• The Journal of the Korea Contents Association
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• v.6 no.3
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• pp.1-11
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• 2006

With the improvement of information telecommunication technology, the various service in broadband integrated services digital networks have a wide range of delay, delay jitter and cell loss probability requirements according to traffic specification. Therefore, the design of appropriate control schemes that can satisfy the cell loss, delay requirements with various traffic specification for B-ISDN is an extremely important challenging problem. In this paper, we propose a priority control scheme using a window counter and a cell counter per each type of class. In the proposed priority control scheme, for satisfying required service quality, we performed the priority control scheme using the delay/loss factors obtained by comparing window counter with cell counter. The performance of proposed control scheme is estimated by computer simulation. In the results of simulation, we verified that the proposed method satisfied per class requirements as the results showed that cell loss probability has a order of video, data, voice and delay time has a order of video, voice and data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10A
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• pp.935-942
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• 2006

The performance of ROF systems can be severely degraded due to nonlinear effects in the channel. Also, Orthogonal Frequency Division Multiplex(OFDM), as a standard for broadband wireless and mobile internet networks, is being proposed for deployment with ROF systems to facilitate the total performance of a system. In this paper, at first, the performance of the OFDM-based RoF system with a Mach-Zehnder(MZ) modulator distortion effects has been analyzed at 5.8GHz. Evaluation of mean-squared error of the proposed OFDM-RoF system was carried out to compare with the conventional single carrier system based RoF link after the modulator distortion case and also for fixed signal to noise ratio(SNR) of 20dB using undistorted OFDM signal. Nominal and offset baising pre-distortion techniques are applied in proposed system to linearize the OFDM-RoF link. Finally, a comparison between the aforementioned pre-distortion techniques applied showed important observation in terms of distortion-free dynamic range and SNR to choose offset pre-distortion technique for our proposed system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.2 no.2
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• pp.63-81
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• 2008

WiMAX has been introduced as a competitive alternative for metropolitan broadband wireless access technologies. It is connection oriented and it can provide very high data rates, large service coverage, and flexible quality of services (QoS). Due to the large number of connections and flexible QoS supported by WiMAX, the uplink access in WiMAX networks is very challenging since the medium access control (MAC) protocol must efficiently manage the bandwidth and related channel allocations. In this paper, we propose and investigate a cost-effective WiMAX bandwidth management scheme, named the WiMAX partial sharing scheme (WPSS), in order to provide good QoS while achieving better bandwidth utilization and network throughput. The proposed bandwidth management scheme is compared with a simple but inefficient scheme, named the WiMAX complete sharing scheme (WCPS). A maximum entropy (ME) based analytical model (MEAM) is proposed for the performance evaluation of the two bandwidth management schemes. The reason for using MEAM for the performance evaluation is that MEAM can efficiently model a large-scale system in which the number of stations or connections is generally very high, while the traditional simulation and analytical (e.g., Markov models) approaches cannot perform well due to the high computation complexity. We model the bandwidth management scheme as a queuing network model (QNM) that consists of interacting multiclass queues for different service classes. Closed form expressions for the state and blocking probability distributions are derived for those schemes. Simulation results verify the MEAM numerical results and show that WPSS can significantly improve the network’s performance compared to WCPS.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.3
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• pp.359-364
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• 2016

As cable TV networks have a media feature that is a broadband wire network, they can provide not only TV broadcasting services but also communication services. Accordingly, the cable TV network is mentioned as the optimal network for convergence of broadcasting and communication services. Recently, Available frequencies of the cable TV network have become insufficient as enhancement of video quality, increment of VoD service, and growth of high-speed internet service. This paper presents a new implementation method of switched digital video (SDV) technology that is introduced for obtaining additional frequency band. In the SDV system, only TV channels requested from viewer are sent and non-requested channels are dropped. The presented SDV uses a sharing method of TV broadcasting and communication service in a same frequency band. This method shows increase of spectrum efficient from switching of TV service channels without building a complex system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12B
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• pp.1522-1536
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• 2011

