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Title Semi-Blind Channel Estimation for LTE DownLink
Author Michelusi, Nicolo
Supervisor Winther, Ole (Intelligent Signal Processing, Department of Informatics and Mathematical Modeling, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2009
Abstract In a MIMO system the number of channel parameters is much larger than in a typical SISO scenario, making the channel estimation task particularly critical. In fact, this increase in the number of channel parameters translates into a smaller estimation accuracy, which is counteracted by transmitting a longer pilot sequence. This in turn negatively impacts the bandwidth efficiency of the system, making pilot based approaches less attractive. In this thesis we investigate the Semi-Blind approach to channel estimation in MIMOOFDM systems, and in particular for LTE downlink. This technique, by exploiting the observations associated to the unknown symbols other then the pilot sequence to perform the channel estimate, potentially leads to an improvement in the estimation accuracy compared to the typical pilot based estimation approach, without requiring a long pilot sequence, despite the large number of parameters typical of a MIMO scenario. Through simulations performed on the LTE system we show that the proposed Semi- Blind approaches lead to significant improvements in the estimation accuracy, both from an MSE and BER perspective, compared to the typical pilot based technique. However, exploiting the true discrete distribution of the unknown symbols is computationally demanding, therefore we propose the use of two approximations on the unknown symbols: the Gaussian and the Constant Modulus assumptions. These, though sub-optimal from a point of view of the estimation accuracy, still lead to significant improvements with respect to the pilot based approach, while reducing the computational overhead incurred when using true discrete distribution of the unknown symbols.
Series IMM-M.Sc.-2009-36
Fulltext
Original PDF ep09_36.pdf (1.09 MB)
Admin Creation date: 2009-06-16    Update date: 2010-08-25    Source: dtu    ID: 244829    Original MXD