Jawad Salehi | Sharif University of Technology (original) (raw)

Papers by Jawad Salehi

Proceedings of SPIE, Apr 29, 2016

In this paper, we investigate the performance of orthogonal frequency division multiplexed quantu... more In this paper, we investigate the performance of orthogonal frequency division multiplexed quantum key distribution (OFDM-QKD) in an integrated quantum-classical wavelength-division-multiplexing system. The presence of an intense classical signal alongside the quantum one generates Raman background noise. Noise reduction techniques should, then, be carried out at the receiver to suppress this crosstalk noise. In this work, we show that OFDM-QKD enables efficient filtering, in time and frequency domains, making it an attractive solution for the high-rate links at the core of quantum-classical networks.

An efficient method for optimal allocation of wavelengths in a hybrid dense-wavelength-division-m... more An efficient method for optimal allocation of wavelengths in a hybrid dense-wavelength-division-multiplexing system, carrying both quantum and classical data, is proposed. The transmission of quantum bits alongside intense classical signals on the same fiber faces major challenges arising from the background noise generated by classical channels. Raman scattering, in particular, is shown to have detrimental effects on the performance of quantum key distribution systems. Here, by using a nearly optimal wavelength allocation technique, we minimize the Raman induced background noise on quantum channels, hence maximize the achievable secret key generation rate for quantum channels. It turns out the conventional solution that would involve splitting the spectrum into only two bands, one for quantum and one for classical channels, is only a suboptimal one. We show that, in our optimal arrangement, we might need several quantum and classical bands interspersed among each other.

Journal of Optical Communications and Networking, May 21, 2015

In this paper, we present a design methodology with implementational insight and evaluate the per... more In this paper, we present a design methodology with implementational insight and evaluate the performance of a multicarrier code-division multiple access (MC-CDMA) system using intensity modulation/direct detection scheme suitable for an indoor visible light communication (VLC) environment. The proposed system is a CDMA system based on an orthogonal frequency division multiplexing (OFDM) platform. To overcome the light-dimming issue, we use a newly proposed methodology, namely, polarity reversed optical OFDM (PRO-OFDM). A unipolar signal is either added to the minimum current or subtracted from the maximum current in the LED linear current range to provide various amounts of dimming. The CDMA part employs Hadamard sequences to provide synchronous resource sharing. Combining the robustness of orthogonal modulation with the flexibility of CDMA schemes makes the proposed system a viable candidate for future indoor wireless communications such as VLC. The performance of the proposed MC-CDMA is evaluated, and mathematical formulations for the proposed system are derived. For example, closed-form equations for the signal-to-interference-plus-noise ratio and bit error rate (BER) performance are obtained. Furthermore, the analytical formulations are used in numerical analysis to verify the BER performance achieved in simulation results.

IEEE Transactions on Wireless Communications, May 1, 2003

One of the most prominent features of code division multiple-access (CDMA) cellular networks is t... more One of the most prominent features of code division multiple-access (CDMA) cellular networks is their ability for applying soft-handoff. This type of handoff results in a better support of seamless communication services, capacity enhancement, QoS improvement, etc. Because of the existence of more parameters and flexibilities compared to hard-handoff, an optimum solution for soft-handoff management and admission control for new

Scientia Iranica, Oct 1, 2016

In this paper, we propose and investigate several crosstalk reduction techniques for hybrid quant... more In this paper, we propose and investigate several crosstalk reduction techniques for hybrid quantum-classical dense-wavelength-division-multiplexing systems. The transmission of intense classical signals alongside weak quantum ones on the same ber introduces some crosstalk noise, mainly due to Raman scattering and non-ideal channel isolation, that may severely a ect the performance of quantum key distribution systems. We examine the conventional methods of suppressing this crosstalk noise, and enhance them by proposing an appropriate channel allocation method that reduces the background crosstalk e ectively. Another approach proposed in this paper is the usage of orthogonal frequency division multiplexing, which o ers e cient spectral and temporal ltering features.

