An investigation into the properties of the ML-NVE in asynchronous OFDM systems

Orthogonal frequency division multiplexing (OFDM) systems require the knowledge of signal-to-noise ratio (SNR) at receiver in order to maximize system performance. In general, SNR can be estimated with the help of noise variance. The existing literatures mostly assume that noise variance is estimated in the case of that channel status information (CSI) is known in advance and synchronization is perfectly achieved. However, CSI generally cannot be obtained in advance and perfect synchronization is impossible in reality. This paper derives the statistical property (including mean, variance, and MSE) of maximum likelihood noise variance estimator (ML-NVE) in an asynchronous OFDM system with estimated channel. And moreover, simulation results are presented to substantiate the derivations.