Sharif Digital Repository

In this paper, we study three types of jammers, namely, pulse-jammer, partial-band jammer, and follower-jammer, in a typical fiber-optic-based spectrally phase-encoded optical code division multiple-access (SPE-OCDMA) system. We analyze, mathematically, the effects of the aforementioned jammers on the performance of an SPE-OCDMA system for two scenarios, namely, ideal noiseless channel with an ideal optimum receiver and an ultrahigh-speed nonlinear receiver based on two-photon-absorption (TPA) in a noisy channel. Also, for each of the above cases, two types of modulation, namely, on-off keying (OOK) and two-code keying (2CK) are investigated and their system performances are compared. It is... 

In this paper, we study three types of jammers, namely, pulse-jammer, partial-band jammer, and follower-jammer, in a typical fiber-optic-based spectrally phase-encoded optical code division multiple-access (SPE-OCDMA) system. We analyze, mathematically, the effects of the aforementioned jammers on the performance of an SPE-OCDMA system for two scenarios, namely, ideal noiseless channel with an ideal optimum receiver and an ultrahigh-speed nonlinear receiver based on two-photon-absorption (TPA) in a noisy channel. Also, for each of the above cases, two types of modulation, namely, ON-OFF keying (OOK) and two-code keying (2CK) are investigated and their system performances are compared. It is... 

Although, enhanced security is often mentioned as a noticeable benefit of Spectrally Phase Encoded Optical CDMA (SPE-OCDMA) systems, the quantity and degree of security enhancement is not considered deeply in the literature. One of the facts in determining the degree of security is to assess the resistance capability of the system against various jammers attacks. In this paper, we introduce and model three types of jammers, namely (Pulse Jammer, Partialband Jammer, and Follower Jammer). We mathematically analyze the effects of the above jammers on the performance of the SPE-OCDMA systems that use On-Off keying (OOK) modulation scheme. It is demonstrated that under certain conditions, the... 

In this work we present a high-throughput, low-complexity design for linear precoding in massive Multiple-Input Multiple-Output (MIMO) systems. Large number of Base Station (BS) antennas in massive MIMO at one hand has caused the performance of linear precoders to be near-optimal and at the other hand has increased their complexity due to the need for the inversion of matrices with large dimensions. To avoid this complexity, approximate inversion methods based on Neumann Series have been proposed. However, in this work, we propose an architecture for Zero Forcing (ZF) precoder based on the Neumann Series approximate inversion that further reduces the complexity by replacing matrix-matrix... 

In this paper, a linear piezoelectric stepper (LPS) motor drive using a resonant converter is proposed. The mechanism of operation of the LPS motor is first described. Then, a single-phase equivalent model of the LPS motor is introduced. In addition, design theory of the driving circuit using a current source inverter for the LPS motor is explained in detail. At the end, simulation and experimental results based on the resonant converter are presented and analyzed to verify the validity of the proposed system  

In this study, a two-user discrete memoryless multiple-access channel with two correlated states known non-causally at the corresponding encoder is considered. Each encoder transmits a message independent of the other encoder's and tries to cooperate with it. To consider cooperative encoders, it is assumed that each encoder strictly-causally receives and finds out the other encoder's transmitted signals and tries to cooperate with the other encoder by transmitting its message. A special case is also studied in which the common part of the states is known at the both encoders, resulting in a larger rate region. For these two scenarios, achievable rate regions are derived using a combination... 

Genetic algorithm for optimization of beam forming in spiral array antenna is used. The goal is to achieve a -20 dB in null over the wide frequency band. Our simulation shows -20 dB over 75 MHz Null Band width, in VHF band. © 2006 IEEE  

Advanced static VAR compensators (ASVCs) are used to improve the transient stability of electric power systems. In this paper we present a new control strategy, which has superior performances compared to the conventional control techniques for these systems. The proposed method utilizes a novel current reference based on the transient energy function (TEF) approach. It also includes the voltage limits in the optimizing process using the Lyapunov theory and linear programming. In addition, it is optimized considering the permissible system conditions. A continuous control of the reactive power flow is also achieved. The proposed ASVC is modeled in single-machine and multimachine systems. In... 

The intrinsic viscosity of very high molecular weight partially hydrolyzed polyacryamide (HPAM), which is mainly used in the EOR processes, was studied in reservoir conditions. The critical concentration that could be helpful in determining the optimized polymer concentration for injection into the reservoir is calculated. The effects of temperature and salt concentration on the parameters are also studied. An experimental model to predict the variations of these parameters with temperature and salt concentration was developed. This is an abstract of a paper presented at the 8th World Congress of Chemical Engineering (Montreal, Quebec, Canada 8/23-27/2009)  

We consider a two-user state-dependent generalized multiple access channel (GMAC) with correlated channel state information (CSI). It is assumed that the CSI is partially known at each encoder noncausally. We first present an achievable rate region using multi-layer Gelfand-Pinsker coding with partial state and message cooperation between the encoders. We then specialize our result to a Gaussian GMAC with additive interferences that are known partially at each encoder. We show that the proposed scheme can remove the common part known at both encoders and also mitigate a significant part of the independent interference via state cooperation when the feedback links are strong. Thus, the... 

