• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.2
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• pp.81-88
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• 2018

Spectrum sensing, the key technology of the cognitive radio networks, is used by a secondary user to determine the frequency state of a primary user. The energy detection in the spectrum sensing determines the presence or absence of a primary user according to the intensity of the allocated channel signal. Since this technique simply uses the strength of the signal for spectrum sensing, it is difficult to detect the signal of a primary user in the low SNR band. In this paper, we propose a way to combine spectrum sensing and support vector machine using wavelet packet decomposition to overcome performance degradation in low SNR band. In our proposed scheme, the sensing signals were extracted by wavelet packet decomposition and then used as training data and test data for support vector machine. The simulation results of the proposed scheme are compared with the energy detection using the AUC of the ROC curve and the accuracy according to the SNR band. With simulation results, we demonstrate that the proposed scheme show better determining performance than one of energy detection in the low SNR band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.4
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• pp.374-380
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• 2015

With explosion of wireless traffic it is required to further investigate the technologies on acquiring available spectrum resources and on sharing frequency with existing users. In 3GPP, it is started to study on feasibility and functional requirement of LTE standard in order to extend cellular services offered on only licensed band to 5 GHz unlicensed band. Operating scenario on LTE in unlicensed band is focused on carrier aggregation with licensed band, and the coexistence with Wi-Fi services in 5 GHz band is concerned as a major requirement. For a single global solution framework for licensed assisted access to unlicensed spectrum, listen-before-talk(LBT) mechanism of European regulation for fair access to channel under the coexistence environments is currently examined in 3GPP. In this paper, we evaluate two types of LBT, frame based equipment and load based equipment, with considering LTE carrier aggregation feature and performances of file transferred time and throughput.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.2
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• pp.117-122
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• 2009

In this paper, the performance of double binary turbo code is analyzed and simulated in ultra wide-band (UWB) systems employing multiple-antenna scheme. We consider both pulse position modulation-time hopping (PPM-TH) and pulse amplitude modulation-direct sequence (PAM-DS) UWB systems. The space time block code (STBC) scheme is adopted as a transmit diversity method. Also, receive diversity scheme is applied. And double binary turbo code is applied to the UWB system.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.6
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• pp.545-555
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• 2020

This paper presented efficient transceiver structure using sub-band processing for underwater communication in terms of covertness and performance improvement. In aspect of covertness, encrypted coded-bits are divided into groups, and center frequency and sub band are determined by coded-bits of each group. Therefore, as center frequencies are changed randomly, it maintain the covertness effectively. In aspect of performance improvement, the performance of underwater communication mainly depends on multi-path propagation characteristics, Doppler-spread, and frame synchronization. Accordingly, in order to overcome these effects, non-coherent energy detector and turbo equalization method are employed in receiver side. Furthermore, optimal frame synchronization was proposed. Through the simulation and lake experiment, performance analysis was conducted. Especially in the lake experiment, as a result of applying optimal frame synchronization method to receiver structure, errors are corrected in most frames.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2119.1_2120.1
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• 2009

UWB(Ultra Wide Band)는 차세대 무선통신 기술로 무선 디지털펄스라고도 한다. GHz대의 주파수를 사용하면서도 초당 수천~수백만 회의 저출력 펄스로 이루어진 것이 큰 특징이다[1]. 기존 무선통신 기술의 양대 축인 IEEE 802.11과 블루투스 등에 비해 속도와 전력소모 등에서 월등히 앞서고 있으며, SoC(System on a Chip)의 저전력 구현에 대한 연구가 활발히 진행되고 있다. OFDM은 크게 FFT(Fast Fourier Transform) 블록, Interpolation /decimation 필터 블록, 비터비 블록, 변복조 블록, 등화기 블록 등으로 구성된다. 고속 시스템에서는 대역효율성이 우수한 OFDM(Orthogonal Frequency Division Multiplexing) 방식을 사용하고 있으며, OFDM 전송방식은 직렬로 입력되는 데이터 열을 병렬 데이터 열로 변환한 후에 부반송파에 실어 전송하는 방식이다. 이와 같은 병렬화와 부반송파를 곱하는 동작은 IFFT와 FFT로 구현이 가능한데, FFT 블록의 구현 비용과 전력소모를 줄이는 것이 핵심사항이라고 할 수 있다. 기존논문에서는 OFDM용 FFT 구조로 단일버터플라이연산자 구조, 파이프라인 구조, 병렬구조 등의 여러 구조가 제안되었다[2]. 본 논문에서는 Radix-8 FFT 알고리즘 기반의 New partial Arithmetic 저전력 FFT 구조를 제안하였다. 제안한 New partial Arithmetic 저전력 FFT구조는 곱셈기 대신 병렬 가산기를 이용 하여 지금까지 사용되는 FFT 구조보다 전력소모를 줄일 수 있음을 보였다.

