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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 41875 (05)
- University: Sharif University of Technology
- Department: Electrical Engineering
- Advisor(s): Marvasti, Farokh
- Abstract:
- In this thesis, we investigate the problem of OFDM channel estimation exploiting channel sparsity. Due to the sparse nature of the scattering objects, most of wireless multipath channel have a sparse impulse response. Therefore it is possible to use the methods in the field of sparse signal processing for the purpose of estimating such channels for better accuracy, and efficient spectrum usage.
First of all the problem of OFDM channel estimation using scattered pilots is stated. Then the so-called IMAT methods together with the other sparse signal processing methods are used for the purpose of estimating channel nonzero taps. Furthermore, since efficient use of spectrum in communication systems is an indispensable concern, we present compressive estimation of OFDM channels using fewer pilots which results in appropriate MSE using fewer number of pilots compared to interpolation based estimation methods. This advantage is much more obvious in the case of channels with large delay spread and short coherence bandwidth. Finally, a new scheme for pilot allocation is proposed. The method is based on minimizing the coherence parameter of DFT sub-matrix associated with the pilot subcarriers. Unlike the usual case of equidistant pilot subcarriers, we show that non-uniform patterns based on cyclic difference sets are optimal. In cases where there are no difference sets, we perform a greedy search method for finding a suboptimal solution - Keywords:
- Sparse Channel Estimation ; Compressive Sensing ; Orthogonal Frequency Division Multiplexing (OFDM) ; Pilot Allocation ; Coherence Parameter ; Interative Algorithm With Adaptive Thresholding (IAAT)
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