Search

Objectives: The aim of this paper is to develop an indoor wireless infrared CDMA system based on Zero Cross Correlation (ZCC) code to minimize the effect of noises, and thus improves the overall performance. Methods/ analysis: Two different configurations of 1-cell and 4-cell are investigated. A mathematical framework to calculate the SNR and the BER under the effect of total noise such as LED shot noise, ambient light shot noise and thermal noise, is derived. The system performance is analysed in terms of SNR and BER, versus the width and length of the room, and number of users, respectively, and then compared with the system based on a Flexible Cross Correlation (FCC) code. Findings: The indoor infrared CDMA based on 4-cell configuration using the ZCC code showed better performance than the system based on 1-cell configuration or using the FCC code. As results, the 4-cell configuration based on ZCC could accommodate a larger number of users rate at the corners and edges of the room. It offered 42% and 150% larger cardinality at the edges, and the corners of the room respectively, compared to the 1-cell configuration. In addition, this system also offered 55%, 47%, 51% larger cardinality at the centre, the edges, and the corners of the room, respectively, in contrast to the FCC code. Application/Improvement: The proposed 4-cell configuration based on ZCC code for indoor wireless infrared CDMA system enhances the cardinality, and offers an excellent degree of mobility.

The RF communication has suffered from the interference and excessive latency issues. It is required a separated setup for transmission and reception of RF waves. To overcome this problem, the VLC system is a chosen technique due to high bandwidth and immunity to interference from electromagnetic sources. In this project, Optisystem Software version 15 has been chosen to study the perfomances of the VLC system in directed LOS. The performance results will be displayed on BER analyser and the simulation that has been done is iterating continuously in order to get the acceptable results. The result indicates that the reading of simulation of 1 user for both bit rate 155Mbps and 622Mbps shows the best result compared to 4 users. Without using any kind of OCDMA system, the number of users will reach the limitations which is not more than 4 users. The number of users influences the performance of the system and the result shows the decrement of BER reading which is lower than 10−9.

We propose a modified OFDM modulation based on multiband scheme for visible light communications (VLC) system. The method called catenated-OFDM VLC system can efficiently boost the propagation distance and combat multipath induced the inter symbol interference and inter carrier interference. Design parameters such as number of optical bands, input power, distance and data rate are varied to see their effect on the system performances. Simulation analysis is done using Optisys software Ver. 11.0. The results show that the proposed system offers a good performance at longer transmission distance of 12 m for input power of 2 dBm in case of Band=3 with 10 Gbps data rate. BER curves also indicates that the proposed system can be operated at very high data rate of 15 Gbps. This exhibits the ability of the proposed system to be one of the candidate for future optical wireless communication system.

This paper considers the combination of two promising technologies: Spatial Modulation (SM) and Non-Orthogonal Multiple Access (NOMA). In contrast to the conventional Multi-Radio Frequency (M-RF) NOMA-SM model, we propose a generalized Single-Radio Frequency (S-RF) model. This model splits each NOMA user data between the spatial bits and modulation bits in a flexible manner. Hence, the S-RF models in the literature are special cases of our proposed model. Besides, our model preserves the energy efficiency property of SM and strikes a compromise between the M-RF and existing S-RF models in terms of Spectrum Efficiency (SE). The SE of the proposed model is evaluated through mutual information analysis with Monte Carlo integration. Moreover, we propose a fair power allocation algorithm based on Equal Signal to Interference plus Noise Ratio (ESINR) for the NOMA-SM users. Besides, we evaluate the Bit Error Rate (BER) performance of the M-RF and S-RF NOMA-SM models and show considerable advantages of the proposed S-RF system.

This paper investigates the performance of an elegance code set algorithm known as Flexible Cross Correlation (FCC) code to be run into a simulation test of proposed RoF system. Executing OCDMA Code into RoF framework is seen as a promising technique for enhancing spectral efficiency and meanwhile enhanced the length of fiber optic cable and data bit rate execution while reduce the passive equipment device. This code can efficaciously reduce the results of phase-induced intensity noise (PIIN), it has the multiple access interference (MAI) cancellation belongs to RoF system and at the same time simple and easy within the code construction. Bit error rate (BER) performance is assessed for this proposed simulation system. The evaluation made based on the performance of fiber length, data bit rate, related with Bit Error Rate (BER) and also the complexity of the system. The extensive simulation results reveal FCC code possibly will accomplish sufficiently up to 51 km at BER 10-9 for data rate 155 Mbps as matched to 622 Mbps with exponentially increases at BER 10-12 error floor and it is fit for short haul networking such as FTTH and local area network (LAN).

