High Sensitivity GPS Receiver

• US 20090079627A1
• Filed: 06/25/2008
• Published: 03/26/2009
• Est. Priority Date: 06/27/2007
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Yeh, Wen-Chang, Sun, Qinfang, Chen, Ho-Chung
• Granted Patent: US 8,270,457 B2
• Time in Patent Office: Days
• US Class Current: 342/357.630
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/36 relating to the receiver frond end
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: H04L 7/0016 correction of synchronization errors

Abstract

A high sensitivity GPS receiver includes an acquisition engine and a tracking engine. The acquisition engine processes GPS satellite data at data rate that is substantially equal to twice the coarse acquisition (CA) code chip rate. This data rate advantageously enables the acquisition engine to process GPS satellite data with relatively less hardware area than traditional GPS acquisition approaches. In one embodiment, the high efficiency acquisition engine may be over-clocked, thereby allowing different phases of a CA code to be correlated quickly. The tracking engine can advantageously processes GPS satellite data at a data rate that does not have an integer relationship to the CA code chip rate.

Claims

1. A configurable correlator for an acquisition channel in a GPS receiver, the configurable correlator comprising:

a pre-summer for receiving resampled digital baseband data, removing Doppler effects, and adding two data samples of Doppler-corrected, digital baseband data;

a delay line for receiving an output of the pre-summer, the delay line including a plurality of registers connected in a daisy-chain and a plurality of tap points provided between certain registers;

a plurality of correlation multipliers for receiving outputs of the plurality of tap points, wherein a number of correlation multipliers is one-half a number of registers;

an adder tree for receiving outputs from the plurality of correlation multipliers;

an adder for receiving an output of the adder tree; and

a correlation memory for receiving an output of the adder and providing an input to the adder.

2. The configurable correlator of claim 1, further comprising a code memory, wherein each correlation multiplier further receives a coarse acquisition code stored in the code memory.

3. A configurable correlator for an acquisition channel in a GPS receiver, the configurable correlator comprising:

a pre-summer including a mixer coupled to resampled digital baseband data and an estimated Doppler frequency, a register coupled to an output of the mixer, and a first adder coupled to an output of the mixer and an output of the register;

a delay line coupled to an output of the adder, the delay line including a plurality of registers connected in a daisy-chain and a plurality of tap points, wherein one tap point is provided after a first register of the plurality of registers and thereafter other tap points are provided after every other register of the plurality of registers;

a plurality of correlation multipliers, each correlation multiplier coupled to a tap point;

an adder tree coupled to outputs of the plurality of correlation multipliers;

a second adder coupled to an output of the adder tree; and

a correlation memory coupled to an output of the adder, wherein the second adder is further coupled to an output of the correlation memory.

4. The configurable correlator of claim 3, further comprising a code memory, wherein each correlation multiplier further receives a coarse acquisition code stored in the code memory.

5. The configurable correlator of claim 3, wherein a final stage of the adder tree is configured to a width that accommodates a full sum with a desired precision.

6. A configurable correlator for an acquisition channel in a GPS receiver, the configurable correlator comprising:

a first processing stage including a pre-summer and a delay line section, wherein the pre-summer provides an output to the delay line section;

one or more subsequent processing stages, each subsequent processing stage including a pre-summer, a stage multiplexer, and a delay line section,

wherein each stage multiplexer receives an output of a corresponding pre-summer and provides an output to a corresponding delay line section,

wherein a stage multiplexer in a first subsequent processing stage further receives an output of the delay line section of the first processing stage, and in any other subsequent processing stage, a stage multiplexer further receives an output of a delay line section from an upstream processing section,

wherein each pre-summer of the first and subsequent processing sections includes a mixer receiving resampled digital baseband data and an estimated Doppler frequency, a register receiving an output of the mixer, and a first adder receiving an output of the mixer and an output of the register,

wherein each delay line section of the first and subsequent processing sections includes a plurality of registers connected in a daisy-chain and a plurality of tap points between certain of the plurality of registers,

a plurality of correlation multipliers, each correlation multiplier coupled to a tap point;

a plurality of adder tree sections, each adder tree section receiving outputs from a corresponding set of correlation multipliers;

a plurality of multiplexers, each multiplexer for receiving an output of a corresponding adder tree section;

a multiplexer selector for receiving an output from each of the plurality of multiplexers;

an additional adder tree section for receiving an output from each of the plurality of multiplexers;

a two-to-one multiplexer for receiving outputs from the multiplexer selector and the additional adder tree section;

a final adder for receiving an output of the two-to-one multiplexer; and

a correlation memory for receiving an output of the final adder, wherein an output of the correlation memory is provided to the final adder.

