• Journal of Korea Society of Digital Industry and Information Management
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• v.10 no.1
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• pp.113-120
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• 2014

In this paper, I present a new echo canceller using the adaptive cascade system identification (CSI) method, which a system response is divided into several responses so that each response is adaptively estimated and combined. Echo cancellation is required for a dual-duplex DSL, in order to allow each individual loop to operate in a full duplex fashion. Echo cancellation was one of the most difficult aspects of DSL design, requiring high linearity and total echo return loss in excess of 70 dB. Especially, for a fickle response, if the response is estimated by an adaptive filter, the filter needs more taps and the performance is decreased. But the response is divided into several responses, the computation complexities are decreased and the performance is increased. For the stage constant n, which represents the number of stages, if the response is not divided (n=1), the computation complexity of multiply is $2N^2$. And if the response is divided into two responses (n=2), the computation complexity of multiply is $2N^2$. Also, if n=3, the computation complexity is ${\frac{2}{3}}N^2$. Therefore, it is known that the computation complexity is decreased as n is increased. Finally, this proposed method is verified through simulation of echo canceller for digital subscriber line (DSL) application.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.4A
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• pp.227-238
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• 2012

In this paper, we propose a practical time-division half-duplex Estimate and Forward (EF) relaying protocol. The conventional EF relaying protocol works well only when the relay node is near the destination node. The proposed EF relaying protocol, however, determines adaptively relay parameters such as the quantization level of relay node and the power allocation between source and relay nodes according to the channel conditions. By doing so, the proposed EF relaying protocol provides low probability of bit error even when the relay node is far from the destination node. Consequently, the proposed EF protocol is suitable for the mobile relay systems. It is shown by simulations that the proposed EF relaying protocol shows lower bit error rate for all relay positions than a conventional EF protocol.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3A
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• pp.197-204
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• 2009

Cyclic delay diversity (CDD) is considered a simple approach to exploit the frequency diversity, to improve the system performance in orthogonal frequency division multiplexing (OFDM) systems. Also, the linear preceding technique can significantly improve the performance of communication systems by exploiting the channel state in formation (CSI). In order to achieve enhanced performance, we propose applying linear preceding to the conventional CDD-OFDM transmit diversity schemes over Rayleigh fading channels. The proposed scheme works effectively with the accurate CSI in time-division-duplex (TDD) OFDM systems with CDD, where the reciprocity is ass umed instead of channel state feedback. For a BER of $10^{-4}$ and the mobility of 3 km/h, simulation results show that a gain of 6 dB is achieved by the proposed scheme over both flat fading and Pedestrian A (Ped A) channels, compared to the conventional CDD-OFDM system. On the other hand, for a mobility of 120 km/h, a gain of 2.7 dB and 3.8 dB is achieved in flat fading and Vehicular A (Veh A) channels, respectively.

• Journal of Advanced Navigation Technology
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• v.23 no.5
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• pp.392-399
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• 2019

In this paper, we have studied wireless time division duplex(TDD) time synchronization technique considering the propagation delay between mobile vehicles. The existing IEEE 1588 precision time protocol(IEEE 1588 PTP) algorithm was applied and the time synchronization between the two nodes was achieved through the propagation delay and clock offset time correction calculated between master slave nodes during wireless TDD communication. The time synchronization process and procedure of IEEE 1588 PTP algorithm were optimized, thereby reducing the propagation delay error sensitivity for real-time moving vehicles. The sync flag signal generated through the time correction has a time synchronization accuracy of max +252.5 ns within 1-symbol(1.74 M symbol/sec, ${\pm}287.35ns$) through test and measurement, and it was confirmed that the time synchronization between master slave nodes can be achieved through sync flag signal generated during GPS disturbance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.11
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• pp.2385-2390
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• 2010

The PRC-999K radio widely used in Korean Army is half-duplex and also has the broadcasting radio wave character that all subscribers listen when one subscriber speaks in time. The radio data communication system configures a 1:1 unicast network between a command post and network members in a military fire control system. The system also applies CSMA/CA technique to avoid data collision and additionally applies SDLC protocol for efficiency and fast communication. This paper shows that allocating address to network members in serial order can reduce data transmitting/receiving time, and thereby a command post needs to broadcast data only one time and the assigned members can reply in order without data collision. It is validated through an experimental test.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.11
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• pp.32-36
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• 2008

In this paper, we investigate the capacity of CDMA/TDD in the inner zone of multimode scenario with dual-band operation where high frequency band is used for TDD in the inner zone and lower frequency band is utilized for FDD in the outer zone. The effects of various system parameters such as cell radius, date rate, and time slot allocation are analyzed.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2019.11a
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• pp.61-62
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• 2019

최근 자원 효율성을 증대하기 위하여 차세대 유무선 통신시스템에서 동일대역 전이중 방식(In-band full-duplex, FDX)을 채택하고 있다. 하지만 전이중 방식은 송수신이 동시에 이루어지기 때문에 하향신호와 상향신호가 더해져 수신된다. 따라서 원하는 신호를 수신하기 위해 자기간섭(SI: self-interference)으로 존재하는 하향 신호를 제거하는 기술이 요구된다. 본 논문에서는 DOCSIS 3.1 기반 케이블 방송시스템에서 2차 구조의 자기간섭신호 제거(SIC: SI cancellation)기술을 제안하고 실시간 성능을 분석한다.

• Journal of Communications and Networks
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• v.10 no.3
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• pp.308-315
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• 2008

When operating in frequency-division duplex (FDD) mode, transmit beamforming in multiple-input single-output (MISO) wireless communication systems typically requires accurate knowledge of downlink channel state information (CSI) at the transmitter. In practical FDD systems, obtaining such downlink CSI at the transmitter is challenging, if not impractical. To circumvent such challenge and support user mobility, we present a new method for transmit beamforming based on simple beam-control commands (BCCs) in MISO FDD mobile systems. We then numerically evaluate the effects of BCC errors in terms of transmit power efficiency, system capacity, and outage probability.

• Proceedings of the KIEE Conference
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• 2001.07d
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• pp.2714-2716
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• 2001

본 논문에서는 일대일 전송에 국한되어 사용되는 전이중 패스트 이더넷 방식을 응용하여 고속 브로드 캐스팅 통신망을 구성하고 실시간 전송을 요구하는 데이터를 효율적으로 전달할 수 있는 알고리듬을 제시한다. 제안된 통신망의 세부구조와 통신망의 데이터 송수신 동작 등을 설명하고, 실시간 데이터 전송을 보장하기 위하여 실시간 메시지 스케줄링 알고리듬을 제시한다. 제시된 알고리듬을 적용하였을 때의 각종 시변수들에 대한 수학적인 분석을 통하여 실시간성 보장에 대한 성능평가를 포함한 통신망 성능 평가를 수행한다. 제안된 통신망 FER(Full-duplex Ethernet networks for Real-time communication)의 실제 구현 및 응용 대상에 대해서 언급한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.05a
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• pp.523-526
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• 2010

FM Radio communication operating mode is half-duplex mode. FM radio network access control shall be used to detect the presence of active transmissions on a multiple-subscriber-access communications network and shall provide a means to preclude data transmissions from conflicting on the network. In this study, we implemented R-NAD(Random Network Access Delay) that is one of network access control method.