• Journal of IKEEE
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• v.3 no.2 s.5
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• pp.259-267
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• 1999

In this paper, a C-band 6-bit phase shifter is designed and fabricated and design techniques for each phase bit are represented. We applied the loaded line type to $5.625^{\circ},\;11.25^{\circ},\;22.5^{\circ}\;and\;45^{\circ}$ phase bits and the hybrid coupled type to $90^{\circ}$ phase bit and the switched line type to $180^{\circ}$ phase bit, respectively on a microstrip copper substrate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.9A
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• pp.2141-2152
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• 1998

In this paper, we design and implement an indoor wireless modem using small signal of ISM band regulation, which can tranceive reliable data streams. We use direct sequence spead spectrum (DS-SS) signaling with synchronous BPSK and QPSK modulation, convolutional coding with viterbi decoding. The radio frequency module uses frequency devision duplexing in 900 MHz band, and the digital module is implemented with FPGAs for the purpose fo ASIC design. The perfomrance of our own acquistion and tracking circuit consisting digital matched filter and decision logic is proved by experiments, and the possibility of file transfer at indoor environment with the entrie system that the modem is connected the PC through RS-232C port is verified.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10B
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• pp.1252-1257
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• 2011

In this paper, efficient functions for audio spectrum mapping with visible spectrum are proposed. Through mapping overall hearing frequency band with visible frequency band, emotional lighting might be possible. We propose a basic linear mapping function and non-linear mapping functions emphasizing specific audio frequency bands. For the algorithm implementation, spectrum analysis method and filter method are introduced. Especially, in this paper, a prototype LED lighting equipment using the digital filter method is implemented. The proposed lighting method can be applied to many LED lighting area using music.

• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.510-518
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• 2013

These days, interest in radio networks for railways has increased both at home and abroad. In response to this trend, not only the existing radio networks which focus on railway control signals but also the next-generation integrated radio network that can send videos and manage mass storage data are actively being investigated. This paper proposes wireless communication methods to establish integrated radio networks for railways. The paper further suggests a candidate frequency band that could be allocated as the frequency band for railways among the frequency bands currently used in Korea. Based on this paper, we can expect that the domestic railroad will operate more efficiently and that security and convenience of the railroad will reach a superior level. In addition, the Korean integrated radio networks for railways, which cope with the changes in the global technology market, will be established.

• Journal of Satellite, Information and Communications
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• v.3 no.1
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• pp.8-14
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• 2008

In this paper, we analyze throughput performance of MF-TDMA scheme and QS MC-DS/CDMA(quasi-synchronous MC-DS/CDMA) scheme based on scrambling on WH sequence and PPGC sequence in early frequency offset caused by high speed transfer terminal. QS MC-DS/CDMA scheme with scrambled WH sequence shows 5.7% higher throughput than MF-TDMA scheme and 8% higher throughput than QS MC-DS/CDMA with PPGC sequence in high speed transfer terminal environment such as maximum 1000Km/h speed with high frequency of Ka-band. Finally, we show that QS MC-DS/CDMA scheme with scrambled WH sequence is more efficient than traditional MF-TDMA scheme at the aspect of throughput in DVB-RCS system with Ka frequency band.