Detecting and compensating for erroneous time measurement for mobile device position calculation
A method implemented by an assisted Global Navigation Satellite System (GNSS) server determines a position of a GNSS receiver. The method includes sending a request for measurement information to the GNSS receiver at a first time and receiving the measurement information from the GNSS receiver in response to the request at a second time, where the measurement information includes position measurement data and a corresponding measured time based on satellite signals received by the GNSS receiver. The measured time is determined to be erroneous when it is outside an accurate time range determined based on at least one of the first time and the second time. A substitute time is identified and the position of the GNSS receiver is determined based on the substitute time when the measured time is erroneous.
1. A method implemented by an assisted Global Navigation Satellite System (GNSS) server for determining a position of a GNSS receiver, the method comprising:
sending a request for measurement information to the GNSS receiver at a first time;
receiving the measurement information from the GNSS receiver in response to the request at a second time, the measurement information including position measurement data and a corresponding measured time based on a plurality of satellite signals received by the GNSS receiver;
determining that the measured time is erroneous when the measured time is outside an accurate time range determined based on at least one of the first time and the second time; and
identifying a substitute time and determining the position of the GNSS receiver based on the substitute time when the measured time is determined to be erroneous.
2. The method of claim 1 , further comprising:
determining the position of the GNSS receiver based on the measured time when the measured time is not determined to be erroneous.
3. The method of claim 1 , wherein determining that the measured time is erroneous comprises determining that the measured time is later than the second time by a predetermined amount.
4. The method of claim 3 , wherein the predetermined amount is determined based on an estimate of a clock error at the GNSS server.
5. The method of claim 1 , wherein determining that the measured time is erroneous comprises determining that the time is earlier than the first time by a predetermined amount.
6. The method of claim 5 , wherein the predetermined amount is determined based on an estimate of a clock error at the GNSS receiver.
7. The method of claim 1 , wherein determining that the measured time is erroneous comprises determining that the time is earlier than the second time by a predetermined amount.
8. The method of claim 7 , wherein the predetermined amount is an approximate time required for the GNSS receiver to collect and send the measurement information.
9. The method of claim 8 , wherein the approximate time is determined based on time taken for a message to be sent to the GNSS receiver and a response to be received.
10. The method of claim 1 , wherein determining the position of the GNSS receiver using the substitute time comprises:
performing time recovery to obtain a recovered time using the substitute time; and
calculating the position of the GNSS receiver using the recovered time.
11. The method of claim 10 , wherein performing time recovery comprises:
performing an iterative time recovery method.
12. The method of claim 10 , wherein performing time recovery comprises:
performing an integrated time recovery method.
13. The method of claim 1 , wherein the substitute time is the second time less a predetermined time interval which approximates an amount of time required for the GNSS receiver to generate and send the measurement information in response to the request for measurement information.
14. The method of claim 1 , wherein the substitute time is the second time less an estimated propagation time for the measurement information sent by the GNSS receiver to be received by the GNSS server.
15. The method of claim 1 , wherein the request for measurement information includes assistance data for assisting the GNSS receiver in locating at least one GNSS satellite of the GNSS satellites providing the plurality of satellite signals.
16. A non-transitory computer readable medium storing code executable by a computer processor for determining a position of a Global Navigation Satellite System (GNSS) receiver, the computer readable medium comprising:
a communication code segment for sending a request for measurement information to the GNSS receiver at a first time and for receiving the measurement information from the GNSS receiver at a second time, the measurement information including position measurement data and a corresponding measured time based on a plurality of satellite signals received by the GNSS receiver;
a time error determining code segment for determining whether the measured time is erroneous, wherein the time error determining code segment determines that the measured time is erroneous when the measured time of the received measurement information is outside an accurate time range determined based on at least one of the first time and the second time; and
a time recovery code segment for determining a recovered time using the measured time when the time error determining code segment determines that the measured time is not erroneous and using a substitute time when the time error determining code segment determines that the measured time is erroneous.
17. The computer readable medium of claim 16 , further comprising:
a positioning determination code segment for calculating the position of the GNSS receiver using the recovered time.
18. The computer readable medium of claim 17 , wherein the substitute time is the second time.
19. The computer readable medium of claim 17 , wherein the substitute time is the second time less a predetermined time interval which approximates an amount of time required for the GNSS receiver to generate and send the measurement information in response to the request for measurement information.
20. A device, comprising:
a communication interface configured to enable sending a request for measurement information to a Global Navigation Satellite System (GNSS) receiver at a first time and to enable receiving the measurement information from the GNSS receiver at a second time, the measurement information including position measurement data and a corresponding measured time based on a plurality of satellite signals received by the GNSS receiver; and
a processor configured to control operations of the communication interface and to execute an algorithm comprising:
determining whether the measured time received through the communication interface is erroneous, wherein the measured time is erroneous when the measured time of the received measurement information is earlier than a lower limit of an accurate time range or later than an upper limit of the accurate time range;
determining a recovered time using the measured time when the measured time is not erroneous and using a substitute time when the measured time is erroneous; and
calculating a geographic location of the GNSS receiver using the recovered time.