A method of transmitting a sequence of transmissions at respective time intervals from a transmitter to a receiver over a wireless multiple-input-multiple-output channel comprising one or more frequency intervals, wherein the method comprises: based on one or more performance criteria evaluated in relation to a previously received transmission from the transmitter, selecting at the receiver a first precoding matrix out of a predetermined set of precoding matrices for transmitting from the transmitter to the receiver at a first of said time intervals; and for one or more successive time intervals in the sequence: determining from said predetermined set of precoding matrices a preferred subset of precoding matrices; based on one or more performance criteria evaluated in relation to the previously received transmission, selecting at the receiver a respective precoding matrix from said predetermined set for transmitting from the transmitter to the receiver on said successive time interval; and feeding back an index of that respective precoding matrix from the receiver to the transmitter using a differential encoding scheme whereby the respective index is indicated relative to said preferred subset; characterised in that the method further comprises transmitting an indication of at least one of the preferred subsets from the receiver to the transmitter, and/or transmitting the size of at least one of the preferred subsets from the receiver to the transmitter. based on one or more performance criteria evaluated in relation to a previously received transmission from the transmitter, selecting at the receiver a first precoding matrix out of a predetermined set of precoding matrices for transmitting from the transmitter to the receiver at a first of said time intervals; and for one or more successive time intervals in the sequence: determining from said predetermined set of precoding matrices a preferred subset of precoding matrices; based on one or more performance criteria evaluated in relation to the previously received transmission, selecting at the receiver a respective precoding matrix from said predetermined set for transmitting from the transmitter to the receiver on said successive time interval; and feeding back an index of that respective precoding matrix from the receiver to the transmitter using a differential encoding scheme whereby the respective index is indicated relative to said preferred subset; characterised in that determining from said predetermined set of precoding matrices a preferred subset of precoding matrices; based on one or more performance criteria evaluated in relation to the previously received transmission, selecting at the receiver a respective precoding matrix from said predetermined set for transmitting from the transmitter to the receiver on said successive time interval; and feeding back an index of that respective precoding matrix from the receiver to the transmitter using a differential encoding scheme whereby the respective index is indicated relative to said preferred subset; characterised in that the method further comprises transmitting an indication of at least one of the preferred subsets from the receiver to the transmitter, and/or transmitting the size of at least one of the preferred subsets from the receiver to the transmitter.