Experimental Analysis of Clipping and Filtering Effects on OFDM Systems

Orthogonal frequency division multiplexing (OFDM) has an advantage of high bandwidth efficiency, but it suffers from high peak-to-average power ratio (PAPR) which causes severe nonlinear distortion in actual devices such as power amplifiers. Several techniques have been proposed in order to reduce PAPR. Among them, clipping and filtering (CAF) is considered attractive due to its simple structure. The CAF can reduce nonlinear distortion in analog devices and as a result out-of-band radiation is reduced. However, it causes the so-called in-band distortion and thus increases signal distortion or error vector magnitude (EVM). In this paper, we analyze the effects of the CAF on the OFDM system through experiment using a real power amplifier. By adjusting the input back-off (IBO) of the power amplifier, we evaluate the increase of the received power for a given EVM and sidelobe level of power spectra that may contribute to adjacent channel interference (ACI). It is shown that by appropriately adjusting the IBO and clipping ratio, the received power can be improved by several dB while maintaining the amount of ACI for a given EVM.