  In this letter, the average mutual information (AMI) of generalized
quadrature spatial modulation (GQSM) is first derived for continuous-input
continuous-output channels. Our mathematical analysis shows that the
calculation error induced by Monte Carlo integration increases exponentially
with the signal-to-noise ratio. This nature of GQSM is resolved by deriving a
closed-form expression. The derived AMI is compared with other related SM
schemes and evaluated for different antenna activation patterns. Our results
show that an equiprobable antenna selection method slightly decreases AMI of
symbols, while the method significantly improves AMI in total.