This article proposes an N-finite Radon transform (N-FRAT) and a discrete framelet transform (FT) for the design of a new orthogonal frequency division multiplexing (OFDM) system. In the proposed system, the inverse FT (IFT) and FT were used instead of the inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) to realize multicarrier modulation and demodulation techniques, respectively. Simultaneously, it was suggested that the N-FRAT technique operate as a data mapper instead of the conventional phase shift keying (PSK) and quadrature amplitude mapping (QAM), which are usually used with the traditional OFDM system. The usage of the N-FRAT and FT in the proposed system led to an increase in the orthogonality between the subcarriers due to the application of IFFT in the N-FRAT, which was added to improve the orthogonality and time–frequency localization properties of the FT. Furthermore the proposed structure improved the bandwidth efficiency through the elimination of the cyclic prefix compared to the traditional system. The proposed system was simulated and compared with other OFDM systems, such as FFT based OFDM using N-FRAT mapping (N-FRAT-FFT-OFDM), FT based OFDM using QAM mapping (QAM-FT-OFDM), and FFT based OFDM using QAM mapping (QAM-FFT-OFDM). The simulation was performed over frequency selective fading channel using MATLAB technical programming language. The results of simulations showed that the new structure outperformed the other three systems by reducing the inter-symbol interference (ISI) and inter-carrier interference (ICI), which then improved the bit error rate (BER) performance.

Optical millimeter-wave signal generation using Stimulated Brillouin Scattering (SBS) is proposed in this work. The performance of generated signal is compared based on different external modulation scheme which are Single-Sideband (SSB) and Double-Sideband (DSB). Dispersion and the fading effect are the main cause for external modulation scheme system performance degrading while producing high Bit Error Rate (BER) when involving long distance delivery in the optical signal. According to simulation results, SBS technique successfully improve the system performance in terms of highest received signal over distance, the lowest bit error rate and coherence input power. The analysis of BER curve and plotting of eye diagram is evaluated to measure the differences of each method performance system.

The performance of the OCDMA systems is governed by numerous quantitative parameters such as the data rate, simultaneous number of users, the powers of transmitter and receiver, and the type of codes. This paper analyzes the performance of the OCDMA system using OFDM technique to enhance the channel data rate, to save power and increase the number of user of OSCDMA systems compared with previous hybrid subcarrier multiplexing/optical spectrum code division multiplexing (SCM/OSCDM) system. The average received signal to noise ratio (SNR) with the nonlinearity of subcarriers is derived. The theoretical results have been evaluated based on BER and number of users as well as amount of power saved. The proposed system gave better performance and save around −6 dBm of the power as well as increase the number of users twice compare to SCM/OCDMA system. In addition it is robust against interference and much more spectrally efficient than SCM/OCDMA system. The system was designed based on Flexible Cross Correlation (FCC) code which is easier construction, less complexity of encoder/decoder design and flexible in-phase cross-correlation for uncomplicated to implement using Fiber Bragg Gratings (FBGs) for the OCDMA systems for any number of users and weights. The OCDMA–FCC_OFDM improves the number of users (cardinality) 108% compare to SCM/ODCMA–FCC system.

Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) system encounters several challenges because the MultipleAccess Interference (MAI) of the overlapping chips as number of simultaneous users’ increases. Objectives: Our objective is to develop SAC-OCDMA system with OFDM modulation, based on Flexible Cross Correlation (FCC) code to limit the effect of noises. Methods/Analysis: The average received signal to noise ratio (SNR) with the effects of total noise such as Phase Induced Intensity Noise (PIIN), shot noise and nonlinearity of subcarriers is derived. In addition to generated the Numerical analyses of proposed system. Findings: The results have been evaluated based on SNR, PIIN, shot noise and number of users as well as the amount of power received. The results show that the proposed system improve the capacity of system performance in term of users and suppress the system impairments, Furthermore, by using FCC code can effectively reduce the effects of total noise and mitigate the Multiple Access Interference (MAI). Therefore the applying of OFDM modulation with SAC-OCDMA system has been proven to be robust against the MAI and surely enhanced the system performance, in term of SNR and high number of user allocated, compare to SubCarrier Multiplexing (SCM)/ SAC-OCDMA system.

