Performance Analysis of DPSK-OCDMA System for Optical Access Network

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.

Recently, free space optical (FSO) communication network has gained popularity because of its unlicensed spectrum, high data rate, low power consumption and ease of installation. Spectral amplitude coded optical code division multiple access (SAC-OCDMA) technique has become significant because of enhanced network capacity, privacy, and simultaneous use of multiple asynchronous users. However, the climatic turbulence causes signal fluctuations and degrades the quality of the received signal. Therefore, to improve the quality of the received signal in this work, SAC-OCDMA technique is integrated with orthogonal frequency division multiplexing (OFDM) technique and performance of such hybrid model is investigated. Two SAC-OCDMA codes are proposed in this work referred as triangular matrix-zero cross correlation (TM-ZCC) and pulse shifting substitution-zero cross correlation (PSS-ZCC) codes. The hybrid model uses the novel one dimensional (1D) SAC-OCDMA codes with two different types of receivers such as modified AND (M-AND), and single photodiode detection (SPD) receivers over Gamma-Gamma fading channel to evaluate the bit error rate (BER) performance of the proposed hybrid model. It is observed from the simulation results that the hybrid SAC-OCDMA-OFDM model with SPD detection receiver performs better in terms of bit error rate (BER) than that of M-AND detection receiver. Furthermore, it is also observed from the simulation results that the hybrid model based on the proposed TM-ZCC code performs better than the proposed PSS-ZCC code in terms of BER and higher FSO distance coverage. The performance of the proposed model is estimated for 20 and 30 active users simultaneously at various data rates. The TM-ZCC and PSS-ZCC codes are generated using MATLAB platform and the proposed hybrid SAC-OCDMA-OFDM model is validated using optisystem version 15 over the Gamma-Gamma fading channel.

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The encoding/decoding scheme based on Fiber Bragg Grating (FBG) for Optical Code Division Multiple Access (OCDMA) system is analyzed and the whole process from transmitting end to receiving end is researched in detail. The mathematical mode including signal transmission, summing, receiving and recovering are established respectively. One of the main sources of Bit Error Rate (BER) of OCDMA system based on FBGs is the unevenness of signal power spectrum, which leads to the chip powers unequal with each other. The Signal to Interfere Ratio (SIR) and BER performance of the system are studied and simulated at the case with uneven distribution of chips’ powers.

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.

Effect of atmospheric turbulence on the BER performance of an optical CDMA FSO link with SIK receiver

In this paper, the performance of a binary polarization shift keying optical code division multiple access (BPolSK-OCDMA) free space optical (FSO) system is investigated in terms of bit error rate (BER) and Q factor under the influence of different atmospheric conditions like clear air, rain, fog, snow etc. It is found that system performance is highly dependent on transmission length and different atmospheric conditions such as fog, rain, snow etc. However, among the atmospheric parameters, the system performance is found to be highly affected under foggy condition.

In this paper, we analyze the bit error rate (BER) performance of synchronous optical code division multiple access (OCDMA) system using an optical zero-correlation zone (ZCZ) sequence set over diffuse link by computer simulation, and evaluate the influence of inter-symbol interference (ISI) on the system. The optical ZCZ sequence set is a set of pairs of binary and bi-phase sequences with zero-correlation zone. As a result, the ISI can suppress by extension of zero-correlation zone.

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.

This paper presents the Direct Sequence Optical Code Division Multiple Access (DS-OCDMA) system using two configurations of the optical source. To encode/decode transmitted data, we used Superstructured Fiber Bragg Grating (S-FBG) as encoders/decoders. We consider three unipolar family codes which are the Prime Sequence (PS), Quadratic Congruence (QC) and the Extended Quadratic Codes (EQC) codes. In order to evaluate the performances of our system in term of Bit Error Rate (BER), we implement the Importance Sampling (IS) technique, which is a variant of the wellknown Monte-Carlo (MC) method. Our simulation results depict that EQC codes outperform QC and PS codes for the DS-OCDMA system using either coherent or incoherent source. We show also that using EQC codes with increasing the optical bandwidth and maintaining the electrical filter leads to improve the performance of incoherent system.

