An optical wireless communication, OWC, system comprising: a multiple input multiple output, MIMO, device (110, 115, 1702, 1720) comprising a baseband device configured to generate modulated baseband signals, wherein the MIMO device is configured to provide a plurality of MIMO device output signals, wherein the plurality of MIMO device output signals comprise electrical signals having MIMO device output signal frequencies, the MIMO device output signal frequencies comprising baseband or RF or intermediate frequencies and wherein each MIMO device output signal represents a respective data stream of a plurality of data streams; conditioning circuitry comprising electrical circuitry configured to receive the plurality of MIMO device output signals output from the MIMO device and perform at least one frequency up conversion process or frequency down conversion process on one or more of the plurality of MIMO device output signals in the electrical domain to produce a plurality of up or down converted signals, wherein the conditioning circuitry comprises a combiner (870, 970, 972, 1170) configured to combine the converted signals to produce at least one conditioned signal representative of the data streams and suitable for transmission using an OWC transmission device; an OWC transmission device comprising at least one transmitter (880, 980, 982, 1080, 1180) for transmitting light and configured to be responsive to the at least one conditioned signal to transmit light representative of the data streams using the at least one transmitter, wherein the plurality of data streams comprise at least a first data stream and a second data stream, and wherein the at least one conditioned signal produced by the conditioning circuitry comprises: a conditioned signal that includes a first portion having a first OWC frequency or range of OWC frequencies and at least a second portion having a second OWC frequency or range of OWC frequencies, wherein the first portion represents the first data stream and the second portion represents the second data stream. a multiple input multiple output, MIMO, device (110, 115, 1702, 1720) comprising a baseband device configured to generate modulated baseband signals, wherein the MIMO device is configured to provide a plurality of MIMO device output signals, wherein the plurality of MIMO device output signals comprise electrical signals having MIMO device output signal frequencies, the MIMO device output signal frequencies comprising baseband or RF or intermediate frequencies and wherein each MIMO device output signal represents a respective data stream of a plurality of data streams; conditioning circuitry comprising electrical circuitry configured to receive the plurality of MIMO device output signals output from the MIMO device and perform at least one frequency up conversion process or frequency down conversion process on one or more of the plurality of MIMO device output signals in the electrical domain to produce a plurality of up or down converted signals, wherein the conditioning circuitry comprises a combiner (870, 970, 972, 1170) configured to combine the converted signals to produce at least one conditioned signal representative of the data streams and suitable for transmission using an OWC transmission device; an OWC transmission device comprising at least one transmitter (880, 980, 982, 1080, 1180) for transmitting light and configured to be responsive to the at least one conditioned signal to transmit light representative of the data streams using the at least one transmitter, wherein the plurality of data streams comprise at least a first data stream and a second data stream, and wherein the at least one conditioned signal produced by the conditioning circuitry comprises: a conditioned signal that includes a first portion having a first OWC frequency or range of OWC frequencies and at least a second portion having a second OWC frequency or range of OWC frequencies, wherein the first portion represents the first data stream and the second portion represents the second data stream.