OCDMA System Research Articles

Development and Performance Improvement of a New Two-Dimensional Spectral/Spatial Code Using the Pascal Triangle Rule for OCDMA System

Abstract This paper introduces a novel code called two dimensional Pascal’s triangle zero cross correlation (2D-PTZCC) for spectral/spatial coding with its structure of the corresponding system to implement in spectral amplitude coding optical code division multiple access (SAC-OCDMA) systems The novel code is derived from a one dimensional zero cross correlation (1D-ZCC) code using Pascal’s triangle rule. The analytical results prove that the proposed code has totally removed the multiple access interference (MAI), in addition the phase induced intensity noise (PIIN) influence is highly reduced due to the zero cross correlation (ZCC) property. Comparing with the recent developed two-dimensional codes like 2D multi diagonal (2D-MD), 2D dynamic cyclic shift (2D-DCS), 2D diluted perfect difference (2D-DPD) and 2D perfect difference (2D-PD) codes for the same code length. The results of simulation show that the suggested code improve the system capacity and increase the number of simultaneous users reaches 29 % and 64 % comparing to 2D-DPD and 2D-PD codes, respectively. As well, it supplies higher signal power and data bit rates whereas it saves effective source power around −0.81dBm for 2D-DCS and 2D-DPD codes and consumes minor light spectral width. The passage from 1D to 2D ameliorated 1.68 times the system capacity and saved around − 4.27 d B m $ - 4.27{\rm{ dBm}}$ the effective power for each user.

Implementation of Spectral Amplitude Coding OCDMA System Based on Multi- Carrier Optical Signal

Incoherent SAC-OCDMA systems are designed to support low cost passive optical networks. However, incoherent nature of these systems limits their capability to support large amount of data. It is therefore necessary to utilize coherent optical sources like laser diode to provide high capacity in terms of data and the number of subscribers. Use of a single laser source in SAC-OCDMA system significantly increases the cost, which reduce its feasibility for deployment at the access domain. This paper proposes a novel technique for the implementation of SAC-OCDMA system using multi carrier laser. This technique can reduce the cost of SAC-OCDMA system by using a single laser for multiple subscribers in the system. Simulation analysis of the proposed SAC-OCDMA system while using random diagonal codes shows that it can support up to 12 Gbps of data at fiber lengths of 25 km.

Implementation of Spectral Amplitude Coding OCDMA System Based on Multi- Carrier Optical Signal

Incoherent SAC-OCDMA systems are designed to support low cost passive optical networks. However, incoherent nature of these systems limits their capability to support large amount of data. It is therefore necessary to utilize coherent optical sources like laser diode to provide high capacity in terms of data and the number of subscribers. Use of a single laser source in SAC-OCDMA system significantly increases the cost, which reduce its feasibility for deployment at the access domain. This paper proposes a novel technique for the implementation of SAC-OCDMA system using multi carrier laser. This technique can reduce the cost of SAC-OCDMA system by using a single laser for multiple subscribers in the system. Simulation analysis of the proposed SAC-OCDMA system while using random diagonal codes shows that it can support up to 12 Gbps of data at fiber lengths of 25 km.

Multiplicative PIC detection for OCDMA systems with non‐negativity constraints

Non-negativity constraints arise naturally in many applications such as medical and astronomical imaging. These constraints have been recently exploited in the optical communication field where a projected parallel interference cancelation detector has been developed within the context of cancelling multi-access interference in upstream on-off-keying optical code division multiple access passive optical networks; the latter possess the property that the transmitted data symbols are non-negative. The authors build upon these results and propose a new parallel interference cancellation structure with better features and improved performance. This detector is characterised by a multiplicative update equation and it exhibits a number of unique and desirable features such as stability and smooth convergence behaviour even for highly loaded systems. Up to our knowledge, this structure has not been proposed before either in optical or in wireless communication field. Simulation results are promising and further improvements are possible.

