• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1999.11b
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• pp.179-183
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• 1999

일반적인 통신 시스템에서 높은 전력을 가지는 출력 신호를 얻기 위하여 고전력증폭기(HPA)의 사용은 필수적이다. 그러나 HPA를 통과한 신호는 AM/AM 및 AM/PM의 비선형왜곡이 발생하는 단점을 가지고 있다. 그 결과 송신신호의 대역내 신호 스펙트럼이 왜곡되고 신호의 대역폭을 확장시켜 인접채널에 간섭을 유발한다. 본 논문에서는 HPA의 비선형 왜곡 특성을 보상하기 위하여 기저대역에서 룩업테이블(LUT)을 이용한 전치왜곡기의 동작 알고리듬을 제안한다. 먼저, LUT의 빠른 초기화를 위하여 송신신호로부터 HPA의 특성을 예측하여LUT를 초기화 시키는 알고리듬을 제안한다. 그리고 통신중에 HPA의 특성이 변화할 경우에 대비하여 평균자승오차를 최소화하는 적응알고리듬을 제안한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.603-610
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• 2006

This paper considers the problem of mitigating CCI(Co-channel Interference) in cellular OFDMA downlink systems. The users in the cell-edge area suffer from large CCIs, and their SINR requirements are hard to be maintained. To guarantee their QoS, we propose a new exclusive sub-carrier allocation and power control algorithm. The performance of the proposed two-step algorithm is simulated in SUI-A path-loss model, and it is compared with that of the conventional algorithm. The simulation results show that the data transmission rate in the cell-edge area was increased by 600Kbps within the same power constraint. The results indicate that with proposed algorithm, the data rate stability can be achieved independently of the user location in the cell.

• Journal of Satellite, Information and Communications
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• v.9 no.3
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• pp.1-4
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• 2014

A radio communication system has interference caused by other radio transmitters operated in co-channel or adjacent channels. Therefore technical specifications are made by considering and investigating the effects of interference between the new system and present systems when the new system will be started to serve in the near future. FTS is used for preventing an abnormal mission and guaranteeing public protection. Recently the next generation FTS's are researched to reinforce the security and to increase the operating capability of simultaneous use. EFTS known as one of the next generation FTS's is suitable for such purposes. In this paper the effects of interference signals on the performance of EFTS are investigated. Noncoherent DPSK and noncoherent CPFSK are considered for the modulation method of EFTS and a FMCW and a pulse RADAR considered as a interferer. The power of FMCW is 20.3dB lower than the power of EFTS and the power of pulse RADAR is 19.1dB lower than that of EFTS. Simulation results show that FMCW interferer reduce $E_b/N_o$ of about 1dB and $E_b/N_o$ of EFTS deteriorates about 0.5dB due to interference signals generated from pulse RADAR.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.4
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• pp.542-550
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• 2001

In this paper, a channel combiner is designed to combine two adjacent digital TV channels without interference to transmit these channels with one broadband antenna. A constant impedance type combiner, consisting of two identical bandpass filters and two identical 3 dB power combiners, is chosen as a channel combiner. The bandpass filter used in the channel combiner also suppresses out-of-band signal caused by digital transmitter's non-linearity. H-plane type bandpass filters and branch-line fewer combiners are adopted in the design. The simulated results of the designed bandpass filter and power combiner show excellent agreement with the theoretical results. Finally, a channel combiner is designed by combining filters with rover combiners and the characteristics are simulated. It is shown that the designed channel combiner shows excellent performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.12
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• pp.1172-1175
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• 2011

In this paper, a design method of multi-tone signals for the measurement of adjacent-channel power-ratios on power amplifiers is suggested. Because most tests for power amplifiers in production are performed with single-tone signals, its testing accuracy is not guaranteed as the signal complexity increases. Therefore, the application of multi-tone signals to the testing is suggested by optimized complex coefficients of each tones for the best statistical similarity to the original modulated signal. From the verification, a 802.11a signal was replaced with a multi-tone signal of N=10, with the complex coefficients generated by the suggested method. The resulting measurements on the ACLR of 2.4 GHz power amplifier showed successful accuracy of less than 1 dB discrepancy.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.3
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• pp.289-293
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• 2013

