Real-time software receiver

• US 20060227856A1
• Filed: 12/22/2005
• Published: 10/12/2006
• Est. Priority Date: 01/10/2003
• Status: Active Grant

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: Ledvina, Brent M., Psiaki, Mark L., Powell, Steven P., Kintner, Paul M. Jr.
• Granted Patent: US 7,305,021 B2
• Time in Patent Office: Days
• US Class Current: 375/150
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 1/7095 Sliding correlator type
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A real-time software receiver that executes on a general purpose processor. The software receiver includes data acquisition and correlator modules that perform, in place of hardware correlation, baseband mixing and PRN code correlation using bit-wise parallelism.

Claims

1. A method for computing prompt and early-minus-late in-phase and quadrature summed accumulations for a plurality of signals from a plurality of channels comprising the steps of:

representing a carrier replica signal from the at least one channel from the plurality of channels as a carrier replica sign and a carrier replica magnitude;

representing signal data from the at least one channel of the plurality of channels as at least one signal word;

computing a baseband mixed sign as a function of the carrier replica sign and the at least one signal word;

computing a baseband mixed magnitude as a function of the carrier replica magnitude;

selecting a pseudo-random number (PRN) code having a prompt PRN code and an early-minus-late PRN code;

representing the prompt PRN code as a prompt PRN code sign;

computing a fully mixed prompt integrand sign as a function of the baseband mixed sign and the prompt PRN code sign;

representing the early-minus-late PRN code as an early-minus-late PRN code sign and an early-minus-late PRN code zero mask;

computing a fully mixed early-minus-late integrand sign as a function of the baseband mixed sign and the early-minus-late PRN code sign;

computing at least one set of prompt integrand value words as a function of the fully mixed prompt integrand sign and the baseband mixed magnitude;

computing at least one set of early-minus-late integrand value words as a function of the fully mixed early-minus-late integrand sign, the baseband mixed magnitude, and early-minus-late PRN code zero mask;

computing prompt in-phase and quadrature summed accumulations for the plurality of channels for an accumulation interval as functions of the number of significant bits in the at least one set of prompt integrand value words and as functions of the values associated with the at least one set of prompt integrand value words; and

computing early-minus-late in-phase and quadrature summed accumulations for the plurality of channels as functions of the number of significant bits in the at least one set of early-minus-late integrand value words and as functions of the values associated with the at least one set of early-minus-late integrand value words.

2. The method as in claim 1 further comprising the step of:

retrieving the carrier replica signal from a carrier replica table, the carrier replica table representing a coarse grid of frequencies.

3. The method as in claim 1 further comprising the steps of:

representing the signal word from the at least one channel as a signal sign and a signal magnitude; and

computing at least one baseband mixed magnitude as a function of the carrier replica magnitude and the signal magnitude.

4. The method as in claim 3 further comprising the step of:

retrieving the carrier replica signal from a carrier replica table, the carrier replica table representing a coarse grid of frequencies.

5. The method as in claim 1 further comprising the steps of:

receiving at least one radio frequency (RF) signal from the at least one channel from the plurality of channels;

digitizing the at least one RF signal; and

mixing the at least one RF signal to form signal data using bit-wise parallelism.

6. The method as in claim 5 wherein the at least one RF signal is a multi-bit signal.

7. The method as in claim 5 further comprising the steps of:

down-converting the at least one RF signal to an intermediate frequency; and

digitizing the intermediate frequency.

8. The method as in claim 5 further comprising the step of:

receiving the at least one RF signal from a global positional source.

9. The method as in claim 1 wherein said step of computing a fully mixed prompt integrand sign is performed using bit-wise parallelism.

10. The method as in claim 1 wherein said step of computing fully mixed early-minus-late integrand sign and is performed using bit-wise parallelism.

11. The method as in claim 1 further comprising the step of:

rotating the in-phase and quadrature summed accumulations to correct for effects of frequency and phase granularity of the signal data.

12. The method as in claim 1 further comprising the step of:

computing navigation data using the prompt in-phase and quadrature summed accumulations and the early-minus-late in-phase and quadrature summed accumulations.

