Sharif Digital Repository

In this paper, we propose a decentralized control scheme for combined motion/force control of nonredundant multi-manipulator robotic systems, cooperatively grasping a rigid body in a prespecifled position/force trajectory. The proposed control scheme uses the impedance method for modeling the internal force exerted by the end effectors to the object. The precise mathematical analysis of the overall dynamical system and the proposed controller are presented and the stability of the overall system is studied. The proposed controller, then, is applied to a cooperative system composed of two PUMA560 manipulators and the simulation results are presented to verify the proposed control scheme  

A facility location problem deals with locating the best place for a group of facilities, among distinct demand points, minimizing a certain locational optimization function. In this paper, distributed, asynchronous, and scalable algorithms are presented for solving a facility location problem known as continuous n-median problem (generalized Fermat-Weber problem) via multi-agent robotic systems. The algorithms are discussed both in continuous and discrete time domain, and their validity is proved. It is also shown that the solution of this facility location problem is the set of points that are the geometric medians of their corresponding Voronoi cells  

Network-on-Chip (NoC) is a precious approach to handle huge number of transistors by virtue of technology scaling to lower than 50nm. Virtual channels have been introduced in order to improve the performance according to a timing multiplexing concept in each physical channel. The incremental effect of virtual channels on power consumption has been shown in literatures. The issue of power saving has always been controversial to many designers. In this paper, we introduce a new technique which tries to adaptively mange the number of virtual channels in order to reduce the power consumption while not degrading the performance of the network without any reconfiguration. Our experimental results... 

Stretched hypercube has recently been introduced as an attractive alternative to the well-known hypercube. Previous research on this network topology has mainly focused on topological properties and VLSI aspects of this network In this paper, we propose some deterministic and adaptive routing algorithms for the stretched hypercubes. The performance of stretched hypercubes using the proposed routing algorithms is then evaluated by means of simulation experiments. Experiments are reahzed under different working loads and for different network actors. © 2008 IEEE  

In a large system, it is neither economical nor efficient to equip each node with a copy of the resource, and it is desirable to distribute the copies of the resource so that certain performance measure is obtained. In this paper we consider the problem of distributing resources in the edge product of networks. The algorithms presented in this paper make use of the known placements for the basic graphs composing the product graph. Therefore, in these placements we avoid the additional costs needed for deploying and rescaling the network. © 2008 IEEE  

Grid scheduling problems are dynamic as the jobs and resources in the system vary overtime. The Rulebased scheduling algorithms are a new trend in grid scheduling which are applicable in dynamic grid environments; The arriving jobs waiting for execution is ordered according to a certain rule and they are dispatched for processing according to that order. Grid scheduling algorithms usually involve more than one objective function. In particular, it is not enough to minimize the Maximum completion time (Makespan) objective function without taking into consideration the lateness of the jobs (Tardiness). In this paper two novel dispatching rules are proposed that aims to minimize the maximum... 

Skin detection has different applications in computer vision such as face detection, human tracking and adult content filtering. One of the major approaches in pixel based skin detection is using Bayesian classifiers. Bayesian classifiers performance is highly related to their training set. In this paper, we introduce a new Bayesian classifier skin detection method. The main contribution of this paper is creating a huge database to create color probability tables and new method for creating skin pixels data set. Our database consists of about 80000 images containing more than 5 billions pixels. Our tests shows that the performance of Bayesian classifier trained on our data set is better than... 

An advantage of steganography, as opposed to other information hiding techniques, is that the embedder can select a cover image that results in the least detectable stego image. In a previously proposed method, a technique based on block texture similarity was introduced where blocks of cover image were replaced with the similar secret image blocks; then indices of secret image blocks were stored in cover image. In this method, the blocks of secret image are compared with blocks of a set of cover images and the image with most similar blocks to those of the secret image is selected as the best candidate to carry the secret image. Using appropriate features for comparing image blocks,... 

This work provides a canonical representation for manipulation of RTL designs. Work has already been done on a canonical and graph-based representation called Taylor Expansion Diagram (TED). Although TED can effectively be used to represent arithmetic expressions at the word-level, it is not memory efficient in representing bit-level logic expressions. In addition, TED cannot represent Boolean expressions at the word-level (vector-level). In this paper, we present modifications to TED that will improve its ability for bit-level logic representation while enhancing its robustness to represent word-level Boolean expressions. It will be shown that for bit-level logic expressions, the Enhanced... 

The planar-adaptive routing algorithm is a simple method to enhance wormhole routing algorithms for fault-tolerance in meshes but it cannot handle faults on the boundaries of mesh without excessive loss of performance. In this paper, we show that this algorithm can further be improved using a flag bit introduced for guiding misrouted messages. So, the proposed algorithm can be used to route messages when fault regions touch the boundaries of the mesh. We also show that our scheme does not lead to diminish the performance of the network and only three virtual channels per physical channels are sufficient for tolerating multiple boundary faulty regions. © 2008 Springer-Verlag Berlin Heidelberg... 

