The present invention relates to transmit power allocation in multi-carrier, multiplexing MIMO communication systems. The present invention especially relates to a MIMO communication device, a method of assigning transmit power to two or more communication channels and a software program product. A multiple-input-multiple-output, MIMO, communication device according to the present invention comprisesa link controller adapted to assign transmit power to two or more transmission channels, each of said transmission channels having preassigned a portion of transmit power for each of a group of subcarriers, said link controller being further adapted to assign, for each subcarrier of said group of subcarriers, at least part of the preassigned transmit power portion of a transmission channel that is not used for transmitting information at the subcarrier, to one or more transmission channels that are used for transmitting information at the subcarrier.