TY - JOUR T1 - Cramer-Rao Lower Bound and EM Algorithm for Envelope-Based SNR Estimation of Nonconstant Modulus Constellations JF - IEEE Transactions on Communications Y1 - 2009 A1 - Wilfried Gappmair A1 - R. López-Valcarce A1 - C. Mosquera VL - 57 ER -