Journal of Lightwave Technology, Aug 1, 2002

In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division... more In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division multiple-access (FO-CDMA) networks. In this analysis, we propose statistical models, based on photon-counting techniques, for some basic elements of the network, such as splitters, combiners, star couplers, and FO-CDMA passive encoders/decoders. By following the statistical variation of the photon-count of the string of pulses that constitutes the address sequence in an FO-CDMA network, we will be able to reveal the quantum-limited optical signal-to-noise ratio (OSNR) required at the transmitter output to meet the performance limits. Moreover, considering receiver thermal noise and source extinction ratio, we explore the role of using an optical preamplifier before the detector and the dependence of the performance on the transmitted power and the weight of the employed optical orthogonal codes (OOCs). Index Terms-Code division multiple access (CDMA), optical CDMA, optical couplers, optical encoder/decoder, optical orthogonal codes, optical preamplifier, photon-counting technique. I. INTRODUCTION A DVANCES in enabling technologies such as erbium-doped fiber amplifiers (EDFAs) and optical encoders/decoders, along with their inevitable and ubiquitous use in fiber-optic based networks, compel us to devise a better mathematical modeling of their performance in the context of bit error rate (BER) in a communication system. Paramount to the performance of various optical devices in a communication system is their statistical input/output signal characteristics. In this work, the preferred statistical model for such optical devices is based upon photon-counting techniques. This modeling, which is related to a more general mathematical approach (namely, branching processes [1]), provides us with a measure of the quantum noisiness of these devices, which will ultimately put a limit on the performance of the system. Among many optical networks that will use various enabling optical devices, optical code division multiple access (CDMA) schemes have been receiving a great deal of attention for the past decade [2]-[12] due to their robust functionality and immense potentials. In this paper, we consider the performance evaluation of the fiber-optic CDMA (FO-CDMA) technique [2]-[4], which is designed for positive systems such as intensity modu-Manuscript

arXiv (Cornell University), Jan 28, 2017

Optimal wavelength assignment in dense-wavelength-division-multiplexing (DWDM) systems that integ... more Optimal wavelength assignment in dense-wavelength-division-multiplexing (DWDM) systems that integrate both quantum and classical channels is studied. In such systems, weak quantum key distribution (QKD) signals travel alongside intense classical signals on the same fiber, where the former can be masked by the background noise induced by the latter. Here, we investigate how optimal wavelength assignment can mitigate this problem. We consider different DWDM structures and various sources of crosstalk and propose several near-optimal wavelength assignment methods that maximize the total secret key rate of the QKD channels. Our numerical results show that the optimum wavelength assignment pattern is commonly consisted of several interspersed quantum and classical bands. Using our proposed techniques, the total secret key rate of quantum channels can substantially be improved, as compared to conventional assignment methods, in the noise dominated regimes. Alternatively, we can maximize the number of QKD users supported under certain key rate constraints.

Journal of Lightwave Technology, Oct 1, 2002

A communication system incorporating a bit rate limiter (BRL) device is analyzed using recently p... more A communication system incorporating a bit rate limiter (BRL) device is analyzed using recently proposed statistical models for power splitters and combiners. We also consider the possible optical attenuation and amplification before and after BRL device. We obtain the total output moment generating function (MGF) of the number of photoelectrons at the receiver end for two possible synchronization procedures. Furthermore, we use saddle-point approximation method to evaluate the system performance considering the effects of shot-noise, thermal noise, and source extinction ratio.

ABSTRACT We propose a general mobility model based on region splitting and mapping each subregion... more ABSTRACT We propose a general mobility model based on region splitting and mapping each subregion on a multi-server node. By using the theory of multi-class Jackson queueing network with multiserver nodes and employing the product-form solution for such queueing networks, we obtain an analytical form for the spatial traffic distribution in a typical region with specific number of users. To this end, we consider the spatial statistical pattern for new and handoff call arrivals and the ratio between these two types of arrivals. At last, we apply our new model to some simple mobility scenarios and compute the resultant active user's location densities.

