A Code Division Multiple Access Communication System for the Low Frequency Band
Enge, Per Kristian
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https://hdl.handle.net/2142/69255
Description
Title
A Code Division Multiple Access Communication System for the Low Frequency Band
Author(s)
Enge, Per Kristian
Issue Date
1983
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Abstract
In this thesis, a code division multiple access (CDMA) communication system for the low frequency (LF) channel is proposed, discussed and analyzed. This LF/CDMA scheme is similar to classical CDMA schemes in that K users share a channel by phase modulating their transmissions with signature sequences. Our LF/CDMA scheme is different in that each user's signature sequence set consists of M orthogonal sequences and thus log(,2)M 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 LF/CDMA scheme. This receiver consists of a bandpass correlator followed by a sampler, a zero memory nonlinearity and M discrete time matched filter/correlators. 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.
We analyze the multiuser error probability (MEP) of the linear receiver by using a Gaussian assumption to find an approximation and a characteristic function method to achieve a sharp upper bound. The approximation and the bound sometimes have substantial discrepancies and these differences are discussed.
Finally, we design two actual sequence sets for our LF/CDMA scheme. Our sequence set design strategy is to minimize the maximum magnitude of the interference that any one user's transmitter can introduce into the receiver of another user. Two sequence designs result, where one is based on additive characters and the other on multiplicative characters. These designs are analyzed and their differences are discussed.
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