• Journal of Communications and Networks
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• 제10권2호
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• pp.137-147
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• 2008

This paper proposes a novel approach to interference avoidance via inter-cell relaying in cellular OFDMA-TDD (orthogonal frequency division multiple access - time division duplex) systems. The proposed scheme, termed asymmetry balancing, is targeted towards next-generation cellular wireless systems which are envisaged to have ad hoc and multi-hop capabilities. Asymmetry balancing resolves the detrimental base station (BS)-to-BS interference problem inherent to TDD networks by synchronizing the TDD switching points (SPs) across cells. In order to maintain the flexibility of TDD in serving the asymmetry demands of individual cells, inter-cell relaying is employed. Mobile stations (MSs) in a cell which has a shortage of uplink (UL) resources and spare downlink (DL) resources use free DL resources to off-load UL traffic to cooperating MSs in a neighboring cell using ad hoc communication. In an analogous fashion DL traffic can be balanced. The purpose of this paper is to introduce the asymmetry balancing concept by considering a seven-cell cluster and a single overloaded cell in the center. A mathematical model is developed to quantify the envisaged gains in using asymmetry balancing and is verified via Monte Carlo simulations. It is demonstrated that asymmetry balancing offers great flexibility in UL-DL resource allocation. In addition, results show that a spectral efficiency improvement of more than 100% can be obtained with respect to a case where the TDD SPs are adapted to the cell-specific demands.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 2002년도 춘계공동학술대회
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• pp.144-151
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• 2002

Future wireless communication systems are expected to provide a broad range of multimedia services in which the asymmetry of traffic load between uplink and downlink is a significant feature. The rode division multiple access system with tune division duplex mode (CDMA/TDD) is a good solution to cope with the traffic asymmetry problem. However. the TDD system is subject to inter-cell interference compared to frequency division duplex (FDD) system. Since both uplink and downlink share the same frequency in TDD. uplink and downlink may interfere each other especially when neighboring cells require different rates of asymmetry. Thus, time slot allocation for tells is an important issue in TDD. In this paper. we propose a genetic algorithm based time slot allocation scheme which maximizes the residual system capacity. The proposed scheme allows that each cell employ different level of uplink/downlink asymmetry and satisfies the interference requirement.

• ETRI Journal
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• 제42권1호
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• pp.138-149
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• 2020

In this paper, we describe a simultaneously transmitted jamming (ST-jamming) for bi-directional in-band full-duplex (IFD) system to improve information security at the physical layer. By exploiting ST-jamming, each legitimate user transmits data samples and jamming samples together in one orthogonal frequency division multiplexing symbol according to given traffic asymmetry. Regardless of the traffic difference in both directions in IFD communication, eavesdropping of confidential information is prevented in both directions simultaneously without the loss of data rate. We first propose an encoding scheme and the corresponding decoding scheme for ST-jamming to be used by the legitimate users. In addition, we study a transceiver structure of the legitimate users including a baseband modem uniquely designed for the use of ST-jamming. The leakage of confidential information at an eavesdropper is then quantified by studying the mutual information between the confidential transmit signals and the received signals of the eavesdropper. Simulation results show that the proposed ST-jamming significantly reduces the leakage of legitimate information at the eavesdropper.

• Asian Journal of Business Environment
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• 제11권4호
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• pp.5-16
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• 2021

Purpose: This study aims to investigate the impact of auditor-client traffic convenience on accrual -based and real earnings management of the client firms. Research design, data and methodology: Using a sample of firms listed in Shanghai and Shenzhen Stock Exchanges over the period of 2007 to 2018, this paper empirically investigates the association between auditor-client traffic convenience and earnings management. We use three measures of auditor-client traffic convenience: railway traffic convenience, expressway traffic convenience, and air traffic convenience. The accrual-based earnings management is measured by abnormal accruals estimated by industry and year using the Modified Jones Model. Results: Findings indicate that traffic convenience is conducive to detecting and restraining positive accrual earnings management and real earnings management. After changing the measurement of independent variable and dependent variable, including potential omitted variables, the results are statistically unchanged. Further, the research shows that traffic convenience can not only improve audit quality, but also lead to higher fee premiums. Auditors didn't share with clients the cost reduction benefits caused by traffic convenience. Conclusions: Traffic convenience provides auditors with easy access to the client firms, alleviating the information asymmetry and improving corporate earnings quality. The findings have implications for regulators, audit practitioners and stakeholders.

• 한국통신학회논문지
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• 제27권8B호
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• pp.752-759
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• 2002

셀의 용량은 자신과 이웃셀에 걸리는 부하에 따라 변한다. 그러나 대부분 호수락제어 알고리즘들은 이런 셀의 부하를 고려하지 않았다. 그래서 비대칭 트래픽이 존재하는 광대역 부호분할 다중접속 시스템에서의 동적 호수락제어 알고리즘을 제시한다. 이 알고리즘은 채널의 환경에 따라 신규호와 핸드오프호의 호수락제어 경계값을 조절함으로써 막힘확률과 끊김확률을 제어하도록 한다. 호의 클래스마다 서비스의 질을 보장할 수 있으며 신규호와 핸드오프호간에 우선순위를 보장할 수 있다. 게다가 제안한 알고리즘은 시스템의 전송량을 감소시키지 않으면서 서비스 품질값을 최적화할 수 있다.

