• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.5B
• /
• pp.517-529
• /
• 2011

In this paper, the parameters of the RTT (Radio Transmission Techniques) for SANET (Ship Ad-hoc NETwork), which is considered for the next generation maritime communication systems, are set up. A channel model has been analyzed based on the practical measured maritime wireless channel in VHF (Very-High Frequency) for SANET system. Also, by considering the frame structure including preamble, guard time and pilots for both single and multi-carrier systems, the BER (Bit Error Rate) performances are evaluated and analyzed in the aspects of channel compensation and channel coding techniques. Based on the simulation results, optimal modulation & coding schemes are suggested for SANET. That is, in single-carrier system by using differential modulation schemes, channel compensation is not necessary. However, channel coding is helpful to achieve additional gain. On the other hand, when 16-QAM modulation is employed in multi-carrier system, the implementation of both channel compensation and channel coding techniques show huge performance gain for various of K values, which are related to different maritime environments, and the rolling effects of wave.

• Journal of Korea Water Resources Association
• /
• v.54 no.5
• /
• pp.289-299
• /
• 2021

This study analyzes bifurcation characteristics of the Seolmacheon experimental catchment by extracting the shape variation of channel network due to variable scale of source basin or threshold area. As the area of source basin decreases, a bifurcation process of channel network occurs within the basin of interest, resulting in the elongation of channel network (increase of total channel length) as well as the expansion of channel network (increase of the source number). In the former case, the elongation of channel reaches overwhelms the generation of sources, whereas, in the latter case, the drainage path network tends to fulfill the inner space of the basin of interest reflecting the opposite trend. Therefore, scale invariance of natural channel network could be expressed to be a balanced geomorphologic feature between the elongation of channel network and the expansion of channel network due to decrease of source basin scale. The bifurcation structure of the Seolmacheon experimental catchment can be characterized by the coexistence of the elongation and scale invariance of channel network, and thus a further study is required to find out which factor is more crucial to rainfall transformation into runoff.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.24 no.12A
• /
• pp.1868-1875
• /
• 1999

The design of LAI(Local Area Identifier), the first paging area for searching the mobile terminal has a close relation with the performance of paging channel in CDMA cellular network. This paper discussed the performance of the forward channel of IS-95 CDMA standard, known as the paging through the related messages such as call control message, channel assignment message, etc. Modeling and simulation work were conducted to quantify the performance of paging channel in terms of traffic handling capacity and blocking levels. The results shown are based on a specific system call model based on the operating system of cell cite. This serves as illustrative guidelines for the proper engineering of common control channel, which has a major impact on the overall performance of cellular network.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.41 no.3
• /
• pp.129-137
• /
• 2018

VOCs have been used as the most definitive resource to reflect customer feedback when developing products and services. However, due to the development of the Internet and the emergence of SNS, VOC is no longer the only channel that represents customer opinions. There are also a number of studies showing that many customers express complaints through channels other than VOCs. In this paper, we analyze the difference between the official VOC data and the data collected through the external channel, and suggest ways to reflect the various opinions of customers. To do this, this study uses keyword analysis that can identify differences according to frequency through social network, modular analysis to distinguish topics according to centrality and similarity, and emotional analysis to confirm word polarity (positive and negative). The results of this study show that the opinions of the customers were different depending on channels such as VOCs and external channels. Therefore, the collected data through VOC as well as external channels should be used in order to reflect the opinions of customers. In particular, this paper confirms that the results of one channel may vary depending on the channel characteristics even for the same channel. This confirms that collecting voc only on certain channels may differ from what real customers require. Therefore, data collected through VOCs as well as external channels must be used to reflect various customer feedback.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.25 no.10A
• /
• pp.1529-1539
• /
• 2000

The contact procedure of access channel necessary to set up the originating call has a close relation with the performance and capacity of the base station system in CDMA cellular network. This paper investigates the structure and the operation of the backward channel of IS-95 CDMA standard and explains the related system parameters. We can derive the throughput of the CDMA access channel depending on the arrivals of the access probes per access channel slot, given the system parameters such as cell radius, the maximum number of retransmission, and the error rates of the access and paging channel. It shows that the performance in throughput is much better in the CDMA IS-95 access channel than in the slotted aloha channel. It also gives the reasonable number of the trafic channels in a cell with the given blocking probability.

