Investigating the effects of filtering, clipping, and power amplification on the performance of OFDM waveforms

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) has become a very popular technique for digital data transmission on multipath fading channels due to its low computational complexity and simple equalization process. However, the multipath component of these types of channels causes a phenomenon known as frequency selective fading. This type of fading can severely degrade or completely eliminate the signal energy of many of the OFDM tones producing an irreducible error rate, even when no noise is present. Consequently, most OFDM systems operating in multipath fading environments utilize some form of forward error correction (FEC) and block interleaving. OFDM waveforms which utilize FEC are usually referred to as coded OFDM (COFDM). One of the main drawbacks of OFDM and COFDM waveforms is the very large peak envelope power to average power ratio (PAPR) which requires the use of very linear power amplifiers (PA) and a large power back-off into the PA. To reduce the PAPR, clipping is typically utilized. In addition, filtering must be applied to OFDM and COFDM waveforms in order to contain their spectral occupancy. This paper will investigate the effects of filtering, clipping and power amplification on the performance of OFDM and COFDM waveforms. The multipath fading channels used for testing will be based on the High Frequency (HF) channels due to their challenging nature.