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ESTIMATION AND IMPROVEMENT OF THE PERFORMANCE OF COMMUNICATION SYSTEMS BASED ON LDPC CODES

Title
ESTIMATION AND IMPROVEMENT OF THE PERFORMANCE OF COMMUNICATION SYSTEMS BASED ON LDPC CODES
Authors
안석기
Date Issued
2013
Publisher
포항공과대학교
Abstract
The objective of this thesis is to estimate and improve the performance of communication systems employing low-density parity-check (LDPC) codes. We firstly propose a hardware-efficient adaptive modulation and coding (AMC) scheme which uses only a single LDPC encoder/decoder with irregular modulation. Two Gray-mapped quadrature-amplitude modulations are employed within a code- word so that the transmission rates of the proposed AMC can be controlled even though the rate of the employed LDPC code is fixed. The rate and degree distribution of the employed LDPC code are selected properly for the proposed scheme. We also optimize the bit-to-symbol mapping for the LDPC code over ir- regular modulation at each transmission rate. The performance of the proposed scheme is compared with that of the AMC scheme with a dedicated LDPC code at each transmission rate. Our second consideration is to estimate the performance of LDPC-coded sys- tems. We propose a novel importance sampling (IS) scheme to estimate the low error-rate performance of LDPC codes over Rayleigh fading channels. The pro- posed scheme exploits the structural weakness of LDPC codes due to trapping sets (TSs). The Rayleigh fading distribution on the bits belonging to a TS is bi- ased by parameter scaling (PS), while the noise distribution on them is biased via mean translation (MT) according to their fading coefficients. The biases in PS and MT are determined so that the variance of the proposed IS estimator is minimized. The proposed IS scheme is compared with the Monte Carlo (MC) simulator and other IS schemes modified from the conventional IS scheme em- ployed for performance estimation of LDPC codes over an AWGN channel. In the last part of this thesis, we propose a novel LDPC-coded frequency- domain equalizer (FDE) for single-carrier block transmission over a doubly- selective channel. The proposed LDPC-coded FDE partitions a received block into multiple subblocks in order to reduce the effect of the time variation of the channel. The nonuniformity in the error statistics of a subblock-based FDE is analyzed, when a one-tap minimum mean-squared error (MMSE) equalizer is employed. The nonuniformity is exploited to remove the drawback of sub- block processing so that the advantage of a subblock-based FDE is maximized. Numerical results show that the proposed FDE has much better performance than other known subblock-based FDEs and has a robust performance over high Doppler environments.
URI
http://postech.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000001627699
http://oasis.postech.ac.kr/handle/2014.oak/2000
Article Type
Thesis
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