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Deployment of small moving cells (SMCs) has been considered in advanced cellular systems, where wireless backhaul links are required between base stations and SMCs. In this paper, we consider signal transmission by means of multiuser beamforming in the wireless backhaul link. We generate the beam weight in an eigen-direction of weighted combination of short- and long-term channel information of the backhaul link. The beam weight can maximize the average signal-to-leakage-plus-noise ratio (SLNR), while providing the transmission robust to SMC mobility. We analyze the performance of the proposed scheme in terms of the average signal-to-interference-plus-noise ratio (SINR) and optimize the transmit power by iterative water-filling. Finally, we verify the performance of the proposed scheme by computer simulation.

In this paper, we consider multi-user signal transmission by means of zero-forcing (ZF) beamforming with an aid of user grouping in spatially correlated massive antenna environments. For the user grouping, we exploit transmission performance loss (TPL) due to nulling out inter-user interference. We partition users into a number of groups so that users in each group experience low TPL. We transmit user signal in each group by means of ZF beamforming, while allocating transmission resource to user groups in an orthogonal manner. Finally, we verify the performance of the proposed scheme by computer simulation.

In this paper, we design a complexity-reduced transmission scheme in massive antenna environments. To reduce the implementation complexity for the generation of beam weight, we design a multi-user parameterized beamforming (MUPB) scheme that can control the beam direction using a single parameter with combined use of maximum ratio transmission and partial zero-forcing scheme that partially nulls out interference. We design the MUPB to maximize the signal-to-leakage plus noise ratio (SLNR). To further reduce the implementation complexity, we optimize the MUPB based on approximated SLNR instead of accurate SLNR. Finally, the performance of the proposed MUPB is verified by computer simulation.

A small moving cell (SMC) system is proposed to be a potential system in the next-generation cellular system. However, it is challenging issue to provide wireless backhaul links to the SMCs which may have high mobility. In this paper, we propose statistical beamforming (SBF) technique to provide the wireless backhaul links in massive MIMO systems. Unlike most of the conventional SBF schemes, we consider multiple antennas at the receiver side where the base station (BS) needs to determine the proper number of SBF beams. We first determines candidates of SBF beams as eigenvectors corresponding to dominant eigenvalues of channel correlation matrix (CCM). The average achievable SINR can be estimated using a Monte-Carlo sampling process without ST-CSI at the BS, then the proper beams and the transmit powers are adjusted by iterative water-filling algorithm. The simulation results show that the proposed SBF scheme is quite feasible for the wireless backhaul of SMCs in high mobility without the feedback of short-term channel information.