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  4. Adaptive Channel Estimator Design for OFDM-Based Wireless Communication Systems
 
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Adaptive Channel Estimator Design for OFDM-Based Wireless Communication Systems

Date Issued
2012
Date
2012
Author(s)
Huang, Yen-Ming
URI
http://ntur.lib.ntu.edu.tw//handle/246246/252563
Abstract
In the design of OFDM-based wireless communication systems, accurate and robust channel estimation is very critical to ensure reliable data recovery. In this thesis, not only perfect timing synchronization is assumed but also pilot-aided for channel estimation is adopted. The objective is to develop an adaptive channel estimator in light of practical concerns according to wireless channel characteristics. Because the channel frequency response (CFR) on data subcarriers can be estimated via the interpolation between two adjacent pilots, we attempt to find the appropriate linear interpolation criteria with no prior channel statistic information on the grounds that the multipath propagation delay and the Doppler shift are taken into consideration. There is one thing that is important for DFT-based interpolation in frequency domain. The utilization of virtual subcarriers is provided as guard bands, but which results in the performance degradation of channel estimation for band edge spectrum. The clarification of this phenomenon is completely given in this thesis. Furthermore, compared with many proposed methods of time domain processing based on the information of channel delay length, the proper threshold selection according to the known noise power is more rational. In this study, inspired from the statistical characteristics of Gaussian noise, two schemes of threshold selection have been proposed. The use of two well-known methods of repetition and linear fashion under different channel delay spreads for edge effect mitigation has also been demonstrated. Turning to the aspect of time domain interpolation, the reasonable assumptions of time-varying channel are correctly clarified. Thus, in spite of the high-speed conditions which act on the Rician fading channel, the restriction of linear interpolation is remarkably loosened by the techniques of carrier frequency offset (CFO) compensation. For the sake of enlarging the usability of linear interpolation, two techniques of Moving Average and DFT-based transition for noise reduction on pilots have been proposed. The strategies for large delay spread channel and fast fading channel are also presented. To confirm the practicability proposed in this thesis in realistic environments, the simulation parameters will follow the specification of LTE. As a result, the power and the latency of computation can be saved effectively with this adaptive channel estimator algorithm design based on channel understanding.
Subjects
OFDM
Channel Estimation
Synchronization
Linear Interpolation
DFT-Based Interpolation
Wireless Channel
Multipath Propagation Delay
Edge Effect
Doppler Shift
Carrier Frequency Offset (CFO)
Long Term Evolution (LTE)
Type
thesis
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ntu-101-R99942136-1.pdf

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