Journal of Lightwave Technology, Dec 1, 2015

We propose orthogonal frequency division multiplexing (OFDM), as a spectrally efficient multiplex... more We propose orthogonal frequency division multiplexing (OFDM), as a spectrally efficient multiplexing technique, for quantum key distribution (QKD) at the core of trustednode quantum networks. Two main schemes are proposed and analyzed in detail, considering system imperfections, specifically, time misalignment issues. It turns out that while multiple service providers can share the network infrastructure using the proposed multiplexing techniques, no gain in the total secret key generation rate is obtained if one uses conventional passive all-optical OFDM decoders. To achieve a linear increase in the key rate with the number of channels, an alternative active setup for OFDM decoding is proposed, which employs an optical switch in addition to conventional passive circuits. We show that by using our proposed decoder the bandwidth utilization is considerably improved as compared to conventional wavelength division multiplexing techniques.

Scientia Iranica, Jul 1, 2004

In this paper, two basic new call admission control policies in soft-handoff regions in Code-Divi... more In this paper, two basic new call admission control policies in soft-handoff regions in Code-Division Multiple-Access (CDMA) cellular networks are compared. The two policies are Independent Decision Policy (IDP), which is, approximately, equivalent to a directed retry policy proposed for non-CDMA cellular networks and Collective Decision Policy (CDP). The merits in this comparison include the tradeoff between carried traffic and quality loss probability while maintaining other traffic parameters (such as blocking and dropping (handoff failure) probabilities) sufficiently low. Using numerical results, it is deduced that the CDP leads to a better overall performance. Another important issue considered in this paper reverts to spatial fairness. In this respect, the necessary modification for the above admission policies is proposed. In these analyses, a modified reverse link dynamic traffic model is employed, built upon Interference-based Call Admission Control (ICAC), by including the shadowing effect in soft-handoff regions.

Journal of Lightwave Technology, Aug 1, 2002

In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division... more In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division multiple-access (FO-CDMA) networks. In this analysis, we propose statistical models, based on photon-counting techniques, for some basic elements of the network, such as splitters, combiners, star couplers, and FO-CDMA passive encoders/decoders. By following the statistical variation of the photon-count of the string of pulses that constitutes the address sequence in an FO-CDMA network, we will be able to reveal the quantum-limited optical signal-to-noise ratio (OSNR) required at the transmitter output to meet the performance limits. Moreover, considering receiver thermal noise and source extinction ratio, we explore the role of using an optical preamplifier before the detector and the dependence of the performance on the transmitted power and the weight of the employed optical orthogonal codes (OOCs). Index Terms-Code division multiple access (CDMA), optical CDMA, optical couplers, optical encoder/decoder, optical orthogonal codes, optical preamplifier, photon-counting technique. I. INTRODUCTION A DVANCES in enabling technologies such as erbium-doped fiber amplifiers (EDFAs) and optical encoders/decoders, along with their inevitable and ubiquitous use in fiber-optic based networks, compel us to devise a better mathematical modeling of their performance in the context of bit error rate (BER) in a communication system. Paramount to the performance of various optical devices in a communication system is their statistical input/output signal characteristics. In this work, the preferred statistical model for such optical devices is based upon photon-counting techniques. This modeling, which is related to a more general mathematical approach (namely, branching processes [1]), provides us with a measure of the quantum noisiness of these devices, which will ultimately put a limit on the performance of the system. Among many optical networks that will use various enabling optical devices, optical code division multiple access (CDMA) schemes have been receiving a great deal of attention for the past decade [2]-[12] due to their robust functionality and immense potentials. In this paper, we consider the performance evaluation of the fiber-optic CDMA (FO-CDMA) technique [2]-[4], which is designed for positive systems such as intensity modu-Manuscript

IEEE Transactions on Wireless Communications, 2004

... CDMA Cellular Networks Farid Ashtiani, Student Member, IEEE, Jawad A. Salehi, Member, IEEE, a... more ... CDMA Cellular Networks Farid Ashtiani, Student Member, IEEE, Jawad A. Salehi, Member, IEEE, and Mohammad R. Aref ... From 1995 to 1999 he was partly working in Power Research Center (PRC) and Niroo Research Institute (NRI) of Iran. ...

