“…According to the constraint (22), only one UL user and one DL user can be scheduled over subcarrier k. Assuming that the scheduled UL user is U m k and the scheduled UL user is D n k , we have s m k ,B,k D s n k ,B,k D 1 and s m 0 ,B,k D s n 0 ,B,k D 0 for m 0 ¤ m k , n 0 ¤ n k . In this case, the constraint (27) can be simplified to Pr˚˛m k ,n,k p m k ,B,k 6 n,k « > 1 , for n D n k and 8k (B.1) Pr˚0 6 n 0 ,k « > 1 , for n ¤ n k and 8k (B.2)…”