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A novel preamble-based frame timing estimator for OFDM systems
, Article IEEE Communications Letters ; Volume 16, Issue 7 , 2012 , Pages 1121-1124 ; 10897798 (ISSN) ; Shayesteh, M. G ; Sharif University of Technology
2012
Abstract
This study presents a novel method for frame timing estimation in OFDM systems. The new method is based on the generation and utilization of a new sequence from the two available preambles in the practical OFDM systems (such as WiMAX and WLAN) for correlation, and is capable of having an extended correlation length. The superior performance of the new method is demonstrated in terms of mean square error (MSE) in comparison with the previous methods
Iterative reconstruction-based method for clipping noise suppression in OFDM systems
, Article IEE Proceedings: Communications ; Volume 152, Issue 4 , 2005 , Pages 452-456 ; 13502425 (ISSN) ; Azmi, P ; Sharif University of Technology
2005
Abstract
An iterative reconstruction-based method for suppression of clipping distortion in OFDM systems is proposed. Analysing the performance of the proposed method in Rician fading channels shows that it outperforms similar techniques, i.e. DFT-based reconstruction and iterative cancellation methods, on both BER performance and computational complexity. © IEE, 2005
An optimum pre-filter for ICA based multi-input multi-output OFDM system
, Article International Journal of Innovative Computing, Information and Control ; Volume 7, Issue 6 , June , 2011 , Pages 3499-3508 ; 13494198 (ISSN) ; Asharif, M. R ; Khosravi, M ; Yamashita, K ; Sharif University of Technology
Abstract
This paper presents an optimum pre-filter for ICA based multi-input multi-output OFDM system. In our former work, we presented a pre-filter solution for multiuser reconstruction in ICA based MIMO-OFDM systems [1,2]. Here, based on the structure of the system and former pre-filter solution, an optimization problem has been designed to give us the optimum pre-filter. The designed problem is based on minimization of the estimation error of ambiguities inherent to ICA in reconstruction of the data after separation. The optimization problem is mathematically solved and a set of optimized coefficients are obtained. Among the obtained set as optimum coefficients, optimum coefficients are acquired...
An optimum pre-filter for ICA based mulit-input multi-output OFDM system
, Article ICETC 2010 - 2nd International Conference on Education Technology and Computer, 22 June 2010 through 24 June 2010 ; Volume 5 , 2010 , Pages V5129-V5133 ; 9781424463688 (ISBN) ; Alsharif, M. R ; Khosravi, M ; Yamashita, K ; Sharif University of Technology
Abstract
This paper presents an Optimum pre-filter for ICA based mulit-input multi-output OFDM System. In our former work, we presented a pre-filter solution for multiuser reconstruction in ICA based MIMO-OFDM systems [1], [2]. Here, based on the structure of the system and former prefilter solution, an optimization problem has been designed to give us the optimum pre-filter. The designed problem is based on minimization of the estimation error of ambiguities inherent to ICA in reconstruction of the data after separation. The optimization problem is mathematically solved and a set of optimized coefficients are obtained. Among the obtained set as optimum coefficients, optimum coefficients are acquired...
Sufficient statistics, classification, and a novel approach for frame detection in OFDM systems
, Article IEEE Transactions on Vehicular Technology ; Volume 62, Issue 6 , 2013 , Pages 2481-2495 ; 00189545 (ISSN) ; Shayesteh, M. G ; Sharif University of Technology
2013
Abstract
This paper addresses the problem of frame detection in orthogonal frequency-division multiplexing (OFDM) systems. Using fourth-order statistics, a novel approach is presented for detection of a preamble composed of two identical parts in the time domain. First, it is demonstrated that sufficient statistics for detection of a periodic preamble do not exist, and conventional methods are not optimal. Next, looking at the detection of a preamble from the viewpoints of hypothesis testing and classification, a new method is presented based on the idea that fourth-order statistics can increase class separability (between-class distance) and consequently improve detection performance. It is proven...
Integer frequency offset recovery in OFDM systems
, Article 18th Asia-Pacific Conference on Communications: "Green and Smart Communications for IT Innovation", APCC 2012, Jeju Island, 15 October 2012 through 17 October 2012 ; 2012 , Pages 641-646 ; Shayesteh, M. G ; Sharif University of Technology
2012
Abstract
This paper addresses the estimation of the integer part of the carrier frequency offset (CFO) in orthogonal frequency division multiplexing (OFDM) systems. A novel method is presented based on the maximum likelihood (ML) approach that jointly estimates the channel impulse response (CIR) and the integer CFO. The new scheme estimates the CIR by using pilots and obtains the estimate of the integer CFO by taking advantage of the effect of the CFO on the CIR and data symbols. The performance of the new method is evaluated in Rayleigh fading channels. The results demonstrate that the proposed scheme significantly outperforms the previous methods
Block circular delay diversity space-frequency codes with the enhanced performance
, Article 2012 6th International Symposium on Telecommunications, IST 2012 ; 2012 , Pages 416-419 ; 9781467320733 (ISBN) ; Shahabinejad, M ; Shahabinejad, M ; Talebi, S ; Sharif University of Technology
Abstract
In this paper, by applying a new permutation to the full-diversity block circular delay diversity (BCDD) space-frequency codes (SFCs), we show that their performance could be enhanced. Furthermore, we propose a new method for performing the permutation in the absence of partial channel state information at the transmitter. This new permutation, which is done based on artificial delay and power profiles (ADPPs), could improve the performance of the BCDD SFCs more than 3 dB as simulation results demonstrate
OFDM pilot allocation for sparse channel estimation
, Article Eurasip Journal on Advances in Signal Processing ; Volume 2012, Issue 1 , March , 2012 ; 16876172 (ISSN) ; Amini, A ; Marvasti, F ; Sharif University of Technology
2012
Abstract
In communication systems, efficient use of the spectrum is an indispensable concern. Recently the use of compressed sensing for the purpose of estimating orthogonal frequency division multiplexing (OFDM) sparse multipath channels has been proposed to decrease the transmitted overhead in form of the pilot subcarriers which are essential for channel estimation. In this article, we investigate the problem of deterministic pilot allocation in OFDM systems. The method is based on minimizing the coherence of the submatrix of the unitary discrete fourier transform (DFT) matrix associated with the pilot subcarriers. Unlike the usual case of equidistant pilot subcarriers, we show that non-uniform...
