Method and Arrangement for Polarization Control in a Communication System

1. A method of controlling the polarization state of signals to be transmitted from a MIMO capable radio base station node of a cell to a plurality of user equipment, said radio base station node comprising a precoder unit connecting a first and a second virtual antenna port to a respective first and second transmit antenna port, the method comprising: controlling a relative phase between transmitted signals from said first transmit antenna port and said second transmit antenna port to provide a predetermined pair of orthogonal polarization states for signals transmitted on said first and said second virtual antenna ports; and interchanging the polarization states of said first and second virtual antenna ports by adapting said relative phase between said transmitted signals continuously in time, to provide transmitted polarized signals with cyclically alternating polarization states, wherein each of the interchanged polarization states is used for transmissions to at least one user equipment in the cell having a corresponding polarization state preference.

2. The method according to claim 1 , comprising the further step of scheduling transmissions to said plurality of user equipment based on a current transmit polarization state in said cell.

3. The method according to claim 2 , further comprising prioritizing said plurality of user equipment prior to scheduling.

4. The method according to claim 1 , further comprising interchanging said polarization states by switching signals from said first and second virtual antenna ports between said first and second transmit antenna ports.

5. The method according to claim 1 , further comprising interchanging said polarization states adaptively.

6. The method according to claim 1 , further comprising interchanging said polarization states in time.

7. The method according to claim 6 , further comprising interchanging said polarization states with regular equal or non-equal time intervals.

8. The method according to claim 1 , further comprising interchanging said polarization states in response to predetermined event triggers.

9. The method according to claim 1 , further comprising said base station node being configured with a plurality of carriers covering a same sector, and adaptively interchanging said polarization state between at least two of said carriers in the frequency domain.

10. The method according to claim 9 , further comprising the step of scheduling user equipment onto one of said plurality of carriers based on at least a reported connection quality performance for said carriers.

11. The method according to claim 10 , further comprising redirecting a user equipment from one carrier to another carrier based on a current polarization state of said carriers and a polarization preference of said user equipment.

12. The method according to claim 9 , comprising the further step of dividing said plurality of carriers into two subsets, each subset having a respective one of said pair of predetermined orthogonal polarization states.

13. The method according to any of claims 1 - 2 or 4 - 9 , wherein said pair of predetermined orthogonal polarization states comprises vertical and horizontal polarization states.

14. A MIMO capable radio base station node, said radio base station node comprising a precoder unit connecting a first and a second virtual antenna port to a respective first and a second transmit antenna port for transmitting signals to a plurality of user equipment, the base station node comprising: a controller configured to control a relative phase between transmitted signals from said first transmit antenna port and said second transmit antenna port to provide a predetermined pair of orthogonal polarization states for signals transmitted on said first and said second virtual antenna ports; and a polarization switch configured to interchange the polarization states of said first and second antenna ports by adapting said relative phase between said transmitted signals continuously in time, to provide transmitted polarized signals with cyclically alternating polarization states wherein the base station node is configured to use each of the interchanged polarization states for transmissions to at least one user equipment in the cell having a corresponding polarization state preference.

15. The radio base station node according to claim 14 , comprising said polarization switch being configured to interchange said polarization states adaptively.

16. The radio base station node according to claim 14 , said radio base station further comprising a scheduler configured to schedule transmissions to said plurality of user equipment based on a current transmit polarization state in a cell of the radio base station node.

17. The Radio base station node according to claim 14 , said base station node being configured with a plurality of carriers covering a same sector, and said polarization switch being configured to adaptively interchange said polarization state between said carriers in the frequency domain.

18. The radio base station node according to claim 17 , said radio base station node being configured to monitor a connection quality statistic for each such carrier, and to inform a radio network control node about said quality, and to redirect user equipment from one carrier to another based on instructions received from said radio network control node.