What is MIMO (multiple-input multiple-output)?
A wireless technique that uses multiple antennas at both the transmitter and the receiver. It raises the transmission rate through spatial multiplexing, sending different data on the same frequency at the same time, or raises reliability through diversity, sending the same data over several paths. The number of streams that spatial multiplexing can send is limited by the smaller of the numbers of transmit and receive antennas.
Japanese name: MIMO(多入力多出力)
MIMO (multiple-input multiple-output) appears in 2 practice questions across 1 topic, including Wireless Communication Basics.
Field: Wireless Communication Basics
When spatial multiplexing works well
Spatial multiplexing needs propagation channels that differ sufficiently. In environments with many reflections, such as among buildings, the channels differ greatly and many streams can be separated. Conversely, when the paths are similar, as in places with clear line of sight, the channels are highly correlated and fewer streams can be used. Because power is divided among the streams, a sufficiently high S/N is also needed.
FAQ
How do MIMO and beamforming differ?
Beamforming is a technique that adjusts the phases of several antenna elements to concentrate radio waves in a particular direction. MIMO refers to the whole approach of transmitting and receiving with multiple antennas, within which spatial multiplexing, diversity and beamforming are used. Massive MIMO forms a beam per terminal by beamforming and combines it with spatial multiplexing.
What does a notation such as 4×4 MIMO mean?
It generally means the number of transmit antennas × the number of receive antennas. 4×4 MIMO can send up to 4 streams by spatial multiplexing. If the terminal has only 2 antennas, at most 2 streams can be sent to it even if the access point has 4.