HTML5 Webook

150/182

compensation amplier itself, and the whole power e-ciency of the power amplier becomes low. It also has the disadvantages that the distortion compensation character-istics are required to be optimized depending on changes of the amplier subject to compensation and the charac-teristics of the compensation amplier itself, and to maintain the good transmission characteristic is dicult.e digital pre-distortion technique is a method to digitally compensate non-linearity with the feedforward system. e Digital Pre-Distortion (DPD) is a technique that in advance obtains the non-linearity of the amplier which is subject to compensation by measuring, etc., and removes the distortion component from the output signal of the amplier by giving the amplier the reverse non-linearity of the input signal. e advantages of the DPD are that a voluntary distortion compensation characteristic can be easily expressed only by multiplying the transmit-ting signal, digitally created, by a corrective coecient, that the DPD is invariable to time, and that the distortion characteristics can be readily corrected, as necessary, by the method of writing the distortion compensation character-istic data in recording elements. ese features can stably maintain the optimal characteristics even aer launching the satellite. e expression of the corrective coecient for the DPD has the approximation by a polynomial and the method of referencing the LUT (Look-up Table). Generically, the handling complexity depends on the amplier charac-teristics and the distortion compensation performance to be materialized. If the frequency dependence of the ampli-er is suciently small, it is promising as a distortion Input power [dB]Output power[dB]Linear lineInput power [dB]Phase shift[deg]Original characteristics of an amplifierCompensated characteristics of an amplifier by digital pre-distortionFiF1　Linearization concept diagram of amplifier by the DPDFiF2　WINDS experiment system diagramIFPatch3.2GHz25.05GHz3.2GHz9.8GHz3.2GHz28.25GHz18.45GHz3.2GHzMODboard〜HPAmixerU/CD/CTranslatormixerSpectrumAnalyzerLNABent‐pipe linkKIZUNA（WINDS）4.8mantennaHPA︓High power amplifierU/C︓Up converterD/C︓Down converter4.4GHz1.2GHzReceiver〜Signal Generator〜Signal Generator(clock signal)〜15.25GHz28 GHz band18 GHz band〜NICT Facilities〜Signal GeneratorHYBRID*Symbol constellation measurement*Spectrum measurement3 Ultra-High-Speed Satellite Communication Technology146　　　Journal of the National Institute of Information and Communications Technology Vol. 64 No. 2 (2017)