• 한국통신학회논문지
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• 제34권5A호
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• pp.421-428
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• 2009

Inter-cell coordination has been an emerging issue for mitigating inter-cell interference in broadband wireless access networks such as IEEE802.16 and 3GPP LTE (Long Term Evolution). This paper proposes uplink/downlink hybrid inter-cell coordination patterns for a TDD (Time Division Duplex)/MC-CDMA (Multi-Carrier Code Division Multiple Access) system. For the performance analysis, closed forms of inter-cell interferences are derived when uplink and downlink transmissions coexist over a multi-cell environment. In the analysis, we find an optimal ratio of downlink transmit powers of BSs (Base Stations) based on the target outage probability and the performance according to ratios of uplink/downlink transmit powers of MSs (Mobile Stations)/BSs is explored. Our numerical results show that interference mitigation utilizing the characteristics of the uplink and downlink power ratio is very effective in improving system performance in terms of QoS.

• 한국전자파학회논문지
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• 제15권6호
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• pp.627-633
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• 2004

순방향 빔형성은 무선 인터넷, VOD(Video-On-Demand), 멀티미디어 서비스 등이 요구되는 최근의 이동통신시스템에서 아주 중요하다. 본 논문은 스마트 안테나 시스템의 순방향 빔형성 구현에 있어서 간과되어서는 안될 필수 고려사항들을 언급하고 이의 성능을 분석한다. 본 논문에서 고려된 사항으로는 캘리브레이션 방법 및 절차, 보조 파일럿 채널의 개념과 그에 따른 단말기 수신 성능, 기지국 HPA전력 할당, 순방향/역방향 처리율 비교 등으로 이는 순방향 빔형성 구현에 있어서 반드시 알고 설계해야 하는 항목이다.

• 한국정보기술응용학회:학술대회논문집
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• 한국정보기술응용학회 2005년도 6th 2005 International Conference on Computers, Communications and System
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• pp.335-338
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• 2005

In this paper, we propose a downlink power control scheme to apply in the unequal error protection multi-code CDMA mobile medicine system. The mobile medicine system contains (i) blood pressure and body temperature measurement value, (ii) ECG medical signals measured by the electrocardiogram device, (iii) mobile patient's history, (iv) G.729 audio signal, MPEG-4 CCD sensor video signal, and JPEG2000 medical image. By the help of the multi-code CDMA spread spectrum communication system with downlink power control scheme and unequal error protection strategy, it is possible to transmit mobile medicine media and meet the quality of service. Numerical analysis and simulation results show that the system is a well transmission platform in mobile medicine.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 2002년도 춘계공동학술대회
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• pp.144-151
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• 2002

Future wireless communication systems are expected to provide a broad range of multimedia services in which the asymmetry of traffic load between uplink and downlink is a significant feature. The rode division multiple access system with tune division duplex mode (CDMA/TDD) is a good solution to cope with the traffic asymmetry problem. However. the TDD system is subject to inter-cell interference compared to frequency division duplex (FDD) system. Since both uplink and downlink share the same frequency in TDD. uplink and downlink may interfere each other especially when neighboring cells require different rates of asymmetry. Thus, time slot allocation for tells is an important issue in TDD. In this paper. we propose a genetic algorithm based time slot allocation scheme which maximizes the residual system capacity. The proposed scheme allows that each cell employ different level of uplink/downlink asymmetry and satisfies the interference requirement.

• 한국통신학회논문지
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• 제35권1B호
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• pp.20-26
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• 2010

이동통신 환경에서 하향링크 스케줄링 기법은 무선 시스템의 성능을 크게 좌우할 정도로 매우 중요하다. 그러나 무선 시스템에서 가장 잘 알려진 기존의 비례 공평성 (Proportional Fairness: PF) 스케줄링 기법은 사용자 별 무선 채널 품질만을 고려하여 자원을 할당하기 때문에 전송해야할 하향 트래픽 유입량이 많은 사용자의 경우 원활한 전송이 불가능하다. 이를 해결하기위해 전송 대기 큐의 크기를 고려하여 자원을 할당하게 될 경우 전송 대기 큐의 누적으로 인해 낮은 채널 품질을 갖는 사용자에게 자원 할당이 집중되어 전체 시스템 전송률을 저하시킨다. 이에 본 논문에서는 하향 트래픽 유입량을 추가적으로 고려하여 기존 PF 스케줄링 알고리즘을 확장함으로써 낮은 채널 품질을 갖는 사용자의 전송이 지연되는 기존 PF 스케줄링 알고리즘의 문제점을 해결하는 동시에 이로 인해 발생할 수 있는 전체 시스템 전송률 저하 문제를 최소화 할 수 있는 트래픽 유입량 기반 하향링크 스케줄링 알고리즘을 제안한다. 모의실험을 통하여 제안한 알고리즘이 기존 스케줄링 알고리즘의 문제점을 해결하고 높은 성능을 보임을 확인하였다.

