MIMO and MRC:-
o LTE system uses MIMO (multiple input multiple output) as advanced multiple antenna technique in order to achieve the ambitious requirements for throughput and spectral efficiency.
o maximal ratio combining (MRC) : is used to enhance link reliability in challenging propagating conditions when signal strength is low and multipath conditions are challenging.
Downlink MIMO:-
o a 2x2 configuration for MIMO i.e. 2 transmit antennas at the base station and 2 receive antennas at the terminal side.
o In downlink MIMO is used in two modes
- Spatial multiplexing: allows to transmit different streams of data simultaneously on the same downlink resource block(s) >>>> increase the data rate
- Transmit diveristy : Here the receiver will has many copies of the transmitted signal
- Transmit diveristy : Here the receiver will has many copies of the transmitted signal
- In case the channel conditions do not allow spatial multiplexing, a transmit diversity
scheme will be used instead, so switching between these two MIMO modes is possible
depending on channel conditions.
scheme will be used instead, so switching between these two MIMO modes is possible
depending on channel conditions.
Uplink MIMO:-
o Uplink MIMO schemes for LTE will differ from downlink MIMO schemes to take into account
terminal complexity issues.
o For the uplink, MU-MIMO can be used.
o Multiple user terminals may transmit simultaneously on the same resource block.
o This is also referred to as spatial domain multiple access (SDMA).
