Optical Code Division Multiplexing Research Articles

Integrated long reach and energy-efficient NGPON-VLC system with OCDM/WDM for smart green buildings

Smart green buildings (SGBs) are composed of numerous services and offer hopeful solutions to the world's continuous and rapid urbanization. Conventional data transmission systems are insufficient to deliver acceptable services because to the sudden surge in high-quality information transmission requirements over long distance for numerous linked residents in SGBs. Consequently, a hybrid next generation passive optical network (NGPON) along with visible light communication (VLC) indoor/outdoor broadcast network is presented in this work to increase the reliability with intelligence, exalted overall efficiency, cost efficiency, and security of SGBs. Bidirectional PON-VLC system incorporates the time and wavelength division multiplexing (TWDM), wavelength division multiplexing (WDM) and optical code division multiplexing (OCDM) techniques. In order to improve system performance, various OCDM codes are used in this work at 10/2.5 Gbps per channel throughput via fiber-VLC channels. According to the simulation results, the modified new zero cross-correlation (MNZCC) code performs better than previous codes and supports 200 active residents at reliable 100 km fiber along with 5 m VLC range. Furthermore, by expanding the received aperture diameter to 25 cm, VLC coverage may be increased till 10 m. Moreover, it provides adequate receiver sensitivities of − 13 to − 12 dB in uplink with − 9.8 to − 6 dBm in downlink for 200 to 600 fields of view angles compared to 00 view angle having sensitivity of − 15 dBm. Additionally, the numerical analysis and comparison performance show that PON-VLC outperforms fiber-VLC link-based scenarios when it comes to noise and channel impairments.

Operating Characteristic Curves of Optical Packet-Switching Using Optical Code-Division Multiplexing for Label Switching

In this paper, the operating characteristic curves (OCCs) of optical code-division multiplexing (OCDM) technology for label switching of an optical packet-switching (OPS) network was evaluated. A node structure for processing the packets, with spectral-amplitude-coding (SAC) labels, considering a balanced detector and an optical switch, was developed and modeled. The effects of decoding noises on the performance of both M-sequence and stuffed quadratic congruence (SQC) labeling systems were addressed. Hypothesis testing was applied to the decoder to investigate the results of label recognition. The null and alternative hypotheses were, respectively, defined as a decoder receiving the matching and mismatching labels. Due to the noise effects, the decoder output may not reflect the label status correctly. Type I error occurs when the null hypothesis is true while accepting the alternative one. Type II error occurs when the alternative hypothesis is true while accepting the null one. Analytic equations of both errors were given, considering a desired packet that was missed and an undesired packet shown in a switched path. The trade-off between these two errors, regarding the decoder threshold, was demonstrated in operating characteristic curves (OCCs). A better OCC could be found when a packet had more labeled payload bits, or when the utilized label code had a lower auto-to-cross-correlation ratio.

High-Speed Spiral-Phase Donut-Modes-Based Hybrid FSO-MMF Communication System by Incorporating OCDMA Scheme

Hybrid free-space optics (FSO) and optical fiber have been viewed as vital transmission techniques to satisfy high bandwidth and extended transmission range requirements under adverse environment conditions in the future last-mile obstruction problem. In this investigation, 80 Gbps data is transmitted on a hybrid FSO and multimode fiber (MMF)-based network using mode division multiplexing of two donut modes, Donut mode 0 and 1, and optical code-division multiplexing (OCDMA) schemes. For the OCDMA schemes, modified new zero-cross-correlation (MNZCC) codes are used, whereas, to add the phases into donut modes, a spiral phase diffuser is used. The purpose of the investigation is to provide an economical, high-speed and advanced last-mile network with adequate resource utilization for hybrid wired/wireless-based systems. The results obtained show achievement of an acceptable BER up to a fixed 100 m FSO link, with the combination of a 385 m MMF link under clear weather conditions. In another case, when the MMF link was fixed at 100 m, an acceptable bit error rate (BER) is achieved at 2.07 km FSO link. Furthermore, the results were obtained in the presence of strong and weak turbulences. A comparison of log-normal and gamma-gamma modeling for scintillations is presented.

