• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2003.05a
• /
• pp.119-123
• /
• 2003

In this paper, a new OFDM scheme, IS-OFDM(Interference Suppressing Orthogonal Frequency Division Multiplexing), which has the capabilities of suppressing narrow-band interference for wide-band wireless communication systems, is introduced. This IS-OFDM system is composed of the parallel stages of ordinary OFDM, and each sub-carrier contains all of the transmitted symbols. Using Hadamard sequences, the transmitted information symbols in the same sub-carriers are separated from the other sub-carriers in the receiver. After analyzing and evaluating the performance of IS-OFDM system using Monte-Carlo simulation, the effective improvements of performance in IS-OFDM compare favorably with that of a conventional OFDM system in a narrow-band channel, is shown.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.12 no.2
• /
• pp.168-175
• /
• 1987

In this paper, a FFH-SS hybrid communication method using digital frequency synthesizer is proposed. This can simultaneously share the same frequency band with conventional band limited communication method without interference. In the experiment the selective hopping pattern is attained by some conbination of serial to parallel conversion of maximal code from pseudo random noise generater, and it is observed that the selective hopping band transition can be more easily achieved when the hop interval is nonuniform than it is uniform. Digital frequency synthesizer is now reported to have very poor spurious suppression ability below 50~60dB, the reason of this is observed from the experimental result, and the way of how to solve this problem is presneted.

• Electronics and Telecommunications Trends
• /
• v.9 no.4
• /
• pp.131-138
• /
• 1994

최근 무선통신의 활성화에 따라, V/UHF(very/ultra high Frequency) 대역에서 한정된 주파수를 효율적으로 이용하기 위한 방법의 하나로서, 점차 점유 주파수 대역의 폭을 축소하여 보다 많은 이용자를 수용하도록 무선 채널의 협대역화가 추진되고 있다. 본 고에서는 먼저 V/UHF 대역 무선 통신에서 채널의 협대역화에 관련된 기술 중에서 현재까지 사용되고 있는 FM(frequency modulation), AM(amplitude modulation) 변조 방식의 장,단점을 살펴본후, 새로운 LM(linear modulation) 변조 방식에 대한 기술적 배경 및 특성을 알아보았다. LM은 SSR(single side band)-AM이 발전한 것으로서, TTIB(transparent tone-in-band), CLT(Cartesian loop transmitter), FFSR(feed-forward signal regeneration), DSP(digital signal processing)등 4가지의 기술이 결합하여 만들어진 것이다. LM 방식에 사용된 4가지 기술을 소개하고, 기존의 변조 방식에 비해 개선된 사항에 대해 서술한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.13 no.10
• /
• pp.982-988
• /
• 2002

This paper summarizes the design concepts and implementation of a Ku-band channel amplifier's engineering model for the communication and broadcasting satellite applications. The selected architecture uses the analog gain control for the FGM(Fixed Gain Mode) and the output level limiting using automatic loop control for the ALC (automatic level control) mode. The Ku-band channel amplifier incorporates several state-of-the-art components including voltage-controlled PIN diode attenuators, and various temperature-compensation circuits. The measured characteristics of the Ku-band channel amplifier are in good agreement with the expected performance. The results show a fixed gain control of 28 dB, and an automatic level control of 16 dB over operating temperature range. The designed engineering model could be used as a channel amplifier for Ku-band communication and broadcasting satellite payload system.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.16 no.1
• /
• pp.26-32
• /
• 2012

In this study, we proposed an intelligent algorithm for the performance improvement of ASK system for giga-bit modem in millimeter band. The proposed intelligent algorithm is a fuzzy logic system. The inputs to the fuzzy logic system are the remainder and integral of remainder that occurred counter of receiver, and the output is bandwidth of LPF. In order to verify the effectiveness of the proposed method, simulation is performed to the proposed system and the fixed bandwidth system, and is confirmed to the BER performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.22 no.3
• /
• pp.345-353
• /
• 2011

An 1.485 Gbit/s video signal transmission system using the carrier frequency of H-band(220~325 GHz) was implemented and demonstrated for the first in domestic. The RF front-end was composed of Schottky barrier diode sub-harmonic mixers(SHM) and frequency triplers, and diagonal horn antennas for transmitter and receiver, respectively. The transmitted carrier frequency of 246 GHz was implemented in the H-band, and LO frequencies of H-band SHM is 120 GHz and 126 GHz for transmit and receive chains, respectively. The modulation scheme is ASK(Amplitude Shift Keying) where IF frequency is 5.94 GHz and the envelop detection was used in heterodyne receiver architecture, and direct detection receiver using ZBD(Zero Bias Detector) was implemented as well. The 1.485 Gbit/s video signal with HD-SDI format was successfully transmitted over wireless link distance of 5 m and displayed on HDTV at the transmitted average output power of 20 ${\mu}W$.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.9C
• /
• pp.1279-1288
• /
• 2004

In this paper, the DMR(Digital Microwave Radio) system-based OFDM(Orthogonal Frequency Division Multiplexing) scheme in microwave channel environments has been proposed and system performances have been evaluated. The existing single carrier DMR system has a complex system structure due to using high-level QAM(Quadrature Amplitude Modulation) modulation scheme and so charmel capacity is limited by sensitive effects from fading. Therefore, in the proposed DMR system, it uses that the OFDM scheme for enhancement of fading distortion and also uses that the band-limited pulse shaping filter instead of windowing for no additional data such as GI/GB and for using efficient of IFFT/FFT block. The performance of OFDM/QPSK-DMR system and single carrier DMR system are analysed by computer simulation using two-ray model under the microwave channel environments The computer simulation results confirm that the fade margin of the proposed OFDM/QPSK-DMR system is highly increased as the number of sub-carriers is larger.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.37 no.6
• /
• pp.609-614
• /
• 2009

The TT&C communication subsystem of STSAT-3 is consisted of communication link to send telemetry data of spacecraft to the ground station and receive command data from ground station. The S-band receiver is used to receive command data from ground station, Engineering Qualification Model of S-band receiver has been designed and manufactured. The Designed S-band Receiver uses a single conversion for a simple frequency conversion, including a DC-DC Converter and EMI Filter. Also, Digital demodulation part designed using FPGA and RS-422 data interface. The performance of S-band Receiver in functional and space environments test satisfies the requirements of STSAT-3.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2006.05a
• /
• pp.615-618
• /
• 2006

The broadband power detector for direct- onversion Six-port output circuit was designed and implementaed in this paper. The power detector should linearly operated to produce the linear amplitude and phase signal fer input RF signal in required broadband. So, the power detector should be designed under conditions of matching circuit with low VSWR. The designed power detectors, which were implemented in L-band with 50 ohm matching and Ku-band with matching circuit and isolator, respectively, were evaluated in the performances.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.39 no.6
• /
• pp.27-27
• /
• 2002

In this paper, the LPA(Linear Power Amplifier) using new analog feedforward linearizer for IMT-2000 frequency band(2110MHz∼2170MHz) is proposed and fabricated. The designed analog feedforward linearizer system possessing the characteristics of stable operation for input power variation is simple structure and small size. When two-tones in IMT-2000 frequency band are applied to an amplifier, this LPA have the average output power is about 30W and the IMD value is below about 60dBc without correcting the circuit. In camparision with an amplifier without feedforward system at the same output power, the supposed analog feedforward linear amplifier posseses improved the IMD characteristics of over 23dB.