MIMO Wireless Channels: Capacity and Performance Prediction

Multiple-input multiple-output (MIMO) communication techniques make use of multi-element antenna arrays at both the TX and the RX side of a radio link and have been shown theoretically to drastically improve the capacity over more traditional single-input multiple output (SIMO) systems [2, 3, 5, 7]. SIMO channels in wireless networks can provide diversity gain, array gain, and interference canceling gain among other benets. In addition to these same advantages, MIMO links can offer a multiplexing gain by opening Nmin parallel spatial channels, where Nmin is the minimum of the number of TX and RX antennas. Under certain propagation conditions capacity gains proportional to Nmin can be achieved [8]. Space-time coding [14] and spatial multiplexing [1, 2, 7, 16] (a.k.a. BLAST ) are popular signal processing techniques making use of MIMO channels to improve the performance of wireless networks. Previous work and open problems. The literature on realistic MIMO channel models is still scarce. For the line-of-sight (LOS) case, previous work includes . In the fading case, previous studies have mostly been conned to i.i.d. Gaussian matrices, an idealistic assumptions in which the entries of channel matrix are independent complex Gaussian random variables [2, 6, 8]. The influence of spatial fading correlation on either the TX or the RX side of a wireless MIMO radio link has been addressed in [3, 15]. In practice, however, the realization of high MIMO capacity is sensitive not only to the fading correlation between individual antennas but also to the rank behavior of the channel. In the existing literature, high rank behavior has been loosely linked to the existence of a dense scattering environment. Recent successful demonstrations of MIMO technologies in indoor-to-indoor channels, where rich scattering is almost always guaranteed.
Definition:
MIMO is a technique for boosting wireless bandwidth and range by taking advantage of multiplexing.MIMO algorithms in a radio chipset send information out over two or more antennas. The radio signals reflect off objects, creating multiple paths that in conventional radios cause interference and fading. But MIMO uses these paths to carry more information, which is recombined on the receiving side by the MIMO algorithms.A conventional radio uses one antenna to transmit a DataStream. A typical smart antenna radio, on the other hand, uses multiple antennas. This design helps combat distortion and interference. Examples of multiple-antenna techniques include switched antenna diversity selection, radio-frequency beam forming, digital beam forming and adaptive diversity combining. These smart antenna techniques are one-dimensional, whereas MIMO is multi-dimensional. It builds on one-dimensional smart antenna technology by simultaneously transmitting multiple data streams through the same channel, which increases wireless capacity.