Framelet Transform-based OFDM (FT-OFDM) was proposed recently as an alternative to traditional Fast Fourier Transform-based OFDM (FFT-OFDM). By using the Framelet Transform, the spectral containment of the channels will be more efficient, since it does not use Cyclic Prefix (CP) that usually used in the traditional model. To improve the error rate performance of FT-OFDM, forward error correction coding is essential. This paper proposes Low-Density Parity-Check (LDPC) coded Framelet Transform-based OFDM (LDPC-FT-OFDM). The use of LDPC coding with FT-OFDM is useful in providing the desired performance at high data rates. The proposed system was tested according to two different coding rates and mapping techniques over Additive White Gaussian Noise (AWGN) and frequency-selective fading channels. The performance of the proposed system was compared to that of the uncoded FT-OFDM, LDPC-FFT-OFDM, and uncoded FFT-OFDM systems. The simulation results showed that the proposed model performs better than the three other models. Hence, the proposed LDPC-FT-OFDM system is a promising solution for high efficient data transmission over wireless channels.

In this paper, we propose an alleviation interference scheme (AIS) for spectral amplitude coding (SAC) – optical code division multiple access (OCDMA) coding system approaches. The AIS SAC-OCDMA systems is demonstrated by utilizing the new flexible cross correlation (FCC) code. The FCC code has advantages, such as flexibility in-phase cross-correlation at any given number of users and weights, as well as effectively reduces the impacts of phase-induced intensity noise (PIIN) and has the multiple-access interference (MAI) cancelation property. The results indicated good performance whereas the FCC (W = 4, K = 150) AIS SAC-OCDMA coding system offers 66%, 172%, 650% and 900% percentage of cardinality enrichments as a contrast to DCS (W = 4, K = 90), MDW (W = 4, K = 55), MFH (W = 4, K = 20) and Hadamard (W = 8, K = 15) codes, respectively. Finally, the FCC AIS SAC-OCDMA coding system has low effective receive power Psr = −21 dBm which is expected to be more significant for future SAC-OCDMA coding systems without requiring any amplification at the receiving plant.

Visible light communication (VLC) technology offers unregulated, unlicensed and huge bandwidth to meet the growing demand in future indoor communication system. One of the major challenge in VLC system is in improving transmission speed with optimize the bandwidth capacity. The method to improve spectral usage is using advanced modulation formats such as orthogonal frequency division multiplexing (OFDM). In this work, a new approach for modulation technique based on multiband OFDM has been developed which capable to improve the spectral efficiency and optimize the data rate. A proposed technique is then adapted in OCDMA-VLC environment to analyse the reliability of the proposed scheme in high capacity network. Different selection of parameter values such as bit rates, number of bands and effective received power will have different effect on the system performance. Numerical result shown that the catenated-OFDM outperforms conventional OFDM by five times spectral efficiency improvement and eight times spectral efficiency improvement at their five and eight number of bands respectively. It is also shown that the proposed catenated-OFDM design is working well even at very high bit rate of 15 Gbps. Moreover, there are enhancement in receiver sensitivity with 7.3 dB power penalty compared to previous work.

Optical millimeter-wave signal generation in Radio over Fiber (RoF) based on external modulators using different modulation schemes such as Single-Sideband (SSB), Double-Sideband (DSB) are experimentally compared. The major fallout for external modulation scheme system performance to downgrade is due to dispersion and the fading effect in optical signal generation while generating high Bit Error Rate (BER) when involving long distance delivery. In this work, we proposed mm-wave signal utilize Stimulated Brillouin Scattering (SBS) scheme which indicates the best performance amongst the scheme based on simulation that it achieves to propagate longest of distance over fiber, highest receiver sensitivity, the lowest BER and coherence of Mach-Zehnder Modulator (MZM) extinction ratio. Mm-wave signal of 40 Ghz and 10 Gb/s data rate was generated with the plotting of eye diagram.

