Аннотация
A goal in the software radio design philosophy is to place the analog-to-digital
converter as near the antenna as possible. This objective has been
demonstrated for the case of a single input signal. Bandpass sampling
has been applied to downconvert, or intentionally alias, the information
bandwidth of a radio frequency (RF) signal to a desired intermediate
frequency. The design of the software radio becomes more interesting
when two or more distinct signals are received. The traditional approach
for multiple signals would be to bandpass sample a continuous span
of spectrum containing all the desired signals. The disadvantage
with this approach is that the sampling rate and associated discrete
processing rate are based on the span of spectrum as opposed to the
information bandwidths of the signals of interest. Proposed here
is a technique to determine the absolute minimum sampling frequency
for direct digitization of multiple, nonadjacent, frequency bands.
The entire process is based on the calculation of a single parameter
: the sampling frequency. The result is a simple, yet elegant, front-end
design for the reception and bandpass sampling of multiple RF signals.
Experimental results using RF transmissions from the U.S. Global
Positioning System Standard Position Service (GPS-SPS) and the Russian
Global Navigation Satellite System (GLONASS) are used to illustrate
and verify the theory.
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