Field trials using coordinated multi-point transmission in the downlink

We report on field trials using CoMP transmission in the downlink of a mobile radio network. Two new features enable over-the-air CoMP transmission from physically separated base stations and terminals. These are distributed synchronization and a fast virtual local area network. Using VLAN tags, terminals feed back the multi-cell channel state information to their serving bases where it is multiplexed with shared data. Both are multicast to other cooperative base stations over the backhaul. In our trials, two terminals are served in two overlapping cells and placed in specific indoor, outdoor-to-indoor and outdoor scenarios. We have realized both intra-site as well as inter-site CoMP. While outage is indeed a big problem at the cell edge with full frequency reuse, with CoMP it is not observed anymore. Average throughput gains by factors 4 to 22 are observed when using CoMP compared to interference-limited transmission while between 27 and 78% of the isolated cell throughput is measured in both cells simultaneously.