Predetermined Null Subspace-Based Channel Estimation on ZP-OFDM and KSP-OFDM
Date Issued
2014
Date
2014
Author(s)
Chang, Yuan-Chi
Abstract
Orthogonal frequency division multiplexing (OFDM) is a popular modulation for broadband wireless digital communication due to the high data rate and robustness against multipath fading channel. Channel estimation plays an important role in OFDM systems because each subcarrier to suffers different attenuation in multipath fading channel. Basically, channel estimation can be divided into three categories, namely, pilot-assisted channel estimation, blind channel estimation, and semi-blind channel estimation. Although pilot-assisted channel estimation is commonly used in practical communication systems, it requires additional pilot symbols to estimate channel state information (CSI) and thus results in a loss in bandwidth efficiency. In order to preserve bandwidth efficiency, blind channel estimation is recently proposed to obtain CSI without any pilot symbol, at the cost of degrading the accuracy of channel estimation estimate quality degradation. While semi-blind channel estimation emerged as a new technique which can allow significant reduction of pilot symbols while offering better performance than blind channel estimation.
In the literature, the existing blind channel estimation estimates the channel impulse response (CIR) by exploiting null subspace of received OFDM blocks which suffers from noise, and results in an unresolvable scalar ambiguity.
In this thesis, a predetermined null subspace-based channel estimation is proposed on ZP-OFDM. Two new methods are proposed on KSP-OFDM, one semi-blind based method with minimum length of known symbols which provides solvable scalar ambiguity, and the other hybrid training based combines conventional optimal training method with predetermined null subspace-based method.
Simulation results show that the proposed inverse channel based channel estimations outperform the conventional channel estimation schemes in medium signal-to-noise power ratio environment.
Subjects
盲通道估測
零填補正交分頻多工
已知符元填補正交分頻多工
預選零子空間
均方差
Type
thesis
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