Transmission of Channel State Information

1 . A method of transmitting, via a radio communications uplink from a user equipment to a node of a cellular wireless network, signalling information relating to Multiple Input Multiple Output channel state information characteristics, that the equipment determines to be highest priority for a downlink, the method comprising:

receiving an indicator from the node indicating a preferred basis of the highest priority signalling information;

compiling the highest priority signalling information according to the preferred basis; and

sending the compiled signalling information to the node.

2 . A method according to claim 1 , wherein the indicator is carried in a message in a Physical Downlink Control Channel indicating an uplink grant.

3 . A method according to claim 1 , wherein the preferred basis comprises an indication relating to a rank of Multiple Input Multiple Output communications upon which the highest priority signalling information is to be based.

4 . A method according to claim 1 , wherein the preferred basis comprises an indication of a frequency sub-banding arrangement on which one or more indications of channel quality is to be based.

5 . A method according to claim 1 , wherein the preferred basis comprises an indication of a frequency sub-banding arrangement on which one or more indications of a precoding matrix index is to be based.

6 . A method according to claim 1 , wherein the indicator indicates on which of two or more pre-configured options of preferred bases the highest priority signalling information should be based.

7 . A method according to claim 6 , wherein said two or more options comprise:

a first option in which a rank of Multiple Input Multiple Output communications is unrestricted by the pre-configuration and an indication of channel quality relates to a whole frequency band of the rather than a sub-band of the frequency band; and

a second option in which a rank of Multiple Input Multiple Output communications is restricted by the pre-configuration to a predetermined value by the node and a plurality of indications of channel quality each relate to a sub-band of the frequency band.

8 . A method according to claim 7 , wherein:

in the first option, a plurality of precoding matrix indices each relate to a sub-band of the frequency band; and

in the second option, a precoding matrix index relates to a whole frequency band rather than a sub-band of the frequency band.

9 . A method according to claim 7 , wherein:

in the first and second options, a plurality of precoding matrix indices each relate to a sub-band of the frequency band.

10 . A method according to claim 6 , wherein:

the indictor indicates which pre-configured option is to be selected as the basis of the highest priority signalling information by the position of the indicator in a frame.

11 . A method according to claim 1 , further comprising:

in response to receipt of an indicator indicating that a rank of Multiple Input Multiple Output communications is restricted to a pre-configured value and a determination that a rank other than the pre-configured value of rank would be preferred; and

sending a first flag to the node indicating that a rank other than the pre-configured value of rank would be preferred.

12 . A method according claim 1 , wherein the indicator indicates a maximum value of rank on which the user equipment should base the highest priority signalling information.

13 . A method according to claim 1 , wherein the indicator indicates a type of codeword to be used for reporting the highest priority signalling information, the type of codeword selected from a set of types of codeword comprising at least:

a first type of codeword selected from a codebook to be a closest codeword in the codebook to a representation of an intended Multiple Input Multiple Output channel state information characteristic; and

a second type of codeword selected from the codebook to be a less close codeword than the first type of codeword to the representation of the intended Multiple Input Multiple Output channel state information characteristic.

14 . A method according to claim 13 , wherein the second type of codeword is selected to be a second closest codeword in the codebook to the representation of the intended Multiple Input Multiple Output channel state information characteristic.

15 . A method according to claim 13 , wherein the set of types of codeword further comprises a third type of codeword selected from the codebook to be a n-th closest codeword to the representation of the intended Multiple Input Multiple Output channel state information characteristic, wherein the factor n is indicator by the indicator.

16 . A method according to claim 13 , wherein the second type of codeword is selected to be the codeword in the codebook that together with the first type of codeword produces an interpolated Multiple Input Multiple Output channel state information characteristic that is closest to the representation of the intended Multiple Input Multiple Output channel state information characteristic.

17 . A user equipment for transmitting to a node of a cellular wireless network, via a radio communications uplink, signalling information relating to Multiple Input Multiple Output channel state information characteristics, that the equipment determines to be highest priority for a downlink, the user equipment comprising at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the user equipment to:

receive an indicator from the node indicating a preferred basis of the highest priority signalling information;

compile the highest priority signalling information according to the preferred basis; and

send the compiled signalling information to the node.

18 . A method of transmitting, via a radio communications uplink from a user equipment to a node of a cellular wireless network, signalling information relating to a Multiple Input Multiple Output channel state information characteristics for a downlink, the method comprising:

determining a preferred rank of Multiple Input Multiple Output communication which is a number of Multiple Input Multiple Output layers that the user equipment would prefer to be used for the downlink; and

dependent on the preferred rank being a rank of one, sending said signalling information in different messages indicating a first and second codeword respectively,

wherein the first codeword is selected from a codebook to be a closest codeword in the codebook to a representation of an intended Multiple Input Multiple Output channel state information characteristic, and the second characteristic is selected to be a less close codeword in the codebook to the representation of the intended Multiple Input Multiple Output channel state information characteristic.

19 . A method according to claim 18 , wherein the second codeword is selected to be the codeword in the codebook that together with the first codeword produces interpolated Multiple Input Multiple Output channel state information characteristic that is closest to the representation of the intended Multiple Input Multiple Output channel state information characteristic

20 . A user equipment for transmitting to a node of a cellular wireless network, via a radio communications uplink, signalling information relating to a Multiple Input Multiple Output channel state information characteristic for a downlink, the user equipment comprising at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the user equipment to:

determine a preferred rank of Multiple Input Multiple Output communication which is a number of Multiple Input Multiple Output layers that the user equipment would prefer to be used for the downlink; and

dependent on the preferred rank being a rank of one, send said signalling information in different messages indicating a first and second codeword respectively,

wherein the first codeword is selected from a codebook to be a closest codeword in the codebook to a representation of the an intended Multiple Input Multiple Output configuration characteristic, and the second characteristic is selected to be a less close codeword in the codebook to the representation of the intended Multiple Input Multiple Output configuration characteristic.