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    Peak-to-average reduction in MC-CDMA based on using different spreading and Despreading codes

    , Article 2002 IEEE Wireless Communications and Networking Conference, WCNC 2002, 17 March 2002 through 21 March 2002 ; Volume 2 , 2002 , Pages 665-668 ; 15253511 (ISSN); 0780373766 (ISBN) Talasaz, A. H ; Kenari, M. N ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2002
    In this paper, we propose a new scheme to reduce Peak-to-As erage Power Ratio (PAPR) in a MC-CDMA system. In this scheme, some codes among the family of signature codes used in the system are utilized only for PAPR reduction. A set of spreading codes and only one despreading code are assigned to each user. The user selects its own spreading code among the assigned set based on which one proides lower PAPR. The numerical results show that despite of its simplicity, our proposed approach substantially reduces the PAPR of MCCDMA system at the expense of not capturing some portions of the transmitted energy in the receiver for some users © 2002 IEEE  

    A method for improving power distribution characteristics of space time block codes

    , Article China Communications ; Volume 17, Issue 6 , 2020 , Pages 223-234 Abbasi, V ; Shayesteh, M. G ; Sharif University of Technology
    Editorial Department of China Communications  2020
    Improving power distribution characteristics of space time block codes (STBCs), namely peak to average power ratio (PAPR), average to minimum power ratio (Ave/min), and probability of transmitting 'zero' by antenna, makes easier their practical implementation. To this end, this study proposes to multiply full diversity STBC with a non-singular matrix in multiple input multiple output (MIMO) or multiple input single output (MISO) systems with linear or maximum likelihood (ML) receivers. It is proved that the obtained code achieves full diversity and the order of detection complexity does not change. The proposed method is applied to different types of STBCs. The bit error rate (BER) and power... 

    Value-Aware low-power register file architecture

    , Article CADS 2012 - 16th CSI International Symposium on Computer Architecture and Digital Systems ; 2012 , Pages 44-49 ; 9781467314824 (ISBN) Ahmadian, S. N ; Fazeli, M ; Ghalaty, N. F ; Miremadi, S. G ; Sharif University of Technology
    In this paper, we propose a low power register file architecture for embedded processors. The proposed architecture, "Value-Aware Partitioned Register File (VAP-RF)", employs a partitioning technique that divides the register file into two partitions such that the most frequently accessed registers are stored in the smaller register partition. In our partitioning algorithm, we introduce an aggressive clock-gating scheme based on narrow-value registers to furthermore reduce power. Experimental results on an ARM processor for selected MiBench workloads show that the proposed architecture has an average power saving of 70% over generic register file structure  

    On the peak-to-average power of OFDM signals based on oversampling

    , Article IEEE Transactions on Communications ; Volume 51, Issue 1 , 2003 , Pages 72-78 ; 00906778 (ISSN) Sharif, M ; Gharavi Alkhansari, M ; Hossein Khalaj, B ; Sharif University of Technology
    Orthogonal frequency-division multiplexing (OFDM) introduces large amplitude variations in time, which can result in significant signal distortion in the presence of nonlinear amplifiers. In this paper, we introduce a new bound for the peak of the continuous envelope of an OFDM signal, based on the maximum of its corresponding oversampled sequence, that is shown to be very tight as the oversampling rate increases. The bound is then used to derive a closed-form probability upper bound for complementary cumulative distribution function of the peak-to-mean envelope power ratio of uncoded OFDM signals for sufficiently large numbers of subcarriers. As another application of the bound for... 

    Selected mapping algorithm for PAPR reduction of space-frequency coded OFDM systems without side information

    , Article IEEE Transactions on Vehicular Technology ; Volume 60, Issue 3 , 2011 , Pages 1211-1216 ; 00189545 (ISSN) Ferdosizadeh Naeiny, M ; Marvasti, F ; Sharif University of Technology
    Selected mapping (SLM) is a well-known technique for peak-to-average-power ratio (PAPR) reduction of orthogonal frequency-division multiplexing (OFDM) systems. In this technique, different representations of OFDM symbols are generated by rotation of the original OFDM frame by different phase sequences, and the signal with minimum PAPR is selected and transmitted. To compensate for the effect of the phase rotation at the receiver, it is necessary to transmit the index of the selected phase sequence as side information (SI). In this paper, an SLM technique is introduced for the PAPR reduction of space-frequency-block-coded OFDM systems with Alamouti coding scheme. Additionally, a suboptimum... 

