• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권10호
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• pp.4662-4677
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• 2018

The dynamic opportunistic device-to-device (DO-D2D) network will frequently emerge in the fifth generation (5G) wireless communication due to high-density and fast-moving mobile devices. In order to improve the Quality of Experience (QoE) of users with different computing capacity devices in the DO-D2D network, in this paper, we focus on the study of how to reduce the packets retransmission delay and satisfy heterogeneous devices. To select as many devices as possible to transmit simultaneously without interference, the concurrent transmitters-selecting algorithm is firstly put forward. It jointly considers the number of packets successfully received by each device and the device's connectivity. Then, to satisfy different devices' demands while primarily ensuring the base-layer packets successfully received by all the devices, the layer-cooperation instantly decodable network coding is presented, which is used to select transmission packets combination for each transmitter. Simulation results illustrate that there is an appreciable retransmission delay gain especially in the poor channel quality network compared to the traditional base-station (BS) retransmission algorithm. In addition, our proposed algorithms perform well to satisfy the different demands of users with heterogeneous devices.

• ETRI Journal
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• 제37권4호
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• pp.707-716
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• 2015

The purpose of a localization system is to estimate the coordinates of the geographic location of a mobile device. The accuracy of wireless localization is influenced by nonline-of-sight (NLOS) errors in wireless sensor networks. In this paper, we present an improved time of arrival (TOA)-based localization method for wireless sensor networks. TOA-based localization estimates the geographic location of a mobile device using the distances between a mobile station (MS) and three or more base stations (BSs). However, each of the NLOS errors along a distance measured from an MS (device) to a BS (device) is different because of dissimilar obstacles in the direct signal path between the two devices. To accurately estimate the geographic location of a mobile device in TOA-based localization, we propose an optimized localization method with a BS selection scheme that selects three measured distances that contain a relatively small number of NLOS errors, in this paper. Performance evaluations are presented, and the experimental results are validated through comparisons of various localization methods with the proposed method.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.436-441
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• 2006

In recent European telecommunication base transceiver stations(BTS) a membrane laminated air filter is reported to replace a heat exchanger in order to cool internal digital units of BTS. The concept of using the air filter is for the direct ambient cooling(DAC) of BTSs without heat loss generally found ill the heat exchanger type BTS. In the present study, a performance evaluation experiment was conducted to investigate the pressure drop characteristics with dust loading and the particle collection efficiency of the air filter for the DAC of BTS.

• Journal of Communications and Networks
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• 제6권3호
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• pp.226-234
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• 2004

This work presents a deterministic channel that rules according to inverse a power propagation law. The proposed channel model allows us to derive the lower bound and upper bound of packet's capture probability in Rayleigh fading and shadowing cellular mobile system. According to these capture probabilities, we analyze the system performance in the case of finite stations and finite communicated coverage of a base station. We also adopted a dynamic backoff window size to discuss the robustness of IEEE 802.11 draft standard. Some suggestions and conclusions from numerical results are given to establish the more strong CSMA/CA protocol.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 통신소사이어티 추계학술대회논문집
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• pp.251-254
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• 2003

In this paper, we develop an effective method for estimating and predicting interference power strength using the IMM(Interacting Multiple Model) algorithm. Based on the proposed interference prediction algorithm, we adjust transmission power of mobile terminals to maintain a certain level of target signal - to - interference- plus -noise- ratio ( SINR ) at the base station. Results of numerical experiments are presented to show a performance profile of the proposed algorithm.

• 한국통신학회논문지
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• 제28권3A호
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• pp.119-128
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• 2003

A space diversity technique was applied to the conventional optimal beamforming structure using antenna arrays at the base station receiver in the wireless mobile communication system to get performance enhancement due to interference rejection and fading resistance ability of it. To demonstrate the benefit of proposed system, we derived output signal to interference plus noise ratio (SINR) of combined signal from all sub-array groups considering the fading effects and compared with the beamforming-only system. From the analysis and simulation results, we showed that the proposed system can provide high performance gain under Rayleigh fading channel.

