Remark 7 An initial feasible point of problem (38) is needed
to initialize Algorithm 2 that can yield a local optimum of
(38). The simple zero-forcing (ZF) beamformer, which nullifies
strong MUI and meanwhile satisfies the rate constraint of its
own user on the access link, can be used for initialization
since Z(0)
R,l , ∀l can be easily calculated via local information
exchange