A Comparison of ''Direct RF Sampling'' and ''Down-Convert & Sampling''
GNSS Receiver Architectures
Proc. of the ION GPS/GNSS Conf., (2003)Аннотация
The new direct RF sampling GNSS receiver front concept has been analyzed,
experimentally tested, simulated, and compared to a traditional superheterodyne
front end that uses mixing to down-convert the signal before sampling.
The goal of this study has been to demonstrate that signal power
and carrier tracking are not adversely influenced by the use of direct
RF sampling. The direct RF sampling strategy that has been examined
uses sampling rates that are much lower than the carrier frequency
but that are more than twice the information bandwidth. Such a system
employs a bandpass filter in front of the analog-to digital converter
to avoid sensitivity loss via aliasing of out-of-band noise and interfering
signals. This design approach has been evaluated analytically to
determine the effects of sample clock jitter, and experimental and
simulation results have been used to confirm the analytical results.
The experiments have used computer data acquisition systems to record
the outputs of direct RF sampling front ends that were connected
to roof-top patch antennas. The results indicate that direct RF sampling
yields equivalent performance to superheterodyne mixing if sample
timing jitter is kept below well defined limits.