Woo Jin Shin Dong In Kim Penalized iterative waterfilling algorithm for multi-cell and multi-user OFDMA systems. 2245-2249 2009 PIMRC http://dx.doi.org/10.1109/PIMRC.2009.5450204 conf/pimrc/2009 db/conf/pimrc/pimrc2009.html#ShinK09