Correlation system for global position receiver

Claim 1

A receiver for receiving and interpreting superimposed signals originating from a plurality of sources, the signals each comprising a code portion identifying the specific source and a data portion transmitting information. the codes 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 in the receiver a substantially increased signal is accumulated while all other accumulations between the signal and other stored codes remain substantially below true correlation levels, the receiver comprising: (a) down-converting means for converting the superimposed signals to a lower frequency, base band signal, the base band signal comprising each of the signals from the separate sources, their individual frequencies having been shifted by differing amounts as a result of Doppler and interference effects; (b) an analog-to-digital conversion means for quantizing the base band signal into a string of chips having binary values; (c) memory means for storing the codes which identify each of the sources; and (d) faster-than-real-time correlation means for correlating the code portions of individual signals with matching codes stored in the memory means and, thus, identifying available sources so that data can be extracted, the correlation means connected to the conversion means to receive the binary chips and connected to the memory means to receive particular codes upon request, the correlation means comprising: (i) a high-speed sampling means for multiple sampling each chip during its duration; (ii) a variable frequency shifting means for shifting the frequency of stored code sequences; (iii) multiplication means for multiplying the frequency shifted stored codes by a sequence of chip values taken from the high-speed sampling means; (iv) accumulator means for accumulating the products of multiplication means; and (v) control means for requesting particular codes, varying their frequency and sequence so that by repeated faster-than-real-time sampling of the digitally-converted, base band signal, the code portion of a signal from a particular source can be correlated with a particular code, thus, permitting the receiver to operate as if it had a plurality of virtual channels whereby each of the plurality of virtual channels can track one of the superimposed signals from the plurality of sources as identified by its code and receive the data portion of the signal transmitted therefrom.