• Journal of Communications and Networks
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• v.6 no.2
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• pp.106-111
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• 2004

The uplink capacity and the interference statistics of the sectors of the cigar-shaped W-CDMA microcells are studied. A model of 9 base station, assumed to be in a long tunnel, is used for the uplink analysis. The capacity and the interference statistics of the microcells are studied for different sector ranges, different propagation exponents, different antenna sidelobe levels, and different bend losses.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3B
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• pp.153-160
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• 2007

Placing antennas of low power base stations below surrounding buildings, as in urban microcells, makes propagation characteristics strongly dependent on the building environment. As a result, propagation in these urban microcells is non-isotropic, so that the assumption of circular cells used in planning of conventional cellular sys toms is no longer valid. Assuming circular cells leads to a more conservative system design, implying more base stations. This work investigates the effect of cell shape, due to non-isotropic propagation, on the out-of-cell interference and Erlang capacity of CDMA system. Propagation is described by measurement derived models for low antennas in a rectangular urban street grid. The analysis is done for soft handoff protocols.

• Journal of Korean Institute of Industrial Engineers
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• v.26 no.2
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• pp.155-164
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• 2000

Recently Fiber-optic Micro-cellular Wireless Network is considered to solve frequent handoffs and local traffic unbalance in microcellular systems. In this system, central station which is connected to several microcells by optical fiber manages the channels. We propose an efficient sectorization algorithm which dynamically clusters the microcells to minimize the blocked and handoff calls and to balance the traffic loads in each cell. The problem is formulated as an integer linear programming. The objective is to minimize the blocked and handoff calls. To solve this real time sectorization problem the Tabu Search is considered. In the tabu search intensification by Swap and Delete-then-Add (DTA) moves is implemented by short-term memory embodied by two tabu lists. Diversification is considered to investigate proper microcells to change their sectors. Computational results show that the proposed algorithm is highly effective. The solution is almost near the optimal solution and the computation time of the search is considerably reduced compared to the optimal procedure.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1999.10a
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• pp.49-49
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• 1999

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1998.10a
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• pp.182-185
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• 1998

In the two-tier CDMA cellular system with microcells and overlaying macrocells, slow-moving mobile user are assigned to microcells and those who move fast are assigned to overlaying macrocells in order to minimize the total number of handoffs. With this consideration the problem is how to find the thresholds by which the system distinguishes fast-moving user from those who move slowly based on the estimated speed of users. In this paper, two methods for the mobile speed estimation are proposed and two operations schemes for micro-macro cellular CDMA system are suggested. Based on these, Optimization models to find the optimal thresholds for micro-macrocell selection, which are subject to the constrains of QoS, are developed in view of minimizing the weighted total number of handoffs. And then algorithms to find optimal solutions of the models are devised.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.9
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• pp.2494-2504
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• 1996

This paper describes about the spread specturm radio wave propagation characteristics in urban microcells. The experiments are carried out with respect to the mean excess delay, the RMS delay spread, and the received maximum peak power in the two kinds of geogrphical areas, LOS area and N-LOS area, especially whose variations are observed while varying the transmission distance and tilting the transmitting antenna. The typical results obtained in pariticular urban sites in Seoul are 300-600 nsec of mean excess delay and about 75 nsec of averaged RMS delay spread for LOS area, and 270-280 nsec of mean excess delay and about 100 nsec for N-LOS area. With the transmitting antenna gilted, obsered in the experiments are increase in RMS delay spread as expected, but increase of the received power at N-LOS areas in particular.

• Journal of the Korean Operations Research and Management Science Society
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• v.26 no.2
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• pp.1-11
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• 2001

This paper considers the scheduling of cell-based handoffs to balance the traffic in a fiber-optic microcelluar system. In the system depending on the order of cell based handoff, periodical balancing of the traffic among microcells can be achieved. The cell based handoff problem is formulated as a dynamic programming and the computational complexity is analyzed. Since the scheduling problem requires real time solution, heuristic algorithms are proposed and the computational results are discussed.

• Journal of the Korea Society for Simulation
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• v.7 no.2
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• pp.63-78
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• 1998

The hierarchical cell structure consists of the macrocell and microcells to increase the system capacity and to achieve broad coverage. The hierarchical cell structure provides services for users in different mobility. In this paper, an analytical queueing model in mobile networks is proposed for the performance evaluation of the hierarchical cell structure. The model for networks with the multiple levels can simplify multi-dimensional ones into one-dimensional queueing model. The computational advantage will be growing as the layers are constructed in multiple levels. The computer simulation is provided for validating the proposed analytical model.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.275-278
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• 2002

본 논문에서는 한국의 전파환경을 도시 계획법에서 지정한 지역세분을 기초로 4개의 대분류와 8개로 소구분하여 Kor-231 모델을 제안하였다. 전파전파 특성을 측정하기 위해 슬라이딩 코릴레이션 기법을 이용한 대역확산 송${\cdot}$수신 방식으로 구현하여 수신전력, 평균 초과지연 그리고 RMS 지연확산을 가장 도시계획적으로 개발된 공업 지역과 주거지역에서 직선 도로에 마이크로셀을 배치하여 도로를 따라 진행하는 LOS와 건물들로 둘러쌓인 N-LOS에서 측정된 데이터를 분석하여 한국의 전파환경에서 잘 적용됨을 확인 하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.1
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• pp.43-51
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• 2015

Upcoming cellular networks such as LTE-advanced and IEEE 802.16m are enhanced by relay stations to support high data rate multimedia services and minimize the shadow zone with low cost. Enhancing the relay stations, however, divides the multihop cellular network into smaller microcells and the distance between microcells is closer, which intends large intra-cell and inter-cell interference. Especially the access link on downlink in the OFDMA cellular network is the throughput bottleneck due to the severe interference caused by base stations and relay stations transmitting large data to mobile stations simultaneously. In this paper, we present interference aware channel allocation algorithm to avoid severe interference on multihop cellular networks with random topology. Proposed algorithm increases SINR(signal to interference plus noise ratio) and decreases number of required control messages for channel allocation, so that increases overall throughput on the networks.