Maps spatial time streams to different transmit chains. This may include one of the following:
Direct mapping – each space time stream is directly mapped to a different transmit chain. When using direct mapping scheme, the number of space time stream must be equal to the number of chains.
Spatial expansion – the space time streams are multiplied by a matrix, and then transmitted through different transmit chains. When using spatial expansion mapping scheme, the space time stream can be fewer than the transmit chain. FFT transformation matrix is selected for spatial expansion purpose.