• 정보와 통신
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• 제6권4호
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• pp.65-73
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• 1989

• 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.

• 한국ITS학회 논문지
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• 제17권4호
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• pp.168-180
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• 2018

모바일 디바이스의 보급과 고품질 서비스의 등장으로 모바일 트래픽이 급격히 증가하여, 셀룰러 네트워크의 과부하가 예상된다. 부하를 줄이고 5세대로 진화하기 위한 방안으로는 D2D 통신이 있다. D2D 통신은 단말 간에 직접 통신하기 때문에 셀룰러 네트워크의 과부하를 줄여, 에너지 효율, 데이터 전송률 그리고 네트워크 성능을 향상시킬 수 있다. 본 논문은 셀룰러 네트워크에서 D2D 통신을 위한 D2D 핸드오버 방안을 제안한다. 셀룰러 네트워크는 3GPP EPS이며, 제안하는 D2D 핸드오버 방안은 기존 EPS와 D2D 통신의 호환성을 고려하여 기존 EPS 핸드오버 과정을 개선하였다. 또한 네트워크 시뮬레이터인 ns-3를 사용하여 제안하는 핸드오버 방안의 우수성을 입증하였다. 시뮬레이션 결과는 제안한 핸드오버 방안이 기존 핸드오버 방식에 비해 CUE 변화량, 패킷 전달 지연 시간 그리고 처리량 측면에서 우수하다는 것을 입증하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권2호
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• pp.468-479
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• 2012

Recent advances in wireless communications and electronics has enabled the development of machine-to-machine (M2M) communications. This communication paradigm has been expected as an automated control and report solution for smart grid. The smart grid enables customers and operators to utilize the collected usage information from a large number of meters with transceivers for efficiency and safety. In this paper, we introduce architecture, requirements and challenges of M2M communications for smart grid. We extract technical issues that should be resolved in M2M communications to support the smart grid via third-generation partnership project (3GPP) cellular networks. We then present the current state of the art of research results to deal with such issues. Finally, we outline the open research issues.

• 정보와 통신
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• 제24권2호
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• pp.64-73
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• 2007

Recently, cross-layer design approach has been greatly attracting researchers' attention as an alternative for improving the performance of wireless data networks. The main reason why cross-layer approaches are particularly well suited for wireless networks is that there exists direct coupling between physical layer and upper layers. Therefore, with cross-layer approach, the protocol designers try to exploit the interaction between layers and promote adaptability at all layers, based on information exchange between layers. In this article we focus on the cross-layer engineering for high data-rate mobile Internet services through cellular networks. First, the general considerations in cross-layer engineering are outlined. Then, we discuss the common approach in literatures, which mainly deals with adaptability in physical and medium access control layer. Finally, we show that the cross-layer engineering taking account of all layers is more adequate for the mobile Internet services cellular network.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.1067-1071
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• 2004

In this paper, the performance enhancement algorithm of channel allocation for voice and data transmission in cellular networks is proposed. The voice activity detection has been applied to dynamic channel allocation procedure to detect and separate the silence and speech among conversation periods. Hence a data user can use the silent period of an active voice channel to transmit its information. To control the selecting of channel allocation policies, the information of number of data in transmission waiting queue has been determined in order to accept the performance measurement. In the simulation results, the improvement of the performance shows via the quality of services, which are an average delay in queue, a blocking probability, and an impact of the proposed scheme is presented in the system.

• Journal of Communications and Networks
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• 제18권3호
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• pp.429-438
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• 2016

In this paper, we investigate an interference mitigation scheme by antenna selection in device-to-device (D2D) communication underlaying downlink cellular networks. We first present the closed-form expression of the system achievable rate and its asymptotic behaviors at high signal-to-noise ratio (SNR) and the large antenna number scenarios. It is shown that the high SNR approximation increases with more antennas and higher ratio between the transmit SNR at the base station (BS) and the D2D transmitter. In addition, a tight approximation is derived for the rate and we reveal two thresholds for both the distance of the D2D link and the transmit SNR at the BS above which the underlaid D2D communication will degrade the system rate. We then particularize on the small cell setting where all users are closely located. In the small cell scenario, we show that the relationship between the distance of the D2D transmitting link and that of the D2D interfering link to the cellular user determines whether the D2D communication can enhance the system achievable rate. Numerical results are provided to verify these results.

• Journal of Communications and Networks
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• 제11권3호
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• pp.279-286
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• 2009

This paper proposes an adaptive mode switching algorithm between two strategies in multiple antenna cellular networks:A single-user mode and a multi-user mode for the broadcast channel. If full channel state information is available at the base station, it is known that a multi user transmission strategy would outperform all single-user transmission strategies. In the absence of full side information, it is unclear what the capacity achieving method is, and thus there are few criteria to decide which of the myriad possible methods performs best given a system configuration. We compare a single user transmission and a multi user transmission with linear receivers in this paper where the transmitter and the receivers have multiple antennas, and find that neither strategy dom inates the other. There is instead a transition point between the two strategies. Then, the mode switching point is determined both ana lytically and numerically for a multiple antenna cellular downlink with correlation between transmit antennas.

• 방송공학회논문지
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• 제26권2호
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• pp.197-207
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• 2021

이동통신 시스템 기반의 재난경보 방송으로 CBS가 정의되어 있다. 이 CBS는 제한된 텍스트 문자만을 전송한다. 따라서 외국인 등 국내 문자에 익숙하지 않은 사용자에게 재난경보 기능을 충분히 제공하기 어려운 단점을 보인다. 또한 CBS 프로토콜은 방송 기법을 이용한다. 이러한 방송 기법은 채널 환경의 심각한 열화가 발생할 경우 재난경보 수신에 실패하는 사용자가 증가하는 단점이 있다. 본 논문에서는 5G 이동통신 기반 재난경보 방송인 5G CBS의 수신 성능 향상을 위한 부가 서비스 기법을 제안한다. 그 수신 성능의 향상을 위해 제안된 방식은 5G CBS가 제공 가능한 수신기 기반 지역맞춤 기능을 효과적으로 이용한다.

• 한국전자파학회논문지
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• 제27권2호
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• pp.208-211
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• 2016

단말 간 직접통신(D2D: Device-to-Device) 기술은 지리적으로 근접한 단말들이 네트워크 인프라를 거치지 않고 직접적으로 통신하는 기술이다. 특히 셀룰러 네트워크에서는 D2D 통신이 셀룰러 자원을 공간적으로 재사용함으로써 주파수 이용 효율을 향상시킬 수 있다. 하지만 셀룰러 단말의 채널 시변성 및 그에 따른 자원 할당 변화로 인해 셀룰러 자원을 재사용하는 D2D 단말의 채널 품질을 지속적으로 유지할 수 없고, 셀룰러 단말 또한 간섭에 의해 성능이 열화될 수 있다. 따라서 본 논문에서는 D2D 링크가 셀룰러 네트워크의 상향링크 자원을 재사용하는 상황에서 셀룰러 단말의 채널 변화로 인한 D2D 통신 링크의 성능 열화를 완화하는 방안으로 비면허 대역 주파수 자원을 D2D 통신에 보조적으로 활용하는 기술을 제안한다. 모의실험을 통해 제안한 기술의 효용성을 검증한다.