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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. 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.

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 OFMULTIPLE ANTENNA TECHNOLOGIES                       Compared to Single                          Antenna (SISO)                          Technologies                          --------------      Transmit  Receive   DataType  Antennas  Antennas  Rate  Distance

 MIMO  Multiple  Multiple    >     >

 MISO  Multiple  Single      =     =

 SIMO  Single    Multiple    =     >

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

MIMO Wireless Router
In 2004, Belkin introduced the first 802.11n wireless router with multiple transmit/receive antennas (see 802.11n). (Image courtesy of Belkin Corporation, www.belkin.com)

MIMO Wireless Router
In 2004, Belkin introduced the first 802.11n wireless router with multiple transmit/receive antennas (see 802.11n). (Image courtesy of Belkin Corporation, www.belkin.com)
References in periodicals archive ?
Space-time processing for MIMO communications. John Wiley & Sons, Ltd, pp.
Furthermore, the Space-Time Block codes provides temporal/spatial multiplexing and have been employed to enhance the reliability of MIMO wireless communication systems and improve the performance of MIMO communications [4].
Nguyen, "Clustering and power management for virtual MIMO communications in wireless sensor networks," Ad Hoc Networks, vol.
However, it is difficult to closely integrate multiple antennas into a compact space while maintaining good isolation between antenna elements to achieve channel separation, particularly for dual-band antenna arrays, and the efficiency of a MIMO communications system is affected by spatial correlations due to the mutual coupling of array elements [4-6].
[10.] Sibille, A., "Time-domain diversity in ultra-wideband MIMO communications," EURASIP Journal on Applied Signal Processing, Vol.
Mohan, "Characterize the indoor multipath propaga-tion for MIMO communications," Asia-Pacific Conference Proceedings, APMC 2005, Vol.
Cottis, "Multi-satellite MIMO communications at Ku-band and above: Investigations on spatial multiplexing for capacity improvement and selection diversity for interference mitigation," EURASIP Journal on Wireless Communications and Networking, Vol.
At the transport layer, TCP performance over MIMO communications was studied (22).
In [17] authors have presented a Pulse Position Amplitude Modulation (PPAM) Space Time Trellis Codes (STTC) for ultra wide band MIMO communications, though at the cost of higher receiver complexity.
Duman (Arizona State U.) and Ghrayeb (Concordia U., Canada) present 11 chapters covering topics such as: fading channels and diversity techniques, capacity and information rates of MIMO channels, space-time block and trellis codes, concatenated codes and iterative decoding, unitary and differential space-time codes, practical issues in MIMO communications and antenna selection for MIMO systems.
An overview of MIMO communications - a key to gigabit wireless, Proceedings of the IEEE international conference on communication, V.92, p.
* Scalable orthogonal frequency-division multiple access and support for MIMO communications technology for increased coverage, lower power consumption, and more efficient spectrum and bandwidth utilization.