Patent ID: 7760139

Claim:
A method for acquiring source signals in a receiver for receiving and interpreting source signals originating from a plurality of sources, each source signal comprising a code portion and a data portion, the codes of the code portions being chosen such that when the receiver correlates the code portion of a signal from a particular source with a matching code stored in a memory, a substantially increased signal is generated, and wherein each signal frequency comprises a base frequency, corrupted by a Doppler shift, the receiver comprising a heterodyne module for converting each of the source signals to a down-converted signal comprising the code and data portions of the corresponding source signal, wherein the code portions comprise a multiplicity of chips, a sampler to convert each down-converted signal into binary signal groupings, and a memory in which code sequences that identify each of the source signals is stored, the method comprising: (1) sampling said down-converted signals at a rate substantially higher than a chip rate; and (2) performing a coarse correlation of the code portions of said sampled signals with the matching code sequences stored in the memory, thereby identifying available source signals, by the steps comprising: (a) shifting the phase of the stored code sequences; (b) multiplying the phase-shifted stored code sequences by a First Signal at frequency ω, the base frequency plus a Doppler angular frequency of a current search bin, thereby producing signal s 11 ; (c) multiplying signal s 11 by said sampled down-converted signal producing signal Q; (d) summing the results of steps (a) through (c) over an epoch, wherein the epoch comprises a plurality of chips; and (e) passing the summed results through a non-linear device, producing signal Qn; (f) creating a Second signal in quadrature with the First signal; (g) multiplying the phase-shifted stored code sequences by the Second signal, producing signal s 22 ; (h) multiplying signal s 22 by said sampled down-converted signal producing signal I; (i) summing the results of steps (f) through (h) over the epoch; (j) passing the summed results through a non-linear device, producing signal In; and (k) summing signals In and Qn, producing a test signal, wherein the performing of said coarse correlation, over a range of different values of frequencies ω, is performed without using any feedback loops, and wherein the performing of said coarse correlation results in the selection of a coarse range of base plus Doppler frequencies, each base plus Doppler frequency designated hereinafter as a Doppler cell, and further results in the calculation of a coarse range of phase-shifted stored code sequences for all GPS satellites in view.