Spatial multiplexing 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. Multiple-input multiple-output, or MIMO, is an abstract mathematical model for multi-antenna communication systems where the transmitter has multiple antennas capable of transmitting independent signals and the receiver is equipped with multiple receive antennas. ... Wireless is an old-fashioned term for a radio receiver, referring to its use as a wireless telegraph. ...

If the transmitter is equipped with N_t antennas and the receiver has N_r antennas, the maximum spatial multiplexing order (the number of streams) is

N_s = min(N_t,N_r)

if a linear receiver is used. This means that N_s streams can be transmitted in parallel, leading to a N_s increase of the spectral efficiency (the number of bits per second and per Hz that can be transmitted over the wireless channel).

Encoding

In a MIMO system with N_t transmitter antennas and N_r receiver antennas, the input-output relationship can be described as

where is the vector of transmitted symbols, are the vectors of received symbols and noise respectively, is the matrix of channel coefficients and is the linear precoding matrix.

Linear precoding implies that a precoding matrix W is used to precode the symbols in the vector to enhance the performance. The column dimension N_s of W can be selected smaller than N_t which is useful if the channel can not support N_s streams.

See also

• MIMO
• Space–time code
• Space–time trellis code
• Wireless communications