Universal acquisition and tracking apparatus for global navigation satellite system (GNSS)

• US 8,401,546 B2
• Filed: 04/26/2010
• Issued: 03/19/2013
• Est. Priority Date: 04/26/2010
• Status: Active Grant

• Current Assignee: Ecole de technologie superieure
• Original Assignee: Ecole de technologie superieure
• Inventors: Fortin, Marc-Antoine, Guay, Jean-Christophe, Landry, Rene Jr
• Primary Examiner(s): HOANG, THAI D
• Application Number:
  US12/767,773
• Publication Number:
  US 20110261805A1
• Time in Patent Office: 1,058 Days
• Field of Search: 370/316, 455/3.02, 455427-430, 455 121- 132, 342/21, 342252-35734, 342/357.36, 34235739-35772, 342/358, 340/985, 701/200, 701/206, 701400-479, 707917-920
• US Class Current: 455/427
• 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 19/31 Acquisition or tracking of other signals for positioning
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: H04B 1/7073 Synchronisation aspects
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

An acquisition and tracking apparatus is provided for tracking digitized spread spectrum navigation signals modulated with a spreading code according to any of a set of modulation types including Binary Phase Shift Keying (BPSK) with and without Frequency Domain Multiplexing Access (FDMA), time multiplexed BPSK, Quadrature Phase Shift Keying (QPSK), sine and cosine Binary Offset Carrier (BOC), modified, complex, and time multiplexed BOC (TMBOC), the apparatus comprising a plurality of universal tracking channels, each coupled to an interrupt module. The universal tracking channel includes a carrier demodulation module, a code generation module, a correlator module, a code frequencies generation module, and a subcarrier combining module for efficiently using the correlator resources in the correlation of the data and the pilot components of the signal within a single universal tracking channel. A corresponding method of operation is also provided.

Claims

1. An acquisition and tracking apparatus for tracking a plurality of spread spectrum navigation signals, each modulated according to one of a set of modulation types on a higher frequency carrier converted into an intermediate frequency signal, the carrier comprising one or more subcarriers and a navigation message modulated with a spreading code, the spreading code comprising a data component for carrying the navigation message, the spreading codes having a nominal epoch which is essentially a multiple of a predetermined time period, the apparatus comprising a plurality N of channel processors, each said channel processors including:

a carrier demodulation module including a local carrier oscillator generating a local carrier frequency for demodulating the carrier from the intermediate frequency signal into a baseband signal;

a code frequency generation module including a local code oscillator generating a code clock (CCK) at a code frequency, for clocking the code generation module;

a code generation module generating replica of the data component, and a periodic interrupt signal which is substantially synchronous with the code epochs of the selected navigation signal;

a subcarrier combining module, generating subcarrier replicas;

a correlator module correlating the baseband signal with the replica of the data component and the subcarrier replicas, and outputting correlation signals sampled with the periodic interrupt signal;

a parameter parsing module for providing operational parameters including a nominal carrier frequency control signal to the local carrier oscillator and a code frequency control signal to the local code oscillator;

a discriminator module for processing the sampled correlation signals and generating a set of data synchronization error signals; and

and an Error Evaluation Module generating a feedback value for adjusting the local carrier frequency and a Code Frequency Feedback signal for adjusting the code frequency.

2. The acquisition and tracking apparatus of claim 1, wherein the carrier further comprises a pilot component modulated with a pilot code, wherein:

the code generation module comprises means for generating replicas of the pilot component; and

the correlator module comprises means for correlating the baseband signal with the replicas of the pilot component, and outputting correlation signals sampled with the periodic interrupt signal.

3. The acquisition and tracking apparatus of claim 1, wherein the set of CDMA modulation types includes Binary Phase Shift Keying (BPSK), Binary Phase Shift Keying (BPSK) with Frequency Domain Multiplexing Access (FDMA), time multiplexed BPSK, Quadrature Phase Shift Keying (QPSK), sine and cosine Binary Offset Carrier (BOC), modified, complex, and time multiplexed BOC (TMBOC).

4. The acquisition and tracking apparatus of claim 3, wherein the set of CDMA modulation types includes Alternate BOC (AltBOC) where two channel processors are used.

