• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1371-1382
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• 2000

IMT-2000 system is the third generation mobile communication system which aims at mobile multimedia services with global roaming. Like 2nd generation system, the IMT-2000 system is also under strong influence of interferences among active subscribers in the multiple access environment. That is, in multiple access environment, signals from one subscriber could interfere with others in the same cell or in the neighboring cells. The interference control in the IMT-2000 systems is much more difficult then the interference control in the 2ndgeneration CDMA cellular systems, since the transmitted power of a subcriber might be different that of others in the IMT-2000 system. In this paper, a parallel interference cancellation with traffic discrimination is proposed which can effectively cancel interferences by grouping the subscribers into several equi-power classes. As a conclusion, simulation results show that the proposed method outperforms the conventional partial PIC scheme in several aspects.

• Electronics and Telecommunications Trends
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• v.27 no.2
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• pp.70-79
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• 2012

스마트폰 사용이 활성화되면서 모바일 데이터 사용량이 급증하고 WiFi뿐만 아니라 펨토셀을 포함한 소형셀(small cell) 인프라가 각광을 받고 있다. 이에 따라, 가정 또는 사무실과 같은 실내에서 음영 지역을 해소하고 한정된 주파수 자원을 효율적으로 사용하여 대용량 데이터 전송 서비스를 가능하게 하는 초소형 기지국 연구에 대한 요구가 많아지고 있다. 또한, 이동통신 기지국의 신규 설치 시 기지국 자체적으로 또는 인접한 기지국 간의 자동 협업을 통하여 기지국 간 간섭을 최소화하고 기지국의 용량을 증대시켜서 셀 커버리지를 최적화하는 기술에 대한 연구가 필요하게 되었다. 이를 위한 방안으로 셀 반경을 극도로 줄여 댁내 또는 소규모 비즈니스 환경에 알맞은 무선 환경을 제공하려고 하는 펨토셀 서비스는 보다 나은 무선 환경을 필요로 하는 사용자 요구에 적극 대응하고, 사업자의 사업 기회를 확대하며, 서비스의 질적 양적 개선 측면에 있어서 가장 중요하게 고려해야 할 기술이다. 본고에서는 SON(Self Organizing Networks) 및 펨토셀 관련 주요 기술적 이슈를 정리하고 현재 진행되고 있는 기술동향에 대하여 살펴 보고자 한다.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.291-292
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• 2008

In orthogonal frequency division multiplexing based wireless system, a pilot signal is often employed to estimate channel state information (CSI). However, the received pilot signal is interfered by other cell interference in multi-cell environments. We consider the estimation of CSI by utilizing orthogonal preambles and channel correlation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5C
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• pp.527-539
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• 2009

In this paper, we propose an asynchonous ICI (Inter-Cell Interference) mitigation techniques for 3GPP LTE MIMO-OFDMA down-link receiver. An increasing in symbol timing misalignments may occur relative to sychronous network as the result of BS (Base Station) timing differences. Such symbol synchronization errors that exceed the guard interval or the cyclic prefix duration may result in MAI (Multiple Access Interference) for other carriers. In particular, at the cell boundary, this MAI becomes a critical factor, leading to degraded channel throughput and severe asynchronous ICI. Hence, many researchers have investigated the interference mitigation method in the presence of asynchronous ICI and it appears that the knowledge of the SCM (Spatial Covariance Matrix) of the asynchronous ICI plus background noise is an important issue. Generally, it is assumed that the SCM estimated by using training symbols. However, it is difficult to measure the interference statistics for a long time and training symbol is also not appropriate for MIMO-OFDMA system such as LTE. Therefore, a noise reduction method is required to improve the estimation accuracy. Although the conventional time-domain low-pass type weighting method can be effective for noise reduction, it causes significant estimation error due to the spectral leakage in practical OFDM system. Therefore, we propose a time-domain sinc type weighing method which can not only reduce the noise effectively minimizing estimation error caused by the spectral leakage but also implement frequency-domain moving average filter easily. By using computer simulation, we show that the proposed method can provide up to 3dB SIR gain compared with the conventional method.

• Journal of Advanced Navigation Technology
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• v.16 no.6
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• pp.988-996
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• 2012

Assuming perfect channel state information (CSI), the conventional interference alignment (IA) algorithm in the uplink cellular system suppresses inter-cell interference (ICI) by aligning ICI to a randomly selected reference vector. However, IA in practice relies on limited feedback between base stations and users, resulting in residual ICI. In this paper, we propose the optimization of the reference vector that minimizes the upper-bound of residual ICI power. Secondly, the iterative IA that designs the direction of transmit and receive filter is proposed to minimize the residual ICI as well as maximize the desired signals. Moreover, we propose the user scheduling method combined with proposed IA schemes which provides the multiuser diversity gain in multi-cell environments. Finally, the performance gain of the proposed IA algorithms compared with the existing IA are analyzed and demonstrated by simulation results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.7
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• pp.1424-1432
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• 2015

