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    Multi-user opportunistic spectrum access with channel impairments [electronic resource]

    , Article AEU - International Journal of Electronics and Communications ; Volume 67, Issue 11, November 2013, Pages 955–966 Majd, A. (Sayyed Arash) ; Salehkalybar, S ; Pakravan, M. R ; Sharif University of Technology
    In this paper, we study the impact of sensing error and channel fading on the decision process of a multiple secondary user network in a primary network whose channel occupancy states are modelled as a Bernoulli process. We present a randomized access strategy to maximize total secondary network throughput. The proposed method guarantees that the probability of collision between primary and secondary users in each channel is less than the predefined value of Pc = ξ. To find the optimal access strategy, we formulate secondary network throughput as an optimization problem. Then, using the KKT method to find the solution, we break the original problem into multiple sub-problems. Then, we employ... 

    Probability of missed detection as a criterion for receiver placement in MIMO PCL

    , Article IEEE National Radar Conference - Proceedings, 7 May 2012 through 11 May 2012, Atlanta, GA ; 2012 , Pages 0924-0927 ; 10975659 (ISSN) ; 9781467306584 (ISBN) Majd, M. N ; Chitgarha, M. M ; Radmard, M ; Nayebi, M. M ; Sharif University of Technology
    IEEE  2012
    Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar  

    MIMO ambiguity function optimization through waveform design

    , Article Proceedings International Radar Symposium, 24 June 2015 through 26 June 2015 ; Volume 2015-August , 2015 , Pages 333-338 ; 21555753 (ISSN) ; 9783954048533 (ISBN); 9783954048533 (ISBN); 9783954048533 (ISBN) Radmard, M ; Majd, M. N ; Chitgarha, M. M ; Karbasi, S. M ; Nayebi, M. M ; Rohling, H ; Rohling, H ; Rohling, H ; Sharif University of Technology
    IEEE Computer Society  2015
    An important tool for assessing a radar's performance is the ambiguity function. On the other hand, many different schemes have been designed for the transmit waveforms of a MIMO radar. For each one, a criterion has been chosen to improve the performace, e.g. achieving better missed detection. In this paper, considering the ambiguity function as the benchmark, we propose a waveform design scheme, which optimizes the ambiguity function of the MIMO radar system  

    Novel coarse timing synchronization methods in OFDM systems using fourth-order statistics

    , Article IEEE Transactions on Vehicular Technology ; Volume 64, Issue 5 , 2015 , Pages 1904-1917 ; 00189545 (ISSN) Mohebbi, A ; Abdzadeh Ziabari, H ; Shayesteh, M. G ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    In this paper, the problem of coarse timing synchronization in orthogonal frequency-division multiplexing (OFDM) systems is investigated, and two new timing metrics with better performance are presented. The new metrics take advantage of two novel differential normalization functions that are based on the fourth-order statistics and are designed depending on the value of carrier frequency offset (CFO). The proposed timing metrics are theoretically evaluated using two different class separability criteria. It is shown that the new schemes considerably increase the difference between the correct and wrong timing points in comparison with previous methods. The computational complexity of the... 

    Robust Wiener filter-based time gating method for detection of shallowly buried objects

    , Article IET Signal Processing ; 2021 ; 17519675 (ISSN) Gharamohammadi, A ; Behnia, F ; Shokouhmand, A ; Shaker, G ; Sharif University of Technology
    Institution of Engineering and Technology  2021
    A robust method for ultra-wideband (UWB) imaging of buried shallow objects based on time gating, Wiener filtering, as well as constant false alarm rate (CFAR) is proposed. Moreover, it is demonstrated that Wiener filtering can be used as a clutter removal tool in UWB signal applications. Basically, the problem with time gating method is that the length of the timing window for unknown targets cannot be determined accurately in advance. In fact, it is a blind methodology and some targets can be missed due to a lack of pre-knowledge about their depth. Imprecise window length selection leads to missing some parts of the target signals along with the clutter, which in turn increases the missed... 

