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Cover: Class MIMO-OFDM Deep Learning Channel Estimation #3: Classical Estimators: Least Squares and MMSE
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Here is the final result, 2 classical channel estimators. List scores hit the NMSI minus 9 dB regardless of SNR, while LMMSI keeps improving up to minus 21 dB. The average LMMSI is almost 7 dB more accurate. Let's get started. Hello, welcome to episode three of the massive MIMO FDM channel estimation series with Deep Neural Networks. Before using Deep Learning, we need a strong classical benchmark. List scores are the simplest one, and LMMSI is optimal for linear estimators when channel statistics are known.
Create a file estimator.py List scores in the pilot subquerier simply divide the received signal by the known pilot. Since the pilot is valued at 1, the estimation is the same as the received signal. The subquerier between pilots is filled with linear interpolation, and the subquerier after the last pilot is extrapolated. The frequency covariance function calculates the correlation matrix between 64 subqueriers from the training data, that is, the average of H times H hermitian.
The LMMC function calculates RHP multiplied by inverse RPP plus sigma squared I, multiplied by the LS estimate. This matrix weights each pilot according to its correlation with the target subquerier and the draw level. Since each sample can have a different SNR, we use the Agen decomposition, RPP equals U lambda U hermitian, so the inverse for any sigma is just 1 over lambda plus sigma squared, and 12,000 samples can be calculated at once in half a second.
Create a file test underscore estimator.py and run it. At -10 dB, LS is very poor, NMSI at +9 dB, meaning the error is larger than the channel itself, while LMMSI is at -0.8 dB. At 0 dB, LS is -0.5 and LMMSI is -4.6 dB. At 20 dB, LS hits -9.2 due to interpolation error, while LMMSI reaches -21 dB. The average LMMSI is 6.96 dB better.
Let's look at the graph. The LS curve flattens at high SNR, because interpolation error cannot be eliminated by increasing power. The LMMSI curve continues to decrease. The right graph shows one antenna at 10 dB SNR, the red LS point is scattered, its interpolation line is rigid, while LMMSI smoothly follows the actual channel. However, LMMSI only uses correlation between subcarriers, and has not yet utilized correlation between 32 antennas.
Done. We have built the least-squares estimator with interpolation and LMMSI with frequency covariance and agent decomposition, and compared their NMSE. In the next episode, we will build a CNN which utilizes the correlation between antennas and subcarriers simultaneously. Currently working on a thesis, dissertation, or research in the field of telecommunications and artificial intelligence? Cerdas Inovasi Digital helps implement communication system research from OFDM and multipath channels, massive MIMO simulations, least squares and MMSE estimators, up to deep learning-based channel estimation with PyTorch, as well as opening Python programming courses for electrical engineering and telecommunications. Want to master the entire series, from basic OFDM up to NMSI and BER evaluation? All 6 episodes, complete with step-by-step PDF guides and source code, are available to premium tutorial subscribers. Subscribe starting at Rp69.000 per month, save 28% with the 12-month package, or one-time payment of Rp999.000 for lifetime access. Want just one class? Buy a single class with lifetime access. Subscribe now at the premium page CerdasInnovasiDigital.com Contact us via WhatsApp, or visit CerdasInovasiDigital.com Thank you for watching, See you in the next episode. Thank you for watching. See you in the next episode.
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