This paper investigates the performance of a spectral amplitude coding (SAC)–OCDMA system design utilizing subcarrier multiplexing techniques for use in the popular fiber-wireless (Fi-Wi) technology. Zero cross correlation code is employed because of its ability to eliminate phase induced intensity noise (PIIN) and the simplicity of using a direct detection technique at the receiving end. The performances are evaluated theoretically to derive the signal-to-noise ratio and results are presented in terms of bit error rates (BER). Results are analyzed to investigate the effect of code weight and variable data rates on the system performance. To validate the results, simulative analysis is also done using Optisys version 6.0. We demonstrated that the ZCC code performed better compared to other code for a BER floor of 10−9 with larger cardinality of subscribers. Results obviously indicate that system performance can be improved with larger code weight. In addition, the choice of lower bit rate is observed to perform better and more suitable for application in this hybrid Fi-Wi network.

A new two-dimensional (2-D) optical code division multiple access (OCDMA) scheme to increase the achievable system capacity is proposed. The code exhibits good cross-correlation property time and wavelength shift. Performances are analyzed on code size and correlation properties affecting two important system parameters, bit error rate (BER) as a function of cardinality generated and optical power transmission requirement. The proposed system can effectively suppress phase-induced intensity noise (PIIN) and has multi-access interference (MAI) cancellation property. Results in a good agreement indicate that 2-D modified double weight (MDW) offers 163.7% and 336.2% larger cardinality compare to 2-D perfect difference code (PDC) and 2-D modified quadratic congruence (MQC) code. By increasing spatial code (N) and keeps similar code length system performance can be further optimized. 2-D MDW (M = 45, N = 18) accommodates 252.2% and 18.3% cardinality increment and low effective transmitted power (Psr) at −17.9 dBm, compare to 2-D MDW (M = 247, N = 3) and (M = 84, N = 9) at 10−9 BER error floor. The architecture of the spectral/spatial MDW OCDMA system with property of MAI cancellation is presented.

There is growing demand for higher bit rates in the access domain due to the emergence of bandwidth-hungry applications such as video-on-Demand and file sharing. Gigabit-capable passive optical network (GPON) is the most important PON. In a hybrid wave division multiplexing/time division multiplexing (WDM/TDM passive optical network (PON), Quadrature amplitude modulation (QAM) is proposed as a way to achieve the necessary high bit rates. In this paper, 2.5-Gb/s hybrid WDM/TDM downstream link is presented, using radio-over-fiber (RoF) techniques in the GPON network, where 16QAM is used at 2.4 GHz frequency. The result shows a good performance with a distance of 25 km for single mode fiber which serves up to 32 users. The analysis was made based on the performance of eye and constellation diagrams. Key words: Hybrid wavelength division multiplexing / Time domain multiplexed -passive optical network (WDM/TDM-PON, radio-over-fiber (RoF), Quadrature amplitude modulation (QAM) modulation.

In this paper, we show details of zero cross correlation (ZCC) code development and investigate performance by measuring bit-error-rates compared to other optical code division multiple access (OCDMA) codes using Avalanche photodiode (APD) and PIN photodetector. We present a configuration to determine how optical OCDMA systems can be applied with PIN and APD photodetector. Analysis of Avalanche photodiode gain optimization is discussed in ZCC code system. We also present analytical and numerical theoretical results for data transmission of spectrally encoded incoherent OCDMA signal and how signal-noise is being affected by using these two photodetectors.

In this work, we proposed Stimulated Brillouin Scattering (SBS) in an optical generation of millimeter waves (mm-waves) for radio over fiber (RoF) system with the transmission of 2.5 Gbps data rate. SBS method is achieved by imposing continuous wave (CW) laser in a single mode optical fiber (SMF) via Mach-Zehnder Modulator (MZM) with Erbium-Doped Fiber Amplifier (EDFA) and two pump lasers. Mm-waves signal of 80 GHz was generated from a 40 GHz radio frequency (RF) synthesizer. Simulation result and the analysis comparison of effective light power are investigated with different SMF loop length from 20 km until 120 km. The performance of SBS system is analysed and the generated of millimeter waves signal can be transmit with length up to 120 km based on eye pattern and Bit Error Rate (BER) curve.

