Joint transmission mode and tilt adaptation in coordinated small-cell networks

We study downlink transmission in a wireless network consisting of small-sized cells, denoted as a small-cell network (SCN). We consider multi-antenna base stations (BSs) and single-antenna users, BS coordination, 3D antenna patterns, and fair scheduling. We investigate the impact of the elevation angle of the BS antenna pattern, denoted as tilt, on the performance of the considered SCN when employing either a conventional uncoordinated transmission mode or a fully coordinated transmission mode. Using the results of this investigation, we propose a novel hybrid-mode transmission technique that can achieve a performance comparable to that of a fully coordinated transmission but with a significantly lower complexity and signaling requirement. The main idea is to divide the coverage area into two so-called vertical regions and jointly adapt the transmission mode and the tilt at the BSs when serving each region. A fair scheduler is used to share the time-slots between the vertical regions and among the users in each region.