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In general, the invention is directed to techniques for directly acquiring P-codes without first acquiring C/A-codes. For example, in one embodiment, a system comprises an assist server to track a P-code signal from a Global Positioning System (GPS) satellite and generate acquisition assistance info

In general, the invention is directed to techniques for directly acquiring P-codes without first acquiring C/A-codes. For example, in one embodiment, a system comprises an assist server to track a P-code signal from a Global Positioning System (GPS) satellite and generate acquisition assistance information from the signal. The system further comprises a mobile unit to receive the acquisition assistance data from the assist server, and to acquire the P-code signal from the satellite based on the acquisition assistance data. The acquisition assistance data may include time-of-week data indicating an initial time offset into a P-code pseudorandom code sequence for the satellite. The mobile unit may include a reference generator to locally generate a reference pseudorandom code sequence based on the time-of-week data.

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1. A method comprising:receiving acquisition assistance data from an assist server; and determining a time offset for a P-code pseudorandom code sequence associated with a signal from a satellite based on the acquisition assistance data. 2. The method of claim 1, further comprising determining a pos

1. A method comprising:receiving acquisition assistance data from an assist server; and determining a time offset for a P-code pseudorandom code sequence associated with a signal from a satellite based on the acquisition assistance data. 2. The method of claim 1, further comprising determining a position for a mobile unit based on the time offset.3. The method of claim 1, wherein the acquisition assistance data includes time-of-week data indicating an initial time offset into the P-code sequence.4. The method of claim 3, wherein determining a time offset comprises locally generating a reference pseudorandom code sequence based on the time-of-week information received from the assist server.5. The method of claim 4, wherein generating a reference pseudorandom code sequence comprises generating the reference pseudorandom code sequence to include contiguous pseudorandom codes within the P-code sequence starting at the initial time offset.6. The method of claim 4, further comprising:digitizing the signal to produce a stream of digital data; buffering an amount of the digital data; and correlating the buffered digital data with the locally generated reference code sequence. 7. The method of claim 6, further comprising setting the amount of buffered digital data based on a time uncertainty value associated with the time-of-week information received from the assist server.8. The method of claim 7, wherein the uncertainty value comprises a predefined uncertainty value.9. The method of claim 6, wherein correlating the buffered digital data with the locally generated reference code sequence comprises synchronizing the digital data and the reference pseudorandom code sequence.10. The method of claim 9, wherein synchronizing the digital data and the reference pseudorandom code sequence comprises:estimating a first bit edge within the digital data stored within memory; and disregarding a number of chips within the digital data and a number of chips within the reference pseudorandom code sequence based on the estimated first bit edge and a time uncertainty value associated with the time-of-week information received from the assist server. 11. The method of claim 6, wherein correlating the buffered digital data with the locally generated reference code sequence comprises dividing the reference code sequence and digital data into blocks of size N, where the block size N is less than a data bit period M associated with the signal plus a time uncertainty value associated with the received time-of-week information.12. The method of claim 6, wherein dividing the reference code sequence and the digital data into blocks include forming blocks from the reference code sequence to have M chips and N?M padded zeros.13. The method of claim 6, wherein correlating the buffered digital data with the locally generated reference code sequence comprises applying a matched filtering operation to each of the blocks to produce a correlation peak having a time offset relative to the reference code sequence.14. The method of claim 13, further comprising:sliding the reference code relative to the digital data of the signal by N?M chips, where N represents the block size and M represents the bit period, when the correlation peak is below a peak threshold; and repeating the matched filter operations. 15. The method of claim 13, wherein sliding the reference code relative to the digital data comprises repeatedly sliding the reference code and performing the correlation process until a total number of shifted chips for the reference code exceed a time uncertainty value associated with the time-of-week information received from the assist server.16. The method of claim 1, further comprising:performing a Doppler search over a number of Doppler hypotheses to identify a Doppler offset for the signal; and using the Doppler offset as an initial frequency offset for acquiring signals from subsequent satellites. 17. The method of claim 16, further comprising:using a first integration time, performing the Doppler search for each of a set of Doppler bins to produce a set of outputs; and increasing the integration time and repeating the process when no valid peak is detected based on the set of outputs. 18. The method of claim 17, further comprising:declaring a preliminary detection when any of the outputs exceed a detection threshold; storing a current Doppler offset associated with the preliminary detection; and validating the preliminary detection by examining the outputs for neighboring Doppler bins of the current Doppler bin. 19. The method of claim 18, wherein validating the preliminary detection comprises examining the outputs for the neighboring Doppler offsets to determine whether a signal strength for the current Doppler offset is maximum relative to the neighboring Doppler offsets.20. The method of claim 1, wherein the acquisition assistance data comprises identification for satellites in view from a mobile unit, time-of-week data for the satellites Doppler information for the satellites, frequency synchronization information, and position information for the satellites.21. The method of claim 1, further comprising:communicating the time offset to the assist server; and receiving position data from the assists server. 