F. Lahouti

University of Tehran, Teheran, Tehrān, Iran

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Publications (97)57.84 Total impact

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    Hamidreza Arjmandi, Farshad Lahouti
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    ABSTRACT: A key pre-distribution scheme (KPS) based on multiple codewords of block codes is presented for wireless sensor networks. The connectivity and security of the proposed KPS, quantified in terms of probabilities of sharing common keys for communications of pairs of nodes and their resilience against colluding nodes, are analytically assessed. The analysis is applicable to both linear and nonlinear codes and is simplified in the case of maximum distance separable codes. It is shown that the multiplicity of codes significantly enhances the security and connectivity of KPS at the cost of a modest increase of the nodes storage. Numerical and simulation results are provided, which sheds light on the effect of system parameters of the proposed KPS on its complexity and performance. Specifically, it is shown that the probability of resilience of secure pairs against collusion of other nodes only reduces slowly as the number of colluding nodes increase.
    07/2014;
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    Siavash Ghavami, Farshad Lahouti
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    ABSTRACT: This paper investigates the capacity and capacity per unit cost of Gaussian multiple access-channel (GMAC) with peak power constraints. We first devise an approach based on Blahut-Arimoto Algorithm to numerically optimize the sum rate and quantify the corresponding input distributions. The results reveal that in the case with identical peak power constraints, the user with higher SNR is to have a symmetric antipodal input distribution for all values of noise variance. Next, we analytically derive and characterize an achievable rate region for the capacity in cases with small peak power constraints, which coincides with the capacity in a certain scenario. The capacity per unit cost is of interest in low power regimes and is a target performance measure in energy efficient communications. In this work, we derive the capacity per unit cost of additive white Gaussian channel and GMAC with peak power constraints. The results in case of GMAC demonstrate that the capacity per unit cost is obtained using antipodal signaling for both users and is independent of users rate ratio. We characterize the optimized transmission strategies obtained for capacity and capacity per unit cost with peak-power constraint in detail and specifically in contrast to the settings with average-power constraints.
    07/2014;
  • Amin Azari, Jalil Seifali Harsini, Farshad Lahouti
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    ABSTRACT: This paper analyzes the performance of clustered decode-and-forward multi-hop relaying (CDFMR) wireless Rayleigh fading networks, and sheds light on their design principles for energy and spectral efficiency. The focus is on a general performance analysis (over all SNR range) of heterogeneous wireless networks with possibly different numbers of relays in clusters of various separations. For clustered multi-hop relaying systems, ad-hoc routing is known as an efficient decentralized routing algorithm which selects the best relay node on a hop-by-hop basis using local channel state information. In this article, we combine ad-hoc routing and cooperative diversity in CDFMR systems, and we derive (i) a closed-form expression for the probability distribution of the end-to-end SNR at the destination node; (ii) the system symbol error rate (SER) performance for a wide class of modulation schemes; and (iii) exact analytical expressions for the system ergodic capacity, the outage probability and the achievable probability of the SNR (power) gain. We also provide simple analytical asymptotic expressions for SER and the outage probability in high SNR regime. Simulation results are provided to validate the correctness of the presented analyses.
    06/2014;
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    ABSTRACT: We apply a recently developed first principles approach that uses transmitted information in bits per joule to quantify the energy efficiency of information transmission for an inter-spike-interval (ISI) code. We investigate single compartment conductance-based model neuron driven by excitatory and inhibitory spikes, where the rate and synchrony in the presynaptic excitatory population may independently vary. We find that for a fixed input rate, the ISI distribution of the post synaptic neuron depends on the level of synchrony and is well-described by a Gamma distribution for synchrony levels less than 50%. For levels of synchrony between 15% and 50% (restricted for technical reasons), we compute the optimum input distribution that maximizes the mutual information per unit energy. This optimum distribution shows that an increased level of synchrony, as occurs in the attention process, reduces the mode of input distribution and the excitability threshold of post synaptic neuron and hence facilitates a more energy efficient neuronal communication.