A new clipped PIC detector for asynchronous upstream OCDMA-PON

Optimization-based approaches have been used to develop several interference cancellation detectors for incoherent direct access OCDMA systems. Some of these interference cancellation detectors exploit the non-negativity of the solution, while other detectors exploit in addition to the non-negativity constraint, the noise variance information. In this paper, we devise a new PIC detector that exploits not only the aforementioned information but also the fact that the amplitude of the solution is confined to a unit hypercube. Up to our knowledge, no such detector exists in the literature. After analyzing the convergence behavior and evaluating the computational complexity of the novel PIC detector, extensive simulations are conducted to assess the performance of the proposed PIC detector. Numerical results show that the proposed PIC significantly outperforms other PIC detectors in terms of both BER and convergence speed.

Design of Variable Weight code for multimedia service in SAC–OCDMA systems

Variable weight (VW) codes for spectral amplitude coding–optical code division multiple access system are useful in multimedia applications. VW code algorithm is proposed which is based on enhanced and modified double weight codes. The proposed algorithm can be used for any combination of weights >2. The cross-correlation among all users is at most 1. This code construction algorithm ensures higher power at receiver for higher-weight users. Lower-weight users receive less power compared with higher-weight users. The difference in received power translates as varying performance, and are useful for multimedia applications. The performance of VW code is analysed using balanced detection (BD) exclusive-OR operation and direct detection with exclusive-OR operation. VW code gives comparable or better performance than previously reported code. It is observed that supportable number of users for higher weight, at bit error rate (BER) of 10−9 (data) are 28, 33 and 35 for random diagonal (RD) code, Khazani-Syed (KS) code and VW code, respectively, using BD. Supportable number of users for lower weight, at BER of 10−4 (voice) are 23, 31 and 37 for RD code, KS code and VW code, respectively, using BD.

Performance analysis of 2-D optical prime codes for optical-CDMA

In this paper, comparative analysis of code performance of distinct optical 2-D codes belonging to the Prime code family have been examined. Various optical 2-D Prime codes such as Low-weight Prime sequence code (LW-PSC), Modified prime-hop code (MPHC), Extended prime-hop code (E-CHPC), Transposed-modified prime code (T-MPC), Transposed-sparse padded modified prime code (T-SPMPC) are considered. Hard-limiting Error Probability (HEP) equations of these codes are used to scrutinize the performance of these codes. Performance of one of the 2-D Prime codes, more specifically MPHC performs best in OCDMA systems where only Multi-user interference effect is considered. This optical 2-D MPHC code possesses very low BER value as compared to universally accepted standard with the increasing user count. MPHC provides robustness to multiple user interference affected OCDMA therefore very much apt for applications where simultaneous access of immense number of active user is required.

Influence of Code Size Variation on the Performance of 2D Hybrid ZCC/MD in OCDMA System

Several two dimensional OCDMA have been developed in order to overcome many problems in optical network, enhancing cardinality, suppress Multiple Access Interference (MAI) and mitigate Phase Induced Intensity Noise (PIIN). This paper propose a new 2D hybrid ZCC/MD code combining between 1D ZCC spectral encoding where M is its code length and 1D MD spatial spreading where N is its code length. The spatial spreading (N) code length offers a good cardinality so it represents the main effect to enhance the performance of the system compared to the spectral (M) code length according to the numerical results.

DW-ZCC code based on SAC–OCDMA deploying multi-wavelength laser source for wireless optical networks

In this paper, double weight zero cross correlation (DW-ZCC) code is proposed for spectral amplitude coding optical code division multiple access (SAC–OCDMA) system. DW-ZCC takes the advantages of two previously proposed SAC-codes namely modified double weight (MDW) and zero-cross correlation (ZCC) codes, while providing optimized code length and maximum cross-correlation of zero. Although the proposed code can be utilized in SAC–OCDMA system with any optical medium, this research work focuses on outdoor wireless optical networks (WON) deploying multi-wavelength laser source, where optical bandwidth is much limited. The mathematical and simulation analysis of proposed system employing direct decoding (DD) is developed, considering the influences of turbulence and system noises including relative intensity noise, optical beat interference (OBI) and receiver noises. It is shown that employing DD detection; it is possible to completely avoid OBI which enhances system capability. The results show that SAC–OCDMA–WON system is noticeably improved using DW-ZCC in term of transmission distance by at least 200 m in comparison with MDW and conventional ZCC codes.

