• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.6
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• pp.545-555
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• 2020

This paper presented efficient transceiver structure using sub-band processing for underwater communication in terms of covertness and performance improvement. In aspect of covertness, encrypted coded-bits are divided into groups, and center frequency and sub band are determined by coded-bits of each group. Therefore, as center frequencies are changed randomly, it maintain the covertness effectively. In aspect of performance improvement, the performance of underwater communication mainly depends on multi-path propagation characteristics, Doppler-spread, and frame synchronization. Accordingly, in order to overcome these effects, non-coherent energy detector and turbo equalization method are employed in receiver side. Furthermore, optimal frame synchronization was proposed. Through the simulation and lake experiment, performance analysis was conducted. Especially in the lake experiment, as a result of applying optimal frame synchronization method to receiver structure, errors are corrected in most frames.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.8
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• pp.768-775
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• 2011

Since error compensation schemes guaranteeing high reliability are required in wireless communication systems for the transmission of the large amount of data, as an efficient error compensation scheme the turbo HARQ scheme combining automatic repeat request and turbo coding has been studied in many places in the literature. In the case of conventional turbo HARQ schemes, the transmitter recognizing NAK signals repetitively sends the whole unit packet to the receiver although the received packet can be partially correctable. Through two successive processes, selection of uncorrectable error data and retransmission of only the relevant parts of the information data, transmission efficiency can be improved. In this paper, we present an error data selection criterion for retransmission using the sign transitions of A Posteriori values and propose a tubo HARQ scheme based on the partial retransmission technique. Through a computer simulation, we show and analyze the performance of the proposed scheme with transmission efficiency.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.11
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• pp.26-32
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• 2014

Single-Carrier Frequency division multiplexing (SC-FDM) has been selected for the uplink transmission technique in 3GPP-LTE since it has an advantage of low peak-to-average power ratio (PAPR) in user's perspective. The receiver typically uses a frequency domain equalizer, which, however, suffers from noise boost and/or residual ISI especially when the channel has deep nulls. In this paper, we propose using turbo equalizer to mitigate such a problem. We provide link level performance comparison and an insight into how many iteration is needed for reasonable performance and complexity.

• Journal of Communications and Networks
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• v.6 no.1
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• pp.9-18
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• 2004

Self-encoded multiple access (SEMA) is a unique realization of random spread spectrum. As the term implies, the spreading code is obtained from the random digital information source instead of the traditional pseudo noise (PN) code generators. The time-varying random codes can provide additional security in wireless communications. Multi-rate transmissions or multi-level grade of services are also easily implementable in SEMA. In this paper, we analyze the performance of SEMA in additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. Differential encoding eliminates the BER effect of error propagations due to receiver detection errors. The performance of SEMA approaches the random spread spectrum discussed in literature at high signal to noise ratios. For performance improvement, we employ multiuser detection and Turbo coding. We consider a downlink synchronous system such as base station to mobile communication though the analysis can be extended to uplink communications.

• Journal of Communications and Networks
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• v.9 no.2
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• pp.150-158
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• 2007

We consider channel-coded multi-input multi-output (MIMO) orthogonal frequency-division multiplexing (OFDM) transmission and obtain a condition on its signal for it to attain the maximum diversity and coding gain. As this condition may not be realizable, we propose a suboptimal design that employs an orthogonal transform and a space-frequency interleaver between the channel coder and the multi-antenna OFDM transmitter. We propose a corresponding receiving method based on block turbo equalization. Attention is paid to some detailed design of the transmitter and the receiver to curtail the computational complexity and yet deliver good performance. Simulation results demonstrate that the proposed transmission technique can outperform the conventional coded MIMO OFDM and the MIMO block single-carrier transmission with cyclic prefixing.

