| 摘要 |
<p>A constellation (12) of satellites (14) which are distributed around the earth serves as a communications infrastructure (12) that supports autonomous position determination and reporting of that position to a remote location (28). Subscriber units (30) are remotely programmed to activate upon the occurrence of an activation event (120) and to record an itinerary (244). In an intelligent tracking embodiment, reporting of position occurs only when a current position deviates from the itinerary (244). If subscriber units (30) can engage in activities (144) which lead to determining their position, they cooperate with the infrastructure (12) to determine their positions. To determine position, location pulses may be transmitted on a regular schedule (106, 144). Location pulses are transported between a fast moving satellite (14) and a subscriber unit (30). Relative movement causes different location pulses to have different propagation delays and Doppler characteristics. By analyzing changes in propagation delays and Doppler characteristics, a procedure (170) determines a position for a subscriber unit (30). <IMAGE></p> |