A reach enhanced hybrid OCDMA-MDM multiplexing based IsOWC system incorporating EDFA, SOA, and RFA

Abstract Reach enhancement in inter-satellite optical wireless communication systems (IsOWC) is an utmost requirement due to ever-increasing internet usage all over the globe. Optical code division multiplexing is prominently incorporated for security enhancement in IsOWC systems, however, limited in terms of total reach. Therefore, in this work, a 120 Gbps capacity-based hybrid OCDMA and mode division multiplexed (MDM) IsOWC is presented using different optical amplifiers such as semiconductor optical amplifier (SOA), erbium-doped fiber amplifier (EDFA), and Raman fiber amplifier (RFA). Moreover, the combined effects of Laguerre–Gaussian (LG) with EDFA/SOA/RFA and Hermite–Gaussian (HG) modes with EDFA/SOA/RFA amplifiers are investigated. Results revealed that the proposed system can cover 5000 km IsOWC link within acceptable BER limits and EDFA with LG modes is found to be the best technique.

Ultra-Low Crosstalk En/Decoder Using an Amplitude-Shaping Technique for 100 Gbps/λ OCDM-PAM-4 Transmission in O-Band

This paper proposes an optimized 16-chip multi-level phase-shifted optical code division multiplexing (OCDM) en/decoder for 4-level pulse amplitude modulation (PAM-4) format by using an amplitude-shaping (AS) technique. The optimized en/decoder can efficiently suppress the crosstalk and the primary beat noise (PBN). The code detection performance for 4-OCDM PAM-4 becomes the lowest to our knowledge. The numerical bit error rate analysis and the back-to-back simulation are shown. We also successfully demonstrate by computer simulation a 100 Gbps/λ enabling by 12.5 GBaud 4-OCDM PAM-4 transmission in O-band over 6×30 km with in-line optical amplifiers.

Performance analysis of polar codes for one-coincidence-coded OCDM networks

A polar code over One-Coincidence-coded optical code-division multiplexing (OCDM) network is proposed, which is suitable for the multi-access optical fiber network. The excellent error correction ability of Polar code was applied to build a low error rate performance of network system. The proposed architecture not only supports lots of users by OCDM technology with spectral amplitude coding scheme to eliminate multiple-access interference, but also support that burst traffic at the same time of data transmitting by few users. The commutation channels will divide into two opposing channel quality, information channel and frozen channel by channel polarization of polar code. The buffer channel is created to support burst user, and it is build-in in information channel. Simulation results show that the proposed architecture can improve the system performance, compared with uncoded network. The proposed algorithm has better bit error rate performance.

Performance Optimization of Diagonal Identity Matrix and Enhanced Double Weight Codes in Terms of Security for Short Haul Communication

Optical code division multiplexing is getting attention because it is an imminent multiple access technology which can cater ever increasing data traffic as well as multiple user access in optical networks. In this work, a zero cross correlation based diagonal identity matrix code is presented and it is compared with the enhanced double weight code to check the superior code in OCDMA system at data speed of 30 Gbps. Effect of some parameters of OCDMA system which prominently affects the security of the system and these are input power, linewidth and modulator extinction ratio. Optimization using single parameter optimization and multiple parameter optimizations has been done. In order to accomplish the work, optiwave optisystem software is used and extensive literature survey is done, issues encountered are carefully checked and to address the issues, proposed system is presented. Results are evaluated in terms of Q factor, bit error rate (BER) and signal to noise ratio. Novelty of proposed work is the search of optimal parameters of both the codes in terms of enhanced security such that eavesdropping at these optimal parameters will become tedious for unauthorized user.

