Dual-phase continuous phase modulation for bandwidth efficient spread-spectrum multiple-access communication
Abstract
A new class of dual-phase, continuous-phase modulated signals is defined for use with spread-spectrum multiple-access systems. The signals are unique in that the information and spreading bits affect the phase separately. These signals are of interest due to their spectral shaping ability and constant envelope. A specific subclass which employs a serial MSK receiver is studied in depth. Arbitrarily close approximations are developed for the autocorrelation and power spectral density of the received signal, for the signal to noise ratio at the receiver's output, and for the probability density function of the output due to the kth interferer. These probability density functions are then used to determine the probability of bit error in the presence of multi-access noise and thermal noise, and to determine a probability of packet failure estimate. Examples are presented for two spreading phase schemes. Specifically, a full response raised cosine and a multi-h partial response raised cosine. Comparisons are shown between these schemes and a BPSK spread-spectrum system. The signal-to-noise ratio comparison demonstrates the benefits of the increased stacking available with spectral shaping. A new density function which models the behavior of our two examples is also presented. The model was determined empirically so its usefulness as a general model is unanswered. Additionally, an efficient method for convolving circularly symmetric two-dimensional probability densities using the image processing technique of back projection is detailed. Its use is demonstrated through the examination of a noncoherent direct sequence spread-spectrum multiple-access system. Finally a brief development of time-spread multiple-access communication is presented. For a single user on a bandlimited channel it can be used to combat the effects of burst noise. Its usefulness as a multiple-access technique is yet to be shown.
Degree
Ph.D.
Advisors
Lehnert, Purdue University.
Subject Area
Electrical engineering
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