National Instruments, BT and the universities of Bristol and Lund have teamed up to undertake field trials of a massive MIMO system at the BT Labs in England.

A research team, whose members were drawn from the group, assessed the performance of a 128-element massive MIMO system operating at 3.5GHz and the trials indicated that this technology could offer spectrum efficiency figures in excess of 100bits/s/Hz, improving upon the capacity of today’s long term evolution (LTE) systems by a factor of 10.

The experimental set-up used the National Instruments software-defined radio (SDR) platform that is being used to define 5G. The researchers programmed FPGAs using NI's LabVIEW communications system design and MIMO application framework.

The goals of the trials were to test massive MIMO spatial multiplexing indoors and improve the understanding of massive MIMO radio channels under mobile conditions with untethered devices. The trials were conducted in a large indoor hall mimicking a stadium environment and outdoors within the Adastral Park campus.

The system was also shown to support the simultaneous transmission of 24 user streams operating with 64QAM on the same radio channel with all modems synchronising over-the-air. It is believed that this is the first time such an experiment has been conducted with truly untethered devices, from which the team were able to infer a spectrum efficiency of just less than 100bit/s/Hz and a sum rate capacity of about 2Gbit/s in this single 20MHz wide channel.

In addition to the indoor trials, a series of outdoor experiments were conducted with the array at a height of around 20 metres. This enabled far-field array characterisation, multi-element handset performance as well as experiments to improve the understanding of the massive MIMO radio channel under mobile conditions to be carried out.

It is expected that massive MIMO, which offers full spatial multiplexing–where multiple data streams are transmitted at the same time and on the same radio channel–will be a fundamental part of 5G networks.

The researchers are now processing the data sets and aim to publish their findings in leading journals in the near future as well as adding enhancements to the system in preparation for further trials.

Initial experiments took place in BT's large exhibition hall and used 12 streams in a single 20MHz channel to show the real-time transmission and simultaneous reception of 10 unique video streams, plus two other spatial channels demonstrating the full richness of spatial multiplexing supported by the system.

See also: Massive MIMO wants to set 5G spectral efficiency »