Friday, September 28, 2012


To multiply throughput of a radio link, multiple antennas (and multiple RF chains accordingly) are put at both the transmitter and the receiver. This system is referred to as Multiple Input Multiple Output (MIMO). A MIMO system with similar count of antennas at both the transmitter and the receiver in a point-to-point (PTP) link is able to multiply the system throughput linearly with every additional antenna. For example, a 2x2 MIMO will double the throughput.

                                             Fig: Multiple Input Multiple Output (MIMO), 2x2
                                            Two antennas at both the transmitter and the receiver.

         MIMO often employs Spatial Multiplexing (SM) to enable signal (coded and modulated data stream) to be transmitted across different spatial domains. Meanwhile, Mobile WiMAX supports multiple MIMO which will maximize spectral efficiency (increase throughput) without shrinking the coverage area. The dynamic switching between these modes based on channel conditions is called Adaptive MIMO Switching (AMS). If combined with AAS (Adaptive Antenna System), MIMO can further boost WiMAX performance.  

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