One of the major issues in the case of satellite communication system, is the issue of handover. Handover can be defined like this. When a call, during its progress, is to be transferred from one physical control mechanism, to another, without interruption in connection, then you require a hand over. Basically why would you like to have the transfer because you would like to maintain a certain amount of link quality. A moving vehicle, moving away from the service area controlling bases station to another bases station, will require a hand over.

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