MIMO in LTE (1)

MIMO is vital for LTE system's performance. From communication channel point of view, below transmission schemes can be used:

1) SISO - single input single output, in other word, non-MIMO

2) SIMO - A single data stream is input into the channel, multiple outputs from the channel, i.e. Rx Diversity. This is to mitigate the effect of multi-path fading by transmitting same information via multiple antennas. The multiple antennas created sufficiently de-correlated channels, therefore signals can be combined at the receiver end. MRC (Maximum Ratio Combining), SC(Selective Combining), EGC(Equal Gain Combining) or IRC(interference rejection combining) can be used at the receiver.

3) MISO - Multiple layer of data stream is input into the channel, single outputs from the channel, i.e. Tx diversity. Depends on the number of Tx antenna ports, SFBC(Space-Frequency Block Coded) or SFBC+FSTD(Frequency Switch Transmit Diversity) can be used for 2x or 4x Tx diversity respectively.

4) MIMO - Multiple-Input, Multiple-Output channel. At Tx side, serial to parallel mapping maps the data stream to multi-parallel streams, and at the Rx side, parallel to serial mapping combine the received data streams back into a single stream.