    01/2014;
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    ABSTRACT: Studying the development of malignant tumours, it is important to know and predict the proportions of different cell types in tissue samples. Knowing the expected temporal evolution of the proportion of normal tissue cells, compared to stem-like and non-stem like cancer cells, gives an indication about the progression of the disease and indicates the expected response to interventions with drugs. Such processes have been modeled using Markov processes. An essential step for the simulation of such models is then the determination of state transition probabilities. We here consider the experimentally more realistic scenario in which the measurement of cell population sizes is noisy, leading to a hidden Markov model. In this context, extrinsic randomness is related to noisy measurements, which are used for the estimation of the transition probability matrix. Intrinsic randomness, on the other hand, is here related to the error in estimating the state probability from small cell populations. Using aggregated data of fluorescence-activated cell sorting (FACS) measurement, we develop a minimum mean square error estimator (MMSE) and maximum likelihood (ML) estimator and formulate two problems to find the minimum number of required samples and measurements to guarantee the accuracy of predicted population sizes using a transition probability matrix estimated from noisy data. We analyze the properties of two estimators for different noise distributions and prove an optimal solution for Gaussian distributions with the MMSE. Our numerical results show, that for noisy measurements the convergence mechanism of transition probabilities and steady states differ widely from the real values if one uses the standard deterministic approach in which measurements are assumed to be noise free.
    10/2013;
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    ABSTRACT: Studying the development of malignant tumours, it is important to know and predict the proportions of different cell types in tissue samples. Knowing the expected temporal evolution of the proportion of normal tissue cells, compared to stem-like and non-stem like cancer cells, gives an indication about the progression of the disease and indicates the expected response to interventions with drugs. Such processes have been modeled using Markov processes. An essential step for the simulation of such models is then the determination of state transition probabilities. We here consider the experimentally more realistic scenario in which the measurement of cell population sizes is noisy, leading to a particular hidden Markov model. In this context, randomness in measurement is related to noisy measurements, which are used for the estimation of the transition probability matrix. Randomness in sampling, on the other hand, is here related to the error in estimating the state probability from small cell populations. Using aggregated data of fluorescence-activated cell sorting (FACS) measurement, we develop a minimum mean square error estimator (MMSE) and maximum likelihood (ML) estimator and formulate two problems to find the minimum number of required samples and measurements to guarantee the accuracy of predicted population sizes using a transition probability matrix estimated from noisy data. We analyze the properties of two estimators for different noise distributions and prove an optimal solution for Gaussian distributions with the MMSE. Our numerical results show, that for noisy measurements the convergence mechanism of transition probabilities and steady states differ widely from the real values if one uses the standard deterministic approach in which measurements are assumed to be noise free.
    IET systems biology. 10/2013; 8(5).
  • Siavash Ghavami, Farshad Lahouti, Lars Schwabe
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    ABSTRACT: In this paper we investigate the consequences of biologically plausible constraints on predictions of the Berger-Levy energy efficient neuron model. As new constraints we consider i) a peak power constraint, ii) peak energy expenditure per ISI constraint, iii) a lower bound on the value of inter spike interval (ISI), and iv) lower and upper bounds on the excitatory postsynaptic potential (EPSP) intensity, λ. Our analysis shows that considering these constraints of the capacity per unit cost maximization problem changes the shape of probability distribution function (PDF) of λ and the ISIs. We show, using numerical solutions of the optimization problem, that the new constraints change the PDFs of λ and the ISIs in term of their shape and location of the peak value. We also derive predictions for how the coefficient of variation (CV) of the ISI is changed, which is easier to characterize experimentally than the full PDF.
    Neural Networks (IJCNN), The 2013 International Joint Conference on; 01/2013
  • Jalil S. Harsini, Farshad Lahouti
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    ABSTRACT: The effective capacity (EC) for a wireless system expresses the maximum arrival source rate that the system can reliably transmit over the wireless channel while fulfilling a probabilistic delay constraint. This paper presents an EC optimization for a multiuser diversity system exploiting proportional opportunistic scheduling at the medium access control layer in conjunction with adaptive modulation and coding (AMC) at the physical layer. We consider the downlink of a time-slotted multiuser system with two different types of channel state information (CSI) at the transmitter, that is, (i) full CSI, whereby each user feeds back its normalized signal-to-noise ratio to the transmitter and (ii) quantized CSI, where each user feeds back the AMC mode for transmission. For each case, we first derive the EC function of the queue service process for the individual users at the medium access control layer. We then design the AMC scheme with power control aiming at maximizing the said function subject to a target packet-error rate constraint. Both independent and identically distributed and time-correlated fading channels are considered. The results illustrate the superior performance of the proposed schemes, when compared with the previous systems such as opportunistic scheduling with single-rate transmission and round-robin scheduling with AMC. Copyright © 2012 John Wiley & Sons, Ltd.