In this paper, we present, several aspects of unipolar optical code-division multiple access (OCDMA) codes, focusing on the flexible in-phase cross-correlation code algorithm and its potential for future optical networks. We briefly present a new class of code namely Flexible Cross Correlation (FCC) code for Spectral-Amplitude Coding (SAC) OCDMA approaches. The main coding properties are reviewed. The FCC code provides simple tridiagonal matrix constructions compared to the other SAC-OCDMA codes such as MDW, MQC and MFH codes. This code possesses such a various advantages, including the easier code construction, less complexity of encoder/decoder design and flexible in-phase cross-correlation for uncomplicated to implement using Fiber Bragg Gratings (FBGs) for the OCDMA systems.

A new code for Spectral Amplitude Coding - Optical Code Division Multiple Access (SAC-OCDMA) is proposed and is called Flexible Cross-correlation (FCC) code. The FCC code possesses various advantages; including easy code construction using Tridiagonal matrix compared to other SAC-OCDMA codes such as MDW, MQC and MFH, shorter code length and the important properties of this code is the flexible cross-correlation. Our results reveal that FCC code can effectively alleviated Phase Induced Intensity Noise (PIIN) and allows large cardinality and improve the bit error rate performance.

This paper focus on a new code for Optical Code Division Multiple Access (OCDMA) system. The proposed code called Sequential Algorithm (SeQ) Code. The SeQ code has properties of minimizing Phase Induced Intensity Noise (PIIN), has the Multiple Access Interference (MAI) cancellation and ease in code construction. The results had shown, the SeQ code can accommodate 200 numbers of simultaneous users at permissible performance analysis BER10-9 compared to DCS, 190 users and MFH130 users, respectively.

Many FSO communication systems are using a conventional technique that is OOK technique in the system. Some enhancement of technique is explained in this paper to decrease the error rate that occurs in the system. The comparison between OOK technique and DDM technique is investigated in order to compare the error rate and power received. The result shows that the performance of DDM technique generates improvement as much as 21% magnitude of BER in the system.

Free Space Optical communication system is a technology that solves the problem of network connectivity. In this system, it contains a coding and technique to control the data that transferred using a laser beam from transmitter station through the atmosphere to receiver station. This technique is to optimize the error rate and improve the signal received. In this paper, the comparison between conventional technique and DDM technique has been recorded. By using a varies beam divergence, DDM technique can support 6.7mrad beam divergence higher than OOK technique and can receive weaker power signal − 90dBm with a minimum level of BER 10−9 compare to OOK technique. This improvement shows DDM technique can perform better performance compared to OOK technique.

This paper presents an improvement design of an Optical Code Division Multiple Access for Radio over Fiber (OCDMA-RoF) system. This improved system is divided into two main subsystems, Central Stations (CS) and Base Station (BS). Implement OCDMA code into RoF system promised a secure, cost-effective, and high-capacity mobile and multimedia wireless services. The analysis was made based on the relationship between length of fiber, frequency carrier, BER performance and number of optical line terminal (OLT) and optical network unit (ONU). The Bit Error Rate (BER) performance was measured, evaluated, and compared through software simulation. Results demonstrate the proposed framework can expand the fiber cable up to 60km and maintain the performance until 500Mbps data bit rate while keep up the BER at 10−9 that is coordinating the understanding of hypothetical expectations and huge change over the past outline of OCDMA-RoF framework. The work exhibited has significant ramifications for future investigations of the OCDMA-RoF framework and may one-day take care of the issue of fiber optic long transmission.

