Digital radio performance when the transmitter spectral shaping follows the power amplifier

A digital radio link in which rectangular RF data pulses drive the high-power amplifier (HPA) and spectral shaping of the transmission is done after the HPA is analyzed. The purpose of the analysis is to quantify detection performance for a variety of design possibilities. These include two approaches to predistortion in the transmitter and two ways of setting decision boundaries in the receiver. Also considered are different signal constellations and numbers of levels (M). It is shown that performance differences among practical system designs increase significantly with M. For example, the spread of minimum distance values among the various designs studied here grows from 4.4 dB for M = 16 to 14.4 dB for M = 256.