• Journal of Korea Multimedia Society
• /
• v.5 no.4
• /
• pp.441-449
• /
• 2002

For multimedia traffics to be supported successfully in wireless network environment, it is necessary to provide Qualify-of-Service(QoS) guarantees among mobile hosts(clients). In order to guarantee the QoS, we have to keep the call blocking probability below a target value during hand-off session. However, the QoS negotiated between the client and the network may not be guaranteed due to lack of available channels for traffic of a new cell, since on service mobile clients should be able to continue their sessions. In this paper, we propose an efficient load-balancing algorithm based on the adaptive bandwidth reservation scheme for enlarging available channels in a cell. Proposed algorithm predicts the direction of clients in a cell and adjusts the amount of the channel to be reserved according to the load status of the cell. This method is used to reserve a part of bandwidths of a cell for hand-off calls to its adjacent cells and this reserved bandwidth can be used for hand-off call prior to new connection requests. If the number of free channels is also under a low threshold value, our scheme use a load-balancing algorithm with an adaptive bandwidth reservation. In order to evaluate the performance of our algorithm, we measure metrics such as the blocking probability of new calls and dropping probability of hand-off calls, and compare with those of existing schemes.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.27 no.6
• /
• pp.120-129
• /
• 2023

To evaluate the vertical loads on railway bridges, conventional load tests are typically conducted. However, these tests often entail significant costs and procedural challenges. Railway conditions involve nearly identical load profiles due to standardized rail systems, which may appear straightforward in terms of load conditions. Nevertheless, this study aims to validate load tests conducted under operational train conditions by comparing the results with those obtained from conventional load tests. Additionally, static and dynamic structural behaviors are extracted from the measurement data for evaluation. To ensure the reliability of load testing, this research demonstrates feasibility through comparisons of existing measurement data with sensor attachment locations, train speeds, responses between different rail lines, tendency analysis, selection of impact coefficients, and analysis of natural frequencies. This study applies to the Dongho Railway Bridge and verifies the applicability of the proposed method. Ten operational trains and 44 sensors were deployed on the bridge to measure deformations and deflections during load test intervals, which were then compared with theoretical values. The analysis results indicate good symmetry and overlap of loads, as well as a favorable comparison between static and dynamic load test results. The maximum measured impact coefficient (0.092) was found to be lower than the theoretical impact coefficient (0.327), and the impact influence from live loads was deemed acceptable. The measured natural frequencies approximated the theoretical values, with an average of 2.393Hz compared to the calculated value of 2.415Hz. Based on these results, this paper demonstrates that for evaluating vertical loads, it is possible to measure deformations and deflections of truss railway bridges through load tests under operational train conditions without traffic control, enabling the calculation of response factors for stress adjustments.

• Journal of Korea Multimedia Society
• /
• v.6 no.7
• /
• pp.1266-1276
• /
• 2003

Multimedia information containing voice and image is transmitted on Internet, which is ten times or hundred times larger than ordinary information. Analysis types for network management in this environment consist of a real time analysis, a basic analysis and an intensive analysis. The intensive analysis is useful for gathering the trend information of specific objects periodically for certain period in order to monitor network status. When SNMP is applied to collect the trend information of intensive analysis, it brings on the increase of network load, the delay of response time and the decrease of data collection accuracy since an agent responds to manager's every polling. In this paper, an efficient SNMP is proposed and implemented to add time variables in the existing SNMP PDU. It minimizes unnecessary traffic in the intensive analysis between manager and agent, and collects trend information more accurately. The results of experiments show that it has compatibility with the existing SNMP, decreases the amount of network traffic greatly and increases the accuracy of data collection.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.19 no.6
• /
• pp.1307-1312
• /
• 2015

As smart-phones become popular, mobile data traffic has been dramatically increasing and intensive researches on the next-generation mobile communication network is in progress to meet the increasing demand for mobile data traffic. In particular, heterogeneous network (HetNet) is attracting much interest because it can significantly enhance the network capacity by increasing the spatial reuse with macro and small cells. In the HetNet, we have several problems such as load imbalance and interference because of the difference in transmit power between macro and small cells and cell range expansion (CRE) can mitigate the problems. In this paper, we propose a new cell selection scheme with adaptive cell range expansion bias (CREB) for ultra dense HetNet and we analyze the performance of the proposed scheme in terms of average cell transmission rate through system-level simulations and compare it with those of other schemes.

• The Journal of the Korea Contents Association
• /
• v.9 no.8
• /
• pp.91-98
• /
• 2009

This paper presents a solution to error avalanche of deciphering where radio noise brings random bit errors in encrypted image data under ubiquitous environment. The image capturing module is to be made comprising data compression and encryption features to reduce data traffic volume and to protect privacy. Block cipher algorithms may experience error avalanche: multiple pixel defects due to single bit error in an encrypted message. The new fault tolerant scheme addresses error avalanche effect exploiting a three-dimensional data shuffling process, which disperses error bits on many frames resulting in sparsely isolated errors. Averaging or majority voting with neighboring pixels can tolerate prominent pixel defects without increase in data volume due to error correction. This scheme has 33% lower data traffic load with respect to the conventional Hamming code based approach.