7. The configurable correlator of claim 6, further comprising a code memory, wherein each correlation multiplier further receives a coarse acquisition code stored in the code memory.

8. The configurable correlator of claim 7, wherein the configurable correlator has 16 processing stages, and wherein each delay line section includes 33 tap points.

9. A method of acquiring a GPS satellite signal, the method comprising:

setting a coherent integration period;

performing coarse coherent integration for the set coherent integration period to determine a first correlation value;

determining whether the first correlation value is greater than a high threshold, wherein the high threshold corresponds to a strong positive correlation between a received GPS signal and a coarse acquisition code, a code phase, and an estimated Doppler frequency;

when the first correlation value is greater than the high threshold, then performing fine coherent integration to refine the coarse acquisition code, the code phase, and the estimated Doppler frequency;

when the first correlation value is not greater than the high threshold, then determining whether the first correlation value is greater than a low threshold, wherein the low threshold corresponds to a weak positive correlation between a received GPS signal and a coarse acquisition code, a code phase, and an estimated Doppler frequency;

when the first correlation value is not greater than the low threshold, then determining whether the set coherent integration period is at a maximum duration; and

when the set coherent integration period is not at the maximum duration, then increasing the set coherent integration period and returning to performing coarse coherent integration.

10. The method of claim 9, further comprising:

when the first correlation value is greater than the low threshold, then determining whether the first correlation value is a false trigger; and

when the first correlation value is not a false trigger, then proceeding to performing fine coherent integration.

11. The method of claim 10, further comprising:

when the first correlation value is a false trigger, then proceeding to determining whether the set coherent integration period is at the maximum duration.

12. The method of claim 9, further comprising:

when the set coherent integration period is at the maximum duration, then setting a non-coherent integration period; and

performing coarse non-coherent integration for the set non-coherent integration period to generate a second correlation value.

13. The method of claim 12, wherein performing coarse non-coherent integration includes:

calculating an intermediate correlation value using a largest possible coherent correlation time; and

accumulating multiple intermediate correlation values based on more than one coarse non-coherent integrations,

wherein the accumulated, multiple intermediate correlation values form the second correlation value.

14. The method of claim 12, further comprising:

determining whether the second correlation value is greater than a predetermined threshold, wherein the predetermined threshold corresponds to a strong positive correlation between a received GPS signal and a coarse acquisition code, a code phase, and an estimated Doppler frequency; and

when the second correlation value is greater than the predetermined threshold, then performing fine non-coherent integration to refine the coarse acquisition code, the code phase, and the estimated Doppler frequency.

15. The method of claim 14, further comprising:

when the second correlation value is not greater than the predetermined threshold, then determining whether the set non-coherent integration period is at a maximum duration; and

when the set non-coherent integration period is not at the maximum duration, then increasing the set non-coherent integration period and returning to performing coarse non-coherent integration.

16. The method of claim 15, further comprising:

when the set non-coherent integration period is at the maximum duration, then the method terminates with an acquisition failure.

17. A method of tracking a GPS satellite signal, the method comprising:

executing a pull-in stage;

determining whether a PLL loop has converged;

when the PLL loop has converged, then determining whether the PLL loop has false convergence;

when the PLL loop does not have false convergence, then executing a transition stage by decreasing PLL loop bandwidth and increasing integration time relative to previous PLL loop bandwidths and integration times;

after the transition stage, determining whether the PLL loop has converged; and

when the PLL loop has converged (second occurrence), then executing a tracking stage.

18. The method of claim 17, wherein determining whether the PLL loop has converged includes comparing a change in an average PLL output with its root-mean-square variation.

19. The method of claim 17, wherein determining whether the PLL loop has false convergence includes comparing a power of an in-phase component to a power of a quadrature component of a frequency- and phase-corrected GPS satellite signal.

20. The method of claim 17, further including:

when the PLL loop has not converged (second occurrence), then returning to executing the transition stage.

