Spatial multiplexing

Spatial multiplexing (often abbreviated SM or SMX) is a transmission technique in MIMO wireless communication to transmit independent and separately encoded data signals, so-called streams, from each of the multiple transmit antennas. Therefore, the space dimension is reused, or multiplexed, more than one time.

If the transmitter is equipped with ${\displaystyle N_{t}}$ antennas and the receiver has ${\displaystyle N_{r}}$ antennas, the maximum spatial multiplexing order (the number of streams) is,

if a linear receiver is used. This means that ${\displaystyle N_{s}}$ streams can be transmitted in parallel, ideally leading to an ${\displaystyle N_{s}}$ increase of the spectral efficiency (the number of bits per second and per Hz that can be transmitted over the wireless channel). The practical multiplexing gain can be limited by spatial correlation, which means that some of the parallel streams may have very weak channel gains.

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