• 인터넷정보학회논문지
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• 제11권3호
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• pp.43-51
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• 2010

본 논문에서는OFDMA-TDD 구조를 갖는 IEEE802.16j 기반의 2-홉 셀룰러 중계시스템에서 non-transparent 방식의 무선 중계기를 이용하여 서비스 영역을 확장할 때, 시스템 전송률 및 하향링크 접근영역(Access zone)과 중계영역(Relay zone)에 대한 최적 무선자원 할당방법을 연구한다. 분석을 위해 먼저 non-transparent 방식의 MAC (Media Access Control) 프레임 구조를 알아보고, 접근영역과 중계영역에서 단말과 중계기 등의 네트워크 구성요소들에 대한 간섭요소들을 조사한다. 모의실험을 통하여 기지국과 중계기의 거리에 따라 확장되는 2-홉 셀 커버리지 크기와 전송률을 분석하고, 분석된 결과를 이용하여 하향링크 접근영역과 중계영역에 대한 최적 무선자원 할당량을 제시한다.

• 한국통신학회논문지
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• 제37A권11호
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• pp.986-992
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• 2012

중첩 융합 네트워크 환경 하에서의 무선 이동통신시스템의 성능개선이 급격히 증가하는 무선 트래픽의 처리를 위해 매우 중요한 이슈로 떠오르고 있다. 그러므로 단말기의 기능성이 좋아짐에 따라 스마트한 지능을 기반으로 자원의 효과적 활용에 적합한 개별 이종네트워크의 특성분석과 특성을 반영하는 시스템측면의 최적화가 매우 중요하다고 할 수 있다. 본 논문에서는 기지국의 소형화와 지능화가 진행되는 가운데 기지국 hotelling과 같은 기지국 집중화를 통한 통합적 최적화가 가능하므로 이에 대응한 이중 가상 셀 시스템에 대해 살펴보고 활용도 측면의 특성을 분석하였다.

• 대한임베디드공학회논문지
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• 제1권1호
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• pp.24-30
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• 2006

With the original Transmission Control Protocol(TCP) design, which is particularly targeted at the wired networks, a packet loss is assumed to be caused by the network congestion. In the wireless environment where the chances to lose packets due to transmission bit errors are not negligible, though, this assumption may result in unnecessary TCP performance degradation. In these days, many papers describe about wireless-TCP which has suggested how to avoid congestion control when packet loss over the wireless network. In this paper, an enhancement scheme is proposed by modifying SNOOP scheme. To enhance the original SNOOP scheme, CPC(Consecutive Packet Control) and ZWSC(Zero Window Size Control) are added. The invocation of congestion control mechanism is now minimized by knowing the cause of packet loss. We use simulation to compare the overhead and the performance of the proposed schemes, and to show that the proposed schemes improve the TCP performance compares to SNOOP by knowing the cause of packet loss at the base station.

• 한국정보통신학회논문지
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• 제5권5호
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• pp.923-930
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• 2001

본 논문은 최근 급속히 증가되고 있는 무선 인터넷에서 발생되는 Short Traffic 서비스의 성능을 향상시키기 위하여, TCP 프로토콜의 폭주제어 알고리즘을 보완하는 응답패킷 분할 기법(SPACK)을 제안하였다. 유선통신 환경과는 달리 무선통신 환경에서는 높은 비트 오류율로 인하여 TCP 프로토콜의 폭주제어 알고리즘이 오동작을 일으키게 된다. 이로 인하여 TCP 프로토콜의 성능은 급격히 저하되어 전체적인 인터넷 서비스의 성능이 떨어지게 된다. 본 논문에서는 이러한 TCP 프로토콜을 성능을 개선시키기 위해 기지국에서 응답패킷을 분할하여 전달하는 SPACK 기법을 제안하였다. 제안된 기법은 컴퓨터 시뮬레이션을 통하여 성능을 분석하였으며, 그 결과 기존의 TCP 프로토콜에 비하여 SPACK을 이용하는 경우 더 높은 성능이 발휘됨을 확인하였다.