Future System-on-Chip (SoC) designs will need efficient on-chip communication architectures that can provide efficient and scalable data transport among the Intellectual Properties (IPs). Designing and optimizing SoCs is an increasingly difficult task due to the size and complexity of the SoC design space, high cost of detailed simulation, and several constraints that the design must satisfy. For efficient design of SoCs, an efficient mapping of IPs onto Networks-on-Chip (NoCs) is highly desirable. Towards this end, we have presented PERMAP, a PERformance-aware MAPping algorithm which maps the IPs onto a generic NoC architecture such that the average communication delay is minimized. This is... 

In this paper, a new approach for decoding real-field codes based on finding sparse solutions of underdetermined linear systems is proposed. This algorithm iteratively estimates the positions and the amplitudes of the sparse errors (or noise impulses) using an Expectation-Maximization (EM) algorithm. Iterative estimation of amplitudes is done in the Expectation step (E-step), while iterative estimation of error positions is done in the Maximization step (M-step). Simulation results show 1-2 dB improvement over Linear Programming (LP) which has been previously used for error correction. ©2008 IEEE  

In pervasive computing environments, a user can access resources and services from any where and at any time; thus a key security challenge in these environments is the design of an effective access control model which is aware of context modifications. Changes in context may trigger changes in authorizations. In this paper, we propose a new context-aware access control model based on role-based access control model for pervasive computing environments. We assign roles to users dynamically based on the long-term context information and tune active role's permissions according to the short-term context information of the users and environment. © 2007 IEEE  

Wireless Sensor Network (WSN) should be capable of fulfilling its mission, in a timely manner. Therefore, we propose a quantitative real-time model for multihop WSN. "Real-time degree" describes the percentage of real-time data that the network can deliver on time from any source to its destination. Most of network properties are considered as random variables and a queuing-theory based model is derived. In this model, the effect of network load on the packets ' delay and the "real-timeliness" of the network are considered. Simulation results are used to validate the proposed model. The simulation results agree very well with the model. © 2007 IEEE  

In this paper, analysis of the throughput and delay in a spectrally phase-encoded optical code-division multiple-access (OCDMA) system, using a simplified slotted packet network protocol is conducted. Steady-state throughput and average packet delay of the system are derived. In evaluating the performance of the system, only multiple access interference is considered and other sources of noise are neglected. Comparing different systems with the fixed bit rate and chip duration leads us to conclude that increasing the code length will improve the performance of networks with small average activity; but in highly active networks, decreasing the code length will result in a significant... 

Peer-to-peer networks are beginning to form the infrastructure of future applications. The use of semantic information to organize nodes in a P2P network is a prosperous approach. In this paper we present a novel method, called Semantic Partition Tree, which organizes nodes in a semantic space, using an upper ontology. In this approach each node can find a target in a time proportioned to the depth of the upper ontology, which is significantly less than the number of nodes in the network. Also we simulated our method with several configurations and measured its performance. The results of the simulation show that our scheme is highly scalable and can be used by real P2P networks. © 2007 IEEE... 

In this paper, a novel design approach for determination of the optimal Fractional Order PID (FOPID) controllers, using the Particle Swarm Optimization (PSO) method is presented. Fractional calculus can provides good performance and robustness for FOPID controllers in comparison with the conventional PID and even other types of classical controllers, because of the arbitrary order of fractional calculus presented in this scheme. This paper demonstrates in details how to employ the PSO method to search efficiently for the optimal FOPID controller parameters in SISO and MIMO systems. The proposed approach is applied to an electromagnetic suspension system as an example to illustrate the design... 

Almost all existing multi-description coding (MDC) schemes are designed for media streaming over Internet. In this work, a wavelet-based video MDC technique is introduced that fits the criteria of media streaming over peer-to-peer networks. Our proposed method assigns descriptions to the senders due to their characteristic (i.e. bandwidth and availability). In contrast to traditional MDC, different descriptions in the proposed method have different importance in remaking the original media. Our simulation results show considerable improvement of video quality at the receiver (up to 10 dB) as compared to the state-of-the-art. ©2007 IEEE  

Level Crossing (LC) Analog-to-Digital converters have been suggested as an asynchronous alternative to conventional schemes. It is our intention to improve the performance of these LC converters. In this paper, we also suggest alternative adaptive and multi-level adaptive LC schemes and use an iterative method to drastically improve the performance of LC converters. The impressive improvement of these schemes make LC converters a potential competitor to other conventional A/D converters such as Sigma Delta Modulators (SDM). ©2007 IEEE  

We consider an internally coded scheme for multicarrier frequency-hopping CDMA (MC-FH-CDMA) communication systems. In this method, the total bandwidth is partitioned into Ns1 disjoint bands and each band is also segmented into Ns2 subbands. Based on the super-orthogonal encoder output and a pseudorandom (PN) sequence, one of the Ns1 bands is selected. Then, the data is transmitted in that band in the form of multicarrier frequency-hopping technique using BPSK modulation. At the receiver front end, we use soft detector, then we apply Viterbi decoding algorithm. We evaluate the performance of the proposed method. The results indicate that our method outperforms the previously presented uncoded...