This Thesis is oriented to the study and proposal of modeling solutions, as well as robust techniques, for low computational complexity channel estimation and prediction for OFDM systems operating over mobile wireless channels. It is also oriented to the development of resource allocation techniques for multiple access systems in this context, which include the typical imperfections of practical implementations of the physical layer in the problem formulation. The main contributions can be grouped as follows.
Parametric and statistical models commonly used for wireless channels are studied, and a novel hybrid modeling technique is developed. This novel technique uses statistical channel information related to the type of mobile applications considered, together with a parametric structure based on the decomposition of the channel trajectory over time into a known orthonormal basis. This channel model allows a simple evaluation of the number of parameters to be estimated, and also allows a trade-off between modeling error and the complexity of the associated structure.
Based on the formulated hybrid channel model, and the distinctive parallelization characteristic of OFDM over a frequency selective fading channel, a time domain recursive channel estimator is developed capable of efficient tracking of the temporal evolution of a flat fading channel. Besides of leading to an estimator robust to the shape of the channel Doppler spectrum, the proposed formulation results in a low computational complexity estimator because direct estimation of the channel Doppler components is avoided, task which involves the use of highly elaborated spectral estimation techniques. Applying analogous concepts to the ones used to model the time variation of the channel, an structure is derived to extend the results to the case of frequency selective fading channels, which inherits the computational efficiency of the flat fading channel estimator as it is based on the same design criteria.
Fair distribution of channel resources on multiuser systems is a natural concern in multicarrier systems, being its implementation critical for the case of mobile channels, where channel state information varies significantly over resource allocation intervals. For this setting, an extension of the proposed estimation scheme is developed for application in the prediction of future channel state information. The developed solution results of lower complexity than similar solutions available in the literature, obtaining a sufficiently large prediction horizon for its application on current resource allocation schemes.
Finally, the performance of the proposed channel estimator/predictor structure is evaluated on a realistic multiuser environment and a characterization technique is proposed for the prediction error associated to practical channel predictors. The inclusion of this characterization in the system resource scheduler formulation, allows a significant improvement on its efficiency as it takes into consideration imperfect channel state information, unavoidable when considering practical implementations.
|Advisor:||Cousseau, Juan E.|
|School:||Universidad Nacional del Sur (Argentina)|
|Source:||DAI-B 72/11, Dissertation Abstracts International|
|Keywords:||Channel estimation, Channel prediction, Mobile radio channels, Multicarriers, OFDM, Resource allocation, Time varying channel, Wireless communications|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be