Sharif Digital Repository

In this paper, we provide the exact multiuser performance analysis of the MC-FH system introduced in [1] in the presence of partial-band interference in both AWGN and fading channels. For comparisons, we also provide the performance analysis of both MC-FH and FFH systems based on Gaussian distribution assumption. The partial-band interference is assumed as a Gaussian zero-mean random process with flat power spectrum on a fraction of the signal bandwidth. Our numerical results indicate that in both channels, the MC-FH system significantly outperforms the FFH system in the applications considered. Further, they indicate that the Gaussian analysis works quite well at high number of users. ©2... 

In this study, the authors investigate the problem of source localisation based on the time difference of arrival (TDOA) in a group of sensors. Aiming to minimise the squared range-difference errors, the problem leads to a quadratically constrained quadratic programme. It is well known that this approach results in a non-convex optimisation problem. By proposing a relaxation technique, they show that the optimisation problem would be transformed to a convex one which can be solved by semi-definite programming (SDP) and Lagrange multiplier methods. Moreover, these methods offer the exact solution of the original problem and the affirmation of its uniqueness. In contrast to other complicated... 

In this paper, we evaluate and compare the multiuser performance of the multicarrier frequency-hopping (MCFH) CDMA system using coherent and non-coherent detections in AWGN and slowly frequency-selective Rayleigh fading channels in a downlink application. For fair comparison, we use BFSK modulation for both cases. Our numerical results indicate that in both AWGN and fading channels, the coherent detection sub-stantially outperforms the non-coherent detection. Furthermore, it has been realized that the performance enhancement due to the diversity order is only observable for coherent detection  

In this correspondence, we focus on the performance analysis of the widely-used minimum description length (MDL) source enumeration technique in array processing. Unfortunately, available theoretical analysis exhibit deviation from the simulation results. We present an accurate and insightful performance analysis for the probability of missed detection.We also show that the statistical performance of the MDL is approximately the same under both deterministic and stochastic signal models. Simulation results show the superiority of the proposed analysis over available results  

This paper introduces an efficient scheme to image steganography by introducing the hidden message (payload) insertion in spatial domain and transforming the stego-image to compressed domain. We apply a recently-proposed LSB method in order to obtain better statistical behavior of the stego-message and subsequently, the obtained stego-image is transformed and quantized in order to enhance the security of hiding. Performance analysis comparisons confirm a higher efficiency for our proposed method. Compared to recently-proposed approaches, our method offers the advantage that it combines an efficient LSB method with transform domain security. © 2009 IEEE  

A new internally coded scheme that combines frequency hopping (FH) and multicarrier (MC) code division multiple access (CDMA) techniques using a super-orthogonal encoder is proposed. In this method, the total bandwidth is partitioned into Ns1 disjoint bands and each band is also segmented into Ns2 subbands. On the basis of a super-orthogonal encoder output and a pseudorandom sequence, one of the Ns1 bands is selected. The data bit is then transmitted in the band in the form of the multicarrier FH (MC-FH) CDMA scheme, that is, Ns2 carriers are transmitted in the Ns2 subbands of the selected band. At the receiver, both hard and soft detectors are used. The performance of the proposed method in... 

In this paper, we study a class of interconnection networks for multiprocessors, called the Stretched-G network, which is based on a base graph G by replacing each edge of the base network with an array of processors. Two interesting features of the proposed topology are its area-efficient VLSI layout and superior scalability over the underlying base network while preserving most of its desirable properties. We conduct a general study on the topological properties of stretched networks. We first obtain their basic topological parameters and derive some embedding results. We then present optimal routing and broadcasting algorithms for such networks. We also present a unified approach to... 

In this paper, the multiuser performance of a multicarrier frequency-hopping (MC-FH)CDMA system employing non-coherent detection is evaluated. We derive the bit error rate of the system for both uncoded and coded systems in AWGN and slowly frequency-selective Rayleigh fading channel, based on Gaussian distribution assumption for the decision variable. We use a practical low-rate convolutional error correcting code, which does not require any extra bandwidth further than what is needed by the uncoded scheme. Our numerical results indicate that the coded scheme significantly outperforms the uncoded scheme in both AWGN and fading channels. Furthermore, it is observed that the performance... 

Network survivability gauges the ability of a network to support the committed Quality of Services (QoS) continuously in the presence of various failure scenarios. We perceive that both performance and availability are integral components of survivability. Therefore, we propose a composite model for survivability that consists of performance and availability analysis. A analytical technique is presented to find the excess loss due to failure (ELF) when the system is operating in gracefully degraded states. An algorithm is proposed to carry out the availability analysis of the network even when the available paths between nodes are non-disjoint. These two models are combined to construct a... 

In this paper, we evaluate and compare the multiuser performance of the Fast Frequency-Hopping (FFH) and the MultiCarrier slow Frequency-Hopping (MC-FH) systems employing non-coherent detection for both uncoded and coded schemes in AWGN and slowly frequency-selective Rayleigh fading channels, based on Gaussian distribution assumption for the decision variable. Our numerical resulte indicate that with non-coherent detection, both systems show the same performance. However, the MC-FH system can be easily implemented using FFT algorithm. Furthermore with a slow hopping rate and high number of carriers, a coherent detection for the MC-FH system is feasible. Our results will indicate that the... 

