Mitigation of multiple access interference using two-dimensional modified double weight codes for optical code division multiple access systems

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.

One Dimensional (1D) Double Weight (DW) code families are one of the coding schemes reported for Spectral Amplitude Coding — Optical Code Division Multiple Access systems. Modified Double Weight code and Enhanced Double Weight code are two algorithms which increase the scope of DW code for even and odd weights respectively. By using above mentioned codes, two Dimensional (2D) codes are generated. For each dimension, one code construction algorithm is used. 2D codes have different code weight combinations like even-odd weight, odd-odd weight etc. Proposed 2D code is compared with 1D and other 2D codes for Bit Error Rate.

We propose newly constructed two-dimensional hybrid codes (2-D hybrid codes) and the corresponding system architecture for a spectral/spatial optical code division multiple access (OCDMA) system. We employ unidimensional (1-D) integer lattice codes and 1-D perfect difference codes to construct the 2-D hybrid codes. This proposed system can suppress the phase-induced intensity noise (PIIN) and has the multiuser interference (MUI) cancellation property. In comparison with the other systems using the 2-D maximal-area matrices codes (2-D MM codes), the 2-D perfect difference codes (2-D PD codes), and the 2-D spatial division multiplexing balanced incomplete block design codes (2-D S-BIBD codes), the numerical results show that the proposed system has the superior performance.

In this paper we study the performance of source matching technique for an optical code division multiple access (OCDMA) system in the presence of source coherence effects and square law detection process. We use a binary-asymmetric channel (BAC) model for an OCDMA system employing an all-optical passive correlator receiver. Source coherence effects lead to relative-intensity-noise (RIN) and phase-induced-intensity-noise (PIIN), which are included in our analysis. Previous studies only considered multiple access interference (MAI) noise, resulting in a Z-channel (where errors only occur for the transmission of data bit zero) model, and neglected RIN and PIIN. The presence of RIN and PIIN leads to errors occurring for both transmitted data bits one and zero, thus a BAC model. We show that source matching gain depends on the normalized source coherence time, defined as the ratio of the optical source coherence time to the bit duration. Our analysis shows that, while MAI limited analysis predicts that increasing the number of users increases the source matching gain, when taking into account RIN and PIIN, source matching gain is both bit rate and source type dependent, and tends to zero for very high numbers of users.

It is important to apply the field Programmable Gate Array (FPGA), and Optical Switch technology as an encoder and decoder for Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) Free Space Optic Fiber to the Home (FSO-FTTH) transmitter and receiver system design. The encoder and decoder module will be using FPGA as a code generator, optical switch using as encode and decode of optical source. This module was tested by using the Modified Double Weight (MDW) code, which is selected as an excellent candidate because it had shown superior performance were by the total noise is reduced. It is also easy to construct and can reduce the number of filters required at a receiver by a newly proposed detection scheme known as AND Subtraction technique. MDW code is presented here to support Fiber-To-The-Home (FTTH) access network in Point-To-Multi-Point (P2MP) application. The conversion used a Mach-Zehnder interferometer (MZI) wavelength converter. The performances are characterized through BER and bit rate (BR), also, the received power at a variety of bit rates.

In this paper, we are proposing a detection scheme known as spectral direct detection technique implemented with fiber bragg grating (FBG) act as encoder/decoder. This FBG based is used to encode and decode the spectral amplitude coding namely modified double weight (MDW) code in optical code division multiple access (OCDMA). This code is used due to its flexibility where its weight can be any even number that greater than two. Moreover, it can maintain the cross-correlation parameter equal to one. The performance of spectral direct detection technique against AND-subtraction technique which is both implemented with FBG based encoder/decoder is compared via simulation in downstream and upstream access network at point to multipoint (P2MP) configuration. The simulation will be carried out using OptiSystem version 6.0 and the performance is characterized through bit error rate (BER) and power received at various bit rate.

This work proposes a new family of 1-D added length codes for use in spectral amplitude coding optical code division multiple access (OCDMA) networks. The proposed structure uses the proposed optical line terminal (OLT ) and optical network units (ONUs) to produce a simple architecture for ease of operation. The OLT transfers the information bits into the code sequences of 1-D added length codes in OCDMA. The ONUs use the code sequences of the 1-D added length codes to perform a modified cross-correlation, which produces the recovered “1” and “0” bits at the photodiodes. The photodiodes remove the interference caused by other simultaneous users, which is called multi-user interference. Additionally, the proposed modified cross-correlation process suppresses the phase-induced intensity noise. The numerical results demonstrate the bit error rate of the proposed system using 1-D added length codes to be better than that of other comparable systems using 1-D M-sequence codes, 1-D composite M-sequence codes, 1-D Hadamard codes, and 1-D MQC codes. The data transmission rate using the 1-D added length codes can reach 2.5 Gbps.