• 한국통신학회논문지
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• 제38B권3호
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• pp.172-179
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• 2013

본 논문에서는 양방향 링크의 채널 상태와 트래픽 부하가 비대칭적인 채널에서 네트워크 코딩을 적용하는 기법과 그 방식에 따른 성능에 대해서 살펴본다. 이러한 양방향 링크의 비대칭성을 반영하기 위해 패딩후 네트워크 코딩(Network Coding after Padding: NaP) 방식과 분할 후 네트워크 코딩(Network Coding after Fragmentation: NaF) 방식을 고려한다. NaP 방식은 지금까지 트래픽 부하의 비대칭성만을 반영하기 위해 고려된 바 있으며, 본 논문에서는 실제로 채널의 상태를 동시에 고려할 경우에는 NaP 방식이 갖는 기존의 이득이 오히려 열화되는 것을 보인다. 또한, NaF 방식이 일반적인 양방향 링크 기법뿐만 아니라 NaP 방식보다 항상 성능이 좋다는 것을 보인다.

• 한국IT서비스학회지
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• 제7권2호
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• pp.137-148
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• 2008

This paper measures and compares the traffic of a series of Massively Multi-player On-line Role Playing Game (MMORPG). The purpose of this analysis is to characterize the MMORPG traffic and compare the traffic characteristics of those games caused by the game structure difference between 2D and 3D environment. The target game is 'Lineage I' and 'Lineage II' which represent world's largest MMORPGs in terms of the number of concurrent users. We collect about 280 giga bytes and 1 tera bytes of packet headers, respectively. We compare packet size, packet inter-arrival time and bandwidth usage of these two games. The MMORPG traffic consists of two kinds of packets: client-generated upstream packets and server-generated downstream packets. We observe that the upstream packet size of payload has grown from 9 bytes to 19 bytes, while the average payload size of downstream packets has grown from 37 bytes to 318 bytes. This asymmetry of growing rate is caused by 3D game structure. Packet inter-arrival time becomes shorter from average 2 milliseconds to 58 microseconds. Bandwidth consumption per client has grown from 4 kbps to 20 kbps. We find that there is a linear relationship between the number of users and the bandwidth usage in both case.

• 한국멀티미디어학회논문지
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• 제16권7호
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• pp.862-869
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• 2013

In order to support a cell-independent traffic asymmetry, the conventional TDD system cannot avoid crossed time slot (CTS) interference. Moreover, the TDD/FDD hierarchical overlay cellular systems is taken into account as a generally accepted cell model in a heterogeneous radio environment. In this paper, we propose an interference resolving radio resource allocation technique in a TDD-OFDMA cellular system that overlays a FDD-CDMA cell. In our proposed scheme, we exploit under-used FDD-CDMA uplink resource by TDD mobile abiding by a region based time slot(TS) allocation which in turn mitigates CTS interference considerably. It is demonstrated that combined with under-used resource utilization scheme based on mobile's location, the proposed technique can reduce CTS interference considerably and support the asymmetric traffic in TDD system.

• The Journal of Korean Physical Therapy
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• 제29권4호
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• pp.218-222
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• 2017

Purpose: Driving is an important activity that is affected by various motor and cognitive deficits after stroke. On the other hand, there is no standard screening tool to evaluate the sitting asymmetry during driving, which is the stereotyped postural characteristic observed in patients with stroke. Therefore, this study compared the buttock pressure during simulated driving between healthy adults and patients with stroke. Methods: Ten post-stroke patients and ten healthy subjects participated in the experiment. The participants experienced simulated driving of 6.1 km during approximately 5 minutes for adaptation. The driving scenario consisted of 3.5 km urban traffic conditions, 10 km straight highway, and 7 km curved or hilly rural roads. Force sensitive application (FSA) was used to analyze the distribution of the buttock pressure on the driver's seat. The symmetry index (SI) was determined using the average buttock pressure of each side of the buttock. The closer SI is to zero, the higher the symmetry of buttock pressure. Results: These studies showed that the SI of healthy subjects was significantly closer to zero than that of the stroke patients. Conclusion: The buttock pressure of the stroke patients showed more asymmetry than that of the healthy subjects during simulated driving. Therefore, a therapeutic approach is needed for symmetrical sitting to improve the driving performance.

• 한국산학기술학회논문지
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• 제10권2호
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• pp.364-369
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• 2009

WiMax, WiBro 등의 무선망에서의 데이터 서비스들은 더 빠른 이동성 확보와 더 높은 데이터 전송 속도의 실현을 목표로 변화와 발전을 계속하고 있다. 이러한 서비스 진화에서는 무선 데이터 통신망에서 가입자의 트래픽 수요를 충족시키고 무선망 구축을 위한 정확한 주파수 소요량 예측이 무엇보다 중요하다. 따라서 본 논문에서는 기존기술 연구의 문제점을 분석하여 데이터 서비스를 위주로 하는 이동 통신망의 주파수 소요량 산출시 고려해야 할 핵심 요소들을 제안하였다. 그것은 첫째 데이터 트래픽의 자기 유사성 특징, 둘째, QoS(Quality of Service)가 고려된 처리용량, 셋째, 기지국 부하율의 비균일 특성, 그리고 마지막으로 FA 증설구조이다. 또한 데이터 서비스를 위주로 하는 이동통신 망에서는 이러한 핵심 요소들을 적용하여 주파수 소요량 산출 표준 모델을 제안하였다.