• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.5A
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• pp.451-458
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• 2006

In this paper, we propose a novel scheduling algorithm for downlink transmission which utilizes scarce wireless resource efficiently in an Orthogonal Frequency Division Multiple Access/Time Division Duplex system. Scheduling schemes which exploit channel information between a Base Station and terminals have been proposed recently for improved performance. Time series analysis is used to estimate the channel state of mobile terminals. The predicted information is then used for prioritized scheduling of downlink transmissions for improved throughput, delay and jitter performance. Through simulation, we show that the total throughput and mean delay of the proposed scheduling algorithm are improved compared with those of the Proportional Fairness and Maximum Carrier to Interference Ratio schemes.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.49-52
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• 2001

본 논문에서는 몬테카를로 기법 및 최소결합손실(MCL : Minimum Coupling Loss)기법을 기반으로 하여 무선통신 서비스간 보호비를 만족시키도록 최적의 보호대역을 자동으로 설정할 수 있는 알고리즘을 개발하고 그 견과를 기술하였다. 여기서 개발된 보호대역 자동 설정 알고리즘은 통계적인 몬테카를로 기법 및 간섭원과 대상 수신기 사이에 간섭이 존재하지 않도록 요구되는 이격도 계산을 위한 최소결합손실기법을 적용하여, 주어진 간섭보호비를 만족할 수 있는 최악의 상황에 대한 보호대역을 먼저 설정한 후 보호대역값을 변화시키면서 희망 수신기에서의 간섭확률을 계산을 통해 최적의 보호대역을 설정할 수 있다. 이 기법은 어떠한 형태의 무선통신 서비스에 대해서도 동시에 두가지의 간섭원이 영향이 미칠 경우에도 적용할 수 있도록 설계되었다. 또한 본 연구에서는 TDD시스템간의 간섭 시나리오를 설정하고, 개발된 보호대역 자동 선정 알고리즘을 사용한 시뮬레이터와 ITU-R에서 개발된 SEAMCAT에 의해 얻어진 보호대역 도출 결과를 비교, 분석함으로써 개발된 알고리즘의 신뢰성을 검증하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9A
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• pp.717-727
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• 2003

The HIPERLAN/2(HIgh PERformance Local Area Network Type2) is one of the wireless LAN standards for providing raw data rates of up to 54 Mbps. The MAC protocol of HIPERLAN/2 is based on TDMA/TDD, and resources in one MAC frame can be allocated dynamically by Access Point(AP). The random channel(RCH) is defined for the purpose of giving a mobile terminal the opportunity to request transmission resources in the uplink MAC frames. It is desirable that the number of RCHs is dynamically adapted by the AP depending on the current traffic situation. Allocation of excessive RCHs may waste radio resources and insufficient RCHs compared to traffic loads may result in many collisions in access attempts. We propose an RCH allocation scheme based on split algorithm in HIPERLAN/2. The simulation and analytic results show that the proposed scheme achieves a higher channel throughput, lower access delay and delay jitter than previously proposed RCH allocation schemes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.4
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• pp.684-690
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• 2003

In this paper, a contention-based reservation access control algorithm and a slot allocation algorithm are proposed for non-real-time bursty traffic services in the wireless ATM networks. In order to reduce the collisions of the reservation request packets, the base station scheduler calculates the transmission probability using the number of RAS minislots and the estimated load of the reservation request packets. And it broadcasts the calculated transmission probability over the downlink control channel. Mobile terminals, which have traffic burst, select randomly a RAS minislot and transmit the reservation request packet by the received transmission probability. The reservation request packet contains the number of packets in the buffer. The slot allocation is based on the buffer status of the received reservation request packets. The base station scheduler allocates slots in proportion to the total number of slots that are requested by each terminal.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.398-398
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• 2009

본 논문에서는 카메라의 원근감을 이용하여 케이블의 모드형상을 추출하는 과정을 제안한다. 제안 기법을 검증하기 위해 디지털 카메라와 캠코더를 이용하여 서로 다른 위치에서 동일 화면을 동시에 촬영하고, 촬영된 영상을 사진 변환프로그램을 통해서 초당 30프레임으로 영상이미지를 추출해 낸다. 추출된 좌.우 영상이미지의 영상좌표를 이용하여 케이블에 부착된 표적의 3차원 위치를 결정한다. 이때 디지털 카메라와 캠코더간의 위치 및 자세는 제안된 종속적 상호표정 방법을 통하여 결정한다. 결정된 케이블의 시간이력으로부터 고유진동수과 감쇠비는 다중 템플릿 매칭 알고리즘(multi-template matching algorithm)기법으로 추출하고, 모드형상은 TDD(Time Domain Decomposition)기법을 통하여 추출한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1A
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• pp.58-64
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• 2009

