Sharif Digital Repository

Dirential frequency hopping (DFH) was introduced as a new technology for reliable high data rate transmission. Since the system utilizes lower transmitting power relative to the other spread spectrum techniques and also principle part of the technique, frequency transition function (FTF), is designed privately and uniformly, the scheme is said to be safe and secure. In spite of previous researches, this paper shows that an intelligent eavesdropper may threat the security of the system by finding FTF and sending jamming signal toward authorized receivers. As a result, regular DFH can not provide consumers with security in wireless networks and hence we propose that FTF should be designed with... 

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  

FPGAs are an appealing solution for the space-based remote sensing applications. However, in a low-earth orbit, configuration bits of SRAM-based FPGAs are susceptible to single-event upsets (SEUs). In this paper, a new protected CLB and FPGA architecture are proposed which utilize error detection and correction codes to correct SEUs occurred in LUTs of the FPGA. The fault detection and correction is achieved using online or offline fast detection and correction cycles. In the latter, detection and correction is performed in predefined error-correction intervals. In both of them error detections and corrections of k-input LUTs are performed with a latency of 2k clock cycle without any... 

Asynchronous circuits have many advantages vs synchronous design styles like high performance and lower power consumption; however, there is a drawback of big overhead in handshake circuitry of these circuits. In this paper, we have reduced the amount of these extra circuits by take advantage of some compiler techniques. The compiler methods can be used innovatively to improve the synthesis results in terms of both power consumption and area, since these code motions lead to removing of completion detection and validity check parts of asynchronous designs. To the best of our knowledge this is the first effort in using the compiler pre-synthesis optimizations in asynchronous circuits to... 

In this paper, a sparsity-aware target localization method in multiple-input-multiple-output (MIMO) radars by utilizing time difference of arrival (TDOA) measurements is proposed. This method provides a maximum likelihood (ML) estimator for target position by employing compressive sensing techniques. Also, for fast convergence and mitigating the mismatch problem due to grid discretization, we address a block-based search coupled with an adaptive dictionary learning technique. The Cramer-Rao lower bound for this model is derived as a benchmark. Simulations results are included to verify the localization performance  

We consider the problem of massive matrix multiplication, which underlies many data analytic applications, in a large-scale distributed system comprising a group of worker nodes. We target the stragglers' delay performance bottleneck, which is due to the unpredictable latency in waiting for slowest nodes (or stragglers) to finish their tasks. We propose a novel coding strategy, named entangled polynomial code, for designing the intermediate computations at the worker nodes in order to minimize the recovery threshold (i.e., the number of workers that we need to wait for in order to compute the final output). We demonstrate the optimality of entangled polynomial code in several cases, and show... 

In this paper, we consider transmission of a Gaussian source over a Gaussian channel under bandwidth compression in the presence of interference known only to the transmitter. We study hybrid digital-analog (HDA) joint source-channel coding schemes and propose two novel coding schemes that achieve the optimal mean-squared error (MSE) distortion. This can be viewed as the extension of results by Wilson et al. [1], originally proposed for sending a Gaussian source over a Gaussian channel in two cases: 1) Matched bandwidth with known interference only at the transmitter, 2) bandwidth compression where there is no interference in the channel. The proposed HDA codes can cancel the interference of... 

Question and answer (Q&A) websites like Stack Overflow are one of the important sources of code examples in which developers can ask their questions and leave their answers about programming issues. Since the number of programmers who use these websites are increasing and a large number of questions and answers are being posted there by them, verifying the quality of all the answers and particularly the code snippets in them is impossible. Consequently, some code snippets might be of low quality and/or with faults. To mitigate this issue, we introduce ExRec (Example Recommender), an Eclipse plugin with which programmers can contribute in improving the quality of code snippets in the answers... 

In this paper, we study the problem of delay minimization in NFV-based networks. In such systems, the ultimate goal of any request is to compute a sequence of functions in the network, where each function can be computed at only a specific subset of network nodes. In conventional approaches, for each function, we choose one node from the corresponding subset of the nodes to compute that function. In contrast, in this work, we allow each function to be computed in more than one node, redundantly in parallel, to respond to a given request. We argue that such redundancy in computation not only improves the reliability of the network, but would also, perhaps surprisingly, reduce the overall... 

In this paper we define critical graphs as minimal graphs that support a given set of rates for the index coding problem, and study them for both the one-shot and asymptotic setups. For the case of equal rates, we find the critical graph with minimum number of edges for both one-shot and asymptotic cases. For the general case of possibly distinct rates, we show that for one-shot and asymptotic linear index coding, as well as asymptotic non-linear index coding, each critical graph is a union of disjoint strongly connected subgraphs (USCS). On the other hand, we identify a non-USCS critical graph for a one-shot non-linear index coding problem. In addition, we show that the capacity region of... 

In this paper, the detection of a coded signal in additive white Gaussian noise and the interference is studied, where there is no knowledge about the correlation between the received symbols and about the noise and interference parameters. The Maximum Likelihood (ML) estimates of the unknown parameters are found, they are substituted in the probability density functions of the observation and the Generalized Likelihood Ratio (GLR) detector is derived. This detector can also be used for the activity detection of a signal in unknown Inter-Symbol Interference (ISI). In this case, the interference is modeled as the unknown correlation between the received symbols. Simulation examples are... 