22. The method of claim 1, further comprising calculating a position based on the time offset.23. A method comprising:receiving acquisition assistance data from an assist server, wherein the acquisition assistance data identifies a set of satellites and includes time-of-week data indicating an initial time offset into a P-code pseudorandom code sequence for each of the satellites; receiving signals from the satellites; digitizing the signals to produce a stream of digital data; buffering an amount of the digital data; locally generating reference P-code pseudorandom code sequences for the satellites based on the respective initial time offsets for the satellites; correlating the digital data with the reference code sequences to identify correlation peaks having respective time offsets; and determining a position for a mobile unit based on the time offsets. 24. The method of claim 23, wherein correlating the digital data with the locally generated reference code sequences comprises:estimating a first bit edge within the digital data stored within memory; and disregarding a number of chips within the digital data and a number of chips within each of the reference pseudorandom code sequences based on the estimated first bit edge and a time uncertainty value associated with the time-of-week information received from the assist server. 25. The method of claim 22, wherein correlating the buffered digital data with the locally generated reference code sequences comprises dividing the reference code sequences and digital data into blocks of size N, where the block size N is less than a data bit period M associated with the signal plus a time uncertainty value associated with the received time-of-week information, and wherein the blocks of the reference code sequence have M chips and N?M padded zeros.26. The method of claim 23, wherein correlating the buffered digital data with the locally generated reference code sequences comprises performing a matched filtering operation to each of the blocks to produce a correlation peak having a time offset relative to the reference code sequence.27. The method of claim 26, further comprising:sliding the reference code for a given satellite relative to the digital data of the signal by N?M chips, where N represents the block size and M represents the bit period, when the correlation peak for a given satellite is below a peak threshold; and repeating the matched filtering operations for the given satellite. 28. The method of claim 27, wherein sliding the reference code relative to the digital data comprises repeatedly sliding the reference code and performing the matched filtering operations until a total number of shifted chips for the reference code exceed a time uncertainty value associated with the time-of-week information received from the assist server.29. The method of claim 23, further comprising:using a first integration time, performing the Doppler search for each of a set of Doppler hypotheses to produce a set of outputs for a first one the signals; and declaring a preliminary detection when any of the outputs exceed a detection threshold; storing a current Doppler offset associated with the preliminary detection; validating the preliminary detection by examining the outputs for the neighboring Doppler offsets to determine whether a signal strength for the current Doppler offset is maximum relative to the neighboring Doppler offsets; and using the Doppler offset as an initial frequency offset for acquiring signals from subsequent satellites. 30. The method of claim 1, further comprising:communicating the time offset to the server; and receiving position data from the server. 31. The method of claim 23, further comprising:performing a Doppler search over a number of Doppler hypotheses to identify a Doppler offset for a first one of the signals; and using the Doppler offset as an initial frequency offset for performing a Doppler search for at least one of the other satellites. 32. A method comprising:receiving acquisition assistance data from server; and directly acquiring a P-code signal from a satellite based on the acquisition assistance data without first acquiring a C-code signal from the satellite. 33. The method of claim 32, wherein the acquisition assistance data includes time-of-week data indicating an initial time offset into the P-code signal.34. The method of claim 33, further comprising locally generating a reference pseudorandom code sequence based on the time-of-week data received from the assist server.35. The method of claim 34, wherein directly acquiring the P-code signal comprises correlating the P-code signal with the locally generated reference code sequence according to the time-of-week data.36. A system comprising:an assist server to track a signal from a Global Positioning System (GPS) satellite and generate acquisition assistance information from the signal; and a mobile unit to receive the acquisition assistance data from the assist server, and to acquire a P-code signal from the satellite based on the acquisition assistance data. 37. The system of claim 36, wherein the acquisition assistance data includes time-of-week data for the satellite indicating an initial time offset into a P-code pseudorandom code sequence.38. The system of claim 37, wherein the mobile unit comprises a reference generator to locally generate a reference pseudorandom code sequence based on the time-of-week data.39. The system of claim 38, wherein the mobile unit correlates the signal and the reference pseudorandom code sequence based on the acquisition assistance data to determine an actual time offset for the signal relative to the code sequence.40. The system of claim 39, wherein the mobile unit stores a time uncertainty value associated with the time-of-week information, and correlates the signal and the reference pseudorandom code according to the time uncertainty value.41. The system of claim 36, wherein the assist server is coupled to a base station for a cellular communication system.42. The system of claim 36, wherein the assist server tracks a C/A-code signal and generates the assistance information from the C/A-code signal.43. The system of claim 36, wherein the assist server tracks a P-code signal and generates the assistance information from the P-code signal.44. An apparatus comprising:an antenna to receive a signal from a satellite; a wireless modem to receive acquisition assistance data from an assist server; a reference generator to generate a reference pseudorandom code sequence based on the acquisition assistance data; and a processor to determine a time offset for a P-code pseudorandom code sequence associated with the signal based on the acquisition assistance data. 45. The apparatus of claim 44, wherein the processor determines a position for a mobile unit based on the time offset.46. The apparatus of claim 44, wherein the acquisition assistance data