2017 IEEE International Conference on Communications (ICC)

In this paper, we investigate multi-quality of service (QoS) routing and spectrum assignment in e... more In this paper, we investigate multi-quality of service (QoS) routing and spectrum assignment in elastic optical networks (EONs) by utilizing network state information in terms of bandwidth usage and holding time of established connections. Toward this aim, two types of traffic, namely big data traffic (BDT) requests, and fixed rate flow requests (FLRs) are considered, where BDTs can tolerate a pre-determined initial delay while FLRs must be served immediately without any delay. We assume that both frequency and time usage of optical bandwidth is slotted, and accordingly optical resources are defined in a two-dimensional (2D) time/frequency domain, where the smallest resource is specified with its time and frequency slot number. Furthermore, we define two controlling coefficients determining the ratio of time and spectrum slots which can be assigned to BDTs. By selecting various values for these coefficients, network manager will be able to support different class of services and change the relative priorities of different classes. In addition, for each coefficient we obtain a threshold determining the upper bound on the number of time or frequency slots allocated to BDTs. Our results highlight the relation between the blocking probability and the value of these thresholds. In particular, the results show that assigning smaller resource blocks will result into lower blocking probability for both FLRs and BDTs. In addition, the maximum initial delay plays an important role in the blocking probability of BDTs.

2021 IEEE Global Communications Conference (GLOBECOM), 2021

Future heterogeneous wireless networks (HetNets) should provide massive connectivity for a large ... more Future heterogeneous wireless networks (HetNets) should provide massive connectivity for a large number of devices. In such networks, the problem of user association and multiple access management is of paramount importance. This paper formulates a statistical representation of the user association problem using users' probability density function. In other words, this paper is a bridge between the dynamic mixed-integer formulation of the user association used in relaxation, game theory, and reinforcement learning approaches and the static user association considered in analytical stochastic geometry methods. To this aim, a novel representation independent of the number of users is derived from the combinatorial user association formulation. Interestingly, we show that for fair user association, the statistical representation is a multi-objective optimization. The first objective is to maximize the network throughput with fairness consideration, and the second objective is to optimize the load balancing in terms of the Shannon entropy. Based on this representation, we introduce an algorithm to optimize user association using the first-order derivative formula. We propose a method that can optimize individual base stations' bias factors inside each tier of a HetNet. Numerical results show that the statistical representation closely tracks the stochastic behavior of the dynamic association. The proposed optimization approach improves the 10% outage rate of a two-tier network by 19% and enhances the load balancing by reducing the load of macro base stations by 22%.

2017 Iran Workshop on Communication and Information Theory (IWCIT), 2017

In this paper, we present a detailed analytical approach to obtain the channel capacity of optica... more In this paper, we present a detailed analytical approach to obtain the channel capacity of optical space-division multiplexing (SDM) systems. To this aim, the nonlinearity effects of optical fiber are modeled as additive white Gaussian noise (GN) process, and accordingly a closed-form formula is derived for SDM capacity. Furthermore, we extend our result to a more generalized case, which includes different bandwidth, center frequency, and transmission powers.

Computer Communications, 2021

2021 Iran Workshop on Communication and Information Theory (IWCIT), 2021

The long-term performance of LiFi networks significantly depends on the location of access points... more The long-term performance of LiFi networks significantly depends on the location of access points. The optimized placement can be determined based on the distribution of users in the room. In this paper, we investigate the placement optimization for average throughput maximization in the presence of asymmetric distributions. In particular, we represent users’ distribution in the indoor environment by the Gaussian mixture model, which is powerful and computationally convenient. Then we obtain the optimized deployment for different scenarios using gradient ascent algorithm. The results show that optimization of deployment significantly improves the average throughput of the network. As the variance of the mixture components increases, the optimized placement approaches a symmetric deployment.

