Importance

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Abstract

An apparatus and method for paging a user terminal (UT) using a satellite communications system having a gateway and one or more satellites, wherein each satellite produces a plurality of beams and each beam includes a plurality of channels. The method of the present invention includes the step of recalling a location of the UT, wherein the recalled location corresponds to a location of the UT at a time t.sub.1. In one embodiment this is accomplished by performing a lookup in a table that includes location information for user terminals at different points in time. The method also includes the step of determining an area, based on the recalled location, within which the UT is assumed to be located at a time t.sub.2, where time t.sub.2 is later in time than time t.sub.1. The next step is to determine a time t.sub.3, where t.sub.3 is equal to or later in time than time t.sub.2, when the following two criteria are satisfied. First a satellite of the one or more satellites has an elevation angle between .theta..sub.1 and .theta..sub.2. Second, all locations within the area are located within a footprint of the satellite (that has an elevation angle between .theta..sub.1 and .theta..sub.2). The elevation angles .theta..sub.1 and .theta..sub.2 can be determined from the perspective of the recalled location. Alternatively, the elevation angle can be determined from the perspective of all locations within the area. This ensures that the UT is in the 'sweet spot' of the satellite (where the gain of signals sent from the satellite are highest) when the UT is paged. A page is then sent from the gateway to the UT on a channel of a beam of the satellite at time t.sub.3. The page can be sent on a channel of every beam of a plurality of beams that make up the footprint of the satellite at time t.sub.3. Alternatively, the page can be sent on a channel of selected beams of the footprint. By waiting until the UT is within the 'sweet spot' to page the UT, less power can be used by the satellite. In addition, this type of operation allows the UT to use an antenna that has a substantial gain only when the UT is within the 'sweet spot'. This allows the use of satellite power to be reduced further.

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First Claim