Space- and frequency-division multiplexing wireless communication scheme. Reproduced from [118
]. (a) Conceptual illustration of multichannel direct data transmissions via an STC digital metasurface. (b) The testbed of the wireless communication system, in which two different colored pictures are transmitted from the transmitter (the left part) to two users (the right part) simultaneously and individually. Block diagram of (c) the transmitting process and (d) the receiving process.