• Proceedings of the KAIS Fall Conference
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• 2011.12b
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• pp.573-576
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• 2011

최근 전국 지방자치단체 관내 마을 단위 근거리 방송에 기존의 케이블 형태의 유선방송이 아닌 무선통신을 사용하고자 하는 수요가 늘고 있다. 이에 본 논문에서는 국내원천 기술인 Binary CDMA 기술을 활용하여 마을단위 원격 방송 및 관제 시스템을 상용화하기 위한 방법들을 제시한다. 주요 연구 내용은 마을단위 환경에 운용될 수 있도록 다중액세스 기술, TDMA 기반의 스케쥴링 기술, 통신거리 확장을 위한 릴레이 기술, 동적 채널 할당 기술이다. 위의 기술들을 활용하여 다양한 마을의 형태에 따라 네트워크 토폴로지 운용이 가능하고 QoS를 보장하는 시스템을 구현할 수 있다.

• 한국정보통신설비학회:학술대회논문집
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• 2003.08a
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• pp.25-28
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• 2003

본 논문은 Ka 밴드(26.5GHz-40GHz)를 사용한 양방향 멀티미디어 시스템의 설계에 대해서 다루고 있다. 우선 무궁화 3호 위성을 이용한 시범사업의 구성 및 운영과정에 대해서 개괄하고, 시범운영에서 발견된 문제점을 소개한다. Ka 밴드 양방향 위성 시스템은 MF-TDMA(Multi-Frequency Time Division Multiple Access) 방식을 사용하여 최대 전송속도 2Mbps 이상이고, QOS(Quality of Service) 제공 등 다양한 기능을 갖추고 있으나 Ka 주파수 특성상 그 안정성에 있어서 어려움을 갖고 있다. 강우감쇄 및 전송 지연 등의 현상들을 소개하고 향후 위성 양방향 시스템의 구성과 응용 서비스를 구현할 때 고려해야 할 사항들에 대해 고찰해 보고, 해결방안을 제시하였다.

• Journal of Communications and Networks
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• v.7 no.3
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• pp.284-293
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• 2005

A critical issue in applications involving networks of wireless sensors is their ability to synchronize, and mitigate the fading propagation channel effects. Especially when distributed 'slave' sensors (nodes) reach-back to communicate with the 'master' sensor (gateway), low power cooperative schemes are well motivated. Viewing each node as an antenna element in a multi-input multi-output (MIMO) multi-antenna system, we design pilot patterns to estimate the multiple carrier frequency offsets (CFO), and the multiple channels corresponding to each node-gateway link. Our novel pilot scheme consists of non-zero pilot symbols along with zeros, which separate nodes in a time division multiple access (TDMA) fashion, and lead to low complexity schemes because CFO and channel estimators per node are decoupled. The resulting training algorithm is not only suitable for wireless sensor networks, but also for synchronization and channel estimation of single- and multi-carrier MIMO systems. We investigate the performance of our estimators analytically, and with simulations.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.5
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• pp.68-75
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• 1994

A new Predistortor that is designed using Feedforward type is proposed to overcome the nonlinearity of HPA (High Power Amplifier). HPA has the nonlinearity of the gain compression and phase distorton, so digital communication system of multi-carrier TDMA needs the linear RF transmitter. Using IMD (Intermodulation Distortion) of drive amplifier, as Feedforward type, the inverse IMD is coupled to the main loop with variable attenuators, phase shifters, and sub-amplifiers well designed. At the input of main amplifier, the over-coupled IMD surpresses the main amplifier 's IMD. Adjusting the level and phase of IMD at the sub loop, C/I of HPA is better than before correction.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.428-433
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• 2000

The characteristics of unsteady heat transfer and boundary layer flow in the SSME turbine rotor passage are investigated with LRN $k-{\varepsilon}$ turbulence model. The unsteady flow and heat transfer in a rotor blade passage as a result of wake/blade interaction is modeled by the inviscid/boundary-layer flow approach. The relevant governing equations are discretized to a system of finite different equations by means of a BTBCS implicit method. These equations have been solved numerically, for the velocity and temperature fields using TDMA method. Heat flux on the blade surface and flow parameters in the rotor passage are calculated with wake interaction. Numerical results show that velocity, pressure, turbulent kinetic energy and heat flux on the blade surface are varied periodically by wake passing.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.1
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• pp.15-22
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• 2013

In oceanic flight routes, HF radio and satellite data links have weather restrictions, long propagation delay and low data throughput. In this paper, we propose oceanic aeronautical communications scheme in the VHF band based on ad-hoc communication. The proposed scheme organizes autonomously a multi-hop network that is divided into multiple local network using aircraft to fly long-distance communication and supports a hybrid type of multiple access, which consists of random access and TDMA (Time Division Multiple Access) scheme. In addition, several algorithms to apply spatial reuse of transmission to multi-hop long range communication environments have been proposed. The proposed system proves performance improvement on delay time as an effective solution to communicate end-to-end on the oceanic flight routes and strengthens the reliability of oceanic aeronautical communication.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.4
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• pp.116-124
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• 2011

For Binary CDMA network, communication can be accomplished only within a Pico-net on the boundary of management by the master station because it manages network resources of each entity. In this research, we try to overcome these limits and extend the application for Binary CDMA system to broad-band network. We suggest a new Binary CDMA router such that network is devised by cell unit and multiple Pico-net and a unique address is assigned to each Pico-cell to relaying data between Pico-cells.

• Journal of the Korea Institute of Military Science and Technology
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• v.15 no.5
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• pp.623-629
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• 2012

In this paper, we analysis the performance of position estimation when adopting Dynamic TDMA(DTDMA) in JTIDS RelNav. JTIDS RelNav is widely understood as a new navigation solution possibly capable to support or take cover of the role of conventional systems including INS or GPS no matter if they are working well or not. By maximizing the efficiency of radio resource management in MAC(Medium Access Control) layer we enhance the system performance without any replacement of hardware.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.1-6
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• 2008

TDM-PON has a disadvantage that entire PON system gets into trouble when only one ONU is out of order and sends optical signal constantly. This paper suggests a scheme to find the fault location. TDMA is impossible when upstream traffic is interrupted by continuous wave signal from a troubled ONU. Therefore, CDMA coding is introduced in separating fault ONUs, and detection algorithm is verified.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.34-43
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• 2007

In the IEEE 802.15.3 Medium Access Control (MAC) protocol, Simultaneously Operating Piconets (SOPs) are linked by the parent/child (P/C) or parent/neighbor (P/N) configuration, which work on a Time Division Multiple Access (TDMA) basis. This provides interference mitigation but the overall throughput is limited because the SOPs share the channel time exclusively. The protocol is not efficient for SOPs if we focus on the combination of interference mitigation and high throughput maintenance. In this paper Public Channel Time Allocation (Public CTA) is proposed, which is able to greatly reduce the inter-piconet interference (IPI) and achieve greater throughput without much loss of link success probability (LSP) in the SOPs. The simulation results based on the SOPs of Direct Sequence Ultra Wideband (DS-UWB) system demonstrate that the proposed scheme effectively supports the coexistence of SOPs, and it can not only significantly improve the overall throughput of SOPs but also maintain high LSP.