Performance improvement of spectral amplitude coding-optical code division multiple access systems using NAND detection with enhanced double weight code

The bit-error rate (BER) performance of the spectral amplitude coding-optical code division multiple access (SACOCDMA) system has been investigated by using NAND subtraction detection technique with enhanced double weight (EDW) code. The EDW code is the enhanced version of double weight (DW) code family where the code weight is any odd number and greater than one with ideal cross-correlation. In order to evaluate the performance of the system, we used mathematical analysis extensively along with the simulation experiment. The evaluation results obtained using the NAND subtraction detection technique was compared with those obtained using the complementary detection technique for the same number of active users. The comparison results revealed that the BER performance of the system using NAND subtraction detection technique has greatly been improved as compared to the complementary technique.     

Performance analysis of spectral-amplitude-coding optical CDMA systems with new subtract exclusive OR detection (SED) using vectors combinatorial (VC) code

This paper investigates the performance of vector combinatorial (VC) code for spectral amplitude coding optical code-division multiple-access (SAC-OCDMA) system using a newly proposed subtract exclusive OR detection (SED) technique. VC code is constructed using Euclidean vector and algebraic ways. One of the important properties of this code is that the maximum cross correlation is one, which means that multi-user interference (MUI) and phase induced intensity noise (PIIN) are reduced. The weight for the VC code can be any positive integer number. The system performance was evaluated by comparing the theoretical studies using related equations and simulation results taken from the commercial optical systems, “VPI? TransmissionMaker 7.1”. Significant improvement in system performances has been observed when the proposed SED technique employing VC code was applied compared to other codes that utilize conventional balance detection techniques for spectral amplitude coding.     

Theoretical bounds for the bit error rate for SAC OCDMA balanced detectors with multiple photodiodes

Photonic Network Communications - In this paper, we derive the theoretical lower and upper bounds for bit error rate (BER) for spectral amplitude coding OCDMA balanced detector (BD) employing...     

Improvement of the bit error rate of a non-coherent OCDMA system for FTTH network applications

In this paper, an optical code division multiple access (OCDMA) system was analysed to improve the bit error rate (BER) performance at 10 Gbps. The improvements to this system were based on a modified double weight code and a NAND subtraction technique and aimed to support the large number of active users in the fibre-to-the-home network. The system performance was investigated through extensive theoretical and numerical simulation analyses. The theoretical and simulation results revealed that the new detection technique exhibits improved BER performance compared to conventional techniques, such as complimentary subtraction techniques. The system performance was characterised by the signal-to-noise ratio, the bit error rate (BER), and various transmit powers ( $P_{sr} - 10$  dBm). The results show that the proposed system, which is based on a new detection technique, can achieve the optimal BER with a high number of users and maintains the error floor transmission rate $(\le 10^{-9})$ .     

A divided spectrum balanced detection technique for intensity noise reduction in SAC OCDMA systems

In this paper we propose a simple divided spectrum balanced detection (DSBD) for spectral amplitude coding (SAC) optical code division multiple access (OCDMA) systems. SAC OCDMA systems are limited by phase induced intensity noise (PIIN), which is a signal dependent source of noise. Our proposed technique reduces the PIIN by dividing the spectrum of the signal into two or more, and detecting each spectrum by a different photodiode. The DSBD scheme reduces the detected optical power at photodetection, thus resulting in a higher mitigation of the PIIN. Theoretical results show that DSBD demonstrate noticeable improvement over traditional balanced detection technique, for example an up to 33% increase in the number of active users can be achieved, and at least 1 × 10⁻³ b/s Hz increase in the spectral efficiency is obtained. However, the SDBD is more complex and append more constrains on system components.     

