MMwave provides food for thought for operators, amid 5G testing spree

Features

ETSI has singled out mmwave as the joker in the pack of 5G, with trials involving the technology surprising even seasoned industry veterans.

Speaking to Mobile Europe at 5G World this week, Adrian Scrase, CTO of standards body ETSI, said trials of spectrum above 6GHz had been throwing up some surprising results, but crucially ones that could ultimately benefit 5G.

He said: “Those who are experimenting with the millimetric wave bands (above 30GHz) are saying that in general they perform better than they first thought, but they perform differently from how they first thought."

Scrase said the initial consensus these bands would solely be line of sight was misguided. He said: “What they’ve shown from the trials is that they are not line of sight, they do behave in very strange ways and they tend to bounce off buildings.”

While this throws up the potential for more complex interference models, Scrase said this could be hiding benefits. He explained: “You can actually very carefully gain benefit from that, so where you don’t have line of sight between two objects, if you can’t see them directly you bounce off an object to cover that particular part of the geography.”

This quirk is feeding back into work on the standard. LTE included built-in interference cancellation called Coordinated Multiple Point (CoMP). An advanced version of this will have to be included in the 5G standard for the mmwave bands, said Scrase.

However, this quirk also does raise issues for operators and vendors centring on latency. He said: “You’ve also got a timing issue because any form of interference cancellation is fine, but if you are trying to have very low latency you can’t have any loss in time to do that cancellation.”

By contrast, tests in the sub-6GHz bands have been relatively plain sailing but Scrase said some performance had been higher than originally expected. 

Findings presented at the trade event in London by Nokia’s Head of 5G Technology David Soldani supported Scrase’s claim of good performance in the lower bands.

A standout figure was the spectral efficiency gain achieved in the 3.5GHz band compared with the baseline for comparison, 2X2 LTE with cross-border antenna. This provides a spectral efficiency of 2bit/s/Hz.

However, in Nokia’s trials with 3.5GHz using 2x2 or 4x2 Massive MIMO, the vendor managed to achieve spectral efficiency of 4bit/s/Hz.

At the same seminar, Leo Lundy, Group CTO of Irish operator Imagine Communications highlighted results from the company’s roll-out of TD-LTE. This technology uses unpaired spectrum and dynamic capacity allocation is considered a bridge between LTE and 5G.

However, Imagine was less bullish about the potential of MIMO. Asked by Mobile Europe what had surprised him about the roll-out, he said the impact of that technology on network performance had been “disappointing”.

“In our deployments MIMO gave very little uplift. It makes very little difference.”