Satellite mobile telephone cell departure prediction
A mobile station ( 4 ) in a satellite mobile telephone system predicts when it will move into another cell on the basis of one set of broadcast information thereby reducing the overall processing burden. The mobile station ( 4 ) can predict with a useful degree of certainty which broadcast control channel (BCCH) frequencies it should listen on when it wakes up on the basis of a stored map of the relative positions of cells. The broadcast information includes information about the current cell's ( 40 ) shape (V 1 , V 2 , V 3 , V 4 , V 5 , V 6 ) and translational (T) and rotational (R) motion.
1. A mobile telephone for a satellite mobile telephone system, the mobile telephone having an active mode during which a telephone call can be processed and an inactive mode during which no telephone call can be being processed, the mobile telephone comprising:
a memory configured to store information related to the movement of a current cell across the Earth's surface the information being valid for a predetermined time interval; and
a processor to process the information and thereby make a prediction of a time at which the mobile telephone will depart the current cell, the processor, upon the mobile telephone entering the active mode, causing the mobile telephone to scan a predetermined set of communication channels, less than all communication channels, if a present time is within the predetermined time interval.
2. The mobile telephone of claim 1 wherein inactive mode comprises a sleep mode to conserve power and an awake mode to receive satellite signals, the processor processing the information to make the cell departure time prediction upon the mobile telephone entering the awake mode.
3. The mobile telephone of claim 1 , further comprising a receiver configured to receive information related to the movement of a current cell across the Earth's surface, the memory storing the received information for subsequent use by the processor to make the cell departure time prediction.
4. The mobile telephone of claim 3 wherein the satellite transmits the information related to the movement of a current cell across the Earth's surface, the receiver being a satellite receiver.
5. The mobile telephone of claim 4 wherein the receiver receives the data from the satellite via a control channel.
6. The mobile telephone of claim 1 , wherein the processor is configured to make the cell departure time prediction for the mobile telephone on the basis of a set of translational vectors included in the information and defining the traversing of the cell over the surface of the Earth.
7. The mobile telephone of claim 1 wherein the processor is further configured to predict a sub-period, during which the mobile telephone will leave the cell, the information related to the movement of a current cell across the Earth's surface remaining unchanged during the period.
8. The mobile telephone of claim 7 wherein the processor is further configured to predict the time within the predicted sub-period when the mobile telephone will leave the cell.
9. The mobile telephone of claim 1 wherein the processor is further configured to initiate a cell selection operation at the predicted cell departure time.
10. The mobile telephone of claim 1 wherein the processor is further configured to select a control channel to be monitored on the basis of the cell departure time prediction.
11. The mobile telephone of claim 1 wherein the processor is further configured to determine a difference between the cell departure time prediction and actual cell departure time and, only if the difference is greater than a predetermined value, cause the mobile telephone to transmit network registration request signals.