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2015, vol. 63, br. 4, str. 11-24
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Poboljšanje sinhronizacije signala u softverskom GPS prijemniku
Improvement of signal synchronization in GPS software receiver
Projekat: Rentabilni izbor novih tehnologija i koncepcija odbrane kroz društvene promene i strateške orijentacije Srbije u 21. veku (MPNTR - 47029)
Sažetak
Prepoznavanje navigaocionih bita u GPS prijemniku realizuje se kroz procese praćenja i detekcije signala. U procesu praćenja signala lokalno generisani signal mora biti sinhronizovan sa primljenim signalom. Karakteristika Costasove fazne petlje, koja se najčešće koristi za sinhronizaciju signala, jeste podložnost uticaju izvora grešaka. Rezultantne greške praćenja faze značajne su u prisustvu slabog ulaznog signala, kao, na primer, kod signala sa malim odnosom signal-šum. Radi poboljšanja sinhronizacije omogućavanja praćenja signala koji emituje strane prijemnika, predlažemo upotrebu non-data-aided (NDA) fazni estimator. Na osnovu praktične obrade GPS signala pokazano je da primena NDA algoritma omogućava veću otpornost na iznenadne promene frekvencije ulaznog signala u odnosu na do sada primenjivani fazni diskriminator u Costasovoj faznoj petlji praćenja. Na osnovu izvršene analize pokazano je, takođe, da predloženo rešenje omogućava stabilan rad, naročito kod signala sa malim odnosom signal-šum.
Abstract
In GPS receivers, navigation bit allocation is performed throughout the process of signal tracking and detection. In the process of signal tracking, the locally generated signal must be synchronized with the received signal. The Costas phase-locked loop (PLL) behavior, which is often used for signal synchronization, is characterized by dominant tracking error sources. The resulting phase tracking errors are significant in the presence of weak signals, i.e. signals with the low signal-to-noise ratio (SNR). In order to improve the signal synchronization and enable signal tracking by the receiver, we here proposed the usage of a non-data-aided (NDA) phase estimator. Based on the practical processing of the GPS signals, it is shown that the applied NDA algorithm is more resistant to sudden changes in frequency (phase) of the input signal than the previously considered phase discriminator in the Costas PLL. Also, we have shown that the solution analyzed here exhibits more stable operation in signal tracking for a low SNR.
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