The authors study a two-user state-dependent generalised multiple-access channel (GMAC) with correlated states. It is assumed that each encoder has 'non-causal' access to channel state information (CSI). They develop an achievable rate region by employing rate-splitting, block Markov encoding, Gelfand-Pinsker multicoding, superposition coding and joint typicality decoding. In the proposed scheme, the encoders use a partial decoding strategy to collaborate in the next block, and the receiver uses a backward decoding strategy with joint unique decoding at each stage. The author's achievable rate region includes several previously known regions proposed in the literature for different scenarios... 

The two-user discrete memoryless state-dependent multiple-access channel with cooperating encoders is considered. It is assumed that the channel is controlled with two independent states such that each of the channel state information is noncausally available at one encoder. Moreover, based on the intrinsic characteristic of wireless networks, it is assumed that each encoder strictly causally receive a noisy version of the transmitted signal of the other encoder. Hence, the encoders can cooperate in transmitting the message to the receiver. An achievable rate region for the channel is derived by use of rate splitting, block Markov encoding and Gelfand-Pinsker multilevel encoding along with... 

We study a two-user state-dependent generalized multiple-access channel (GMAC) with correlated states. It is assumed that each encoder noncausally knows partial channel state information. We develop an achievable rate region by employing rate-splitting, block Markov encoding, Gelfand-Pinsker multicoding, superposition coding and jointly typical decoding. In the proposed scheme, the encoders use a partial decoding strategy to collaborate in the next block, and the receiver uses a backward decoding strategy with a joint unique decoding at each stage. Our achievable rate region includes several previously known rate regions proposed in the literature for different scenarios of multiple-access... 

in this paper detection and the accuracy of measurement of range, velocity and DOA in PCL radar for optimized parameters is considered. It is shown that, in order to measure the bistatic characteristics of a target, we can process the monostatic ambiguity function and extract the bistatic factors by proposed Algorithm. ©2006 IEEE  

The flux and torque hysteresis bands are the only gains to be adjusted in direct torque control (DTC). The torque ripple and harmonic loss of motor and switching loss of inverter greatly Influence them. Hence, these variables must be observed in the control process to maximize performance of the system. In this paper, the effects of flux and torque hysteresis bands on inverter switching loss, harmonic loss, and torque ripple of induction motor are investigated. In order to find their optimum values, a cost function consisting motor harmonic losses, torque ripples, and inverter switching losses is defined. Minimizing this cost function leads to the optimum value of the hysteresis bands of... 

In this paper, a flux search controller is proposed to increase the efficiency of a direct torque controlled induction motor with light load. The reference flux value is determined through a two stage minimization algorithm with the amplitude of the stator current as the objective function. In the transient state, a great flux step is used to speed up the convergence. In the steady state, a noise cancellation algorithm is used to let using small flux step and improves the steady state behavior of flux controller. Simulation and experimental confirm the fast dynamics of the proposed method and its superiority compared to the other optimal flux search controllers. © 2005 IEEE  

For a fading full-duplex decode-and-forward relay channel, the authors analytically derive optimum power allocation schemes subject to individual power constraints at the source and the relay. The authors prove that the problem is a convex optimisation problem over the feasible power set, and by proposing a systematic technique to solve min-max problems, optimum power allocations are derived in closed-forms. Finally, for a Rayleigh-fading channel model, optimum power allocations are derived and the respective achievable rate and an upper bound are evaluated. The implications of the derived theoretical results are discussed through some graphs  

In this paper the accuracy of measurement with respect to some parameters like baseline variance and DOA estimation and bistatic RCS is considered. The Radar designer can find the appropriate parameters to having the minimum error in target localization and maximum coverage range. © 2006 IEEE  

In this work we introduce new model for energy-delay product and the performance of 80-nm SOI-CMOS circuits for the range of Vdd=0.1-1.5V and Vth=0-0.8V, are analyzed to find optimal Vdd and Vth BSIMSOI3.3 model (level 57) is used to verify the answers. We show that Energy-Delay Product (EDP) isn't appropriate metric for gate sizing problem. And a new design metric is introduced as a generalization of EDP. This metric is used to determine the transistor sizing for complex circuits based on the specified delay and energy constrains. In this case, unlike the conventional energy delay product metric, delay and energy can be considered with different emphasis. The complete design flowcharts and... 

In the present work the effect of simultaneous doping of carbon and nickel on the microstructural, optical, and electrical properties of barium strontium titanate (BST) is investigated. Thin films of BST were prepared by the sol-gel method in six different compositions ((Ba0.6Sr0.4)(NixCyTi1-x-y)O3): x = y = 0.00 (BST), x = 0.04 y = 0.00 (BST4N), x = 0.04 y = 0.01 (BST4N-1C), x = 0.04 y = 0.02 (BST4N-2C), x = 0.04 y = 0.03 (BST4N-3C), and x = y = 0.04 (BST4N-4C). Structural features and chemical bonds of the films were studied by TGA/DSC, XRD, FT-IR, and FE-SEM. The electrical and optical properties of the films were analysed by impedance spectroscopy and UV–VIS spectroscopy. The results...