• ETRI Journal
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• v.26 no.5
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• pp.443-451
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• 2004

Since the publication of Alamouti's famous space-time block code, various quasi-orthogonal space-time block codes (QSTBC) for multi-input multi-output (MIMO) fading channels for more than two transmit antennas have been proposed. It has been shown that these codes cannot achieve full diversity at full rate. In this paper, we present a simple feedback scheme for rich scattering (flat Rayleigh fading) MIMO channels that improves the coding gain and diversity of a QSTBC for 2$^n$ (n=3, 4, ${\cdots}$) transmit antennas. The relevant channel state information is sent back from the receiver to the transmitter quantized to one or two bits per code block. In this way, signal transmission with an improved coding gain and diversity near to the maximum diversity order is achieved. Such high diversity can be exploited with either a maximum-likelihood receiver or low-complexity zero-forcing receiver.

• Electronics and Telecommunications Trends
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• v.27 no.2
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• pp.51-58
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• 2012

1990년대 말부터 IMO(International Maritime Organization)의 SOLAS(Safety of Life at Sea) 조약에 따라 300톤 이상의 모든 선박에 GMDSS(Global Maritime Distress & Safety System)를 탑재함으로써 전 세계 어디에서나 선박의 조난 및 안전 통신을 위한 육 해상 통합시스템의 기틀이 마련되었다. 최근에는 GMDSS의 현대화와 e-Navigation 개발전략에 따라 해상통신 기술의 디지털화와 음성에서 데이터 통신으로의 큰 변화가 예상된다. 이에 GMDSS 중심의 해상통신 기술현황을 위성, MF(Medium Frequency), HF(High Frequency), VHF(Very High Frequency) 등 다양한 통신 기술에 따라 설명하고 e-Navigation 개발전략에 따라 해상통신 기술의 발전 방향을 살펴보도록 한다.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.6
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• pp.819-827
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• 2013

Compared to legacy frequency hopping communications, future radio communications are required the secure and high data rate, ad-hoc network communication. In this paper, we have designed the network communication structure on the frequency hopping mode, and analyzed the performance of synchronization on the frequency hopping network radio systems. The design results are shown the initial sync. phase of approximately 9 hops and the traffic packet phase of approximately 30 hops. Also, we have simulated the performance on the communication conditions which are carrier bandwidth of 50kHz, user data rate of 64kbps and OQPSK modulation scheme in AWGN. In the simulation, we analyzed the correlation and the performance of synchronization success. The result of simulation show 99% probability for synchronization success at $E_b/N_o$ -4dB.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.784-787
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• 1999

This paper describes a direct digital frequency synthesizer using the CORDIC algorithm, which can be implemented efficiently for a digital sinusoid synthesis. To optimize the hardware design parameters, we perform numerical analysis of the quantization effects for the CORDIC-based architecture. A pipelined architecture is employed to obtain a high data throughput,. We estimate and summarize its hardware costs for a variable accuracy, and a CORDIC-based architecture for 9 bit accuracy is emulated in FPGA.

• Communications for Statistical Applications and Methods
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• v.23 no.5
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• pp.411-421
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• 2016

Large frequency limiting distributions of two errors in realized covariance are investigated under noisy and non-synchronous high frequency sampling situations. The first distribution characterizes increased variance of the realized covariance due to noise for large frequency and the second distribution characterizes decreased variance of the realized covariance due to discretization for large frequency. The distribution of the combined error enables us to determine the sampling frequency which depends on a nuisance parameter. A consistent estimator of the nuisance parameter is proposed.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.3 no.2
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• pp.26-32
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• 2004

This paper represents analysis on domestic technical regulation of high speed power line communications(PLC). Also it gives comparison of regulations for several countries which include U.S., Europe, and Japan. Power line communications radiates harmful interference in below 30MHz. This may intervene other radio equipments. The technical regulation must protect interference and provide clean radio environment. Finally this paper gives the proposal which is drafted by field tests for introducing high speed PLC.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.7 s.361
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• pp.81-87
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• 2007

While conventional frequency reuse techniques for cellular communication systems divide frequency resources into multiple regions and each mobile is statically assigned to a certain frequency region, frequency reuse techniques for cellular OFDMA communication systems can be regarded as dynamic scheduling problems of finding best-fitted subcarriers for each packet transmission. Unlike conventional frequency reuse techniques allocating mutually exclusive frequency resources to adjacent cells, this paper proposes the use of a frequency reuse technique with irregular frequency allocation patterns assigned statically based on the cell numbers. This paper shows that the use of irregular frequency patterns can allow efficient interference avoidance and high data throughputs comparable to those with carefully planned frequency patterns.

• Journal of Korea Multimedia Society
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• v.9 no.6
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• pp.728-734
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• 2006

Carrier interferometry code is considered as a promising scheme that provides significant performance improvement via frequency diversity effect. Space-time coding is commonly employed to achieve a performance gain through space diversity. The combination of these techniques and forward error correction coding will lead to enhanced system capacity and performance. This paper presents a low-density parity check (LDPC) coded space-time orthogonal frequency division multiplexing (OFDM) transmission scheme with carrier interferometry code for high-capacity and high-performance mobile multimedia communications. Computer simulations demonstrate that the proposed mobile multimedia transmission system offers a considerable performance improvement of approximately 9dB in terms of Eb/No in the Rayleigh fading channel with relatively low delay spread, in comparison with space-time OFDM. Performance gains are further increased, comparing with traditional OFDM systems.

• Electronics and Telecommunications Trends
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• v.38 no.2
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• pp.85-95
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• 2023

Space optical communication technology capable of large-capacity, high-speed, and low-latency communication can reduce the size, weight, and power consumption of radio frequency communications in existing satellite systems, thereby reducing launch costs, accommodating additional science instruments, and extending lifetime. Despite the high technical difficulty, various projects are being carried out in advanced countries regarding space technology for use in national security and defense, earth observation, and space communications. We review the advantages, key components, and development trends of space optical communication technology, which is attracting attention in applications such as satellite communications, intersatellite linking, and deep space communications.

• ETRI Journal
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• v.28 no.4
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• pp.509-512
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• 2006

In a real environment, sound recordings are commonly distorted by channel and background noise, and the performance of audio identification is mainly degraded by them. Recently, Philips introduced a robust and efficient audio fingerprinting scheme applying a differential (high-pass filtering) to the frequency-time sequence of the perceptual filter-bank energies. In practice, however, the robustness of the audio fingerprinting scheme is still important in a real environment. In this letter, we introduce alternatives to the frequency-temporal filtering combination for an extension method of Philips' audio fingerprinting scheme to achieve robustness to channel and background noise under the conditions of a real situation. Our experimental results show that the proposed filtering combination improves noise robustness in audio identification.