Impact of FWM on the Performance of 2-D Time-Wavelength OCDMA Systems

A derivation of a general formula for the bit error rate of 2-D time-spreading wavelength-hopping optical code division multiple access systems under the impact of four-wave mixing (FWM) is presented. The effect of many system parameters such as the transmitted power per chip, code properties, wavelength spacing, and transmission fiber length is investigated. The analysis reveals that the generated FWM light contributes not only as an additional crosstalk component, but also produces as extra three noise terms, namely, signal-FWM, interferer-FWM, and FWM–FWM noise. Theoretical results show the detrimental effect of FWM on the system performance at high chip power levels; resulting in a 4-dB penalty at a power of 15 dBm. Furthermore, the paper presents many aspects useful in the system design.

Towards higher scalability of hybrid optical CDMA network

A novel approach for improving the number of simultaneous users in a hybrid OCDMA-OTDMA network is proposed and analysed. OCDMA system is based on two-dimensional wavelength-hopping time-spreading codes with multi-wavelengths picosecond carriers. The scalability increase was achieved by adding a third dimension to separate OCDMA user groups within OTDMA time slots by assigning them into different wavelength bands. We have shown this will scale-up the system capacity proportionally to the number of assigned wavelength bands. A self-clocking all-optical time gate was then demonstrated as an effective means for suppressing the growing detrimental multi access interference noise resulted from this capacity increase.

Analysis and Design of Adaptive OCDMA Passive Optical Networks

OCDMA systems can support multiple classes of service by differentiating code parameters, power level and diversity order. In this paper, we analyze BER performance of a multi-class 1D/2D OCDMA system and propose a new approximation method that can be used to generate accurate estimation of system BER using a simple mathematical form. The proposed approximation provides insight into proper system level analysis, system level design and sensitivity of system performance to the factors such as code parameters, power level and diversity order. Considering code design, code cardinality and system performance constraints, two design problems are defined and their optimal solutions are provided. We then propose an adaptive OCDMA-PON that adaptively shares unused resources of inactive users among active ones to improve upstream system performance. Using the approximated BER expression and defined design problems, two adaptive code allocation algorithms for the adaptive OCDMA-PON are presented and their performances are evaluated by simulation. Simulation results show that the adaptive code allocation algorithms can increase average transmission rate or decrease average optical power consumption of ONUs for dynamic traffic patterns. According to the simulation results, for an adaptive OCDMA-PON with BER value of 1e-7 and user activity probability of 0.5, transmission rate (optical power consumption) can be increased (decreased) by a factor of 2.25 (0.27) compared to fixed code assignment.

Performance Analysis of FWM in 2-D Time-Spreading Wavelength-Hopping OCDMA Systems

Performance Analysis of FWM in 2-D Time-Spreading Wavelength-Hopping OCDMA Systems

Performance Analysis of FWM in 2-D Time-Spreading Wavelength-Hopping OCDMA Systems

Performance Analysis of FWM in 2-D Time-Spreading Wavelength-Hopping OCDMA Systems

Development of new two-dimensional spectral/spatial code based on dynamic cyclic shift code for OCDMA system

Abstract In this paper, a new two-dimensional spectral/spatial codes family, named two dimensional dynamic cyclic shift codes (2D-DCS) is introduced. The 2D-DCS codes are derived from the dynamic cyclic shift code for the spectral and spatial coding. The proposed system can fully eliminate the multiple access interference (MAI) by using the MAI cancellation property. The effect of shot noise, phase-induced intensity noise and thermal noise are used to analyze the code performance. In comparison with existing two dimensional (2D) codes, such as 2D perfect difference (2D-PD), 2D Extended Enhanced Double Weight (2D-Extended-EDW) and 2D hybrid (2D-FCC/MDW) codes, the numerical results show that our proposed codes have the best performance. By keeping the same code length and increasing the spatial code, the performance of our 2D-DCS system is enhanced: it provides higher data rates while using lower transmitted power and a smaller spectral width.

