Determination of uplink MIMO transmission state for a UE

1 . A method for determining an uplink (UL) multiple-input multiple-output (MIMO) transmission state for at least a first user equipment (UE), the method being performed by a network node, the method comprising:

obtaining interference affecting network information for the first UE; and

signalling an indication of the UL MIMO transmission state towards the first UE, wherein

the UL MIMO transmission state reflects a rank value, and

the rank value is based on the interference affecting network information.

2 . The method of claim 1 , wherein

the method further comprises: selecting the rank value as a maximum rank value for the first UE to use for UL communication with the network node,

the maximum rank value is selected based on the interference affecting network information, and

the UL MIMO transmission state is selected based on the maximum rank value.

3 . The method of claim 2 , wherein the method further comprises:

signalling an indication of the maximum rank value towards the first UE.

4 . The method of claim 3 , wherein the indication of the selected maximum rank value is signalled as downlink control information, DCI.

5 . The method of claim 3 , wherein the indication of the selected maximum rank value is signalled in parameter maxRank in a configuration information element for a Physical Uplink Shared Channel, PUSCH.

6 . The method of claim 3 , wherein the indication of the selected maximum rank value is signalled in a medium access control, MAC, control element, CE, message, or in a radio resource control, RRC, message.

7 . The method of claim 3 , wherein one maximum rank value is selected per each carrier used by the first UE for UL communication with the network node.

8 . The method of claim 3 , wherein one maximum rank value is selected per each bandwidth part usable by the first UE for UL communication with the network node, and wherein the indication of the selected maximum rank value indicates over which bandwidth part the UL communication is to be used by the first UE for the UL communication with the network node.

9 . The method of claim 3 , wherein the indication of the selected maximum rank value indicates a configuration of sounding reference signal ports to be used by the first UE for the UL communication with the network node.

10 . The method of claim 9 , wherein one maximum rank value is selected per each configuration usable by the first UE for UL communication with the network node, and wherein the indication of the selected maximum rank value indicates which configuration to be used by the first UE.

11 . The method of claim 3 , wherein the maximum rank value is selected for UL communication in terms of UL data communication or UL control communication.

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

determining a biasing value based on the interference affecting network information from the first UE; and

selecting the UL MIMO transmission state based on of the biasing value and channel measurements for the first UE.

13 . The method of claim 12 , wherein the UL MIMO transmission state is defined by at least one of: a transmit precoder matrix indicator (TPMI), a transmission rank indicator (TRI), a sounding reference signal resource indicator (SRI).

14 . The method of claim 13 , wherein the TPMI, TRI, and/or SRI is selected based on optimizing spectral efficiency, and wherein the biasing value is an offset spectral efficiency value that biases selection of TPMIs, TRIs, and/or SRIs with lower rank over TPMIs, TRIs, and/or SRIs with higher rank.

15 . The method of claim 12 , wherein one biasing value is selected for the first UE served by a TRP of the network node, or wherein one biasing value is selected for a group of UEs comprising the first UE served by the TRP of the network node, or wherein one biasing value is selected for each UE of the group of UEs served by the TRP of the network node, or wherein one biasing value is selected for each UE of the group of UEs served by the TRP of the network node and at least one other TRP of the network node.

16 . The method of claim 1 , wherein the interference affecting network information pertains to at least one of: traffic load in a cell served by the network node, traffic load in a cell neighbouring the cell served by the network node, number of receiver radio chains in the network node.

17 . The method of claim 1 , wherein the interference affecting network information pertains to at least one of: average traffic load in a system in which the network node is operating, number of receiver radio chains in a network node serving a cell neighbouring the cell served by the network node, number of antenna ports at the first UE, frequency carrier used by the first UE for UL communication with the network node, number of aggregated carriers used by the first UE for UL communication with the network node, which link budget the first UE has, which priority communication of the first UE has, which type of application the UL communication with the network node pertains to, which power scaling scheme is applied at the first UE, which type of power class the first UE belongs to, which type of device the first UE is.

18 . A network node for determining an uplink (UL) multiple-input multiple-output (MIMO) transmission state for at least a first user equipment (UE), the network node comprising processing circuitry, the processing circuitry being configured to cause the network node to:

obtain interference affecting network information for the first UE; and

signal an indication of the UL MIMO transmission state towards the first UE, wherein the UL MIMO transmission state reflects a rank value, and wherein the rank value is based on the interference affecting network information.

19 . A non-transitory computer readable storage medium storing a computer program for determining an uplink (UL) multiple-input multiple-output (MIMO) transmission state for at least a first user equipment (UE), the computer program comprising computer code which, when run on processing circuitry of a network node, causes the network node to:

obtain interference affecting network information for the first UE; and

signal an indication of the UL MIMO transmission state towards the first UE, wherein the UL MIMO transmission state reflects a rank value, and wherein the rank value is based on the interference affecting network information.