• Annual Conference of KIPS
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• 2014.04a
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• pp.177-179
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• 2014

컨텐츠 중심 네트워크(CCN)는 데이터 송수신을 위해 IP 주소로 종단 간 1:1 연결을 맺어야 하는 기존 인터넷의 비효율성을 해결하고자 등장한 미래 인터넷 기술 중 하나이다. CCN은 IP 주소 대신 컨텐츠의 이름을 사용하여 라우팅을 수행하며 네트워크상의 노드들이 컨텐츠를 저장하고 컨텐츠를 요청하는 인근의 소비자들에게 배포하는 방식을 사용한다. 하지만 기존의 CCN은 최초 데이터 패킷이 도착한 하나의 경로로만 컨텐츠를 수신하고 이후에 도착한 데이터 패킷은 폐기하기 때문에 전송률과 대역폭 측면에서 비효율적이다. 따라서 본 논문에서는 다수의 노드에 서로 다른 데이터 청크를 요청하여 다중경로를 통해 컨텐츠를 효율적으로 수신하는 기법을 제안한다.

• International Journal of Internet, Broadcasting and Communication
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• v.11 no.1
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• pp.60-68
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• 2019

In this paper, we propose the adaptive beamforming algorithm for the MIMO (Multi-Input Multi-Out)-OFDMA(Orthogonal Frequency Division Multiplexing Access)system to improve the performance. The performance of MIMO-OFDMA systems is greatly decreased in the wireless channel environment with multiusers, because the received signals are much distorted by a cochannel interference (CCI) during the space-time decoding. The proposed approach can track the DOA of each signal from the multiple antennas of the desired user without being greatly dependent on the impinging angle. And beams are directed toward the multiple transmitters of the desired user while null beams are directed toward interference directions. Therefore, we can can effectively cancel CCI and mitigate the impairment of delay spread while preserving the STC(space time code) diversity. BER performance improvement is investigated through computer simulation by applying the proposed approach to MIMO-OFDMA system in a multipath fading channel with CCI.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.2
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• pp.113-120
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• 2021

The Distance Measuring Equipment (DME) is a ground-based aircraft navigation system and is considered as an infrastructure that ensures resilient aircraft navigation capability during the event of a Global Navigation Satellite System (GNSS) outage. The main problem of DME as a GNSS back up is a poor positioning accuracy that often reaches over 100 m. In this paper, a novel approach of applying deep reinforcement learning to a DME pulse design is introduced to improve the DME distance measuring accuracy. This method is designed to develop multipath-resistant DME pulses that comply with current DME specifications. In the research, a Markov Decision Process (MDP) for DME pulse design is set using pulse shape requirements and a timing error. Based on the designed MDP, we created an Environment called PulseEnv, which allows the agent representing a DME pulse shape to explore continuous space using the Soft Actor Critical (SAC) reinforcement learning algorithm.

• Journal of IKEEE
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• v.28 no.3
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• pp.465-468
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• 2024

In this paper, we propose a synthetic aperture radar based on FMCW using a nonlinear radar platform. we construct a nonlinear radar platform with different transmit and receive frequencies using FMCW signals. The platform moves along a 1.5 m path to acquire second harmonics signals, implementing a nonlinear SAR (synthetic aperture radar). Multiple nonlinear targets were placed in an indoor multipath environment with linear objects to detect weak second harmonics. After undergoing the SAR focusing precess, a 2D hamming window was applied to enhance the focusing performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.3
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• pp.1373-1392
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• 2017

WiFi Direct (WD) is a state of the art technology for a Device-to-Device (D2D) communication in 802.11 networks. The performance of the WD system can be significantly affected by some key factors such as the type of application, specifications of MAC and PHY layer parameters, and surrounding environment etc. It is, therefore, important to develop a system model that takes these factors into account. In this paper, we focus on investigating the design parameters of the PHY layer that could maximize the efficiency of the WD 802.11 system. For this purpose, a basic theoretical model is formulated for a WD network under a 2x2 Multiple In Multiple Out (MIMO) TGn channel B model. The design level parameters such as input symbol rate and antenna spacing, as well as the effects of the environment, are thoroughly examined in terms of path gain, spectral density, outage probability and Packet Error Rate (PER). Thereafter, a novel adaptive algorithm is proposed to choose optimal parameters in accordance with the Quality of Experience (QoE) for a targeted application. The simulation results show that the proposed method outperforms the standard method thereby achieving an optimal performance in an adaptive manner.

