In particular, the transformation relies on a reversal of the decoding and
encoding orders. For example, if users on the MAC are decoded in order starting
with user 1 and ending with user K (so that user K sees no interference),
then the users on the BC are encoded in reverse order from user K to user 1
(so that user 1 sees no interference). With this decoding order, the rate for
user k on the MAC is