HPA non-linear distortions in DVB-T systems simulation and measurement

The new digital standards adopted in Europe for broadcast communication systems use the orthogonal frequency division multiplexing (OFDM) technique which is characterised by non-constant envelope signals. This fact is in contrast with the employment of RF high power amplifiers (HPAs) which are typically non-linear and utilised with low output back off (OBO) in order to maximise the power efficiency. The consequent generation of intermodulation products (IMPs) is responsible for bit error rate (BER) degradation and adjacent channel interference (ACI). This article presents Itelco's experience in this area, outlining the DVB-T performance dependence from the OBO. Moreover the improvements achievable by AM/AM-AM/PM predistortion and by RF non-linear memory compensation are analysed both by simulation and measurements.