{'fraction_non_alphanumeric': 0.028836251287332648, 'fraction_numerical': 0.0010298661174047373, 'mean_word_length': 5.437086092715232, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Channel Estimation for MIMO-OFDM Systems in Non-sample-Spaced Multipath Channels

The decision-directed space-alternating generalized expectation-maximization (SAGE) algorithm is introduced in [1] to estimate the channel and track the channel varying for OFDM systems with transmitter diversity. However, this method is based upon a discrete Fourier transform (DFT), which will cause power leakage and result in an error floor in a multipath channel with non-sample-spaced time delays. In order to overcome this problem, a low rank approximation method is presented by using the signal subspace of the channel frequency autocorrelation matrix. Furthermore, a modified fast subspace tracking algorithm is introduced to adaptive estimate the signal subspace by using a space–time block coded training blocks sent at regular interval. Simulation results show the advantages of the proposed technique for MIMO-OFDM systems in time-varying non-sample-spaced wireless channels.