COST VERSUS RELIABILITY ANALYSIS OF NEW TREE-BASED HYBRID PROTECTION ARCHITECTURE FOR OPTICAL CODE DIVISION MULTIPLE ACCESS SYSTEM

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.

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.

Analysis of electrically configurable spectral phase encoding techniques for optical CDMA

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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.

The performance of 2D wavelength/time optical code division multiple access (OCDMA) system is adversely affected by the presence of noise at its physical layer. It is present in the form of Multiple Access Interference (MAI) and beat noise in OCDMA systems and degrades its performance. In this paper an attempt has been made to determine as well as to mitigate the effect of noise using either Optical Hard Limiter (OHL) or Coherent detection technique for a system employing prime sequence permutations over time spreading optical orthogonal codes (OOCs). Investigations reveal that performance of system is severely affected by noise and it can be improved by using coherent detection as well as hard limiter. Specifically for this PC/OOC coding technique, it has been reported in the results that coherent detection for reducing the noise outperforms the use of optical hard limiter.

A superstructured fibre Bragg grating (SSFBG) decorrelator for rejecting multi-user interference (MUI) in a synchronous optical code division multiple access (OCDMA) system is proposed and investigated. The decorrelator is formed by appropriately defining the superstructure of a weak fibre Bragg grating. Theoretical results arrived at using coupled mode theory show that it is possible to make the MUI practically zero at the sampling instant provided there is perfect bit synchronisation among the users accessing the OCDMA system. A theoretical investigation on the degradation of optical signal to interference ratio (OSIR) is also conducted by statistically modelling the jitter likely to result in the bit synchronisation mechanism of the system.

A parallel combinatory (PC)-hybrid pulse interval modulation-optical code division multiple access (hPIM-OCDMA) system is proposed. In the PC-hPIM-OCDMA system, a user chooses e among K code sequences assigned to the user and sends e2b-ary PIM symbols for a given frame, where b is the number of bits per PIM symbol. The PC-hPIM-OCDMA system can offer higher bit rate than hPIM-OCDMA systems, and then it can reduce the effect of MAI, without reducing the bit rate. The bit error rate (BER) of PC-hPIM-OCDMA is derived, by considering that the dominant interference is MAI, which is caused by cross-correlation of strict optical orthogonal codes (SOOCs). Numerical results show that the PC-hPIM-OCDMA system can offer lower BER and accommodate more users than hPIM-OCDMA systems.

This paper presents recent proposals that have been made in the field of optical pulse shaping techniques based on the space-time duality, with an especial attention to their application for the design of encoder/decoder pairs in all-fibre Optical Code Division Multiple Access (OCDMA) systems. Two different proposals are presented, one based on an Optical Fourier Transformer using a dispersive media and the other based on the temporal self-imaging effect. Fiber Bragg Gratings are used as dispersive elements and electro-optic modulators for the amplitude or phase coding, allowing the electrical reconfiguration of the codes. Experimental results, both for coherent and incoherent schemes, are shown for the two systems transmitting at data rates of 1.25 Gbps and 10 Gbps respectively with a fixed codification rate of 10 Gcps and using a subset of the Hadamard codes with a length of 8 chips.

We proposed newly two-dimensional (2- D ) spectral amplitude coding optical code division multiple access (OCDMA) scheme using modified double weight (MDW) code capable of suppressing phase-induced intensity noise (PIIN). The architecture of the spectral/spatial MDW OCDMA system with the property of multi-access interference cancellation is presented. The proposed code exhibits good cross-correlation property. At the optimized data transmission rate of 0.745 Gbps, 2-D MDW, M = 63, N = 3, reaches maximum cardinality of 200% increases compared to 2- D perfect difference code, M = 57, N = 3. The performance is severely deteriorated if the data rate further increases above 0.745 Gbps. The proposed code meets the optical transmission requirements at 10−9 bit error rate error floor, with lowest effective transmitted power ( P sr), −17.5 dBm, in comparison to the others through minimizing interference noise that result in PIIN suppression. The proposed system reaches optimum requirements performance in terms of cardinality, data transmission rate, and low effective transmitted power.

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.

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.

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.

In optical packet switching (OPS) and optical code division multiple access (OCDMA) systems, label generation and processing are key technologies. Recently, several label processors have been proposed and demonstrated. However, in order to recognize N different labels, N separate devices are required. Here, we propose and experimentally demonstrate a large-scale, multiple optical code (OC)-label generation and processing technology based on multi-port, a fully tunable optical spectrum synthesizer (OSS) and a multi-wavelength electro-optic frequency comb generator. The OSS can generate 80 different OC-labels simultaneously and can perform 80-parallel matched filtering. We also demonstrated its application to OCDMA.

In this PhD dissertation multi-rate models are examined for the performance analysis of telecommunication networks through mathematical analysis and simulation. Particular emphasis is given to optical networks. The main goal is the development of analytical models for the calculation of network performance metrics, such as blocking probabilities, transmission delay and utilization of the common channel. The proposed analytical models are distinguished according to the network technologies. Three different technologies are considered: A) Wavelength routed optical networks. B) Optical access networks. C) Wireless Internet access networks. Multi-rate loss models are proposed for the performance evaluation of wavelength routed optical networks. Firstly, the case of a single link is considered and then a mesh all-optical network is examined. In addition, analytical models are proposed for Optical Packet Switching (OPS) networks, for the case of an all-optical OPS switch and of an OPS mesh network. Multi-rate analytical models are proposed for the evaluation of the performance of Passive Optical Networks (PONs) implementing different multiple access methods. For the case of Time Division Multiple Access (TDMA) the Ethernet PON is studied, which supports multiple service-classes. Regarding the Wavelength Division Multiplexing (WDM) PONs a hybrid WDM-TDMA PON is considered and the call-level performance is evaluated. Calls are distinguished by their arrival process, which can be random or quasi random, by their bandwidth requirements, which can be fixed of elastic and by their behavior during their service, which can be calls of fixed transmission rate or calls that alternate between ON and OFF periods. Finally multi-rate loss models are proposed for the case of Optical Code Division Multiple Access (OCDMA) PONs that take into account the user activity and the presence of additive noise in the transmission channel. For the performance analysis of wireless Internet access networks analytical models are proposed, which implement the IEEE 802.11 protocol or the IEEE 802.11e protocol. The proposed analysis calculated the saturation throughput and the end-to-end packet delay as a function of the Medium Access Control (MAC) delay and the queueing delay. In all cases the accuracy of the proposed models is validated through simulation.