• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.603-610
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• 2006

This paper considers the problem of mitigating CCI(Co-channel Interference) in cellular OFDMA downlink systems. The users in the cell-edge area suffer from large CCIs, and their SINR requirements are hard to be maintained. To guarantee their QoS, we propose a new exclusive sub-carrier allocation and power control algorithm. The performance of the proposed two-step algorithm is simulated in SUI-A path-loss model, and it is compared with that of the conventional algorithm. The simulation results show that the data transmission rate in the cell-edge area was increased by 600Kbps within the same power constraint. The results indicate that with proposed algorithm, the data rate stability can be achieved independently of the user location in the cell.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.1 no.2
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• pp.145-158
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• 1997

Method for synchronizing multimedia data is needed to support continuous transmission of multimedia data through a network in a bounded time and it also required for supporting continuous presentation of multimedia data with the required norminal playout rate in distributed network environments. This paper describes a new synchronization method for supporting delay-sensitive multimedia Presentation without degration of Quality of services of multimedia application. It mainly aims to support both intermedia and intermedia synchronization by absorbing network variations which may cause skew or jitter. In order to remove asynchonization problems, we make use of logical time system, dynamic buffer control method, and adjusting synchronization intervals based on the quality of services of a multimedia. It might be more suitable for working on distribute[1 multimedia systems where the network delay variation is changed from time to time and no global clock is supported. And it also can effectively reduce the amount of buffer requirements needed for transfering multimedia data between source and destination system by adjusting synchronization intervals with acceptable packet delay limits and packet loss rates.

• The KIPS Transactions:PartB
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• v.9B no.5
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• pp.549-554
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• 2002

This paper proposes a UQoSM (User Qualify of Service Middleware) framework for multimedia application systems. UQoSM system is extended the existing event service model added to the event monitoring, reflective event filtering and event dispatcher for supporting multimedia application systems. Especially, this paper is concentrated on providing suitable reflective event filtering function for multimedia application service system in order to meet various user requirements under inter-based environment. It means this system provides high QoS to users. In addition, it results in decreasing network traffic as unnecessary event information is filtered from network.

• Information and Communications Magazine
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• v.15 no.7
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• pp.75-94
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• 1998

In this paper, HFC CATV networks are introduced. HFC CATV networks are currently considered as a most effective and plausible solution for subscriber access networks in the information superhighway, among others such as ADSL and B-WLL. The advantages of HFC CATV networks include its broad upstream and downstream channel bandwidths, much wider than PSTN's and its readiness. The HFC CATV networks are already well spread among the general subscribers in Korea. This fact will shorten the installation period and significantly reduce its cost. In addition, The structure and channel environment of the HFC CATV networks are introduced. At the same time, in this paper included are major problems in the HFC CATV networks and the solutions for these problems. Also discussed are data transmission, medium access control, IEEE802.14, and MCNS for standardizations. Moreover, additional telecommunications service activities in both Korea and other countries, using HFC CATV networks are also included. The topics which are covered in detail are the ones such as interoperation between HFC CATV networks and trunk line and the digital transmission performance test for the CATV networks. In the performance test, it is concluded that HFC CATV networks can satisfy the QoS for various additional services if the number of the subscribers in a cell is limited to less than 500 and other minor requirements are satisfied. Based on all these discussions and conclusions, HFC CATV networks are suggested in this paper for the subscriber access networks of the so called information superhighway.

• Journal of IKEEE
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• v.7 no.1 s.12
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• pp.97-106
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• 2003

In ARQ based error control, imperfect error detection leaves error remains on a packet. Aiming for a reduction of error remains in multicopy transmission ARQ system, we propose a rule of requesting a retransmission and deciding a correct copy, (identified as $(m, \;{\sigma})$rule). While the probability of error remains is reduced by the employment of the $(m, \;{\sigma})$ rule at multicopy transmission ARQ, delay and throughput performance may be degraded in comparison with those of conventional single copy transmission ARQ. Thus, we develop an analytical method to evaluate the performance trade-off in multicopy transmission ARQ following the $(m, \;{\sigma})$ rule. From the numerical results obtained by the analytical method, we investigate the effect of channel characteristics on the performance of error remains, packet loss, throughput, and packet delay, and confirm that the adaptability of the $(m, \;{\sigma})$ rule to conform to various QoS requirements with ease.

