Automatic vehicle location systems
First Claim
1. An automatic vehicle location system comprising a control center and a plurality of mobile units, each mobile unit comprising means for deriving a current position signal from external radio signals, prediction means responsive to a previously derived current position signal and to predicted motion of the mobile unit to derive a predicted position signal, means for comparing the current position signal with the predicted position signal and means for transmitting a positional update and a velocity signal to the control center in dependence on the result of the comparison, the control center comprising prediction means responsive to the positional update and the velocity signal to derive a predicted position signal for that mobile unit.
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Abstract
An automatic vehicle location center includes a control center and a plurality of mobile units. Each mobile unit is able to derive a current position from external radio signals. A prediction is responsive to this current position signal and to predicted motion of the mobile unit to derive a predicted position signal. The predicted and current positions signals are compared and the current position signal is transmitted to the control center in dependence on the result of the comparison. The control center has a predictor, similar to that in each mobile unit, responsive to the current position signal and to predicted motion of the mobile unit to derive a predicted position. This position data is only transmitted from a mobile unit to the control center if the predicted position signal differs significantly from the actual position.
38 Citations
12 Claims
- 1. An automatic vehicle location system comprising a control center and a plurality of mobile units, each mobile unit comprising means for deriving a current position signal from external radio signals, prediction means responsive to a previously derived current position signal and to predicted motion of the mobile unit to derive a predicted position signal, means for comparing the current position signal with the predicted position signal and means for transmitting a positional update and a velocity signal to the control center in dependence on the result of the comparison, the control center comprising prediction means responsive to the positional update and the velocity signal to derive a predicted position signal for that mobile unit.
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11. An automatic vehicle location system comprising a control center and a plurality of mobile units, each mobile unit comprising means for deriving a current position signal from external radio signals, prediction means responsive to a previously derived current position signal and to predicted motion of the mobile unit to derive a predicted position signal, means for comparing the current position signal with the predicted position signal and means for transmitting a positional update and a velocity signal to the control center in dependence on the result of the comparison, the control center comprising prediction means responsive to the positional update and the velocity signal to derive a predicted position signal for that mobile unit, in which each prediction means derives predicted motion for a mobile unit from the velocity signal and from time elapsed since derivation of the positional update signal last sent to the control center, and in which the positional update and velocity signal are transmitted from a mobile unit to the control center when the result of the comparison is that the difference between current and predicted signals exceeds a predetermined threshold;
said system further including means for altering the threshold, in which the threshold altering means is responsive to the current position signal to automatically alter the threshold.
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12. A mobile unit for use in an automatic vehicle location system comprising means for deriving a current position signal, prediction means responsive to a previously derived current position signal and to a velocity signal from the mobile unit to derive a predicted postion signal for the mobile unit, means for comparing the current position signal with the predicted position signal, and means for transmitting a positional update and a velocity signal to a control center in dependence on the result of the comparison.
Specification