Using optical code-division multiple-access techniques in Michelson interferometer vibration sensor networks

This study proposes a spectral-amplitude-coding optical code-division multiple-access (SAC-OCDMA) framework for accessing the vibration frequency of a test object by using a Michelson interferometer vibration sensor (MIVS). Each sensor node possesses an individual signature codeword, and liquid crystal spatial light modulator (LC-SLM) encoders/decoders (codecs) are adopted to provide excellent orthogonal properties in the frequency domain. The proposed LC-SLM-based OCDMA system mitigates multiple access interference among all sensor nodes. When optical beams strike and are reflected by the object, the sensing interferometer becomes sensitive to external physical parameters such as temperature, strain, and vibration. The MIVS includes a Michelson interferometer placed at a specific distance from the test object on a designed vibration platform. A balanced photodetector (BPD) was used to convert the light output of the LC-SLM decoders into electrical signals, and a digitizing oscilloscope was used to Fourier transform the BPD electrical signal output, thereby yielding the vibration frequency of the test object. The results showed that the proposed sensor network with an interferometer can be used as a distributed highly sensitive sensor to obtain mechanical values. This study provides a new optical sensor network for current vibration frequency measurements.

A new family of 2D-wavelength-time codes for OCDMA system with direct detection

A new family of two dimensional wavelength-time codes is proposed in this paper. Based on one-dimensional ZCC, it allows a higher cardinality without increasing the code length, while conserving the same correlation properties. Thus, the direct detection at the receiver can be used, thereby simplifying the architecture of wavelength-time OCDMA scheme. The performance of the system was evaluated by referring to the Q factor, the BER and the eye pattern diagrams.

Two-Dimensional Optical CDMA System Parameters Limitations for Wavelength Hopping/Time-Spreading Scheme based on Simulation Experiment

Abstract A new family of two-dimensional optical hybrid code which employs zero cross-correlation (ZCC) codes, constructed by the balanced incomplete block design BIBD, as both time-spreading and wavelength hopping patterns are used in this paper. The obtained codes have both off-peak autocorrelation and cross-correlation values respectively equal to zero and unity. The work in this paper is a computer experiment performed using Optisystem 9.0 software program as a simulator to determine the wavelength hopping/time spreading (WH/TS) OCDMA system performances limitations. Five system parameters were considered in this work: the optical fiber length (transmission distance), the bitrate, the chip spacing and the transmitted power. This paper shows for what sufficient system performance parameters (BER≤10−9, Q≥6) the system can stand for.

Comparison between Conventional OCDMA and Subcarrier Multiplexing SAC OCDMA System Based on Single Photodiode Detection

This paper demonstrates the comparison between conventional OCDMA system and subcarrier multiplexing (SCM) SAC-OCDMA system by applying Recursive Combinatorial (RC) code based on single photodiode detection (SPD). SPD is used in the receiver part to reduce the effect of multiple access interference (MAI) which contributes as a dominant noise in incoherent SAC-OCDMA systems. From this analysis, the performance of SCM OCDMA network could be improved by using lower data rates and higher received power. The hybrid SCM OCDMA system shows better performance compare to conventional OCDMA system although the number of users involved is very high. This is because, for hybrid SCM OCDMA system, the number of users can be increased by increasing the number of subcarriers without affect the number of code length and optical codes. Increasing the number of subcarriers will enhance the power consumption by applying hybrid SCM system in OCDMA compared to the conventional OCDMA system. This is because increasing the number of users for hybrid SCM system does not affects the number of code length and the number of optical codes but only increase the number of subcarriers. Thus, hybrid SCM OCDMA system has to increase spectral efficiency and produce better performance compared to conventional of OCDMA system.

Design and Analysis of Self-Healing Tree-Based Hybrid Spectral Amplitude Coding OCDMA System

This paper presents an efficient tree-based hybrid spectral amplitude coding optical code division multiple access (SAC-OCDMA) system that is able to provide high capacity transmission along with fault detection and restoration throughout the passive optical network (PON). Enhanced multidiagonal (EMD) code is adapted to elevate system’s performance, which negates multiple access interference and associated phase induced intensity noise through efficient two-matrix structure. Moreover, system connection availability is enhanced through an efficient protection architecture with tree and star-ring topology at the feeder and distribution level, respectively. The proposed hybrid architecture aims to provide seamless transmission of information at minimum cost. Mathematical model based on Gaussian approximation is developed to analyze performance of the proposed setup, followed by simulation analysis for validation. It is observed that the proposed system supports 64 subscribers, operating at the data rates of 2.5 Gbps and above. Moreover, survivability and cost analysis in comparison with existing schemes show that the proposed tree-based hybrid SAC-OCDMA system provides the required redundancy at minimum cost of infrastructure and operation.