Sharif Digital Repository

In this paper, we introduce a new and advanced algorithm, namely, multiple-shift algorithm for code acquisition in optical code-division multiple access (CDMA) systems using unipolar optical orthogonal codes (OOCs) as signature sequences. We analyze the performance of the newly proposed algorithm and obtain a bound on its performance and show its advantage in reducing the mean time of synchronization when compared with other synchronization methods. The algorithm can be used with many different receiver structures, like active or passive correlator with or without hardlimiter(s). However, in this paper, we only consider the simple active correlator structure for further discussions and... 

In this letter, we introduce a whole new approach in defining and representing optical orthogonal codes (OOCs), namely, outer-product matrix representation. Instead of applying commonly used approaches based on inner product to construct OOC codes, we use the newly defined approach to obtain a more efficient algorithm in constructing and generating OOC codes. The outer-product matrix approach can obtain a family of OOC codes with a cardinality closer to the Johnson upper bound, when compared with the previously defined accelerated greedy algorithm using the inner-product approach. We believe the new look introduced in this letter on OOCs could help to devise new approaches in designing and... 

In this paper, we propose using a soft-input decoder for the decoding of internally convolutional coded Poisson noise-dominated fiber-optic code-division multiple-access (CDMA) communication systems using optical orthogonal codes. We first compute the coded symbol log-likelihoods at the output of the Poisson noise-dominated channel, which is then used by a soft-input maximum-likelihood decoder, for a fiber-optic CDMA system assuming both on-off keying and binary pulse position modulation schemes. Furthermore, we develop a discrete soft-output channel model for a Poisson noise-dominated channel, with which we evaluate the upper bound on the bit error probability of the internally coded... 

In this paper, a new spreading technique for intensity modulation direct detection fiber-optic code-division multiple-access (FO-CDMA) communication systems is proposed. This new spreading technique is based on generalized optical orthogonal codes (OOC) with large cardinality and minimal degradation in performance when compared with a more optimum system, namely, an optical CDMA system using OOC with autocorrelation and cross-correlation value bounded by one, i.e., OOC (λ = 1). To obtain the performance of such systems, we use a recently introduced communication scheme, namely, frame time-hopping (FTH)-CDMA with random coding. It is discussed that systems with generalized OOC patterns and... 

In this paper, we consider the structure and performance of a multistage decoding scheme for an internally bandwidth efficient convolutionally coded Poisson fiber-optic code division multiple access (CDMA) communication system. The decoder is implemented electronically in several stages in which in each stage, the interfering users' coded bit decisions obtained in the previous stage is applied for computing the likelihood of the coded symbols of the desired user. The first stage is a soft-input Viterbi decoder for the internally coded scheme, in which the soft-input coded symbol likelihood values are computed by considering the multiuser interference as a noise signal. The likelihood of... 

Due to the low cardinality of optical orthogonal codes (OOCs) with a correlation value of 1, the capability of an internal channel-coding scheme cannot be applied effectively for an increasing number of simultaneous users in a typical fiber-optic code division multiple-access (FO-CDMA) system. In this paper, we consider applying the internal channel-coding scheme to the framed time-hopping (FTH) FO-CDMA system. Due to the extremely high cardinality of the spreading sequence in FTH FO-CDMA, the technique highlights the ability of the internal channel-coding scheme to increase the effective number of users in an FO-CDMA system. For the FTH FO-CDMA system, we only consider a Poisson... 

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... 

Considering the space of constant-weight sequences as the reference set for every optical orthogonal code (OOC) design algorithm, we propose a classification method that preserves the correlation properties of sequences. First, we introduce the circulant matrix representation of optical orthogonal codes and, based on the spectrum of circulant matrices, we define the spectral classification of the set Sn,w of all (0, 1)-sequences with length n, weight w, and the first chip 1. Then, as a method for spectrally classifying the set Sn,w, we discuss an algebraic structure called multiplicative group action. Using the above multiplicative group action, we define an equivalence relation on Sn,w in... 

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.... 

