An Assisted GPS Acquisition Method using L2 Civil Signal in Weak Signal Environment

Abstract

Recently, there has been increasing demands on the positioning capability in weak signal environment such as inside building and urban area. The present assisted GPS technology uses GPS L1 signals only. Meanwhile, according to the GPS modernization plan, Block IIR-M GPS satellite will be first launched in 2005, transmitting the civil code in L2 frequency as well as in L1 frequency with the updated signal structure. Since the L2 civil code has a worst-case cross correlation performance of 45 dB (over 251 times better than 21 dB cross correlation performance of the L1 C/A code), it will be much more effective in weak signal environment. This paper proposes an assisted GPS acquisition method using L2 civil signals. It will show that the acquisition success rate of the proposed assisted GPS acquisition method is better than that of the existing assisted GPS method using L1 signals in the same environment. The constellation of the next generation GPS satellites is scheduled to launch in 2005. Therefore, in order to design and test the assisted GPS acquiring the L2 civil signal, it is necessary to design a signal generator which can generate the L2 civil signal. The signal generator will be designed using the pseudo random noise (PRN) code generation method and navigation message protocol defined in GPS ICD PIRN 200C-007B. Finally, through the simulations using the designed signal transmitter, the success rate of the proposed assisted GPS acquisition method will be compared with that of the existing assisted GPS method to show the performance improvements.