    Optimum power allocation in parallel poisson optical channel

    , Article 2009 10th International Conference on Telecommunications, ConTEL 2009, Zagreb, 8 June 2009 through 10 June 2009 ; 2009 , Pages 285-288 ; 9789531841313 (ISBN) Alem Karladani, M. M ; Sepahi, L ; Jazayerifar, M ; Kalbasi, K ; Sharif University of Technology
    In this paper we investigate the Shannon capacity of single and parallel Poisson channels in different scenarios. At first, by examining the capacity equation of the single Poisson channel, the minimum average power that maximizes the capacity is found. Then, applying the method of Lagrange multipliers on the capacity expression of the parallel Poisson channel, we obtain the optimum power allocation maximizing the parallel Poisson channel capacity  

    PAPR reduction of OFDM signals using harmony search algorithm

    , Article 2011 18th International Conference on Telecommunications, ICT 2011, 8 May 2011 through 11 May 2011, Ayia Napa ; 2011 , Pages 90-94 ; 9781457700248 (ISBN) Kermani, E. M ; Salehinejad, H ; Talebi, S ; Sharif University of Technology
    Orthogonal frequency division multiplexing (OFDM) is one of the widely used multiplexing techniques in wireless communications and especially cognitive radio networks. One of the key challenges of this technique is its high peak to average power ratio (PAPR) of the transmitted signal. This paper, introduces a new approach to PAPR reduction of OFDM signals using harmony search algorithm (HSA) based on the partial transmit sequence (PTS) method. The simulation results demonstrate that the proposed algorithm has better PAPR reduction performance as an accurate and low complexity approach for OFDM systems  

    Peak to Average Power Ratio Reduction in OFDM Systems

    , M.Sc. Thesis Sharif University of Technology Kahookar Toosi, Hossein (Author) ; Marvasti, Farrokh (Supervisor)
    High peak to average power ratio (PAPR) is one major drawback of OFDM system which highly affects the performance if untreated. Several methods have been proposed to overcome this problem. In all these methods reduction in PAPR is gained through a tradeoff with another system figure such as mean transmit power, bandwidth or BER. In this thesis we investigate high PAPR problem in OFDM, and we will introduce some methods proposed to alleviate it. These methods are divided into two classes; methods in the first class are based on finding a peak cancelling signal and methods in second class rely on solving a discrete optimization problem. We give a general formulaion for the methods in second... 

    Compressive Sensing PAPR Mitigation in OFDM Systems

    , M.Sc. Thesis Sharif University of Technology Salami Kavaki, Hassan (Author) ; Mashhadi, Saeed (Supervisor)
    Orthogonal Frequency Division Multiplexing (OFDM) is a digital transmission method developed to meet the increasing demand for higher data rates in communications which can be used in both wired and wireless environments. This thesis describes the issue of the Peak to Average Power Ratio (PAPR) in OFDM system, based on compressed sensing at the receiver of a peak-reducing sparse clipper applied to an OFDM signal at the transmitter. By choosing proper clipping threshold, clipping signal will be sparse so locations, magnitudes, and phases of the clipping signal can be recovered by compressed sensing method. We demonstrate that in the absence of optimization algorithms at the transmitter,... 

    Wideband Doherty Power Amplifier with Designed Back-Off Power for Cellular Base Stations

    , M.Sc. Thesis Sharif University of Technology Zafari, Ali (Author) ; Memarian, Mohammad (Supervisor) ; Safarian, Amin Ghasem (Co-Supervisor)
    The Emergence of modern wireless communication standards and the need to use the frequency spectrum efficiently has made communication system designers exert complex modulation schemes. One of the results of such designs that has a direct impact on the design procedure of power amplifiers is that there will be signals with high peak to average power ratio.The obvious consequence of this manner in the design of communication systems would be the reduction of power amplifier efficiency due to its operation in its back-off region. The solution will be to use load modulated power amplifiers such as Doherty amplifier which brings up the problem of limited bandwidth.In this thesis, we tackle this... 

