Performance analysis of a digital radio system with filtering after the transmitter power amplifier.

The performance of the digital radio system working in a nonlinear environment, measured in terms of the minimum distance of the received constellation with respect to the decision region boundaries, is analyzed. This analysis compares different signal processing strategies, including predistortion of the signal constellation, to compensate for the transmitter power amplifier nonlinearity. Also, different signal constellations are considered and several numbers of point (16, 64, and 256). The main conclusion is that data predistortion to obtain a square QAM constellation outperforms almost all other design configurations considered. For example, relative to a conventional design (no predistortion), improvements of 8.5 dB and 12.5 dB are possible, respectively, for 64-level and 256-level modulations.