Performance Limit for Least-Square Based Channel Estimation and Its Extension for Doppler Shift Estimation in OFDM Systems
Date Issued
2006
Date
2006
Author(s)
Huang, Sheng-Yu
DOI
en-US
Abstract
In the coherent detection systems, the knowledge of the channel states is necessary to recover the transmitted information signal. The problem of estimating channel parameters such as relative delay, attenuation and phase has been addressed in the literature. In the realistic channel condition the overlapped multipath components (at most one symbol apart) may happen in many communication environments. In this thesis, we are interested in the problem of solving overlapped multipath components in the closely-spaced multipath scenario because this is one of the most challenging situation in the channel estimation process.
Many channel estimation techniques have been proposed based on least-square criterion or to give the approximate least-square estimates. In the first part of this research, we describe a least-square algorithm to incorporate a prior knowledge of the transmit and receive filters into the channel estimation procedure. It is shown that the composite channel lies on the subspace formed by the impulse responses of the transceiver filters. We will investigate the impact of not modelling the time delays exactly when constructing this hypothesis subspace. Moreover, a lower and an upper bound of mean-square-error (MSE) for least-square based algorithms are derived, which show how the performance depends on the delay hypothesis spacing and oversampling ratio.
The second part of the thesis discusses the problem of inter-carrier interference (ICI) due to Doppler spread channel in orthogonal frequency division multiplexing (OFDM) transmission. The Doppler spread in mobile radio channel distort the orthogonality among subcarriers resulting in ICI, which seriously degrades the performance of systems. It is observed that the Doppler shifts looks like the "delay" in the frequency domain. The least-square technique can be directly extended to estimate Doppler shifts for OFDM systems. We will give a guidance in selecting some implementation parameters such as path hypothesis spacing, oversampling factor and the width of the correlation window for the least-square based channel estimation algorithms.
Subjects
最小平方法
密集間隔多路徑通道
正交頻分多工
都卜勒位移
Least-square
Closely-spaced multipath channel
OFDM
Doppler shift
Type
thesis
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