    Wide-band high-efficiency Ku-band power amplifier

    , Article IET Circuits, Devices and Systems ; Vol. 8, issue. 6 , December , 2014 , p. 583-592 ; 1751858X Yousefi, A ; Medi, A ; Sharif University of Technology
    A 37 dBm power amplifier (PA) is designed on a 0.25 μm optical T-gate pseudomorphic high electron mobility transistor (pHEMT) technology. The design of this two-stage PA along with a step-by-step design procedure is presented in this paper. This methodology can be used for design of PA in different technologies and frequencies. The PA delivers 5 W output power over the frequency band of 13-19 GHz. It shows average power-added efficiency of 37% and large signal gain of 15 dB in measurements which is consistent with simulation results. The output power and efficiency of the realised amplifier reach maximums of 37.6 dBm and 45%, respectively. Considering output power, bandwidth, chip area and... 

    PAPR reduction of OFDM signals by novel global harmony search in PTS scheme

    , Article International Journal of Digital Multimedia Broadcasting ; Volume 2012 , November , 2012 ; 16877578 (ISSN) Salehinejad, H ; Talebi, S ; Sharif University of Technology
    The orthogonal frequency division multiplexing (OFDM) modulation technique is one of the key strategies for multiuser signal transmission especially in smart grids and wind farms. This paper introduces an approach for peak-to-average power ratio (PAPR) reduction of such signals based on novel global harmony search (NGHS) and partial transmit sequence (PTS) schemes. In PTS technique, the data block to be transmitted is partitioned into disjoint subblocks, which are combined using phase factors to minimize PAPR. The PTS requires an exhaustive search over all combinations of allowed phase factors. Therefore, with respect to the fast implementation and simplicity of NGHS technique, we could... 

    Cognitive MIMO radars: An information theoretic constrained code design method

    , Article European Signal Processing Conference, 28 August 2016 through 2 September 2016 ; Volume 2016-November , 2016 , Pages 2215-2219 ; 22195491 (ISSN) ; 9780992862657 (ISBN) Naghsh, M. M ; Haj Mirza Alian, E ; Modarres Hashemi, M ; Nayebi, M. M ; Sharif University of Technology
    European Signal Processing Conference, EUSIPCO  2016
    A novel information theoretic code design approach for cognitive multiple-input multiple-output (MIMO) radars is proposed in the current paper. In the suggested solution, we consider an agile multi-antenna radar with spectral cognition and design optimized transmission codes considering practical limitations such as peak-to-average power ratio (PAR) and spectral coexistence in a spectrally crowded environment. As exact performance expressions for the detector is not analytically tractable in this case, an information theoretic approach is taken into account to design the transmission codes. Simulation results illustrate the efficiency of the proposed method  

    An Ultra Low-power Low-offset Double-tail Comparator

    , Article 17th IEEE International New Circuits and Systems Conference, NEWCAS 2019, 23 June 2019 through 26 June 2019 ; 2019 ; 9781728110318 (ISBN) Khorami, A ; Saeidi, R ; Sharifkhani, M ; Taherinejad, N ; Cadence; FAB - Mixed-Signal Foundry Experts; Infineon ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    In double tail comparators, the pre-amplifier amplifies the input differential voltage and when the output Vcm of the pre-amplifier becomes larger than Vth of the latch input transistors, the latch is activated and finalizes the comparison. As a result, the pre-amplification delay is fixed to a value and cannot be set at the minimum required delay, to save power and improve offset. In fact, when the latch is activated the pre-amplifier output differential voltage is still growing but the latch finishes the comparison before the maximum differential gain is formed and applied to the latch. In this paper, a comparator is proposed in which the preamplifier is turned off when the maximum gain is... 

    A low-power low-offset charge-sharing technique for double-tail comparators

    , Article Microelectronics Journal ; Volume 102 , August , 2020 Khorami, A ; Saeidi, R ; Sachdev, M ; Sharif University of Technology
    Elsevier Ltd  2020
    A charge sharing technique for high-speed double-tail comparators is presented. This technique is applied to the pre-amplifier stage of the dynamic comparators so that the maximum differential gain is applied to the latch during the latching process reducing the input referred offset voltage. In dynamic comparators a large portion of the input referred offset voltage is coming from the latch, and the proposed technique is introduced to alleviate this issue. Monte- Carlo simulations show that the proposed technique reduces the offset voltage from 16 mV to 8 mV. Due to the charge sharing technique, the pre-amplifier draws just enough power for its operation reducing the average power by 40%... 

