• Journal of Communications and Networks
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• v.9 no.3
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• pp.247-253
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• 2007

In this paper, downlink capacity of time duplex division (TDD) based cellular wireless networks utilizing fixed hopping stations is investigated. In the network, a number of fixed subscriber stations act as hopping transmission stations between base stations and far away subscribers, forming a cellular and ad hoc mobile network model. At the radio layer, TDD code division multiple access (CDMA) is selected as the radio interface due to high efficiency of frequency usage. In order to improve the system performance in terms of downlink capacity, we propose different time slot allocation schemes with the usage of fixed hopping stations, which can be selected by either random or distanced dependent schemes. Performance results obtained by computer simulation demonstrate the effectiveness of the proposed network to improve downlink system capacity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.9
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• pp.3075-3093
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• 2014

In this paper, we consider an advanced wireless user, called primary-secondary user (PSU) who is capable of harvesting renewable energy and connecting to both the primary network and cognitive radio networks simultaneously. Recently, energy harvesting has received a great deal of attention from the research community and is a promising approach for maintaining long lifetime of users. On the other hand, the cognitive radio function allows the wireless user to access other primary networks in an opportunistic manner as secondary users in order to receive more throughput in the current time slot. Subsequently, in the paper we propose the channel access policy for a PSU with consideration of the energy harvesting, based on a Partially Observable Markov decision process (POMDP) in which the optimal action from the action set will be selected to maximize expected long-term throughput. The simulation results show that the proposed POMDP-based channel access scheme improves the throughput of PSU, but it requires more computations to make an action decision regarding channel access.

• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.9
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• pp.849-854
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• 2016

5G New Radio Access Technology(: RAT) is studied by many researchers because the current radio frequency is insufficient to accommodate the increased mobile communication data traffic. However, there are few researches to study on the issue whether the wired mobile network can accommodate the new RAT. Therefore, in the paper, the study on the issue whether the Radio over Fiber(: RoF) system can accommodate the new RATs such as millimeter wave communication, terahertz communication, and optical wireless communication. As a result of the study, only millimeter wave communication deserve to be considered in ten years and even RoF system may not support the increased bandwidth of the millimeter wave communication when beamforming is used.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.17 no.2
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• pp.61-72
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• 2007

With the increasing growth of Internet and wireless IP networks, Multimedia systems need to be envisaged as information resources where users can access anywhere and anytime. However, efficient services in these multimedia systems are open and challenging research problem due to user mobility, limited resources in wireless devices and expensive radio bandwidth. To implement multimedia services over heterogeneous network, the IP header compression scheme can be used for saving bandwidth. In this paper, we present an efficient solution for header compression, which is modified form of ECRTP. It shows an architectural framework adopting modified ECRTP when IP tunneling network using GRE over IPSec is implemented. We have conducted simulations in order to analyze the effects of different header compression techniques while delivering real-time services to the wireless access network through secured IP Network. The impacts on performance have been investigated through a series of experiments.

• Journal of Korea Society of Industrial Information Systems
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• v.17 no.2
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• pp.11-18
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• 2012

Smart Dynamic Pricing has been introduced to address the under-utilised network resources problem in mobile telecommunications systems. In this paper, we investigate the applicability of Smart Dynamic Pricing and its signalling models into Cognitive Radio Systems. Cognitive Radio System is defined as one in which cognitive radios are employed to access shared spectrum and/or dynamically allocated spectrum. Network elements, protocols, traffic and control channels, and system architecture are proposed for the implementation of Smart Dynamic Pricing in Cognitive Radio System. It is found that Smart Dynamic Pricing and its signalling models can be applied to Cognitive Radio Systems.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.05a
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• pp.348-351
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• 2000

In order to enact the technical standard of RF(Radio Frequency) in domestic, this paper analyzes the trends and the technical specifications of high performance radio local area network, for example HIPERLAN(Europe), U-Nll(U.S.A), broadband mobile access system(Japan). The contents of this paper are helpful to make a rule for the desirable national technical standard of high performance radio local area network.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.8
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• pp.3809-3822
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• 2017

Wireless Sensor Networks hold the limelight because of significant potential for distributed sensing of large geographical areas. The radio duty cycling mechanism that turns off the radio periodically is necessary for the energy conservation, but it deteriorates the network congestion when the traffic load is high, which increases the packet loss and the delay too. Although many papers for WSNs have tried to mitigate network congestion, none of them has mentioned the congestion problem caused by the radio duty cycling of MAC protocols. In this paper, we present a simple and efficient congestion control technique that operates on the radio duty cycling MAC protocol. It detects the congestion by checking the current queue size. If it detects the congestion, it extends the network capacity by adding supplementary wakeup times. Simulation results show that our proposed scheme highly reduces the packet loss and the delay.

• Journal of Communications and Networks
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• v.5 no.4
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• pp.290-302
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• 2003

Ultra wide band (UWB) radio has recently attracted increased attention due to its expected unlicensed operation, and potential to provide very high data rates at relatively short ranges. In this article we briefly describe some main candidate multiple access and modulation schemes for UWB communications, followed with their power spectral density calculation and properties. We also present some illustrative capacity results, and provide a discussion of the impact of network topology on multiple access capacity.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2004.10a
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• pp.623-626
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• 2004

최근 이동망 경쟁활성화 및 이용자 후생확대를 위하여 로밍, MVNO, 사이트 공유(site sharing), 매스트 공유(mast sharing), 무선접속망 공유(radio access network sharing), 무선 코어망공유(radio and core network sharing) 등 다양한 제도들이 검토되고 있다. 이 가운데 로밍과 MVNO제도가 현시점에서 가장 보편적으로 이용되고 있다. 논문은 이동망 네트워크 공유제도에 대하여 로밍과 MVNO제도를 중심으로 분석하고, 마지막으로 국내 이동통신 시장에 적용될 수 있는 바람직한 정책적 시사점을 도출하고자 한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.8
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• pp.3821-3841
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• 2019

Cloud radio access networks (C-RANs) have been regarded in recent times as a promising concept in future 5G technologies where all DSP processors are moved into a central base band unit (BBU) pool in the cloud, and distributed remote radio heads (RRHs) compress and forward received radio signals from mobile users to the BBUs through radio links. In such dynamic environment, automatic decision-making approaches, such as artificial intelligence based deep reinforcement learning (DRL), become imperative in designing new solutions. In this paper, we propose a generic framework of autonomous cell activation and customized physical resource allocation schemes for energy consumption and QoS optimization in wireless networks. We formulate the problem as fractional power control with bandwidth adaptation and full power control and bandwidth allocation models and set up a Q-learning model to satisfy the QoS requirements of users and to achieve low energy consumption with the minimum number of active RRHs under varying traffic demand and network densities. Extensive simulations are conducted to show the effectiveness of our proposed solution compared to existing schemes.