13. The method as in claim 1 further comprising the step of

retrieving the carrier replica signal from a carrier replica table, the carrier replica table representing a coarse grid of frequencies.

14. The method as in claim 1 wherein said step of computing a baseband mixed magnitude comprises the steps of:

representing the at least one signal word as a signal sign and a signal magnitude; and

computing the baseband mixed magnitude as a function of the carrier replica magnitude and the signal magnitude.

15. The method as in claim 1 further comprising the step of

generating the PRN code using the bit-wise parallelism according to the steps of:

formulating a tabulated function for use in translating code chip and timing values into PRN code using the bit-wise parallelism;

generating at least one prompt PRN code in real-time;

choosing at least one chip value from the at least one prompt PRN code, the at least one chip value corresponding to at least one data interval that contains at least one sample of a data word, the at least one chip value having a known timing relative to the at least one data interval;

transforming the known timing into a time grid index; and

translating the at least one chip value and the time grid index during the at least one data interval into the PRN code using the bit-wise parallelism for the at least one data interval, said step of translating resulting from the use of the tabulated function.

16. The method as in claim 15 further comprising the step of:

computing the time grid index as a function of a time offset index and an auxiliary table index.

17. The method as in claim 15 further comprising the step of:

computing the time grid index iteratively as a function of a previously-computed time grid index, the at least one prompt PRN code, and the timing values associated with the at least one prompt PRN code.

18. A node in a computer network capable of carrying out the method according to claim 1.

19. A communications network comprising at least one node for carrying out the method according to claim 1.

20. A computer data signal embodied in electromagnetic signals traveling over a computer network carrying information capable of causing a computer system in the network to practice the method of claim 1.

21. A computer readable medium having instructions embodied therein for the practice of the method of claim 1.

22. A method for generating over-sampled prompt and early-minus-late pseudo-random number (PRN) codes in a bit-wise parallel format comprising the steps of:

formulating a tabulated function for use in translating code chip and timing information into over-sampled prompt and early-minus-late PRN code in the bit-wise parallel format;

generating at least one prompt PRN code in real-time;

choosing at least one chip value from the at least one prompt PRN code, the at least one chip value corresponding to at least one data interval that contains at least one sample of a data word, the at least one chip value having a known timing relative to the at least one data interval;

transforming the relative timing into a time grid index; and

translating the at least one chip value and the time grid index during the at least one data interval into the over-sampled prompt and early-minus-late PRN codes in bit-wise parallel format for the at least one data interval, said step of translating resulting from the use of the tabulated function.

23. The method as in claim 22 further comprising the step of:

computing the time grid index as a function of a time offset index and an auxiliary table index.

24. The method as in claim 22 further comprising the step of

computing the time grid index iteratively as a function of a previously-computed time grid index, the at least one prompt PRN code, and timing values associated with the at least one prompt PRN code.

25. A method for using over-sampled prompt and early-minus-late pseudo-random number (PRN) code replica data words that are stored in a bit-wise parallel representation in a pre-computed table consisting of the steps of:

selecting the over-sampled prompt and early-minus-late PRN code based on over-sampled prompt and early-minus-late PRN code start time as measured relative to an RF data sample time, said step of selecting substantially matching the midpoint of the over-sampled prompt and early-minus-late PRN code with a desired PRN code midpoint; and

bit-shifting the over-sampled prompt and early-minus-late PRN code data words, said step of bit-shifting insuring that the over-sampled prompt and early-minus-late PRN code start time corresponds with a pre-selected sample interval.

26. A method for tracking the phase of a pseudo-random number (PRN) code to track the timing of its chips comprising the steps of:

latching PRN code phase, carrier phase, epoch counters, and carrier frequencies at a pre-specified time;

computing a pseudo range using the PRN code phase and the epoch counters;

tracking and updating the PRN code phase and the carrier phase by estimating code chipping rate and carrier Doppler shift inputs; and

computing the PRN code phase at the pre-specified time as a function of the updated code chipping rate and the pre-specified time.