Comments on ´Simple formulas for SIMO and MISO ergodic capacities´

A recently published Letter rediscovers a simple closed-form expression for the ergodic capacity integral when the instantaneous signal-to-noise ratio (SNR) follows the gamma distribution with an integer shape parameter, i.e. the Erlang distribution. In this Comment, a few earlier references for the exactly same expression are pointed out and a precision problem is discussed, overlooked by the original Letter, affecting the direct application of the proposed formulas.