• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.12
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• pp.948-953
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• 2017

When using a high-power amplifier(HPA) for high-speed communication, the nonlinear characteristics of the HPA deteriorate power efficiency, bit error rate(BER) performance, and spectral efficiency. Because it is inevitable to use the HPA to obtain sufficient transmission power for high-speed communication, it is necessary to compensate for nonlinearity of the HPA by using a predistorter. In this study, a predistorter was used to compensate for the nonlinearity of the HPA, and the nonlinear distortion was compensated using the predistorter. Simulation results show that the compensation of the nonlinearity of the HPA using the predistorter achieves a BER performance similar to that of an ideal linear amplifier, and that the spectral mask is also satisfied.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.4
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• pp.415-423
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• 2016

High PAPR (Peak-to-Average Power Ratio) characteristic causes some problems like system performance degradation and OOB (Out-of-Band) power increasement under the HPA (High Power Amplifier) nonlinearity condition. UFMC (Universal Filtered Multi-Carrier) and FBMC (Filter Bank Multi-Carrier) are regarded as 5G(Generation) candidate waveforms. In this paper, we evaluate and analyze performance of these systems with DFT-s (Discrete Fourier Transform Spreading) technique under the nonlinear HPA environment. In this paper, we describe OFDM (Orthogonal Frequency Division Multiplexing), UFMC, FBMC, DFT-s-OFDM, DFT-s-UFMC, and DFT-s-FBMC system, and evaluate BER (Bit Error Rate) performance of these systems. As simulation results, BER performance degradation by HPA nonlinearity of DFT-s-OFDM and DFT-s-UFMC is greatly overcome by DFT spreading technique. However, BER performance degradation by HPA nonlinearity of DFT-s-FBMC system is little overcome.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.4
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• pp.369-376
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• 2016

In this paper, we propose and design a SSD(Simultaneous Single band Duplex) system using 5G(Generation) candidate modulations. Especially, we consider HPA(High Power Amplifier) nonlinearity in the proposed system. And then, we evaluate and analyze performance of the proposed system. As simulation results, performance of SSD-OFDM(Orthogonal Frequency Division Multiplexing), SSD-FMC (Universal Filtered Multi-Carrier), and SSD-FBMC(Filter Bank Multi-Carrier) is severely degraded by HPA nonlinearity. However, performance of SSD-OFDM, SSD-UFMC, and SSD-FBMC is similar in the same condition. That is, OFDM, UFMC, and FBMC have a similar PAPR(Peak to Average Power Ratio) characteristic. Finally, we can confirm that the proposed SSD system can not cancel(SI) self-interference effectively by strong HPA nonlinearity. That is, Reducing PAPR is important in order to avoid effect of HPA nonlinearity in the proposed SSD system.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.10
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• pp.8-16
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• 2010

An orthogonal frequency division multiplexing (OFDM) system is a special case of multicarrier transmission, where a single data stream is transmitted over a number of lower-rate subcarriers. One of the main reasons to use OFDM is to increase robustness against frequency-selective fading or narrowband interference. However, in the radio systems the distortion introduced by high power amplifiers (HPA's) such as traveling wave tube amplifier (TWTA) considered in this paper, is also critical. Since the signal amplitude of the OFDM system is Rayleigh-distributed, the performance of the OFDM system is significantly degraded by the nonlinearity of the HPA in the OFDM transmitter. In this paper, we propose a simplicial canonical piecewise-linear (SCPWL) model based digital predistorter to compensate for nonlinear distortion introduced by an HPA in an OFDM system. Computer simulation is carried on an OFDM system under additive white Gaussian noise (AWGN) channels with 16-QAM and 64-QAM modulation schemes and modulator/demodulator implemented with 1024-point FFT/IFFT. The simulation results demonstrate that the proposed predistorter achieves significant performance improvement by effectively compensating for the nonlinearity introduced by the HPA.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.6
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• pp.3-14
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• 2016

