MIMO = Multiple Input Multiple Output
  • 2 or more transmitters and 2 or more receivers.
  • MIMO transmits several streams whereas SIMO or MISO transmits only one stream.
  • If there are N streams, there will be at least N antennas (here only 2).
  • By spatially separating N streams across at least N antennas, N receivers
    will be able to fully reconstruct the original data streams
  • MIMO requires N antennas in transmitter and receiver and by this way it can transmit N streams in the same radio resources on the same time. Currently, N=2 and there are 2 2 antennas on the eNodeB and 2 antennas on the UE.
  • It allows to transmit 2 TB (Transport Block) on the same subframe for a given UE and by this it boosts the radio performance
  • The transmissions from each antenna must be uniquely identifiable so that each receiver can determine what combination of transmissions has been received. This identification is usually done with pilot signals, which use orthogonal patterns for each antenna.
  • There are several MIMO methods.
    The stream are sent on the same time, on the same frequency.
  • Each antenna on the receiver receives the 2 TB (the red and the blue one). There are able after to separate them. 
  • The 2 TB are same on the same time and on the same frequencies (PRB). The receiver can separate them because it knows the characteristics of transmission for each antennas in real time. There are a lot of RE use for the reference signal of each antenna to allow the UE to distinguish them. 
  • If the UE is not able to separate the 2 TB (because the 2 transmission paths are not enough different or the radio condition are bad) the transmitter send the same TB on the 2 antennas.