====== MIMO ======

Far user uses STBC scheme
Near user uses beamforming

===== Question: How to get Near user channel estimate? =====

===== Same linear precoder for Near and Far users =====
* linear precoder is a number of stream controller
* after equalization, scalar decoding
* if we beamform for near user, can we do nulling for far user

$Y_n = H_n\left( \sqrt{\alpha}\, U_n S X_n + \sqrt{1-\alpha}\, U_n X_f \right) + Z_n$

{{/home/alm002/nobackup/notes/RLT/Superposition_Encoding/MIMO/equation_01.png?type=equation}}

$H_n = V_n \Sigma_n U_n$

{{/home/alm002/nobackup/notes/RLT/Superposition_Encoding/MIMO/equation_02.png?type=equation}}

$V_n^+ Y_n = \sqrt{\alpha}\, \Sigma_n S X_n + \sqrt{1-\alpha}\, \Sigma_n X_f + Z'_n$

{{/home/alm002/nobackup/notes/RLT/Superposition_Encoding/MIMO/equation_03.png?type=equation}}


===== Only a linear precoder Near user =====
* decoding is not a piece of cake

$Y_n = \left( \sqrt{\alpha}\, U_n S X_n + \sqrt{1-\alpha}\, X_f \right) + Z_n$

{{/home/alm002/nobackup/notes/RLT/Superposition_Encoding/MIMO/equation_04.png?type=equation}}