Aman Jain Sanjeev R. Kulkarni Sergio Verdú Minimum energy per bit for Gaussian broadcast channels with common message and cooperating receivers. 740-747 2009 Allerton https://doi.org/10.1109/ALLERTON.2009.5394932 conf/allerton/2009 db/conf/allerton/allerton2009.html#JainKV09