Performance analysis of digital radio links with nonlinear transmit amplifier and data predistorter with memory

A method of introducing an adaptive digital predistortion circuit to compensate for the nonlinearity produced in digital radio systems by the high-power amplifier (HPA) is proposed. The method is attractive for its simplicity (two digital finite-impulse response (FIR) filters) and because of the inherent adaptability to any nonlinearity. The simplicity of the predistorter is worth noting; only two parameters (α₁ and α₃) need to be estimated in place of tens of the third-order kernel coefficients, as proposed in previous schemes. The performance gain is about 3 dB for a 64 quadrature amplitude modulation (QAM) system without predistortion and 1 dB for a system with memoryless data predistortion. The corresponding values for the 256 QAM system are 4 dB and 1.5 dB, respectively