Cell re-selection in a cellular telecommunications network

1. A method in a wireless cellular telecommunications device camped on a serving cell, the device storing a first parameter obtained from system information of a first cell different from the serving cell, the method comprising:

measuring an attribute of a signal received from a candidate cell;

determining if the candidate cell is a closed subscriber group cell; and

evaluating the candidate cell for re-selection,

wherein, if the candidate cell is determined to be a closed subscriber group cell, the evaluation of the candidate cell for re-selection is based on at least the measured attribute irrespective of the first stored parameter, said first stored parameter indicating a minimum value for the measured attribute.

2. A method according to claim 1 , in which the device has a second stored parameter obtained from a closed subscriber group cell and in which the first cell is not a closed subscriber group cell,

wherein, if the candidate cell is determined to be a closed subscriber group cell, the evaluation of the candidate cell for re-selection is based on at least the measured attribute and the second stored parameter.

3. A method according to claim 2 , in which if the evaluation is based on at least the measured attribute and the second stored parameter, the evaluation includes determining if the cell meets re-selection requirements,

wherein, if the measured attribute fails to exceed the second stored parameter by a first pre-determined amount, determining that the candidate cell does not to meet reselection requirements.

4. A method according to claim 3 , in which the first predetermined amount is one of 0 dB or +10 dB.

5. A method according to claim 1 ,

wherein the device has a second stored parameter obtained from system information of a second cell which is a closed subscriber group cell,

the method in which, if the candidate cell has an identifier equivalent to an identifier of the second cell and the candidate cell is determined to be a closed subscriber group cell, the evaluation of the candidate cell for re-selection is based on at least the second stored parameter, else

the evaluation of the candidate cell for re-selection is performed without using the second stored parameter.

6. A method according to claim 5 , in which the identifier is a locally unique identifier.

7. A method according to claim 6 , in which the identifier is a physical layer identifier.

8. A method according to claim 7 , in which the identifier is a primary scrambling code.

9. A method according to claim 8 , in which, if the candidate cell has a carrier frequency matching a carrier frequency of the second cell and the candidate cell has a primary scrambling code matching the primary scrambling code of the second cell and the candidate cell is determined to be a closed subscriber group cell, the evaluation of the candidate cell for re-selection is based on at least the measured attribute and the second stored parameter, else

the evaluation of the candidate cell for re-selection is performed without using the second stored parameter.

10. A method according to claim 7 , in which the identifier of the first cell is a physical layer cell identifier.

11. A method according to claim 1 , in which, if the evaluation is performed without using the stored parameter, the evaluation of the candidate cell includes:

determining if the measured attribute exceeds a predetermined default value; and

if the measured attribute fails to exceed the predetermined default value, determining that the candidate cell does not meet re-selection requirements.

12. A method according to claim 1 , in which the candidate cell is one of a UTRAN cell and a GERAN cell.

13. A method according to claim 1 , further comprising performing reselection from the serving cell to the candidate cell based on the evaluation.

14. A method according to claim 1 , in which the evaluation of the candidate cell includes:

acquiring system information of the candidate cell, the system information including a parameter;

determining if the measured attribute exceeds the candidate cell parameter by a second predetermined amount; and

if the measured attribute exceeds the candidate cell parameter by the second predetermined amount, performing re-selection to the candidate cell.

15. A method according to claim 14 , in which the second predetermined amount is 0 dB.

16. A method according to claim 1 , in which the stored parameter indicates a minimum required receive level.

17. A method according to claim 1 , in which the measured attribute is received signal code power (RSCP).

18. A method according to claim 1 , in which the serving and candidate cells are of the same wireless radio network or of different wireless radio networks.

19. A wireless cellular telecommunications device adapted to:

camp on a serving cell;

store a first parameter obtained from system information of a first cell different from the serving cell;

measure an attribute of a signal received from a candidate cell;

determine if the candidate cell is a closed subscriber group cell; and

evaluate the candidate cell for re-selection,

wherein, if the candidate cell is determined to be a closed subscriber group cell, the evaluation of the candidate cell for re-selection is based on at least the measured attribute irrespective of the first stored parameter, said first stored parameter indicating a minimum value for the measured attribute.

20. A non-transitory computer-readable storage medium having stored thereon instructions which can be executed by a device to:

camp on a serving cell;

store a first parameter obtained from system information of a first cell different from the serving cell;

measure an attribute of a signal received from a candidate cell;

determine if the candidate cell is a closed subscriber group cell; and

evaluate the candidate cell for re-selection,

wherein, if the candidate cell is determined to be a closed subscriber group cell, the evaluation of the candidate cell for re-selection is based on at least the measured attribute irrespective of the first-stored parameter, said first stored parameter indicating a minimum value for the measured attribute.