IMU-assisted polarization division multiplexed MIMO wireless communication

1. A method of performing radio transmissions in a wireless communication network, the method comprising, in a wireless terminal:

receiving a multiple input multiple output, MIMO, transmission from an access node of the wireless communication network;

estimating a spatial orientation of an antenna array of the wireless terminal based on measurements performed by at least one sensor of the wireless terminal; and

based on the estimated spatial orientation, filtering out a polarization crosstalk from the received MIMO transmission,

the polarization crosstalk being associated with the spatial orientation of the antenna array of the wireless terminal.

2. The method of claim 1 , wherein

the MIMO transmission

uses a first set of time-frequency resources,

uses a first MIMO spatial channel,

uses a first receive polarization state; and

the polarization crosstalk is associated with a further MIMO transmission by the access node, wherein the further MIMO transmission

uses a second set of time-frequency resources which at least partially overlaps the first set of time-frequency resources,

uses a second MIMO spatial channel which at least partially overlaps the first MIMO spatial channel, and

uses a second receive polarization state which differs from the first receive polarization state.

3. The method of claim 2 , wherein

based on the estimated spatial orientation, the wireless terminal filtering out the polarization crosstalk further comprises:

the wireless terminal filtering outer the polarization cross-talk based on a terminal-specific filter function using the estimated spatial orientation as an input.

4. The method of claim 3 , wherein

the filter function is pre-configured in the wireless terminal.

5. The method of claim 3 , wherein

the filter function comprises a filter matrix.

6. The method of claim 5 , further comprising:

determining a condition of a channel matrix representing the filtered channel.

7. The method of claim 6 , further comprising:

in response to determining that the channel matrix is ill-conditioned: triggering the access node to improve an isolation of the MIMO transmissions.

8. The method of claim 7 , wherein

the channel matrix is ill-conditioned if a condition number of an inverse of the filter matrix exceeds a condition number threshold.

9. The method of claim 7 , wherein:

the channel matrix is ill-conditioned if an overall power of the inverse of the filter matrix is less than an overall power threshold.

10. The method of claim 7 , wherein

triggering the access node to improve an isolation of the MIMO transmissions further comprises:

triggering the access node to use a different first set of time-frequency resources.

11. The method of claim 7 , wherein

triggering the access node to improve an isolation of the MIMO transmissions further comprises:

triggering the access node to use different precoding vectors for the MIMO transmissions.

12. A wireless terminal, comprising:

at least one sensor;

an antenna array having antenna elements being associated with respective ones of two mutually orthogonal polarization planes; and

a processor being arranged for

receiving a multiple input multiple output, MIMO, transmission from an access node of the wireless communication network;

estimating a spatial orientation of the antenna array of the wireless terminal based on measurements performed by the at least one sensor of the wireless terminal; and

based on the estimated spatial orientation, filtering out a polarization crosstalk from the received MIMO transmission,

the polarization crosstalk being associated with the spatial orientation of the antenna array of the wireless terminal.

13. A method of controlling radio transmissions in a wireless communication network, the method comprising in an access node of the wireless communication network:

controlling a first multiple input multiple output, MIMO, transmission between the access node and a first wireless terminal

to use a first set of time-frequency resources,

to use a first MIMO spatial channel, and

to use a first transmit polarization state;

controlling a second MIMO transmission between the access node and a second wireless terminal

to use a second set of time-frequency resources which at least partially overlaps the first set of time-frequency resources,

to use a second MIMO spatial channel which at least partially overlaps the first MIMO spatial channel, and

to use a second transmit polarization state which differs from the first transmit polarization state;

the controlling of the MIMO transmissions comprising precoding the MIMO transmissions to allow for a filtering of mutual polarization crosstalk of the MIMO transmissions,

the respective polarization crosstalk being associated with a spatial orientation of an antenna array of the respective wireless terminal.

14. The method of claim 13 , wherein precoding the MIMO transmissions further comprises:

the first MIMO transmission being mapped into a null-space of a second channel matrix of the second MIMO transmission, and

the second MIMO transmission being mapped into a null-space of a first channel matrix of the first MIMO transmission.

15. The method of claim 13 , further comprising

receiving, from any one of the wireless terminals, a trigger to improve an isolation of the MIMO transmissions.

16. The method of claim 15 , wherein

receiving, from any one of the wireless terminals, a trigger to improve an isolation of the MIMO transmissions further comprises:

receiving a trigger to use a different set of time-frequency resources.

17. The method of claim 15 , wherein

receiving, from any one of the wireless terminals, a trigger to improve an isolation of the MIMO transmissions further comprises:

receiving a trigger to use different precoding vectors for the MIMO transmissions.

18. The method of claim 14 , wherein

precoding the MIMO transmissions further comprises:

precoding the first MIMO transmission based on a vector of and on the second channel matrix of the second MIMO transmission, and

precoding the second MIMO transmission based on a vector of and on the first channel matrix of the first MIMO transmission.