MIMO (Multiple Input Multiple Output) Concept
In conventional wireless communication, when a single antenna was employed at the source and the destination, multipath effects were encountered due to obstacles in the transmission path such as buildings, hills etc. resulting in scattered wave fronts of the EM wave. These may then take different paths to reach the same destination which further accounts for fading of the signal at the receiver.
MIMO is a communication technique that makes use of multiple antennas at the source as well as the destination, allowing parallel transmissions to take place simultaneously at the same transmission frequeny with different data transmitted on differnet carriers. Since the data is transmitted at the same frequency on different carriers simultaneously, the signals must undergo large amount of interference. Actually, MIMO employs OFDM technique, where data is transmitted on orthogonal carriers, therefore no interference problem.
With such a system, the amount of output can be increased by simultaneously transmitting different streams of data on different transmitting antennas at the same time. The data streams may parallel mix up in the air but they can be recovered at the receiver’s end by the method of spatial sampling or multiple antennas at the receiver and corresponding signal processing algorithm.
MIMO, thus eliminates the troubles caused due to multipath propagation and in fact takes advantage of this effect. MIMO is an integral part of LTE and enhances the performance of the system. Although it adds complexity to the system in terms of processing and the number of antennas but it adds the advantage of achieving far high data rates than that achieved by OFDM and provides much improved spectral efficiency.