Due to the advance of broadband communication networks including the Internet, the release of diverse media, and the busy life cycle of modern people, it became difficult to watch TV programs strictly according to the program schedule. Instead, demand to download and watch the programs at any time on TV is increasing. In order to meet the demand, terrestrial DTV broadcasters developed a TV service which provides various on-demand contents by integrating terrestrial DTV network and the Internet without enforcing viewers to subscribe broadcasting services such as IPTV or CableTV, and standardized it as OHTV(Open Hybrid TV). In this paper, we explain the current status of OHTV standard and worldwide hybrid TV services and their technical standards. We also provide a strategy for the next version of OHTV standard in order to enhance the value of OHTV.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.9A
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• pp.790-795
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• 2011

The need for broadband wireless data networks such as IEEE 802.16e WiMAX systems increases as a variety of wireless information devices like smart phones are adopted rapidly in everyday life. Since most of mobile applications employ TCP as their transport layer protocol, the performance improvement of TCP in WiMAX systems is crucial. This paper proposes an efficient method to transmit uplink piggyback ACK packets by exploiting the uplink packet buffering which happens because of the resource allocation scheme of the WiMAX systems. The proposed method can support not only the ACK filtering but also the merging of the piggyback ACK packets. As a result, the bandwidth reduction in the piggyback ACK packet transmission leads to the improvement of the downlink throughput. The simulation results show that the bandwidth for the ACK packets reduces more than 90%, and the downlink throughput increases at least 30%.

• Journal of the Korea Society of Computer and Information
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• v.13 no.4
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• pp.133-140
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• 2008

The cable TV network has delivered downward broadcasting signals from distribution centers to subscribers. Since the traditional coaxial cable has been upgraded by the Hybrid Fiber Coaxial(HFC) cable, the upward channels has expanded broadband services such as Internet. This upward channel is vulnerable to ingress noises. When the noises from the children nodes accumulated in an amplifier exceeds a certain level, that node has to be cut off to prevent the noise propagation. The node selection problem(NSP) is defined to select nodes so that the noise in each node does not exceed the given threshold value and the sum of Profits of selected nodes can be maximized. The NSP has shown to be NP-hard. In this paper, we have proposed heuristics to find the near-optimal solution for NSP. The experimental results show that interval partitioning is better than greedy approach. Our heuristics can be used by the HFC network management system to provide privileged services to the premium subscribers on HFC networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1B
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• pp.8-19
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• 2010

In this paper, we propose the NCP (Network Control Platform)-based defense mechanism against DDoS (Distributed Denial of Service) attacks in order to guarantee the transmission of normal traffic and prevent the flood of abnormal traffic. We also define defense modules, the threshold and packet drop-rate used for the response against DDoS attacks. NCP analyzes whether DDoS attacks are occurred or not based on the flow and queue information collected from SR (Source Router) and VR (Victim Router). Attack packets are dopped according to drop rate decided from NCP. The performance is simulated using OPNET and evaluated in terms of the queue size of both SR and VR, the transmitted volumes of legitimate and attack packets at SR.

• The KIPS Transactions:PartC
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• v.19C no.2
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• pp.119-126
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• 2012

This paper covers the service quality of packet-based voice service that is provided over wireless broadband (WiBro) and high speed downlink packet access (HSDPA) systems. Using a measurement software that has been developed in the course of preparing a advanced service quality management scheme for the packet-based voice service over wireless networks, a huge scale of experiment is conducted to measure the real quality of the voice service. Based on our analysis of the measurement results, the service quality of the voice service is supposed to be quite good over both wireless systems. In addition, another experiment to investigate the effect of degradation of wireless transmission conditions on the service quality of the voice service shows the values of wireless service metrics in which mean opinion score (MOS) starts to decrease.

• ETRI Journal
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• v.37 no.5
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• pp.877-887
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• 2015

This paper is a first-hand summary on our comprehensive live trial of cellular-assisted device-to-device (D2D) communications currently being ratified by the standards community for next-generation mobile broadband networks. In our test implementation, we employ a full-featured 3GPP LTE network deployment and augment it with all necessary support to provide realtime D2D connectivity over emerging Wi-Fi-Direct (WFD) technology. As a result, our LTE-assisted WFD D2D system enjoys the required flexibility while meeting the existing standards in every feasible detail. Further, this paper provides an account on the extensive measurement campaign conducted with our implementation. The resulting real-world measurements from this campaign quantify the numerical effects of D2D functionality on the resultant system performance. Consequently, they shed light on the general applicability of LTE-assisted WFD solutions and associated operational ranges.