Sharif Digital Repository

In this paper, a novel multiple antenna, high-resolution eigenvalue-based spectrum sensing algorithm based on the FFT of the received signal is introduced. The proposed platform overcomes the SNR wall problem in the conventional energy detection (ED) algorithm, enabling the detection of the weak signals at -10 dB SNR. Moreover, the utilization of FFT for the input signal channelization provides a simple, low-power design for a high-resolution spectrum sensing regime. A real-time, low-area, and low-power VLSI architecture is also developed for the algorithm, which is implemented in a 0.18 μm CMOS technology. The implemented design is the first eigenvalue-based detection (EBD) architecture... 

An Eigenvalue-based detection (EBD) scheme, is proposed as an efficient method to overcome the noise uncertainty and the SNR wall problem in conventional energy detection (ED) schemes. Despite remarkable efforts made to analyze the EBD performance, a VLSI implementation is missing in literature. In this paper, a new FFT-based EBD algorithm is introduced, which eliminates the need for filter banks and discrete wavelet packet transform to channelize the input signal. The proposed method enables the utilization of the EBD algorithm in high-resolution spectrum sensing approaches. Moreover, it enables the detection of signals with SNRs as low as -10 dB. A low-power, area-efficient yet real-time... 

In this paper, we analyze the cooperative diversity of amplify-and-forward half-duplex relay networks under longterm power constraints. The system model we consider consists of one transmit-receive pair and an arbitrary number of relays. This paper analyzes bit error rate and network diversity for two different power distribution scenarios in network. Using the derived network error probability, the distributed signal to noise ratio for network is introduced  

This research presents virtual prototyping and performance evaluation of a series elastic torque actuator developed for augmenting lower extremity exoskeletal systems employing biomechanical framework. For this purpose, experimental kinematical data of the lower extremity were collected for walking and backpack load carrying. Forward dynamics simulation of the movements under investigation is performed in a biomechanical framework consisting of a musculoskeletal model with ten degrees-of-freedom actuated by eighteen Hill-type musculotendon actuators per leg to perform the muscle functional analysis. Muscle torque analysis results employed for optimal design and selection of components in the... 

Afacile, seed-less and one-pot method was developed for synthesis of gold nanoflowers with multiple tips through reduction of HAuCl4 with deep eutectic solvent at room temperature. This solvent is ecofriendly, low-cost, non-toxic and biodegradable and can act as both reducing and shape-controlling agent. In this protocol, highly branched and stable gold nanoflowers were obtained without using any capping agent. The obtained products were characterized by different techniques including, field emission scanning electron microscopy, transmission electron microscopy, x-ray diffraction andUV-vis spectroscopy. The as-prepared gold nanoflowers exhibit efficient surface-enhanced Raman scattering... 

The In this paper, an Adaptive Particle Swarm Optimization (APSO) method is proposed for parameter identification of highly coupled electromechanical systems. Using some modifications on the APSO, better computational efficiency is achieved. In this way, the speed of real-time identification procedure is improved. In addition, to show the effectiveness of the proposed method, it is implemented on a real ball on plate setup and its dynamic model is achieved. Both the simulation and the experimental results show that parameter identification of the proposed algorithm is significantly improved when compared with other existing identification methods based on the traditional PSO and Genetic... 

In this paper, we investigate the error probability, diversity analysis and outage capacity of a general multiple-antenna equal-gain receive combining (EGC) scheme with an arbitrary number of antennas at high signal-to-noise (SNR) ratio. As will be shown, the proposed approach which is based on Taylor expansion provides a powerful tool for analysis of EGC schemes in terms of diversity and outage capacity. The approximations used in this approach lead to low complexity solutions that are very close to exact values, as shown by the simulation results. ©2009 IEEE  

A discussion covers the general descriptions and basic properties of ionic liquids (IL); main application areas, e.g., solvent replacement, purification of gases, homogenous and heterogeneous catalysis, biological reactions media, and removal of metal ions; and results of the research and works relating to gas solubility measurement and thermodynamic modeling of gas solubility with focus on acid gas solubility in IL. This is an abstract of a paper presented at the CHISA 2012 - 20th International Congress of Chemical and Process Engineering and PRES 2012 - 15th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction (Prague, Czech Republic... 

Several lower extremity exoskeletal systems have been developed for augmentation purpose. Common actuators, have important drawbacks such as complexity, and poor torque capacities. The main scope of this research is to propose a series elastic actuator for lower extremity exoskeletal system which was designed based on muscle functional analysis. For this purpose, a biomechanical framework consisting of a musculoskeletal model with ten degrees-of-freedom actuated by eighteen Hill-type musculotendon actuators per leg is utilized to perform the muscle functional analysis for common daily human activities. The simulation study illustrated functional differences between flexor and extensor... 

In this article, an adaptive nonlinear controller is designed to synchronize two uncertain fractional-order chaotic systems using fractional-order sliding mode control. The controller structure and adaptation laws are chosen such that asymptotic stability of the closed-loop control system is guaranteed. The adaptation laws are being calculated from a proper sliding surface using the Lyapunov stability theory. This method guarantees the closed-loop control system robustness against the system uncertainties and external disturbances. Eventually, the presented method is used to synchronize two fractional-order gyro and Duffing systems, and the numerical simulation results demonstrate the... 

In this letter, we use G/T as a figure of merit to evaluate the performance of time-modulated arrays (TMA). The noise performance of a receiver, which is periodically switched on and off, is quite different from that of a conventional receiver. We analytically investigate the noise performance of a TMA. Based on this analysis, the figure of merit, G/T, of the TMA structure is investigated, including the details of the receiver hardware. Moreover, the G/T of the TMA is compared with that of a phased array. The comparison indicates that the TMA structure provides the same or even better performance compared to a phased array system, which demonstrates the capability of TMA in providing... 

The Time Modulated Array (TMA) provides multiple radiation beams at different frequencies, by turning the radiating elements on and off. In this paper, we propose to add polarization diversity to a wireless communication link by leveraging the capabilities of the TMA. The proposed architecture switches between two orthogonal polarizations, instead of turning the antenna off, providing polarization diversity for the receivers. We show that the beams of each polarization at the sidebandsare exactly the same. However, the switching sequence should be optimized for the fundamental frequency to provide the same radiation level at each sideband. Two different switching sequences are proposed,... 

New experimental results are presented for the solubility of carbon dioxide, hydrogen sulfide in the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]) at temperatures range from (303.15 to 353.15) K and pressures up to about 2 MPa. The solubility of the mixture of CO2/H2S in [C8mim][PF6] under various feed compositions were also measured at temperatures of (303.15, 323.15 and 343.15) K and the pressure up to 1 MPa. The solubility of carbon dioxide and hydrogen sulfide increased with increasing pressure and decreased with increasing temperature and the solubility of H2S is about three times that of CO2 in the particular ionic liquid studied. The measured data were...