The Experts below are selected from a list of 32979 Experts worldwide ranked by ideXlab platform
Jawad A Salehi - One of the best experts on this subject based on the ideXlab platform.
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multirate differentiated qos and multilevel fiber optic cdma system via optical logic gate elements
Journal of Lightwave Technology, 2009Co-Authors: Hamzeh Beyranvand, B M Ghaffari, Jawad A SalehiAbstract: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.
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multiclass multistage and multilevel fiber optic cdma signaling techniques based on advanced binary optical logic gate elements
IEEE Transactions on Communications, 2009Co-Authors: B M Ghaffari, Jawad A SalehiAbstract: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.
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code division multiple access techniques in optical fiber networks part iii optical and logic gate Receiver Structure with generalized optical orthogonal codes
IEEE Transactions on Communications, 2006Co-Authors: S Mashhadi, Jawad A SalehiAbstract:In this paper, we present a deep insight into the behavior of optical code-division multiple-access (CDMA) systems based on an incoherent, intensity encoding/decoding technique using a well-known class of codes, namely, optical orthogonal codes (OOCs). As opposed to parts I and II of this paper, where OOCs with cross-correlation $lambda = 1$ were considered, we consider generalized OOCs with $1 leq lambda leq w$ , where $w$ is the weight of the corresponding codes. To enhance the performance of such systems, we propose that use of optical AND gate Receiver, which, in an ideal case, e.g., in the absence of any noise source except the optical multiple-access noise, is optimum. Using some basic laws on probability, we present direct and exact solutions for OOCs with $lambda = 1,2,3,ldots,w$ , with optical AND gate as Receiver. Using the exact solution, we obtain empirical solutions that can be easily used in optimizing the design criteria of such systems. From our optimization scheme, we obtain some fresh insight into the performance of OOCs with $lambdageq 1$ . In particular, we can obtain some simple relations between $ P_ e min$ (minimum error rate), $L_min$ (minimum required OOC length), and $N_max$ (maximum number of interfering users to be supported), which are the most desired parameters for any optical CDMA system design. Furthermore, we show that in most practical cases, OOCs with $lambda = 2$ or $3$ perform better than OOCs with $lambda = 1$ , while having a much bigger cardinality. Finally, we show that an upper bound on the maximum weight of OOCs are on the order of $sqrt2lambda L$ where L is the length of the OOCs used in systems.
B M Ghaffari - One of the best experts on this subject based on the ideXlab platform.
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multirate differentiated qos and multilevel fiber optic cdma system via optical logic gate elements
Journal of Lightwave Technology, 2009Co-Authors: Hamzeh Beyranvand, B M Ghaffari, Jawad A SalehiAbstract: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.
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multiclass multistage and multilevel fiber optic cdma signaling techniques based on advanced binary optical logic gate elements
IEEE Transactions on Communications, 2009Co-Authors: B M Ghaffari, Jawad A SalehiAbstract: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.
Ramjee Prasad - One of the best experts on this subject based on the ideXlab platform.
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design and performance of multicarrier cdma system in frequency selective rayleigh fading channels
IEEE Transactions on Vehicular Technology, 1999Co-Authors: Shinsuke Hara, Ramjee PrasadAbstract:This paper presents the advantages and disadvantages of a multicarrier code-division multiple-access (MC-CDMA) system. The transmitter/Receiver Structure and, the bandwidth of transmitted signal spectrum are compared with those of a conventional direct-sequence (DS) CDMA system, and an MC-CDMA design method, how to determine the number of subcarriers and the length of guard interval is discussed. The bit error rate (BER) lower bounds for DS-CDMA and MC-CDMA systems are derived and their equivalence is theoretically demonstrated. Finally, the BER performance in downlink and uplink channels with frequency-selective Rayleigh fading is shown by computer simulation.
S Pasupathy - One of the best experts on this subject based on the ideXlab platform.
