Method and apparatus for acquisition, tracking, and sub-microsecond time transfer using weak GPS/GNSS signals

A GPS/GNSS receiver circuit for high-sensitivity GPS/GNSS signal acquisition and tracking, including a front end section and a signal processing section, the front end section receiving a GPS/GNSS signal from satellites and producing a digitized complex baseband signal, the signal processing section comprising:

• an input terminal for receiving an M-bit block of the baseband signal of the received signal, the M-bit block including an M-bit sequence of the navigation data, the M-bit sequence being known to be contained in a longer known B-bit sequence having a known navigation data bit pattern;
• a process controller including:
• a frequency selector configured to select a frequency f0p for compensating apparent Doppler shift in the received signal;
• and
• a bit boundary selector configured to select a trial bit boundary location t0s for determining navigation data bit boundaries of the received signal, the trial bit boundary location corresponding to start time for capturing the received signal;
• a phase rotator configured to compensate the Doppler shift in the M-bit block using the trial frequency f0p;
• a synchronous summer configured to partition the M-bit block into M successive sub-blocks, and synchronously sum samples of each sub-block using a periodicity of one period of C/A code, so as to produce M compressed sample blocks each having N-samples and a length of one period of C/A code;
• a cross correlator configured to cross-correlate each of the M compressed sample blocks with N cyclic shifts of one period of reference C/A code for a selected satellite so as to produce an N-by-M correlation matrix;
• a correlator memory configured to hold the N-by-M correlation matrix, kth column of the correlation matrix consisting of N complex values of an N-value correlation function of the kth compressed sample block, Kth row of the correlation matrix corresponding to M bits of the M-bit block at the K-lth cyclic shift;
• a data-shift correlator coupled to said correlator memory, configured to correlate each row of the correlation matrix with a selected M-bit sequence of the known B-bit sequence by shifting the selected M-bit sequence from one end to the other of the known B-bit sequence so as to produce (B−M+1) data-shift correlation values for each row;
• a magnitude calculator configured to calculate magnitude of data-shift correlation values;
• and
• a maximum value determiner configured to determine the data-shift correlation value having a greatest magnitude MAGMAX and parameters associated therewith, after receiving, from the magnitude calculator, the magnitude for predetermined combinations of the frequencies and the trial bit boundary locations, wherein the associated parameters includes:
• frequency f0MAX indicating a measured apparent Doppler shift of the received signal;
• bit boundary location t0MAX providing a bit boundary location of the captured M-bit sequence;
• a row index KMAX of the correlation matrix indicating a location of a code epoch of C/A code of the received signal;
• and
• an amount of shift JMAX of the selected M-bit sequence within the known B-bit sequence, the amount of shift indicating a location of a start bit of the captured M-bit sequence with respect to the known B-bit sequence.