NEC says it achieved multiple highly-stable simultaneous terminal connections and transmission capacity in a real office environment through distributed-MIMO in the 28GHz millimetre-wave frequency band.

The distributed-MIMO approach differs from massive-MIMO in that it uses a large number of antennas spread around an area, as opposed to a single array of many antennas.

Approximately three times the number of simultaneous connections and transmission capacity was achieved when compared to cases without distributed-MIMO in the 28GHz frequency band, according to the company.

Furthermore, transmission deterioration from obstacles was also reduced.

Challenges in applying massive-MIMO techniques in the millimetre-wave band include difficulty in achieving stable connections and spatial multiplexing due to the characteristics of radio waves, such as short wavelength and large attenuation due to reflection and shielding.

NEC has already commercialised massive-MIMO in the sub 6GHz frequency band. The propagation and transmission trials in a real office environment using a distributed-MIMO technique for the radio units of a 28GHz band base station system, demonstrated simultaneous connections with multiple terminals and increased capacity.

NEC's approach calibrates and coordinates phase and amplitude between distributed antennas, resulting in approximately three times the number of simultaneous connections and transmission capacity when compared to cases where a distributed-MIMO system is not used.

Further demonstrations are planned to show how stable and high transmission speeds can be achieved in environments where stable millimetre-wave communication is difficult due to obstacles and densely arranged terminals, such as in stadium seating.