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CFO estimation in OFDM systems and effects of nonlinear power amplifiers

It is well known that Carrier frequency offset (CFO) is a performance limiting factor in orthogonal frequency division multiplexing (OFDM) systems. In this paper, we present maximum-likelihood estimators (MLE) for the CFO in OFDM systems in static and time-varying channels and evaluate the Cramer-Rao lower bounds (CRLB) for both cases. In addition, we examine the effect of power amplifiers' (PA) nonlinearity, which can be either memoryless or with memory. This nonlinearity impacts the system performance in several ways including higher BER and degraded channel estimation accuracy. In this paper, we analyze the effect of PA nonlinearity with memory on CFO estimation, quantifying the performance degradation caused by PA nonlinearity and the gain provided by employing predistortion filters.