VIRTUAL REAL-TIME CLOCK BASED ON TIME INFORMATION FROM MULTIPLE COMMUNICATION SYSTEMS

• US 20080018530A1
• Filed: 10/27/2006
• Published: 01/24/2008
• Est. Priority Date: 03/27/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Farmer, Dominic
• Granted Patent: US 7,551,129 B2
• Time in Patent Office: Days
• US Class Current: 342/357.02
• CPC Class Codes: G04R 20/02 the radio signal being sent by a satellite, e.g. GPS
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 56/005 compensating for timing error by adjustment in the receiver

Abstract

Method and apparatus to implement a “virtual” real-time clock at a terminal based on time information from multiple communication systems. At least one system (e.g., GPS) provides “absolute” time information for the virtual real-time clock, and at least one other system (e.g., a cellular system) provides “relative” time information. The virtual real-time clock is “time-stamped” with absolute time as it becomes available from the first system. Relative time (which may be received from multiple asynchronous transmitters) is mapped to the timeline of the virtual real-time clock as it is received from the second system. Absolute time at any arbitrary time instant on the timeline may then be estimated based on the absolute time from the first system and the relative time from the second system. Absolute times from the first system for two or more time instants may also be used to calibrate the relative time from the second system.

Claims

1. A method for determining a position of a receiver unit in a wireless communication system, comprising:

obtaining absolute time from a first communication system for a first time instant;

receiving relative time information from a second communication system;

estimating absolute time at a second time instant based on the absolute time for the first time instant and the relative time information from the second communication system; and

determining the position of the receiver unit based at least in part on the absolute time estimate for the second time instant.

2. The method of claim 1, wherein the absolute time for the first time instant is obtained from a position fix determined for the first time instant.

3. The method of claim 1, further comprising:

going to sleep for a duration of time between the first and second time instants determined based on an estimated stability of time for the second communication system.