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.423-426
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• 2005

In this paper, we propose a receiver that combines a channel detector with a channel decoder to retrieve information from ISI and AWGN in an iteratively manner. The receiver, evolving from a system of a PRML detector and a RS decoder, consists of a SOVA detector followed by a LDPC decoder and has them exchange information iteratively. Rather than handling extrinsic reliabilities explicitly as in Turbo equalization, we take hard-decision values from the LDPC decoder and mix them with the channel output in a certain ratio as input for SOVA. The scheme, simply modified to the one-way structure of a SOVA and a LDPC decoder, shows improved performance with iteration numbers as well as the combining ratio of the channel output and the feedback output. We additionally analyze the receiver with a simple theoretical model and present some valuable properties.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.7A
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• pp.994-1004
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• 2000

In this paper, bitstreams are composed of using H.263 for a moving picture coding in the band-limited and error-prone environment such as wireless environment. EREC sub-frames are implemented by applying the proposed EREC algorithm in order to be UEP for the real data parts of implemented bitstreams. Because those are able to do resynchronization with a block unit, propagation of the error can be minimized, and the position of the important bits such as INTRADC and MVD can be known. Class is separated using the position of these important bits, and variable puncturing tables are designed by the class informations and the code rates of turbo codes are differently designed in according to the class. Channel coding used the turbo codes, and an interleaver to be designed in the turbo codes does not eliminate redundancy bits of the important bits in applying variable code rates of EREC sub-frames unit and is always the same at the transmitter and the receiver although being variable frame size. As a result of simulation, UEP with the code rate similar to EEP is obtained a improved result in the side of bit error probability. And the result of applying it to image knows that the subjective and objective quality have been improved by the protection of important bits.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.5
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• pp.344-352
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• 2020

Covertness and performance are very important design goals in the underwater communications. To satisfy both of them, we proposed efficient underwater communication model which combined multiband and direct sequence spread spectrum method in order to improve performance and covertness simultaneously. Turbo coding method with 1/3 coding rates is used for channel coding algorithm, and turbo equalization method which iterately exchange probabilistic information between equalizer and decoder is used for receiver side. After optimal threshold value was set in Rake processing, this paper analyzed the performance by varying the number of chips were 8, 16, 32 and the number of bands were from 1 to 4. Through the simulation results, we confirmed that the performance improvement was obtained by increasing the number of bands and chips. 2~3 dB of performance gain was obtained when the number of chips were increased in same number of bands.

• ETRI Journal
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• v.31 no.6
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• pp.795-802
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• 2009

This paper presents the design of an advanced terrestrial digital multimedia broadcasting (AT-DMB) baseband receiver SoC. The AT-DMB baseband is incorporated into a hierarchical modulation scheme consisting of high priority (HP) and low priority (LP) stream decoders. The advantages of the hierarchical modulation scheme are backward compatibility and an enhanced data rate. The structure of the HP stream is the same as that of the conventional T-DMB system; therefore, a conventional T-DMB service is possible by decoding multimedia data in an HP stream. An enhanced data rate can be achieved by using both HP and LP streams. In this paper, we also discuss a time deinterleaver that can deinterleave data for a time duration of 384 ms or 768 ms. The interleaving time duration is chosen using the LP symbol mapping scheme. Furthermore, instead of a Viterbi decoder, a turbo decoder is adopted as an inner error correction system to mitigate the performance degradation due to a smaller symbol distance in a hierarchically modulated LP symbol. The AT-DMB baseband receiver SoC is fabricated using 0.13 ${\mu}m$ technology and shows successful operation with a 50 mW power dissipation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.7
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• pp.1531-1538
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• 2015

In this paper, we proposed receiver structure based on an iterative turbo equalization to cope with phase difference between two sensors in MIMO underwater communication channel. In a space-time coded system, it is often assumed that there are no phase errors among the multiple transmitter and receiver chains. In this paper, we have studied the effect of the phase errors between different transmit sensors and different propagation paths in the environment of MIMO underwater communication system, and have shown through BER performance by computer simulations that the bit-error-rate performance can be severely degraded. A decision-directed estimation and compensation algorithm has been proposed to minimize their effects on the system performance. In this paper, we investigate the phase differences and their effects on multiple-input and multiple-output systems, and propose a compensation algorithm for underwater channel model to minimize their effects.