• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.5
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• pp.783-790
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• 2022

The development of SNS and video platforms provided an opportunity to explode the activation of content production and consumption. However, in the legacy system, due to the host-based location-oriented data transmission, there are inherent limitations in efficient operation and management. As an alternative to this, a Contents Centric Network (CCN) was studied. In this paper, when intermediate nodes located between the information provider and the information requester between the real-time streaming services in the CCN environment move or restrict their use, failure through monitoring of wireless reception strength to solve problems like disconnection of transmission quality at the information consumer. We propose a stable intermediate node management mechanism through active response before occurrence.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.5
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• pp.1042-1050
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• 2014

The performance of underwater acoustic(UWA) communication system is sensitive to the Inter-Symbol Interference(ISI) due to delay spread develop of multipath signal propagation. And due to limited frequency using acoustic wave, UWA is a low transmission rate. Thus, it is necessary technique of Space-time code, equalizer and channel code to improve transmission speed and eliminate ISI. In this paper, UWA communication system were analyzed by simulation using these techniques. In the result of simulation, the proposed Turbo Equalization method based on layered Space Time Codes has improved performance compared to conventional UWA communication.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.6
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• pp.48-55
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• 2009

The feedback interference channels are those made through the multipaths that are built by moving and stationary objects around transmit and receive antennas mounted at the same point. This paper describes the method to measure the feedback interference channels in the rural regions and sides of highways and the analysis on channel characteristic parameters. Using the measured samples, we estimated scattering functions, delay power spectra, and Doppler power spectra, and we analyzed the channels using eight parameters including coherence bandwidth, coherence time, maximum excess delay, average excess delay, rms delay spread, Doppler shift, Doppler spread, and spread factor, and delay and Doppler cumulative distributions. Even though many observations are made, note that the feedback signals of high Doppler frequencies and large energy are observed in the sides of highways due to high speed vehicles while low Doppler frequencies occurred in the rural region due to rare traffic.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.2
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• pp.181-188
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• 2012

In this paper, the measurement data is analyzed and channel parameters are derived through MIMO Channel measurements at 781MHz considering outdoor multi-path environment. 781MHz frequency band currently operates the DTV system. However, it will be allocated new mobile communication frequency band. The channel characteristics at 781MHz seem to be similar existing mobile communication system at 900MHz but a study on channel characteristics of signal transfer process is necessary because there is incomplete study in mobile networks at 781MHz. To avoid interference with Korean DTV broadcasting, we measured channel characteristics in city/suburban areas of Jeju island by channel sounder and $4{\times}4$ antenna of the ETRI(Korea Electronics and Telecommunications Research Institute). Path Loss, Delay Spread, Angular Spread and K-factor were derived based on measured data.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.1
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• pp.52-57
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• 2016

We introduce a hybrid scheduling in a multi-path poor scattering full-duplex (FD) system, which consists of one multi-antenna FD base station and a large number of single-antenna half-duplex mobile stations. Our hybrid scheduling utilizes partial channel state information at the transmitter. In particular, unlike the conventional scheduling method using opportunistic transmission for both uplink and downlink, the proposed scheme combines a random transmit beamforming for downlink and a zero forcing beamforming for uplink. As our main result, via computer simulations, it is shown that the proposed scheme has a superior sum-rate performance than that of the conventional scheduling method beyond a certain signal-to-noise ratio regime.

• Journal of Satellite, Information and Communications
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• v.2 no.2
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• pp.1-9
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• 2007

In this paper, we describe the performance degradation of satellite Wibro system and compensation method in the high-speed railroad channel environment. High-speed railroad channel environment is divided into LOS channel and tunnel. In the LOS channel, signal blocking caused by railroad power feeder structures can be a critical problem which is can be solved with antenna diversity. On the other hand, multi path interference phenomenon, representable by propagation model of Optic Fiber, occurred in the tunnel may be another obstacle. These satellite Wibro system performance degradations in railroad channel environment are addressed and adequate compensation methods are proposed and verified through computer simulation. In addition, the ICI caused by Doppler shift in OFDM system is analyzed with its compensation method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.7A
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• pp.529-536
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• 2003

In this Paper, a new DCT HLMS DFE(Discrete Cosine Transform Hierarchical Least Mean Square Decision Feedback Equalizer) algorithm is proposed to improve the convergence speed and MSE(Mean Square Error) performance of a receive channel equalizer in ATSC(Advanced Television System Committee) 8VSB(Vestigial Side Band) digital terrestrial TV system. The proposed algorithm reduces the eigenvalue range of input data autocorrelation by transforming LMS (Least Mean Square) DFE into the subfilter of hierarchical structure. Moreover, the use of DCT and power estimation algorithm makes it possible to reduce the eigenvalue deviation of input data which results from distortion and delay of the receive signal in the miulti-path environment. Simulation results show that proposed DCT HLMS DFE has SNR improvement of approximately 3.8dB, 5dB and 2dB as compared to LMS DFE when the equalized symbol error rate is 0.2 in ATTC defined digital terrestrial TV broadcasting channels A, B and F, respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.3 s.345
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• pp.10-17
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• 2006

For orthogonal frequency division multiplexing (OFDM), cyclic prefix (CP) should be longer than the length of channel impulse response, resulting in a loss of bandwidth efficiency. In this letter, the CP reconstruction (CPR) technique is first applied to a multi-input multi-output (MIMO)-OFDM system with insufficient CP. The intercarrier interference (ICI) from multiple transmit antennas is so large for MIMO system that it can not be sufficiently suppressed with the conventional CPR procedure used in single-input single-output (SISO) system. A new minimum mean-square error (MMSE) equalization and ordering process is proposed for MIMO system to suppress the ICI during the CPR procedure. By applying the proposed CPR algerian to MIMO-OFDM system, we can obtain both the benefits of multiplexing gai and spectral efficiency gain.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.6
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• pp.10-10
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• 2002

This paper introduces the high-resolution channel estimation technique which are used to estimate the first arrival multipath delay component. The proposed technique yields the precise estimate of the first time arrival which is directly related to the performance of TDOA-based position location. The proposed technique utilizes the transformed auto-correlation function of received common pilot signal in frequency domain, its samples compose the hermitian Toeplitz matrix at sequel. Then the time delay components could be estimated with precision by the analysis of eigen-structure of corresponding matrix. In this paper, obeying the modified CODIT model, the performance of the PR-IPDL(Pseudo Random-Idle Period Downlink) and TA-IPDL(Time Aligned-Idle Period Downlink considered as 3GPP position location technique will be exploited systematically through the computer simulations with applying the proposed technique.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.6
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• pp.268-276
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• 2002

This paper introduces the high-resolution channel estimation technique which are used to estimate the first arrival multipath delay component. The proposed technique yields the precise estimate of the first time arrival which is directly related to the performance of TDOA-based position location. The proposed technique utilizes the transformed auto-correlation function of received common pilot signal in frequency domain, its samples compose the hermitian Toeplitz matrix at sequel. Then the time delay components could be estimated with precision by the analysis of eigen-structure of corresponding matrix. In this paper, obeying the modified CODIT model, the performance of the PR-IPDL(Pseudo Random-Idle Period Downlink) and TA-IPDL(Time Aligned-Idle Period Downlink considered as 3GPP position location technique will be exploited systematically through the computer simulations with applying the proposed technique.