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ABSTRACT: In this paper, we present and analyze a novel all-optical multilevel multiclass optical code division multiple access (OCDMA) system, using optical analog-to-digital converter (ADC) and advanced optical logic gate elements. In such OCDMA network, users are distributed in M different classes. Furthermore, power level with which users in class j, j = 2, ..., M, transmit optical pulses, is twice the power level at which users of class j - 1 transmit their optical pulses. We achieve optical transmitter structure that satisfies these conditions using power control schemes. Also, we suggest two receiver structures for the aforementioned multiclass multilevel system. The first and simple receiver structure is based on optical AND logic gate elements. The second structure uses an optical ADC as well as optical AND logic gates. We obtain the performance for the aforementioned two types of receivers and compare their results with the traditional one-level OCDMA system. We show that using the proposed multilevel multiclass scheme improves system performance considerably by means of decreasing error probability as well as increasing the network capacity.
IEEE Journal of Selected Topics in Quantum Electronics 11/2010; · 3.78 Impact Factor
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ABSTRACT: In this paper we present and investigate a digital design and implementational details of a wireless optical CDMA (OCDMA) system based on generalized optical orthogonal codes (OOCs). A detailed digital implementation analysis and transmitter/receiver architectures in the context of the above design are fully studied. We analyze various subsystems for a wireless OCDMA system including detector and receiver structure, acquisition, and tracking blocks as well as evaluating their performance in a typical wireless OCDMA communication system. By analyzing two main parts of the system, namely, chip-level detector and OCDMA receiver blocks we evaluate the performance of the overall system. Analytical and simulation results are presented to depict system performance. Results on the design and implementation of such systems in this paper indicate the viability and the importance of OOC based wireless OCDMA technology to satisfy certain applications need in a wider communication system worldwide. Finally we describe an experimental prototype where we highlight the main aspects of the implementation of the system.
IEEE Journal on Selected Areas in Communications 01/2010; · 3.41 Impact Factor
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ABSTRACT: In this paper, we present a novel multirate, differentiated quality of service (QoS) optical CDMA (OCDMA) system using multilevel signaling technique. The emphasis is on OCDMA systems employing multi-length variable-weight optical orthogonal codes (MLVW-OOC) as signature sequence. We begin by presenting a two-class variable-weight OCDMA system in which all users have the same energy level in one bit duration. As a consequence, high weight users transmit their corresponding optical pulses at a lower power while low weight users transmit their corresponding optical pulses at a higher power level. We show that using this multilevel signaling technique, while employing the well known optical AND logic gate receiver structure, we achieve a considerable improvement in the performance of low-weight (high-power) users while the performance of high-weight (low-power) users not altered in comparison to one-level system. In the next step, we indicate that by using the recently introduced multistage receiver structure, which employs advanced optical logic gate elements, interferences at different power levels are distinguishable so that the performance of both high-weight and low-weight users are improved. Furthermore, we employ multilevel signaling technique in OCDMA system based on MLVW-OOC (multirate, differentiated QoS system). We show that using multilevel signaling technique in such a system results to the performance improvement. To analyze the performance of the system we obtain a closed-form relation expressing an upper bound on the probability of error of the system. Finally, to validate the upper bound, the analytical results are compared to the results of system simulation. The numerical closeness between the analytical and system simulation reveals the tightness of the obtained upper bound, hence making them quite useful in evaluating the above system's performance.
Journal of Lightwave Technology 11/2009; · 2.78 Impact Factor
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ABSTRACT: In this paper we introduce and propose novel signaling methods and receiver structures based on advanced binary optical logic gates for fiber-optic code division multiple access (FO-CDMA) systems using all-optical signal processing. In the proposed system the users of the network are categorized into multiple classes. Users of each class transmit at the same power level but different from the levels of the other classes' users. Using a combination of optical OR, AND and XNOR logic gates for the receiver structure we show that such a network not only takes the full advantages of all-optical signal processing but also demonstrates a considerable throughput efficiency when compared to ordinary FO-CDMA systems. The proposed receiver structure mitigates the effect of interfering users from the other classes by rejecting some specified power level combinations from the other classes. The depth of interference cancellation is a function of the corresponding number of power levels and the number of stages applied to the optical logic gates in use. In our analysis we choose the generalized form of optical orthogonal codes (OOC), i.e., OOCs with cross-correlation value greater than one, as the signature sequence. We begin by emphasizing on two-level systems, that is, when the users can select one out of two power levels for signal transmission. However, for multilevel FO-CDMA we obtain a closed-form relation for the upper bound on the probability of error.We will show that under the ideal case the increase in throughput resulting from the proposed multilevel system is proportional to the number of classes or power levels in use. Our analytical results are compared to the results of an extensive system simulation. The numerical closeness between, the analytical and system simulation, indicates the accuracy with which we have modeled mathematically our proposed signaling using advanced binary optical logic gates in FO-CDMA.
IEEE Transactions on Communications 06/2009; · 1.68 Impact Factor
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ABSTRACT: In this paper we study and present an in-depth analysis on the operability and the viability of a typical wireless optical CDMA (OCDMA) local area network. Three receiver structures for OCDMA systems, using optical orthogonal codes (OOC) with minimum auto and cross-correlations as signature sequence, namely, correlation, correlation with hard-limiter, and chip-level detection are studied and proposed for such a network. For the synchronization circuit design the performance of two algorithms for OOC based OCDMA networks, namely, simple serial-search and multiple-shift in the context of wireless OCDMA LAN are studied. Furthermore, we study a synchronization method based on matched filtering and show that it presents a much better performance in our wireless OCDMA system. The effect of sampling rate and its performance on tracking circuit is analyzed. Bit-error-rate (BER) analysis is performed by photon counting methodology. Multi-user interference (MUI), ambient light, and photodetector dark current are considered in our analysis. Our analysis strongly indicates the viability and practicality of such systems in certain important wireless optical communications systems.
IEEE Transactions on Communications 01/2009; · 1.68 Impact Factor