    Transactions on Emerging Telecommunications Technologies. 10/2012; 23(6).
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    Hamid Khodakarami, Farshad Lahouti
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    ABSTRACT: In this paper, a link adaptation and untrusted relay assignment (LAURA) framework for efficient and reliable wireless cooperative communications with physical layer security is proposed. Using sharp channel codes in different transmission modes, reliability for the destination and security in the presence of untrusted relays (low probability of interception) are provided through rate and power allocation. Within this framework, several schemes are designed for highly spectrally efficient link adaptation and relay selection, which involve different levels of complexity and channel state information requirement. Analytical and simulation performance evaluation of the proposed LAURA schemes are provided, which demonstrates the effectiveness of the presented designs. The results indicate that power adaptation at the source plays a critical role in spectral efficiency performance. Also, it is shown that relay selection based on the signal to noise ratio of the source to relays channels provides an interesting balance of performance and complexity within the proposed LAURA framework.
    IEEE Transactions on Communications 08/2012; · 1.75 Impact Factor
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    ABSTRACT: A scheme for detection of abnormality in molecular nano-networks is proposed. This is motivated by the fact that early diagnosis, classification and detection of diseases such as cancer play a crucial role in their successful treatment. The proposed nano-abnormality detection scheme (NADS) comprises of a two-tier network of sensor nano-machines (SNMs) in the first tier and a data gathering node (DGN) at the sink. The SNMs detect the presence of competitor cells as abnormality that is captured by variations in parameters of a nano-communications channel. In the second step, the SNMs transmit micro-scale messages over a noisy micro communications channel (MCC) to the DGN, where a decision is made upon fusing the received signals. The detection performance of each SNM is analyzed by setting up a Neyman-Pearson test. Next, taking into account the effect of the MCC, the overall performance of the proposed NADS is quantified in terms of probabilities of misdetection and false alarm. A design problem is formulated, when the optimized concentration of SNMs in a sample is obtained for a high probability of detection and a limited probability of false alarm.
    05/2012;
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    Roghayeh Joda, Farshad Lahouti
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    ABSTRACT: In this paper, delay-limited transmission of quasi-stationary sources over block fading channels are considered. Considering distortion outage probability as the performance measure, two source and channel coding schemes with power adaptive transmission are presented. The first one is optimized for fixed rate transmission, and hence enjoys simplicity of implementation. The second one is a high performance scheme, which also benefits from optimized rate adaptation with respect to source and channel states. In high SNR regime, the performance scaling laws in terms of outage distortion exponent and asymptotic outage distortion gain are derived, where two schemes with fixed transmission power and adaptive or optimized fixed rates are considered as benchmarks for comparisons. Various analytical and numerical results are provided which demonstrate a superior performance for source and channel optimized rate and power adaptive scheme. It is also observed that from a distortion outage perspective, the fixed rate adaptive power scheme substantially outperforms an adaptive rate fixed power scheme for delay-limited transmission of quasi-stationary sources over wireless block fading channels. The effect of the characteristics of the quasi-stationary source on performance, and the implication of the results for transmission of stationary sources are also investigated.
    IEEE Transactions on Communications 02/2012; · 1.75 Impact Factor
  • H. Khodakarami, F. Lahouti
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    ABSTRACT: A secure link adaptation framework is proposed, which exploits the inherent fluctuations of wireless fading channels for high-performance communications and physical layer security in the presence of an eavesdropper. The authors use very sharp channel codes intended for reliability and demonstrate that they also provide security, when successfully incorporated in the link adaptation design framework and the security constraint is not very stringent. Two scenarios are considered in which the transmitter has access to the eavesdropper channel state information either instantaneously or statistically. The proposed secure link adaptation framework is formulated to maximise the spectral efficiency of the communication, whereas both reliability and security constraints are provisioned. Different designs are considered when the security constraint is quantified by instantaneous bit error rate (BER), average BER or leakage probability. For the problem with instantaneous BER constraint, an efficient analytical solution and a numerical solution are presented. A closed-form analytical solution is also provided for secure link adaptation with average BER constraint, whereas the problem with the leakage constraint is tackled numerically. Extensive results and detailed analysis are provided to draw insights on the effects of different design parameters on the performance.
