But α1 cos θ1 = n1,I , α2 cos θ2 = n2,I , α1 sin θ1 = n1,Q, α2 sin θ2 = n2,Q are Gaussianrandom variables, zero-mean, variance σ2 F/2 and statistically independent. For convenience,define nI = n1,I + n2,I and nQ = n1,Q + n2,Q. They are two statistically independent Gaussian random variables with zero mean and variance σ2 F. Therefore (11.92) can bewritten as
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