Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2001-09-19
2003-10-28
Beaulieu, Yonel (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S215000, C701S216000
Reexamination Certificate
active
06640189
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable
REFERENCE TO MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
The present invention relates to Global Positioning Systems (GPS), and more particularly, to methods of improving GPS satellite acquisition and reacquisition performance by utilizing navigation information from an integrated Global Positioning/Inertial Guidance (referred to herein as “GP/IG”) navigation system.
In order to provide position information, a GPS receiver must acquire four or more satellites from the GPS constellation. “Acquiring” a satellite means to synchronize to a timing code that the satellite produces. Typically the timing code from the satellite includes a pseudo-random (PR) data stream embedded in a waveform that the satellite continuously broadcasts. Each satellite in the GPS constellation is characterized by a unique PR code, and the transmission of that code begins at a particular time each day. Thus, synchronizing to a particular PR code from a satellite identifies the particular satellite, and provides time-of-day (TOD) information accurate to within the propagation delay from the satellite to the receiver. The GPS receiver independently maintains the same PR code that the satellite produces. The PR code that the GPS receiver receives from the satellite is delayed with respect to the code maintained in GPS receiver due to the propagation delay from the satellite to the receiver. To acquire the satellite, the GPS receiver delays its own version of the PR code with respect to the code it receives from the satellite until the codes match. The amount of delay the receiver adds corresponds to the propagation delay (and thus the distance) to the satellite.
In order to acquire a satellite (or reacquire if the satellite signal drops out for an extended period), the GPS receiver must “guess” an initial delay, then incrementally increase the delay while searching for a code match. The better the guess, the shorter the time needed to match the codes and declare acquisition. Since the delay is directly related to the distance from the receiver to the satellite, an accurate estimate of the distance to the satellite may be used to generate an accurate guess of the initial delay.
GPS navigation systems are widely used and are rapidly being incorporated into many newly manufactured commercial vehicles. Such vehicles often operate in city environments, however, resulting in substantial blackout periods while in so-called “urban canyons,” i.e., while between tall buildings that obscure the line-of-sight to one or more of the GPS satellites. Further, due to the nature of such city environments, a satellite may come into view for brief periods, sometimes only fractions of a second, in the gaps created by cross streets. Prior art search techniques generally require too much time to find the delay value required for synchronization with the satellite signal to take advantage of these brief windows of opportunity in which the satellite is in view.
FIG. 1
illustrates a block diagram of a prior art GPS navigation unit
10
receiving a first signal
12
from first satellite
20
, a second signal
14
from second satellite
22
, third signal
16
from third satellite
24
and fourth signal
18
from fourth satellite
26
. GPS navigation unit
10
includes an antenna
28
, an RF receiver
30
, an RF amplifier
32
, a GPS system digital signal processor (DSP)
34
, a correlator
36
, reference PR patterns
38
.
In operation, antenna
28
receives the first signal
12
from the first satellite
20
and communicates the signal
12
to RF receiver
30
. The RF amplifier
32
amplifies the signal
12
from the receiver
30
and passes the signal
12
to the GPS DSP
34
, the digital signal processor for the entire GPS unit. The DSP
34
includes a correlator
36
that incrementally compares the pseudo random code embedded in the first signal
12
from first satellite
20
to all of the stored bit patterns
38
and provides an indication (i.e., a correlation peak) when a match occurs. Stored bit patterns
38
are complete, time-dependent listings of the pseudo random code “signatures” used to uniquely identify each satellite. The DSP
34
shifts each of the stored bit patterns
38
in time against the first signal
12
until the correlator
36
indicates a match. A match in the codes identifies the first satellite
20
, and the amount of shift delay indicates the amount of propagation delay between the satellite and the GPS unit
10
. Once the DSP
34
indicates a match, the first satellite
20
is “acquired.” Typical prior art GPS receivers include multiple processing channels (i.e., multiple correlators) that simultaneously search through the possible PR codes to acquire multiple satellites. Only one such channel is shown in FIG.
1
. Once all four (or more) satellites are acquired, the GPS unit
10
determines its position by way of triangulation methods well known in the art.
When the line of sight to one of the four satellites is obstructed (e.g., a building lies between the satellite and the GPS unit), the signal from that satellite “drops out,” i.e., the obstruction attenuates the signal amplitude so that the receiver can no longer detect it. When the line of sight to the satellite is restored, the GPS unit must reacquire the satellite before position data will again be available. The prior art reacquisition algorithms typically begin searching for the lost satellite signal by incrementally delaying the corresponding PR code through the correlator (as described herein), with respect to an initial delay value, until a correlation peak occurs. In some prior art systems, the initial delay value is simply set to zero, i.e., the algorithm assumes no prior knowledge of the satellite location with respect to the GPS receiver. Other prior art systems may estimate the initial delay as the last delay used in the correlator prior to the signal dropping out. In either case, the amount of time necessary to reacquire the satellite may be substantial, especially if the position of the GPS receiver has significantly changed. Hence, a general need exists for a method of improving the acquisition and reacquisition performance of GPS receiving systems. It is an object of the present invention to substantially overcome the above-identified disadvantages and drawbacks of the prior art.
U.S. Pat. No. 6,125,325, entitled “GPS receiver with cross-track hold,” assigned to SiRF Technology, Inc. (Santa Clara, Calif.), describes a terrestrial C/A code GPS receiver system that derives along track position information while tracking as few as two GPS satellites by use of conventional altitude hold and a cross track hold mode in which the maximum expected deviation of the vehicle from the expected track is estimated by, for example, knowledge or prediction of the width of the roadway or other track. To maintain accuracy, cross track hold is alternated with clock hold to update the cross track estimate when changes in vehicle direction are detected or when a predetermined period has elapsed.
U.S. Pat. No. 6,041,280, entitled “GPS car navigation system,” assigned to SiRF Technology, Inc. (Santa Clara, Calif.), describes a GPS car navigation system that derives GPS position update information from motion of the car along the actual track. Turns along the track are detected when they actually occur and are compared with the predicted turns so that the time and position at the actual turn can be used to update the then current GPS derived position of the vehicle. Updating position information with actual turn data improves the accuracy of GPS navigation especially during single satellite navigation.
U.S. Pat. No. 6,018,704 entitled “GPS receiver,” (no assignee listed)—first inventor: Kohli; Sanjai (Manhattan Beach, Calif.), describes a terrestrial C/A code GPS receiver system that operates as an odometer to measure vehicle distance traveled by processing signals from GPS satellites to determine along track information relative to the track being followed by the vehicle and
Humphrey Ian
Perlmutter Michael S.
Beaulieu Yonel
Fibersense Technology Corporation
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