Design And Analysis Of a Multi-channel Optical Fibre Lan Based On Modified Csma/cd Protocol

Nowadays, optical communication is widely employed by telecommunication providers in the whole world due to its ability to support high bit rate applications. The urge to provide end-to-end fibre connectivity arises to overcome the bottleneck problem that occurs when packets are transmitted on the slower speed medium such as copper. In optical transmission, bandwidth utilisation can be improved further by using multiple wavelengths or channels in a single fibre. This thesis discusses the implementation of multiple wavelengths technique for Local Area Network (LAN) environment. It proposes a new Ethernet-based protocol that uses multiple wavelengths for transmission, which runs on a single fibre. Ethernet/IEEE 802.3 is chosen because of its widespread employment in today's network and the ability of extending the transmission rate up to gigabit transmission. Even though light does not collide with each other, receiver contention might occur if more than one signal arrives at the receiver at the same time. Therefore, some arbitration mechanism is needed to synchronise the transmission and the tuning time of the respective transmitter and receiver. The proposed design is based on the physical bus topology with n number of connected nodes and m number of operating wavelengths. All nodes are able to listen to all wavelengths. A fast control unit is used, which is responsible for packet scheduling. The packets are scheduled based on a pre-computed time. Both transmitter and receiver will be asked to tune to the· allocated wavelength. The transmitter can start transmitting and the receiver will start tuning at a specified time. Control packets are used for handshaking purposes. The main operation is placed at the control unit so that no added complexity is experienced by the receiver. Thus, this technique further reduces the cost. A suitable range of channels is obtained from the result. The network performance is evaluated against several design parameters by comparing the performance of each channel. The result shows a significant improvement whereby the throughput and efficiency are increased and average delay is minimised compared to the conventional system

Optical code division multiple access codes comparison in free space optics and optical fiber transmission medium

Performance of three different Optical Code Division Multiple Access codes namely Prime Code (PC), Quadratic Congruence (QC), and Khazani-Syed (KS) code are compared in Free Space Optic (FSO) and optical fiber transmission. The simulation results show that efficiency of a code family is medium-dependent. While one code family performs the best in fiber medium, it is not necessary that it acts the same in FSO. For instance, KS with code weight of 6 provides BER 10-12 at 600 m distance, while other codes cannot even reach to the threshold 10-9 at this point. However this code shows vulnerability against fiber dispersion. At 5 km fiber, it provides BER of 10-7, even less then PC with 10-8. In that point KS code with weight 6 attains the best performance with BER of 10-11

Performance evaluation of an efficient RZ-MQAM modulation scheme in all-optical OFDM transmission systems

All optical orthogonal frequency division multiplexing (AO-OFDM) technique is a promising technique and employed in many military applications for data transmission over long distance. But AO-OFDM signals are very sensitive to nonlinear distortion and these systems suffer from nonlinear impairments. This paper describes a novel nonlinear phase noise reduction technique by decreasing interaction time between subcarriers in AO-OFDM transmission systems. This technique mitigates the effects of nonlinearity on all-optical OFDM transmission systems and improves performance of transmission systems. The proposed AO-OFDM transmission system has been successfully simulated and analyzed for estimating phase noise due to cross-phase modulation, self-phase modulation and four-wave mixing. The proposed RZ-8QAM AO-OFDM system with 29 subcarriers is examined and the transmission distance is fixed at 550km

A new code for optical code division multiple access systems

A new code structure based on Double-Weight (DW) code families is proposed for Spectral-Amplitude-Coding Optical Code Division Multiple Access (OCDMA) system. The constraint of a constant weight of 2 for the DW code can be relaxed using a mapping technique. By using this technique, codes that have a larger number of weight can be developed. Modified Double-Weight (MDW) Code is another variation of a DW code family that can has a variable weight greater than two. The MDW code possesses ideal cross-correlation properties and exists for every natural number n. A much better performance can be provided by using the MDW code compared to the existing codes such as Hadamard and Modified Frequency-Hopping (MFH) codes. This has been demonstrated from the theoretical analysis and simulation

Variable-Weight Optical Code Division Multiple Access System using Di erent Detection Scheme, Journal of Telecommunications and Information Technology, 2016, nr 3

