO transmission.

Modified decoding and detection scheme for spectral amplitude coding optical CDMA systems

In this reported work, a modified decoding and detection scheme with dispersion compensation is investigated for spectral-amplitude-coding optical code division multiple access (SAC-OCDMA) systems. For simultaneously decoding and compensating the chromatic dispersion of signals in the 40 km-long standard single-mode fibre transmission, based on reconstruction equivalent-chirp method the array configuration of fibre Bragg grating (FBG) segments can be controlled with a quadratic dispersion of −680 ps/nm for an extra time delay. The traditional triple-branch signal detection (TBSD) scheme is then modified and the principle of multiuser interference elimination is theoretically analysed. The simulated results show that, without adding a dispersion compensation device, the modified TBSD scheme adopting the FBG decoder can realise the decoding and detection function in SAC-OCDMA.