In the noncoherent methods for UWB-IR (ultra-wideband impulse radio), block coded modulation (BCM) is better than the transmitted reference (TR) systems in terms of the energy efficiency and data rate. However, even BCM suffers from the performance degradation in the presence of strong inter-frame interference and inter symbol interference. We propose the transmitted reference based on the BCM (TR-BCM) which is the hybrid system of TR and BCM. Performance evaluation shows that the performance of TR-BCM is better than that of BCM in the high SNR range.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.2
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• pp.63-72
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• 2018

Theoretical modelling and computational results for frequency coordination are presented based upon minimum coupling loss regarding the same or different wireless systems. Essential parameters involved in frequency coordination are discussed in view of system characteristics, propagation model, availability and protection ratio, frequency dependent rejection or adjacent channel interference ratio, discrimination angle, and its computational results are also evaluated. To illustrate frequency coordination procedure, received interference power between fixed wireless system of victim and mobile base station of interferer are analyzed in urban or sub-urban area and also compared with maximum allowable interference power as functions of discrimination angle and distance for assumed system parameters. The proposed method will play a practical role in technical analysis on co-existence or interoperability for the various wireless systems needed for frequency coordination.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.12
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• pp.2649-2656
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• 2010

MC-DS-CDMA is technique where a single data symbol is transmitted at multiple subcarriers which are orthogonal to each other. With this technique, frequency diversity can be achieved. The performance of uplink MC-DS-CDMA systems with the application of MRRC antenna diversity over time variant channels is analyzed. Time variant channels lead to interchannel interference which increases the bit error rate in the receiver. The BER performance of this system over multipath fading environment is evaluated, considering the channel estimation error, carrier frequency offset, and the nonlinear high power amplifier.

• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.115-119
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• 2017

Intermodulation distortion degrades the S/N(signal-to-noise) of the original signal and also affects the adjacent channels. Intermodulation distortion is mainly caused by the nonlinear characteristics of the power amplifier. If the power amplifier with nonlinear characteristics has a memory effect, the intermodulation distortions occurred in the power amplifier are generated in various and complex forms. The predistorter is used as a way to improve intermodulation distortions. In order to efficiently utilize the performance of the predistorter, the memory effect of the power amplifier must be reduced. In this paper, we describe the design method of bias circuit to reduce the memory effect in power amplifiers. To reduce the memory effect, the bias circuit must have a high impedance for the signal and a low impedance for the envelope(modulating signal) and the second harmonic component of the signal. To verify the performance of the bias circuit designed considering the memory effect, a power amplifier operating at 170 ~ 220MHz was designed and implemented. The designed bias circuit has a large impedance in the operating frequency band and low impedance in the envelope signal and the second harmonic of the signal. As a result of the performance measurement, it was found that the asymmetric intermodulation distortion component is improved by 3.7dB.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.05a
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• pp.681-684
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• 2015

Power amplifier is an essential component for transmitting signals to a remote receiver in wireless communication systems. Power amplifier is a non-linear device in general, and the nonlinear distortion becomes severer as the output power increases. The nonlinearity results in spectral regrowth, which leads to adjacent channel interference, and decreases the transmit signal quality. To linearize power amplifiers, many techniques have been developed so far. Among the techniques, digital pre-distortion is known as the most cost and performance effective technique. However, the linearization performance falls down abruptly when the power amplifier operates in its saturation region. This is because of the severe nonlinearity. To relieve this problem, this paper proposes a new adaptive predistortion technique. The proposed technique controls the adaptive algorithm based on the power amplifier input level. Specifically, for small signals, the adaptive predistortion algorithm works normally. On the contrary, for large signals, the adaptive algorithm stops until small signals occur again. By doing this, wrong coefficient update by severe nonlinearity can be avoided. Computer simulation results show that the proposed method can improve the linearization performance compared with the conventional digital predistortion algorithms.