Establishing colocated second cell using a second scrambling code by a femto base station
In a cellular communications network, it may be desirable for a large number of basestations to share one or a small number of scrambling codes. When a basestation identifies a desired scrambling code, which is also being used by another nearby basestation, steps are taken such that a location area update is triggered whenever a mobile communications device moves from a coverage area of the nearby basestation into a coverage area of said basestation. Further, the basestation establishes a first cell, using the desired scrambling code, and also establishes a second cell also served by the basestation, using a second scrambling code. By ensuring that mobile devices are preferentially served by the second cell, the possibility of interference with the nearby basestation is reduced.
1. A method for use in a basestation of a cellular communications network, the method comprising:
identifying a desired scrambling code for use by the basestation, the desired scrambling code also being used by another nearby basestation;
using the desired scrambling code in a first cell served by the basestation; and
establishing a second cell also served by the basestation, using a second scrambling code.
2. A method as claimed in claim 1 , comprising:
setting cell reselection parameters such that any user equipment roaming into the first cell reselects to the second cell.
3. A method as claimed in claim 1 or 2 , comprising:
receiving from a management system a list comprising at least one allowed scrambling code for femtocell basestations; and
detecting, in information broadcast by at least one macrocell basestation, at least one scrambling code available in an area containing the basestation;
wherein the desired scrambling code is a scrambling code detected in information broadcast by the at least one macrocell basestation; and
wherein the second scrambling code is on the list of scrambling codes received from the management system.
4. A method as claimed in claim 1 , further comprising:
setting a power of the first cell as a function of data service activity.
5. A method as claimed in claim 4 , comprising setting the power of the first cell as an inverse function of a data channel power.
6. A method as claimed in claim 5 , comprising setting the power of the first cell as an inverse function of a long term average data channel power.
7. A method as claimed in claim 4 , comprising activating the first cell only when the data channel is not active.
8. A method as claimed in claim 1 , further comprising:
switching the first cell on and off at regular time intervals.
9. A method as claimed in claim 1 , further comprising:
using a single RACH demodulator in the first cell and in the second cell.
10. A method as claimed in claim 1 , wherein the first cell transmits on only a subset of the channels on which the second cell transmits.
11. A method as claimed in claim 1 , comprising establishing the basestation such that a location area update is triggered whenever a mobile communications device moves from a coverage area of the nearby basestation into a coverage area of said basestation.
12. A method as claimed in claim 11 , wherein the step of establishing the basestation such that a location area update is triggered comprises selecting a MIB value tag for said basestation that differs from a MIB value tag of the nearby basestation.
13. A method as claimed in claim 11 , wherein the step of establishing the basestation such that a location area update is triggered comprises setting a PLMN value for said basestation that differs from a PLMN value of the nearby basestation.
14. A basestation, for use in a cellular communications network, the basestation comprising:
one or more interfaces for communicating with other entities in the cellular communications network;
memory; and
one or more processors, the one or more processors configured to
identify a desired scrambling code for use by the basestation, the desired scrambling code also being used by another nearby basestation;
use the desired scrambling code in a first cell served by the basestation; and
establish a second cell also served by the basestation, using a second scrambling code.
15. A basestation as claimed in claim 14 , the one or more processors further configured to:
set cell reselection parameters such that any user equipment roaming into the first cell reselects to the second cell.
16. A basestation as claimed in claim 14 , the one or more processors further configured to:
set a power of the first cell as a function of data service activity.
17. A basestation as claimed in claim 16 , the one or more processors further configured to:
set the power of the first cell as an inverse function of a data channel power.
18. A basestation as claimed in claim 17 , the one or more processors further configured to:
set the power of the first cell as an inverse function of a long term average data channel power.
19. A basestation as claimed in claim 16 , the one or more processors further configured to:
activate the first cell only when the data channel is not active.
20. A basestation as claimed in claim 14 , the one or more processors further configured to:
switch the first cell on and off at regular time intervals.
21. A basestation as claimed in claim 14 , the one or more processors further configured to:
use a single RACH demodulator in the first cell and in the second cell.
22. A basestation as claimed in claim 14 , wherein the first cell transmits on only a subset of the channels on which the second cell transmits.
23. A basestation as claimed in claim 14 , the one or more processors further configured to:
establish the basestation such that a location area update is triggered whenever a mobile communications device moves from a coverage area of the nearby basestation into a coverage area of said basestation.
24. A basestation as claimed in claim 23 , wherein the step of establishing the basestation such that a location area update is triggered comprises selecting a MIB value tag for said basestation that differs from a MIB value tag of the nearby basestation.
25. A basestation as claimed in claim 23 , wherein the step of establishing the basestation such that a location area update is triggered comprises setting a PLMN value for said basestation that differs from a PLMN value of the nearby basestation.