A secure channel coding (joint encryption-channel coding) scheme provides both data security and reliability in one combined process to achieve faster processing and/or more efficient implementation. The issue of using quasi-cyclic low-density parity-check (QC-LDPC) codes in a symmetric-key secure channel coding scheme is addressed. A set of this class of LDPC codes has recently been recommended by the NASA Goddard Space Flight Center for near-earth and deep-space communications. The proposed scheme provides an efficient error performance, an acceptable level of security and a low-complexity practicable implementation. The results indicate that the proposed scheme can efficiently employ... 

Overloaded code division multiple access being the only means of the capacity extension for conventional code division multiple access accommodates more number of signatures than the spreading gain. Recently, ternary Signature Matrices with Orthogonal Subsets (SMOS) has been proposed, where the capacity maximization is 200%. The proposed multi-user detector using matched filter exploits the twin tree hierarchy of correlation among the subsets to guarantee the errorless recovery. In this paper, we feature the non-ternary version of SMOS (i.e., 2k-ary SMOS) of same capacity, where the binary alphabets in all the k constituent (orthogonal) subsets are unique. Unlike ternary, the tree hierarchy... 

We consider the designing of a new set of uniquely decodable codes for uncoded synchronous overloaded CDMA system that exists for arbitrary values of spreading gain (code length). A fast and recursive method of construction is proposed where the orthogonal Hadamard matrix of least dimension (two), as the basis of construction regularizes a ternary pattern which is further leveraged to attain a rich simplicity in decoder design. The simplicity gained in designing of the proposed Comparison Aided Decoder (CAD) is prominent enough to neglect the marginal sacrifice in Bit Error Rate (BER) as compared to the optimum Maximum Likelihood Decoder (MLD) for noisy transmission. Despite its low complex... 

In this study, the authors consider the designing of a new set of uniquely decodable codes for uncoded synchronous overloaded code division multiple access for the number of codes exceeding the assigned code length. For the construction, the proposed recursive method at iteration-k generates a matrix that can be classified into k orthogonal subsets of different dimensions. Out of them, all besides the largest (binary Hadamard) one are ternary in nature. There resides an inbuilt twin tree structured cross-correlation hierarchy that facilitates an advantageous balance between the auto and intergroup cross-correlation for the signatures in a subset. This opportunity is further leveraged by the... 

In Cognitive Radio (CR), in order to avoid interference in the Primary Users (PU), some subcarriers need to be deactivated. In systems based on Multicarrier Code Division Multiple Access (MC-CDMA), this causes losing orthogonality among different spreading codes, leading to poor Bit Error Rate (BER) performance. The performance of such system can be improved by using Generalized Hadamard Codes (GHC) instead of conventional Hadamard codes which avoids the loss of orthogonality. This is due to the fact that unlike conventional Hadamard codes, GHC are conjectured to exist for any arbitrary length. In this paper, we propose using a novel spreading code, namely, GHC for synchronous MC-CDMA in CR... 

The focus of the paper is on cross-layer transmission based on rateless coding for relay networks. In the proposed method, rateless coding is used at the packet level and a separate physical layer coding is used at the physical layer. As rateless codes are originally designed and optimized for erasure channels, using these codes at the physical layer can lead to significant performance degradation. The proposed scheme has the advantage of a cross-layer design which uses a rateless code at the packet level modeled by an erasure channel. Based on the analysis and simulation results provided in this paper, the cross-layer scheme results in earlier successful decoding at the destination  

This paper focuses on cross-layer transmission based on rateless coding for relay channels. In the proposed method, rateless coding is used at packet level and a separate physical layer coding is used at the physical layer. As rateless codes are originally designed and optimized for erasure channels, using these codes at the physical layer can lead to significant performance degradation. The proposed scheme has the advantage of a cross-layer design which uses a rateless code at the packet level modeled by an erasure channel. Based on the analysis and simulation results provided in this paper, there is an exact tradeoff between physical layer code rate and rateless code depth, and the optimum... 

Data traversal in Network-on-Chips (NoCs) is threated by crosstalk fault seriously. Crosstalk fault leads to mutual influence between adjacent wires of NoCs and as a result endangers the reliability of data in NoCs. Crosstalk fault is strongly dependent on the transition patterns appearing on the wires of NoCs. Among these transitions, Triplet Opposite Directions (TODs) impose the worse crosstalk effects to the wires of NoCs. This paper proposes an efficient numerical-based coding mechanism called Summation-based-Subtracted-Added-Penultimate (S2AP) which alleviates crosstalk faults. This is done by completely removing TODs which are the main source of crosstalk faults in the channels of... 

The reliable transfer in Network on Chips (NoCs) can be threatened by crosstalk fault occurring in wires. Crossstalk fault is due to inter-wire coupling capacitance that based on the patterns of transitions appearing on the wires, significantly limits the reliability of NoCs. Among these transitions, 101 and 010 bit patterns impose the worst crosstalk effects to wires. This work intends to increase the reliability of NoCs against crosstalk faults by applying an improved Fibonacci-based numeral system, called Doubled-Penultimate Fibonacci (DP-Fibo). In the DP-Fibo coding algorithm, code words without ‘101’ and ‘010’ bit patterns are produced to reduce crosstalk faults. Experimental results...