• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.1
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• pp.183-189
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• 2018

This paper proposes distributed file placement and coverage expansion techniques for mitigating the traffic bottleneck in backhaul for small-cell networks. In order to minimize the backhaul load with limited memory space, the proposed scheme controls the coverage and file placement of base station according to file popularity distribution and memory space of base stations. In other words, since the cache hit ratio is low when there is small memory capacity or widespread file popularity distribution, the base stations expand its coverage and cache different set of files for the user located in overlapped area to exploit multiple cached file sets of base stations. Our simulation results show that the proposed scheme outperforms the conventional cache strategy in terms of network throughput when there is small memory capacity or widespread file popularity distribution.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.12
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• pp.2806-2811
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• 2013

New technologies such as multi-antenna and small cell were proposed as key technology for the next generation mobile system to cope with the explosively increasing mobile data traffic. In particular, heterogeneous mobile communication network which can improve spatial reuse factor by exploiting macro and small cells simultaneously is attracting attention. However, the heterogeneous network has a problem that the utilization of small cells becomes low because the transmit power of macro base stations is much higher than that of small base stations and then the probability that mobile stations are attached to the macro base stations becomes high. This problem is dominant in uplink. The concept of cell range expansion bias to mitigate the problem was proposed by 3GPP and the corresponding standardization is in progress. In this paper, we analyze the downlink performance of the heterogeneous mobile communication network based on a system level simulator with the cell range expansion bias in terms of average cell spectral efficiency.

• Information and Communications Magazine
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• v.32 no.4
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• pp.72-79
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• 2015

이동셀은 최근 급증하고 있는 모바일 트래픽을 수용함과 동시에 사용자 중심의 유연한 네트워크를 구성하기 위한 이동형 기지국이다. 본 고에서는 이동셀의 필요성과 그 개념을 소개하고, 인접한 이동셀 간 데이터 및 제어 정보의 교환을 제공하는 이동셀의 사이드홀 통신을 설명한다. 또한, 이동형 환경을 고려한 사이드홀 링크 관리 기술을 살펴보고 그 연구 결과를 간략하게 소개한다.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.3
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• pp.32-38
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• 2015

In this paper, we propose a smallcell local caching algorithm under user's context in smallcell environment. The proposed system reduces traffic to core network and the network cost, but increases it's performance. The proposed algorithm precache suitable files using smallcell's regional characteristics and target's personality. It can adjusts a storage allocation to make effective usage of our limited cache storage capacity. In order to evaluate the performance of the proposed cache algorithm, we define the cache efficiency, the decrement of core network traffic. The simulation results show that the proposed algorithm can improve performance by about 200% compared to existing web cache scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.10
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• pp.654-663
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• 2014

Heterogeneous network (HetNet) with the various types of cells, e.g., with the different cell size and transmit power, has been introduced to improve the cell coverage and areal capacity in cellular mobile communication system. In this paper, we consider a practical situation in which all cells share the same wireless resource while some of them have a limited backhaul capacity. More specifically, we formularize a cell association problem that utilizes the minimum wireless resource while satisfying the quality of service (QoS) of all users in terms of their transmission time constraint, and propose a distributed algorithm to find the optimal solution. In the event of bottleneck at the backhaul link in some small cells, the proposed algorithm off-loads some users to the adjacent cell with the less congested backhaul capacity. Finally, we verify that the proposed algorithm supports the more numbers of users to satisfy the specified level of QoS than the conventional user association scheme under the limited access and backhaul capacities.

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

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.5
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• pp.13-18
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• 2016

In Long Term Evolution-Advanced (LTE-A), small cell enhancement(SCE) has been developed as a cost-effective way of supporting exponentially increasing demand of wireless data services and satisfying the user quality of service(QoS). However, there are many problems such as the transmission rate and transmission quality degradation due to the dense and irregular distribution of a large number of small cells. In this paper, we propose a clustering based interference management scheme in dense small cell network. We divide the small cells into different clusters according to the reference signal received power(RSRP) from user equipment(UE). Within a cluster, an almost blank subframe(ABS) is implemented to mitigate interference between the small cells. In addition, we apply the power control to reduce the interference between the clusters. Simulation results show that proposed scheme can improve Signal to Interference plus Noise Ratio(SINR), throughput, and spectral efficiency of small cell users. Eventually, proposed scheme can improve overall cell performance.

• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.162-165
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• 2017

In an effort to compensate the rising of the data throughput demand nowadays, there have been many research works to optimize the radio resource and increase the capacity of the network. At the present, small cell network, mmWave band and beamforming technology are leading the trend and becoming the core solutions of the fifth generation (5G) cellular networks. Since the propagation characteristics of radio wave in the mmWave band is quite different from the conventional bands, the communication systems which work in these bands have to be redesigned. In this paper, a 3D simulation model is discussed for cellular network at 60 GHz in outdoor environments. Coverage analysis and system performance is carried out for a small cell system in the typical urban environment including street canyon simulation scenario. In addition, the beamforming technique is considered to evaluate the throughput improvement. Simulation results show that the mmWave small cell systems is expected to be one of the major candidate technologies to satisfy the requirements of 5G in terms of data rate.

• Information and Communications Magazine
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• v.31 no.7
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• pp.66-72
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• 2014

최근 스마트폰의 보급으로 인해 모바일 데이터 요구량이 급속하게 증가함에 따라 효율적인 기지국 운영이 중요시되고 있다. 현재 기지국은 단말들의 트래픽 요구량에 관계없이 항상 켜져 있지만, 트래픽 요구량이 비교적 낮은 경우 불필요한 기지국의 전원을 오프함으로써 상당한 에너지를 절약할 수 있음이 밝혀졌다. 본고에서는 매크로셀, 릴레이, 소형셀, 무선랜 등 다양한 종류의 네트워크가 혼재하는 환경에서 기지국의 전원을 켜고 끔으로써 에너지를 절약하는 기술의 현황을 알아본다.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.4
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• pp.394-400
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• 2018

A heterogenous network is the one of key technologies for 5G, where one cell is divided into small cells in order to extend coverage and support high data rates. Divided cells aggravates the intercell interference problem as the cell edge increases. In order to avoid the intercell interference, it is the best to allocate the different spectrum for each cells. However, it also decreases the spectral efficiency. Therefore, the trade-off between the spectral efficiency gain and the signal quality loss by the interference should be considered for an efficient spectrum sharing in the heterogenous network. The adaptive modulation is the method to change the transmitted bit according to the channel quality, which is adopted as the standard in the most practical communication systems. It should be considered to applied the performance analysis into the practical systems. In this paper, the overall cell data rates is analyzed for the heterogenous network under the adaptive modulation. The Monte Carlo simulation results verify the correctness of the analysis.