• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.8
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• pp.86-94
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• 2009

An idea to improve the performance of error correction with the amplification of input symbol errors is proposed to ease the mismatching problem which occurs in the hardware implementation of the differential analog PRML decoder. The differential analog PRML decoder is the decoder with two blocks of trellis diagram one of which is without branches of "0" and the other one is without the branches of "1". Decoding is performed by comparing the outputs of two blocks. The decoding error is likely to occur when the difference of two outputs is very small and the hardware implementation is not precise due to mismatching. The proposed idea is to increase the discrimination margin for the output "0" and "1" by amplifying the symbol error while the larger path metrics are saturated. To show the performance improvement of decoding with the proposed idea, simulation results are included

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2000.08a
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• pp.77-80
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• 2000

본 논문은 IEEE 802.11a에 의해 규정되어진 데이터 율 12Mbps, 부호화 율 1/2, 구속장이 7인 무선LAN용 비터비 디코더를 설계하고 구현한다. 구현에 앞서 각 구속장에 따른 전달함수를 구하여 각 구속장 별 first event 에러 확률과 비트 에러 확률을 구한다. 4bit연성판정을 위해 입력 심볼을 16단계로 양자화 하였으며 역 추적을 위한 방식으로 메모리를 사용하는 대신 새로운 알고리듬을 적용한 레지스터 교환방식을 사용함으로써 majority voting을 가능하도록 하였다 고속의 데이터를 처리하기 위해 병렬구조를 갖는 설계를 FPGA 칩을 사용하여 구현하였고 AWGN 환경 하에서 성능검증을 하였다.

• The Journal of the Acoustical Society of Korea
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• v.24 no.7
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• pp.410-415
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• 2005

Recently, most of the speaker verification systems are based on the pattern recognition approach method. And performance of the pattern-classifier depends on how to classify a variety of speakers' feature parameters. In order to classify feature parameters efficiently and effectively, it is of great importance to enlarge variations between speakers and effectively measure distances between feature parameters. Therefore, this paper would suggest the positively mixed model scheme that can enlarge inter-speaker variation by searching the individual model with world model at the same time. During decision procedure, we can maximize inter-speaker variation by using the proposed mixed model scheme. We also make use of a symbol probability weighting function in this system so as to reduce vector quantization errors by measuring symbol probability derived from the distance rate of between the world codebook and individual codebook. As the result of our experiment using this method, we could halve the Detection Cost Function (DCF) of the system from $2.37\%\;to\;1.16\%$.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.39 no.1
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• pp.66-75
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• 2002

For the theoretical performance analysis of Viterbi Decoder for wireless LAN with data rate 12Mbps, code rate 1/2 and constraint length 7 defined in IEEE 802.11a, the transfer function is derived using Cramer's rule and the first-event error probability and bit error probability is derived under the AWGN. In the design process, input symbol is quantized into 16 steps for 4 bit soft decision and register exchange method instead of memory method is proposed for trace back, which enables the majority at the final decision stage. In the implementation, the Viterbi decoder based on parallel architecture with pipelined scheme for processing 12Mbps high speed data rate and AWGN generator are implemented using FPGA chips. And then its performance is verified in real time.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.12
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• pp.2153-2158
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• 2008

XML is one of standard web languages. XML has a syntax architecture consisted of tags, which are used to descript contents and structures of a XML document. In XML documents, missing of markup tag is one of common factors generating incomplete inputs. Usually, editors will recognize incomplete inputs as syntax errors. And so, when editors find them, they will highlight lines in which syntax errors happened, and execute appropriate error handling routines. But, there are no more parsing actions. In this paper, we propose a method to recognize incomplete input strings and keep parsing phases going. To recognize pars missed grammatically in incomplete inputs and create them newly, we use an expanding parsing table. It includes additional parsing actions for newly generated input symbols. Through the information, incomplete inputs will be completed and parsing steps will be finished successively. Therefore, users can be assured that they make always correct XML documents, even if inputs are incomplete, and can not be nervous about input faults.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.7A
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• pp.529-536
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• 2003

In this Paper, a new DCT HLMS DFE(Discrete Cosine Transform Hierarchical Least Mean Square Decision Feedback Equalizer) algorithm is proposed to improve the convergence speed and MSE(Mean Square Error) performance of a receive channel equalizer in ATSC(Advanced Television System Committee) 8VSB(Vestigial Side Band) digital terrestrial TV system. The proposed algorithm reduces the eigenvalue range of input data autocorrelation by transforming LMS (Least Mean Square) DFE into the subfilter of hierarchical structure. Moreover, the use of DCT and power estimation algorithm makes it possible to reduce the eigenvalue deviation of input data which results from distortion and delay of the receive signal in the miulti-path environment. Simulation results show that proposed DCT HLMS DFE has SNR improvement of approximately 3.8dB, 5dB and 2dB as compared to LMS DFE when the equalized symbol error rate is 0.2 in ATTC defined digital terrestrial TV broadcasting channels A, B and F, respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.3 s.345
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• pp.59-67
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• 2006

OFDM (Orthogonal frequency Division Multiplexing) systems convert serial data stream to N parallel data streams and modulate them to N orthogonal subcarriers. Thus spectrum utilization efficiency of the OFDM systems are high and high-speed data transmission is possible. However, with the OFDM systems using the same modulation method at all subcarriers, the error probability is dominated by the subcarriers which experience deep fades. Therefore, in order to enhance the performance of the system adaptive modulation is required, with which the modulation methods of the subcarriers are determined according to the estimated SNRs. The IEEE 802.11a system selects various transmission speed between 6 and 54 Mbps according to the modulation mode. There are three typical methods for SNR estimation: Direct estimation method uses the frequency domain symbols to estimate SNR directly by minimizing MSE (Mean Square Error), EVM method utilizes the distance between the demodulated constellation points and received complex values, and the method utilizing the Viterbi algorithm uses the cumulative minimum distance in decoding process to estimate the SNR indirectly. Through comparison analyses of three methods we propose a new SNR estimation method, which employs both the EVM method and the Viterbi algorithm. Finally, we perform extensive computer simulations to confirm the performance improvement of the proposed adaptive OFDM systems on the basis of IEEE 802.11a.