Sharif Digital Repository

With increasing importance of exoskeletons as rehabilitation apparatuses, suitable and delicate control strategies has received much attention. In order to control the exoskeleton, there should be a complete understanding of torques produced by the limb itself which makes the musculoskeletal modeling of the limb essential but also complex. In addition, the musculoskeletal model can be used to discover the user's desired movement to control the exoskeleton. In this paper a complete musculoskeletal model for the elbow with two degrees of freedom is developed and simulated. Next the model is used to determine user's desired movement. Finally based on this evaluation, an exoskeleton model is... 

Considering the weaknesses of cryptography algorithms and the attacks performed against them, cryptography alone cannot guarantee the security of communication in a wireless network. With regard to the developments in wireless communication networks brought about by smart array antennas, security can be sought in the physical layer as well, aiming to restrict the access of the data in a wireless network and limit it to authorized users only in order to further restrain malicious data accesses. In this paper, we analysis a strategy for restricting data access using smart array antennas and present the results in security by a parameter called exposure region. For this strategy afterwards we... 

In this article, the authors introduce and propose an overloaded Synchronous Optical Code Division Multiple Access (SOCDMA) based on Unipolar Walsh Code (UWC) for fiberoptic communication systems. Given μ as the number of chips, it is shown that 2L - 2 active users can be supported by the proposed system. In this system the users of the network are categorized into two groups. Users of each group transmit at the same power level but different from the level of the other group's users. Using the UWC properties we propose a simple receiver that cancels multiple-user interference (MUI) completely. Moreover, we obtain the optimal power level of each group in order to minimize the probability of... 

Methods of human semen assessment are quite wide ranging. In this paper, we use background subtraction methods in order to detect progressive sperms whose quality of movement strongly influence fertility. Robust Principal Component Analysis (RPCA) is a powerful algorithm which has been used recently for background subtraction purposes. Sperm tracking problem can also be defined as a background subtraction problem. In RPCA algorithm, data is represented by a low rank plus sparse matrix. In our approach, the foreground data is recovered through such matrix decomposition. We compare the RPCA approach with four other background subtraction methods in order to check accuracy of algorithm as a... 

This paper studies detecting matrices in random dense and sparse Code Division Multiple Access (CDMA) systems. Detecting matrices were originally introduced in the coin weighing problem. Such matrices can be used in CDMA systems in over-loaded scheme where the number of users is greater than the number of chips. We drive some conditions in the large system limit for binary and bipolar random CDMA systems to ensure that any random matrix is a detecting matrix. Furthermore, we extend our results to sparse random ternary matrices that have been using in the sparse CDMA literature. Finally, a construction method for the sparse detecting matrices is introduced  

The electrooculogram (EOG) artifact is one of the main contaminators of electroencephalographic recording (EEG). EOG can make serious problems in results and interpretations of EEG processing. Rejecting contaminated EEG segments result in an unacceptable data loss. Many methods were proposed to correct EOG artifact mainly based on regression and blind source separation (BSS). In this study, we proposed an automatic correction method based on maximum likelihood estimation. The proposed method was applied to our simulated data (real artifact free EEG plus controlled EOG) and results show that this method gives superior performance to Schlögl and SOBI methods  

The incidence of apnea-bradycardia episodes in preterm infants may lead to neurological disorders. Prediction and detection of these episodes are an important task in healthcare systems. In this paper, a coupled hidden Markov model (CHMM) based method is applied to detect apnea-bradycardia episodes. This model is evaluated and compared with two other methods based on hidden Markov model (HMM) and hidden semi-Markov model (HSMM). Evaluation and comparison are performed on a dataset of 233 apnea-bradycardia episodes which have been manually annotated. Observations are composed of RR-interval time series and QRS duration time series. The performance of each method was evaluated in terms of... 

The FT reaction involves the conversion of syngas which is derived from natural gas or coal to different kinds of products according to the operating conditions and the type of the catalyst. In other words, it is a practical way to convert solid fuel (coal) and natural gas to various hydrocarbons (C1-C60) and oxygenates such as alkanes, alkenes etc. The main products of the reaction are naphtha and gasoline. This paper deals with developing a proper product distribution model for FT process using the appropriate kinetic model, optimizing the respective rate constants while applying them in product distribution equations. The results revealed only 8.09% deviations from the olefin experimental... 

Mobile Worldwide Interoperability for Microwave Access (Mobile WiMAX) is a wireless access technology based on IEEE 802.16e. The two most important concepts are introduced in the MAC layer of Mobile WiMAX networks, handover and load balancing. In this paper, we have focused on balancing the load of the system, using handover mechanisms suggested by mobile WiMAX. The proposed algorithm, WQLB, concentrates on controlling the system load and keeping it in a balanced state by using a handover process. Also, the algorithm is designed to utilize resources efficiently, supporting QoS. As load definition is an essential criterion in load balancing algorithms, we have suggested a new load model for... 

A multiple input multiple output (MIMO) radar system is an emerging research field which has attracted many studies in recent years. This type of radar, unlike conventional phased array radar, can transmit different probing signals via its antennas, that may be correlated or uncorrelated with each other. This waveform diversity offered by MIMO radar systems enable superior capabilities compared to conventional phased array radar. Many papers have introduced different ways for beamforming of MIMO radar. In this paper it is desirable to analysis some methods for beamforming of MIMO radars with planar arrays constellation and examine their 3D result beam-pattern of such constellations for... 