Proceedings of SPIE, Apr 29, 2016

In this paper, we investigate the performance of orthogonal frequency division multiplexed quantu... more In this paper, we investigate the performance of orthogonal frequency division multiplexed quantum key distribution (OFDM-QKD) in an integrated quantum-classical wavelength-division-multiplexing system. The presence of an intense classical signal alongside the quantum one generates Raman background noise. Noise reduction techniques should, then, be carried out at the receiver to suppress this crosstalk noise. In this work, we show that OFDM-QKD enables efficient filtering, in time and frequency domains, making it an attractive solution for the high-rate links at the core of quantum-classical networks.

An efficient method for optimal allocation of wavelengths in a hybrid dense-wavelength-division-m... more An efficient method for optimal allocation of wavelengths in a hybrid dense-wavelength-division-multiplexing system, carrying both quantum and classical data, is proposed. The transmission of quantum bits alongside intense classical signals on the same fiber faces major challenges arising from the background noise generated by classical channels. Raman scattering, in particular, is shown to have detrimental effects on the performance of quantum key distribution systems. Here, by using a nearly optimal wavelength allocation technique, we minimize the Raman induced background noise on quantum channels, hence maximize the achievable secret key generation rate for quantum channels. It turns out the conventional solution that would involve splitting the spectrum into only two bands, one for quantum and one for classical channels, is only a suboptimal one. We show that, in our optimal arrangement, we might need several quantum and classical bands interspersed among each other.

Journal of Optical Communications and Networking, May 21, 2015

In this paper, we present a design methodology with implementational insight and evaluate the per... more In this paper, we present a design methodology with implementational insight and evaluate the performance of a multicarrier code-division multiple access (MC-CDMA) system using intensity modulation/direct detection scheme suitable for an indoor visible light communication (VLC) environment. The proposed system is a CDMA system based on an orthogonal frequency division multiplexing (OFDM) platform. To overcome the light-dimming issue, we use a newly proposed methodology, namely, polarity reversed optical OFDM (PRO-OFDM). A unipolar signal is either added to the minimum current or subtracted from the maximum current in the LED linear current range to provide various amounts of dimming. The CDMA part employs Hadamard sequences to provide synchronous resource sharing. Combining the robustness of orthogonal modulation with the flexibility of CDMA schemes makes the proposed system a viable candidate for future indoor wireless communications such as VLC. The performance of the proposed MC-CDMA is evaluated, and mathematical formulations for the proposed system are derived. For example, closed-form equations for the signal-to-interference-plus-noise ratio and bit error rate (BER) performance are obtained. Furthermore, the analytical formulations are used in numerical analysis to verify the BER performance achieved in simulation results.

IEEE Transactions on Wireless Communications, May 1, 2003

One of the most prominent features of code division multiple-access (CDMA) cellular networks is t... more One of the most prominent features of code division multiple-access (CDMA) cellular networks is their ability for applying soft-handoff. This type of handoff results in a better support of seamless communication services, capacity enhancement, QoS improvement, etc. Because of the existence of more parameters and flexibilities compared to hard-handoff, an optimum solution for soft-handoff management and admission control for new

Scientia Iranica, Oct 1, 2016

In this paper, we propose and investigate several crosstalk reduction techniques for hybrid quant... more In this paper, we propose and investigate several crosstalk reduction techniques for hybrid quantum-classical dense-wavelength-division-multiplexing systems. The transmission of intense classical signals alongside weak quantum ones on the same ber introduces some crosstalk noise, mainly due to Raman scattering and non-ideal channel isolation, that may severely a ect the performance of quantum key distribution systems. We examine the conventional methods of suppressing this crosstalk noise, and enhance them by proposing an appropriate channel allocation method that reduces the background crosstalk e ectively. Another approach proposed in this paper is the usage of orthogonal frequency division multiplexing, which o ers e cient spectral and temporal ltering features.

