Jianshu Zhang 0002 Sergiy A. Vorobyov Arash Khabbazibasmenj Martin Haardt Sum rate maximization in multi-operator two-way relay networks with a MIMO AF relay via POTDC. 1-5 2013 EUSIPCO https://ieeexplore.ieee.org/document/6811690/ conf/eusipco/2013 db/conf/eusipco/eusipco2013.html#ZhangVKH13