Ofdm System Linear Power Amplifier, Baseband Adaptive Pre-distortion Study

RF and MW power amplifiers are the essential compenents in communication and Radar systems. With the development of linear modulation technique, the usage of such non-constant envelop modulation techniques as QAM,QPSK,OFDM, is caused high linearity of power amplifier.In this article,some algorithm research and simulations of baseband adaptive predistortion about non-linear PA of OFDM system as follows:Firstly, some models and coefficients about SALEH and arc-tangent coming from early articles, are improved and opitimized and the simulating results of these models is compared with actual PA's nonlinearity.Secondly,the ACPR of developed one-by-one iterative predistortion algorithm is -57.594dB,which is increased 1.1013dB with the old ones. At the same time ,the error vector magnitude (EVM) and the amplitude error(AE) are also better. The inter-modulation products and ACPR to two tone signal(2009.5MHz and 2010.5MHz) are simulated with QR decomposed RLS predistortion algorithm, in this method ,the 3rd inter-modulation products is depressed with 16dB,5th one with 6dB,7th one with 3dB, and the ACPR is depressed with 27.21dB comparing to no predistortion.At last, some system simulations are carried through in different conditions. In the condition of non-considering modulation and demodulation error and adding one-by-one iterative predistortion algorithm, the 3rd inter-modulation products is depressed with 21dB,5th one with 8 dB,7th one with 5dB. In the condition of considering modulation and demodulation error and adding one-by-one iterative predistortion algorithm, the 3rd inter-modulation products is depressed with 27dB,5th one with 13 dB,7th one with 7dB. In the condition of non-considering modulation and demodulation error and adding QR decomposed RLS predistortion algorithm, the 3rd inter-modulation products is depressed with 26dB,5th one with 12 dB,7th one with 6 dB. In the condition of considering modulation and demodulation error and adding QR decomposed RLS predistortion algorithm, the 3rd inter-modulation products is depressed with 30 dB,5th one with 16 dB,7th one with 10 dB. The ACPR is depressed with 15dB in the condition of non-considering modulation and demodulation error and adding adaptive predistortion comparing with no predistortion, with 17dB in the condition of considering modulation and demodulation error and adding one-by-one iterative predistortion algorithm ,with 20dB in the condition of considering modulation and demodulation error and adding QR decomposed RLS predistortion algorithm...