• Journal of Korea Multimedia Society
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• v.11 no.12
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• pp.1697-1705
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• 2008

Several studies made for wireless mesh networks aim to optimize the capacity for wireless networks. Aside from protocol improvements, researches were also done on the physical layer particularly on modulation techniques and antenna efficiency schemes. This paper is concerned with the capacity improvements derived from using spatial diversity with smart adaptive array antennas. The use of spatial diversity, which has been widely proposed for use in cellular networks in order to lessen frequency re-use, can be used in mesh networks both to minimize co-channel interference (CCI) and enable multiple transmissions. This paper aims to study the capacity region and bounds in using smart antennas for single-channel multi-radio systems in relation to the number of spatial diversity or sectors as defined by the beam angle $\beta$.

• Journal of Ecology and Environment
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• v.42 no.3
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• pp.111-119
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• 2018

Background: Juniperus chinensis L. populations are distributed locally on several areas including coastal cliffs which are difficult to access in the central eastern Korea. Wild populations inhabit relatively barren environments such as rocky areas and cliffs, which are very sensitive to even minor environmental disturbances including artificial interventions and natural disturbances, and thus demonstrate great fluctuations in the population size and density. This study aims to analyze the genetic diversity, differentiation, and genetic structure of each population in order to provide useful data required to establish a substantial conservation strategy of J. chinensis. Results: The genetic diversity of J. chinensis at the population level (P = 78.7%, h = 0.282, S.I. = 0.420) was somewhat higher compared with those measured in the same genus, Juniperus. The genetic differentiation degree among nine populations established naturally in central eastern Korea was 11.50% and that among sub-populations within the same area was 5.52%. On the other hand, genetic variation of individuals within the populations was 82.93%. But frequency of the main allele was different among loci. In particular, fixation of allele frequency and occurrence of rare allele in the highly isolated population suggest a likelihood that genetic drift would occur in populations of this plant. As the result of analysis on the genetic structure of nine populations, nearby populations and isolated populations tended to form separate clusters from each other as the hypothetical number of clusters (K) increase. Conclusions: This result implies that if the population size of J. chinensis is reduced due to environmental change and artificial and/or natural disturbances in the future, it could affect negatively on the genetic diversity of the plant species. In order to maintain and conserve genetic diversity of J. chinensis, ecological network, which can help genetic exchange among the local populations, should be prepared, and conservation strategies in situ as well as ex situ are also required with continuous monitoring.

• Korean Journal of Community Nutrition
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• v.12 no.5
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• pp.583-591
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• 2007

The purpose of this study was to assess the diet diversity, food habit and nutrient intake of obese adults who were visiting the health promotion center. This study was accomplished with the 138 obese adults (men = 103, women= 35) aged over 20 years old whose BMI were above $25 kg/m^2$. Nutrient adequacy ratio (NAR), the number of foods (Dietary Variety Score DVS), and food group consumed (Dietary Diversity Score, DDS) by using the data from the three days record were analyzed and the food habit and lifestyle were assessed by self reporting questionnaire. The average enemy intake of men was 2150.2 kcal which was significantly higher than that of women (p < 0.05). The intake ratio of carbohydrate, protein and fat over total energy was 54.8% : 19.3% : 25.8% in men, 59.5% : 17.8% : 22.6% in women respectively. Frequency of the breakfast in a week above 4, $2{\sim}3$ time and under one time was 75.7% 10.7% and 9.7% in men 77.1%, 5.7% and 14.3% in women respectively. frequency of eating between meals in a day under one time was 73.8% in men, 57.1% in women (p < 0.05). The average DDS and DVS was $3.63{\pm}0.07$ and $14.10 {\pm}3.45$, respectively which was significantly correlated with MAR (r=0.40 in DDS, r=0.64 in DVS, p < 0.01). The most frequent style of food pattern was DMGFV = 01101 in 35% of men, and DMGFV= 01111 in 37.1% of women. Our results show that dietary diversity and variety are useful parameters far evaluating nutrient intakes in obese adults. These findings suggest that nutritional education based on obese persons' eating behavior and eating diversity may be required to increase educational efficiency of weight control programs.

• The Journal of the Acoustical Society of Korea
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• v.36 no.1
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• pp.39-48
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• 2017

CDMA (Code Division Multiple Access) is promising medium access control schemes for underwater acoustic sensor networks because of its robustness against frequency-selective fading and high frequency-reuse efficiency. In this paper, we design diversity schemes of underwater CDMA transceiver for the forward and reverse links. User data are multiplexed by Walsh code and a pseudo random noise code acquisition process is added for phase error correction before decoding the user data at the receiver. Then, the diversity reception using equal gain combining and maximal ratio combining is performed in order to minimize performance degradation caused by rich multipath fading of underwater acoustic channel. We evaluated the performance of diversity transceiver through lake experiment, which was performed at Lake Kyungcheon, Mungyeong city using two transmitters and two receivers placed 460 m apart at an average depth of 40 m. The lake experiment results show that user data are recovered with error-free in both of the forward and reverse links.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.8 no.4
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• pp.420-425
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• 2003

