5.5.3 The optimum detector Note that f(rs,)is usually called likelihood function. Maximum-likelihood (ML):to select the s,that max the f(rs,). Denoted by, =arg max,(f(rls) Obviously,when the symbols are equally probable,we have,ML=MAP Equally-probable case is very common,thus ML is widely used in practical. Let PM(r,s)=f(rs)P(s) MAP is equivalent to:sm=arg max、PM(r,sm） The Optimum Detector: Maximum a posterior probability (MAP):to s MAP: Max a posterior probability s,that max the P(sr).Denoted by, ML: Maximum-likelihood Min-Dist Minimum-distance s =arg maxs (P(sIr) Max-Corr:Maximum Correlation Note that P(s,r)is often called a posterior probability. UESTC-Digital transmission through the AWGN channel Prof李晓峰 11