sentences:  Let sk denote the "k"th user transmit symbol vector.For user "k", a linear transmit precoding matrix, Wk, which transforms the data vector sk to the "M" ×1 transmitted vector Wk × sk, is employed by the BSs.The received signal vector at the "k"th user is given by formula_1,
  
  where nk" = ["nk,"1, …, "nk,Nk" ]T denotes the noise vector for the "k"th user, and (.