• 한국컴퓨터정보학회논문지
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• 제20권9호
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• pp.61-66
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• 2015

We investigate rate scheduling and power allocation problem for a delay constrained CDMA systems. Specifically, we determine an energy efficient scheduling policy, while each user maintains the short term (n time slots) average throughput. More importantly, it is shown that the optimal transmission strategy for the uplink is same as that of the downlink, called uplink and downlink duality. We then examine the performance of the optimum transmission strategy for the uplink and the downlink for various system environments.

• 대한산업공학회지
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• 제29권2호
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• pp.150-156
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• 2003

The IEEE 802.11 MAC (Media Access Control) Protocol supports two modes of operation, a random access mode for nonreal-time data applications processed by Distributed Coordinated Function (DCF), and a polling mode for real-time applications served by Point Coordinated Function (PCF). It is known that the standard IEEE 802.11 is insufficient to serve real-time traffic. To provide Quality of Service (QoS) of real-time traffic, we propose the Downlink-first scheduling with Earliest Due Date (EDD) in Contention Free Period (CFP) with suitable admission control. The capacity and deadline violation probability of the proposed system is analyzed and compared to the standard pair system of downlink and uplink. Analytical and simulation results show that the proposed scheme is remarkably efficient in view of the deadline violation probability.

• Journal of Communications and Networks
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• 제9권3호
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• pp.247-253
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• 2007

In this paper, downlink capacity of time duplex division (TDD) based cellular wireless networks utilizing fixed hopping stations is investigated. In the network, a number of fixed subscriber stations act as hopping transmission stations between base stations and far away subscribers, forming a cellular and ad hoc mobile network model. At the radio layer, TDD code division multiple access (CDMA) is selected as the radio interface due to high efficiency of frequency usage. In order to improve the system performance in terms of downlink capacity, we propose different time slot allocation schemes with the usage of fixed hopping stations, which can be selected by either random or distanced dependent schemes. Performance results obtained by computer simulation demonstrate the effectiveness of the proposed network to improve downlink system capacity.

• Journal of Magnetics
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• 제21권3호
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• pp.330-339
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• 2016

A magnetic field sensing system with a single primary sensor and multiple reference sensors deployed locally and orthogonally, was proposed for downlink signal reception and interference cancelling for Through-the-Earth Communication (TEC). This paper mathematically analyzes a design optimization process for a search coil magnetometer (SCM), and applies that process to minimize the bandwidth of the primary SCM for TEC signal reception and the volume of reference SCMs for multiple distributions. The primary SCM achieves a 3-dB bandwidth of 7 Hz, a sensitivity threshold of 120 fT/${\surd}$Hz, and a volume of $2.32{\times}10^{-4}m^3$. The entire sensing system volume is as small as $10^{-2}m^3$. Experiments with interference from industrial frequency harmonics demonstrated an average of 36 dB and 18 dB improvements in signal-to-interference ratio and signal-to-interference plus noise ratio, respectively, using multichannel recursive-least-squares algorithm. Thus, the proposed sensing system can reduce the interference effectively and allows reliable downlink signal reception.

• 대한전자공학회논문지TC
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• 제41권11호
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• pp.67-72
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• 2004

본 논문에서는 cdma2000-1x FDD 시스템의 순방향 링크 송신 성능 향상을 위해 공통빔(파이럿, 페이징, 싱크 채널)과 개별통화 채널에 대한 진폭과 위상을 정합 시키는 빔 형성 기법을 제안한다. 기존의 기법에서는 상이한 두 채널간의 위상이 정확히 일치함을 가정하여 시스템의 성능이 평가 되었다. 그러나 실제 CDMA 시스템 환경에서는 두 채널간의 위상이 상이할 경우 비트 오율이 심각히 열화 되므로 현실적으로 기존의 제안된 방법은 사용할 수 없다. 따라서 기존의 순방향 빔 형성 기법과 달리 제안된 순방향 빔 형성기법, 즉 공통채널과 통화채널의 크기와 위상을 맞추기 위한 빔합성 기법을 적용하여 기존 방법대비 낮은 비트오율로 양질의 통신이 가능함을 확인하였다.