Massive MIMO Multicasting in Noncooperative Cellular Networks

Abstract

We study the massive multiple-input multiple-output (MIMO) multicast transmission in cellular 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 show that when each BS knows the perfect channel state information (CSI) of its own served users, the asymptotically optimal beamformer at each BS is a linear combination of the channel vectors of its multicast users. Moreover, the optimal combining coefficients are obtained in closed form. Then we consider the imperfect CSI scenario where the CSI is obtained through uplink channel estimation in timedivision duplex systems. We propose a new pilot scheme that estimates the composite channel which is a linear combination of the individual channels of multicast users in each cell. This scheme is able to completely eliminate pilot contamination. The pilot power control for optimizing the multicast beamformer at each BS is also derived. Numerical results show that the asymptotic performance of the proposed scheme is close to the ideal case with perfect CSI. Simulation also verifies the effectiveness of the proposed scheme with finite number of antennas at each BS.Comment: to appear in IEEE JSAC Special Issue on 5G Wireless Communication System

Hybrid Multicast Transmission for Public Safety Network in 5G

“…Consider the perfect CSI scenario for simplicity; the multicast problem is formulated as the max-min fairness (MMF) problem [10] as follows: …”

“…The block diagonalization (BD) precoding algorithm is derived with the same manner as the null space method based interference cancellation method from (9) and (10), where the precoding matrix Ω 0,BD guarantees that the precoded channel matrix of a specific FR lies within the null space of the joint channel matrix of other FRs in the same group; hence interferences from all other FRs are eliminated. The mathematical notations are similar to (9) and (10) and are omitted for simplicity.…”

“…In this work we investigate the multicast for PSN in 5G scenario by focusing on the 3D massive MIMO channel model based on the mutual coupling channel model. In the form of physicallayer multicast beamforming, multicast can significantly increase system capacity and spectrum efficiency [7][8][9][10][11][12][13]. In terms of theoretical analysis, the general wireless multicast beamforming problem is NP-hard problem.…”

“…In terms of theoretical analysis, the general wireless multicast beamforming problem is NP-hard problem. In massive MIMO scenario, this problem can be solved in asymptotic analysis with closed-form solutions [10,11], which is important for the design for PSN. Existing literatures have focused on the asymptotic analysis for multicast problem under both perfect channel state information (CSI) scenario and imperfect CSI scenario, which are performed under Rayleigh fading channel model.…”

“…The optimization of hybrid unicast/multicast precoding is barely investigated and highly challenging. As indicated in [10], even the multicast beamforming problem by itself is already NP-hard, and its optimal solution cannot be obtained efficiently in general. For this reason, this work focuses on the development of a heuristic approach based on null space interference cancellation.…”