• Journal of Communications and Networks
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• v.15 no.3
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• pp.266-275
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• 2013

The exact closed-form expressions for outage probability and bit error rate of spectrum sharing-based multi-hop decode-and-forward (DF) relay networks in non-identical Rayleigh fading channels are derived. We also provide the approximate closed-form expression for the system ergodic capacity. Utilizing these tractable analytical formulas, we can study the impact of key network parameters on the performance of cognitive multi-hop relay networks under interference constraints. Using a linear network model, we derive an optimum relay position scheme by numerically solving an optimization problem of balancing average signal-to-noise ratio (SNR) of each hop. The numerical results show that the optimal scheme leads to SNR performance gains of more than 1 dB. All the analytical expressions are verified by Monte-Carlo simulations confirming the advantage of multihop DF relaying networks in cognitive environments.

• Journal of the Semiconductor & Display Technology
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• v.10 no.3
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• pp.1-6
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• 2011

In this paper, the IC(Integrated Circuit) for multi-channel synchronous communication was designed by using FPGA and VHDL language. The existing chips for synchronous communication that has been used commercially are composed for one to two channels. Therefore, when communication system with three channels or more is made, the cost becomes high and it becomes complicated for communication system to be realized and also has very little buffer, load that is placed into Microprocessor increases heavily in case of high speed communication or transmission of high-capacity data. The designed IC was improved the function and performance of communication system and reduced costs by designing 8 synchronous communication channels with only one IC, and it has the size of transmitter/receiver buffer with 1024 bytes respectively and consequently high speed communication became possible. It was designed with a communication signal of a form various encoding. To detect errors of communications, the CRC-ITU-T logic and channel MUX logic was designed with hardware logics so that the malfunction can be prevented and errors can be detected more easily and input/output port regarding each communication channel can be used flexibly and consequently the reliability of system was improved. In order to show the performance of designed IC, the test was conducted successfully in Quartus simulation and experiment and the excellence was compared with the 85C3016VSC of ZILOG company that are used widely as chips for synchronous communication.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.8
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• pp.815-823
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• 2011

Combustion phenomena in porous media combustors are widely used in industrial fields for the combustion of lowgrade fuels and the regeneration of combustion heat. However, studies of combustion phenomena in porous media have been limited, because these phenomena are difficult to observe, and the configurations of porous media are complex. We propose a simple model combustor: a multi-channel combustor that consists of many layers of combustion channels made of quartz plates. We conducted an experimental observation of the flames in the multi-channel combustor and obtained experimental results for the flame stabilization limits. Flames formulated in the multi-channel combustor showed variation in the spatial distribution depending on the heat transfer between neighboring channels. A simple analytical model was developed and the variation in the flammability limits of the multi-channel combustor was discussed. This study will enhance our understanding of flame behavior in a porous-media combustor.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.4
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• pp.560-574
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• 2010

In this paper, the relationship between the energy efficiency and spectrum efficiency in a two-cell cellular network is obtained, and the impact of multi-antenna on the energy efficiency of cellular network is analyzed and modeled based on two-state Markovian wireless channels. Then, the energy efficiency of multi-cell cellular networks with co-channel interference is investigated. Simulation results verify the proposed model and the energy-spectrum efficiency tradeoffs in cellular networks with multi-antenna and co-channel interference.

• Journal of the Korean Society of Clothing and Textiles
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• v.37 no.4
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• pp.467-481
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• 2013

The study examined the main effect of the reward channel and reward time of customer loyalty programs for on-offline shopping channels; in addition, it investigated the interaction effect of the reward channels and merchandise as well as the interaction effect of the reward time and merchandise. An online apparel shopping web experiment was conducted with a 2 (reward channel: online channel reward vs. offline channel reward) ${\times}2$ (reward time: immediate vs. delayed) ${\times}2$ (merchandise: online channel product vs. offline channel products) between-subject factorial design. An online shopping channel was considered the core-shopping channel and a department store was considered the cross-shopping channel. Loyalty program value, core-channel loyalty and cross-channel loyalty were measured as dependent variables. A total of 845 shoppers (who had experiences in shopping in both channels) participated in the experiment. The results of the study revealed (1) the main effect of the reward channel on loyalty program value, core-channel loyalty and cross-channel loyalty [online>offline channel rewards], (2) the main effect of reward time on loyalty program value, core-channel loyalty and cross-channel loyalty [immediate>delayed reward], and (3) the interaction effect of the reward channel and merchandise on loyalty program value, core-channel loyalty, and cross-channel loyalty. (4) Finally the study found that loyalty program value affected cross-channel loyalty indirectly through core-channel loyalty. This study suggested diverse theoretical and managerial implications for multi-channel retailers.

