CIR denoising refers to the process of reducing noise in the Channel Impulse Response (CIR) estimates obtained during channel estimation, enhancing the accuracy of the estimate. Time-domain windowing functions are used for CIR denoising due to their ability to reduce spectral leakage and suppress noise components effectively. Each window function has specific characteristics that influence its effectiveness in denoising.
Here is a brief summary of the purpose of w in the nrChannelEstimate function:
- w is defined as a raised cosine window, which helps to smoothly taper the edges of the CIR, reducing spectral leakage and noise. It is extended and shifted to align it with the main part of the CIR.
- Interpolators are created for virtual pilots, which help in estimating the channel at the edges of the frequency band. This is to combat the Gibbs Phenomenon caused by the FFT/IFFT perfomed later.
- Certain processing steps are performed on the Least Squares (LS) channel estimate using the virtual pilot interpolators to widen and improve the estimate.
- An Inverse Discrete Fourier Transform (IDFT) is performed on the channel estimate to get the CIR.
- The CIR is denoised through element wise multiplication with the window w.
- A Discrete Fourier Transform (DFT) is performed on this CIR to get the denoised channel frequency response, which is then used in further processing steps.
The following paper can be referred to for a description of the basic techniques of LS estimation and CIR denoising:
Van de Beek, J.-J., O. Edfors, M. Sandell, S. K. Wilson, and P. O. Borjesson. “On Channel Estimation in OFDM Systems." Vehicular Technology Conference, IEEE 45th, Volume 2, IEEE, 1995.
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