@article {ValcarceMosqueraTCOM08, title = {Cramer-Rao Lower Bound and EM Algorithm for Envelope-Based SNR Estimation of Nonconstant Modulus Constellations}, journal = {IEEE Transactions on Communications}, volume = {57}, number = {6}, year = {2009}, month = {june}, pages = {1622 - 1627}, author = {Wilfried Gappmair and R. L{\'o}pez-Valcarce and C. Mosquera} }