Orthogonal frequency division multiplexing (OFDM) is an effective technique for high-speed digital transmission over timedispersive\r\nchannels. However, for coherent detection, a reliable channel estimation (CE) is required. OFDM is characterized by\r\nits high peak-to-average power ratio (PAPR), which makes it very sensitive to nonlinear distortions that may affect the channel\r\nestimation accuracy leading to a bit error rate (BER) performance degradation. In this paper, we present closed-form BER\r\nexpression for OFDM with a pilot-assisted CE in a nonlinear and frequency-selective fading channel. We discuss how, and to\r\nwhat extent, the nonlinear degradation affects the BER performance with the CE based on a time/frequency division-multiplexed\r\n(TDM/FDM) pilot. The analysis is based on a Gaussian approximation of the nonlinear noise due to both HPA amplitude\r\nlimitation and quantization. We also evaluate the estimator�s mean square error (MSE) with both TDM and FDM pilots. Our\r\nresults show that pilot-assisted CE using FDMpilot is more sensitive to nonlinear distortions than the CE using a TDMpilot, since\r\nits pilot subcarriers are affected by nonlinear noise due to both the HPA and the quantization.
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