21. The method of claim 17, further including:

when the PLL loop is not converging (first occurrence), then returning to executing the pull-in stage.

22. The method of claim 17, further including:

when the PLL loop does have false convergence, then determining whether a PLL is set to a last possible setting; and

when the PLL is not set to a last possible setting, then using another PLL setting and returning to executing the pull-in stage.

23. The method of claim 22, further including:

when the PLL is set to a last possible setting, then terminating the method with a tracking failure.

24. The method of claim 17, further including:

determining whether the PLL loop is diverging;

when the PLL loop is diverging, then returning to executing the pull-in stage; and

when the PLL loop is not diverging, then returning to executing the tracking stage.

25. A high-sensitivity GPS receiver comprising:

an antenna;

an analog section for receiving an output of the antenna;

a digital section for receiving an output of the analog section; and

a processor for receiving an output of the digital section,

wherein the digital section includes a plurality of acquisition channels, at least one acquisition channel comprising a configurable correlator, the configurable correlator comprising;

a pre-summer for receiving resampled digital baseband data, removing Doppler effects, and adding two data samples of Doppler-corrected, digital baseband data;

a delay line for receiving an output of the pre-summer, the delay line including a plurality of registers connected in a daisy-chain and a plurality of tap points provided between certain registers;

a plurality of correlation multipliers for receiving outputs of the plurality of tap points, wherein a number of correlation multipliers is one-half a number of registers;

an adder tree for receiving outputs from the plurality of correlation multipliers;

an adder for receiving an output of the adder tree; and

a correlation memory for receiving an output of the adder and providing an input to the adder.

26. A high-sensitivity GPS receiver comprising:

an antenna;

an analog section for receiving an output of the antenna;

a digital section for receiving an output of the analog section; and

a processor for receiving an output of the digital section,

wherein the digital section includes a plurality of acquisition channels, at least one acquisition channel comprising a configurable correlator, the configurable correlator comprising;

a pre-summer including a mixer coupled to resampled digital baseband data and an estimated Doppler frequency, a register coupled to an output of the mixer, and a first adder coupled to an output of the mixer and an output of the register;

a delay line coupled to an output of the adder, the delay line including a plurality of registers connected in a daisy-chain and a plurality of tap points, wherein one tap point is provided after a first register of the plurality of registers and thereafter other tap points are provided after every other register of the plurality of registers;

a plurality of correlation multipliers, each correlation multiplier coupled to a tap point;

an adder tree coupled to outputs of the plurality of correlation multipliers;

a second adder coupled to an output of the adder tree; and

a correlation memory coupled to an output of the adder, wherein the second adder is further coupled to an output of the correlation memory.

27. A method of acquiring a GPS satellite signal, the method comprising:

setting a coherent integration period;

performing a coarse coherent integration for the set coherent integration period to determine a first correlation value;

determining whether the first correlation value is greater than a high threshold, wherein the high threshold corresponds to a strong positive correlation between a received GPS signal and a coarse acquisition code, a code phase, and an estimated Doppler frequency;

when the first correlation value is greater than the high threshold, then performing fine coherent integration to refine the coarse acquisition code, the code phase, and the estimated Doppler frequency;

setting a non-coherent integration period;

performing coarse non-coherent integration for the set non-coherent integration period to generate a second correlation value;

determining whether the second correlation value is greater than a predetermined threshold, wherein the predetermined threshold corresponds to a strong positive correlation between a received GPS signal and a coarse acquisition code, a code phase, and an estimated Doppler frequency; and

when the second correlation value is greater than the predetermined threshold, then performing fine non-coherent integration to refine the coarse acquisition code, the code phase, and the estimated Doppler frequency,

wherein performing the fine coherent integration and the fine non-coherent integration determines an acquired GPS signal.

28. The method of claim 27, wherein

when the first correlation value is not greater than the high threshold, then determining whether the first correlation value is greater than a low threshold, wherein the low threshold corresponds to a weak positive correlation between a received GPS signal and a coarse acquisition code, a code phase, and an estimated Doppler frequency;

when the first correlation value is greater than the low threshold, then determining whether the first correlation value is a false trigger; and

when the first correlation value is not a false trigger, then proceeding to performing fine coherent integration.