Method for detecting an earliest arrival time using categorization of code in received signal
A method for detecting a probe signal at an estimated code delay and an estimated doppler frequency includes: (i) dividing a period of the probe signal into sections each of a predetermined duration; (ii) assigning to each section one of a multiple code categories, each code category being indicative of a signal pattern of the probe signal within the section; and (iii) selecting multiple phase categories for a sinusoidal signal, each phase category being indicative of a range of phases in the sinusoidal signal. Thereafter, the method includes (i) receiving a signal from which the probe signal is to be detected; (ii) dividing the received signal into sections each of the predetermined duration; (iii) assigning each section of the received signal both a corresponding code category and a corresponding phase category, based respectively on the estimated code delay and the doppler frequency; and (iv) separately accumulating sections of the received signal according to the assigned code and phase categories of each section.
1. In a receiver, a method for detecting an earliest arrival time among one or more components of a digitized complex-valued received signal, the received signal being a periodic PRN code-modulated signal, wherein each component of the received signal arrives at the receiver over one of multiple signal paths, the method comprising:
(i) dividing each period of the received signal into sections;
(ii) assigning to each section one of a plurality of code categories, each assigned code category corresponding to a signal pattern of the corresponding portion of the periodic PRN code within the section;
(iii) selecting an assigned code category corresponding to a signal pattern that includes at least one signal transition in the real portion of PRN code
(iv) accumulating sample values of sections corresponding the assigned code category over one or more periods of the PRN code, the real and imaginary parts of the sample values being accumulating separately;
(v) detecting the signal transition in the accumulated sample values of the real portion, and detecting a peak value in the accumulated sample values of the imaginary portion that precedes the signal transition in the real portion; and
(vi) deeming the peak value's time of arrival to be the detected earliest arrival time.
2. The method of claim 1 , wherein the received signal corresponds to a probe signal transmitted from a satellite.
3. The method of claim 2 , further comprising determining a pseudorange based on the time of arrival.
4. The method of claim 1 , wherein the real and imaginary portions correspond, respectively, to sample values of in-phase and quadrature portions of a received signal down-converted at a predetermined intermediate frequency.