Recently, researches for new waveforms have been carried in order to satisfy KPI for 5G mobile communication system. UFMC and FBMC are well known as ways to reduce OOB power. In this paper, we analyze spectrum of OFDM, UFMC, and FBMC system under nonlinear HPA environment. And then we evaluate and analyze performance of these systems under the same environment. As simulation results, OOB power of OFDM, UFMC, and FBMC increases with HPA nonlinearity increasement. Especially, OOB power of FBMC is the largest increase due to HPA nonlinearity. Also, BER performance of these systems is degraded by increasement of HPA nonlinearity. Therefore, In this paper, we can confirm that a system with low-complexity and high-speed processing is advantageous, because BER performance and OOB power characteristic of these systems are degraded to similar level, when these systems are implemented in real world.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2A
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• pp.166-173
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• 2004

Satellite communication system uses a high non-linear HPA(high power amplifiers) in the earth station and satellite transponder. Therefore, it is important to consider the nonlinear effect of HPA on the communication system. In this paper, we find the variation of power spectrum density by nonlinearity HPA and the change of harmonic component according to IBO (input back-off). When the BPSK is used for satellite communication system, we analyze BER performance including the external co-channel interference (CCI) and the adjacent channel interference (ACI) resulting from the HPA nonlinearity. BER degrades as ACI magnitude grows up when the uplink SNR, uplink SIR (signal to co-channel interference power ratio) and downlink SIR are constant at some level. In case there is only non-linear HPA in the satellite, it is shown that BER considerably depends on the ACI magnitude ACI. When there are two non-linear HPAs in the both earth station and satellite, much BER degradation results from the CCI and ACI.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.7
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• pp.692-697
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• 2004

OFDM system is very useful for the multi-path channel and highly bandwidth-efficient system. However, OFDM signal shows the high PAPR so that nonlinear distortion can happen in the HPA(high power amplifier). This paper studies BER performance variation according to IBO(input back off) values when the predistorter is used fur the compensation for the HPA nonlinearity. In case of the SSPA(solid state power amplifier) of nonlinearity parameter p=0.5 and IBO=0㏈, the system with predistorter is poorer than the one without predistorter. But this situation is inverted, if IBO is increased from 0㏈ to 3㏈. So, we can find that there is a threshold value of IBO for the predistorter to effectively compensate for the nonlinear SSPA when the sub-carrier number and p value are changed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6A
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• pp.488-498
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• 2005

The DAB(Digital Audio Broadcasting) service which is based on the Eureka-147 of Europe is developed to DMB(Digital Multimedia Broadcasting) service that is divided into Terrestrial DMB and Satellite DMB. The Satellite DMB is a new broadcasting service, which will service multi-channel multimedia broadcasting by the portable receiver or the vehicle receiver. In this paper, we consider that link level performance of satellite DMB system A which is based on the COFDM(Coded Orthogonal Division Multiplexing). It uses the OFDM method which is sensitive to nonlinearity, so we analyze the effect of the HPA(High Power Amplifier) nonlinearity. And then we define the appropriate back-off value by performing the link level simulation considering back-off effect. Also we consider the effect of frequency and time offset, and then confirm the overall link level performance by analyzing and verifying a suitable synchronization method for satellite DMB system A.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.122-127
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• 2003

In this paper, an adaptive predistortion scheme is proposed to compensate nonlinear distortions caused by high power amplifiers (HPA) in OFDM systems. A complex Wiener-Hammerstein model (WHM) is used to describe input-output relationship of HPA with linear dynamics. The predistorter is directly identified by complex power series model with memory, which is an approximate inverse of the HPA expressed by the WHM. The effectiveness of the proposed adaptive compensation scheme is validated by numerical simulation for 64QAM-OFDM systems.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.5
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• pp.68-75
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• 1994

A new Predistortor that is designed using Feedforward type is proposed to overcome the nonlinearity of HPA (High Power Amplifier). HPA has the nonlinearity of the gain compression and phase distorton, so digital communication system of multi-carrier TDMA needs the linear RF transmitter. Using IMD (Intermodulation Distortion) of drive amplifier, as Feedforward type, the inverse IMD is coupled to the main loop with variable attenuators, phase shifters, and sub-amplifiers well designed. At the input of main amplifier, the over-coupled IMD surpresses the main amplifier 's IMD. Adjusting the level and phase of IMD at the sub loop, C/I of HPA is better than before correction.