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(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. The IEEE 802.11n wireless standard, expected in 2009, uses MIMO to increase maximum speed to 100 Mbps and beyond, double the 802.11a and 11g wireless standards.

MIMO, MISO and SIMO
Following are the advantages of using multiple antennas rather than one. The terminology is "M" for multiple, "S" for single, "I" for input and "O" for output; however, the inputs and outputs relate to the air, not the device. This is a peculiar notation; nevertheless, multiple inputs (MI) means multiple transmitters are sending multiple data streams "into" the air. Multiple outputs (MO) means multiple receivers are receiving multiple data streams "out of" the air. See 802.11n, antenna diversity, beamforming and HSPA.

 ARCHITECTURE AND ADVANTAGES OF
 MULTIPLE ANTENNA TECHNOLOGIES

                           Compared to
                           Single Antenna
                           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

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)