Intensity noise (IN) or phase induced intensity noise (PIIN) is the key limiting factor of the performance in spectral amplitude coding optical code division multiple access (SAC OCDMA) systems. The PIIN can be mitigated in SAC OCDMA by splitting the signals and detecting each signal by a different photodiode if the independence between the split signals can be achieved. In this paper, we derive the upper and lower bounds for the bit error rate (BER) for a system that implements multiple photodiode structured balanced detectors. Additionally, a simulation using Optisystem is conducted to compare the performance of the conventional balanced detector and an ideal multi photodiode balanced detector.

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We proposed the multipolar inserting zeros (MIZ) code for direct-sequence optical code division multiple access (OCDMA) systems. This code is designed to correspond with the judgment based on linear convolution. Simulation results showed that it can provide a lower multiuser interference than the conventional Gold sequence. With the same number of users, the bit error rate in the OCDMA system coded by MIZ can be reduced by several decuples than that coded by Gold, and the source power needed to reach a BER of 1×10?9 can also be reduced by several decibels. So the performance of OCDMA can be improved.

In this paper, we investigate the performance of optical code division multiple access system using the diagonal eigenvalue unity (DEU) code as a promising code for future optical networks. A comparison between the utilization of the NAND subtraction detection technique and the spectral direct detection (SDD) technique is presented to investigate which one provides better performance with the DEU code. In addition, a complete mathematical analysis for the two cases is presented. The performance of the two techniques is evaluated in terms of signal to noise ratio, bit error rate (BER), the effective received power, and phase induced intensity noise. Also, the variable weight DEU code is discussed. It demonstrates success for triple-play services (audio, video, and data) using the SDD technique to provide different quality of service (QoS) values to users. The results show that the SDD technique supports a larger number of users, reduces the receiver complexity, and provides better performance than the NAND subtraction technique. For a minimum acceptable BER of 10?9 for a telecommunication system, the direct detection technique supports 265 users, while the NAND subtraction supports 150 users only for (weight W = 3). Also, with variable weights in a single system, the performance of users with high weight is always better compared to that of lower weight users.

Effects of the Random Diagonal code link parameters on the performance of an OCDMA scheme for high-speed access networks

In an incoherent optical code division multiple access (OCDMA) system using amplitude spectral coding (SAC), which exceeds 1.5 Gbps, it is difficult or impossible to make a transmission with a bit error rate better than 10–9. For this, it is necessary to associate an error correction code (ECC) to the SAC-OCDMA system. In this paper, we proposed an architecture of a two-dimensional SAC-OCDMA system (spectral (w) and spatial (s)) using multi-diagonal code (MD) as spreading code and low-density parity check code (LDPC) as ECC. According to the properties of the MD code and the proposed architecture, the phase induced intensity noise is eliminated, which has improved the performance of the system. The theoretically results shows that LDPC/2D-SAC-OCDMA allowing more than 40 users to be multiplexed compared to a non-coded 2D SAC-OCDMA system. This combination allowed us to increase the cardinality of the LDPC/SAC-OCDMA (W/S) system without using an optical hard limiter.

Chromatic and temperature induced dispersion can both severely affect incoherent high data rate communications in optical fibre. This is certainly also true for incoherent optical code division multiple access (OCDMA) systems with multi-wavelength picosecond code carriers. Here, even a relatively small deviation from a fully dispersion compensated transmission link can strongly impact the overall system performance, the number of simultaneous users, and the system cardinality due to the recovered OCDMA auto-correlation being strongly distorted, time-skewed, and having its full width at half maximum (FWHM) value changed. It is therefore imperative to have a simple tunable means for controlling fibre chromatic or temperature induced dispersion with high sub-picosecond accuracy. To help address this issue, we have investigated experimentally and by simulations the use of a semiconductor optical amplifier (SOA) for its ability to control the chirp of the passing optical signal (OCDMA codes) and to exploit the SOA ability for dispersion management of a fibre link in an incoherent OCDMA system. Our investigation is done using a 19.5 km long fibre transmission link that is exposed to different temperatures (20 °C and 50 °C) using an environmental chamber. By placing the SOA on a transmission site and using it to manipulate the code carrier’s chirp via SOA bias adjustments, we have shown that this approach can successfully control the overall fibre link dispersion, and it can also mitigate the impact on the received OCDMA auto-correlation and its FWHM. The experimental data obtained are in a very good agreement with our simulation results.

In this paper the Double Weight code (DW) family which is used as a proposed code in optical spectral code division multiple access system (OSCDMA) has been studied using the Modified Double Weight code (MDW) which has across correlation value equals to one. By eliminating the intersection columns of this code we can reduce the cross correlation value from one to zero. This code is named Zero Cross-correlation Code (ZCC) [1]. Therefore, the Multiple Access Interference (MAI) can be reduced. Also, a general equation is used to generate the basic matrix of the code with the cross correlation equal zero instead of that in the existing construction technique. In this paper, we also show the advantages of this equation. All of these studies concentrate on the basic matrix of modified double weight code with zero cross correlation value.