5G, Mobile Network

The road to 5G is still being paved and while advances have been made by a number of telecommunications companies and research groups, there is still a lot to be done before you will be able to experience 5G mobile network speeds through your handset.

In one such quest towards highly efficient 5G wireless connectivity, Universities of Bristol and Lund, National Instruments (NI), and BT, joined hands to undertake trials of a massive MIMO system at the BT Labs in Adastral Park, Suffolk.

The goals were to test massive MIMO spatial multiplexing indoors and improve the understanding of massive MIMO radio channels under mobile conditions with untethered devices. While carrying out these field experiments, the team obtained promising results indicating that this technology could offer spectrum efficiency figures in excess of the 100 bits/s/Hz mark, improving upon the capacity of today’s long term evolution (LTE) systems by ten times.

The engineers behind the trails expected that techniques such as massive MIMO, which offers full spatial multiplexing – where multiple data streams are transmitted at the same time and on the same radio channel – will become a crucial part of future 5G networks; the next generation of mobile technology. The research team assessed the performance of a 128 element Massive MIMO system operating at 3.5 GHz at BT’s Adastral Park campus.

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 ten unique video streams, plus two other spatial channels demonstrating the full richness of spatial multiplexing supported by the system.

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 un-tethered 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 circa two Gbits/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.

The experimental system uses the same flexible SDR platform from NI that leading wireless researchers in industry and academia are using to define 5G. To achieve accurate, real-time performance, the researchers took full advantage of the system’s FPGAs using LabVIEW Communications System Design and the recently announced NI MIMO Application Framework. As lead users, both the Universities of Bristol and Lund worked closely with NI to implement, test and debug this framework prior to its product release. It now provides the ideal foundations for the rapid development, optimization and evaluation of algorithms and techniques for massive MIMO.

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.

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