    KNNDIST: A non-parametric distance measure for speaker segmentation

    , Article 13th Annual Conference of the International Speech Communication Association 2012, INTERSPEECH 2012 ; Volume 3 , 2012 , Pages 2279-2282 ; 9781622767595 (ISBN) Mohammadi, S. H ; Sameti, H ; Langarani, M. S. E ; Tavanaei, A ; Sharif University of Technology
    A novel distance measure for distance-based speaker segmentation is proposed. This distance measure is nonparametric, in contrast to common distance measures used in speaker segmentation systems, which often assume a Gaussian distribution when measuring the distance between two audio segments. This distance measure is essentially a k-nearest-neighbor distance measure. Non-vowel segment removal in preprocessing stage is also proposed. Speaker segmentation performance is tested on artificially created conversations from the TIMIT database and two AMI conversations. For short window lengths, Missed Detection Rated is decreased significantly. For moderate window lengths, a decrease in both... 

    Receivers' positioning in multiple-input multiple-output digital video broadcast-terrestrial-based passive coherent location

    , Article IET Radar, Sonar and Navigation ; Volume 6, Issue 7 , 2012 , Pages 603-610 ; 17518784 (ISSN) Radmard, M ; Khalaj, B. H ; Chitgarha, M. M ; Nazari Majd, M ; Nayebi, M. M ; Sharif University of Technology
    IEEE  2012
    Using multiple illuminators of opportunity at the transmit side and multiple antennas at the receiver side in a passive coherent location (PCL) scheme is expected to improve the detection performance. However, in such multiple-input multiple-output (MIMO) configuration choosing the position of the receivers is an obstacle that can have significant influence on the resulting performance. In this study, the authors consider the case of digital video broadcast (DVB)-T stations as non-cooperative transmitters and introduce a procedure based on the probability of missed detection to properly place receive antennas in a MIMO digital video broadcasting (DVB)-T based PCL configuration  

    Spatial diversity gain of MIMO single frequency network in passive coherent location

    , Article Scientia Iranica ; Vol. 21, Issue. 6 , 2014 , pp. 2186-2199 ; ISSN: 10263098 Radmard, M ; Majd, M. N ; Chitgarha, M. M ; Khalaj, B. H ; Nayebi, M. M ; Sharif University of Technology
    Recently, it has been shown that applying MIMO technology, i.e. using multiple antennas at the transmit side and multiple antennas at the receive side, improves the performance of object detection and localization. In such scenarios, the spatial diversity specifically helps overcome the fading of the cross section of the object, leading to reduced probability of missed detection. Such a phenomenon is, in fact, the dual of probability of bit error reduction in communication systems due to diversity gain. Despite the importance of such performance enhancement, this subject has not been sufficiently investigated in the PCL (Passive Coherent Location) schemes, where the transmitters (or... 

    Choosing the position of the receiver in a MISO passive radar system

    , Article European Microwave Week 2012: "Space for Microwaves", EuMW 2012, Conference Proceedings - 9th European Radar Conference, EuRAD 2012 ; 2012 , Pages 318-321 ; 9782874870293 (ISBN) Chitgarha, M. M ; Majd, M. N ; Radmard, M ; Nayebi, M. M ; Sharif University of Technology
    By combining the two ideas of MIMO (Multiple Input Multiple Output) and PCL (Passive Coherent Location) in radar, one can achieve the advantages of both recently developed techniques simultaneously. While using multiple antennas at the receive side provides a spatial diversity of the object to be detected, using multiple illuminators of opportunity, most importantly, makes the radar covert to the interceptors. One obstacle in such MIMO configuration is choosing the positions of the receive antennas. In this paper, after analyzing the Neyman-Pearson detector for the DVB-T based PCL, we introduce the probability of missed detection as a criterion to place the receive antenna. Here, we only... 

    A robust short-circuit fault diagnosis for high voltage DC power supply based on multisensor data fusion

    , Article 10th International Power Electronics, Drive Systems and Technologies Conference, PEDSTC 2019, 12 February 2019 through 14 February 2019 ; 2019 , Pages 659-664 ; 9781538692547 (ISBN) Ayoubi, R ; Kaboli, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Short-circuit fault (SCF) detection is mandatory in a high voltage DC power supply (HVPS) to prevent fatal damage. The majority of converters employ a single sensor to detect the SCF. This attribute increases the interference vulnerability of the fault detection (FD) system in the presence of noise. Therefore, miss detections and false alarms are possible to occur. Miss detections and false alarms are harmful catastrophes in most applications. A commonly used method to suppress the noise impacts is using a low-bandwidth low-pass filter. However, the use of the low-bandwidth low-pass filter reduces the speed of FD due to the filter delay. This paper proposes a fast FD algorithm based on...