In this paper, we present a new method to solve tracking problem. The proposed method combines sparse representation and motion estimation to track an object. Recently. sparse representation has gained much attention in signal processing and computer vision. Sparse representation can be used as a classifier but has high time complexity. Here, we utilize motion information in order to reduce this computation time by not calculating sparse codes for all the frames. Experimental results demonstrates that the achieved result are accurate enough and have much less computation time than using just a sparse classifier  

To scavenge the energy from the environment and extend the network lifetime, some wireless sensor networks (WSNs) have been equipped with energy harvesters recently. However, the variable amount of environmental energy can affect the reliability of energy harvesting wireless sensor networks (EH-WSNs). In addition, data transmission over a wireless media is vulnerable. Hence, utilizing suitable error control schemes are necessary to improve the reliability. Regarding this point, Automatic Repeat Request (ARQ) and Cooperative ARQ (C-ARQ) schemes are applied in this generation of WSNs. Conventional ARQ as well as C-ARQ scheme are considered and examined through simulation. A comparative... 

In this work we present a sparse dictionary learning method, specifically tuned to solve the tracking problem. Recently, sparse representation has drawn much attention because of its genuineness and strong mathematical background. In this paper we present an online method for dictionary learning which is desirable for problems such as tracking. Online learning methods are preferable because the whole data are not available at the current time. The presented method tries to use the advantages of the generative and discriminative models to achieve better performance. The experimental results show our method can overcome many tracking challenges  

Since tracking algorithms should be robust with respect to appearance changes, online algorithms has been investigated recently instead of offline ones which has shown an acceptable performance in controlled environments. The most challenging issue in online algorithms is updating of the model causing tracking failure because of introducing small errors in each update and disturbing the appearance model (drift). in this paper, we propose an online generative tracking algorithm in order to overcome the challenges such as occlusion, object shape changes, and illumination variations. In each frame, color distribution of target candidates is obtained and the candidate having the lowest distance... 

This paper presents a new transform domain to evaluate the goodness of fit of natural image data to the common Benford's Law. The evaluation is made by three statistical fitness criteria including Pearson's chi-square test statistic, normalized cross correlation and a distance measure based on symmetrized Kullback-Leibler divergence. It is shown that the serial combination of variance filtering and block 2-D discrete cosine transform reveals the best goodness of fit for the first significant digit. We also show that the proposed transform domain brings reasonable fit for the second, third and fourth significant digits. As an application, the proposed transform domain is utilized to detect... 

This paper addresses the estimation of the integer part of the carrier frequency offset (CFO) in orthogonal frequency division multiplexing (OFDM) systems. A novel method is presented based on the maximum likelihood (ML) approach that jointly estimates the channel impulse response (CIR) and the integer CFO. The new scheme estimates the CIR by using pilots and obtains the estimate of the integer CFO by taking advantage of the effect of the CFO on the CIR and data symbols. The performance of the new method is evaluated in Rayleigh fading channels. The results demonstrate that the proposed scheme significantly outperforms the previous methods  

In this paper we study the statistical properties of the Signal to Noise Ratio (SNR) of the dual-hop relaying link in a cooperative wireless communication system in the presence of channel estimation errors for Decode and Forward (DF) relaying protocol. Then for assessment of the system performance the Symbol Error Rate (SER) is considered. Two approaches are introduced for SER calculation from which the second one results in a closed form solution. Finally the second approach is used to find an optimum power allocation scheme for transmission of pilot and data symbols at the source and the relay terminals that results in minimizing the SER and considerable amount of power saving. Also Monte... 

In this paper, we study and analyze the performance of matched and partially-matched receivers for a typical ultra wide-band Spectrally-Encoded Spread-Time (SE/ST) CDMA in the presence of multiple tone jammers. We investigate a scenario where there is no information about the jammer frequencies in the transmitter side while it is desirable to cancel it in the receiver side. We will demonstrate the performance of the SE/ST system would be improved through partially matched filter at the receiver. In addition, we approximate the two-dimensional RAKE receiver by a simple one-dimensional RAKE for the scenario where there are K asynchronous users. Furthermore, closed form formula for the... 

In this paper, an underwater wireless sensor network (UWSN) is modeled with the help of queueing theory in order to evaluate the maximum stable throughput of the network. To this end, a new scenario for multi-layer mobile UWSN is considered. Then, a new MAC algorithm comprised of random access scheme (like MACAW) and CDMA-based data transmission along with a simplified routing algorithm is proposed. In order to analyze the considered UWSN scenario, we propose two related queueing networks, one for modeling the wireless node mobility and the other for representing the process of multi-hop packet transmission according to considered MAC and routing algorithms. Finally, the maximum stable... 

Classical sampling theorem states that by using an anti-aliased low-pass filter at the Nyquist rate, one can transmit and retrieve the filtered signal. This approach, which has been used for decades in signal processing, is not good for high quality speech, image and video signals where the actual signals are not low-pass but rather sparse. The traditional sampling theorems do not work for sparse signals. Modern approach, developed by statisticians at Stanford (Donoho and Candes), give some lower bounds for the minimum sampling rate such that a sparse signal can be retrieved with high probability. However, their approach, using a sampling matrix called compressive matrix, has certain...