Generation of multi-satellite GPS signals in software

1. A computer-implemented method for testing a GPS receiver, the method comprising:

reading one or more GPS files from a computer memory, wherein each of the one or more GPS files contains data for a plurality of GPS satellites;

receiving parameters for a GPS receiver;

selecting two or more GPS satellites out of the plurality of GPS satellites;

generating two or more GPS signals for the two or more GPS satellites, wherein each of the two or more GPS signals contains data for a respective GPS satellite of the two or more selected GPS satellites;

operating on the two or more GPS signals using the received parameters for the GPS receiver to generate two or more calculated GPS signals;

re-sampling each of the two or more calculated GPS signals to a common rate, wherein said re-sampling each of the calculated two or more GPS signals to the common rate comprises aligning each of the calculated two or more GPS signals to the common rate;

adding the two or more re-sampled GPS signals together to create a composite GPS signal;

generating the composite GPS signal using a hardware signal generator, wherein the composite GPS signal is operable to test the GPS receiver; and

repeating said re-sampling, adding, and generating the composite GPS signal multiple times in an iterative manner to test the GPS receiver.

2. The method of claim 1 , further comprising:

receiving user input specifying one or more conditions for the one or more GPS signals, wherein the one or more conditions comprise at least one of:

power level for the one or more GPS satellites;

initial Doppler level;

initial pseudorange;

urban canyon effects;

atmospheric parameters;

solar activity; or

weather.

3. The method of claim 1 ,

wherein said selecting the two or more GPS satellites receiving additional user input selecting the two or more GPS satellites.

4. The method of claim 1 ,

wherein said selecting the two or more GPS satellites comprises automatically selecting the two or more GPS satellites.

5. The method of claim 1 ,

wherein the parameters of the GPS receiver comprise one or more of:

location of the GPS receiver; or

movement characteristics of the GPS receiver.

6. The method of claim 1 , wherein said operating comprises one or more of:

calculating an offset for a carrier frequency for each of the two or more GPS signals;

calculating a rate change due to a Doppler shift for each of the two or more GPS signals; or

scaling an amplitude of each of the two or more GPS signals.

7. The method of claim 1 ,

wherein said selecting the two or more satellites comprises selecting using one or more factors, wherein the one or more factors include at least one of:

a pseudorandom check;

a Doppler frequency check;

a satellite elevation check;

a satellite health check; or

a fit interval check.

8. The method of claim 1 , wherein said calculating comprises calculating one or more of:

delay for each of the one or more GPS signals;

doppler shift;

doppler spreading;

clock bias;

clock drift; or

power attenuation.

9. The method of claim 1 , further comprising:

reading test results back from the GPS receiver; and

displaying the test results.

10. The method of claim 1 , further comprising:

executing a graphical program, wherein the graphical program comprises a plurality of interconnected nodes that visually indicate functionality of the graphical program;

wherein the graphical program is executable to perform to said operating.

11. The method of claim 10 , further comprising:

creating the graphical program, wherein said creating the graphical program comprises:

arranging a plurality of nodes on a display; and

interconnecting the plurality of nodes in response to user input.

12. The method of claim 10 ,

wherein the graphical program comprises a block diagram portion and a user interface portion.

13. The method of claim 10 ,

wherein the graphical program comprises a graphical data flow program.

14. The method of claim 10 ,

wherein, during execution of the graphical program, the graphical user interface is displayed on a display of a first computer system and the block diagram executes on a second computer system.

15. The method of claim 10 , further comprising:

reading test results back from the GPS receiver; and

displaying the test results in the graphical user interface.

16. A non-transitory computer accessible memory medium which stores program instructions for simulating GPS signals to test a GPS receiver, wherein the program instructions are executable by a processor to perform:

reading one or more GPS files, wherein each of the one or more GPS files contains data for a plurality of GPS satellites;

receiving parameters for the GPS receiver;

selecting two or more GPS satellites out of the plurality of GPS satellites;

generating two or more GPS signals for the two or more GPS satellites, wherein each of the two or more GPS signals contains data for a respective GPS satellite of the two or more selected GPS satellites;

operating on the two or more GPS signals using the received parameters for the GPS receiver to generate two or more calculated GPS signals;

re-sampling each of the two or more calculated GPS signals to a common rate, wherein said re-sampling each of the calculated two or more GPS signals to the common rate comprises aligning each of the calculated two or more GPS signals to the common rate;

adding the two or more re-sampled GPS signals together to create a composite GPS signal, wherein the composite GPS signal is operable to be generated using a hardware signal generator, wherein the composite GPS signal is operable to test the GPS receiver; and

repeating said re-sampling, adding, and generating the composite GPS signal multiple times in an iterative manner to test the GPS receiver.

17. The non-transitory memory medium of claim 16 , wherein the program instructions are executable by a processor to further perform:

executing a graphical program, wherein the graphical program comprises a plurality of interconnected nodes that visually indicate functionality of the graphical program;

wherein the graphical program is executable to perform to said operating.

18. The non-transitory memory medium of claim 17 , wherein the program instructions are executable by a processor to further perform:

reading test results back from the GPS receiver; and

displaying the test results in the graphical user interface.

19. A system for testing a GPS receiver, the system comprising:

a processor;

a memory medium coupled to the processor;

a hardware RF generator coupled to a GPS receiver;

wherein the memory medium stores program instructions which are executable by the processor to:

read one or more GPS files, wherein each of the one or more GPS files contains data for a plurality of GPS satellites;

receive parameters for a GPS receiver;

select two or more GPS satellites out of the plurality of GPS satellites;

generate two or more GPS signals for the two or more GPS satellites, wherein each of the two or more GPS signals contains data for a respective GPS satellite of the two or more selected GPS satellites;

operate on the two or more GPS signals using the received parameters for the GPS receiver to generate two or more calculated GPS signals;

re-sample each of the two or more calculated GPS signals to a common rate, wherein said re-sampling each of the calculated two or more GPS signals to the common rate comprises aligning each of the calculated two or more GPS signals to the common rate; and

add the two or more re-sampled GPS signals together to create a composite GPS signal;

repeat said re-sampling and adding the composite GPS signal multiple times in an iterative manner;

wherein the hardware RF generator is configured to generate the composite GPS signal for each iteration, wherein the composite GPS signal is used to test the GPS receiver.