Time varying channels cause a loss of orthogonality among the subcarriers of an Orthogonal Frequency Division Multiplexing (OFDM) symbol and lead to inter-carrier interference (ICI) and degradation in performance. In this work, we propose an enhanced Maximum Ratio Combining (MRC) scheme, which takes into consideration the colored nature of ICI in a frequency selective channel. In DVB-T/T2, continual pilots (CoPs) are used at the receiver side to estimate the noise power per receive antenna. We show that a significant gain can be achieved, when the noise power per subcarrier is fed to the MRC block instead of the average noise power per antenna. We propose to use a window over the set of CoPs to estimate the localized noise power instead of the average noise power. The optimum size of the window depends on many factors such as the Doppler shift, additive white Gaussian Noise (AWGN) power and channel frequency selectivity. Motivated by the unequal pilot spacing of the CoPs as well as the frequency correlation of the noise power in a doubly selective channel we propose a simple weighting criterion for the noise window samples, which provides a good performance over a wide range of SNR and Doppler shift.
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