No abstract

Compared with the Global Navigation Satellite System (GNSS), the asynchronous pseudolite (PL) navigation system does not provide corrections for the frequency deviation between PL signals. To realize precise positioning, a reference receiver is utilized to reduce the effect of frequency deviation between PLs via the differential method using carrier phase measurements. However, there exists time deviation between the user and reference receivers due to their asynchronous clocks. With this time deviation, the effect of frequency deviation between PLs cannot be removed thoroughly. Theoretical derivation and experimental verification indicate that the residual error in double difference of carrier phase measurements is proportional to the frequency deviation between PLs and the time deviation between receivers. To solve this problem, two approaches, refer to hardware and software methods, are proposed, which are experimentally proven to be feasible.

No abstract

Due to its flexibility in calculating frequency spectrum, the chirp z-transform (CZT) has been used in various applications where high-frequency resolution is desirable, e.g. the acquisition of global positioning system (GPS) signals. However, the CZT is very time consuming when dealing with the very large size of input data. Thus, typically, only 1 ms data is used for GPS signal acquisition. In this Letter, the authors improve the acquisition precision and sensitivity of the CZT-based acquisition by extending coherent integration time. To reduce computation load, they introduce a down-sampling operation to the extended data without degrading acquisition performance. Results show that the CZT-based acquisition with a coherent integration time of 10 ms obtains a frequency error of 5.9 Hz for the carrier-to-noise ratio (CNR) of 25 dB-Hz and can acquire signals with a CNR down to 22 dB-Hz.