(70) The maximum σ/σ w value can be obtained as σ σ w = min η OSNR φ (2 γς ) - φ (2 γ (1 - ς )) - 2 γς Φ ( - 2 γς ) + 2 γ (1 - ς )Φ ( - 2 γ (1 - ς )) + 2 γς , η DSNR 2 γ .