Journal of Lightwave Technology, Aug 1, 2002

In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division... more In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division multiple-access (FO-CDMA) networks. In this analysis, we propose statistical models, based on photon-counting techniques, for some basic elements of the network, such as splitters, combiners, star couplers, and FO-CDMA passive encoders/decoders. By following the statistical variation of the photon-count of the string of pulses that constitutes the address sequence in an FO-CDMA network, we will be able to reveal the quantum-limited optical signal-to-noise ratio (OSNR) required at the transmitter output to meet the performance limits. Moreover, considering receiver thermal noise and source extinction ratio, we explore the role of using an optical preamplifier before the detector and the dependence of the performance on the transmitted power and the weight of the employed optical orthogonal codes (OOCs). Index Terms-Code division multiple access (CDMA), optical CDMA, optical couplers, optical encoder/decoder, optical orthogonal codes, optical preamplifier, photon-counting technique. I. INTRODUCTION A DVANCES in enabling technologies such as erbium-doped fiber amplifiers (EDFAs) and optical encoders/decoders, along with their inevitable and ubiquitous use in fiber-optic based networks, compel us to devise a better mathematical modeling of their performance in the context of bit error rate (BER) in a communication system. Paramount to the performance of various optical devices in a communication system is their statistical input/output signal characteristics. In this work, the preferred statistical model for such optical devices is based upon photon-counting techniques. This modeling, which is related to a more general mathematical approach (namely, branching processes [1]), provides us with a measure of the quantum noisiness of these devices, which will ultimately put a limit on the performance of the system. Among many optical networks that will use various enabling optical devices, optical code division multiple access (CDMA) schemes have been receiving a great deal of attention for the past decade [2]-[12] due to their robust functionality and immense potentials. In this paper, we consider the performance evaluation of the fiber-optic CDMA (FO-CDMA) technique [2]-[4], which is designed for positive systems such as intensity modu-Manuscript

arXiv (Cornell University), Jan 28, 2017

Optimal wavelength assignment in dense-wavelength-division-multiplexing (DWDM) systems that integ... more Optimal wavelength assignment in dense-wavelength-division-multiplexing (DWDM) systems that integrate both quantum and classical channels is studied. In such systems, weak quantum key distribution (QKD) signals travel alongside intense classical signals on the same fiber, where the former can be masked by the background noise induced by the latter. Here, we investigate how optimal wavelength assignment can mitigate this problem. We consider different DWDM structures and various sources of crosstalk and propose several near-optimal wavelength assignment methods that maximize the total secret key rate of the QKD channels. Our numerical results show that the optimum wavelength assignment pattern is commonly consisted of several interspersed quantum and classical bands. Using our proposed techniques, the total secret key rate of quantum channels can substantially be improved, as compared to conventional assignment methods, in the noise dominated regimes. Alternatively, we can maximize the number of QKD users supported under certain key rate constraints.

Journal of Lightwave Technology, Oct 1, 2002

A communication system incorporating a bit rate limiter (BRL) device is analyzed using recently p... more A communication system incorporating a bit rate limiter (BRL) device is analyzed using recently proposed statistical models for power splitters and combiners. We also consider the possible optical attenuation and amplification before and after BRL device. We obtain the total output moment generating function (MGF) of the number of photoelectrons at the receiver end for two possible synchronization procedures. Furthermore, we use saddle-point approximation method to evaluate the system performance considering the effects of shot-noise, thermal noise, and source extinction ratio.

ABSTRACT We propose a general mobility model based on region splitting and mapping each subregion... more ABSTRACT We propose a general mobility model based on region splitting and mapping each subregion on a multi-server node. By using the theory of multi-class Jackson queueing network with multiserver nodes and employing the product-form solution for such queueing networks, we obtain an analytical form for the spatial traffic distribution in a typical region with specific number of users. To this end, we consider the spatial statistical pattern for new and handoff call arrivals and the ratio between these two types of arrivals. At last, we apply our new model to some simple mobility scenarios and compute the resultant active user's location densities.

