Co-Channel Interference Suppression for OFDM Systems over Frequency-Selective Fading Channels
Date Issued
2005
Date
2005
Author(s)
Ni, Ching-Sheng
DOI
en-US
Abstract
Inspired by the multiuser detection theory, we exploit the signal structure of the sub-carriers and develop multiuser detectors to suppress co-channel interference (CCI) of
unknown statistics for orthogonal frequency division multiplexing (OFDM) systems by considering each sub-carrier as an individual user and CCI as other unknown users. The
linear minimum mean square error multiuser detectors (LMMSE MUD) of sub-carriers are proposed, which require no a prior information of CCI by using adaptive implementations. With known received waveforms of all sub-carriers, the proposed multistage interference canceller (MIC) based on multistage MUD improves the LMMSE MUD by eliminating the residual interference from other sub-carriers in the soft estimate of
the LMMSE MUD by making use of tentative decisions. With the information of fre-quency location of the partial-band CCI, the LMMSE MUD and the MIC are proposed
in frequency domain to significantly reduce the complexity with similar performance according to the complexity analysis. When the tentative decisions are highly reliable,
further improvements can be achieved by the enhanced multistage interference canceller (EMIC) which replaces the combining at the second stage of the MIC. With the our
developed algorithm, the combining of the EMIC can be correctly generated from those of the LMMSE MUDs of interfered sub-carriers, which shows the EMIC can be realized without a prior information of CCI.
In OFDM systems with mutually un-orthogonal sub-carriers, the complexity to generate the combining of the EMIC is huge even if the CCI is a very narrowband signal.
To reduce the complexity of the EMIC, the generalized multistage interference canceller
(GMIC), an intermediate mode of the MIC and the EMIC, is proposed whose combining only assumes couples of adjacent sub-carriers of the desire sub-carrier are precisely
removed. Due to the high sensitivity of the EMIC to the incorrect tentative decisions, the GMIC even outperforms the EMIC in OFDM systems with mutually un-orthogonal
sub-carriers. The GMIC along with the generalized parameter generation algorithm is proposed to jointly suppress CCI and ICI over time-varying channels.
Subjects
正交分頻多工系統
共通道雜訊
OFDM
Co-Channel Interference
Type
thesis