Global positioning system and global positioning method with improved sensitivity by detecting navigation data inversion boundaries

• US 6,297,770 B1
• Filed: 05/23/2000
• Issued: 10/02/2001
• Est. Priority Date: 05/23/2000
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Hirata, Seiichiro, Ueda, Fumio
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/576,027
• Time in Patent Office: 497 Days
• Field of Search: 342/357.05, 342/357.06, 342/357.12, 342/357.13, 701/213, 455/12.1
• US Class Current: 342/357.62
• CPC Class Codes: G01S 19/05 providing aiding data
• CPC Class Codes: G01S 19/243 Demodulation of navigation message
• CPC Class Codes: G01S 19/246 involving long acquisition integration times, extended snapshots of signals or methods specifically directed towards weak signal acquisition
• CPC Class Codes: G01S 19/254 relating to Doppler shift of satellite signals
• CPC Class Codes: G01S 19/256 relating to timing, e.g. time of week, code phase, timing offset
• CPC Class Codes: G01S 19/258 relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence

Abstract

A Global Positioning System (GPS) forms a C/A code sequence by summing, beginning from a polarity inversion boundary determined by a correlation peak position detector, chips at corresponding positions in PN frames constituting each bit of navigation data; calculates pseudo ranges by computing correlation between the C/A code sequence and a reference C/A code sequence generated by the GPS terminal; and determines the position of the GPS terminal using the pseudo ranges and navigation data. The navigation data detected inside the GPS terminal is used when a received electric field detected by a received electric field intensity detector is greater than a threshold level, and the navigation data received from an external system is used when the received electric field is below the threshold level. Thus, the number of PN frames to be integrated is limited because the polarity inversion boundaries of the navigation data are detected, and hence the sensitivity (S/N ratio) is sufficient. Communication between a terminal and a base station is not always required for determining the position because the GPS terminal does not always obtain the Doppler information from the base station, reducing communication cost.

Claims

1. A Global Positioning System (GPS) including an external system that receives a GPS signal from a satellite and extracts navigation data and Doppler information from the GPS signal, and a GPS terminal connected to the external system through a communication medium and receiving the GPS signal from the satellite, wherein each bit of the navigation data includes a plurality of PN frames, each frame including many chips arranged in a pattern, said GPS terminal comprising:

a frequency converter for converting frequency of the GPS signal received by the GPS terminal;

an analog-to-digital (A/D) converter for converting the GPS signal passing through the frequency converter into corresponding GPS data;

a memory for storing the GPS data as stored GPS data for a time interval;

a Doppler correction section for Doppler correction of the stored GPS data to produce Doppler corrected data, using Doppler information from one of the GPS terminal and the external system;

means for sequentially dividing the Doppler corrected data into a plurality of data blocks with a length of a navigation data bit in accordance with navigation data supplied from one of the GPS terminal and the external system;

means for calculating, for each of the data blocks, a cumulative sum of chips for corresponding positions in individual PN frames in the data block;

means for multiplying each cumulative sum by a corresponding navigation data bit and for outputting a plurality of products of the cumulative sums and the navigation data bits;

means for summing the plurality of products for respective chip positions; and

means for computing correlation between a set of sums of the products and a PN code sequence generated in the GPS terminal, and for calculating a pseudo range between the GPS terminal and the satellite from a correlation peak at a maximum correlation.

2. The Global Positioning System according to claim 1, further comprising means for shifting divisions of the data blocks if the correlation peak is less than a threshold level, and for supplying new data blocks to said means for calculating a cumulative sum.

3. The Global Positioning System according to claim 2, wherein said means for shifting divisions of the data blocks shifts the divisions to maximize the correlation, and said means for computing correlation determines the pseudo range from the correlation peak.

4. The Global Positioning System according to claim 1, further comprising a received electric field detector for detecting intensity of a received electric field, wherein said means for sequentially dividing the GPS data divides, when the received electric field is greater than a threshold level, the GPS data passing through the Doppler correction section into the data blocks in accordance with the navigation data obtained from the GPS signal received by the GPS terminal, and divides, when the received electric field is less than the threshold level, the GPS data in accordance with the navigation data supplied from the external system.

