Sharif Digital Repository

To mitigate environmental pollution and food contamination caused by inappropriate and excessive herbicide usage, most potent herbicides should be screened to control rice weeds. A research trial was executed for assessing the comparative efficacy of different herbicides to control rice field weeds and to evaluate the toxicity on rice under normal (distilled water) as well as different salinity levels (4 and 8 dS m-1). The study was designed to select the most potent herbicide and its appropriate dose for weed control of rice crop in coastal areas. Fourteen herbicidal treatments were included weed free crop, Pretilachlor (0.25, 0.50, 0.375 and 0.75 kg a.i. ha-1), Propanil + Thiobencarb (0.6... 

An accurate examination of deformability of rock samples in response to any change in stresses is deeply dependent on the reliable determination of properties of the rock as analysis inputs. Although Young’s modulus (E) can provide valuable characteristics of the rock material deformation, the direct determination of E is considered a time-consuming and complicated analysis. The present study is aimed to introduce a new hybrid intelligent model to predict the E of granitic rock samples. Hence, a series of granitic block samples were collected from the face of a water transfer tunnel excavated in Malaysia and transferred to laboratory to conduct rock index tests for E prediction. Rock index... 

The digital radio receivers often have fast analog to digital converters delivering vast amount of data. However, in many cases, the signal of interest represents a small proportion of that bandwidth. A Digital Down Converter (DDC) is a filter that extracts the signal of interest from the incoming data stream. In this paper we first introduce an algorithm based on FFT which can be applied for simultaneous frequency shifting and decimating of Intermediate Frequency (IF) band signals, then a simplified iterative algorithm is suggested to improve the quality of reconstructed baseband signal. ©2007 IEEE  

In this paper we propose a new method for estimating the mixing matrix, A, in the linear model X = AS, for the problem of underdetermined Sparse Component Analysis (SCA). Contrary to most existing algorithms, in the proposed algorithm there may be more than one active source at each instant (i.e. in each column of the source matrix S), and the number of sources is not required to be known in advance. Since in the cases where more than one source is active at each instant, data samples concentrate around multidimensional subspaces, the idea of our method is to first estimate these subspaces and then estimate the mixing matrix from these estimated subspaces. ©2007 IEEE  

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  

In the realization of adaptive beamforming algorithms, the least-mean-squares (LMS) algorithm had been the most popular scheme used for Smart Antenna systems. This Paper proposes an alternate scheme in the form of the Normalized LMS (NLMS) algorithm with active tap detection for WCDMA systems. By taking advantage of spatial filtering, the proposed scheme promises to reduce the bandwidth required for transmitting data by improving convergence rate. The performance of the Frequency Domain NLMS algorithm in the presence of multipath effects and multiple users is analyzed using simulations. This analysis is compared to that of LMS algorithm and suggests improvement in the convergence rate and... 

Feed-forward is one of the best methods for linearizing microwave power amplifiers, but due to device tolerance in implementation of the system components, the practical Inter-Modulation Rejection (IMR) value may differ quite much from the theoretical IMR value. One of the methods to improve the practical performance of the system is using the multi-loop configuration. Here we have introduced the multi-loop feedforward systems and we have estimated the practical IMR values of the system using Monte-Carlo analysis. As the analysis shows, although the number of components in a multi-loop system is increased with respect to a simple feed-forward system, but the difference between the practical... 

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  

Transcranial Doppler ultrasound can be used to detect circulating cerebral eraboli. Embolie signals have characteristic transient chirps suitable for wavelet analysis. We have implemented and evaluated the first online selective selective wavelet transient enhancement filter to amplify embolic signals in a preprocessing system. Our approach is similar to wavelet de-noising for signal enhancement, but, in order to retain blood flow information, we do not use traditional threshold methods. The selective wavelet amplifier uses the matched filter properties of wavelets to enhance embolic signals significantly and improve classification performance using a novel noise tolerant approach. Even the... 

In this paper, we analyze the performance of a wireless infrared system with code division multiple access (CDMA) technique using optical orthogonal codes (OOCs). Performance improvement is shown when power control is applied to the system. Noting the advantages of pulse position modulation (PPM), we have used chip-level binary PPM scheme. To mention some of these advantages we can name average required power reduction and BER improvement in comparison to on-off keying (OOK). The obtained results show that power control is a mandatory part of the design in a wireless infrared system using OOC. ©2007 IEEE  

In this paper, we propose an energy-aware node-eentric load balancing algorithm that constructs a load balanced tree in sensor networks of asymmetric architecture. We show that the proposed energy-aware algorithm creates routing trees with better load balancing across the network and longer network life time compared to the other proposed algorithms. We also introduce a network information gathering (NIG) protocol that can collect the required information (load and neighboring information) from nodes and forward them to the base station. This protocol can be used by all centralized systems that require some additional information about nodes in the network. ©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... 