• Journal of KIISE:Computer Systems and Theory
• /
• v.26 no.8
• /
• pp.957-965
• /
• 1999

그룹간 공동 작업이나 화상 회의와 같은 그룹 통신의 수요가 늘어나면서 멀티캐스팅을 이용한 효율적인 데이타 전송에 대한 요구가 증가하고 있다. 특히 오디오나 비디오 데이타와는 달리 공동 문서 작업이나 그룹간 문서 전송을 위한 데이타 처리를 위해서는 어느 정도의 시간 손실이 있더라도 신뢰성을 보장할 수 있는 멀티캐스트 프로토콜이 요구된다. 그러나 멀티캐스트 전송에서의 신뢰성을 보장하기 위하여 손실 패킷에 대한 재전송 패킷이 전체 그룹으로 멀티캐스트 되는 것은 네트워크 상에 트래픽을 폭증시키는 요인이 된다. 이에 본 논문에서는 지역 그룹에서의 오류 회복을 위한 재전송 제한 기법을 제안하여 손실 패킷의 재전송 과정에서 발생하는 트래픽의 폭주를 제어하고자 한다. 이것은 재전송 패킷이 중복없이 다중 수신자에게 전송될 수 있도록 하여 그룹 내의 재전송 패킷의 양을 줄이고 필요없는 중복 패킷이 네트워크의 효율을 저하시키는 것을 방지하고자 하는 데 그 목적이 있다. Abstract As the size and the geographic span of communication groups increases, efficient data transmission schemes using Multicast service become more and more essential. Especially, unlike audio and video applications, for some collaborative applications and other data delivery components which require ordered and lossless delivery of data, Reliable Multicast Service is needed to ensure consistent presentation across multiple views. Thus error recovery by retransmission of loss data is provided in order to guarantee the reliability of multicast transmission protocol. However, redundant retransmission packets by multicast may cause traffic implosion on the Internet and it can be aggravated with continuous retransmission.This paper describes a Restricted Retransmission Mechanism as an error recovery method of multicast service in a local group, which can handle traffic implosion in retransmission process. It reduces redundant retransmission packets flowing into a local group and supports reliable multicast transmission. The goal of this mechanism is to reduce retransmission packets and decrease the load for group members and networks.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.3A
• /
• pp.261-270
• /
• 2007

The Delay Threshold-based Priority Queueing (DTPQ) scheme has been shown useful for scheduling both real-time (RT) and non-real-time (NRT) service traffic in mobile broadband wireless access (MBWA) systems. The overall system capacity can be maximized subject to their QoS requirement by the DTPQ scheme, which takes the urgency of the RT service into account only when their head-of-line (HOL) packet delays exceed a given delay threshold. In practice, the optimum delay threshold must be configured under the varying service scenarios and a corresponding traffic load, e.g., the number of RT and NRTusers in the system. In this paper, we propose an adaptive version of DTPQ scheme, which updates the delay threshold by taking the urgency and channel conditions of RT service users into account. By evaluating the proposed approach in an orthogonal frequency division multiple access/time division duplex (OFDM/TDD)-based broadband mobile access system, it has been found that our adaptive scheme significantly improves the system capacity as compared to the existing DTPQ scheme with a fixed delay threshold.

• Journal of the Korean Society for Railway
• /
• v.11 no.1
• /
• pp.61-68
• /
• 2008

Resilient modulus has been used for characterizing the stress-strain behavior of subgrade soils subjected to traffic loadings. With the recent release of the M-E Design Guide, highway agencies are further encouraged to implement the resilient modulus test to improve subgrade design. The subgrade design for the trackbed, however, is primarily relying on the static test results such as $K_{30}$ and deformation modulus, Ev. Therefore applicability of the resilient modulus for the design of trackbed needs to be evaluated. In this study, physical property tests, unconfined compressive tests and resilient modulus tests were conducted to assess the resilient and permanent strain behavior of 14 cohesive subgrade soils. A predictive model for estimating the resilient modulus is proposed based on the results of unconfined compressive tests and tangent elastic modulus, unconfined compressive strength, failure strain, secant modulus at peak, and yield strain. The predicted resilient moduli using the predictive models compared satisfactorily with measured ones. Although the permanent strain occurs during the resilient modulus test, the permanent behavior of subgrade soils is currently not taken into consideration.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.13 no.6
• /
• pp.203-210
• /
• 2013

Majority of the wireless ad hoc routing protocols are proposed to find feasible routes without considering the network load, end-to-end link quality and bandwidth requirements of the application. Therefore, protocol may not provide sufficient quality of service (QoS) to a high speed traffic such as multimedia. In this paper, we propose a path-quality and bandwidth-estimation based routing protocol (PBBR) for the high quality multimedia stream that can meet the application's bandwidth requirements and find the best reliable route. The novelty of this protocol is to select a reliable path to respond the application's requirements based on available bandwidth at each intermediate node and end-to-end path loss ratio. Obtained results from the simulation demonstrates that our protocol can achieve sufficient performance in terms of throughput and end-to-end delay.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2015.05a
• /
• pp.63-66
• /
• 2015

As smart-phones become popular, mobile data traffic has been dramatically increasing and intensive researches on the next-generation mobile communication network is in progress to meet the increasing demand for mobile data traffic. In particular, heterogeneous network (HetNet) is attracting much interest because it can significantly enhance the network capacity by increasing the spatial resue with macro and small cells. In the HetNet, we have several problems such as load imbalance and interference because of the difference in transmit power between macro and small cells and cell range expansion (CRE) can mitigate the problems. In this paper, we propose a new cell selection scheme with adaptive cell range expansion bias (CREB) for ultra dense HetNet and we analyze the performance of the proposed scheme in terms of average cell transmission rate through system-level simulations and compare it with those of other schemes.