A method for reporting channel state information, CSI, from a mobile station to a base station in a mobile communication system in which a plurality of downlink and at least one uplink component carriers are configured for communication between the base station and the mobile station, the method comprising the following steps performed by the base station: transmitting from the base station a trigger message that triggers the reporting of CSI for at least one of the plurality of downlink component carriers, the trigger message being transmitted in a subframe n Trigger, and receiving (S02, S03) from the mobile station the triggered reporting of CSI for the at least one of the plurality of downlink component carriers based on reference signals present on the at least one of the plurality of downlink component carriers, in a subframe n Report later than n Trigger, wherein the reference signals, on the basis of which the CSI is to be reported, are present in a subframe n RS on the at least one of the plurality of downlink component carriers, where n Trigger ≤ n RS < n Report, wherein the triggered reporting of CSI is reported a-periodically by the mobile station, wherein the triggered reporting of CSI includes: a wideband channel quality indicator, CQI, value per codeword which is calculated receiving downlink transmission using a single precoding matrix in all sub-bands; and a selected single precoding matrix indicator, PMI, or a first and second PMI corresponding to the selected single PMI, wherein the single PMI is selected from the codebook subset assuming downlink transmission on the set of sub-bands, S, and wherein the reported PMI and the reported CQI values are calculated conditioned on a reported rank indicator, RI, or are calculated conditioned on RI = 1. transmitting from the base station a trigger message that triggers the reporting of CSI for at least one of the plurality of downlink component carriers, the trigger message being transmitted in a subframe n Trigger, and receiving (S02, S03) from the mobile station the triggered reporting of CSI for the at least one of the plurality of downlink component carriers based on reference signals present on the at least one of the plurality of downlink component carriers, in a subframe n Report later than n Trigger, wherein the reference signals, on the basis of which the CSI is to be reported, are present in a subframe n RS on the at least one of the plurality of downlink component carriers, where n Trigger ≤ n RS < n Report, wherein the triggered reporting of CSI is reported a-periodically by the mobile station, wherein the triggered reporting of CSI includes: a wideband channel quality indicator, CQI, value per codeword which is calculated receiving downlink transmission using a single precoding matrix in all sub-bands; and a selected single precoding matrix indicator, PMI, or a first and second PMI corresponding to the selected single PMI, a wideband channel quality indicator, CQI, value per codeword which is calculated receiving downlink transmission using a single precoding matrix in all sub-bands; and a selected single precoding matrix indicator, PMI, or a first and second PMI corresponding to the selected single PMI, wherein the single PMI is selected from the codebook subset assuming downlink transmission on the set of sub-bands, S, and wherein the reported PMI and the reported CQI values are calculated conditioned on a reported rank indicator, RI, or are calculated conditioned on RI = 1.