Species composition, community structure and biodiversity of marine benthic community were studied in the intertidal zone of Seoam, Busan. A total of 75 species of benthic marine plants including 4 Cyanophyta, 6 Chlorophyta, 17 Phaeophyta, 47 Rhodophyta and 1 Magnoliophyta are listed. The dominant marine plants were melobesioidean algae, Chondracanthus tenellus, Sargasium thunbergii, Corallina spp., and Phyllospadix japonica and Ulva pertusa was added in summer. Chthamalus challengeri and Mytilus edulis were dominant zoobenthic species in the upper and middle intertidal zone. The algal species diversity index based on coverage was 1.81; 2.25 from frequency; 2.19 from average of total frequency and coverage, and 1.80 from importance value. The algal diversity indices estimated from different sources were quite different. This means that the index value changes depending on the sources used to calculate the species diversity index, indicating how important it is to select the based data and that it is necessary to standardize the methodology when studying later the algal diversity index. On the other hand, the number of species identified in this study has been found to be reduced by 65% at highest, compared with the result of the investigation that was conducted in the coast of Busan.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.7 s.110
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• pp.629-637
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• 2006

It is important to design the high-speed communication system in the hostile channel. Due to the frequency diversity, FD-OFDM that can be used for the high-speed communication is more robust to the noise or interference than ordinary OFDM. However, even the FD-OFDM becomes degraded in th ε strong narrow band interference channel. In this paper, we propose an AFD-OFDM system and analyze the communication performances in order to find out the more robust communication system in the hostile channel. So, the AFD-OFDM system can cover the drawback of the FD-OFDM and improve the BER performance than FD-OFDM. From the simulation results, FD-OFDM shows better performance than the ordinary OFDM. Furthermore, AFD-OFDM shows more excellent performance than FD-OFDM in the strong narrow interference channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.10A
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• pp.1177-1188
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• 2004

This paper describes and analyzes the performance of MB-OFDM UWB system that is suggested as one of standards in IEEE 802.15 TG3a for UWB application. UMBchannel model that has been contributed in IEEE 802.15 SG3a is a wideband channel model of 6Ghz bandwidth, so we modify it to have 3 subband channels that are obtained by filtering conventional U Channel, considering center frequency hopping and system bandwidth. From simulations, we compare performances of MB-OFDM system in AWGN and WB channel and verify the frequency and time domain diversity gains from time End frequency spreading technique. We also compare and analyze the performance of proposed SFBC MB-OFDM with that of conventional MB-OFDM system. Simulation results show SFBC MB-OFDM system outperforms conventional MB-OFDM system about 1.5dB of Eb/No at target BER of 10$^{-m4}$./.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.50-58
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• 2008

The use of space-division multiple access(SDMA) in the downlink of multiuser multi-input/multi-output(MIMO) wireless transmission systems can provide substantial gains in system throughput. When the channel state information(CSI) is available at the transmitter, a considerable performance improvement can be attained by adapting the transmission rates to the reported CSI. In addition, to combat frequency selective fadings in wideband wireless channels, bit-interleaved coded OFDM(BIC-OFDM) modulation schemes are employed to provide reliable packet delivery by utilizing frequency diversity through channel coding. In this paper, we propose an adaptive modulation and coding(AMC) scheme combined with an opportunistic scheduling technique for the MIMO BIC-OFDM with bandwidth-limited feedback channels. The proposed scheme enhances the link performance by exploiting both the frequency diversity and the multiuser diversity. To reduce the feedback information, the proposed AMC scheme employs rate adaptation methods based on an OFDM symbol rather than on the whole subchannels. Simulation results show that the proposed scheme exhibits a substantial performance gain with a reasonable complexity over single antenna systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.3
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• pp.260-267
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• 1992

In this paper, the performance of frequency hopped(FH) M-ary frequency shift keyed(MFSK)system is analyzed with the fading channel and the multione famming. In general, the performance degradation of FH/MFSK system is due to the Rayleigh fading and the multitone jamming environment. In order to improve the system performance. the time diversity is used. When the time diversity is applied to the Rayleigh fading and the mulitone jamming, we get around 18dB and 19dB improvements. respectively. And when it is applied to both the Rayleigh fading and the multitone jamming, we get around 4 dB improvement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.8A
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• pp.775-783
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• 2006

In this paper, the new technique combining beamforming with space-time coding is proposed for an orthogonal frequency division multiplexing(OFDM) system with multi-input multi-output(MIMO). When MIMO-OFDM system is employing Nt(the number of transmitterantenna) beamfomers and one S-T decoder at Nr receiver antennas, Nt signals removed CCI are outputted at the beamformer and then diversity gain can be got through space-time decoding. As the proposed technique can reduce cochannel interference and get diversity gain in the multi-user environment, the performance of MIMO-OFDM system is very improved. BER performance improvement and convergence behavior of the proposed approach are investigated through computer simulation by applying it to MIMO-OFDM system in the multi-user environment.