Patent ID: 6246874
Filing Date: 2001-06-12
Classification: H04B,H04W

Abstract:
A satellite communication system adapted to transfer a call from a first spot beam to a second spot beam wherein the call is being transmitted between a satellite and a subscriber unit located in the first spot beam, the system comprising:a first processor, the first processor being adapted to:track a movement of the subscriber unit relative to a satellite based coordinate system;identify the second spot beam from among a plurality of spot beams;estimate a time at which to transfer the call that is dependent on the position of the subscriber unit relative to the satellite based coordinate system; andgenerate a signal to cause the satellite to transfer the call at the time;a second processor being adapted to respond to the signal generated by the first processor;a first antenna being associated with the satellite fore generating the first spot beam; anda second antenna being associated with the satellite for generating the second spot beam;wherein the first antenna and the second antenna are controlled by the second processor; andwherein the system is further adapted to transfer the call from a first satellite to a second satellite wherein the first processor is further adapted to(a) determine the position of the subscriber unit at the estimated time;(b) determine the position of the satellite at the estimated time;(c) calculate an angle of elevation using the position of the subscriber unit and the position of the satellite;(d) compare the angle of elevation to a threshold angle to determine whether the subscriber unit is moving out of the first footprint into a second footprint that is generated by the second satellite;(e) substitute a new time for the estimated time, if the angle of elevation is not less than the threshold angle and thereafter repeat steps (a)-(d); and(f) cause the first satellite to transfer the call to the second satellite when the angle of elevation is less than the threshold angle.