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Clipping noise cancellation in OFDM systems using oversampled signal reconstruction
, Article IEEE Communications Letters ; Volume 6, Issue 2 , 2002 , Pages 73-75 ; 10897798 (ISSN) ; Sharif, M ; Marvasti, F ; Sharif University of Technology
2002
Abstract
Clipping the OFDM signals in the digital part of the transmitter is one of the simplest methods to reduce the peak factor. However, it suffers from additional clipping distortion, peak regrowth after digital to analog conversion, and out-of-band radiation in the case of oversampled sequence clipping. In this letter, we use oversampled sequence clipping to combat the effect of peak regrowth and propose a method to reconstruct the clipped samples and mitigate the clipping distortion in the presence of channel noise at the expense of bandwidth expansion. We show through extensive simulations that by slightly increasing the bandwidth of the system, we can significantly improve the performance...
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) ; Gharavi Alkhansari, M ; Hossein Khalaj, B ; Sharif University of Technology
2003
Abstract
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...
Analysis of C-2C DAC Mismatch Effects in SAR ADCs
, M.Sc. Thesis Sharif University of Technology ; Sharif Khani, Mohammad (Supervisor)
Abstract
Analog to digital converters is one of the main building blocks of today's circuits. These circuits play an important role in signal processing. Since these circuits consist of analog and digital sections, a large percentage of the power consumed in a circuit is allocated to this section. Therefore, in applications such as medical devices, wearable applications and wireless technology where power control is very important and necessary, reducing the power of analog to digital converters is very important. One of the simplest analog-to-digital converters from the design point of view is Successive Approximation Register (SAR) analog-to-digital converters. This type of analog-to-digital...
A novel BEM- based channel estimation algorithm for time variant uplink OFDMA system
, Article International Conference on Advanced Communication Technology, ICACT, 7 February 2010 through 10 February 2010 ; Volume 2 , Feb , 2010 , Pages 1289-1293 ; 17389445 (ISSN) ; 9788955191455 (ISBN) ; Tabatabavakili, V ; Samsami Khodadad, F ; Hosseinnezhad, M ; Safaei, A ; Sharif University of Technology
2010
Abstract
IN this paper the effect of different channel estimation approaches in OFDMA uplink system which are based on Basis Expansion Model (BEM) and widely used to consider time varying channels are discussed. It has been shown in previous works that modeling error will be reduced by applying oversampled BEM with cost of increasing sensitivity to noise. This problem will be solved by combining oversampled BEM and MMSE channel estimator with cost of increasing computational complexity. In this paper a novel channel estimation approach is represented in which by combining oversampled BEM and low rank MMSE in frequency domain, almost the same performance as the full rank MMSE has been achieved while...