5. The acquisition and tracking apparatus of claim 1, wherein the Error Evaluation Module comprises:

a set of programmable loop filters including;

a first loop filter of configurable orders 0, 1, and 2, filtering the error signals, and generating a feedback value for adjusting the local carrier frequency to substantially a frequency of the higher frequency carrier;

and second and third loop filters, each of one of configurable orders 0, 1, and 2, filtering the error signals; and

an Improved Dual Estimator Module coupled to the outputs of the second and third loop filters, and generating a Code Frequency Feedback signal for adjusting the code frequency to be substantially equal a predetermined multiple of the frequency of the code epoch.

6. The acquisition and tracking apparatus of claim 1, wherein:

the local carrier oscillator comprises means for generating a carrier phase signal;

the local code oscillator comprises means for generating a code phase signal;

each of the carrier phase and the code phase being sampled with the periodic interrupt signal,

the acquisition and tracing apparatus further comprises;

a master clock module generating a global time signal including a global interrupt pulse; and

a global interrupt manager, distributing the global time signal to channel processors and collecting accumulated data, including at least one of the correlation signals and the sampled carrier and code phase signals, from each channel processors and forwarding the accumulated data to a computer host for further processing.

7. The acquisition and tracking apparatus of claim 2, wherein the code generation module comprises:

a code counter clocked by the code clock (CCK);

a data code memory for storing a data code sequence, which corresponds to a data code sequence of the selected navigation signal and, sequentially addressed by the code counter outputting a primary data memory code bit stream is a primary part of the replica of the data component;

a data code shift register having a tap spacing input which defines a delay spacing, to programmably delay the primary data memory code bit stream and generate prompt (P_data), early (E_data), and late (L_data) versions of it, the delay between the early and prompt versions being equal to the delay between the prompt and late versions, the delay being determined by a tap spacing command included in the operational parameters and coupled operatively to the tap spacing input;

a pilot code memory for storing a pilot code sequence which corresponds to a pilot code sequence of the selected navigation signal and, sequentially addressed by the code counter outputting a primary pilot memory code bit stream, which is a primary part of the replica of the pilot code component;

a pilot code shift register having a tap spacing input which defines a delay spacing, to programmably delay the primary pilot memory code bit stream and generate prompt (P_data), early (E_data), and late (L_data) versions of it, the delay between the early and prompt versions being equal to the delay between the prompt and late versions, the delay being determined by the tap spacing command.

8. The apparatus of claim 3, wherein at least one of the navigation signals includes modulation with at least one of data and pilot secondary spreading codes, the code generation module further comprises:

a Secondary Chip Register for buffering secondary data and pilot code chips periodically received from the parameter parsing module;

an exclusive OR gate for modifying the primary data memory code bit stream with the buffered secondary data code chip which is a secondary part of the replica of the data code component; and

an exclusive OR gate for modifying the primary pilot memory code bit stream with the buffered secondary pilot code chip which is a secondary part of the replica of the pilot code component.

9. The acquisition and tracking apparatus of claim 7, wherein at least one of the navigation signals includes modulation in which data and pilot codes are time multiplexed, the code generation module further comprises a Time Multiplexed BPSK (TMBPSK) Module including:

a frequency divider circuit for dividing the frequency of the code clock (CCK) by a factor and generating a “

Slower Clock”

signal;

a first single-bit selector for substituting the code clock (CCK) with the “

Slower Clock”

signal for clocking the binary code counter;

a Code Generator for generating a Pseudo Random Noise (PRN) code signal 664;

a time multiplexer for multiplexing the PRN code signal with the primary pilot memory code bit stream to generate an Effective Spreading Code;

a second single-bit selector for substituting the primary pilot memory code bit stream with the Effective Spreading Code for modification with the secondary data code chip by the exclusive OR gate.

10. The acquisition and tracking apparatus of claim 1, wherein:

the code generation module comprises a data code shift register for delaying the replica of the data component by a programmable amount; and

the correlator module comprises means for correlating the baseband signal with the delayed replica, and forwarding the correlation result to a computing host for evaluation.

11. The apparatus of claim 2, wherein the correlator module comprises a data correlator array for correlating the baseband signal with the replicas of the data component including subcarrier replicas, and a pilot correlator array for correlating the baseband signal with the replicas of the pilot component including pilot subcarrier replicas.

