Massive MIMO multicasting in noncooperative multicell networks

We study the massive MIMO (multiple-input multiple-output) multicast transmission in multicell networks, where each base station (BS) is equipped with a large-scale antenna array and transmits a common message using a single beamformer to multiple mobile users. We first consider the case when each BS knows the perfect channel state information (CSI) of all its served users. We show that the asymptotically optimal beamformer structure at each BS is a linear combination of the channel vectors of its multicast users. The optimal combination coefficients are also obtained in closed form. Then we consider the imperfect CSI scenario where each BS obtains the CSI through uplink channel estimation. We propose a novel pilot scheme that estimates the compound channel rather than the individual channels of multicast users in each cell. This scheme is able to completely eliminate pilot contamination. The optimal power control of pilot transmission is also derived. Numerical results show that the performance of the proposed pilot scheme with pilot power control is close to that of the perfect CSI case.