Multistream space-time coding by spatial spreading, scrambling and delay diversity

The use of multiple transmitter and receiver antennas allows to transmit multiple signal streams in parallel and hence to increase communication capacity. To distribute the multiple signal streams over the MIMO channel, linear space-time codes have been shown to be a convenient way to reach high capacity gains with a reasonable complexity. The space-time codes that have been introduced so far are block codes, leading to the manipulation of possibly large matrices. To reduce complexity, we propose a flexible spatial spreading and scrambling framework which allows to transmit an aribtrary number of streams. The number of streams would in practice be adjusted to fit the channel rank. Special cases of partial scrambling, in the case in which Nrx is an integer fraction of Ntx, or no scrambling, when Nrx ≥ Ntx, are also considered.