• Journal of Positioning, Navigation, and Timing
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• v.9 no.2
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• pp.43-50
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• 2020

In this paper a low power Spreading Code Authentication (SCA) sequence with a BPSK(1) modulation at a frequency offset of +7.161 MHz is tested for authentication purposes, the Galileo E1OS is used as base signal. The tested signals comprise a Galileo constellation with 5 satellites including the Galileo OS Navigation Message Authentication (OSNMA) and a low power offset BPSK (OBPSK(7,1)) as SCA component. The signals are generated with the software based MuSNAT-Signal-Generator. The generated signals were transmitted Over-The-Air (OTA) using a Software-Defined-Radio (SDR) as pseudolite. With a real-environment-testbed the performance of the SCA in real channel conditions (fading and multipath) was tested. A new SCA evaluation scheme is proposed and was implemented. Under real channel conditions we derive experimental threshold values for the new SCA evaluation scheme which allow a robust authentication. A Security Code Estimation and Replay (SCER) spoofing attack was mimicked on the real-environment-testbed and analyzed with the SCA evaluation scheme. It was shown that the usage of an OBPSK is feasible as an authentication method and can be used in combination with the OSNMA to improve the authentication robustness against Security SCER attacks.

• The Journal of the Acoustical Society of Korea
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• v.19 no.5
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• pp.53-59
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• 2000

In this paper, considering configuration of the earth and environment of country, it is classified a radio propagation environment Multipath propagation measuring system based on PN code correlation detection method is built to study a wave propagation characteristics of 1.95GHz. Considering the characteristic artificial structure of country, Cihwa plant superintendent area has been selected for basic and accurate measurement a radio propagation characteristic. The experiments are carried out with respect to the RMS delay Spread and the received power in the two kind of geographical areas, LOS (Line of Sight) and N-LOS (Non Line of Sight). The measurement result of that received power of LOS area is -1.6∼-28.8dBm, RMS delay spread is 0.023㎲∼0.22㎲ and received power of N-LOS area is 16∼36.5dBm and RMS delay spread is 0.068∼0.37㎲.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.5
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• pp.815-821
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• 1994

Short-term fading in a mobile radio channel is mainly caused by multipath reflected wave by local scatterers or natural obstacles surrounding a mobile unit. In this paper, we analyze probability density function(PDF), level crossing rate(LCR) and widths and depths of fades for the measured field strength data in Seoul and Daejeon areas. As a result, the satatistical distribution of signal variations within any small area with the constant mean value becomes the Rayleigh distribution The variation of fade depths is small regardless of the environment such as urban, suburban. etc. However, the variation of fade widths is large with the change of circumstantial structures and environment. the maximum level crossing rate is obtained near the mean value.

• Journal of Digital Contents Society
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• v.12 no.3
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• pp.355-360
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• 2011

In this paper, the performance of OFDM (Orthogonal Frequency Division Multiplexing) was assessed by using computer simulations performed using Matlab. We analyzed channel estimation algorithm for adaptive modulation techniques and effect of system using designed simulator in Multimedia wireless communication multipath fading channel environment. Also, we analyzed performance of adaptive OFDM systems that apply adaptive equalizer using guided result through BER. In result, in case of adaptive modulation OFDM systems that modulation mode changes according to channel state, we knew that adaptive modulation OFDM systems have gains of about 7dB performance than general system (BER=$10^{-1}$). Thus we know that adaptive OFDM propose systems is required for efficient transmission in the high speed Multimedia wireless communication channel environment.

• Journal of Digital Contents Society
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• v.5 no.1
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• pp.28-34
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• 2004

In this paper, we have analyzed the block error probability of orthogonal multicarrier 16 QAM signal in a frequency selective Rician fading environment. The block error probability is evaluated with several parameters such as normalized propagation delay $(\gamma/T_S),$, bit energy to noise power ratio $(E_b/N_0),$ and desired signal to undesired signal power ratio (DUR) in fast fading and slow fading channels. In the fast fading channel, The result shows that the block error probability rather in the fast fading channel achieves better performance than in the slow fading channel, when the error correction capability is one or two.