Maziar Sanjabi Meisam Razaviyayn Zhi-Quan Luo Optimal Joint Base Station Assignment and Beamforming for Heterogeneous Networks. 1950-1961 2014 62 IEEE Trans. Signal Process. 8 https://doi.org/10.1109/TSP.2014.2303946 db/journals/tsp/tsp62.html#SanjabiRL14