MIMO

MIMO

(Multiple Input/Multiple Output) Pronounced "my-mo," it is the use of multiple transmitters and receivers (multiple antennas) on wireless devices for improved performance. When two transmitters and two or more receivers are used, two simultaneous data streams can be sent, which double the data rate. Multiple receivers alone allow greater distances between devices. For example, the IEEE 802.11n (Wi-Fi) wireless standard uses MIMO to increase speed to 100 Mbps and beyond, doubling at minimum the 802.11a and 11g rates. MIMO antennas are also used in WiMAX and LTE.

MIMO, MISO and SIMO
The M, S, I and O relate to the air, not the device. For example, multiple inputs (MI) means multiple transmitters send multiple data streams "into" the air. Multiple outputs (MO) means multiple receivers acquire multiple data streams "out of" the air (see illustration below). See 802.11n, antenna diversity, beamforming and HSPA.

 ARCHITECTURE AND ADVANTAGES OF
 MULTIPLE ANTENNA TECHNOLOGIES

                           Compared to
                           Single Antenna (SISO)
                           Technologies
       Transmit  Receive   Data
 Type  Antennas  Antennas  Rate     Distance

 MIMO  Multiple  Multiple  Greater  Greater range

 MISO  Multiple  Single    Same     Same range but
                                     More Reliable

 SIMO  Single    Multiple  Same     Greater range

 M = Multiple   S = Single
 I = Input      O = Output

MIMO Wireless Router

This "Pre-N" wireless router from Belkin uses two transmitters and three receivers to provide 108 Mbps between its access point and Belkin Pre-N cards in laptops. Introduced in 2004, this was the first "Preliminary-802.11n" system on the market (see 802.11n). (Image courtesy of Belkin Corporation, www.belkin.com)