12. The apparatus of claim 7, wherein the code frequency generation module comprises:

a code frequency oscillator generating a code super clock;

a first programmable sin-cosine divider for dividing the code super clock by a factor to generate a first raw sub-carrier signal, selectively programmed to have one of;

a cosine or a sine phase relationship to the code clock;

a Sub-carrier 2 Shift Register having a tap spacing input which defines a delay spacing, to programmably delay the first raw sub-carrier signal and generate prompt (SC2P), early (SC2E), and late (SC2L) versions of a first subcarrier replica signal, the delay between the early and prompt versions being equal to the delay between the prompt and late versions, the delay being determined with the tap spacing command included in the operational parameters and coupled operatively to the tap spacing input.

13. The apparatus of claim 12, wherein the code frequency generation module further comprises:

a Sub-Carrier Clock Divider (SC-CK Div) for dividing the code super clock by a first programmable factor (Div-Count 2) to generate an intermediate square wave;

a second programmable sin-cosine divider for dividing the intermediate square wave by a factor and to generate a second raw sub-carrier signal, selectively programmed to have one of a cosine or a sine phase relationship to the code clock;

a Sub-carrier 1 Shift Register (SC 1 SR) having a tap spacing input which defines a delay spacing, to programmably delay the second raw sub-carrier signal and generate prompt (SC1P), early (SC1E), and late (SC1L) versions of a second sub-carrier replica signal, the delay between the early and prompt versions being equal to the delay between the prompt and late versions, the delay being determined with the tap spacing command coupled operatively to the tap spacing input.

14. The apparatus of claim 13, wherein the code frequency generation module further comprises a Code Clock Divider (SC-CK Div) for dividing the intermediate square wave by a second programmable factor (Div-Count 1) to generate the code clock (CCK).

15. The apparatus of claim 14, the frequency of the of the local code oscillator being set to equal the nominal code frequency of the selected one of the navigation signals, and first and second programmable factors (Div-Count 2 and Div-Count 1) being set to unity one when no subcarrier replica signals are required.

16. The apparatus of claim 10, wherein the data code shift register comprises:

a variable spacing tap controlled by a VSC Delay control signal, the variable spacing tap outputting a variable spacing “

M_tap”

code signal; and

a variable spacing correlator for correlating the variable spacing “

M_tap”

code signal with the baseband signal to generate a variable spacing correlation (VSC) value.

17. The apparatus of claim 16, further comprising a selector for selecting an in-phase component “

I”

of the baseband signal, alternatively uncorrelated or correlated with subcarriers as determined by a programmable parameter (VSC_select).

18. The apparatus of claim 1, wherein the subcarrier combining module comprises:

a first subtractor operable to combine early and late versions of the first subcarrier signal (SC1E and SC1L) into a first difference signal (SC1Diff);

a first multiplier (M17) for multiplying a programmable first data weighting factor (α

-data) with SC1Diff;

a second multiplier (M20) for multiplying the first data weighting factor (α

-data) with the prompt version of the first subcarrier signal (SC1P);

a second subtractor for combining the early and late versions of the second subcarrier signal (SC2E and SC2L) into a second difference signal (SC2Diff);

a third multiplier (M18) for multiplying a programmable second data weighting factor β

-data) with SC2Diff to generate a combined data sub-carrier SC_Ddata;

a fourth multiplier (M19) for multiplying the second data weighting factor (β

-data) with the prompt version of the second subcarrier signal (SC2P);

a first adder for adding the outputs of the first and third multipliers (M17 and M18) to generate a combined difference data sub-carrier SC_Ddata for correlating with the baseband signal in the correlator module; and

a second adder for adding the outputs of the second and fourth multipliers (M20 and M19) to generate a combined prompt data sub-carrier SC_Pdata for correlating with the baseband signal in the correlator module.

19. The acquisition and tracking apparatus of claim 18, the subcarrier combining module further comprising:

a fifth multiplier (M13) for multiplying a programmable first pilot weighting factor (α

-pilot) with SC1Diff;

a sixth multiplier (M16) for multiplying the first pilot weighting factor (α

-pilot) with the prompt version of the first subcarrier signal (SC1P);

a seventh multiplier (M14) for multiplying a programmable second pilot weighting factor (β

-pilot) with SC2Diff to generate a combined data sub-carrier SC_Dpilot;

a eights multiplier (M15) for multiplying the second pilot weighting factor (β

-pilot) with the prompt version of the second subcarrier signal (SC2P);

a third adder for adding the outputs of the first and third multipliers (M17 and M18) to generate a combined difference pilot sub-carrier SC_Dpilot for correlating with the baseband signal in the correlator module; and

a fourth adder for adding the outputs of the second and fourth multipliers (M20 and M19) to generate a combined prompt pilot sub-carrier SC_Ppilot for correlating with the baseband signal in the correlator module.

