GPS receiver and method for processing GPS signals

DETAILED DESCRIPTION This invention concerns apparatus and methods for computing the position of a mobile, or remote, global positioning system (GPS) receiver with very low received signal levels.
As illustrated in FIGS.
1A-1D, a GPS receiver 10 has first circuitry for receiving and processing pseudorandom sequences transmitted by a number of GPS satellites.
The first circuitry is configured to perform conventional correlation operations on the received pseudorandom sequences to determine pseudoranges from the GPS receiver to the GPS satellites.
Accordingly, the first circuitry is referred to herein as a conventional GPS receiver 12.
The GPS receiver 10 also includes second circuitry coupled to the conventional GPS receiver 12.
The second circuitry is configured to receive and process the pseudorandom sequences during blockage conditions.
Blockage conditions are those conditions where the conventional GPS receiver 12 may have difficulty acquiring and/or tracking GPS signals from GPS satellites, such as occasions where the GPS signals have very low signal to noise ratios, urban canyon conditions where GPS signals are blocked due to tall buildings, tunnels and other obstacles, conditions where the GPS receiver 10 is being operated under cover of trees or other foliage, in building applications where GPS receiver 10 is being operated indoors, and other blockage conditions as will be appreciated by those skilled in the art.
The second circuitry is referred to herein as a snapshot GPS receiver 14 which processes the pseudorandom sequences by digitizing and storing GPS data made up of a predetermined record length of the received pseudorandom sequences.
Once the GPS data has been stored, snapshot GPS receiver 14 performs fast convolution operations on the stored data to determine the pseudoranges.
The manner in which these computations are performed are discussed in detail below.
As illustrated in FIGS.
1A-1D, GPS receiver 10 includes two signal paths, corresponding to conventional GPS receiver 12 and snapshot GPS receiver 14