Receiver Hardware Considerations - Fundamentals of Global Positioning System Receivers: A Software Approach - page 127

overall gain is about 100 dB. The input signal can either be down converted
and then digitized or directly digitized without frequency translation. Although
direct digitization seems to have some advantages, with today's technology a
down conversion approach is simpler to build. It appears that I-Q channel down
conversion does not have much advantage over a single channel conversion for
a software GPS receiver. Direct digitization can be used to alias several narrow
input signals into the same baseband. Several experimental setups to collect data
are presented. The number of quantization bits is discussed. One or two bits
may be enough for GPS application with degradation of receiver sensitivity. If
antijamming is of concern, a large number of bits needed. The conversion of
data from real to complex and from complex to real are discussed. Finally, the
impact of sampling frequency accuracy is discussed.
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