• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.10
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• pp.865-873
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• 2013

In the cellular networks adopting femtocells, the macrocell users can suffer from severe interference by the femtocells. In this paper, we propose a distributed transmission power control scheme for femtocells to protect macrocell users. With the proposed scheme, when a macrocell user experiences outage due to severe interference, it informs the interfering femtocell base station (BS) of the outage occurrence, via the macrocell BS. Then, the femtocell BS reduces the transmission power to protect the macrocell user. The proposed scheme does not require too much control information among the macrocell BS, the macrocell users, and the femtocell BS. Moreover, the computational complexity in femtocell BS is very low. By using simulation, we show that the performance of the proposed scheme is good enough to use in practice, in spite of its simplicity.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.6
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• pp.9-21
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• 2013

Tracking is a process which explores user equipment (UE) in the area of tracking in terms of cells. In this paper, two tracking schemes based on macrocell-microcell tiers in hierarchical LTE networks, PMMT and IMMT, are evaluated. In this network, UE can receive a signal from macrocells and overlapping microcells, and can be called from each macrocell or microcell-tier in the PMMT. Also, the UE can be called from the combined macrocell-tier and microcell-tier in the IMMT. Finally, we analyze the optimization of load balance between marcocell-tier and microcell-tier, and an analytical model is developed to evaluate those two arrangements.

• 전자공학회논문지 IE
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• v.43 no.1
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• pp.39-45
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• 2006

The increment of user at mobile communication system requires the need of increased system capacity. To increase the system capacity can be realized by decreasing the size of cell. But, this method causes various problems. Therefore, it be used the hierarchical cellular system with macrocell and microcell for a efficient working. The users feel more inconvenience about the drop of connected call than the block of new call. Therefore, it is to be desired that the dropping rate of handoff call is lowered. At this paper, we use non reversible hierarchical scheme and fixed channel assignment scheme at the hierarchical cellular system with macrocell and microcell for the call process strategy. We analyze the system performance in accordance with the number of guard channel for handoff.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.1
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• pp.50-61
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• 2014

Operating small cell with existing macro cell is of interest in wireless communication technology to enhance network capacity. Closed-access small cell allows the access of users registered in it and causes severe interference to nearby users connected to macrocell. We propose a dynamic channel allocation for small cells in the same building that first aim to minimize call-drop of the nearby macrocell users, and then want to reduce interferences between the small cells. Since the interference effect of small cells on the nearby macrocell users mainly depends on the small cells' position, the proposed algorithm includes a self-configuration to flexibly allocate frequency channels according to the variation of downlink quality of the macrocell users. Furthermore the algorithm is very simple and practical, which is main contribution of this paper. We observe that the proposed algorithm provides 82-94% of maximum achievable throughput.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.5
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• pp.451-458
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• 2013

This paper proposes a cross-tier interference avoidance scheme to improve femtocell performance in single frequency heterogeneous cellular networks (SFHCN). The scheduled macrocell users located close femtocell base stations cause serious interference to those femtocells so that the performance of femtocell is dramatically deteriorated. To solve this problem, this paper proposes an interference avoidance scheme by reversing the uplink and downlink frames of such femtocells. After reversing the uplink and downlink frames, femtocell base station relays the macrocell user data as well as transmitting its own data. In the 1st relaying link, femtocell and macrocell users transmit their data respectively divided uplink frames and in the 2nd relaying link, femtocell base station transmit macrocell and femtocell data using a simultaneously superposition coding scheme. Computer simulation results confirm performance improvement of proposed scheme.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.1
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• pp.73-81
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• 2007

This paper analyzes the performance of the handover in an overlaid micro/macro cellular system suited for mobile communication environments. In proposed model, it is analyzed the performance of case that subscriber who move with high speed does handover to a macrocell instead of doing handover by microcell. For an easy analysis, a circle shaped cell model are assumed both in microcell and macrocell. The reservation channel scheme is adopted in microcell for a low-speed mobile while a scheme using queue is used in macrocell for a high-speed mobile. The analytic results show that the proposed scheme provides a lower handover failure relatively than in a non-overlaid cellular system with slightly increased new call blocking probability.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.4
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• pp.79-86
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• 2006

This study was investigated to corrosion resistance of Cr-bearing rebars to macrocell corrosion caused by concrete with crack. Ten types of steel bars having different Cr contents were embedded in concretes with imitation crack. The corrosion resistance of the Cr-bearing rebar was examined by measuring half-cell potential, macrocell corrosion current, corrosion area and weight loss up to 105 cycles of salt spray testing. The results revealed that the Cr content required for corrosion resistance in a macrocell corrosion environment caused by chloride ion gap of $3kg/m^3$ was 9% or more. The corrosion-resisting performance of Cr-bearing rebar was particularly noticeable with a Cr content of 11% or more.

• Proceedings of the Korea Information Processing Society Conference
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• 2015.10a
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• pp.325-326
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• 2015

스몰셀은 저전력으로 단거리에 작동하는 기지국을 설치하는 기술로서 저렴한 비용으로 매크로셀의 커버리지 확대와 트래픽 분산을 위한 해결책으로 주목받고 있다. 하지만, 스몰셀의 운영은 기존 매크로셀 구조의 변화를 야기함으로써 여러가지 문제점들을 발생시킨다. 이에 본 논문에서는 매크로셀 유저에게 허용된 오수신 확률을 보장하면서 최대의 전력을 할당할 수 있는 전력 할당 기법을 제안하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.5
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• pp.280-292
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• 2014

Recently, heterogeneous networks consisting of small-cells on top of traditional macro-cellular network has attracted much attention, because traditional macro-cellular network is not suitable to support more demanding mobile data traffic due to its limitation of spatial reuse. However, due to the transmit power difference between macro- and small-cells, most users are associated with macro-cells rather than small-cells. To solve this problem, enhanced inter-cell interference coordination (eICIC) has been introduced. Particularly, in eICIC, the small-cell coverage is forcibly expanded to associate more users with small-cells. Then, to avoid cross-tier interference from macro-cells, these users are allowed to receive the data during almost blank subframe (ABS) in which macro-cells almost remain silent. However, this approach is not sufficient to balance the load between macro- and small-cells because it only expands the small-cell coverage. In this paper, we propose a load balance scheme improving proportional fairness for heterogeneous networks employing eICIC. In particular, the proposed scheme combines the greedy-based user association and the ABS rate determination in a recursive manner to perform the load balance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.12A
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• pp.1806-1814
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• 2000

본 논문에서는 CDMA 계층구조 셀룰러 시스템에서 매크로 셀 기지국과 통신을 하는 고속 이동국과 마이크로 셀 기지국과 통신을 하는 저속 이동국의 비 그리고 소프트 핸드오프 영역 비에 따른 기지국이 받는 간섭전력과 시스템 용량을 구하였다. 매크로 셀 기지국과 통신을 하는 고속 이동국이 마이크로 셀 기지국과 통신을 하는 저속 이동국보다 많을수록 기지국이 받는 간섭전력은 증가하며 따라서 시스템 용량은 감소한다. 그러나 소프트 핸드오프 영역의 증가로 기지국이 받는 간섭전력은 감소하명 시스템 용량은 상당히 증가한다.