This paper organizes the performance of twodimensional (2-D) Modified Double Weight (MDW) code for Optical Code Division Multiple Access (OCDMA) system by employing Avalanche Photodiodes (APD) as a gain. To accomplish the perfection system capacity, their cardinality, bit error rates (BER) and noise interferences are analyzed. With 2-D MDW with APD able to recovered the cardinality at least 61%, which able to reduce the BER of 10−9 Obviously, the proposed system maximally suppressed PIIN and shot noise which is a major factor affecting BER at high effective received power (Psr). Thus, this system shows an improvement of the system by applying APD instead of PIN diodes.

In this paper, an indoor optical wireless CDMA system based on zero cross correlation (ZCC) code is investigated under the influence of ambient light noise. We consider line of sight communication links between multiple emitters and receivers. We first establish an analytical expression of bit error rate and then validate its estimations with the simulated results. The finding results show a great matching between the theoretical estimations and simulation results. Whereas at BER of 10−9, there is no difference in terms of the effective received power while there is a variation of about only 1 dB at channel attenuation.

In this paper, we will focus on the modulation format used to produce the optical pulses, which are return to zero (RZ), and non-return to zero (NRZ). Bit error rate (BER) performance is assessed for OCDMA-RoF system. OCDMA-RoF system is viewed as a promising method for improving spectral efficiency and in the meantime diminish hardware equipment. The execution of RZ against NRZ is looked at through software simulation. We utilized two systems designed as follows: the first system used a RZ pulse generator and the second system used is NRZ pulse generator, and both frameworks were tried with 8 Optical Line Terminal (OLT) at the transmitter and 8 Optical Network Units (ONU) at the receiver without an erbium doped fiber amplifier (EDFA). It has been found that the NRZ pulse generator in this framework is prevalent than the RZ pulse generator for all re-enactment results. The performances are described through the received power at various bit rates and also an RF spectrum signal of NRZ and RZ format.

This article investigates the comparative between the Bit Error Rate (BER) performance of Phase Shift Keying (PSK) and quadrature amplitude modulation (QAM) based on Space Time Block Coded Orthogonal Frequency-Division Multiplexing based on Discrete Framelet transform (STBC-FT-OFDM) system. This comparison is accomplished through simulation programs for different constellation points numbers for M-PSK and M-QAM (M = 4, 16, and 64) over an Additive White Gaussian Noise (AWGN), and Rayleigh multipath fading channels. The simulation results showed that the M-QAM modulation technique gave preferable BER performance compared with M-PSK modulation technique at all cases of constellation points and channels.

High speed transmission is the most important thing that needed in free space optical (FSO) communication. It can send and receive data speedily. However FSO have interference during transmission. Usually strong turbulence is the main interference affected in FSO. This paper focuses on increase the high speed transmission in FSO communication by using new dual diffuser modulation (DDM) technique under the influence of the strong turbulence. Strong turbulence can affected the wave front cause to fluctuating signal and ultimately receiver can turn into saturate or loss signal. DDM technique enhances the detecting bit ‘1’ and bit ‘0’ and improves the power received to encounter with turbulence effect. The numerical result shows that the DDM technique support higher bit rate above 10Gbps and capable to operate at low power transmit. The finding also reveals that DDM can spread the effect of the diffuser up to 1Gbps. The result of the evaluation can provide more knowledge on the feasibility of FSO communication deployment under atmospheric turbulence condition especially for a high speed transmission.

The paper presents a method for the development of a new class of zero cross correlation optical code for Optical Code Division Multiple Access (OCDMA) system using Spectral Amplitude Coding. The proposed code is called Modified Zero Cross Correlation Code (MZCC). The code has minimum length and can be constructed quite simply for any number of users and for any code weights. The code has better spectrum slicing properties and noise performance in term of Bit Error Rate. The Modified Zero Cross Correlation Code will be demonstrated in simulation using OptiSys. 6.0 to observe noise performance which is better as compared to the existing Zero Cross Correlation Code.

A zero cross-correlation (ZCC) code is proposed to reduce the impact of system impairment and multiple access interference (MAI) in spectral amplitude coding optical code division multiple access (SAC–OCDMA) system. Bit-error-rate (BER) performance is derived taking into account the effect of some noises. The key to an effective OCDMA system is the choice of efficient address codes with good or almost zero correlation properties for encoding the source. The use of ZCC code can eradicate phase induced intensity noise (PIIN) which will contribute to better BER. Thus, we demonstrate, theoretically, the performance of optical ZCC code. It is shown that optical ZCC code can accommodate more users simultaneously for the typical error rate of optical communication system of 10 −9 . The result indicates that the established system not only preserves the capability of suppressing MAI, but also improves bit-error-rate performance as compared to the conventional coders.

