Massive MIMO is one of the candidate technologies being considered for inclusion in the 5G specifications and has shown real progress in the lab. For those not familiar with the concept, Massive MIMO takes MIMO to an extreme using hundreds of antennas at the base station utilizing full spatial multiplexing - multiple data streams are transmitted at the same time using the same frequency. Ideally, base stations could be constructed with hundreds of low-cost antennas rather than the sectorized high power remote radio heads widely used today to enhance coverage, improve power efficiency and attain higher spectral efficiency.
Last year, researchers at the University of Bristol in the UK and Lund University in Sweden demonstrated a 128 antenna Massive MIMO base station prototype (128 receive and 128 transmit antennas) to produce an astounding 146 b/s/Hz spectrum efficiency mark in just 20 MHz of spectrum. An impressive milestone, no doubt, but of course, these tests were conducted in the controlled environment of the lab.
British Telecom (BT), the largest provider of telecommunications services in the UK, took note of this work and reached out to Professors Mark Beach and Andrew Nix at Bristol to test their Massive MIMO prototype in more demanding environments. Instead of a controlled lab, BT sought to test the system in a variety of different scenarios including both indoor and outdoor settings.
The Bristol team took their system on the road to BT’s Adastral Park campus where the initial experiments were staged in a large exhibition hall. The first test implemented 12 data streams in a single 20MHz channel at 3.5 GHz 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. Outdoor test showed similar results at a range of 20 meters.
In another experiment, the prototype supported 24 simultaneous user uplink streams each using 64QAM on the same radio channel with all modems synchronizing over-the-air to achieve a spectrum efficiency of just less than 100bit/s/Hz and an aggregate capacity approaching two Gbits/s in this single 20MHz wide channel. Not quite the results that Bristol and Lund demonstrated in 2016 in their labs but clearly close enough to justify the excitement of the promise of Massive MIMO and its potential impact on our wireless networks.
Collaborations between universities and industry are vitally important to moving innovative research forward, and this work between BT and Bristol is a great example of this type of collaboration to move Massive MIMO from theory to reality. Expect to see more of these types of partnerships as we continue down the road to 5G.