An analysis of maximum likelihood estimation method for bit synchronization and decoding of GPS L1 C/A signals
Tóm tắt
In weak GNSS signal environments, extending integration time is paramount to improving the GNSS receiver’s sensitivity. Furthermore, sufficient coherent integration can help to mitigate multipath and cross-correlation false locks and avoid squaring loss. However, extending integration time is limited by the navigation message data bit, if present. The maximum likelihood (ML) estimation method has been shown as the most effective way to estimate the navigation bit boundary locations (i.e., bit synchronization) and subsequently estimate the data bit values (i.e., bit decoding) in the presence of noise alone. In this paper, the performance of ML bit synchronization and decoding is systematically assessed as a function of the number of data bits, the effect of Doppler error and received signal power in different tracking modes (i.e., phase-locked mode and frequency-locked mode). In addition, the theoretical performance models of ML bit synchronization and decoding are developed based on statistical theory. The experimental validation of the developed performance models and analyses is reported. For GPS L1 C/A signals, it is shown that for ML bit synchronization, using 100 data bits, the successful synchronization rate (SSR) can reach to about 100% with C/N0 as low as 20 dB-Hz with no Doppler error. The performance degradation caused by Doppler error is not significant if the Doppler error is within 5 Hz, and with the maximum tolerance of 25 Hz, while for ML bit decoding, the successful decoding rate (SDR) of the 2-bit sequence can reach to about 100% with C/N0 as low as 25 dB-Hz with no Doppler error. The performance degradation caused by Doppler error is not significant if the Doppler error is within 2 Hz. Both theoretical and simulation results establish that the upper bound of Doppler error for a 2-bit sequence is 12.5 Hz.
Tài liệu tham khảo
MediaTek: MT3336 Product Summary. MediaTek Inc, Hsinchu City; 2012.
Fastrax: IT600 OEM GPS Receiver Module Data Sheet, rev.1.6. Fastrax Ltd, Finland; 2012.
u-blox: UBX-G6010 Product Summary. u-blox AG, Thalwil, Switzerland; 2011.
Akos DM, Normark PL, Lee JT, Gromov KG, Tsui JBY, Schamus J: Low Power Global Navigation Satellite System (GNSS) Signal Detection and Processing in Proceedings of ION GPS. Salt Lake City; 2000:784-791.
van Diggelen F, Abraham C: Indoor GPS Technology. CTIA Wireless-Agenda Dallas; 2001.
DiEsposti R: GPS PRN code signal processing and receiver design for simultaneous all-in-view coherent signal acquisition and navigation solution determination, in Proceedings of ION NTM, San Diego, 22–24. January 2007.
Djuknic GM, Richton RE: Geolocation and assisted GPS. Computer 2001, 34(2):123-125.
Akopian D, Syrjarinne J: A network aided iterated LS method for GPS positioning and time recovery without navigation message decoding, in Position Location and Navigation Symposium 2002 . Palm Springs April 2002, 15–18: 77-84.
Van Dierendonck AJ: GPS receivers. In Global Positioning System: Theory and Applications, Vol. I. Edited by: Parkinson BW, Spilker JJJr. Washington: American Institute of Aeronautics and Astronautics; 1996:329-407.
Zeidan NI, Garrison JL: Bit synchronization and Doppler frequency removal at very low carrier to noise ratio using a combination of the Viterbi algorithm with an extended Kalman filter, in Proceedings of ION GPS/GNSS 2003 . Portland 2003, pp. 616-627.
Psiaki ML, Jung H: Extended Kalman filter methods for tracking weak GPS signals, in Proceedings of ION GPS 2002 . Portland 2002, pp. 2539-2553.
Kokkonen M, Pietila S: A new bit synchronization method for a GPS receiver, in Proceedings of the IEEE Position Location and Navigation Symposium . Palm Springs, CA 2002, pp. 85-90.
Soloviev A, Van Grass F, Gunawardena S: Decoding navigation data messages from weak GPS signals. IEEE Trans. Aerospace and Electronic Systems 2009, 45: 2.
Ren T, Petovello MG, Basnayake C: Requirements analysis for bit synchronization and decoding in a standalone high-sensitivity GNSS receiver, in Ubiquitous Positioning, Indoor Navigation, and Location Based Service (UPINLBS) . Helsinski 2012, 1-9.
Shivaramaiah NC, Dempster AG, Rizos C: Exploiting the secondary codes to improve signal acquisition performance in Galileo receivers, in Proceedings of ION GNSS . Savannah, GA 2008, 1497-1506.
Ward PW, Betz JW, Hegarty CJ: Satellite signal acquisition, tracking, and data demodulation. In Understanding GPS, Principles and Applications. Edited by: Kaplan ED, Hegarty CJ. Norwood: Artech House; 2006:192-194.
Sklar B: Digital Communications. Upper Saddle River, NJ: Prentice-Hall; 1988:183-204.
Haykin S: Communication Systems. 4th edition. New York: Wiley; 2001:349-417.
Petovello MG, O’Driscoll C, Lachapelle G: Weak signal carrier tracking using extended coherent integration with an ultra-tight GNSS/IMU receiver in. Toulouse, France: Proceedings of ENC-GNSS; 2008:22-25.