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Widely Linear MMSE Receivers for Linear Dispersion Space-Time Block-Codes
2016Co-Authors: Amirhossein S Aghaei, Konstantinos N Plataniotis, S Pasupathy, Student Member, Senior Member, Life FellowAbstract:Abstract—This paper proposes a new Receiver Structure for linear-dispersion (LD) codes, subsuming orthogonal, quasi-orthogonal and V-BLAST codes. We suggest to use widely-linear minimum-mean-squared-error (WL-MMSE) estimates of trans-mitted symbols in lieu of the sufficient statistics for maximum likelihood (ML) detection of these symbols. Proposed Structure offers both optimal (ML) and suboptimal solutions. Simulation results show that the suboptimal Receiver performs close to the optimal one, while reducing the Receiver’s complexity. Structure of the proposed Receiver is particularly studied for orthogonal and quasi-orthogonal LD codes. Specifically, it is proved that Alamouti’s combining scheme provides WL-MMSE estimates of the transmitted symbols. Index Terms—Improper complex random vector, linear dis-persion codes, MIMO systems, space-time codes, widely-linear estimation. I
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widely linear mmse Receivers for linear dispersion space time block codes
IEEE Transactions on Wireless Communications, 2010Co-Authors: Amirhossein S Aghaei, Konstantinos N Plataniotis, S PasupathyAbstract:This paper proposes a new Receiver Structure for linear-dispersion (LD) codes, subsuming orthogonal, quasiorthogonal and V-BLAST codes. We suggest to use widely-linear minimum-mean-squared-error (WL-MMSE) estimates of transmitted symbols in lieu of the sufficient statistics for maximum likelihood (ML) detection of these symbols. Proposed Structure offers both optimal (ML) and suboptimal solutions. Simulation results show that the suboptimal Receiver performs close to the optimal one, while reducing the Receiver's complexity. Structure of the proposed Receiver is particularly studied for orthogonal and quasi-orthogonal LD codes. Specifically, it is proved that Alamouti's combining scheme provides WL-MMSE estimates of the transmitted symbols.
H V Poor - One of the best experts on this subject based on the ideXlab platform.
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joint channel estimation equalization and data detection for ofdm systems in the presence of very high mobility
IEEE Transactions on Signal Processing, 2010Co-Authors: Erdal Panayirci, Habib Senol, H V PoorAbstract:This paper is concerned with the challenging and timely problem of joint channel estimation, equalization, and data detection for uplink orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency selective and very rapidly time varying channels. The resulting algorithm is based on the space alternating generalized expectation maximization (SAGE) technique which is particularly well suited to multicarrier signal formats leading to a Receiver Structure that also incorporates interchannel interference (ICI) cancelation. In order to reduce the computational complexity of the algorithm, band-limited, discrete cosine orthogonal basis functions are employed to represent the rapidly time-varying fading channel by the discrete cosine serial expansion coefficients. It is shown that, depending on the normalized Doppler frequency, only a small number of expansion coefficients is sufficient to approximate the channel perfectly and there is no need to know the correlation function of the input signal. In this way, the resulting reduced dimensional channel coefficients are estimated and the data symbols detected iteratively with tractable complexity. The proposed SAGE joint detection algorithm updates the data sequences serially and the channel parameters are updated in parallel, leading to a Receiver Structure that also incorporates ICI cancelation. Computer simulations show that the cosine transformation represents the time-varying channel very effectively and the proposed algorithm has excellent symbol error rate and channel estimation performance even with a very small number of channel expansion coefficients employed in the algorithm, resulting in substantial reduction of the computational complexity.
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iterative turbo soft interference cancellation and decoding for coded cdma
IEEE Transactions on Communications, 1999Co-Authors: Xiaodong Wang, H V PoorAbstract:The presence of both multiple-access interference (MAI) and intersymbol interference (ISI) constitutes a major impediment to reliable communications in multipath code-division multiple-access (CDMA) channels. In this paper, an iterative Receiver Structure is proposed for decoding multiuser information data in a convolutionally coded asynchronous multipath DS-CDMA system. The Receiver performs two successive soft-output decisions, achieved by a soft-input soft-output (SISO) multiuser detector and a bank of single-user SISO channel decoders, through an iterative process. At each iteration, extrinsic information is extracted from detection and decoding stages and is then used as a priori information in the next iteration, just as in turbo decoding. Given the multipath CDMA channel model, a direct implementation of a sliding-window SISO multiuser detector has a prohibitive computational complexity. A low-complexity SISO multiuser detector is developed based on a novel nonlinear interference suppression technique, which makes use of both soft interference cancellation and instantaneous linear minimum mean-square error filtering. The properties of such a nonlinear interference suppressor are examined, and an efficient recursive implementation is derived. Simulation results demonstrate that the proposed low complexity iterative Receiver Structure for interference suppression and decoding offers significant performance gain over the traditional noniterative Receiver Structure. Moreover, at high signal-to-noise ratio, the detrimental effects of MAI and ISI in the channel can almost be completely overcome by iterative processing, and single-user performance can be approached.