    IET Communications 01/2012; 6(3):353-362. · 0.72 Impact Factor
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    ABSTRACT: In a cooperative relay network, a relay (R) node may facilitate data transmission to the destination (D) node when the latter node cannot correctly decode the source (S) node data. This paper considers such a system model and presents a cross-layer approach to jointly design adaptive modulation and coding (AMC) at the physical layer and the truncated cooperative automatic repeat request (C-ARQ) protocol at the data-link layer for quality-of-service (QoS)-constrained applications. The average spectral efficiency and packet loss rate of the joint C-ARQ and AMC scheme are first derived in closed form. Aiming to maximize the system spectral efficiency, AMC schemes for the S-D and R-D links are optimized, whereas a prescribed packet-loss-rate constraint is satisfied. As an interesting application, joint link adaptation and blockage mitigation in land mobile satellite communications (LMSC) with temporally correlated channels is then investigated. In LMSC, the S node data can be delivered to the D node when the S-D is in the outage, therefore provisioning the QoS requirements. For applications without instantaneous feedback, an optimized rate selection scheme based on the channel statistics is also devised. Detailed and insightful numerical results are presented, which indicate the superior performance of the proposed joint AMC and C-ARQ schemes over their optimized joint AMC and traditional ARQ counterparts.
    IEEE Transactions on Vehicular Technology 10/2011; · 2.06 Impact Factor
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    H. Arjmandi, F. Lahouti
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    ABSTRACT: This paper addresses the problem of efficient data gathering based on distributed source coding (DSC) in wireless sensor networks (WSNs) with a complexity constrained data gathering node (DGN). A particular scenario of interest is a cluster of low complexity sensor nodes among which, one node is selected as the cluster head (CH) or the DGN. Utilizing DSC allows for reducing the required rate of communications by exploiting the dependency between the nodes observations in a distributed manner. We consider a DSC-based rate allocation structure, which takes into account the CH (DGN) memory and computational constraints. Specifically, this is accomplished, respectively, by limiting the number of nodes whose data may be stored at the CH and exploited during decoding, and the number of nodes that can be jointly (de)compressed using DSC. Based on this structure, we investigate two WSN resource optimization problems aiming at: (i) minimizing the total network cost and (ii) maximizing the network lifetime. To these ends, optimal dynamic programming solutions based on a trellis structure are proposed that incur substantially smaller computational complexity in comparison to an exhaustive search. Also, a suboptimal yet high performance solution is presented whose complexity grows in polynomial order with the number of network nodes. Numerical results demonstrate that the proposed rate allocation structure and solutions, even with limited complexity, allow for exploiting most of the available dependency and hence the achievable compression gain.
    IEEE Sensors Journal 10/2011; · 1.48 Impact Factor
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    ABSTRACT: This paper presents performance analysis and cross-layer design approaches for hybrid ARQ (HARQ) protocols in wireless networks, which employ adaptive modulation and coding (AMC) in conjunction with adaptive cooperative diversity and are subject to time-correlated fading channels. We first consider a point-to-point scenario, i.e., non-cooperative HARQ with AMC. Utilizing a Markov channel model which accounts for the temporal correlation in the successive transmission of incremental redundancy by the HARQ protocol, we derive the system throughput and the packet loss probability based on a rate compatible punctured convolutional code family. Next, we consider a cooperative HARQ (CHARQ) scheme in which a relay node, also equipped with AMC, retransmits redundancy packets when it is able to decode the source information packet correctly. For this scenario, we also derive the throughput and packet loss performance. Finally, we present a cross-layer AMC design approach which takes into account the hybrid ARQ protocol at the link layer. The results illustrate that including AMC in the HARQ protocols leads to a substantial throughput gain. While the performance of the AMC with HARQ protocol is strongly affected by the channel correlation, the CHARQ protocol provides noticeable performance gains over correlated fading channels as well.
    IEEE Transactions on Wireless Communications 04/2011; · 2.42 Impact Factor
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    Mehrdad Valipour, Farshad Lahouti
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    ABSTRACT: In this paper, channel optimized distributed multiple description vector quantization (CDMD) schemes are presented for distributed source coding in symmetric and asymmetric settings. The CDMD encoder is designed using a deterministic annealing approach over noisy channels with packet loss. A minimum mean squared error asymmetric CDMD decoder is proposed for effective reconstruction of a source, utilizing the side information (SI) and its corresponding received descriptions. The proposed iterative symmetric CDMD decoder jointly reconstructs the symbols of multiple correlated sources. Two types of symmetric CDMD decoders, namely the estimated-SI and the soft-SI decoders, are presented which respectively exploit the reconstructed symbols and a posteriori probabilities of other sources as SI in iterations. In a multiple source CDMD setting, for reconstruction of a source, three methods are proposed to select another source as its SI during the decoding. The methods operate based on minimum physical distance (in a wireless sensor network setting), maximum mutual information and minimum end-to-end distortion. The performance of the proposed systems and algorithms are evaluated and compared in detail.
