Estimation of the channel impulse response length and the noise variance for OFDM systems

A new method is proposed for the estimation the channel impulse response (CIR) length and the noise variance for orthogonal frequency division multiplexing (OFDM) systems. To estimate the CIR length and the noise variance, the difference between the statistical characteristics of the additive noise and the mobile radio channel is exploited. This difference lies in the fact that the true CIR coefficients are located within the CIR length, whereas the additive noise of an estimated channel tap is uniformly distributed over the whole length of the estimated CIR. Moreover, the CIR length changes more slowly than its coefficients. An auxiliary function is established to describe these characteristics. The CIR length and the noise variance can be estimated by varying the parameters of the auxiliary function. The proposed method provides reliable information on the estimated CIR length even at signal-to-noise ratios (SNRs) of 0 dB.