Journal of Lightwave Technology, Dec 1, 2015

We propose orthogonal frequency division multiplexing (OFDM), as a spectrally efficient multiplex... more We propose orthogonal frequency division multiplexing (OFDM), as a spectrally efficient multiplexing technique, for quantum key distribution (QKD) at the core of trustednode quantum networks. Two main schemes are proposed and analyzed in detail, considering system imperfections, specifically, time misalignment issues. It turns out that while multiple service providers can share the network infrastructure using the proposed multiplexing techniques, no gain in the total secret key generation rate is obtained if one uses conventional passive all-optical OFDM decoders. To achieve a linear increase in the key rate with the number of channels, an alternative active setup for OFDM decoding is proposed, which employs an optical switch in addition to conventional passive circuits. We show that by using our proposed decoder the bandwidth utilization is considerably improved as compared to conventional wavelength division multiplexing techniques.

Scientia Iranica, Jul 1, 2004

In this paper, two basic new call admission control policies in soft-handoff regions in Code-Divi... more In this paper, two basic new call admission control policies in soft-handoff regions in Code-Division Multiple-Access (CDMA) cellular networks are compared. The two policies are Independent Decision Policy (IDP), which is, approximately, equivalent to a directed retry policy proposed for non-CDMA cellular networks and Collective Decision Policy (CDP). The merits in this comparison include the tradeoff between carried traffic and quality loss probability while maintaining other traffic parameters (such as blocking and dropping (handoff failure) probabilities) sufficiently low. Using numerical results, it is deduced that the CDP leads to a better overall performance. Another important issue considered in this paper reverts to spatial fairness. In this respect, the necessary modification for the above admission policies is proposed. In these analyses, a modified reverse link dynamic traffic model is employed, built upon Interference-based Call Admission Control (ICAC), by including the shadowing effect in soft-handoff regions.

Journal of Lightwave Technology, Aug 1, 2002

In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division... more In this paper, we present a new methodology for analysis of all-optical fiber-optic code-division multiple-access (FO-CDMA) networks. In this analysis, we propose statistical models, based on photon-counting techniques, for some basic elements of the network, such as splitters, combiners, star couplers, and FO-CDMA passive encoders/decoders. By following the statistical variation of the photon-count of the string of pulses that constitutes the address sequence in an FO-CDMA network, we will be able to reveal the quantum-limited optical signal-to-noise ratio (OSNR) required at the transmitter output to meet the performance limits. Moreover, considering receiver thermal noise and source extinction ratio, we explore the role of using an optical preamplifier before the detector and the dependence of the performance on the transmitted power and the weight of the employed optical orthogonal codes (OOCs). Index Terms-Code division multiple access (CDMA), optical CDMA, optical couplers, optical encoder/decoder, optical orthogonal codes, optical preamplifier, photon-counting technique. I. INTRODUCTION A DVANCES in enabling technologies such as erbium-doped fiber amplifiers (EDFAs) and optical encoders/decoders, along with their inevitable and ubiquitous use in fiber-optic based networks, compel us to devise a better mathematical modeling of their performance in the context of bit error rate (BER) in a communication system. Paramount to the performance of various optical devices in a communication system is their statistical input/output signal characteristics. In this work, the preferred statistical model for such optical devices is based upon photon-counting techniques. This modeling, which is related to a more general mathematical approach (namely, branching processes [1]), provides us with a measure of the quantum noisiness of these devices, which will ultimately put a limit on the performance of the system. Among many optical networks that will use various enabling optical devices, optical code division multiple access (CDMA) schemes have been receiving a great deal of attention for the past decade [2]-[12] due to their robust functionality and immense potentials. In this paper, we consider the performance evaluation of the fiber-optic CDMA (FO-CDMA) technique [2]-[4], which is designed for positive systems such as intensity modu-Manuscript

IEEE Transactions on Wireless Communications, 2004

... CDMA Cellular Networks Farid Ashtiani, Student Member, IEEE, Jawad A. Salehi, Member, IEEE, a... more ... CDMA Cellular Networks Farid Ashtiani, Student Member, IEEE, Jawad A. Salehi, Member, IEEE, and Mohammad R. Aref ... From 1995 to 1999 he was partly working in Power Research Center (PRC) and Niroo Research Institute (NRI) of Iran. ...

