Background estimation of power amplifier nonlinearities for OFDM signals

A method of estimating the third-order distortion coefficient of a memoryless amplifier is presented for the case of an OFDM signal. The estimate is obtained from correlation of the existing PRBS sequences BPSK modulated onto the OFDM pilots with in-band pilot distortion products at the amplifier output. The estimate was used for digital pre-distortion of the amplifier, with 8-10 dB measured improvement in the adjacent channel power ratio (ACPR). The method can be used for real-time estimation of nonlinearities without unduly affecting the communication link.