• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.6
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• pp.465-470
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• 2013

In this paper, we introduce a modulation code design problem where best selection of two-dimensional codewords are determined to reduce two-dimensional (2D) Intersymbol Interference (ISI) and Interpage Interference (IPI), while when these codewords are randomly arranged on the storage, isolated pixel cannot be formed. Codeword selection problem and isolated pixel detection problem are formulated as integer program models and we develop a cutting plane algorithm where a valid cut is generated to remove current feasible solution to avoid isolated pixel by solving the isolated pixel detection subproblem. Using the proposed method, $4{\times}2$ 6/8 codewords with non-isolated pixel are found.

• The KIPS Transactions:PartC
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• v.12C no.2 s.98
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• pp.223-228
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• 2005

The existing mobile communication system called DS/CDMA system, which is serviced widely nowadays, has some problems such as the severe ISI and multiple access interferences under the multi-path fading channel when applied to high-speed data transmission like multimedia transmission. To compensate these problems, we propose a sub-code multi-code hybrid DS/FH (Frequency Hopping) SS (Spread Spectrum) System by combining the multi-code system that restrains the multiple access interference with the hybrid DS/FH SS technique that reduces ISI(Intersymbol Interference) effect for high-speed transmission. Moreover, we implement and propose the sub-code technique to remedy the problems of the generic multi-code system. To verify the performance of the proposed system, the computer simulations are executed under the various channel environments.

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.392-399
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• 2014

The underwater acoustic communication is characterized by doubly spread channels, which are the delay spread due to multiple paths and the doppler spread due to environmental fluctuations or a moving platform. An equalizer is used to remove the inter-symbol interferences that the delay spread causes, but an equalizer doesn't use an acoustic environment such as a multipath. However, a passive time-reversal mirror is simpler than an equalizer because a matched filter is implemented numerically at the receiver structure along with one-way propagation. In this paper, a passive time-reversal mirror is applied to remove interferences due to a multipath in sea-going experimental data in East Sea in Oct. 2010 and improved communication performance is confirmed. The performance is verified by comparing the signal-to-interference plus noise ratio before/after passive time-reversal mirror. It is also performed independently of the passive time-reversal mirror and adaptive equalizer and the bit error rate is compared to verify the performance of underwater acoustic communication.

• The Journal of the Acoustical Society of Korea
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• v.38 no.5
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• pp.587-592
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• 2019

ISI (Inter Symbol Interference) reduces the performance of UAComm (Underwater Acoustic Communication). This paper shows that the performance of UAComm can be improved through the spatiotemporal diversity method that is the combination of spatial diversity and temporal diversity methods. By using spatiotemporal diversity, the array aperture was reduced to increase the efficiency of the UAComm system. It is also verified using the experimental data of BLAC18 (Biomimetic Long range Acoustic Communication 18) conducted in October 2018.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.6
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• pp.11-16
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• 2017

Multi-level holographic data storage requires modulation codes for avoiding two dimensional inter-symbol interference (2D-ISI). Modulation codes can remove the fatal ISI pattern of neighboring the largest and the smallest symbols. In this paper, we propose a 4-level 4/6 modulation code and its trellis encoding for error correction. The proposed 4/6 modulation code prevents that the symbol 0 and 3 are not adjacent in any direction. Also, we compare the proposed modulation code with the same code rate modulation codes for four-level holographic data storage.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.12A
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• pp.1161-1167
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• 2005

In this Paper, a concept of virtual smart antenna (SA) is introduced for orthogonal Sequency division multiplexing (OFDM)-based cellular systems with a frequency reuse factor equal to 1. The OFDM-based cellular system is robust to multipath channels but has a disadvantage that the intercell interference (ICI) caused by adjacent base stations is large at the edge of a cell. In this paper, after deriving the symbol timing offset estimation scheme for the OFDM signal received from multiple base stations in a quasi-static fading channel, the ICI cancellation method based on virtual smart antenna is proposed using the steering vector formed by the symbol timing offset of the desired signal and interference signals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.9
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• pp.739-743
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• 2013

In this paper, a two-dimensional (2-D) channel code for magnetic patterned media is proposed. Patterned media records an information bit on a magnetized dot. Since the space between adjacent tracks is narrow in order to increase the storage density, inter-track interference (ITI) and inter-symbol interference (ISI) can be problems. The amplitude of a bit signal can be corrupted by the 2-D ISI. The signal of the bit surrounded by the same value can be especially destructive, i.e. when its value is the same as the values of the eight surrounding bits. The proposed modulation coding scheme improves the decoding performance of patterned media by preventing this worst case and provides a better code rate than conventional channel codes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.6
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• pp.1323-1329
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• 2014

In this paper, we analyzed efficient decoding scheme with FTN (Faster than Nyquist) method that is transmission method faster than Nyquist theory and increase the throughput. we proposed viterbi equalizer model to minimize ISI (Inter-Symbol Interference) when FTN signal is transmitted. the proposed model utilized interference as branch information. In this paper, to decode FTN singal, we used turbo equalization algorithms that iteratively exchange probabilistic information between soft Viterbi equalizer (BCJR method) and LDPC decoder. By changing the trellis diagram in order to maximize Euclidean distance, we confirmed that performance was improved compared to conventional methods as increasing throughput of FTN signal.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.10
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• pp.569-573
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• 2014

Holographic data storage is a strong contender to become the next-generation data storage method. Its major weaknesses are two-dimensional intersymbol interference between neighboring pixels and interpage interference caused by storing multiple pages in a single volume of hologram. In this paper, we present a trellis encoding scheme of 6/8 balanced modulation code, to address the two weaknesses. The proposed modulation coding scheme captures on characteristics of the balanced code: the scheme relaxes IPI and enables error correction by exploiting the trellis structure. The proposed method showed improved SNR over the conventional 6/8 modulation code.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.9
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• pp.12-17
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• 2016

In the holographic data storage system (HDSS), the data regarding the volume of a storage medium are recorded and read by the page, and the transmission rate and storage capacity can be increased because of two-dimensional, page-oriented data processing; furthermore, the multi-level HDSS can store more than one bit per pixel. For this same reason, however, and unlike conventional data-storage systems, the HDSS is hampered by two-dimensional (2D) intersymbol interference (ISI) and interpage interference (IPI). Progress regarding the published papers on 2D ISI, which is more severe in the multi-level HDSS, continues; however, mitigation of both 2D ISI and IPI in terms of the multi-level HDSS has not yet been studied. In this paper, we therefore propose a 4-level balanced-modulation code that simultaneously mitigates 2D ISI and IPI.