A user equipment for reporting channel state information to a base station in a communication system, the user equipment comprising: a receiver which, in operation, is configured to receive from the base station data in subframes in a time domain, the subframes including a first set of subframes and a second set of subframes that differs from the first set of subframes wherein CSI reporting of a higher spectral efficiency is configured for the second set of subframes than the first set of subframes; circuitry which, in operation, is configured to determine first CSI for the first set of subframes according to a first set of channel state values, the first set of channel state values configured for the first set of subframes, and determines second CSI for the second set of subframes according to a second set of channel state values, the second set of channel state values configured for the second set of subframes and different from the first set of channel state values, wherein the first set of channel state values includes 16 index levels n (where n = 0, 1,... 14, or 15) and the second set of channel state values includes the 16 index levels and a subset consisting of a defined number of index levels larger than 15, the channel state value at each index level larger than 15 in the second set of channel state values has a higher spectral efficiency than the channel state value at index level 15 included in the first set of channel state values, and is configured to prepare a CSI report indicating the first CSI and the second CSI, wherein the first CSI is signaled as an absolute index level value using four bits and the second CSI is signaled differentially to the first CSI as a value which, when added to the first CSI, indicates an index level from the second set; and a transmitter which, in operation, is configured to transmit the CSI report. a receiver which, in operation, is configured to receive from the base station data in subframes in a time domain, the subframes including a first set of subframes and a second set of subframes that differs from the first set of subframes wherein CSI reporting of a higher spectral efficiency is configured for the second set of subframes than the first set of subframes; circuitry which, in operation, is configured to determine first CSI for the first set of subframes according to a first set of channel state values, the first set of channel state values configured for the first set of subframes, and determines second CSI for the second set of subframes according to a second set of channel state values, the second set of channel state values configured for the second set of subframes and different from the first set of channel state values, wherein the first set of channel state values includes 16 index levels n (where n = 0, 1,... 14, or 15) and the second set of channel state values includes the 16 index levels and a subset consisting of a defined number of index levels larger than 15, the channel state value at each index level larger than 15 in the second set of channel state values has a higher spectral efficiency than the channel state value at index level 15 included in the first set of channel state values, and is configured to prepare a CSI report indicating the first CSI and the second CSI, wherein the first CSI is signaled as an absolute index level value using four bits and the second CSI is signaled differentially to the first CSI as a value which, when added to the first CSI, indicates an index level from the second set; and a transmitter which, in operation, is configured to transmit the CSI report.