Method and device for feedback transmission in a radio communication system

1. A method for transmitting feedback information for beam shaping in a radio communication system having a plurality of subscriber stations and a base station, with the base station having an antenna device with a plurality of antenna elements, the method comprising the steps of:

emitting a downlink signal, via the antenna device, weighted in each case with coefficients of an actual weighting vector to one of the plurality subscriber stations;

estimating a direction of a control vector in an M-dimensional vector space by the subscriber station by measurements of the downlink signal;

determining a change of the direction estimated using a direction of a reference control vector;

transmitting information representative of the change to the base station as feedback information; and

matching the weighting vector using the representative information.

2. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 1 , wherein the control vector and weighting vector are parallel vectors.

3. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 2 , wherein the information representative of the change is a vectorial difference between a new control vector that has the estimated direction and the reference control vector.

4. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 3 , wherein components of a vectorial difference of the change are limited to two values respectively corresponding to a positive or negative difference between corresponding components of the reference control vector and the new control vector.

5. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 4 , wherein an extent of the matching of the weighting vector is set greater the faster the direction of the control vector changes.

6. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 5 , the method further comprising the steps of:

calculating a step width;

multiplying the vectorial difference by the step width; and

adding a result of the vectorial difference multiplied by the step width to achieve the matching of the weighting vector.

7. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 6 , wherein all steps of the method are periodically repeated.

8. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 7 , wherein the control vector is taken as the reference control vector for a succeeding period of the method.

9. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 7 , wherein the reference control vector is an image of the weighting vector reflected at the subscriber station, and the reference control vector is matched using the representative information in a same way the weighting vector is adapted.

10. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 9 , wherein the subscriber station performs an estimation of the weighting vector used by the base station and, if there is a deviation between the weighting vector and the reference control vector, adapts the reference control vector.

11. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 7 , the method further comprising the step of periodically multiplying both the control vector and the weighting vector by a forget factor, with the forget factor being a real number between 0 and 1.

12. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 11 , wherein the forget factor is a constant.

13. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 11 , wherein the forget factor is a function of an amount of at least one control vector.

14. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 1 , the method further comprising the step of assigning an amount to the control vector that is set smaller the faster the direction of the control vector changes.

15. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 1 , wherein components of the control vectors and weighting vectors are complex-significant.

16. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 15 , wherein the components of the control vectors and weighting vectors consist of an amount and phase.

17. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 1 , wherein components of the control vectors estimated by the subscriber station are transmitted to the base station for use as weighting vectors.

18. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 17 , wherein, during initialization, the components of the control vectors are transmitted with a lesser accuracy than estimated by the subscriber station.

19. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 1 , wherein, for initialization, control vectors are estimated separately both from each other at the subscriber station and from weighting vectors at the base station.

20. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 1 , wherein fixed, predetermined control vectors are used for initialization.

21. A method for transmitting feedback information for beam shaping in a radio communication system having a plurality of subscriber stations and a base station, with the base station having an antenna device with a plurality of antenna elements, the method comprising the steps of:

emitting a downlink signal weighted in each case with coefficients of an actual weighting vector to one of the plurality of subscriber stations;

estimating a direction of a control vector by the subscriber station using measurements of the downlink signal;

scaling the control vector using a scaling rule;

transmitting components of the control vector, save for a predetermined component, to the base station; and

restoring the control vector at the base station via the scaling rule.

22. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 21 , wherein the scaling rule contains a scaling of the predetermined component to a fixed value.

23. A method for transmitting feedback information for beam shaping in a radio communication system as claimed in claim 21 , wherein at least a most significant bit of each component is transmitted several times.

24. A subscriber station for use in a method for transmitting feedback information for beam shaping in a radio communication system having a plurality of subscriber stations and a base station, wherein the base station includes an antenna device, having a plurality of antenna elements, which emits a downlink signal weighted in each case with coefficients of an actual weighting vector to the subscriber station, the subscriber station comprising:

a measuring and processing unit for estimating a direction of a control vector in an M-dimensional vector space using measurements of the downlink signal, and for comparing the estimated direction with a direction of a reference control vector; and

parts for transmitting information representative of a change of the direction estimated to the base station.

25. A subscriber station for use in a method for transmitting feedback information for beam shaping in a radio communication system having a plurality of subscriber stations and a base station, wherein the base station includes an antenna device, having a plurality of antenna elements, which emits a downlink signal weighted in each case with coefficients of an actual weighting vector to the subscriber station, the subscriber station comprising:

a measuring and processing unit for estimating a direction of a control vector in an M-dimensional vector space using measurements of the downlink signal, and for scaling the control vector using a scaling rule; and

parts for transmitting the components of the control vector, save for a predetermined component, to the base station.