Neighboring cell list generation in a mobile satellite communication system

1. A method of operating a mobile station in a satellite communication system wherein the mobile station is capable of communicating alternatively with a first satellite or a second satellite of the satellite communication system, the method comprising:

on a plurality of occasions, receiving a set neighboring cell data transmitted in a broadcast from one of the first and second satellites, the set comprising first and second data portions relating to communication with the first and second satellites, respectively;

upon a first of the plurality of occasions, decoding the first and second data portions; and

upon subsequent ones of the plurality of occasions, decoding only a selected one of the first and second data portions.

2. The method of claim 1 wherein only the second data portion is decoded upon subsequent ones of the plurality of occasions if no alert message is received by the mobile station.

3. The method of claim 2 , further comprising modifying the set of neighboring cell data in response to decoding the second data portion.

4. The method of claim 1 wherein only the first data portion is decoded upon subsequent ones of the plurality of occasions if an alert message is received by the mobile station.

5. The method of claim 4 , further comprising modifying the set of neighboring cell data in response to decoding the first data portion.

6. A mobile station in a satellite communication system having a plurality of satellites, the mobile station comprising:

a receiver capable of communicating alternatively with a first satellite or a second satellite of the plurality of satellites, the receiver receiving a set of neighboring cell data transmitted in a broadcast from one of the first and second satellites on a plurality of occasions, the received data set comprising first and second data portions relating to communication with the first and second satellites, respectively; and

a decoder to decode the received data set, the decoder configured to decode the first and second data portions upon a first of the plurality of occasions that the receiver receives the data set, and to decode only a selected one of the first and second data portions upon subsequent ones of the plurality of occasions that the receiver receives the data set.

7. The mobile station of claim 6 wherein the receiver is configured to receive an alert message and the decoder is configured to decode only the second data portion upon subsequent ones of the plurality of occasions if no alert message is received by the receiver.

8. The mobile station of claim 7 , further comprising a data structure to store the set of neighboring cell data in response to decoding the second data portion.

9. The mobile station of claim 6 wherein the receiver is configured to receive an alert message and the decoder is configured to decode only the first data portion upon subsequent ones of the plurality of occasions if an alert message is received by the receiver.

10. The mobile station of claim 9 , further comprising a data structure to store the set of neighboring cell data in response to decoding the first data portion.

11. A method of operating a mobile station in a satellite mobile telephone system, the method comprising the steps of:

decoding all of a set of neighbouring cell data transmitted in a broadcast channel to generate a neighbouring cell list;

making signal measurements for the cells in said list and a current serving cell;

decoding a portion only of the set of neighbouring cell data transmitted in the broadcast channel and modifying the neighbouring cell list in dependence thereon; and

making signal measurements for the cells in said modified list and the current serving cell.

12. A method according to claim 11 , including:

comparing said measurements for the cells in said modified list and the current serving cell; and

if the best measurement is not for the currently serving cell, camping on the cell to which the best measurement applies.

13. A mobile station for a satellite mobile telephone system, the mobile station comprising transceiver means and control means, wherein the control means is programmed so as to cause the mobile station to operate according to claim 11 .

14. A method according to claim 11 , including the steps of decoding a further portion of said set on reception of a decode instruction in the broadcast channel and modifying the neighbouring cell list in dependence thereon.

15. A method according to claim 14 , wherein the data in said portion changes more rapidly than the data in said further portion.

16. A method according to claim 11 , wherein the neighbouring cell data comprises information identifying a beacon frequency for each cell.

17. A method of operating a mobile satellite telephone system comprising the steps of:

transmitting neighbouring cell data in a broadcast channel, the neighbouring cell data comprising a first portion relating to cells served by a first satellite in an orbit having a first plane and a second portion relating to cells served by a second satellite in an orbit having a second, different plane; and

transmitting neighbouring cell data in the broadcast channel, wherein the second portion of the cell data being modified in dependence on the relative motion of the first and second satellites.

18. A method according to claim 17 , wherein the neighbouring cell data comprises information identifying a beacon frequency for each cell.

19. A method according to claim 18 , including transmitting a decode instruction when data in the first portion of the cell data is modified.