Channel Impulse Response Length and Noise Variance Estimation for OFDM Systems With Adaptive Guard Interval

A new algorithm estimating Channel Impulse Response (CIR) length and noise variance for Orthogonal Frequency-Division Multiplexing (OFDM) systems with adaptive Guard Interval (GI) length is proposed. To estimate the CIR length and the noise variance, the different statistical characteristics of the additive noise and the mobile radio channels are exploited. This difference is due to the fact that the variance of the channel coefficients depends on the position within the CIR, whereas the noise variance of each estimated channel tap is equal. Moreover, the channel can vary rapidly, but its length changes more slowly than its coefficients. An auxiliary function is established to distinguish these characteristics.