Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2002-09-17
2003-12-30
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490
Reexamination Certificate
active
06670915
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to navigation satellite receivers, and more particularly to methods and systems for assisting a navigation receiver initialization with system-time information.
DESCRIPTION OF THE PRIOR ART
Global positioning system (GPS) and satellite positioning system (SPS) receivers use signals received from several earth-orbiting satellites in a constellation to determine user position and velocity, and other navigational data. A navigation receiver that has just been turned on does not yet know where it is, how much its crystal oscillator is in error, nor what time it is. It may however, know time to within three seconds or better, and its rough position to within a hundred kilometers. The exact time and satellite carrier frequencies are needed to find and lock onto the satellite transmissions, and so a search must be made of all the possibilities. Reducing the range of possibilities will lead directly to quicker initializations a first position fix.
A GPS receiver that is associated with a cellphone or that can communicate over the Internet can be assisted in many ways by network servers connected to other GPS receivers that already have satellite-lock and are tracking. A telephone or network communication channel can be used to contribute key bits of information to a navigation receiver to help it initialize faster. One of the present inventors, Paul McBurney, and others, have recently filed several United States Patent Applications that relate to aiding GPS receiver clients. These are summarized in Table I, and all such patent applications have been assigned to the same Assignee, and are incorporated herein by reference.
TABLE I
Docket
USPTO
USPTO
Number
Title
Inventors
Filing Date
Serial No.
734-01
Satellite Navigation Receiver and Method
P. McBurney,
11 Oct. 2000
09/687,044
of
A. Woo
734-02
Infrastructure-Aiding for Satellite
P. McBurney,
28 Feb. 2001
09/797,521
Navigation Receiver and Method
A. Woo
734-03
High sensitivity GPS Receiver and
P. McBurney,
19 Feb. 2002
10/079,245
Reception
A. Woo
734-04
Total Correction Strategy
Stephen J,
19 Feb. 2002
10/079,217
Edwards,
P.McBurney
734-05
Method and System for Position
S.Edwards,
19 Feb. 2002
10/079,244
Calculation from Calculated Time
P.McBurney
736-06
Computing Network Path Delays so
H.Matsushita,
19 Feb. 2002
10/079,251
Accurate Absolute Time can be
P.McBurney
Forwarded from a Server to a Client
736-07
No Preamble Frame Sync
Akira Kimura,
19 Feb. 2002
10/079,250
P.McBurney
736-08
Thin Client
P.McBurney,
19 Feb. 2002
10/079,249
C.Rasmussen,
F.Vaucher,
K.Victa
736-09
Software Crystal Oscillator
H.Matsushita,
19 Feb. 2002
10/079,248
P.McBurney
738-10
High Sensitivity Infrequent Use of Sensors
P.McBurney,
19 Feb. 2002
10/079,247
K.Victa
738-11
Real Time Clock
P.McBurney
19 Feb. 2002
10/079,253
738-12
Shared Reference Station
C.Rypinski,
19 Feb. 2002
10/079,252
M.Junkar
The GPS satellites transmit a 50-bps navigation (NAV) data message that repeats every 12.5 minutes. It comprises system time, satellite ephemeris, and almanac information that is critical to a GPS receiver in acquiring signal lock on enough satellites and producing its navigation solutions. There are twenty-five frames that each take 30-seconds, each frame has five subframes, and each subframe has ten words. A Z-count at the beginning of each subframe gives its transmission time from the satellite. Ephemeris is the first three subframes, and subframes
4
-
5
are almanac data spread over fifty pages. One whole data frame of NAV data is 1500-bits long, and thus takes thirty seconds to transmit.
The NAV-data cannot be reliably received and demodulated if its signal level is too weak. Such can occur indoors or below decks. So high sensitivity receivers need to receive informational assistance from a third party over a different channel that contributes current NAV-data. If local-receiver system-time is known, the z-count information can be plugged into an otherwise generic NAV-data message obtained from the third party.
Each data frame is divided into five subframes
1
-
5
, and each subframe is 300-bits long, e.g., ten 30-bit words. Thus it takes six seconds to transmit each 300-bit, 10-word subframe. Every subframe starts with a telemetry (TLM) word of 30-bits, followed by a hand-over word (HOW) of 30-bits. Both 30-bit words comprise 24-bits of data and 6-bits of parity. There are eight words of data payload in each subframe.
The TLM word at the front of each 300-bit subframe begins with an 8-bit preamble. The preamble allows the start of a subframe to be recognized, and thereafter provides a primary mechanism for the receiver to be synchronized.
The first 300-bit subframe transmits the satellite vehicle (SV) clock correction data after the TLM word and HOW. The second subframe transmits the first part of the SV-ephemeris data. The third subframe transmits the second part of the SV-ephemeris data. Subframes four and five are used to transmit different pages of system data. The fourth subframe also begins with the TLM word and HOW, and the data payloads rotate over 12.5 minutes to transmit the lengthy information about the ionosphere, UTC, and other data. An entire set of twenty-five frames (125 subframes) makes up the complete Navigation Message that is sent over such 12.5 minute period. The fifth subframe begins with the TLM word and HOW, and its data payload also rotates over 12.5 minutes to transmit the rather large almanac.
The clock data parameters describe the SV-clock and its relationship to GPS time. The ephemeris data parameters describe SV-orbits for short sections of the satellite orbits. Normally, a receiver gathers new ephemeris data each hour, but it can use old data for up to four hours without much error. The ephemeris parameters are used with an algorithm that computes the SV position for any time within the period of the orbit described by the ephemeris parameter set. The almanacs are approximate orbital data parameters for all SV's. The ten-parameter almanacs describe SV orbits over extended periods of time, and is sometimes useful for months.
The signal-acquisition time of a GPS receiver at start-up can be significantly speeded by having the current almanac. available. The approximate orbital data is used to preset the receiver with the approximate position and carrier Doppler frequency of each SV in the constellation.
Norman F. Krasner describes a way to deal with NAV-data messages that cannot be read because the carrier signal levels are too weak, in METHOD AND APPARATUS FOR SATELLITE POSITIONING SYSTEM BASED ON TIME MEASUREMENT, U.S. Pat. No. 6,239,742 B1, issued May 29, 2001. A base station is used to record parts of the NAV-data message and these are compared to similar data from a remote SPS receiver. The remote SPS receiver receives parts of the NAV-data message directly from satellites visible to it. The NAV-data recorded by the base station includes with it correct time identification, so matching up the two overlapping-in-time parts can assist the remote SPS receiver in finding its correct system time. Such comparison is not done at the remote mobile receiver, but rather back at the base station.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and system for assisting navigation satellite reception and receiver initialization of GPS and SPS receivers.
It is another object of the present invention to provide a method and system for reducing the time necessary for GPS and SPS receivers to initialize.
It is a further object of the present invention to provide a satellite-navigation system that is cost effective.
Briefly, an SPS receiver embodiment of the present invention comprises a radio receiver for measuring pseudoranges to orbiting SPS satellites, a local real time clock accurate within three seconds of true SPS system time, and a communication channel to receive NAV-data rebroadcasts from a server. Such server is associated with its own private navigation receiver that has direct satellite signal reception that is strong enough to reli
Kimura Akira
McBurney Paul W.
eRide, Inc.
Mull Fred H
Tarcza Thomas H.
LandOfFree
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