国家重点实验室 o The bad channel W W:U1→(Y,Y2) ⊕ W C(W）=I(UY,Y) 随机U2 W The good channel W+ W+:U2→(Y,Y2,U) U W C(W)=I(U:Y,Y,U) U2 W 13 The bad channel W￾The good channel W + 13 1 12 W U YY : (, ) − → CW IU YY ( ) = ;, ( ) 112 − 2 12 1 W U YYU : (, , ) + → ( ) ( ) CW IU YY U = ;, 212 1 +