5. The Global Positioning System according to claim 4, further comprising a position determining section for determining position of the GPS terminal from the pseudo range and the navigation data extracted from the GPS signal received by the GPS terminal when the received electric field is greater than a threshold level, and supplied from the external system when the received electric field is less than the threshold level.

6. The Global Positioning System according to claim 1, wherein said GPS terminal further comprises a position determining section for determining position of the GPS terminal from the pseudo range obtained by the GPS terminal and the navigation data received by the external system.

7. The Global Positioning System according to claim 2, wherein said means for shifting divisions of the data blocks shifts the divisions of the data blocks by a predetermined amount if the correlation peak is less than a threshold level to enable detection of the correlation peak.

8. The Global Positioning System according to claim 2, wherein said means for shifting divisions of the data blocks shifts the divisions of the data blocks roughly at a first step, and then slightly at a second step to converge to the correlation peak.

9. The Global Positioning System according to claim 1, wherein the Doppler correction section carries out Doppler correction of the C/A code sequence in the GPS signal received by the GPS terminal using the Doppler information obtained from the navigation data supplied by one of the GPS terminal and the external system.

10. The Global Positioning System according to claim 1, wherein said Doppler correction section carries out a Doppler correction of the C/A code sequence by Doppler correction of the GPS signal received by the GPS terminal.

11. The Global Positioning System according to claim 4, wherein the received electric field detector changes a correlation calculation interval in response to the electric field level detected.

12. The Global Positioning System according to claim 4, wherein the received electric field detector changes a summation interval in response to the electric field level detected.

13. A Global Positioning System (GPS) terminal connected through a communication medium to an external system that receives a GPS signal from a satellite and extracts navigation data and Doppler information from the GPS signal, wherein the GPS terminal receives the GPS signal from the satellite, and each bit of the navigation data includes a plurality of PN frames, each PN frame including many chips arranged in a pattern, said GPS terminal comprising:

a frequency converter for converting frequency of the GPS signal received by the GPS terminal;

an analog-to-digital (A/D) converter for converting the GPS signal passing through the frequency converter into corresponding GPS data;

a memory for storing the GPS data as stored GPS data for a time interval;

a Doppler correction section for Doppler correction of the stored GPS data to produce Doppler corrected data, using Doppler information from one of the GPS terminal and the external system;

means for sequentially dividing the Doppler corrected data into a plurality of data blocks with a length of a navigation data bit in accordance with navigation data supplied from one of the GPS terminal and the external system;

means for calculating, for each of the data blocks, a cumulative sum of chips for corresponding positions in individual PN frames in the data block;

means for multiplying each cumulative sum by a corresponding navigation data bit and for outputting a plurality of products of the cumulative sums and the navigation data bits;

means for summing the plurality of products for respective chip positions; and

means for computing correlation between a set of sums of the products and a PN code sequence generated in the GPS terminal, and for calculating a pseudo range between the GPS terminal and the satellite from a correlation peak at a maximum correlation.

14. A Global Positioning method in a system including an external system that receives a Global Positioning System (GPS) signal from a satellite and extracts navigation data and Doppler information from the GPS signal, and a GPS terminal that is connected to the external system through a communication medium and receives the GPS signal from the satellite, wherein each bit of the navigation data includes a plurality of PH frames, each PN frame including many chips arranged in a pattern, said Global Positioning method comprising:

converting frequency of the GPS signal received by the GPS terminal;

analog-to-digital converting the GPS signal, after converting frequency, into corresponding GPS data;

storing the GPS data for a time interval as stored GPS data;

Doppler correcting the stored GPS data to produce Doppler corrected data, using Doppler information from one of the GPS terminal and the external system;

sequentially dividing the Doppler corrected data into a plurality of data blocks with a length of a navigation data bit in accordance with navigation data supplied from one of the GPS terminal and the external system;

calculating for each of the data blocks a cumulative sum of chips at corresponding positions in individual PN frames in the data block;

multiplying each cumulative sum by a corresponding navigation data bit, and outputting a plurality of products of the cumulative sums and the navigation data bits;

summing the plurality of products for respective chip positions;

computing correlation between a set of sums of the products and a PN code sequence generated in the GPS terminal; and

calculating a pseudo range between the GPS terminal and the satellite from a correlation peak at a maximum correlation.