Field trials of downlink multi-cell MIMO

Multi-cell MIMO technique theoretically promises large improvement in spectral efficiency and fairness in cellular networks and is regarded as the key enabling technique for solving the troublesome issue of inter-cell interference. To evaluate its practical performance in the cellular network, we have implemented the real-time downlink multi-cell MIMO trial system operating over bandwidth of 20 MHz. The initial field trial indeed shows a significant spectral efficiency gain of downlink multi-cell MIMO over the traditional single-cell transmissions in an indoor deployment of two operating base stations and two terminals. Particularly, several principal operation modes of multi-cell MIMO are evaluated and compared in the field trial measurements, including coherent joint transmission (JT), non-coherent JT and interference nulling. The field trial results agree quite well with expectations from theory.