• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.413-419
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• 2014

Underwater acoustic channel has time-variability. Time varying channel which disturbs the continuous transmission of information data reduces the underwater acoustic communication performance. In this paper, we show the temporal coherence as time-variability of channel and indicate throughput efficiency in accordance with transmission time of information data. Then we analyzed influence of underwater channel time-variability on communication throughput efficiency. We confirmed that the throughput efficiency reduced when the time-variability of the channel increased via lake trial.

• Journal of KIISE
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• v.43 no.12
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• pp.1412-1419
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• 2016

In cognitive radio sensor networks (CRSNs), secondary users (SUs) can occupy licensed bands opportunistically without causing interferences to primary users (PUs). SUs perform spectrum sensing to detect the presence of PUs. Sensing time is a critical parameter for spectrum sensing that can yield a tradeoff between sensing performance and secondary throughput. In this study, we investigate new approaches for spectrum sensing by exploring the tradeoff from a) spectrum sensing for PU detection (SSPD) and b) spectrum sensing for secondary throughput (SSST). In the proposed scheme, the first sensing result of the current frame determines the dynamic performance of the second spectrum sensing. Energy constraint in CRSNs leads to maximized network energy efficiency via optimization of sensing time. Simulation results show that the proposed scheme of SSPD and SSST improves network performance in terms of energy efficiency and secondary throughput, respectively.

• Journal of Korea Society of Industrial Information Systems
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• v.22 no.1
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• pp.33-40
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• 2017

In this Paper, Analyse the Steady State Behavior of TCP and TFRC with Packet Error when both TCP and TFRC Flows Co-exist in the Network. First, Model the Network with TCP and TFRC Connections as a Discrete Time System. Second, Calculate Average Round Trip Time of the Packet Between Source and Destination on Packet Loss Environment. Then Derive the Steady State Performance i.e. Throughput of TCP and TFRC, and Average Buffer Size of RED Router Based on the Analytic Network Model. The Throughput of TCP and TFRC Connection Decrease Rapidly with the Growth of Sending Window Size and Their Transmission Rate but Their Declines become Smoothly when the Number of Sending Window Arrives on Threshold Value. The Average Queue Length of RED Router Increases Slowly on Low Transmission Rate but Increases Rapidly on High Transmission Rate.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.3
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• pp.513-519
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• 2018

OFDM modulation has been used for a transmission scheme in 4G LTE (Long Term Evolution) and Wi-Fi systems to mitigate the effects of frequency selective fading channels. An OFDM modulation is a block transmission scheme because an OFDM symbol consists of multiple subcarriers with narrow bandwidth. Therefore, all OFDM symbols in a frame should be filled out with data and padding bits. Depending on the amount of data, more padding bits than information bits can occupy the last OFDM symbol. Such inefficiency causes the loss of throughput. To overcome this problem, an efficiency padding method is proposed by using the property of DFT (Discrete Fourier Transform). In the proposed method, symbol duration of the last symbol is changed depending on the number used data subcarriers in the last symbol. With numerical evaluation, it is examined that throughput enhancement achieved by the proposed method can be about 20% depending a transmission scheme and data length.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.4
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• pp.29-39
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• 2009

The need for radio spectrum is recently considered as a huge hurdle towards the rapid development of wireless networks. Large parts of the spectrum are allocated to licensed radio services in proprietary way. However, enormous success of the wireless services and technologies in the unlicensed bands has brought new ideas and innovations. In recent years cognitive radio has gained much attention for solving the spectrum scarcity problem. It changes the way spectrum is regulated so that more efficient spectrum utilization is possible. Multi-hop relay technology on the other hand has intensively been studied in the area of ad hoc and peer-to-peer networks. But in cellular network, only recently the integration of multi-hop capability is considered to enhance the performance significantly. Multi-hop relaying can extend the coverage of the cell to provide high data rate service to a greater distance and in the shadowed regions. Very few papers still exist that combine these methods to maximize the spectrum utilization. Thus we propose a network architecture combining these two technologies in a way to maximize the system throughput. We present the throughput capacity equations for the proposed system model considering various system parameters like utilization factor by the primary users and primary users' transmission radius and through extensive numerical simulations we analyze the significance of work.