The bit error rate (BER) performance of direct sequence optical code division multiple access with cascaded optical amplifiers is analytically investigated in presence of fiber group velocity dispersion (GVD) and self phase modulation (SPM). Super Gaussian-shaped optical orthogonal codes are employed as address sequence for intensity modulation direct detection technique. The signal to noise power ratio for the proposed system is calculated on account of receiver, optical amplifier, and multiuser access interference noises. The system performance is determined as a function of optical signal power, code length, code weight, number of simultaneous users, fiber length, and order of Super Gaussian. The power penalty suffered by the system is evaluated at BER of 10-9. The numerical results show that the BER performance of the proposed system is highly dependent on the input signal power, bit rate, fiber length, and shape of the chip. It is found that the performance of the proposed system can be improved significantly in presence of GVD and SPM using Gaussian shaped chip.

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.

High-capacity communication networks are built to provide high throughput and low latency to accommodate the growing demand for bandwidth. However, the provision of these features is subject to a robust underlying network, which can provide high capacity with maximum reliability in terms of the system's connection availability. This work optimizes an existing 2D spectral-spatial optical code division multiple access (OCDMA) passive optical network (PON) to maximize connection availability while maintaining desirable communication capacity and capital expenditure. Optimization is performed by employing ring topology at the feeder level, which is used to provide a redundant path in case of connection failures. Furthermore, high transmission capacity is ensured by utilizing a pseudo-3D double-weight zero cross-correlation (DW-ZCC) code. The analysis is performed with Optisystem simulations to observe the performance of the system in terms of bit error rate (BER), received power, and eye openings. It is observed that the introduction of ring topology at the feeder level of the PON does not impact the overall transmission capacity of the system. The system can still support maximum transmission capacity at receiver sensitivities of up to -19 dB. Reliability analysis also shows that the optimized ring-based architecture can provide desirable connection availability compared to the existing system.

A new underwater optical wireless communication (UOWC) system utilizing optical code division multiple access (OCDMA) is proposed based on diagonal permutation shift (DPS) code. Different data rates of 2.5 Gb/s, 5 Gb/s, and 10 Gb/s are transmitted simultaneously in this model, where three channels are utilized, each is assigned with a distinct DPS code-sequence. Additionally, laser diodes operating in the green spectrum range are modulated to carry the OCDMA optical signals of each channel. Moreover, attenuation caused by different types of waterbodies are considered. These waterbodies include those who are located near harbors like harbor I (HA I) and harbor II (HA II), near the coast that are known as coastal sea (CS), inside sea water ‘pure sea (PS)’, and in clear oceans (CL). The performance of the UOWC utilizing OCDMA/DPS code system is evaluated through bit error rate (BER), quality factor , and eye diagrams. The accomplished results assure a successful transmission of the three channels underwater for ranges of 13 m for PS, 10 m for CL, 7.2 m for CS, 4.3 m for HA I, and 3 m for HA II with BER below 10-5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${10}^{-5}$$\\end{document} at data rate 10 Gb/s.

The transmission of both optical code division multiple-access (OCDMA) and wavelength division multiplexing (WDM) users on the same band is investigated. Code pulses of spectral amplitude coding (SAC)/optical code division multiple-access (CDMA) are overlaid onto a multichannel WDM system. Notch filters are utilized in order to suppress the WDM interference signals for detection of optical broadband CDMA signals. Modified quadratic congruence (MQC) codes are used as the sig- nature codes for the SAC/OCDMA system. The proposed system is sim- ulated and its performance in terms of both the bit-error rate and Q-factor are determined. In addition, eavesdropper probability of error-free code detection is evaluated. Our results are compared to traditional nonhybrid systems. It is concluded that the proposed hybrid scheme still achieves acceptable performance. In addition, it provides enhanced data confiden- tiality as compared to the scheme with SAC/OCDMA only. It is also shown that the performance of the proposed system is limited by the interference of the WDM signals. Furthermore, the simulation illustrates the trade- off between the performance and confidentiality for authorized users.