GPS-based centralized tracking system with reduced energy consumption
First Claim
1. A method for identifying location of an asset to be tracked comprising the steps of:
- receiving signals transmitted from a plurality of Global Positioning System (GPS) satellites at said asset;
detecting a GPS telmetry word preamble (TWP) and measuring data related to propagation differences between signals transmitted from GPS satellites and received at said asset;
deriving satellite identifications for each of said GPS satellites;
maintaining an auxiliary GPS (AGPS) data base and a GPS hand-over word (HOW) table to determine TWP start time at said asset;
computing an estimated location of said asset from said measured data, AGPS and HOW data and a clock in approximate synchronization with GPS time;
encoding and transmitting to a central station the satellite identifications and the computed estimated position;
decoding, at said central station, data received from said asset; and
calculating, at said central station, a corrected location of said asset based upon the transmitted data and data derived from at least one receiver spaced apart from said asset.
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Accused Products
Abstract
A communication method reduces both the asset energy requirements and communication channel occupancy in a reduced order GPS asset tracking system. The asset is provided with an indication of its position so as to allow detection of substantial movement of the asset at the asset. Reduced order GPS data derived at the asset, such as a railcar, is compressed to allow for shorter railcar data transmission times. This, in turn, reduces both the transmitter energy requirements and communication-channel occupancy, while allowing substantial railcar position changes to be conveniently detected at the railcar. This capability can be used to save further substantial railcar energy by, for example, reporting to the central station less frequently when the railcar position is unchanging.
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Citations
12 Claims
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1. A method for identifying location of an asset to be tracked comprising the steps of:
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receiving signals transmitted from a plurality of Global Positioning System (GPS) satellites at said asset; detecting a GPS telmetry word preamble (TWP) and measuring data related to propagation differences between signals transmitted from GPS satellites and received at said asset; deriving satellite identifications for each of said GPS satellites; maintaining an auxiliary GPS (AGPS) data base and a GPS hand-over word (HOW) table to determine TWP start time at said asset; computing an estimated location of said asset from said measured data, AGPS and HOW data and a clock in approximate synchronization with GPS time; encoding and transmitting to a central station the satellite identifications and the computed estimated position; decoding, at said central station, data received from said asset; and calculating, at said central station, a corrected location of said asset based upon the transmitted data and data derived from at least one receiver spaced apart from said asset. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A reduced order global positioning system (GPS) asset tracking system comprising:
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a tracking unit on an asset to be tracked for receiving signals from a plurality of GPS satellites, determining a time window during which a GPS telemetry word preamble (TWP) is expected, detecting the TWP and measuring data related to propagation differences between signals received from a plurality of GPS satellites deriving satellite identifications for each of said GPS satellites, maintaining an auxiliary GPS (AGPS) data base and a GPS hand-over word (HOW) table to determine a TWP start time, computing an estimated position from each of the measured, AGPS and HOW data and from a clock in approximate synchronization with GPS time, and encoding and transmitting the satellite identifications and the computed estimated position, and a central station adapted to decode received data from said asset and to calculate a corrected location of said asset based upon the transmitted data and data derived from at least one receiver spaced apart from said asset and adapted to receive said signals from said plurality of GPS satellites. - View Dependent Claims (8, 9, 10)
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11. A method of determining, at the tracked asset, an approximate position of the asset comprising the steps of:
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energizing a receiver for a time interval during which a Global Positioning System (GPS) telemetry word preamble (TWP) is expected; processing a GPS signal received during said time interval to acquire code and data-bit timing for four GPS satellite signals; recognizing a TWP starting edge in each satellite signal; choosing a signal with a lowest GPS index as a reference signal and establishing bit or codeword edges as markers in each signal; maintaining an auxiliary GPS (AGPS) data base and a GPS hand-over word (HOW) table to determine TWP start time at the asset; reading a marker count from the AGPS data base during a measurement instant selected to be interger marker periods after the starting edge of the TWP in the reference signal; measuring marker counts and phases for a measurement instant, the counts being measured with respect to the starting edge of the TWP in each satellite signal; reading a pre-determined transmitter marker period and frame-time differences from the AGPS data base and then calculating propagation time differences; reading a HOW time value from the reference signal and calculating the reference signal transmission time; calculating remaining transmission times; using the calculated transmission times with approximate ephemerides from the AGPS data base to determine satellite locations; and using the determined satellite locations to calculate the asset position. - View Dependent Claims (12)
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Specification