| 摘要 |
A satellite system including at least two satellites having on-board processing capability so that data messages may be exchanged and the position of mobile units may be determined with direct access from multiple ground control facilities. The satellites transmit data and poll individual mobile units upon command by one or more of the control facilities and receive replies from the mobile units including the mobile units' altitude and other data of interest to the control facility. At least two satellites communicate with one another by means of a cross-link communication path. Computer processing apparatus is included on the satellites to compute the ranges between the mobile units and each of the satellites from the replies received from the mobile units, and to store and process messages. The position information and messages are transmitted to at least one of the control facilities. It is preferred that the control facilities employ TDMA or FDMA protocols in the uplinks to the satellites. The on-board processing makes it readily possible for a number of control facilities to gain access to the satellites directly rather than through a central earth station, and to increase the capacity of a discrete address polling system for a given allocation of radio frequency spectrum. A discrete address polling system is one where each mobile unit is polled on an individual basis by only responding to polls that contain its identification. |
