On downlink beamforming with small cells in wireless heterogeneous systems

In this letter, we study downlink beamforming for wireless heterogeneous networks with two groups of users. The users in one group (group 1) are supported by the smallcell base station (SBS) as well as the macrocell base station (MBS), while the users in the other group (group 2) are supported by the MBS only. The MBS is equipped with an antenna array for downlink beamforming. We formulate a convex optimization problem, which can be solved by semidefinite programming (SDP) relaxation, for downlink beamforming that takes advantage of the presence of the SBS for group 1, but also takes into account the interfering signal from the SBS for group 2.