Yusuke Ohwatari Anass Benjebbour Junichiro Hagiwara Tomoyuki Ohya Reduced-complexity transmit power optimization techniques for multiuser MIMO with per-antenna power constraint. 34-38 2008 Allerton https://doi.org/10.1109/ALLERTON.2008.4797532 conf/allerton/2008 db/conf/allerton/allerton2008.html#OhwatariBHO08