?
Q
2
0
]
(
13
)
With (6) and (13), a solution for ΔQj, i.e. the adjustments to the precode matrix can be expressed as:
ε[ΔQ1. . . ΔQNu]=?H+(HH+)?1M1??(14)
where ?H+(HH+)?1 is identified as the pseudo inverse of the aggregate channel and MI is identified as the interference or crosstalk matrix. We can make some important observations about this solution: The solution only depends on prior channel information, i.e. the channel H as it was during the latest sounding. There is no need to know the updated channel (as in (7)). This matrix can be stored and reused until the next sounding. The crosstalk matrix MI consists entirely of the interference channels as measured at the respective receivers. This information is already implicitly available in the current 11ac training sequence. The only new requirement is that this information has to be communicated back to the MU transmitter.
