Uplink calibration system without the need for a pilot signal

1. An antenna array for a mobile communications system comprising:

a plurality of receive paths, an individual one of the receive paths being connected between an antenna element and an analogue-to-digital converter, the analogue-to-digital converter digitizing a receive signal to form a digitized receive signal,

a calibration signal processor connected to the analogue-to-digital converters of the plurality of the receive paths, wherein the calibration signal processor comprises

a cross-analyzer for cross-analyzing the digitized receive signals of the plurality of receive paths with each other,

an averager for forming a temporal average of an output of the cross-analyzer, the temporal average indicating a receive signal relationship between the digitized receive signals of the plurality of receive paths, and

a comparator for comparing the receive signal relationship with a predetermined relationship and for determining a deviation between the receive signal relationship and the predetermined relationship,

wherein the calibration signal processor is adapted to define a reference receive path and to use the temporal average of the receive signal relationship to calibrate of at least one of the plurality of receive paths.

2. The antenna array of claim 1 , wherein the antenna elements are equally spaced, preferably by a distance equal to or greater than half a wavelength of the receive signal.

3. The antenna array of claim 1 , wherein the receive signal relationship comprises at least one of a phase relation between the receive paths and an amplitude relation between the receive paths.

4. The antenna array of claim 1 , wherein the calibration signal processor is adapted to use the deviation as a correctional value to correct the calibration of at least one of the at least two receive paths.

5. The antenna array of claim 1 , wherein the calibration signal processor further comprises an estimator for estimating the predetermined relationship.

6. The antenna array of claim 5 , wherein the estimator comprises a function fitting module for fitting a plurality of receive signal relationships between the reference path and other ones of the receive paths, and for estimating the predetermined relation based on a function parameter of a function fitted to the plurality of receive signal relationships.

7. The antenna array of claim 1 further comprising an adaptive filter for removing effects of at least one of a gain ripple and a phase ripple of analogue filters in the plurality of receive paths.

8. The active antenna array of claim 1 , wherein the calibration signal processor further comprises an calibration initiator adapted to determine an amount of randomness in the receive signals, to initiate a calibration process if the amount of randomness exceeds a predefined initiation threshold, and to suspend the calibration process if the amount of randomness is lower than a predefined suspension threshold.

9. The active antenna array of claim 8 , wherein the calibration initiator is adapted to evaluate a number of users currently being in communication with the antenna array.

10. A method for calibrating a plurality of receive paths carrying receive signals comprising:

digitizing the receive signals to form digitized receive signals,

cross-analyzing the digitized receive signals of the plurality of receive paths with each other,

forming a temporal average of a result of the cross-analyzing, the temporal average indicating a receive signal relationship between the digitised receive signals of the plurality of receive paths,

defining a reference receive path using the temporal average of the receive signal relationship to calibrate of at least one of the at least two receive paths,

comparing the receive signal relationship with a predetermined relationship; and

determining a deviation between the receive signal relationship and the predetermined relationship.

11. The method of claim 10 , wherein the receive signals are received via an antenna array having antenna elements that are equally spaced, preferably by a distance equal to or greater than half a wavelength of the receive signal.

12. The method of claim 10 , wherein the receive signal relationship comprises at least one of a phase relation between the plurality of receive paths and an amplitude relation between the plurality of receive paths.

13. The method of claim 10 , further comprising:

using the deviation as a correctional value to correct the calibration of the plurality of the receive paths.

14. The method of claim 10 , further comprising:

estimating the predetermined relationship.

15. The method of claim 14 , wherein the plurality of receive paths comprises a reference path, the method further comprising:

fitting a plurality of receive signal relationships to a function, and

estimating the predetermined relationship based on a function parameter of a function fitted to the plurality of receive signal relationships.

16. The method of claim 10 , further comprising filtering the receive signals by means of an adaptive filter for removing the effects of at least one of a gain ripple and a phase ripple of analogue filters in the plurality of receive paths.

17. The method of claim 10 , further comprising:

determining an amount of randomness in the receive signals,

initiating the calibration if the amount of randomness exceeds a predefined initiation threshold, and

suspending the calibration if the amount of randomness is lower than a predefined suspension threshold.

18. The method of claim 17 wherein the initiating or the suspension is based on an evaluation of a number of user currently being in communication with the antenna array.

19. A computer program product comprising a non-transitory computer-usable medium having control logic stored therein for causing a computer to manufacture an antenna array for a mobile communications network comprising:

a plurality of receive paths, an individual one of the receive paths being connected between an antenna element and an analogue-to-digital converter, the analogue-to-digital converter digitizing a receive signal to form a digitized receive signal,

a calibration signal processor connected to the analogue-to-digital converters of the plurality of the receive paths, wherein the calibration signal processor comprises

a cross-analyzer for cross-analyzing the digitized receive signals of the plurality of receive paths with each other,

an averager for forming a temporal average of an output of the cross-analyzer, the temporal average indicating a receive signal relationship between the digitized receive signals of the plurality of receive paths, and

a comparator for comparing the receive signal relationship with a predetermined relationship and for determining a deviation between the receive signal relationship and the predetermined relationship,

wherein the calibration signal processor is adapted to define a reference receive path and to use the temporal average of the receive signal relationship to calibrate of at least one of the plurality of receive paths.

20. A computer program product comprising a non-transitory computer-usable medium having control logic stored therein for causing an antenna to execute a method for calibrating a plurality of individual radio signals comprising:

digitizing the digitized receive signals to form digitized receive signals,

cross-analyzing the receive signals of the plurality of receive paths with each other,

forming a temporal average of a result of the cross-analyzing, the temporal average indicating a receive signal relationship between the digitized receive signals of the plurality of receive paths,

defining a reference receive path,

using the temporal average of the receive signal relationship to calibrate of at least one of the at least two receive paths, and

comparing the receive signal relationship with a predetermined relationship and for determining a deviation between the receive signal relationship and the predetermined relationship.