In this paper, a new internally coded time-hopping optical code-division multiple-access (TH/OCDMA) scheme for fiber-optic communication systems is proposed, and its multiple-access performance is evaluated using optical orthogonal codes (OOCs). In the proposed method, the duration of each bit is divided into Ns frames, each one containing L chips. Two signature codes, namely, one pseudonoise (PN) sequence and one OOC, are assigned to each user. During each bit interval, based on the output of an channel encoder and the user's dedicated PN sequence, one of the Ns frames is selected, in which W pulses are transmitted in W chips, marked by the user's OOC. We consider three detectors at the... 

we study the uplink performance of wireless infrared code-division multiple access (CDMA) networks using OOK with optical orthogonal codes (OOC's). The analysis is performed in two cases assuming a cellular network architecture, in which all users are uniformly distributed in the cell's area. The first case is when all users transmit with the same power and no power control mechanism is used. Then, the system that deploys power control mechanism is analyzed and the performance improvements are demonstrated. The impact of imperfect power control which is caused by errors in channel estimation is also analyzed and the analytical and numerical results for all cases are included. The results... 

In this paper, we introduce a new and advanced algorithm, namely, multiple-shift algorithm for code acquisition in optical code-division multiple access (CDMA) systems using unipolar optical orthogonal codes (OOCs) as signature sequences. We analyze the performance of the newly proposed algorithm and obtain a bound on its performance and show its advantage in reducing the mean time of synchronization when compared with other synchronization methods. The algorithm can be used with many different receiver structures, like active or passive correlator with or without hardlimiter(s). However, in this paper, we only consider the simple active correlator structure for further discussions and... 

Among all proposed structures for optical networks, the optical packet switching (OPS) scheme, due to its practical implementation of IPs in an optical configuration and the consequent advantages, is a prizeworthy candidate for being employed in metropolitan area network and local area network communication levels. One of the few problems frequently met using the OPS structure in the fiber-optics realm is the lack of optical buffers, thus deteriorating the system's flexibility and quality of service. For example, optical label switching networks that have been developed recently based on the generalized multiprotocol label switching protocol, profoundly suffer from this setback which is... 

Among all proposed structures for optical networks, the optical packet switching (OPS) scheme, due to its practical implementation of IPs in an optical configuration and the consequent advantages, is a prizeworthy candidate for being employed in metropolitan area network and local area network communication levels. One of the few problems frequently met using the OPS structure in the fiber-optics realm is the lack of optical buffers, thus deteriorating the system's flexibility and quality of service. For example, optical label switching networks that have been developed recently based on the generalized multiprotocol label switching protocol, profoundly suffer from this setback which is... 

The performance of a three-dimensional optical code-division multiple-access system based on polarization-wavelength-time codes is investigated. The unwanted effects of multiple access interference are first studied and an accurate enough expression is given for the upper bound of the bit error rate. The proposed expression is obtained by decomposing the three-dimensional polarization-wavelength-time codes into horizontally and vertically polarized two-dimensional wavelength-time codes that are assumed to be statistically independent. It is shown by Monte Carlo simulation that the assumption of independence gives accurate enough bit error rate, whenever the number of chips is much larger... 

In this paper, we analyze the performance of a wireless infrared system with code division multiple access (CDMA) technique using optical orthogonal codes (OOCs). Performance improvement is shown when power control is applied to the system. Noting the advantages of pulse position modulation (PPM), we have used chip-level binary PPM scheme. To mention some of these advantages we can name average required power reduction and BER improvement in comparison to on-off keying (OOK). The obtained results show that power control is a mandatory part of the design in a wireless infrared system using OOC. ©2007 IEEE  

Due to the low cardinality of optical orthogonal codes (OOCs) with, a correlation value of 1, the capability of an internal channel-coding scheme cannot be applied effectively for an increasing number of simultaneous users in a typical fiber-optic code division multiple-access (FO-CDMA) system. In this paper, we consider applying the internal channel-coding scheme to the framed time-hopping (FTH) FO-CDMA system. Due to the extremely high cardinality of the spreading sequence in FTH FO-CDMA, the technique highlights the ability of the internal channel-coding scheme to increase the effective number of users in an FO-CDMA system. For the FTH FO-CDMA system, we only consider a Poisson...