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In this paper, the authors describe direct-sequence Code-Division Multiple-Access (CDMA) systems with M-ary modulation in which channel estimation, coherent demodulation, and decoding are iteratively performed without the use of any training or pilot symbols. An expectation maximization channel-estimation algorithm for the fading amplitude and interference-plus-noise Power Spectral Density (PSD) is proposed for CDMA systems with low-density parity-check codes. The elimination of pilot symbols simplifies the system design and allows either an enhancement in information throughput or greater spectral efficiency by increasing the information-symbol duration.
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