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Taking a Closer Look at MIMO Radio Systems (.PDF Download)

March 22, 2019
Taking a Closer Look at MIMO Radio Systems (.PDF Download)

This article introduces the rationale and techniques associated with multiple-input, multiple-output (MIMO) based communication systems. The communication impairments due to multipath channels are discussed to provide the base motivation for the application of the MIMO technique. In particular, it explores the use of orthogonal frequency-division multiplexing (OFDM) and spatial multiplexing for equalizing broadband wireless channels with non-selective fading.

Fading Channels

The presence of multiple reflections and multiple communication paths between two radio terminals causes signal fading impairments to a wireless-communication link. Both selective and non-selective fading exist. Non-selective fading happens when the frequency components over the signal bandwidth are dynamically attenuated by the same amount and do not create any signal distortion—only temporal signal loss. Selective fading is the case when smaller frequency segments of the signal’s spectrum are attenuated relative to the other remaining frequency segments. When this occurs, the signal spectrum is distorted, which in turn creates a communication impairment that’s independent of signal level.