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Spread spectrum systems offer high immunity to interference
and frequency selective fading. However, this advantage
is dependent on accuate receiver synchronization. The
code acquisition scheme in the direct-sequence spread
spectrum (DS/SS) system usually employs a passive
correlator,the matched filter, as the first dwell
stage of the detector.And then, it is followed by the
integration andthe majority-logic verfication processes. The
search strategy analyzed in this thesis is that of a
straight serial search, whereby the uncertainy
region is assumed equal to the code length. The
verification mode is to effectively eliminate catastrophic
false alarms, therefore increasing the statistical reliability.
The DS/SS code acquisition system is an
immediate-rejection/two-dwell hybrid system. The spread spectrum
code acquisition using the matched filter in the presence of
additive white Gaussian noise and data modulation is
investigated. From the simulation results, we can
obtain explicit relationship between the system
performance and the design parameters, such as
the received SNR (signal to noise ratio),
the threshold value, and the mean acquisition time.
In addition to the computer simulation using the Matlab,
the code acquisition algorithm is implemented on the DSP
module (TI TMS320C44 with A/D,D/A interface). Real-time
ASCII data transmission through the wire between two PCs
is realized by C-language programing. For the purpose of
reducing the calculation time of DSP, we apply only
the first-dwell stage of the detector.
Keywords：
direct sequcnce spread spectrum system
, DSP module, matched filter, code acquisition,
synchronization, coherent detection.
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