MMSE Detector
We make the following assumptions in the following derivation. The source
bits of one user are uncorrelated with the past and future bits from itself
and all bits from other users. (i.e. 
).
The noise 
is white, and zero mean and uncorrelated with the source.
(i.e. 
and 
).
Where 
is a vector the length of 
with a 1 at index 
, and zeros elsewhere.
Now, set 
