LTE May Make Way For Massive MIMO

The energy use would also go down, said Marzetta: “If you double the number of antennas you can cut back the energy use by half.” Adding to that energy saving, the technology would also require a change in base station design, which would cut energy use further.

Reducing energy several ways

Hundreds of dumb antennas at the top of the mast would require managing with intelligence close by, so finally the intelligence in mobile phone masts would move up the tower, eliminating the wasteful transmission of high frequency signals and allowing the more efficient network backhaul to be extended up the tower, perhaps on fibre optics.

All that sounds unarguable, but this is still a concept, and only one of several options for the future of mobile networks, said Marzetta. Before anything like this could happen, the theory needs to be worked out fully, and other network technology companies need to get on board.

One drawback is it requires the networks to use the TDD scheme that shares network access by timeslots, instead of frequencies. TDD is out of fashion, said Marzetta, and operators are heavily invested in schemes using different frequencies – known as FDD.

(In an earlier stage of the contest to provide 4G networks, from which LTE emerged as the front runner, its rival WiMax was criticised for not meeting operators’ needs and providing an FDD option.)

Another option for future mobile network generations includes an increased use of femtocells and picocells, effectively using conventional network cells but making them smaller and cheaper and using very many more of them, so everyone has greater use of the cell they are attached to.

And finally, another option is “co-operative MIMO” where a MIMO effect is produced by using several base stations that might be several kilometres apart. This would provide a big separation of antennas which improves the power of MIMO, but it would require a lot of bandwidth between the base stations to co-ordinate their operation.

Network change in a recession

Whichever option happens, the change over is likely to be very slow indeed, of course. The roll-out of LTE is happening slowly, at least partly because many operators are still managing the change-over from 2G to 3G, and now face the fall-out of the recession.

LTE has reached the attention of governments (or at least the UK’s former Labour government) as a way to provide broadband to more citizens. However, most operators are still at the stage of testing the technology.

Dr Marzetta is hoping to gather support from other vendors and operators, and to this end has presented the idea of Massive MIMO in a paper (PDF) at the 2010 Communication Theory Workshop in Cancun, Mexico, in May.

Among the other technologies shown at the Open Day, was a cell tower which combines solar and wind power