2017 IEEE International Conference on Communications (ICC)

In this paper, we investigate multi-quality of service (QoS) routing and spectrum assignment in e... more In this paper, we investigate multi-quality of service (QoS) routing and spectrum assignment in elastic optical networks (EONs) by utilizing network state information in terms of bandwidth usage and holding time of established connections. Toward this aim, two types of traffic, namely big data traffic (BDT) requests, and fixed rate flow requests (FLRs) are considered, where BDTs can tolerate a pre-determined initial delay while FLRs must be served immediately without any delay. We assume that both frequency and time usage of optical bandwidth is slotted, and accordingly optical resources are defined in a two-dimensional (2D) time/frequency domain, where the smallest resource is specified with its time and frequency slot number. Furthermore, we define two controlling coefficients determining the ratio of time and spectrum slots which can be assigned to BDTs. By selecting various values for these coefficients, network manager will be able to support different class of services and change the relative priorities of different classes. In addition, for each coefficient we obtain a threshold determining the upper bound on the number of time or frequency slots allocated to BDTs. Our results highlight the relation between the blocking probability and the value of these thresholds. In particular, the results show that assigning smaller resource blocks will result into lower blocking probability for both FLRs and BDTs. In addition, the maximum initial delay plays an important role in the blocking probability of BDTs.

2021 IEEE Global Communications Conference (GLOBECOM), 2021

Future heterogeneous wireless networks (HetNets) should provide massive connectivity for a large ... more Future heterogeneous wireless networks (HetNets) should provide massive connectivity for a large number of devices. In such networks, the problem of user association and multiple access management is of paramount importance. This paper formulates a statistical representation of the user association problem using users' probability density function. In other words, this paper is a bridge between the dynamic mixed-integer formulation of the user association used in relaxation, game theory, and reinforcement learning approaches and the static user association considered in analytical stochastic geometry methods. To this aim, a novel representation independent of the number of users is derived from the combinatorial user association formulation. Interestingly, we show that for fair user association, the statistical representation is a multi-objective optimization. The first objective is to maximize the network throughput with fairness consideration, and the second objective is to optimize the load balancing in terms of the Shannon entropy. Based on this representation, we introduce an algorithm to optimize user association using the first-order derivative formula. We propose a method that can optimize individual base stations' bias factors inside each tier of a HetNet. Numerical results show that the statistical representation closely tracks the stochastic behavior of the dynamic association. The proposed optimization approach improves the 10% outage rate of a two-tier network by 19% and enhances the load balancing by reducing the load of macro base stations by 22%.

2017 Iran Workshop on Communication and Information Theory (IWCIT), 2017

In this paper, we present a detailed analytical approach to obtain the channel capacity of optica... more In this paper, we present a detailed analytical approach to obtain the channel capacity of optical space-division multiplexing (SDM) systems. To this aim, the nonlinearity effects of optical fiber are modeled as additive white Gaussian noise (GN) process, and accordingly a closed-form formula is derived for SDM capacity. Furthermore, we extend our result to a more generalized case, which includes different bandwidth, center frequency, and transmission powers.

Computer Communications, 2021

2021 Iran Workshop on Communication and Information Theory (IWCIT), 2021

The long-term performance of LiFi networks significantly depends on the location of access points... more The long-term performance of LiFi networks significantly depends on the location of access points. The optimized placement can be determined based on the distribution of users in the room. In this paper, we investigate the placement optimization for average throughput maximization in the presence of asymmetric distributions. In particular, we represent users’ distribution in the indoor environment by the Gaussian mixture model, which is powerful and computationally convenient. Then we obtain the optimized deployment for different scenarios using gradient ascent algorithm. The results show that optimization of deployment significantly improves the average throughput of the network. As the variance of the mixture components increases, the optimized placement approaches a symmetric deployment.