Hybrid Beamforming for Reduction of Inter-Beam Interference in Millimeter-Wave Cellular Systems

In millimeter-wave (mm-wave) cellular systems, beamforming antennas are necessary at both the base station ( ) and mobile station ( ) to compensate for high attenuation in mm-wave frequency bands and to extend the transmission range. The beamforming antennas also allow each to serve a number of s simultaneously, providing a substantial gain in system capacity. In space-division multiple access (SDMA) systems, the challenge is the inter-beam interference (IBI) caused by adjacent beams that are formed by the in the same cell and in neighboring cells. The beams that are formed toward in each cell may generate significant interference to in neighboring cells, especially for MSs at the cell boundary. In this paper, we propose four different digital precoding techniques (Type-1, Type-2, Type-3, and Type-4) to reduce IBI in mm-wave cellular systems with a hybrid beamformer. Simulation results show that the proposed techniques can reduce the IBI in mm-wave cellular systems effectively, compared with a single-cell multiuser case.