The mesh structure has been used as the underlying topology for many practical multicomputers, and has been extensively studied in the past. In this paper, we investigate some topological properties of meshes. In particular, we study the problem of finding the number of nodes located at a given distance from a given node (surface area) and the number of nodes located within a given distance from a given node (volume), and have derived some expressions calculating these numbers  

Several analytical models of fully adaptive routing (AR) in wormhole-routed networks have recently been reported in the literature. All these models, however, have been discussed for routing algorithms with deadlock avoidance. Recent studies have revealed that deadlocks are quite rare in the network, especially when enough routing freedom is provided. Thus the hardware resources, e.g. virtual channels, dedicated for deadlock avoidance are not utilised most of the time. This consideration has motivated researchers to introduce fully adaptive routing algorithms with deadlock recovery. This paper describes a new analytical model of a true fully AR algorithm with software-based deadlock... 

In this study, the performance of a spectral-amplitude-coding optical code division multiple access (SAC-OCDMA) system in the asynchronous regime is evaluated using a Gaussian approximation of the decision variable for codes with fixed cross-correlation used in SAC-OCDMA systems. The authors consider the effect of phase-induced intensity noise (PIIN), thermal noise and shot noise. Moreover, the validity of the Gaussian approximation is confirmed by a Kolmogorov-Smirnov fitness test. For sake of comparison, the bit error rate (BER) of the asynchronous SAC-OCDMA system is also plotted numerically in comparison with the BER of the synchronous SAC-OCDMA. They show that a SAC-OCDMA system without... 

The compute-and-forward (CMF) method has shown a great promise as an innovative approach to exploit interference towards achieving higher network throughput. The CMF was primarily introduced by means of information theory tools. Although there have been some recent works discussing different aspects of efficient and practical implementation of CMF, there are still some issues that are not covered. In this study, the authors first introduce a method to decrease the implementation complexity of the CMF method. They then evaluate the exact outage probability of the authors proposed simplified CMF scheme, and hereby provide an upper bound on the outage probability of the optimum CMF in all... 

In this letter, a new molecular modulation scheme for nanonetworks is proposed. To evaluate the scheme, a system model based on the Poisson distribution is introduced. The error probability of the proposed scheme as well as that of two previously known schemes, the concentration and molecular shift keying modulations, are derived for the Poisson model by taking into account the error propagation effect of previously decoded symbols. The proposed scheme is shown to outperform the previously introduced schemes. This is due to the fact that the decoding of the current symbol in the proposed scheme does not encounter propagation of error, as the decoding of the current symbol does not depend on... 

One of the challenging problems in real-time data-parallel processing applications is to schedule tasks to different servers aiming to increase data locality for higher efficiency or lower delay, and at the same time, doing load balancing to stabilize the system of server-queues. We target this problem, and discuss efficient real-time task scheduling algorithms aimed not only to stabilize the system when the arrival rate is in the capacity region (i.e. throughput optimality condition), but also to minimize the mean delay of all tasks in heavy traffic regime when the arrival rate approaches the capacity boundary (i.e. heavy-traffic optimality condition). In this paper, we point out the data... 

This paper proposes an efficient parallel algorithm for computing Lagrange interpolation on k-ary n-cube networks. This is done using the fact that a k-ary n-cube can be decomposed into n link-disjoint Hamiltonian cycles. Using these n link-disjoint cycles, we interpolate Lagrange polynomial using full bandwidth of the employed network. Communication in the main phase of the algorithm is based on an all-to-all broadcast algorithm on the n link-disjoint Hamiltonian cycles exploiting all network channels, and thus, resulting in high-efficiency in using network resources. A performance evaluation of the proposed algorithm reveals an optimum speedup for a typical range of system parameters used... 

In this paper, an analytical performance model for adaptive wormhole routing in the hypercube-based optical transpose interconnection system (OTIS-hypercube) is proposed and validated. Using this model, the performance merits of the OTIS-hypercube are discussed. We also compare the performance of the OTIS-hypercube with that of equivalent hypercube network under different implementation constraints. Compared to pure simulation results, the presented model can serve as a more appropriate and compact method to display the performance characteristics of OTIS-hypercube networks. © 2007 Elsevier Inc. All rights reserved  

Parallel computers, such as multiprocessors system-on-chip (Mp-SoCs), multicomputers and cluster computers, are consisting of hundreds or thousands multiple processing units and components (such as routers, channels and connectors) connected via some interconnection network that collectively may undergo high failure rates. Therefore, these systems are required to be equipped with fault-tolerant mechanisms to ensure that the system will keep running in a degraded mode. Normally, the faulty components are coalesced into fault regions, which are classified into two major categories: convex and concave regions. In this paper, we propose the first solution to calculate the probability of... 

Many fully-adaptive algorithms have been proposed to overcome the performance limitations of deterministic routing in networks used in high-performance multicomputers, such as the well-known regular n-D torus. This paper proposes a simple yet reasonably accurate analytical performance model to predict message communication latency in tori networks. This model requires a running time of O(1) which is the fastest model yet reported in the literature. Extensive simulations reveal that the new performance model maintains a reasonable accuracy when the network operates under different traffic conditions. The model is then used to perform an extensive investigation into the performance merits of...