The Role of Small Cells, Coordinated Multipoint, and Massive MIMO in 5G

5G will have to support a multitude of new applications with higher peak and user data rates, reduced latency, enhanced indoor coverage and more. This will be achieved by more flexible and larger spectrum usage. The present paper is aiming at advanced techniques for higher spectral efficiency and optimized cell-edge user coverage. We suggest a smart combination of three techniques that exploits obvious synergies and keeps the complexity low. The first pillar is a powerful interference mitigation framework based on joint transmission coordinated multipoint (JT CoMP). Second, densification of network nodes is achieved by integrating small cells seamlessly into this framework like macro-cells, to serve the expected traffic growth in ten or more years from now. Third, more antennas (massive MIMO) are used because they promise increased robustness and reduced complexity of interference mitigation, mainly due to vertical beam-forming effects. We highlight recent achievements in the transition from theoretical to practical concepts and note future research directions. We demonstrate in macro-plus-small-cell scenarios measured in Berlin that improved performance can be achieved by means of flexible clustering and efficient user selection. Moreover, we show in multi-cell scenarios measured in Stockholm that advanced channel estimation and prediction works very well also in the field.