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[主观题]
A channel has all input x consisting of the numbers +1 and -1 used with the probabilities
PX(1)=PX(-1)=1/2.The output y is the sum of x and an independent noise random variable n with the probability density pn(n)=1/4 for -2≤n≤2 and pn(n)=0 elsewhere.In other words,the conditional probability density of y condition on x is given by pY|X(y|x)=1/4 for -2≤y-x≤2 and pY|X(y|x)=0 elsewhere. (1)Find and sketch the output probability density for the channel. (2)Find I(X;Y). (3)Suppose that the output is transformed into a new discrete random variable x defined z=1 for y>1;z=0 for -1≤y≤+1;z= -1 for y<-1.Find I(X;Z)and interpret your result. (4)For a discrete X,Y ensemble,let Z be a new ensemble with elements determined by the elements in the Y ensemble,z=z(y).Show that if P(x|z(y))=P(x|y),then I(X;Z)=I(X;Y).
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