Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2000-04-06
2001-08-28
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490, C342S357490, C375S213000
Reexamination Certificate
active
06281837
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to satellite positioning systems in general, and, more particularly, to a telecommunications-based auxiliary system that assists a wireless terminal in determining its position from signals transmitted from one or more navigation satellites.
BACKGROUND OF THE INVENTION
A satellite positioning system, such as the Global Positioning System (“GPS”), comprises a constellation of satellites that transmit signals that can be used by a wireless terminal to determine, in well-known fashion, the wireless terminal's position. Typically, the signals transmitted by each satellite convey three types of information: (1) satellite trajectory data, (2) system timing, and (3) ranging information. When a wireless terminal can acquire the signals from three or more satellites the wireless terminal can determine its position through triangulation, as is well-known in the art.
FIG. 1
depicts a schematic diagram of a satellite positioning system in the prior art.
Although a conventional wireless terminal can determine its position with some degree of accuracy, fluctuations in the ionosphere and the atmosphere and jitter in the transmitted signals themselves prevent a conventional wireless terminal from determining its position with a high degree of accuracy. To mitigate the effects of these factors and thus improve the degree of accuracy with which a wireless terminal can ascertain its position, another satellite positioning system, typified by the Differential Global Positioning System (“DGPS”), was developed.
FIG. 2
depicts a schematic diagram of a Differential Global Positioning System.
As is well-known in the prior art, DGPS comprises terrestrial reference receiver
205
, whose position is static and exactly known through conventional survey techniques, in addition to satellite constellation
203
and wireless terminal
201
. The theory underlying DGPS is that when wireless terminal
201
is in close proximity (e.g., within 50 miles) to terrestrial reference receiver
205
, both wireless terminal
201
and terrestrial reference receiver
205
are expected to experience the same ionospheric and atmospheric fluctuations and signal jitter. Terrestrial reference receiver
205
uses the signals from satellite constellation
203
to estimate its position, and, using its known exact position, calculates the error between its estimated position and its known exact position. That error or “difference” is a vector that represents the inaccuracy of the estimated position from the ionospheric and atmospheric fluctuations and signal jitter. The difference vector is broadcast by terrestrial reference receiver
205
to wireless terminal
201
in real time. When wireless terminal
201
estimates is position through conventional means, it uses the difference vector received from terrestrial reference receiver
205
to subtract out the effects of the ionospheric and atmospheric fluctuations and signal jitter.
FIG. 3
depicts a schematic diagram of a Tidget® satellite positioning system in the prior art. The wireless receiver in a Tidget system does not compute the position of the wireless terminal. Instead, the wireless receiver in a Tidget system acts like a wireless repeater in that it receives the signals from the satellite constellation and then relays the unprocessed signals to a remote processing facility, which uses the signals to determine the position of the Tidget wireless terminal. An advantage of a Tidget system is that is reduces the cost of the wireless terminal by eliminating from the wireless terminal the expensive circuitry that would otherwise be needed to compute the position of the wireless terminal. When it is more advantageous that a remote facility know the location of the wireless terminal than that the wireless terminal know its own location, a Tidget system is advantageous in that it relays, in effect, the position of the wireless terminal to the remote facility.
FIG. 4
depicts a schematic diagram of a Tendler® satellite positioning system in the prior art. A wireless terminal constructed in accordance with this system comprises both the circuitry needed to determine its position from a satellite constellation and a wireless telephone transmitter to transmit the determined position to another party via a wireless telecommunications system.
Regardless of the advances made in satellite positioning systems, limitations still exist. Typically, the strength of the signals from the satellite constellation is too attenuated in buildings and other shadowed environments for a wireless terminal to receive. Furthermore, a wireless terminal can take several minutes to acquire the signals from the satellites it needs to determine its position.
SUMMARY OF THE INVENTION
Some embodiments of the present invention are capable of assisting a wireless terminal in determining its position based on signals transmitted from one or more navigation satellites. In particular, a wireless terminal that is assisted by an embodiment of the present invention can be less expensive than wireless terminals in the prior art. Furthermore, a wireless terminal that is assisted by an embodiment of the present invention is able to receive and use weaker signals than wireless terminals in the prior art; and still furthermore, a wireless terminal that is assisted by an embodiment of the present invention is capable of determining its location far more quickly that wireless terminals in the prior art.
An auxiliary system in accordance with an embodiment of the present invention assists a wireless terminal by apportioning the tasks of signal acquisition and signal processing that are normally borne by the wireless terminal alone between the wireless terminal and the auxiliary system. In particular, the requirements normally imposed on a wireless terminal in the prior art are off-loaded onto the auxiliary system that can provide useful information to the wireless terminal over a wireless telecommunications link.
It is possible to divide the signal acquisition and signal processing tasks between the wireless terminal and the auxiliary system because each signal transmitted by each satellite in a satellite positioning system's constellation carries two distinct kinds of information that are responsive to independent acquisition and independent processing. The two kinds of information are: (1) ranging information, and (2) information about the satellites' ephemerides.
The information about the satellites' ephemerides is the same for all receivers, regardless of their position. In contrast, the ranging information, which indicates to the receiver its distance from each satellite, is location dependent and can be received only by the wireless terminal itself. Therefore, the auxiliary system can assist the wireless terminal by acquiring the information about the satellites' ephemerides, by partially processing it and by transmitting it to the wireless terminal in a form that is useful to the wireless terminal. The auxiliary system cannot, however, acquire the ranging information for the wireless terminal.
By having the auxiliary system acquire the information about the satellites' ephemerides for the wireless terminal, the signal acquisition and signal processing demands of the wireless terminal are reduced. Furthermore, the wireless terminal can actually use the partially processed information from the auxiliary system to assists the wireless terminal in acquiring the ranging signals quickly and when they are weak.
When the wireless terminal is capable of providing the functionality of a wireless telecommunications terminal (e.g., a cellular telephone, a hand-held data entry device, etc.), the circuitry for determining the wireless terminal's location, in accordance with some embodiments of the present invention, can be added to the wireless terminal for moderately little cost.
REFERENCES:
patent: 4313183 (1982-01-01), Saylors
patent: 5515062 (1996-05-01), Maine et al.
patent: 5615173 (1997-03-01), Brumley et al.
patent: 5689245 (1997-11-01)
Richton Robert Ellis
Vannucci Giovanni
Breyer Wayne S.
DeMont Jason Paul
DeMont & Breyer LLC
Lucent Technologies - Inc.
Phan Dao
LandOfFree
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