• Journal of electromagnetic engineering and science
• /
• v.11 no.2
• /
• pp.133-142
• /
• 2011

Coded cooperation that integrates channel coding in cooperative transmission has gained a great deal of interest in wireless relay networks. The performance analysis of coded cooperation protocol with multiple relays is investigated in this paper. We show that the diversity order achieved by the coded cooperation in a multi-relay wireless network is not only dependent on the number of cooperating relays but is also dependent on the code-rate of the system. We derive the code-rate bound, which is required to achieve the full diversity gain of the order of cooperating nodes. The code-rate required to achieve full diversity is a linearly decreasing function of the number of available relays in the network. We show that the instantaneous channel state information (CSI)-based relay selection can effectively alleviate this code-rate bound. Analysis shows that the coded cooperation with instantaneous CSI-based relay selection can achieve the full diversity, for an arbitrary number of relays, with a fixed code-rate. Finally, we develop tight upper bounds for the bit error rate (BER) and frame error rate (FER) of the relay selection based on coded cooperation under a Rayleigh fading environment. The analytical upper bounds are verified with simulation results.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2010.10a
• /
• pp.427-430
• /
• 2010

MOST Network는 오디오와 비디오 데이터를 실시간으로 전송하는 동기식데이터 영역과 패킷데이터를 전송하는 비동기식 데이터 영역, 네트워크 관리를 위한 명령, 상태, 진단 정보를 전송하는 control Channel로 구성되어 있다. 본 논문에서는 비동기식 데이터 영역과 Control Channel의 데이터를 캡처 및 분석하는 모듈을 설계 및 구현한 후 실제 MOST 네트워크를 구축하여 검증해 보았다. 구현한 시스템을 바탕으로 고가의 장비를 별도로 보유하지 않더라도 MOST Network의 비동기식 데이터 영역과 Control Channel의 데이터를 확인할 수 있으며, 분석이 가능한 시스템을 제안하였다.

• Journal of Contemporary Eastern Asia
• /
• v.19 no.1
• /
• pp.123-143
• /
• 2020

This study examines the interplay between the reactions of YouTube users and North Korean propaganda. Interesting enough, the study has noticed changes in the strict media environment under young leader Kim. Messages delivered by the communist regime to the outside world appeared to resemble those of 'normal' countries. Although North Korean YouTube was led mainly by the account operator, visitors from different nations do comment on the channel, which suggests the possibility of building international communities for propaganda purposes. Overall, the study observed a sparsely connected social network among ordinary commenters. However, the operator did not exercise tight control over peer-to-peer communication but merely answered questions and tried to facilitate mass participation. In contrast to the many news clips, the documentary content on North Korea's YouTube channel did not explicitly advocate for North Korea's current political positions.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.38B no.3
• /
• pp.172-179
• /
• 2013

In this paper, we consider network-coded bi-directional relaying (NCBR) schemes over an asymmetric channel, in which bi-directional links have the different channel quality, as well as the asymmetric traffic load. In order to deal with asymmetric nature, two different types of NCBR schemes are considered: network coding after padding (NaP) and network coding after fragmentation (NaF). Even if NaP has been known as only a useful means of dealing with the asymmetry in traffic load up to now, our analysis shows that its gain can be significantly lost by the asymmetry in channel quality, under the given bit error performance constraint. Furthermore, it is shown that NaF always outperforms NaP, as well as traditional bi-directional relaying scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.8 no.3
• /
• pp.778-798
• /
• 2014

This paper proposes a novel exposed-terminal-eliminated medium access control (ETE-MAC) protocol by combining channel reservation, collision avoidance and concurrent transmissions to improve multi-access performance of the multihop wireless networks. Based on the proposed slot scheduling scheme, each node senses the control channel (CCH) or the data channel (DCH) to accurately determine whether it can send or receive the corresponding packets without collisions. Slot reservation on the CCH can be simultaneously executed with data packet transmissions on the DCH. Therefore, it resolves the hidden-terminal type and the exposed-terminal type problems efficiently, and obtains more spatial reuse of channel resources. Concurrent packet transmissions without extra network overheads are maximized. An analytical model combining Markov model and M/G/1 queuing theory is proposed to analyze its performance. The performance comparison between analysis and simulation shows that the analytical model is highly accurate. Finally, simulation results show that, the proposed protocol obviously outperforms the link-directionality-based dual-channel MAC protocol (DCP) and WiFlex in terms of the network throughput and the average packet delay.