A MIMO transmitter has a modulator (40,41,42, 120, 122) a demultiplexer 100 arranged to divide the information into one or more demux streams for transmission over different ones of the channels, and a diversity splitter (110) to derive one or more sub-streams of the same information. A decorrelator (120) such as a scrambler (150, 155) decorrelates the sub-streams before or after the modulation. The arrangement is configurable to vary in use a ratio of demultiplexing and of diversity splitting. This balances between the gains from diversity and spatial multiplexing, without needing major changes to the transmit and receive processing.