• Journal of Broadcast Engineering
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• v.19 no.6
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• pp.826-835
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• 2014

Recently, spatial modulation (SM) schemes are considered to improve the reception performance in spatially correlated channel environments. SM schemes utilize a switching method between multiple transmitters to reduce the correlation among multiple transmitters to reduce the correlation of each received signals and can support transmission additional bits using antenna combinations without extra bandwidth. Therefore, SM schemes can overcome correlation interference of conventional MIMO in urban wireless channels. However, the performance comparisons between SM schemes are not yet performed in correlated urban wireless channels. In this paper, some representative SM schemes are compared and a suitable SM-MIMO system in correlated urban wireless channels is proposed.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.2
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• pp.313-320
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• 2018

The importance of sensors on a self-driving vehicle has rising since it act as eyes for the vehicle. Lidar sensors based on laser technology tend to yield better image quality with more laser channels, thus, it has higher detection accuracy for obstacles, pedistrians, terrain, and other vechicles. However, incorporating more laser channels results higher unit price more than ten times, and this is a major drawback for using high channel lidar sensors on a vehicle for actual consumer market. To come up with this drawback, we propose a method of integrating multiple low channel, low cost lidar sensors acting as one high channel sensor. The result uses four 16 channels lidar sensors with small form factor acting as one bulky 64 channels sensor, which in turn, improves vehicles cosmetic aspects and helps widespread of using the lidar technology for the market.

• Journal of KIISE:Information Networking
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• v.31 no.1
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• pp.37-52
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• 2004

Broadcast has been often used to disseminate the frequently requested data efficiently to a large volume of mobile units over a single or multiple channels. Since the mobile units have limited battery power, the minimization of the access time for the broadcast data is an important problem. There have been many research efforts that focus on the improvement if the broadcast techniques by providing indexes on the broadcast data. In this paper, we studied an efficient index allocation method for the broadcast data over multiple physical channels, which cannot be coalesced into a single high bandwidth channel. Previously proposed index allocation techniques either require the equal size of index and data or have a performance degradation problem when the number of given physical channels is not enough. These two problems will result in the increased average access time for the broadcast data. To cope with these problems, we propose an efficient tree- structured index allocation method for the broadcast data with different access frequencies over multiple physical channels. Our method minimizes the average access time for the broadcast data by broadcasting the hot data and their indexes more often than the less hot data and their indexes. We present an in-0e0th experimental and theoretical analysis of our method by comparing it with other similar techniques. Our performance analysis shows that it significantly decrease the average access time for the broadcast data over existing methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7C
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• pp.680-690
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• 2006

In this paper, we present a bit allocation scheme based on grouped sub-channels for MIMO-OFDM (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) systems using V-BLAST (Vertical-Bell laboratories LAyered Space-Time) detector. A fully adaptive modulation and coding scheme may provide optimal performance in the MIMO-OFDM systems, however it requires excessive feedback information. Instead, SBA (Simplified Bit Allocation) scheme for reduction of feedback overhead, which applies the same modulation and coding to all the good sub-channels, may be considered. The proposed scheme in this paper named SBA-GS (Simplified Bit Allocation based on Grouped Sub-channels) groups sub-channels and assigns the same modulation and coding to the set of selected sub-channel groups. Simulation results show that the proposed scheme achieves comparable bit error rate performance of the conventional SBA scheme, while significantly reducing the feedback overhead in multipath channels with small delay spreads.

• Membrane Journal
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• v.18 no.4
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• pp.325-335
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• 2008

In this study, we used multi-channels ceramic membrane having larger permeate volume per unit time rather than tubular membrane. The hybrid process for advanced drinking water treatment was composed of granular activated carbons (GAC) packing between module inside and outside of multi-channels microfiltration membrane. Instead of natural organic matters (NOM) and fine inorganic particles in natural water source, modified solution was prepared with humic acid and kaolin. Kaolin concentration was fixed at 30mg/L and humic acid was changed as $2{\sim}10\;mg/L$ to inspect effect of organic matters. As a result, both resistance of membrane fouling ($R_f$) and permeate flux (J) were highly influenced by concentration of humic acid. Also, in result of water-back-flushing period (FT) effect, the shorter FT was the more effective to reduce membrane fouling and to enhance permeate flux because of frequent water-back-flushing. However, the optimal FT condition was 8 min when operating costs were considered. Then, the hybrid process using multi-channels ceramic membrane and GAC was applied to lake water treatment. As a result, average treatment efficiencies in our experiment using the hybrid process were 98.02% for turbidity, 75.64% for $UV_{254}$ absorbance, 7.18% for TDS and 84.73% for $COD_{Mn}$.