国家重点实验室 Symmetry assumption and Capacity o Bhattacharyya parameter Z(wW)兰∑√W(y10)w(y1西 o The parameters C(W)and Z(W)are used as measures of rate and reliability. Define the decision region for message m,D=yAIf(y)=m For codes with two codewords,the error probability,when message 2 is transmitted,is P.(eI2)=∑Pw(ylx2) yeD For yeD1,Py(ylx)P(ylx2)for ML decoding 。经过简单处理，有P.(2)≤∑VRyx)R) yeD 进而P,(em)≤∑VP(yIx)P(y) known as the Bhattacharyya bound on error probability 7 Symmetry assumption and Capacity Bhattacharyya parameter The parameters C(W) and Z(W) are used as measures of rate and reliability. Define the decision region for message m, For codes with two codewords, the error probability, when message 2 is transmitted, is 经过简单处理，有 进而 7 ( ) ( | 0) ( |1) y Y ZW W y W y ∈   { | () } N m Y   =∈ = y y f m 1 2 ( | 2) ( | ) Pe P B N ∈ = y y x  For y ∈ 1, for ML decoding 1 2 (| ) (| ) P P N N yx yx ≥ 1 1 2 ( | 2) ( | ) ( | ) Pe P P B NN ∈ ≤ y y x y x  1 2 ( | ) ( | ) ( | ) P em P P B NN ≤ y y x y x known as the Bhattacharyya bound on error probability