Mimo systems

A multiple-input-multiple-output (MIMO) transmitter for transmitting wireless communication signals over a wideband communication channel to a receiver, the MIMO transmitter comprising:

• a digital signal processor configured to perform pre-coding on a plurality Ns of data streams;
• a plurality NRF of radio-frequency (RF) chains each configured to pass a pre-coded data stream from the digital signal processor to generate a signal representing that pre-coded data stream;
• a lens antenna array comprising an array of NT antenna elements;
• and
• a selecting unit coupled between the plurality of NRF of RF chains and the lens antenna array, the selecting unit comprising a plurality of separate coupling units each configured to couple a respective RF chain to a selective sub-array of NTBRF antenna elements concurrently for transmitting the signal representing the pre-coded data stream passed through that RF chain,
• wherein each coupling unit further comprises a set of phase shifter modules configured to adjust at least one of an amplitude or a phase of each selected wireless communication signal to be communicated via that RF chain.