• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.10
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• pp.1925-1934
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• 1994

In this paper, it was studied the method of performance improvement of trellis encoded 4-ray continuous phase FSK with nonconstant frequency space when permitted complexity. It was used the nonconstant mapper in order to produce nonconstant frequency, fixed maximum symbol values 3, -3 for comparision in similar bandwidth, changed symbol values 1, -1 from 0.5 to 3.0 as symmetry. Free Euclidean distance evaluation of all encoder/nonconstant mapper combinations, which is the parameter of performance of error probability, was performed with the trellis-based algorithm, we analyzed the characteristics of those.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12A
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• pp.933-940
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• 2009

This paper proposes a robust detection scheme for quasi-orthogonal space-time block code over time-selective fading channels. The proposed detector performs interference cancellation and decision feedback equalization to remove the inter-antenna interference and inter-symbol interference when the channel varies from symbol to symbol. Cholesky factorization is used on the channel Gram matrix after performing interference cancellation to obtain feed forward equalizer and feedback equalizer. It is shown by simulations that the proposed detection scheme outperforms the conventional detection schemes and the exiting detection schemes to time-selectivity.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.3 no.1 s.4
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• pp.117-125
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• 2004

Space-time coding and modulation exploit the presence of multiple transmit antennas to improve performance on multipath Rayleigh fading channels. In this paper, we propose the Trellis-Coded Differential Space Time Modulation-OFDM system with multiple symbol detection. The Trellis-code perform the set partition with unitary group codes. The Viterbi decoder containing new branch metrics is introduced in order to improve the bit error rate (BER) in the differential detection of the Unitary differential space time modulation. Also, we describe the Viterbi algorithm in order to use this branch metrics. Our study shows that such a Viterbi decoder improves BER performance without sacrificing bandwidth and power efficiency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.10
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• pp.1020-1023
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• 2011

In this paper, we present a symbol remapping method of BRGC M-ary QAM signal by using LLR soft bit decision information which is obtained after iterative decoding process. In order to reconstruct estimated transmitted signal constellation, we have to use exponential or hyperbolic tangent(tanh) function resulting in high implementation complexity. The BRGC mapping rule enables us to use a recursive operation. In addtion, we reduce the implementing complexity by using a curve fitting algorithm.

• Journal of Broadcast Engineering
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• v.21 no.4
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• pp.552-561
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• 2016

In OFDM system, frequency-domain sub-carriers of a symbol generally consist of data sub-carriers and scattered pilot sub-carriers and in the receiver, channel is estimated through time-axis interpolating pilot sub-carriers of several OFDM symbols. However, time-axis interpolation fails to keep track of rapid channel variation caused by fast moving receiver. Although symbol by symbol channel estimation without time-axis interpolation enables fast estimation, the performance is severely degraded for a long delay spread channel in a single frequency networks (SFNs) because of insufficient pilot sub-carriers. In this paper, a channel estimation scheme for OFDM receiver in a fast mobile SFN channel is proposed. The proposed scheme is applied to DVB-T receiver to improve the Doppler mobile performance in SFN channel.

• Journal of Broadcast Engineering
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• v.16 no.1
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• pp.85-95
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• 2011

In this paper, we propose an alternative carrier phase independent timing recovery method for VSB receivers. The Gardner algorithm may not estimate a timing offset in VSB systems when the residual carrier phase offset is contained in the signal. We use the conjugate multiplication of received signals for cancelling out the carrier phase offset. Then Gardner algorithm is employed for extracting the spectral line. The proposed method generates a consistent timing error even in the presence of the carrier phase offset.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.283-286
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• 2003

In this paper, we represent an implementation of burst QPSK receiver for underwater acoustic communication. Transmitter sends 5,000 symbols at 25kHz frequency with 200 kHz D/A sampling rate. The received signal is sampled at 100 kHz. Implemented receiver acquires the frame synchronization, coarse symbol timing estimate, and coarse phase offset estimate using 32 symbol length preamble. The estimated phase offset is used to initiate of 2nd order PLL. The transmission experiment results show that PLL is a mandatory to compensate Doppler shift due to the variation of tidal current.

• Proceedings of the Korea Information Processing Society Conference
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• 2005.05a
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• pp.553-556
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• 2005

ANSI C 언어는 UNIX 시스템에서 뿐만 아니라 DOS 환경에서 수행되는 C 컴파일러와 각종 지원 도구가 개발되어 보급됨으로써 오늘날 널리 사용되는 범용 프로그래밍 언어 중 하나이다. EVM(Embedded Virtual Machine)은 ANSI C 언어와 SUN사의 Java 언어 등을 모두 수용할 수 있는 임베디드 시스템을 위한 가상 기계이며, SIL(Standard Intermediate Language)은 EVM에서 실행되는 중간언어로 다양한 프로그래밍 언어를 수용하기 위해서 객체지향 언어와 순차적 언어를 모두 수용하기 위한 연산 코드 집합을 갖고 있다. EVM을 위한 ANSI C 컴파일러는 ANSI C 언어를 받아 들여 EVM의 중간 언어인 SIL 코드를 출력한다. ANSI C 컴파일러에서 어휘 분석과 구문 분석 과정에서 인식되는 명칭에 대해서 그 속성들을 수집하고 이용한다. 이 속성들은 명칭이 명시적으로 혹은 묵시적으로 정의되는 곳에서 심벌 테이블에 수집된다. 본 논문에서는 수집된 정보가 올바르게 되었는지 확인하기 위하여 심벌 테이블에 있는 정보를 다시 ANSI C 언어로 복원시키는 역변역기(detranslator)를 구현하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6A
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• pp.659-665
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• 2008

If ranging processes are not frequent in an uplink OFDMA system, the timing synchronization between base and mobile stations may not be maintained. Especially in the case of infrequent random accesses in a large cell, timing offsets can be considerable and the destroyed orthogonality of OFDMA signals may result in the degraded performance. This paper proposes a novel random access scheme for uplink OFDMA systems, which support the orthogonality of OFDMA signals with timing offsets by allowing a random access OFDMA symbol shorter than a normal one. In order to make uplink OFDMA systems robust to timing offsets, the proposed scheme inserts a zero-padding region in an OFDMA symbol.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.5
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• pp.2347-2352
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• 2012

In this paper, a new alternating equalizer and its differential adjustment algorithm are proposed. The proposed alternating equalizer achieves equalization effectively using an algorithm performing symbol decisions based on soft/hard decision. In addition, it is possible to improve the initial blind convergence speed and steady-state error performance simultaneously by adjusting the equalizer differentially according to the relative reliability of the symbol decisions by soft/hard decision devices. The simulation results on 16/64-QAM constellations under multipath propagation channel and additive noise conditions confirmed to support usefulness of the proposed method.