Patent ID: 8391341
Filing Date: 2013-03-05
Classification: G01S,H04B

Abstract:
1. A method of sub-microsecond time transfer in a GPS/GNSS receiver using a weak GPS/GNSS signal from a satellite, the method comprising: receiving a digitized complex baseband signal of the GPS/GNSS signal, the baseband signal carrying a received PN code having a code period and a navigation message having data bits, each data bit corresponding to twenty code periods; generating a generated PN code for the satellite; using a delay-locked loop to keep the generated PN code time-aligned with the received PN code; generating a timing signal indicating code epochs of the generated PN code, each code epoch marking a beginning of each period and being tagged with a modulo-20 number; cross-correlating the baseband signal and the generated PN code for each code period controlled by the timing signal, so as to output a complex correlation value at each code epoch, a sequence of the complex correlation values forming a navigation data stream representing the navigation message; locating data bit boundaries of the navigation data stream and generating bit sync pulses at the bit boundaries, locating data bit boundaries including: detecting a target segment in the navigation message and determining a data bit location of the target segment in the navigation message, the detecting the target segment including: Determining transmission time of the target segment from the satellite based on the determined data bit location, wherein the transmission time has a certain time ambiguity; solving the certain time ambiguity using approximate time obtained from a source external to the GPS/GNSS receiver; and correcting the transmission time for a propagation delay so as to obtain sub-microsecond time transfer.