OFDM Signal Degradation by Amplifiers and Measuring Method of the Nonlinearity

Abstract

An OFDM signal is easily degraded by amplifier nonlinearity. A method for measuring such nonlinearity has been developed and tested in two ways : vector measurement using the two-tone method and comparison between a sinc-shaped input signal and the output signal. Four amplifier characteristics were measured with the methods and represented as AM-AM/AM-PM conversion characteristics. Using these results, computer simulation was run to determine the effect of nonlinearity. OFDM signals were generated and the CN ratios were measured. The results agreed with those of the experiments. Testing of the predistortion in the amplifier with the most remarkable AM-PM characteristic confirmed the simulated predistortion.