As the wireless communication technologies are being studied for application to maritime communication networks in a fusion of marine industries and IT technology, interference coordination techniques have been studied in the maritime heterogeneous networks. In this paper, we develop a simulator for measuring, verifying and evaluating performance of a maritime heterogeneous network. Unlike other previous simulators, the developed simulator applies enhanced inter-cell interference coordination (eICIC) that are being introduced in the 3GPP Release 10 for mitigating the cross-tier interference between ships. Furthermore, we investigate the effects of almost blank subframes (ABS) and cell range expansion (CRE) on the throughput of small cells in maritime heterogeneous networks by using the developed simulator.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.957-966
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• 1998

In this paper an imrpoved Signal-to-Interference ratio(SIR)-based call admission control(CAC) algorithm for DS-CDMA cellular system is proposed and its performance is analyzed. This algorithm uses Residual-Capacity defined asthe additional number of initial calls that a base station can accept such that system-wide outage probability will guaranteed to remain below a certain level. the residual capcity at each cell is calculated according to the reverse-link SIR measured not only at the home cell but also the adjacent cells. Then the adjacent cell interference-coupling coefficient .betha. is used. In this work we propose an improved algorithm that .betha. varies according to the traffic load of the home cell. The influence of traffic condition on system performance, namely blocking probability and outage probability, is then examined via simulation. The performance of the improved algorithm is evaluated both under homogeneous and hot spot traffic loads. The results show that the improved algorithm outperforms conventional algorithms under all load values. Under over-load situation, especially, the improved algorithm gives almost constant outage performance the QoS(quality of service) can be guranted.

• Electronics and Telecommunications Trends
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• v.24 no.3
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• pp.32-43
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• 2009

가정 또는 사무실과 같은 실내의 음영지역을 해소하고 한정된 주파수 자원을 효율적으로 사용하여 다수의 사용자에게 보다 좋은 무선 환경을 제공함으로써 대용량 데이터 전송 서비스를 가능하게 하는 초소형 기지국 연구에 대한 요구가 많아지고 있다. 이에 따라 이동통신 기지국의 신규 설치시 기지국 자체적으로 또는 인접한 기지국간의 자동 협업을 통하여 기지국간 간섭을 최소화하고 기지국의 용량을 증대시켜서 셀 커버리지를 최적화하는 기술에 대한 연구가 필요하게 되었다. 이를 위한 방안으로 셀 반경을 극도로 줄여 댁내 또는 소규모 비즈니스 환경에 알맞은 무선환경을 제공하려고 하는 펨토셀 서비스는 보다 나은 무선 환경을 필요로 하는 사용자 요구에 적극 대응하고, 사업자의 사업기회를 확대하며, 서비스의 질적 양적 개선 측면에 있어서 가장 중요하게 고려해야 할 기술이다. 본 고에서는 이러한 펨토셀 관련 주요 기술적 이슈를 정리하고 현재 진행되고 있는 기술 동향에 대하여 살펴보고자 한다.

• Information and Communications Magazine
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• v.26 no.11
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• pp.29-35
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• 2009

가정 또는 사무실과 같은 실내의 음영지역을 해소 하고 한정된 주파수 자원을 효율적으로 사용하여 다수의 사용자에게 보다 좋은 무선 환경을 제공함으로써 대용량 데이터 전송 서비스를 가능하게 하는 초소형 기지국 연구에 대한 요구가 많아지고 있다. 이에 따라, 이동통신 기지국의 신규 설치 시 기지국 자체적으로 또는 인접한 기지국간의 자동 협업을 통하여 기지국간 간섭을 최소화하고 기지국의 용량을 증대시켜서 셀 커버리지를 최적화하는 기술에 대한 연구가 필요하게 되었다. 이를 위한 방안으로 셀 반경을 극도로 줄여 댁내 또는 소규모 비즈니스 환경에 알맞은 무선환경을 제공하려고 하는 펨토셀 서비스는 보다 나은 무선 환경을 필요로 하는 사용자 요구에 적극 대응하고, 사업자의 사업 기회를 확대하며, 서비스의 질적 양적 개선 측면에 있어서 가장 중요하게 고려해야 할 기술이다. 본 고에서는 이러한 펨토셀 관련 주요 기술적 이슈를 정리하고, 현재 진행 되고 있는 표준화 현황 및 기술 동향에 대하여 알아본다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.1A
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• pp.58-66
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• 2011

In this paper, we propose a self-organized frequency allocation scheme for femto-cell deployment to avoid intercell interference, thereby reducing cell-registration failure. The proposed scheme follows two steps which if necessary manipulate frequency-band reallocation of existing femto-cells to accomodate newly incoming femto-cells. In the first step named "initial frequency allocation", each femto-cell collects neighboring femto-cells' frequency usage state by listening the broadcasting channels, and then selects one of interference-free frequency-bands. If no inference-free band is available, the second step named "frequency adjustment" starts, where frequency-band reallocation is properly performed from the aspect of overall performance improvement. Numerical results shows that the proposed scheme outperforms the best SINR scheme, which has been practically applied to femto-cell deployment, in terms of cell-registration failure probability and system overhead.