In this paper, we propose an dynamic random channel allocation scheme increasing probability of channel acquisition and reducing delay by limiting the number of minimum RCHs(Random CHannels) as an optimal factor $\beta$. The MAC protocol of HIPERLAN/2 is based on TDMA/TDD and MT(Mobile Terminal) can obtain chance of traffic transmission through channel competition in RCH period. And AP(Access Point) can dynamically schedule the number of RCHs based on the number of the collision in each RCH of the previous frame. Therefore, the proposed scheme increases a probability of channel acquisition and reduces delay by means of guaranteeing the number of minimum RCHs. With a practical Internet traffic, it is concluded that by the proposed scheme the delay reduction of the order of 19% and slightly better throughput are obtained compared to the conventional algorithm.

• Journal of Digital Contents Society
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• v.7 no.3
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• pp.161-168
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• 2006

Wibro(Wibro - Wireless Broadband Internet ) is a system that can accept effectively the IP-based Wireless data traffic with upward / downward asymmetric transfer characteristic by using a Wirelss broadband transfer technology in OFDMA/TDD (Orthogonal frequency Division Multiple Access/Time Division Duplex). Wibro service should support handover to maintain connection continuously in movement because the service is based on If system which is different from cellular system. Current Micro Mobility system and general Mobile If system has got a problem of delayed speed and lost packets during handover. IETF protocol has been proposed for minimizing this problem and its standardization is under process, mainly focused on Mip4, Mip6 and Mipshop WG. This article studies and analyzes an effective method of minimizing handover delay to improve the problem of WiBro system and its revitalization & outlook.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.8C
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• pp.667-679
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• 2010

The use of femtocells in buildings and homes has been widely studied as a means to enlarge the cell coverage and increase the network capacity of mobile communication systems. Femtocells for Mobile WiMAX (M-WiMAX) using time division duplexing (TDD) requires frame synchronization with neighboring base stations to avoid interference between uplink and downlink signals. In this paper, we propose a new frame synchronization method for femtocell using IEEE 802.11 based wireless backhaul, which transfers the time information of mobile network to femtocells via the beacon signal provided by IEEE 802.11. Also, in order to reduce timing error of the proposed method, we modify the collision avoidance scheme in the transmitter of IEEE 802.11 and apply a timing estimation technique designed in the sense of least squares to the receiver of IEEE 802.11. Through computer simulations using the proposed scheme, we evaluate the performance of frame synchronization for femtocells and show that the recovered timing information satisfies the timing specification defined by M-WiMAX standard.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5B
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• pp.310-316
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• 2005

In this paper, we proposed and evaluated ARAH(Adaptive Random Access algorithm for HIPERLAN/2) to improve system performance. In this paper, HIPERLAN/2 uses OFDM(Orthogonal Frequency Division Multiplexing) modulation scheme to select appropriate PHY mode by Radio Channel Quality, Proposed the ARAH scheme uses these 7 PHY mode when mobile terminal determines the RCH(Random CHannel) number for random access. In this paper, these 7 PHY mode divided into two group, good and bad, and will be given high priority to mobile terminals which are in a good group. In the result of performance evaluation. ARAH algorithm, ARAH has a better performance of throughput and delay than existing algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9A
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• pp.702-709
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• 2003

In this paper, we propose an efficient and QoS-aware MAC scheduling algorithm for Bluetooth, which considers both throughput and delay performance of each Master-Slave pair in scheduling decisions, and thus, attempts to maximize overall performance. The proposed algorithm, MTDPP (Modified Throughput-Delay Priority Policy), makes up for the drawbacks of T-D PP (Throughput-Delay Priority Policy) proposed in [6] and improves the performance. Since Bluetooth employs a master-driven TDD based scheduling algorithm, which is basically operated with the Round Robin policy, many slots may be wasted by POLL or NULL packets when there is no data waiting for transmission in queues. To overcome this link wastage problem, several algorithms have been proposed. Among them, queue state-based priority policy and low power mode-based algorithm can perform with high throughput and reasonable fairness. However, their performances may depend on traffic characteristics, i.e., static or dynamic, and they require additional computational and signaling overheads. In order to tackle such problems, we propose a new scheduling algorithm. Performance of our proposed algorithm is evaluated with respect to throughput and delay. Simulation results show that overall performances can be improved by selecting suitable parameters of our algorithm.