In this paper a Variable Weight OCDMA (VW-OCDMA) system using KS code with Direct Decoding (DD), Complementary Subtraction (CS) and AND subtraction detections is proposed. System performance is analyzed using mathematical approximation and software simulation. In mathematical analysis, the e ects of Phase-Induced Intensity Noise, shot noise and thermal noise are taken into account. Bit Error Rate of di erent users is plotted as a function of received optical power per chip with varying the bit rates and number of active users. It has been shown that for di erent bit rates and number of users, system using DD has better performance than the system applying CS and AND detection. Using DD scheme, the number of active users are 100 while this value is 27 and 25 in case of using CS and AND detection, respectively, when the received optical power per chip is {10 dBm

Simultaneous vibration and humidity measurement using a hybrid WDM/OCDMA sensor network

In this paper a hybrid Wavelength Division Multiplexing (WDM) and Optical Code Division Multiple Access (OCDMA) sensor network is proposed to detect vibration and humidity simultaneously. Evaluation of the results for the proposed system is demonstrated using simulation setup. OCDMA is used for detection of vibration levels while WDM is for sensing humidity changes. Fiber Bragg gratings (FBGs) is used in both systems. In OCDMA FBGs were used as filter to form the OCDMA code and sensors to senses the vibration. In WDM FBGs were used as sensor alone to sense the humidity

Comprehensive Investigation and Evaluation of an Indoor 3D System Performance Based on Visible Light Communication

The abstract discusses the significance of Visible Light Communication (VLC) as an efficient and cost-effective solution in the era of green technology. VLC not only provides illumination but also high-speed data transmission through existing infrastructure, making it ideal for indoor positioning systems (IPS) with minimal interference with the Radio Frequency (RF) spectrum and enhanced security. While previous research has mainly focused on positioning accuracy, this paper delves into the performance evaluation of a VLC-based indoor system. The study examines key performance parameters, namely Signal-to-Noise Ratio (SNR) and path loss, in a Line of Sight (LOS) scenario. It employs a single LED and ten different photodiode (PD) locations in a 3D room. MATLAB simulations demonstrate the system's effectiveness, achieving a good SNR with low path loss. Additionally, the research highlights the importance of optimizing the PD's position to maximize signal strength while minimizing noise and losses

Investigation of circulation noise effect on SAC-OCDMA system with ring topology

In this paper, we investigate the performance of an OCDMA system with ring topology where number of the spans can be more than one. Effect of circulation noise is evaluated beside of shot noise and thermal noise. Through analytical approach, it is shown that higher amount of amplifier gain, produces higher amount of circulation noise. Also by increasing the number of nodes, the strength of the circulation noise is reduced and the ratio of this reduction is more for lower amplifier gain. For example, with increasing number of the nodes from 3 to 8, the amount of log variance of circulation noise increases only 1 unit (-13 to -14) for amplifier gain 20 dBm, while this value is 4 units (from -15 to -19) if gain is 10 dBm

OCDMA multi service with zero cross correlation code in free space optics

In this paper a variable weight code for Optical Code Division Multiple Access (OCDMA) is proposed to provide differentiated services in optical network. We call it multi service zero cross correlation (MS-ZCC) where it has zero-cross correlation. Using simulation, the performance of this code is compared with the conventional variable weight (VW)-ZCC code in free space optic (FSO) environment. The newly proposed code MS-ZCC shows an improvement of 300 meters link distance for weight 2 and 8, compared to VW-ZCC

Evaluation of optical code division multiple access (OCDMA) encoding techniques for free space optics (FSO)

Free space optics (FSO) was found to have numerous applications in next generation networks, whilst optical code division multiple access (OCDMA) can be used to provide many facilities and its implementation in FSO environment has attracted several researchers. The aim of this paper is to express the achievements of these studies comprising proposed techniques in mitigating the effect of turbulence on the system. Also some defects of the mentioned studies are discussed, and suggestions for potential future researches will be provided. Furthermore, spectral amplitude coding (SAC) is implemented in FSO utilizing two different sources: light-emitting diode (LED) and laser array and their performances is compared via simulation. It is shown that considering bit error rate (BER) being equal to 10-3 as a threshold, in strong turbulence the maximum achieved distance with LED is 800 m. In the same situation using laser array can improve the distance up to 1600 m