Data transmission over a reduced number of physical antennas

1. A method, implemented by a radio access node comprising four logical antenna ports respectively mapped to four physical antennas, the method comprising:

responsive to a loss of data transmission from one of the four physical antennas, transmitting reference signals representing the four logical antenna ports on the remaining three physical antennas, each reference signal representing a respective antenna port of the four logical antenna ports; and

scaling transmission power of a physical antenna transmitting more than one of the reference signals based on the number of the reference signals the physical antenna transmits.

2. The method of claim 1 , further comprising remapping the four logical antenna ports to the remaining three physical antennas using an antenna mapping matrix prestored in the radio access node, and transmitting from the remaining three physical antennas in accordance with the remapping.

3. The method of claim 1 , wherein scaling the transmission power comprises reducing the transmission power of the physical antenna by half when the physical antenna transmits two reference signals.

4. The method of claim 1 , further comprising remapping the four logical antenna ports to the remaining three physical antennas using a precoding matrix including a power scaling factor corresponding to the number of reference signals to be transmitted on the physical antenna.

5. The method of claim 1 , wherein the method further comprises:

mapping two of the four logical antenna ports to respective co-polarized antennas of the three remaining physical antennas; and

mapping both of the other two of the four logical antenna ports to the physical antenna and scaling the transmission power of the physical antenna in response, wherein the physical antenna has an orthogonal polarization to the co-polarized antennas.

6. The method of claim 1 , further comprising, in response to the loss of data transmission:

selecting a remapping matrix from a group of prestored remapping matrices based on a current antenna transmission scheme, each remapping matrix representing a remapping adapted to a respective antenna transmission scheme; and

transmitting on the remaining three physical antennas in accordance with the antenna transmission scheme of the selected remapping matrix.

7. The method of claim 1 , further comprising:

transmitting the reference signals in accordance with a transmit diversity scheme for a Physical Broadcast Channel, a Physical Control Format Indicator Channel, a Physical Downlink Control Channel, a Physical Hybrid ARQ Indicator Channel, and/or a Physical Downlink Shared Channel;

wherein two of the remaining three physical antennas are main branches in the transmit diversity scheme and the physical antenna transmitting more than one of the reference signals is a diversity branch on which power of transmissions is scaled by a power scaling factor.

8. The method of claim 7 , wherein the power scaling factor aligns transmission power on the diversity branch to transmission power on the main branches.

9. A radio access node comprising:

four physical antennas;

processing circuitry communicatively coupled to the four physical antennas and configured to:

map four logical antenna ports to the four physical antenna ports;

responsive to a loss of data transmission from one of the four physical antennas, transmit reference signals representing the four logical antenna ports on the remaining three physical antennas, each reference signal representing a respective antenna port of the four logical antenna ports; and

scale transmission power of a physical antenna transmitting more than one of the reference signals based on the number of the reference signals the physical antenna transmits.

10. The radio access node of claim 9 , wherein:

the radio access node further comprises a memory; and

the processing circuitry is further configured to remap the four logical antenna ports to the remaining three physical antennas using an antenna mapping matrix prestored in the memory, and transmit from the remaining three physical antennas in accordance with the remapping.

11. The radio access node of claim 9 , wherein to scale the transmission power, the processing circuitry is configured to reduce the transmission power of the physical antenna by half when the physical antenna transmits two reference signals.

12. The radio access node of claim 9 , wherein the processing circuitry is further configured to remap the four logical antenna ports to the remaining three physical antennas using a precoding matrix including a power scaling factor corresponding to the number of reference signals to be transmitted on the physical antenna.

13. The radio access node of claim 9 , wherein the processing circuitry is further configured to:

map two of the four logical antenna ports to respective co-polarized antennas of the three remaining physical antennas; and

map both of the other two of the four logical antenna ports to the physical antenna and scale the transmission power of the physical antenna in response, wherein the physical antenna has an orthogonal polarization to the co-polarized antennas.

14. The radio access node of claim 9 , wherein the radio access node further comprises a memory, and the processing circuitry is further configured to, in response to the loss of data transmission:

select a remapping matrix from a group of remapping matrices, prestored in the memory, based on a current antenna transmission scheme, each remapping matrix representing a remapping adapted to a respective antenna transmission scheme; and

transmit on the remaining three physical antennas in accordance with the antenna transmission scheme of the selected remapping matrix.

15. The radio access node of claim 9 , wherein the processing circuitry is further configured to:

transmit the reference signals in accordance with a transmit diversity scheme for a Physical Broadcast Channel, a Physical Control Format Indicator Channel, a Physical Downlink Control Channel, a Physical Hybrid ARQ Indicator Channel, and/or a Physical Downlink Shared Channel;

wherein two of the remaining three physical antennas are main branches in the transmit diversity scheme and the physical antenna transmitting more than one of the reference signals is a diversity branch on which power of transmissions is scaled by a power scaling factor.

16. The radio access node of claim 15 , wherein the power scaling factor aligns transmission power on the diversity branch to transmission power on the main branches.

17. A non-transitory computer readable medium storing a computer program product for controlling a radio access node comprising four logical antenna ports mapped to four physical antennas, the computer program product comprising software instructions which, when run on a processor of the access node, causes the access node to:

responsive to a loss of data transmission from one of the four physical antennas, transmit reference signals representing the four logical antenna ports on the remaining three physical antennas, each reference signal representing a respective antenna port of the four logical antenna ports; and

scale transmission power of a physical antenna transmitting more than one of the reference signals based on the number of the reference signals the physical antenna transmits.