A Comparison of Direct Radio Frequency Sampling and Conventional GNSS Receiver Architectures

The novel concept of a direct radio frequency (RF) sampling receiver front end was analyzed, experimentally tested, and compared with a traditional superheterodyne front end that uses mixing to downconvert the signal before sampling. This study's goal was to demonstrate that signal power and phase are not adversely influenced by the use of direct RF sampling. The direct RF sampling strategy examined in this work uses sampling rates that are much lower than the carrier frequency but more than twice the signal bandwidth. Such a system employs a bandpass filter in front of the analog-to-digital converter (ADC) to avoid sensitivity loss via aliasing of out-of band noise and interfering signals. This design approach was evaluated analytically to determine the effects of sample clock jitter, and experimental results using GPS signals were used to confirm the analytical results. The results indicate that direct RF sampling yields performance equivalent to that of superheterodyne mixing.