{'fraction_non_alphanumeric': 0.024907749077490774, 'fraction_numerical': 0.0, 'mean_word_length': 5.458333333333333, '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}}
Transmit/receive filter optimization for doubly-selective underwater acoustic channels

Orthogonal Frequency Division Multiplexing (OFDM) is receiving increased interest for use in underwater acoustic communication systems. It is well-known that OFDM decomposes linear time-invariant channels into a set of parallel (non-interfering) channels via a Fourier basis. However, underwater acoustic communication channels can suffer from significant Doppler effects; for time-varying channels, inter-channel interference occurs and may have a dramatic impact on the performance. Doubly-selective channels and block-based transmissions are examined. In contrast to much work on pulse shape design, a signal-to-interference plus noise ratio metric is considered as the metric for waveform design. Prior work is extended through the use of an alternate view of the cost function which is easier to optimize and yields improved results at high SNR. Numerical results on the mutual information reveal significant gains over classical zero-padded OFDM and the pulse shape designs of Lattice OFDM.