OCDMA System Using Two Code Keying Encryption Introducing a SOA Based CMUX And CDEMUX Over a WDM System

This paper introduces an Optical Code Division multiplexing (OCDMA) system using two code keying encryptions. In this paper proposed OCDMA system is designed using Semiconductor optical amplifiers (SOAs) which has nonlinear character and can implementor different logic functions. SOA based 2 × 1 Codeword Multiplexer (CMUX) is designed to multiplex the user data and a 1 × 2 Codeword DE Multiplexer (CDEMUX) to demodulate the user data. Then a multiple user access is provided using WDM system to design the whole OCDMA system. Transmission distance of 70 km is achieved with acceptable bit error rate and Q factor. Open eye diagram is also verified at the receiving end.

Performance analysis of 2D-OCDMA system in long-reach passive optical network

In this paper, a performance analysis is reported for optical code division multiplexing (OCDM) system for long-reach passive optical network (LR-PON) systems by taking into account multiple access interference (MAI), single-mode fiber (SMF) channel effects and receiver noise. The mathematical model representing the 2-D optical code parameters for different receiver structures used in optical code division multiplexing access (OCDMA) are developed, optimized and implemented using Matlab simulations, where channel imperfections, such as attenuation losses and chromatic dispersion have been considered. In the proposed system configuration, we have investigated the probability of error for Back-to-Back (B2B) with conventional correlation receiver (CCR), SMF with CCR receiver and SMF channel with successive interference cancelation (SIC) receiver. Additionally, SMF channel with SIC receiver system performance has been addressed by taking into account two key metrics, such as BER and Q-factor as function of simultaneous users, and fiber length, respectively. We have managed to substantially improve simultaneous multiuser data transmission over significant fiber lengths without use of amplification, where Q-factor of 6 at fiber length of 190 and 120 km, while a SIC receiver using 5 stages cancelation is employed for 2D prime hop system (2D-PHS) and for 2D hybrid codes (2D-HC), respectively.

Label Stacking Scenarios in Hybrid Wavelength and Code-Switched GMPLS Networks

Multi-protocol label switching (MPLS) is a promising solution to implement high-speed internet protocol (IP) networks by reducing the layer number. To meet the increasing demand for data traffic, optical packet switching (OPS) is integrated under IP to provide high bandwidth to end users. Generalized MPLS (GMPLS) is perfectly compatible with the routing algorithm in IP/MPLS as it supports packet-switching functions. In this paper, we investigate the label stacking scenarios in GMPLS networks. In GMPLS, label stacking is done to reduce the node complexity by appending multiple labels to a single packet. Wavelength-division multiplexing (WDM) and optical code-division multiplexing (OCDM) signals have been widely used as identifying labels. As the labels can be permutated among the wavelengths or code dimensions, the structure of a label stack can be varied. However, studies on the relationship between label stacking scenarios and network performance are limited. To investigate this issue, we propose three label stacking models: sequential code distribution; sequential wavelength distribution, and random label distribution. The simulation results show that the sequential wavelength assignment, wherein the labels are uniformly distributed among the wavelengths, exhibits the best system performance in terms of the label-error rate (LER).

Collective compensation of an inter-chip intensity discrepancy for a 4ch QPSK FE-SOCDM system with Si-based ODFT and electrical DFT

An intensity-sloped optical code with an optical chip-pulse stream generated by Si-based ODFT suffers from crosstalk and signal-to-noise (SNR) degradation. To mitigate these problems related to code-orthogonality reduction, we propose a simple intensity-discrepancy-compensation scheme that involves adjusting the chip-level intensity in the digital-domain. We numerically show a 0.1 dB SNR improvement for 40 Gb/s quadrature phase-shift keying (QPSK) Fourier-encoded synchronized optical code division multiplexing (FE-SOCDM) signal when multiplexing 1 dB/chip intensity-sloped optical codes. A proof-of-principle experiment achieves a 0.3 dB received power improvement using intensity-discrepancy compensation for two optical code multiplexing signals with 1.5 dB/chip.

