LTE May Make Way For Massive MIMO

While the world waits for LTE (or “4G”) to replace today’s 3G mobile phone networks, scientists are concocting the next generation after LTE – and it could use base stations constructed from hundreds of cheap antennas, which save energy by beaming signals directly to phones.

The idea – still a concept in the minds of researchers – would require a big change in the way networks are provided, but could provide a huge increase in throughput along with massive energy savings, according to its champion Tom Marzetta, group leader of Bell Labs’ communications and signal processing research group in New Jersey.

MIMO to the extreme

“It’s MIMO to the extreme,” Marzetta said to eWEEK Europe when we met him at an open day run by Bell Labs in France.

If that location is a surprise, the venerable research unit – which was actually set up by Alexander Graham Bell, and has been owned by AT&T for the greater part of its life – is now owned by Alcatel Lucent, and has a French location at Villarceaux just south of Paris.

At the open day, various research projects strutted their stuff, with high-tech demonstrations. But Marzetta, presenting a theoretical view of the next-but-one generation of wireless, was armed only with a flip-chart.

MIMO (multiple input multiple output) uses several antennas at both ends of the link, to create multiple channels between the devices. It’s well understood and included in the latest (IEEE 802.11n) version of  Wi-Fi.

Marzetta’s idea, tentatively called “large scale MIMO” or “Masive MIMO” uses even more antennas on the base station but “shares” the throughput gains between many terminals.

Using 20MNHz of spectrum, a Massive MIMO base station could have a throughput of 1200Mbps per cell, compared with 74Mbps per cell with LTE, said Marzetta. Each Massive MIMO unit would deliver 60bps per Hz of frequency

This would be delivered by around 400 antennas, which could serve about forty phones with 28Mbps each, forming tight beams to each one, either directly by line of sight, or using scattering and reflection.

The uplink would also be massively faster than today’s technology, because the Massive MIMO station would be a good listener as well as a good talker, sorting out directional signals from the phones using it.