• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.4
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• pp.669-678
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• 1994

This paper presents a new data predistortion technique with memory to compensate for the nonlinearities of high-power amplifiers (HPA`s) in digital radio systems employing QAM signal formats. In contrast with the conventional data predistortion technique which is designed to reduce nonlinearity of memoryless HPA`s, the proposed technique in this paper compensates not only for nonlinear warping of the signal constellation but also for clustering of the signal points caused by transmitter pulse sharping filter with memory. A practical implementation method which can reduce the size of memory at the predistortion stage is described by utilizing symmetry of QAM constellation format and Modulo-4 operation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.1
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• pp.40-52
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• 1997

It has been known that the OFDM-based terrestrial broadcasting systems are significantly more sensitive to nonlinear distortion in high-power amplifiers (HPA's) than the broadcasting systems using single-carrier modulation technique. In this paper, an adaptive precompensator which can compensate the nonlinear effect of the HPA for OEDM systems is proposed. The proposed precompensator consists of a compensation table, realized by memory (RAM), and an adaptive algorithm which can update the values of the compensation table more efficiently using a

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.10
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• pp.895-902
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• 2012

In this paper, we propose a novel equalizer to compensate for the group delay including AM/PM nonlinear distortion characteristics by the nonlinear power amplifier (PA). The group delay characteristic is a nonlinear non-constant time delay that appears differently depending on each frequency component. The phase distortion by AM/PM characteristics arising from the power amplifier is a major factor to increase group delay. By the group delay distortion, the signal in the constellation expands and is rotated. Considering the problem mentioned above, the nonlinear time delay that appears differently depending on each frequency component is classified as a static group delay and AM/PM characteristic of PA, the different phase transitions depending on the size of input signal as a dynamic group delay. Static group delay estimates and compensate for phase distortions in the frequency domain with type-based method and dynamic group delay compensates for phase rotation in the time domain. We confirmed that the group delay compensation techniques were enough to compensate the group delay characteristics including AM/PM characteristics of the power amplifier.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.605-608
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• 2001

This paper proposes LUT based predistorter using interpolater to reduce nonlinear distortion which was generated by HPA. We minimized performance degradation from the reduced LUT size with linear interpolation. We updated LUT using LMS algorithm using input data as reference data. As a result, it is shown that when the size of the LUT is 8, linear interpolation is the most outstanding performance in the view of performance and H/W complexity.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.211-214
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• 1998

The high power amplifier (HPA) for broadcasting transmitter systems has nonlinear property in terms of input signal power. Hence, it produces AM/AM and AM/PM modulation to the modulated signal. Therefore, the non-linearity results in bandwidth expansion and nonlinear distortion to in-band signal. In this paper, we propose a simple sain-based predistorter that requires less computational burden and less time for the full initialization of the pre-distorter ROM table.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.12 s.103
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• pp.1229-1238
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• 2005

OFDM(Orthogonal Frequency Division Multiplexing) communications system is very attractive for the high data rate wireless transmission. However, it may be distorted in the nonlinear HPA(High Power Amplifier) since OFDM signal has hish PAPR(Peak-to-Average Power Ratio). In this paper, a new method using control tone is studied for reducing the PAPR and we call it PCT(PAPR Control Tone) method. This proposed PCT method is to assign control tones for PAPR reduction at the predefined sub-carriers. After IFFT(Inverse Fast Fourier Transform) and PAPR calculation, the OFDM data signal of the lowest PAPR is selected to transmit. Unlike the conventional method, it can cut down the computational complexity because it does not require the transmission and demodulation process of side information about the phase rotation. Furthermore, if this method is made up in parallel configuration, it can solve the time delay problem so that it can be processed in real time processing. This proposed method is compared with the conventional selected mapping(SLM) technique. We find out the PAPR reduction performance and BER when the number of control tone is 6 and nonlinear HPA is considered.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1341-1347
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• 2000

For the DRT satellite transponder system, BER and total SNR to be required in the earth terminal are evaluated under the condition of HPA nonlinearity in the FBJ(full-band jamming) or PBJ(partial-band jamming) of uplink and downlink. In case that the satellite Inter bandwidth( Ws) is same to the earth terminal bandwidth($W_r$),in conditions of uplink JSR 10[dB], downlink JSR 10[dB] and processing gain 30[dB], linear transponder system shows that uplink SNR needs to be 14.2[dB] to achieve the total SNR 10[dB] requirement in downlink SNR 14[dB]. However, Nonlinear transponder system with OBO(output backoff) 2[dB] requires 20.1 [dB] uplink SNR. From the above results, the nonlinearity of HPA in the satellite transponder causes the degradation of BER performance so that it is of interest to consider the power increase.

• Journal of Advanced Navigation Technology
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• v.10 no.1
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• pp.20-25
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• 2006

In these days, OFDM(Orthogonal Frequency Division Multiplexing) is adopted to support high-speed data communication based on multi-path RF channel, but it has some weak point. One of those is that it has a higher PAR(peak-to-average power ratio) compared with single-carrier method. If some PAR of the transmitted signal is high, nonlinear amplitude distortion has occurred when it pass through the HPA(high power amplifier). There is a solution to prevent nonlinear distortion using higher peak power HPA, but it makes inefficiency and a cost problem. In this paper, we choose the SLM(Selected Mapping) scheme, which transmit the lowest PAR signal after OFDM symbol mapping, in various schemes reducing PAR for OFDM system. And we derived the performances of SLM method in fading channel through computer simulations.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.1
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• pp.64-69
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• 2005

In this paper, we analyzed the nonlinear performance on the DS/CDMA Communication System. At the $BER=10^{-4}$, uniform chip waveforms have similar performance in the linear channel. However, non-uniform chip waveforms have about more 0.5[dB] power gain than the conventional raised-cosine chip waveforms. In the nonlinear HPA, non-uniform chip waveforms have worse BER performance than the uniform chip waveforms because of the high PAPR. In other words, non-uniform chip waveforms show similar performance as uniform chip waveforms if IBO (input back on) of 15[dB] is given.

• Proceedings of the IEEK Conference
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• 2001.06a
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• pp.185-188
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• 2001

In this paper, we design and implement high-power amplifier with 18 watt for W-CDMA repeater. We simulate microwave circuits using RF simulator, ADS1.3 and optimize the circuit to obtain the linear and high power using Harmonic balance method. Harmonic balance is an excellent method in the analysis of nonlinear system. The HPA is fabricated on tefron substrate($\varepsilon_{{\gamma}}$=3.48, h=0.5mm, T=0.035mm). From the measured result, the HPA has gain of 52dB, 1 dB compression power of 52.8dBm and good ACPR (Adjacent Channel Power Radio) performance.l Power Radio) performance.