Packets Buffering Enhancement with Hybrid Coding Labels for Virtual Optical Memory

For the practical deployment of optical packet switching (OPS) system, realizing all-optical buffering is a critical issue. In this paper, we present a hybrid labelling scheme based on optical code-division multiplexing (OCDM) over generalized multi-protocol label switching (GMPLS) network. The virtual optical memory is implemented by assigning queuing packets with different coded-WDM labels. The proposed hybrid labels combine the advantages of wavelength-division multiplexing (WDM) with spectral-amplitude-coding (SAC) OCDM. Due to the cyclic-shift property of arrayed-waveguide grating (AWG) and maximal-length sequence (M-sequence) codes, blocks of label generating and processing in node organization can be built in low complexity. Furthermore, utilizing hybrid coding technique in the buffering node increases the efficiency of label generating and processing. Derivation of the probability of packet missing is done to quantify the buffering performance of virtual optical memory. Simulation results show that the hybrid-coded labels, as compared to the conventional OCDM labels, are able to buffer the data packets with a relatively low probability of packet missing under similar label length.

Noise Suppression Using Amplitude-Shaping OCDM With 16-Chip Multi-Level Phase-Shifted En/Decoder

We propose an amplitude-shaping (AS) technique to shape an en/decoded signal in 10-Gb/s coherent time-spreading optical-code division multiplexing (OCDM) with ON– OFF keying modulation format, using 16-chip multi-level phase-shifted keying en/decoders. By employing this technique, the primary beat noise and the multiple access interference can be suppressed, and the code detection performance is improved. The bit error rate and the power penalty of the $8\times 10$ Gb/s AS-OCDM, obtained from the calculation and the simulation, are improved, in comparison with the conventional OCDM system.

Development of authentication code for multi-access optical code division multiplexing based quantum key distribution

One-weight authentication code for multi-user quantum key distribution (QKD) is proposed. The code is developed for Optical Code Division Multiplexing (OCDMA) based QKD network. A unique address assigned to individual user, coupled with degrading probability of predicting the source of the qubit transmitted in the channel offer excellent secure mechanism against any form of channel attack on OCDMA based QKD network. Flexibility in design as well as ease of modifying the number of users are equally exceptional quality presented by the code in contrast to Optical Orthogonal Code (OOC) earlier implemented for the same purpose. The code was successfully applied to eight simultaneous users at effective key rate of 32 bps over 27 km transmission distance.

Packet Loss Rate Differentiation in slotted Optical Packet Switching OCDM/WDM

We propose a multi-class mechanism for Optical Code Division Multiplexing (OCDM), Wavelength Division Multiplexing (WDM) Optical Packet Switch (OPS) architecture capable of supporting Quality of Service (QoS) transmission. OCDM/WDM has been proposed as a competitive hybrid switching technology to support the next generation optical Internet. This paper addresses performance issues in the slotted OPS networks and proposed four differentiation schemes to support Quality of Service. In addition, we present a comparison between the proposed schemes as well as, a simulation scheduler design which can be suitable for the core switch node in OPS networks. Using software simulations the performance of our algorithm in terms of losing probability, the packet delay, and scalability is evaluated.

Optical code division multiplexing in the design of encoded fiber Bragg grating sensors

The design of spectrally encoded fiber Bragg grating (FBG) sensors is proposed in order to incorporate more information in the optical measurement system. This information can provide full distinction between sensors operating at the same wavelength range. The encoded sensors are inspired by Optical Code Division Multiplexing (OCDM) techniques, specifically, we used Optical Orthogonal Codes (OOC) in order to define the spectral shape of the FBG sensors, providing them with a unique spectral signature. As a result we demonstrated the detection and tracking of the proposed sensors which allows effective measurement of temperature or strain even under overlapping conditions. The interrogation of the proposed encoded sensors could be performed easily and in real time through the autocorrelation product between the reflected spectrum and each sensor codeword. A simple addition to this identification method is implemented in order to remove any error in the interrogation process. Furthermore, a simulation of the proposed sensors under overlapping conditions is performed in order to test the distinction capability of the system. Finally the manufacturing and measurement of the sensors is described.

