Transmission of reference signals from a terminal device
There is provided mechanisms for transmission of reference signals. A method is performed by a terminal device. The terminal device comprises at least two physical antenna ports. The method comprises obtaining channel information. The method comprises determining, for at least one given precoder in a codebook, an uplink reference signal to physical antenna port mapping based on the channel information. The method comprises transmitting uplink reference signals in the physical antenna ports according to the determined mapping.
1. A method for transmission of reference signals, the method being performed by a terminal device, the terminal device comprising at least two physical antenna ports, the method comprising:
determining a mapping between an uplink reference signal and a physical antenna port based on channel correlation or average received signal power; and
based on the determined mapping, transmitting an uplink reference signal using one or more of said at least two physical antenna port.
2. the method according to claim 1 , wherein
determining the mapping comprises estimating expected transmission rank for upcoming uplink data transmission from the channel correlation or average received signal power, and
the mapping is based on the expected transmission rank.
3. The method according to claim 1 , wherein
the mapping is for at least one precoder in a codebook,
the at least one precoder defines transmission of at least one spatial layer, and
the mapping is determined to select one or more of said at least two physical antenna ports to use for transmitting said at least one spatial layer.
4. The method according to claim 3 , wherein
determining the mapping comprises determining channel correlation of each pair of physical antenna ports included in said at least two physical antenna ports, and
a pair of physical antenna ports that is included in said at least two physical antenna ports and that has highest channel correlation is mapped to the same spatial layer in the precoder.
5. The method according to claim 4 , wherein
determining the mapping comprises determining average received signal power of each pair of physical antenna ports included in said at least two physical antenna ports, and
a pair of physical antenna ports that is included in said at least two physical antenna ports and that has the highest average received signal power is mapped to at least one spatial layer having non-all zero-valued coefficients in the at least one precoder.
6. The method according to claim 5 , wherein a pair of physical antenna ports that is included in said at least two physical antenna ports and that has the lowest average received signal power is mapped to at least one spatial layer having all zero-valued coefficients in the at least one precoder.
7. The method according to claim 3 , wherein at least one row but less than all rows in the at least one precoder consists of all zero-valued coefficients.
8. The method according to claim 3 , further comprising:
transmitting uplink data in the at least two physical antenna ports using one of the at least one given codebook based precoder as applied according to the determined mapping.
9. The method according to claim 8 , wherein the uplink data is transmitted on a physical uplink shared channel, PUSCH.
10. The method according to claim 1 , wherein
the terminal device is configured to operate in at least two frequency bands, and
the mapping is frequency selective such that different mappings are applied in the at least two frequency bands.
11. The method according to claim 1 , wherein each of the at least two physical antenna ports is fed by its own power amplifier.
12. The method according to claim 1 , wherein each of the at least two physical antenna ports is operatively connected to only a single antenna element or an array of at least two antenna elements.
13. The method according to claim 12 , wherein the antenna element or the array of at least two antenna elements of at least two of the physical antenna ports are arranged at the terminal device to point in at least two mutually different pointing directions.
14. The method according to claim 1 , wherein each uplink reference signal defines a sounding reference signal (SRS) port.
15. The method according to claim 1 , wherein the uplink reference signal is transmitted over 5G New Radio (NR) air interface.
16. A terminal device for transmission of reference signals, the terminal device comprising at least two physical antenna ports and processing circuitry, the processing circuitry being configured to cause the terminal device to: determine a mapping between an uplink reference signal and a physical antenna port based on channel correlation or average received signal power; and
based on the determined mapping, transmit an uplink reference signal using one or more of said at least two physical antenna ports.
17. A computer program product comprising a non-transitory computer readable medium storing a computer program comprising instructions which, when run on processing circuitry of a terminal device comprising at least two physical antenna ports causes the terminal device to: determine a mapping between an uplink reference signal and a physical antenna port based on channel correlation or average received signal power; and
based on the determined mapping, transmit an uplink reference signal using one or more of said at least two physical antenna ports.