Tight geometric bound for Marcum Q-function

A new geometric bound is proposed for the Marcum Q (MQ)-function. The proposed bounds are derived by the geometric interpretation of the first-order MQ-function, Q(a,b). It has been shown by previous researchers that Q(a,b) can be viewed as the probability that a complex, Gaussian random variable Z with real, nonzero mean lies outside of a circular region. Based on the interpretation, the new multi-sectors bound proves to be very tight and outperforms all previously proposed bounds.