• Journal of the Korea Society for Simulation
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• v.17 no.4
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• pp.89-97
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• 2008

In wireless personal area networks (WPANs), the successful design of channel time allocation algorithm is a key factor in guaranteeing the various quality of service (QoS) requirements for the stringent real-time constraints of multimedia services. In this paper we propose a channel time allocation algorithm for achieving a high quality transmission and high channel error tolerance of MPEG stream in the IEEE 802.15.3 high-rate wireless PANs. Our algorithm exploits the characteristics of MPEG stream. When a new MPEG stream arrives, a DEV models it by the traffic envelope and delivers the traffic envelope to the piconet coordinator (PNC) along with the channel time request. The PNC performs channel time allocation according to the envelope. Performance of the proposed scheme is investigated by simulation and analysis. Our results show that compared to conventional scheme, the proposed scheme is very effective and provides a good performance under typical channel error conditions.

• Journal of Information Processing Systems
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• v.7 no.2
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• pp.261-270
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• 2011

The IEEE 802.16 standard is supposed to provide a wide-range broadband wireless service, but it leaves the implementation of the wireless resource scheduler as an open issue. We have studied the scheduling problem and propose a two level scheduling (TLS) scheme with support for quality of service and fairness guarantees for downlink traffic in a WiMAX network. A central controller Base Station has a number of users, and each mobile subscriber station has different channel conditions. The same mobile subscriber station may have different service requirements at different times in the WiMAX network. Based on OPNET simulation, the results show our scheduling algorithm can increase the network throughput, maintain relative fairness, and lower delay over the round robin and weighted round robin algorithms.

• Journal of Korean Institute of Industrial Engineers
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• v.34 no.4
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• pp.445-459
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• 2008

This paper addresses a call admission control(CAC) scheme giving handoff calls a priority over new calls for OFDMA wireless communication systems. The characteristics of OFDMA system and a variety of user QoS (Quality of Service) requirements are incorporated into the proposed CAC scheme which consists of several optimization modules for the system resource(subcarriers and power) allocations. The mathematical models and its solution methods for the embedded resource allocation problems are proposed. Some extensive computational experiments are conducted to illustrate the superiority of our CAC.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7A
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• pp.770-777
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• 2007

Smaller cell size in the micro-cell or pico-cell structure brings about more frequent hand-overs between cells, and higher speed movement of the mobile terminal makes short the permissible time interval for executing these hand-over procedures. In this situation the hand-over failure may occur or some packets may be lost during the hand-over. Moreover a rapid degradation of throughput is triggered by packet re-transmission for compensating such errors. The QoS (Quality of Services) of mobile multimedia applications with higher bits rate requirements and higher speed mobility are severely affected by even shot service interruption. This paper proposes a new hand-over scheme to provide seamless services in the next generation mobile communication systems. Simulation is done to evaluate the performance of the proposed scheme based on its hand-over failure rate and packet loss rate.

• The Journal of the Korea Contents Association
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• v.5 no.3
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• pp.217-225
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• 2005

Currently the research on input-queued ATM switches is one of the most active research fields. Many achievements have been made in the research on scheduling algorithms for input-queued ATM switches and also applied in commerce. The scheduling algorithms have the characteristics of improving throughput, satisfying QoS requirements and providing service fairly. In this paper, we studied on an implementation of scheduler which arbitrates the input-queued ATM switches efficiently and swiftly. The proposed scheduler approximately provides $100\%$ throughput for scheduling. The proposed algorithm completes the arbitration for N-port VOQ switch with 4-iterative matching. Also the proposed algorithm has a merit for implementing the scheduling algorithm with 1/2 area compared to that of iSLIP scheduling algorithm which is widely used. The performance of the proposed scheduling algorithm is superior to that of iSLIP in 4-iterative matching.