Performance Analysis of Multicode OCDM Networks Supporting Elastic Transmission With QoS Differentiation

A multicode optical code-division multiplexing (OCDM) is proposed to support the dynamic changes in the requested traffic demand in OCDM networks by adapting the number of allocated codes according to the requested transmission rate. In order to support time-variant data rates and multiservice transmissions; a multicode variable-weight 2D one-coincidence frequency hopping code/optical orthogonal code (OCFHC/OOC) is employed as the signature code in the proposed system. Two multicode assignment methods, namely, random multicode assignment (RMA) policy and uniform multicode assignment (UMA) policy, are presented. For each code assignment method, we drive the probability density function (pdf) of the number of active codes in each wavelength group. The bit error probability (BEP), the probability of degradation, and the blocking probability are derived as network performance key parameters. The proposed system has a simplified routing and code assignment process with a lower blocking probability. Our numerical results indicate that the network teletraffic capacity and blocking probability can be improved significantly using UMA policy and call admission control.

Optical Code-Division Multiplexing (OCDM) Networks Adopting Code-Shift Keying/Overlapping PPM Signaling: Proposal and Performance Analysis

Optical code-division multiplexing (OCDM) systems use short pulses compared with bit-duration to achieve high transmission rate. The use of short pulses poses several problems as a result of group velocity dispersion (GVD), intersymbol interference (ISI) (due to avalanche photodiode (APD) buildup time), and receivers limited bandwidth. In this paper, an OCDM system employing code-shift keying (CSK) and overlapping pulse-position modulation (OPPM) signaling is proposed and theoretically investigated. By using CSK while maintaining same data rate, the chip duration can be increased to counteract the GVD effect in 2D OCDM systems. Moreover, by increasing the chip duration, the chip rate is decreased and the stringent requirement on receiver bandwidth is relaxed. In addition, using overlapping property in OPPM allows for further chip duration increase. We consider using correlation receivers with hard-limiters and APDs at the receiver side. The bit error probability (BEP) of the proposed system is derived taking into account the impacts of APD noise, thermal noise, GVD, ISI, and multiple-access interference (MAI). A performance comparison between OOK-, PPM-, OPPM-OCDM and the proposed system is carried out. Our results reveal that the use of CSK/OPPM-OCDM with data rate constraint allows the reduction of MAI, GVD and ISI effects with improved spectral efficiency.

Design of Hybrid WDM/OCDM Add/Drop Filters and Its Experimental Demonstration for Passive Routing in Metropolitan and Access Integrated Network

We have proposed a newly metropolitan and access integrated network to provide services to long-reach depopulated households due to geographical difficulty, with smooth and energy-saving upgrade of the system. The feasibility of the system based on hybrid wavelength division multiplexing (WDM) and optical code division multiplexing (OCDM) is investigated from the viewpoints of add-drop multiplexing (ADM) operation and WDM/OCDM crosstalk. The ADM operation is verified when the adding, dropping, and transmitting signals are simultaneously operated, by examining the structure of multiplexer. The range of the input signal power to the multiplexer is derived. The crosstalk impact of WDM and OCDM is reduced by apodizing the filter device. By using the apodized devices, 16 × 1.25 Gb/s OCDM is successfully demonstrated at a wavelength band of 3.2 nm in C-band. From the results, the feasibility of 160-channel hybrid multiplexing in a proposed network is estimated.

Study in F.O.C. Multiplexing Techniques-A Review

Study in F.O.C. Multiplexing Techniques-A Review Communication network bandwidth requirement is growing at stunning rate, consequently numerous multiplexing techniques have been proposed by contributors for the augment in spectral efficiency from time to time. In this view the paper presents profound review on numerous multiplexing techniques for fiber optic communication, such as wavelength division multiplexing, optical time division multiplexing, optical code division multiplexing, optical orthogonal division multiplexing, mode division multiplexing, space division multiplexing, polarization division multiplexing and duty cycle division multiplexing technique.