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A Code Division Multiple Access Communication System for the Low Frequency Band.
ILLINOIS UNIV AT URBANA COORDINATED SCIENCE LAB
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In this thesis, a code division multiple access CDMA communication system for the low frequency LF channel is proposed, discussed and analyzed. This LFCDMA scheme is similar to classical CDMA schemes in that K users share a channel by phase modulating their transmissions with signature sequences. Our LFCDMA scheme is different in that each users signature sequence set consists of M orthogonal sequences and thus log 2M bits of information are transmitted by choosing among the signature sequences. Additionally, the users use r-phase modulation and our model includes an impulsive non-Gaussian noise source to model LF atmospheric noise. We derive a locally optimum small signal receiver structure for our LFCDMA scheme. This receiver consists of a bandpass correlator followed by a sampler, a zero memory nonlinearity and M discrete time matched filtercorrelators. We analyze the performance of this structure in combined multiple access, impulsive and Gaussian noise. When the noise is dominated by either its multiple access or Gaussian component, the receiver predominantly operates in the linear region of the nonlinearity and performance is similar to that of a linear receiver.
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