The Capacity Loss of Dense Constellations
  We determine the loss in capacity incurred by using signal constellations with a bounded support over general complex-valued additive-noise channels for suitably high signal-to-noise ratio. Our expression for the capacity loss recovers the power loss of 1.53dB for square signal constellations. 
Tobias Koch, Alfonso Martinez and Albert Guill\'en i F\`abregas
cs.IT math.IT