A new dual-diffuser modulation (DDM) technique improve the performance of the conventional intensity modulation/direct detection (IM/DD) for On Off Keying (OOK) in term of data bit rate and propagation distance. This new modulation technique employs two transmitters and two receivers to create a robust modulation with optimizing the reduction scintillation index, enhance the power received and improve the threshold signal level. At the transmitters, the laser exits combine with low cost phase screen diffuser to create a ‘new’ superior laser beam characteristic in order to combat atmospheric turbulence effectively. Meanwhile at the receivers, the signal will be subtracted. The analysis result shows that in comparison various data bit rates at BER10−9, the DDM is capable to operate excellent under small power launched where the bit rate can achieved above 10Gbps at 5dBm power transmit. Meanwhile for phase screen diffuser effect, the DDM optimizes the performance of diffuser where the data bit rate can reached approximately 1.5Gbps and the conventional IM/DD-OOK only performed at 0.155Gbps.

Dense wavelength division multiplexing system is a system for coupling and transmitting the optical signals at different wavelength through the single fiber. Such technology is important in order to increase the capacity in optical communication system and to meet the growing demands of bandwidth. However, there are some limiting factors related to the data rate and capacity in this system. These limiting factors can be linear or nonlinear. Theoretically, the nonlinearities in fiber arise as the number of data channel, transmission length, data rate and input power level increase. In this project, the objective is focused towards analyzing on the nonlinearities effect by compensating the linear effect in the fiber. Dispersion Compensation Fiber (DCF) and linear loss EDFA compensation have been used in single mode fiber (SMF) channel to ensure the communication quality for the design. The proposed dispersion compensation DC-DWDM transmission system with 16 and 32 channels for 10Gbps with a channel spacing of 0.8nm was designed and simulated. The BER performance with various input power levels in the range of −10dBm up to 10dBm, and fiber length greater than 50km are analyzed. It has been shown that for fixed length of the fiber, the only variable that can be manipulated to lower the nonlinear contribution is the input power. The higher the input power the higher the nonlinear contribution. However, if the input power is low, the bit rate should be low to maintained transmission at the expected BER (BER < 10–12)

A detailed of code construction for an Optical Code Division Multiple Access (OCDMA) system with flexible cross correlation is presented to reduce the effect of interference thus optimizing the code length. In this paper, the proposed code called Flexible Cross Correlation (FCC) code. The FCC code can be constructed using a simple tridiagonal matrix compared to other OCDMA codes such as MDW and DCS codes thus the FCC code possesses various advantages including easy code construction and less complexity of encoder/decoder design. As a result, OCDMA system performance significantly improved by using FCC code with flexible cross correlation instead of fixed cross correlation such as MDW, MFH and DCS codes.

In this paper, a class of discrete Radon transforms namely Finite Radon Transform (FRAT) was proposed as a modulation technique in the realization of Orthogonal Frequency Division Multiplexing (OFDM). The proposed FRAT operates as a data mapper in the OFDM transceiver instead of the conventional phase shift mapping and quadrature amplitude mapping that are usually used with the standard OFDM based on Fast Fourier Transform (FFT), by the way that ensure increasing the orthogonality of the system. The Fourier domain approach was found here to be the more suitable way for obtaining the forward and inverse FRAT. This structure resulted in a more suitable realization of conventional FFT- OFDM. It was shown that this application increases the orthogonality significantly in this case due to the use of Inverse Fast Fourier Transform (IFFT) twice, namely, in the data mapping and in the sub-carrier modulation also due to the use of an efficient algorithm in determining the FRAT coefficients called the optimal ordering method. The proposed approach was tested and compared with conventional OFDM, for additive white Gaussian noise (AWGN) channel, flat fading channel, and multi-path frequency selective fading channel. The obtained results showed that the proposed system has improved the bit error rate (BER) performance by reducing inter-symbol interference (ISI) and inter-carrier interference (ICI), comparing with conventional OFDM system.