20. The acquisition and tracking apparatus of claim 2, further including a TMBOC Multiplexer module for dynamically assigning the weighting factors (α

-pilot, α

-data, β

-pilot, β

-data) to weighting factors received from a set of weighting factors (α

, β

weights), the assignments being controlled according to a specified pattern, the TMBOC Multiplexer module comprising;

a pattern memory for storing the specified pattern;

a pattern counter for cyclically addressing the pattern memory, the pattern counter being reset by the periodic interrupt and clocked by the effective code clock;

a set of weight selectors being controlled by a data output of the pattern memory to select the weighting factors (α

-pilot, α

-data, β

-pilot, β

-data) from among the set of weighting factors (α

, β

weights) according to the pattern stored in the pattern memory.

21. The apparatus of claim 1, further including:

a selector for selecting one of a plurality of available navigation signals in the form of wide band digitized intermediate frequency (IF) signals, for acquisition and tracking; and

a customizable IF Filter for filtering out frequencies that are outside the frequency range of the selected navigation signal.

22. The apparatus of claim 2, further comprising:

an Accumulator Buffer, for coherently or non-coherently accumulating outputs of the correlator module;

in the Discriminator Module, means for generating a set of combined data and pilot synchronization errors from the pilot and data correlations received from the Accumulator Buffer, the operation of the Discriminator Module being controlled by modulation type information received from a Parameter Parsing Module;

a Dual Estimator Module, generating a Code Frequency Feedback signal for adjusting the code clock (CCK); and

a set of Loop Filters for filtering the set of combined data and pilot synchronization errors to achieve loop stability and sending the filtered values to the Dual Estimator Module, and for sending a filtered carrier frequency feedback value to the numerically controlled local carrier oscillator.

23. A global navigation satellite signal receiver system, comprising:

an acquisition and tracking apparatus for tracking a plurality of spread spectrum navigation signals, each modulated according to one of a set of modulation types on a high frequency carrier with a navigation message riding on a spreading code which comprises a combination of a primary data code component for carrying the navigation message;

a primary pilot code component;

secondary data and pilot code components; and

a plurality of data and pilot subcarrier components, the apparatus comprising a plurality N of channel processors, each channel processor receiving a selected one of the navigation signals, and including;

a code generation module generating local code replicas of code components of the spreading code of said selected signal;

a carrier demodulation module, demodulating the carrier of said selected signal into a baseband signal;

a code frequency generation module clocking the code generation module and generating local subcarrier replicas of subcarrier components of the spreading code of said selected signal;

a subcarrier combining module combining the local subcarrier replicas to generate combined subcarrier replicas and multiplying said combined subcarrier replicas with weighting factors;

a correlator module correlating the baseband signal with the local code replicas and the weighted combined subcarrier replicas into a set of correlation results; and

a Local Interrupt Module receiving the correlation results therefrom and controlling the generating of the local code replicas and local subcarrier replicas.

24. An acquisition and tracking apparatus for tracking a plurality of spread spectrum navigation signals, each modulated according to one of a set of modulation types on a high frequency carrier with a navigation message riding on a spreading code which comprises a combination of a primary data code component for carrying the navigation message;

a primary pilot code component;

secondary data and pilot code components; and

a plurality of data and pilot subcarrier components, the apparatus comprising a plurality N of channel processors, each channel processor receiving a selected one of the navigation signals, and including;

a code generation module generating local code replicas of code components of the spreading code of said selected signal;

a carrier demodulation module, demodulating the carrier of said selected signal into a baseband signal;

a code frequency generation module clocking the code generation module and generating local subcarrier replicas of subcarrier components of the spreading code of said selected signal;

a subcarrier combining module combining the local subcarrier replicas to generate combined subcarrier replicas and multiplying said combined subcarrier replicas with weighting factors;

a correlator module correlating the baseband signal with the local code replicas and the weighted combined subcarrier replicas into a set of correlation results; and

a Local Interrupt Module receiving the correlation results therefrom and controlling the generating of the local code replicas and local subcarrier replicas.