• Journal of IKEEE
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• v.1 no.1 s.1
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• pp.83-92
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• 1997

Multipath ATM switch architectures have the potential to accommodate easily the design of high-speed and large capacity ATM switches which can handle a very large amount of switching throughputs. However, the multipath architecture inevitably encounters out-of-sequence problems. We propose a multipath switch model to analyze the out-of-sequence phenomenon. And we analyze the out-of-sequence performance dependency on the architecture parameters : the number of multipath, the trunk utilization, the switch size, and the number virtual channels/trunk. Indexing terms : ATM switch, Multipath archltecture, Out-of-sequence performance, Cell sequence integrity, Analytical model.

• Journal of Broadcast Engineering
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• v.20 no.5
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• pp.748-755
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• 2015

In this paper, sharing based admission control scheme is suggested for both service differentiation and improvement of wavelength utilization efficiency in burst switching networks. To provide service differentiation and high wavelength utilization efficiency, some of the wavelengths on a output link are shared with all classes and the others are used for the highest class exclusively. Markov based analysis is applied to the suggested scheme for the performance analysis and the numerical results are derived. The results are: The performance of lower traffic is more improved by the more number of shared wavelengths in case that the higher traffic or lower traffic is arrived equally or that the input rate of lower traffic is low. Another result is that the sharing effect of wavelengths is a little bit lowered when lower traffic passes the threshold.

• Journal of Advanced Navigation Technology
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• v.16 no.2
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• pp.219-226
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• 2012

Since OFDM(Orthogonal Frequency Division Multiplexing) technology is applied into LTE(Long Term Evolution)/LTE-Advanced system, it is important to estimate the spectrum sharing and to analyze interference in LTE system based on the characteristics of frequency assignment. Therefore, in this paper, a study on the adjacent channel interference between two operators/systems to provide LTE services. For co-existence of LTE systems, the relative capacity loss and the relative throughput loss in uplink and downlink have been simulated to evaluated ACIR(Adjacent Channel Interference Ratio) values with 5% loss rate. Some parameters such as the location of user, aggressor bandwidth, and the separation offset affect the required ACIR value for spectrum sharing, and these results and interference analysis schemes in this article can provide reliable reference for LTE RF standardization and efficient frequency utilization in future.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.6
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• pp.1145-1152
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• 2021

In order to optimize the performance of 1.4P large storage, the characteristics of each chunk mode were investigated, and the chunk 512K mode was selected in terms of I/O speed. NVME storage system was configured and used to measure data server performance of large storage. By measuring the change in throughput according to the number of threads of the 1.4P large storage, the characteristics of the large storage system were identified, and it was confirmed that the performance was up to 133Gbps with a block size of 32KB. As a result of data transmission/reception experiment using globus-url-copy of GridFTP, it was found that this large storage has a throughput of 33Gbps.

• Journal of Broadcast Engineering
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• v.25 no.4
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• pp.609-619
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• 2020

In accordance with a demand for high quality video streaming, it needs high data rate in limited bandwidth and more traffic congestion occurs. In particular, when providing real time video service, packet loss rate and bit error probability increase significantly. To solve these problems, a raptor code, which is one of FEC(Forward Error Correction) techniques, is pervasively used in the application layers as a method for improving real-time service quality. In this paper, we propose a method of determining image transmission parameters based on various deep neural networks to increase transmission efficiency at a similar level of image quality by using raptor codes. The proposed neural network uses the packet loss rate, video encoding rate and data rate as inputs, and outputs raptor FEC parameters and packet sizes. The results of the proposed method present that the throughput is 1.2% higher than that of the existing multimedia transmission technique by optimizing the transmission efficiency at a PSNR(Peak Signal-to-Noise Ratio) level similar to that of the existing technique.