Patent ID: 7701998

Claim:
A method for determining a position of a signal transmitter, the method comprising: receiving a direct sequence spread spectrum signal from the transmitter in each of at least three physically separated sensors whose respective positions are known, the signal representing a set of symbols, correlating, in each of the sensors a representation of the received signal with at least one local spreading sequence to determine a respective estimated transmission delay of the received signal, the received direct sequence spread spectrum signal having a nominal chip period, the correlating producing a chip level synchronization at least within an uncertainty region of one half nominal chip period, and calculating a distance between the signal transmitter and each of the at least three sensors based on the respective estimated transmission delays, wherein the correlating further comprises: over-sampling the representation of the received signal within the uncertainty region to obtain a corresponding over-sampled representation of the received signal, the over-sampling being equivalent to a reduced chip period which is shorter than the nominal chip period, selecting a local spreading sequence containing poly-phased symbol values which are different from the set of symbols represented by the received signal, the selected local spreading sequence having a nominal chip period being equivalent to the reduced chip period, and cross-correlating the over-sampled representation of the received signal with the selected local spreading sequence to obtain an improved uncertainty region which is more limited than one half nominal chip period.