    Effect of different traffic patterns on power consumption of sleep mode in the IEEE 802.16e MAC

    , Article 2007 IEEE International Conference on Telecommunications and Malaysia International Conference on Communications, ICT-MICC 2007, Penang, 14 May 2007 through 17 May 2007 ; February , 2007 , Pages 649-653 ; 1424410940 (ISBN); 9781424410941 (ISBN) Mohammadpour Nejatian, N ; Nayebi, M. M ; Ashtiani, F ; Sharif University of Technology
    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  

    Metric based symbol predistortion for peak power reduction of space frequency coded OFDM systems

    , Article IEEE Transactions on Consumer Electronics ; Volume 56, Issue 3 , October , 2010 , Pages 1643-1651 ; 00983063 (ISSN) Ferdosizadeh Naeiny, M ; Jafarnia Jahromi, A ; Marvasti, F ; Sharif University of Technology
    In this paper, a metric based symbol predistortion method is introduced for Peak to Average Power Ratio (PAPR) reduction of the Space Frequency Block Coded (SFBC) Orthogonal Frequency Division Multiplexing (OFDM) systems with two transmitter antennas. In the proposed method, a metric is defined which shows the contribution of each frequency domain symbol to the time domain samples with high amplitude at both antennas. Then, the symbols with the highest metric values are chosen and predistorted such that the peak powers are reduced while the SFBC relationship between two antennas holds constant. Three variants of this method will be introduced. Then, this technique is extended to the general... 

    Full diversity space time block codes with improved power distribution characteristics

    , Article Physical Communication ; Volume 39 , 2020 Abbasi, V ; Shayesteh, M. G ; Sharif University of Technology
    Elsevier B.V  2020
    In this paper, we introduce a technique for improving power distribution characteristics of space time block codes (STBCs) which include peak to average power ratio (PAPR), average to minimum power ratio (Ave/min), and probability of transmitting “zero” by antenna. We consider STBCs in multiple input multiple output (MIMO) and multiple input single output (MISO) systems that achieve full diversity for linear or maximum likelihood (ML) receivers. It is proved that by multiplying a specific non-singular square matrix by the code matrix, a new code is obtained that achieves full diversity and the power distribution characteristics are improved. The proposed technique is general can be applied... 

    PAPR Reduction in MIMO-OFDM Systems

    , Ph.D. Dissertation Sharif University of Technology Ferdosizadeh Naeiny, Mahmoud (Author) ; Marvasti, Farrokh (Supervisor)
    In this thesis, some algorithms for PAPR reduction of OFDM systems are investigated and some of these methods are extended to MIMO-OFDM systems. Two types of multiple antenna OFDM systems are considered; OFDM systems with spatial multiplexing for increasing the data rate and OFDM systems with spatial diversity for improvement of the symbol error rate. For the systems of the first type we have proposed two PAPR reduction algorithms. In the first method, the signals of transmitter antennas are clipped and filtered independently. Then, at the receiver side an iterative algorithm is proposed to compensate for the clipping noise. In the second method, we have extended TR method to spatial... 

    PAPR reduction of space-frequency coded OFDM systems using active constellation extension

    , Article AEU - International Journal of Electronics and Communications ; Volume 65, Issue 10 , 2011 , Pages 873-878 ; 14348411 (ISSN) Naeiny, M. F ; Marvasti, F ; Sharif University of Technology
    Active Constellation Extension (ACE) is one of the techniques introduced for Peak to Average Power Ratio (PAPR) reduction of OFDM systems. In this technique, the constellation points are extended such that the PAPR is minimized but the minimum distance of the constellation points does not decrease. In this paper, an iterative ACE method is proposed for the PAPR reduction of OFDM systems with spatial diversity of Space Frequency Block Coding (SFBC). The proposed method is such that the PAPR is reduced simultaneously at all antennas, while the spatial encoding relationship still holds. In this method, at each iteration, the antenna with maximum PAPR is selected and the ACE algorithm is...