includes time-of-week data indicating an initial time offset into the P-code sequence.47. The apparatus of claim 44, further comprising:an analog-to-digital converter to produce a stream of digital data from the GPS signal; and a medium to buffer an amount of the digital data. 48. The apparatus of claim 47, wherein the processor sets the amount of buffered digital data based on a time uncertainty value associated with the time-of-week information received from the assist server.49. The apparatus of claim 47, wherein the processor correlates the buffered digital data with the locally generated reference code sequence to determine a correlation peak for the signal.50. The apparatus of claim 47, wherein the processor synchronizes the digital data and the reference pseudorandom code sequence.51. The apparatus of claim 50, wherein the processor synchronizes the digital data and the reference pseudorandom code by estimating a first bit edge within the digital data stored within memory, and disregarding a number of chips within the digital data and a number of chips within the reference pseudorandom code sequence based on the estimated first bit edge and a time uncertainty value associated with the time-of-week information received from the assist server.52. The apparatus of claim 47, wherein the processor divides the reference code sequence and digital data into blocks of size N, where the block size N is less than a data bit period M associated with the signal plus a time uncertainty value associated with the received time-of-week information, and correlates the buffered digital data with the locally generated reference code sequence to determine a correlation peak.53. The apparatus of claim 52, wherein the processor forms blocks from the reference code sequence to have M chips and N?M padded zeros.54. The apparatus of claim 52, wherein the processor slides the reference code relative to the digital data of the signal by N?M chips, where N represents the block size and M represents the bit period, when the correlation peak is below a peak threshold; and repeating the matched filter operations.55. The apparatus of claim 54, wherein the processor repeatedly sliding the reference code and performing the correlation process until a total number of shifted chips for the reference code exceed a time uncertainty value associated with the time-of-week information received from the assist server.56. The apparatus of claim 44, wherein the processor performs a Doppler search over a number of Doppler hypotheses to identify a Doppler offset for the signal, and uses the Doppler offset as an initial frequency offset for acquiring signals from subsequent satellites.57. The apparatus of claim 56, wherein the processor performs the Doppler search for each of a set of Doppler bins using a first integration time to produce a set of outputs, and increases the integration time and repeats the process when no valid peak is detected based on the set of outputs.58. The apparatus of claim 57, wherein the processor declares a preliminary detection when any of the outputs exceed a detection threshold, stores a current Doppler offset associated with the preliminary detection, and validates the preliminary detection by examining outputs for neighboring Doppler offsets.59. The apparatus of claim 44, wherein the acquisition assistance data comprises identification for satellites in view from a mobile unit, time-of-week data for the satellites Doppler information for the satellites, frequency synchronization information, and position information for the satellites.60. The apparatus of claim 44, wherein the processor comprises a digital signal processor (DSP).61. A computer-readable medium comprising instructions for causing a programmable processor to:receive acquisition assistance data from an assist server; and determine a time offset for a P-code pseudorandom code sequence associated with a signal from a satellite based on the acquisition assistance data. 62. The computer-readable medium of claim 61, wherein the instructions cause the processor to determine a position for a mobile unit based on the time offset.63. The computer-readable medium of claim 61, wherein the acquisition assistance data includes time-of-week data indicating an initial time offset into the P-code sequence.64. The computer-readable medium of claim 63, wherein the instructions cause the processor to locally generating a reference pseudorandom code sequence based on time-of-week data received from the assist server.65. The computer-readable medium of claim 63, wherein the instructions cause the processor to set an amount of buffered digital data representing the signal based on a time uncertainty value associated with the time-of-week information received from the assist server.66. The computer-readable medium of claim 64, wherein the instructions cause the processor to:estimate a first bit edge within the digital data stored within memory; and disregard a number of chips within the digital data and a number of chips within the reference pseudorandom code sequence based on the estimated first bit edge and a time uncertainty value associated with the time-of-week information received from the assist server. 67. The computer-readable medium of claim 64, wherein the instructions cause the processor to divide the reference code sequence and digital data into blocks of size N, where the block size N is less than a data bit period M associated with the signal plus a time uncertainty value associated with the received time-of-week information, and to correlate the buffered digital data with the locally generated reference code sequence to determine a correlation peak.68. The computer-readable medium of claim 67, the instructions cause the processor to form blocks from the reference code sequence to have M chips and N?M padded zeros.69. The computer-readable medium of claim 67, the instructions cause the processor to slide the reference code relative to the digital data of the signal by N?M chips, where N represents the block size and M represents the bit period, when the correlation peak is below a peak threshold; and repeat the matched filter operations.70. The computer-readable medium of claim 69, the instructions cause the processor to repeatedly slide the reference code and performing the correlation process until a total number of shifted chips for the reference code exceed a time uncertainty value associated with the time-of-week information received from the assist server.71. A method comprising:receiving acquisition assistance data from an assist server; directly acquiring a P-code signal from a satellite based on the acquisition assistance data without first acquiring a C-code signal from the satellite; and determining a time offset for a P-code pseudorandom code sequence associated with said P-code signal.