In any satellite communication, the Doppler shift associated with
the satellite's position and velocity must be calculated in order
to determine the carrier frequency. If the satellite state vector
is unknown then some estimate must be formed of the Doppler-shifted
carrier frequency. One elementary technique is to examine the
signal spectrum and base the estimate on the dominant spectral
component. If, however, the carrier is spread (as in most satellite
communications) this technique may fail unless the chip
rate-to-data rate ratio (processing gain) associated with the
carrier is small. In this case, there may be enough spectral energy
to allow peak detection against a noise background. In this thesis,
we present a method to estimate the frequency (without knowledge of
the Doppler shift) of a spread-spectrum carrier assuming a small
processing gain and binary-phase shift keying (BPSK) modulation.
Our method relies on an averaged discrete Fourier transform along
with peak detection on spectral match filtered data. We provide
theory and simulation results indicating the accuracy of this
method. In addition, we will describe an all-digital hardware
design based around a Motorola DSP56303 and high-speed A/D which
implements this technique in real-time. The hardware design is to
be used in NMSU's implementation of NASA's demand assignment,
multiple access (DAMA) service.
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