A Multibeam Ka-band Satellite to offer High Speed Internet service to state and private universities and high schools based on 2007-2008 academic year statistical data is proposed. For this goal an optimum coverage on Iran has been created using MATLAB software. These data were transferred to 1:250000 digital map of Iran using ILWIS software. After reading the coordinates of cities located in each contour, which were more than 640 locations, we proceeded to calculate traffic specifications of each beam. After frequency planning for beams, the power and dimension of earth stations were designed. Finally the technical specifications of the proposed satellite to serve nationwide users are... 

In this work, we have examined the distributed consensus averaging problem from a novel point of view considering the need for privacy and anonymity. We have proposed a method for incorporating security into the scalable average consensus mechanisms proposed in the literature. Random Offsets Method (ROM) is lightweight, transparent and flexible since it is not based on cryptography, does not require any change in the fusion system and can be used optionally by some nodes who care about their privacy. In this method, which is based on noisiflcation of nodes' information, we achieve robustness against n - 1 colluding adversaries in a network of n nodes, which is maximum level of robustness... 

In this paper, we study the effect of some traffic patterns on energy consumption for IEEE 802.16e nodes while operating in the sleep mode. In the sleep mode, a Mobile Subscribe Station (MSS) sleeps for a sleep interval and wakes up at the end of this interval in order to check buffered packet(s) at Base Station (BS) destined to it. If there is no packet, the MSS increases the sleep window up to the maximum value and sleeps again. For a more general traffic pattern, we evaluate the average power consumption. Based on our analysis, we conclude that traffic pattern plays an important role in power consumption. ©2007 IEEE  

Double talk detector is the essential part of an echo canceller to keep the adaptive filter from divergence in presence of near-end speech. This work is a contribution to propose a new double talk algorithm based on power, this method detects double-talk quickly; also it can distinguish the double-talking when the channel has the varying gain. In this paper, we first present an analytical discussion describing this new method and then we show the simulation result to compare our proposed algorithm in both performance and complexity with Giegel algorithm-the most successful one in line echo cancellers. ©2007 IEEE  

Denoising of corrupted images has been a classical problem in image processing. In this paper we propose a new approach for image noise reduction using wavelet transform. In this method an improved version of thresholding neural networks (TNN) is used to find the optimum threshold values in the sense of minimum mean square error (MMSE). Based on these optimum thresholds a novel cycle-spinning based method is used to reduce image artifacts. In this method, we utilize two thresholding schemes as the thresholding operator of cycle-spinning. A neighbor dependent thresholding scheme is employed as its first shrinkage step and a simple wavelet thresholding with the optimum derived threshold values... 

We evaluate the performance of the internally coded partial-band DS-CDMA scheme first introduced in [1], in a multipath Rayleigh fading channel. The scheme of [1] is based on frequency-hopping (FH) and direct-sequence (DS) spread spectrum techniques. The total bandwidth is divided into Ns subbands. The output of a super-orthogonal encoder and a pseudorandom (PN) sequence selects one subband, in which the user's data is sent in the form of DS-CDMA signal using the second PN sequence. We consider soft detection at the receiver front end. We obtain the upper and lower bounds on the bit error rate. For comparison, we also consider the conventional DS-CDMA system. It is shown that for the same... 

There are applications where important and critical data should be sent to all nodes in a wireless Ad-hoc network. Flooding and its variants are typically used to achieve this target. Network coding can also be used for broadcasting in such an environment. Energy consumption in the network, coverage and total delay are all important parameters that should be considered when an algorithm is evaluated. In this article, a reliable and energy efficient single source broadcasting algorithm is proposed based on network coding. This algorithm guarantees the delivery of desired messages to all network nodes, consumes less energy compared and reduces the total delay compared to other algorithms. This... 

In this paper applications of an iterative method in some signal recovery problems are introduced. It is proved that the distorting effect of linear operators can be removed completely using the iterative scheme. The inverse of monotonic functions can also be made indirectly by the method. A novel approach for separating the messages of different subscribers in a CDMA network will be proposed as well, relying on the recursive approach. It would be shown that Sigma Delta Modulated signals can be decoded via the iterative procedure. We will prove both analytically and with simulations that a broad class of nonlinear operators including speech and image codecs can be approximately inverted with...