A new timing synchronization approach for OFDM systems
, Article International Congress on Ultra Modern Telecommunications and Control Systems and Workshops, 5 October 2011 through 7 October 2011, Budapest ; 2011 ; 21570221 (ISSN) ; 9781457706820 (ISBN) ; Shayesteh, M. G ; Sharif University of Technology
Abstract
In this paper, we propose a novel timing synchronization method for Orthogonal Frequency Division Multiplexing (OFDM) systems. The new method takes advantage of symmetrical correlation between some parts of the transmitted training symbol and produces an impulse-like timing metric. While reducing the complexity, our method provides an easy and efficient way for timing estimation. The proposed method does not need any differential cross-correlation or frequency correction to produce an impulse-like timing metric. It is shown that the new timing metric outperforms the previously presented methods in fading channels
An improved timing estimation method for OFDM systems
, Article IEEE Transactions on Consumer Electronics ; Volume 56, Issue 4 , 2010 , Pages 2098-2105 ; 00983063 (ISSN) ; Shayesteh, M. G ; Manaffar, M ; Sharif University of Technology
2010
Abstract
In this paper, we propose an improved timing estimation method for orthogonal frequency division multiplexing (OFDM) systems. The proposed preamble-aided method is independent of the preamble structure and is based on taking advantage of the whole products available from a given preamble for its correlation. Capable of having an extended correlation length far beyond those used by the previous methods, the proposed scheme presents an estimator with a remarkable performance in severe noise conditions. Further, we introduce a reduced complexity estimator along with the complexity assessments. We finally evaluate the performance of the proposed method in terms of mean square error (MSE). The...
Mathematical modeling of nonlinearity impairments in optical OFDM communication systems using multiple optical phase conjugate
, Article 2013 Iran Workshop on Communication and Information Theory ; 2013 ; 9781467350235 (ISBN) ; Beyranvand, H ; Salehi, J. A ; Sharif University of Technology
2013
Abstract
In this paper, we present a mathematical model for the idea of using more than one optical phase conjugate (OPC) module for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems in long-haul fiber optic channels. The four-wave mixing (FWM) formulation is derived for three different scenarios in which different numbers of OPC modules are used. The simulation results reveal that using more than one OPC modules leads to a much better BER performance operating on a typical OFDM system
A proposed equivalent channel power delay profile for a millimeter wave wireless OFDM system and optimum guard interval evaluation in a built-up area propagation scenario
, Article Wireless Personal Communications ; Volume 69, Issue 4 , 2013 , Pages 1223-1239 ; 09296212 (ISSN) ; Farzaneh, F ; Sharif University of Technology
2013
Abstract
Vertical plane launching ray tracing method has been applied for a real urban scenario and the delay characteristics of received signals in the overall coverage area have been extracted. Using these parameters, an equivalent channel power delay profile (ECPDP) has been introduced for the overall coverage area. For a millimeter wave wireless OFDM system, the optimum guard interval length which maximizes the mean of signal to interference and noise ratio has been simulated. Also, using the proposed ECPDP, the optimum guard interval length has been analytically extracted and compared with the simulated one
SINR analysis of time and frequency offsets in OFDM systems
, Article Proceedings - Conference on Local Computer Networks, LCN, 4 October 2011 through 7 October 2011 ; October , 2011 , Pages 855-859 ; 9781612849287 (ISBN) ; Khalaj, B. H ; Sharif University of Technology
2011
Abstract
In this paper, the impact of both time offsets (TOs) and carrier frequency offsets (CFOs) on the average output signal-to-interference-plus-noise ratio (SINR) in a frequency selective channel is investigated with a novel approach. First, TOs are partitioned into five cases based on how they occur. Then the mathematical models for different cases are derived. Considering CFOs and benefiting from the obtained models, closed-form expression for the SINR in each case is derived. It is proved that, SINR is independent of the observed subcarrier for the given TO and CFO. Besides, it is shown that the performance of the affected system deteriorates rapidly as the number of subcarriers increases. It...
Robust timing and frequency synchronization for OFDM systems
, Article IEEE Transactions on Vehicular Technology ; Volume 60, Issue 8 , Oct , 2011 , Pages 3646-3656 ; 00189545 (ISSN) ; Shayesteh, M. G ; Sharif University of Technology
2011
Abstract
This paper deals with timing and frequency synchronization in orthogonal frequency-division multiplexing (OFDM) systems. A robust multistage scheme that works in the time domain, independent of the preamble structure, is proposed. After coarse-timing estimation, joint timing and integer frequency synchronization is performed. Then, fractional frequency correction is carried out, and finally, fine-timing estimation completes the synchronization process. The new timing estimation method is flexible and can be adjusted according to the degree of channel distortion. Furthermore, frequency synchronization is efficiently accomplished with an estimation range that is as large as the bandwidth of...
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) ; Marvasti, F ; Sharif University of Technology
Abstract
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...
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) ; Salehinejad, H ; Talebi, S ; Sharif University of Technology
2011
Abstract
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