System and method for time-of-flight determination using categorization of both code and phase 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 component signals of a received signal, the received signal having embedded therein a probe signal, the probe signal being a periodic signal that repeatedly encodes a pseudo-random (PRN) code, each period of the probe signal being of a predetermined duration, the received signal having a duration exceeding two or more times the predetermined duration, the method comprising:
(i) dividing the received signal into sections;
(ii) assigning to each section of the received signal one of a plurality of categories, based on both an estimated delay and an estimated doppler frequency experienced in transit by the received signal, including one or more transition-encompassing categories, wherein each transition-encompassing category represents a section of the probe signal that includes a signal transition;
(iii) sampling the received signal into samples of two sample types, the sample types being in-phase samples and quadrature samples;
(iv) accumulating the sections of the received signal assigned to the transition-encompassing categories separately by both their assigned categories and their sample types;
(v) detecting one of the signal transitions in the accumulated sections of in-phase samples, and detecting a time of arrival of a peak value in the corresponding accumulated sections of quadrature samples, wherein the time of arrival precedes the signal transition; and
(vi) deeming the time of arrival to be the detected earliest arrival time.
2 . The method of claim 1 , wherein each category relates to a phase of a sinusoidal signal of the estimated doppler frequency.
3 . The method of claim 1 , further comprising determining a pseudo-range based on the time of arrival and the estimated delay.
4 . The method of claim 1 , wherein the received signal has been down-converted from a carrier frequency to a predetermined intermediate frequency prior to sampling.
5 . The method of claim 1 , wherein the received signal is derived from a probe signal transmitted from a satellite.
6 . In a receiver, an apparatus for detecting an earliest arrival time among one or more component signals of a received signal, the received signal having embedded therein a probe signal, the probe signal being a periodic signal that repeatedly encodes a pseudo-random (PRN) code, each period of the probe signal being of a predetermined duration, the received signal having a duration exceeding two or more times the predetermined duration, the apparatus comprising:
(i) an analog-to-digital circuit that divides the received signal into sections and samples each section of the received signal into samples of two sample types, the sample types being in-phase samples and quadrature samples;
(ii) a category assignment circuit which categorizes each section of the received signal to one of a plurality of categories, based on both an estimated delay and an estimated doppler frequency experienced in transit by the received signal, including one or more transition-encompassing categories, wherein each transition-encompassing category represents a section of the probe signal that includes a signal transition;
(iii) an accumulator that accumulates the sections of the received signal assigned to the transition-encompassing categories separately by both their assigned categories and their sample types; and
(v) a processor circuit that (a) detects one of the signal transitions in the accumulated sections of in-phase samples, (b) detects a time of arrival of a peak value in the corresponding accumulated sections of quadrature samples, wherein the time of arrival precedes the signal transition, and (c) outputs the time of arrival to be the detected earliest arrival time.
7 . The apparatus of claim 6 , wherein each category relates to a phase of a sinusoidal signal of the estimated doppler frequency.
8 . The apparatus of claim 6 , wherein the processor further determines a pseudo-range based on the time of arrival and the estimated delay.
9 . The apparatus of claim 6 , further comprising a front-end circuit that down-converts the received signal from a carrier frequency to a predetermined intermediate frequency prior to sampling.
10 . The apparatus of claim 6 , further comprising an antenna that derives the received signal from a probe signal transmitted from a satellite.