Maximizing the AWGN-Channel Capacity of the GQAM Constellation with Two Degrees of Freedom

This paper studies the channel capacity of the discrete-input continuous-output channel in which the input signal constellation has a rectangular-grid shape and the noise is additive white Gaussian. The channel capacity of such a system depends on the two parameters defining the shape of the constellation and the signal-to-noise ratio. We study the capacity as a function of these variables.