• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2006.11a
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• pp.175-177
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• 2006

This letter deals with non-pilot-aided symbol timing estimation methods in an orthogonal frequency division multiplexing (OFDM) system. To do this, OFDM system uses a frequency diversity scheme over two consecutive data symbols. Our approach can be viewed as an expansion of Schmidl's and Minn's correlation methods. Using the OFDM signal equipped with frequency diversity, however, symbol timing is accurately estimated without additional training symbol and a second-order diversity gain is achieved.

• Journal of the Korea Society of Computer and Information
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• v.23 no.7
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• pp.11-17
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• 2018

In this paper, we propose how to improve the lack of diversity in collaborative filtering, using tag scores contained in items rather than ratings of items. Collaborative filtering has excellent performance among recommendation system, but it is evaluated as lacking diversity. In order to solve this problem, this paper proposes a method for supplementing diversity lacking in collaborative filtering by using tags. By using tags that can be used universally without using the characteristics of specific articles in a recommendation system, The proposed method can be used.

• ETRI Journal
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• v.21 no.4
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• pp.29-40
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• 1999

In this paper, we show the robustness of a proposed system using both a frequency diversity and a time diversity effect when the channel assumptions are relaxed such that all sub-bands are not independent fading. We take time-repetition coding with interleaving such that the repetition code symbols are spaced sufficiently far apart to guarantee time diversity. We also incorporate offset multicarriers into a proposed multicarrier DS-CDMA system in a different way compared to that of [10] to reduce the total multiple access interference. When we take a convolutional encoder instead of a time-repetition encoder, and again use both time diversity and frequency offset, then we can obtain the significant performance gain.

• Journal of Advanced Navigation Technology
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• v.15 no.6
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• pp.1053-1058
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• 2011

In this paper, we propose a concatenated single antenna diversity system to assure the data transmission reliability between flight type air nodes which move according to their atypical orbit, then analyze its performance. The proposed system achieve a diversity gain using single antenna and a coding gain from convolutional code simultaneously. Simulation result about the bit error rate(BER) of the proposed system shows that its BER performance is about 9.5dB greater than convolutional code at $10^{-4}$ and about 14dB greater than space time block code at $10^{-3}$ which has a full diversity gain. In addition, compared with space time trellis code with diversity gain and coding gain, the proposed system shows the better 4dB at a BER of $10^{-5}$. Therefore, it is necessary that concatenated single antenna diversity should be adopted to the reliable data transmission of flight type air nodes.

• Journal of electromagnetic engineering and science
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• v.10 no.3
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• pp.99-103
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• 2010

Motivated by recent works on spectrum-sharing systems, this paper investigates the effects of transmit diversity on the peak interference power limited cognitive radio(CR) networks. In particular, we derive the ergodic and outage capacities of a spectrum-sharing system with multiple transmit-antennas. To derive the capacities, peak interference power constraint is imposed to protect the primary receiver. In a CR transmitter and receiver pair with multiple antennas at the transmitter side, the allowable transmit power is distributed over the transmit-antennas to achieve transmit diversity at the receiver. We investigate the effect of this power distribution when a peak interference power constraint is imposed to protect the primary receiver. We show that the transmit diversity does not improve the ergodic capacity compared to the single-antenna system. On the other hand, the transmit diversity significantly improves the outage capacity. For example, two transmit-antennas improve the outage capacity 10 times compared to the single-antenna with a 0 dB interference constraint.

• Asia pacific journal of information systems
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• v.15 no.2
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• pp.149-170
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• 2005

This study assessed diversity in MIS research by examining 357 articles published in Journal of MIS Research from 1991 to 2003. The classification system developed by Vessey et al.(2002) was employed to examine research diversity of the articles. The classification system comprises four key characteristics of diversity such as research topic, research method, level of analysis, and reference discipline. The results of our study were also compared with Vessey et al,(2002)'s results to address problems in current MIS research and to suggest some recommendations for the future MIS research in Korea.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.4
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• pp.200-205
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• 2011

In multipath fading channel, diversity is essential to mitigate the impairments. In this paper, we have proposed the angle diversity scheme called ATTD(Angle Time Transmit Diversity) instead of Alamouti's STTD(Space Time Transmit Diversity) and have analyzed the performance of the proposed scheme when signal powers caused by the transmission to different angles are different. Based on it, we have measured the wireless vector-channel in the urban area, which has lots of high-story buildings, using the data collected from the 8 by 4 smart array antenna system that we made. According to the measured data, the received signals from different angles have different signal powers. Our performance analysis results show that the proposed scheme has better performance than the space diversity scheme when the received path signal power is at least -7dB compare to the strongest path signal power.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.1
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• pp.72-82
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• 2009

In OFDMA systems, cyclic delay diversity can improve the system performance due to diversity effects. However, applying cyclic delay diversity to block-hopping SC-FDMA systems can affect the performance in two contrary ways: positive effect due to increased frequency diversity and negative effect caused by increased frequency selectivity. Hence, the delay value for cyclic delay diversity should be carefully selected to maximize the system performance. This paper discusses these two contrary effects and proposes a method of determining the delay value of cyclic delay diversity for block-hopping SC-FDMA systems.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.175-185
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• 2008

In this paper, we investigate the effect of cooperative and selection relaying schemes on multiuser diversity in downlink cellular systems with fixed relay stations (RSs). Each mobile station (MS) is either directly connected to a base station (BS) and/or connected to a relay station. We first derive closed-form solutions or upper-bound of the ergodic and outage capacities of four different downlink data relaying schemes: A direct scheme, a relay scheme, a selection scheme, and a cooperative scheme. The selection scheme selects the best access link between the BS and an MS. For all schemes, the capacity of the BS-RS link is assumed to be always larger than that of RS-MS link. Half-duplex channel use and repetition based relaying schemes are assumed for relaying operations. We also analyze the system capacity in a multiuser diversity environment in which a maximum signal-to-noise ratio (SNR) scheduler is used at a base station. The result shows that the selection scheme outperforms the other three schemes in terms of link ergodic capacity, link outage capacity, and system ergodic capacity. Furthermore, our results show that cooperative and selection diversity techniques limit the performance gain that could have been achieved by the multiuser diversity technique.

• Journal of electromagnetic engineering and science
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• v.5 no.1
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• pp.1-7
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• 2005

The implementation of a simple analog in-phase combiner is presented for a high capacity radio relay system with space diversity. It provides good performance in terms of simple hardware and easy control, and measured results are in good agreement with simulated ones. To suggest practical applications, signatures with/without diversity are measured for STM-1 signal of 64-QAM radio relay system combined with a 13-tap equalizer, and they provided more than 25 dB fade depth at 10$^{-3}$ BER under the frequency selective fading condition.