    IEEE Transactions on Signal Processing 01/2011; · 2.81 Impact Factor
  • Mehrdad Taki, Farshad Lahouti
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    ABSTRACT: We consider a primary and a cognitive user transmitting over a wireless fading interference channel. A discrete rate link adaptation scheme is proposed to maximize the average spectral efficiency of the cognitive radio, while a minimum average spectral efficiency for the primary user is provisioned. The discrete rate scheme for interfering transmission is devised based on two sets of modulation and coding pairs for the primary and cognitive links. The primary transmitter adapts its rate (modulation and coding) solely based on signal to interference plus noise ratio of its link; however, the cognitive transmitter influences the primary link rate by imposing a proper SINR. The adaptive modulation and coding mode selection and power control at the cognitive transmitter are optimized based on SINR of both links. The problem is then cast as a nonlinear discrete optimization problem for which a fast and efficient suboptimum solution is presented. We also present a scheme with rate adaptive and constant power cognitive radio. An important characteristic of the proposed schemes is that no computation overhead is imposed on primary radio due to cognitive radio activity. Numerical results and comparison with the interweave approach to cognitive radio demonstrate the efficiency of the proposed solutions.
    IEEE Transactions on Wireless Communications 01/2011; 10:2929-2939. · 2.42 Impact Factor
  • IEEE Transactions on Wireless Communications. 01/2011; 10:877-889.
  • Kamal Rahimi Malekshan, Farshad Lahouti
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    ABSTRACT: In mobile Ad-hoc networks forwarding data through intermediate relays extends the coverage area and enhances the network throughput. Dynamic assignment of routes for data transmission from sources to destinations that is optimized based on channel conditions in a cross-layer manner could provide improved performance. We consider a general multiuser two-hop transmission, where each flow is subject to a constraint on the end-to-end buffering delay and its associated packet loss rate as a quality of service requirement. The objective is to maximize the weighted sum-rate between source destination pairs, while the QoS requirement is satisfied. We introduce two new cross-layer dynamic route selection schemes in this setting that are designed involving physical, MAC, and network layers. In cross-layer opportunistic dynamic route selection, the routes are assigned dynamically based on the instantaneous state of fading channels. In time division cross-layer dynamic route selection, the route for data transmission is scheduled based on the average quality of links. Simulation results show that our proposed cross-layer dynamic route selection schemes provide superior performance in comparison to prior art.
    IEEE 22nd International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2011, Toronto, ON, Canada, September 11-14, 2011; 01/2011
  • Mehrdad Taki, Farshad Lahouti
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    ABSTRACT: This paper presents novel joint link adaptation and user selection (JLAUS) schemes to maximize a weighted sum of the average rates of wireless links sharing a spectrum, while their possibly different minimum required average rates and quality of service constraints are provisioned. The schemes take into account the instantaneous SNR of all links and select a link for transmission and set its rate and power in a jointly optimized manner. The links operate based on adaptive modulation and coding and power control over heterogeneous wireless fading channels. Two JLAUS schemes are presented. The first scheme provides a framework for integrated analysis and design of link adaptation and user selection and relies on a partitioning of the space of link SNRs into regions. In this setting, the second scheme offers a particular JLAUS design, which enjoys a polynomial design complexity. The design is performed before the transmission starts, based on closed form solutions. The proposed schemes can be easily applied to a multiple access or a broadcast network. Numerical results demonstrate how the proposed JLAUS schemes outperform the benchmark schemes, or effectively meet various user requirements.
    01/2011;

Publication Stats

243 Citations
57.84 Total Impact Points

Institutions

  • 2006–2013
    • University of Tehran
      • • Center of Excellence for Applied Electromagnetic Systems
      • • School of Electrical and Computer Engineering
      • • College of Engineering
      Teheran, Tehrān, Iran
  • 2000–2009
    • University of Waterloo
      • Department of Electrical & Computer Engineering
      Waterloo, Quebec, Canada
  • 2007
    • University of Guilan
      • Department of Electrical Engineering
      Resht, Gīlān, Iran