Patent ID: 7702002
Filing Date: 2010-04-20
Classification: G01S,H04B

Abstract:
1. A method of receiving a signal with a receiver, said signal transmitted at a predetermined carrier frequency from one of a plurality of transmitters, said signal including a waveform modulated according to a periodically-repeating pseudonoise (PN) sequence that uniquely identifies the transmitter that sent the signal, said signal used in determining a location of the receiver, said method comprising: at the receiver, receiving electromagnetic energy in the vicinity of said carrier frequency, and digitizing said energy for a predefined period of time; hypothesizing one of said plurality of transmitters and an associated hypothesized signal and providing a set of reference frequency samples corresponding to said hypothesized signal; hypothesizing a first residual frequency; selecting from said digitized energy a first subset of data of length at least equal to two repetitions of said periodically-repeating PN sequence, thereby defining a first data block; responsive to said first data block, calculating a first set of data frequency samples; pruning said first set of data frequency samples responsive to said hypothesized first residual frequency to provide a periodically-spaced first subset of said first set of data frequency samples, wherein said periodically-spaced first subset includes a plurality of samples having indices spaced relative to one another by an integer K, wherein K is the number of PN sequences in said first data block; computing a first correlation series from said periodically-spaced first subset of said first set of data frequency samples and said set of reference frequency samples; computing a first final correlation series comprising at least said first correlation series; and examining said first final correlation series to determine whether a matched condition occurs between said transmitted signal and said hypothesized signal.