Discrete multiwavelet critical-sampling transform (DMWCST) has been proposed instead of fast Fourier transform (FFT) in the realization of the orthogonal frequency division multiplexing (OFDM) system. The proposed structure further reduces the level of interference and improves the bandwidth efficiency through the elimination of the cyclic prefix due to the good orthogonality and time-frequency localization properties of the multiwavelet transform. The proposed system was simulated using MATLAB to allow various parameters of the system to be varied and tested. The performance of DMWCST-based OFDM (DMWCST-OFDM) was compared with that of the discrete wavelet transform-based OFDM (DWT-OFDM) and the traditional FFT-based OFDM (FFT-OFDM) over flat fading and frequency-selective fading channels. Results obtained indicate that the performance of the proposed DMWCST-OFDM system achieves significant improvement compared to those of DWT-OFDM and FFT-OFDM systems. DMWCST improves the performance of the OFDM system by a factor of 1.5–2.5 dB and 13–15.5 dB compared with the DWT and FFT, respectively. Therefore the proposed system offers higher data rate in wireless mobile communications.

This paper analyzes the performance of the OS-CDMA system using OFDM technique to enhance the channel data rate, to save power and increase the number of user of OSCDMA systems. This system compared with previous hybrid subcarrier multiplexing/optical spectrum code division multiple-access (SCM/OSCDMA) system. The average received SNR with the nonlinearity of subcarriers is derived. The theoretical results have been evaluated based on BER and number of users as well as amount of power saved. The proposed system gave better performance and save around −6 dBm of the power as well as increase the number of users twice compare to SCM/OSCDMA system. In addition it is robust against interference and much more spectrally efficient than SCM/OSCDMA system. The system was designed based on Flexible Cross Correlation (FCC) code.

This paper focus on mitigating the atmospheric turbulence effect in free space optical communication using new dual diffuser modulation (DDM) technique. Phase screen diffuser located on transmitter create ‘new’ beam wave to propagate through turbulence more efficiently. This technique uses two transmitter and differential mode detection at the receiver. The result shows that for the receiving power performance at acceptable BER 10−9 under the strong turbulence condition, the improvement of DDM technique approximately 99% and 66% if compare with Conventional intensity modulation for direct detection of On-off keying (CIM/DD-OOK) and Partially coherent beam On-off Keying (PCB-OOK). At 2.5 Gbps data bit rate the magnitude of BER for DDM technique increase with 12 magnitudes or equivalent to 100% improvement and the CIM/DD-OOK with diffuser only 2 magnitudes which give the 33% improvement.

Orthogonal frequency division multiplexing (OFDM) is a very interesting approach for high data rate transmission in a multipath fading environment that leads to intersymbol interference (ISI). In this paper, two steps are used to improve the error rate performance of OFDM system. First, the discrete multiwavelet transform (DMWT) is proposed instead of fast Fourier transform (FFT) to obtain high orthogonality between subcarriers and hence reduce (ISI). Second, the performance of OFDM based on DMWT is examined for different modulation schemes such as M-PSK (M-ary phase shift keying) and M-QAM (M-ary quadrature amplitude modulation) to achieve high data rate. The simulation results demonstrated that, for high capacity data rate transmission, the M-QAM modulation is better than the M-PSK modulation.

A new class of code called Flexible Cross-Correlation (FCC) for Spectral-Amplitude Coding Optical Code-Division Multiple-Access (SAC-OCDMA) systems has been de-veloped. The FCC code has advantages, such as flexible cross-correlation property at any given number of users and weights, as well as effectively reduces the impact of Phase-Induced Intensity Noise (PIIN) and Multiple-Access Interference (MAI) cancellation property. The results revealed that the FCC code can accommodate 150 users, where FCC code offers 66%, 172%, 650% and 900% improvement as a contrast to 90, 55, 20 and 15 numbers of users for Dynamic Cyclic Shift (DCS), Modified Double Weight (MDW), Modified Frequency Hoping (MFH) and Hadamard codes, respectively, for a permissible Bit Error Rate (BER) of 10−9 •