Transmit Precoding Based Low Complexity Codebooks and Finite Feedback Rate for Space Shift Keying MIMO Systems

Transmit Precoding (TPC) considerably improves the performance of Space Shift Keying (SSK) systems. Codebook-based TPC is able to tackle several difficulties encountered by non-codebook TPC techniques. Channel State Information (CSI) is required at the receiver only, and the index of the best codeword is easily identified and fed-back from receiver to transmitter with low rate message. Motivated by these advantages, this paper contributes to the codebook-based TPC in the following aspects. First, the paper presents a Factorized form of the Full-Combination (FC) codebook with phase rotation only, and shows that only four phases are needed, which significantly simplifies practical implementation. As a second contribution, the paper introduces two statistically filtered codebooks: Index-Filtration FC and Average-Filtration FC. These codebooks considerably reduce system complexity due to their small codebook size, while maintaining almost the same BER of the FC codebook. As a third contribution, this paper proposes a new codeword selection criteria based on Long term statistics of the CSI (LCSI), instead of the conventional criteria using instantaneous CSI. This reduces the feedback rate of the index of the selected codeword while providing performance improvement over non-precoded SSK. Simulation results show the effectiveness of the proposed codebooks and the performance improvement with LCSI selection criteria.     

Variable cross-correlation code construction for spectral amplitude coding optical CDMA networks

We present, for the first time, several aspects of incoherent optical code-division multiple access (OCDMA) codes, focusing on the flexible variable cross-correlation code allocation and its potential for future optical networks. We briefly present a new version of the Random Diagonal (RD) codes for Spectral-Amplitude Coding (SAC) OCDMA approaches. We then concentrate on the properties specific to such schemes allowing for its increased scalability and flexibility. The main coding properties are reviewed. The RD codes provide simple matrix constructions compared to the other SAC-OCDMA codes such as Hadamard, MQC and MFH codes. This code possesses such a numerous advantages, including the efficient and easy code construction, simple encoder/decoder design, existence for every natural number n, and variable in-phase cross-correlation and easy to implement using Fiber Bragg Gratings (FBGs). Finally, a new detection scheme called “NAND” detection is developed for the variable cross-correlation RD code.     

Development of a new code family based on SAC-OCDMA system with large cardinality for OCDMA network

We have proposed a new Multi-Diagonal (MD) code for Spectral Amplitude – Coding Optical Code Division Multiple Access (SAC-OCDMA). Although this new MD code has many properties, one of the important properties of this code is that the cross correlation is always zero. Simplicity in code construction and flexibility in cross correlation control has made this code a compelling candidate for future OCDMA applications. The Multiple access interference (MAI) effects have been successfully and completely eliminated. Based on the theoretical analysis MD code is shown here to provide a much better performance compared to Modified Quadratic Congruence (MQC) code and Random Diagonal (RD) code. Proof-of-principle simulations of encoding with 5 and 10 users with 622 Mb/s data transmission at a BER of 10⁻¹² have been successfully demonstrated together with the DIRECT detection scheme.     

Performance evaluation of Fi-Wi network based on SCM–optical code division multiple access architecture

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.     

Optimization of free space optics parameters: An optimum solution for bad weather conditions

Free Space Optics Systems (FSO) is one of the most effective solutions, especially for atmospheric turbulence due to the weather and environment structure. Free space optics system suffers from various limitations. A well-known disadvantage of FSO is its sensitivity on local weather conditions-primarily to haze and rain, resulting in substantial loss of optical signal power over the communication path. The main objective of this article is to evaluate the quality of data transmission using Wavelength Division Multiplexing (WDM) with highlighting several factors that will affect the quality of data transmission. The results of these analyses are to develop a system of quality-free space optics for a high data rate transmission. From the result analysis, FSO wavelength with 1550 nm produces less effect in atmospheric attenuation. Short link range between the transmitter and receiver can optimize the FSO system transmission parameters or components. Based on the analysis, it is recommended to develop an FSO system of 2.5 Gbps with 1550 nm wavelength and link range up to 150 km at the clear weather condition of bit-error-rate (BER) 10⁻⁹.