Peak-to-Average Power Reduction in Digital Television Transmitters

Orthogonal Frequency Division Multiplexing (OFDM) is one of the modulation techniques used in digital video broadcasting systems. A significant disadvantage of OFDM is that it has a high peak-to-average power ratio (PAPR). This means that the output amplifiers of digital television transmitters must be designed to handle signals that are far in excess of the mean levels. These amplifiers are expensive. One way to reduce the PAPR is to digitally limit the peak value before the signals reach the amplifier. Various clipping techniques have been described in the literature. This paper describes the application of the most effective of these techniques to the European digital video broadcasting system. It is shown that the PAPR can be reduced without significant increase in bit error rate. In practical systems, amplifier non-linearities cause unwanted out-of-band power which may interfere with adjacent television channels. Simulation results are presented for systems with and without clipping and for varying amplifier characteristics showing that clipping substantially reduces the level of out-of-band power.