Question: What is MIMO (Multiple Input Multiple Output)?
MIMO (Multiple Input Multiple Output) is the main technology of 802.11n wireless standard that uses multiple transmitter and receiver antennas to increase data throughput and wireless range. This is much efficient technology to transmit and receive data in much higher data rate as compared to traditional way by just leveraging one antenna.
These smart antennas can work as reception or transmission automatically and dynamically on the air, adjusting for the best data path in order to reduce the wireless interference or signal blocking, especially in indoor environment.
In order to make use of this wireless feature, the wireless router or access point (AP) and also the wireless adapter on end device, such as laptop and mobile phone must support MIMO.
The wireless router needs multiple antennas and must fully support all features of 802.11n to attain the highest speed possible. With more antennas then only it is able to provide much higher data throughput. A wireless adapter with three antennas can have a speed of 600 Mbps, whereas an adapter with two antennas has a speed of 300 Mbps.
Normally 802.11n wireless router or access point supports 2x2 or 3x3 MIMO. What do they mean? A 2x2 MIMO wireless device indicates 2 antennas at the transmit end and 2 antennas at the receive end, whereas a 3x3 MIMO wireless device means 3 antennas at the transmit end and 3 antennas at the receive end.
If we see this from end consumer devices view, those 2x2 MIMO end devices are typically standard notebooks and laptops. 3x3 MIMO devices are only high end laptops like the MacBook Air and business class units from Dell, Lenovo and HP.
Note: Just for your information. The earlier wireless standards, such as 802.11a, 802.11b and 802.11g use SISO (Single Input Single Output) by making use of 1 antenna for data transmission and 1 antenna for data receiving.