what is MIMO

MIMO (multiple input, multiple output) is an antenna technology for wireless communications in which multiple antennas are used at both the source (transmitter) and the destination (receiver). The antennas at each end of the communications circuit are combined to minimize errors and optimize data speed. MIMO is one of several forms of smart antenna technology, the others being MISO (multiple input, single output) and SIMO (single input, multiple output).

In conventional wireless communications, a single antenna is used at the source, and another single antenna is used at the destination. In some cases, this gives rise to problems with multipath effects. When an electromagnetic field (EM field) is met with obstructions such as hills, canyons, buildings, and utility wires, the wavefronts are scattered, and thus they take many paths to reach the destination. The late arrival of scattered portions of the signal causes problems such as fading, cut-out (cliff effect), and intermittent reception (picket fencing). In digital communications systems such as wireless Internet, it can cause a reduction in data speed and an increase in the number of errors. The use of two or more antennas, along with the transmission of multiple signals (one for each antenna) at the source and the destination, eliminates the trouble caused by multipath wave propagation, and can even take advantage of this effect.

MIMO technology has aroused interest because of its possible applications in digital television (DTV), wireless local area networks (WLANs), metropolitan area networks (MANs), and mobile communications.

Re: what is MIMO

The advantage of MIMO

Advantages of MIMO are increased WiFi range and performance. An 802.11n station connected to a legacy 802.11g AP will be able to connect at higher speeds at a greater distance. For instance, if a legacy station connecting to the AP from a distance of 25ft had a speed of 1Mbps, with 802.11n MIMO the station could have a speed of 2Mbps. The range of the 2Mbps has increased allowing the user to stay connected at a further distance.

When a radio sends a signal it is reflected creating multiple copies of the radio signal. Each one of these copies is a spatial stream. Current or legacy systems using Single-Input Single Output (SISO) can only send or receive a single spatial stream at one time. MIMO allows multiple antennas to send and receive multiple spatial streams at the same time. This allows antennas to transmit and receive simultaneously.