03 December 2019

Is there a poor mobile signal? In that case, buy a few metres of radio stripe and set it up where it's practically invisible. Researchers at LiU and Ericsson have developed patented technology to make this possible: antennas by the metre.

Giovanni Interdonato and Emil Björnson
Giovanni Interdonato and Emil Björnson Anna Nilsen
The mobile technology currently available works well when the conditions are good. But needs are changing and increasing as the technology improves. It may happen that your mobile fails to find a signal immediately when you want to pay for parking, or that a video suffers from lag before reaching the end. This is often a result of position: you are midway between two mobile masts, and the coverage is poorer there.
“This is a limitation of the current technology: it’s inevitable that the signal is weaker between masts, and at indoor locations”, says Emil Björnson, associate professor of communication systems at LiU.

The most recent antenna technology, known as “Massive MIMO”, uses many small antennas that jointly direct the signal towards the user, and this helps, but problems remain. One solution is to install many distributed antennas much closer to the users, but this brings with it the need for miles of cables and some type of highly complex processing unit. Further, this may not be possible in some locations, or indoors where many people or units are gathered in a small area, such as a sports arena, shopping centre or large factory.

Radio stripe in printed electronics

Emil Björnson, together with the industrial doctoral student Giovanni Interdonato, Professor Erik G Larsson and researchers at Ericsson, has now come up with a concept for a radio stripe, based on printed electronics. The stripe holds antennas, processing units and the necessary power supply.

“We placed the antennas and processing units in the cable. We already know how to deliver power through network cables, and we just need to extend that technology”, says Emil Björnson.

The radio stripe can be mounted anywhere it is needed, even in sites of architectural heritage where mobile masts are definitely not welcome, in shopping centres, and in sports arenas. They then act as a supplement to the existing mobile masts. The stripe is thin, conformable, and can be easily hidden.

Radio stripe with processing unitThe higher frequencies the smaller components. Photo credit Anna Nilsen“With this new technology the signal is not directional, but comes from all directions at the same time. This means that we can use even lower power levels. Thus the signal is strong just in a small area, exactly where your mobile needs it.”

It will not be necessary to change the mobile phones themselves.
“No, the mobile doesn’t need to know how the network is arranged”, Emil Björnson assures us.

Mobile World Congress

The concept was on show at the Mobile World Congress trade fair in Barcelona in February this year, where it aroused considerable interest.
“Oh yes – most people said that the solution was innovative, but completely obvious when they saw how we had reasoned”, he says.

The researchers and Ericsson have applied for several patents to protect the technology.
“Of course, we don’t know exactly how the technology will develop, and we don’t know what people will need in the future, so we have applied for patents to cover broad areas. We believe that this change will be introduced in small steps. And even if I regard it as 6G technology, the radio strip can work with the 5G standard, just as the massive MIMO technology developed for 5G is currently being used for 4G.”

There is, of course, one snag. While the antennas used for the normal frequency bands of the current 5G technology, 3.5 GHz, are small, they are slightly too big to fit into a cable.

“But if we increase the frequency to 10 GHz or 28 GHz, as will happen in 5G because it increases the capacity for data traffic, all the components will fit into a cable. The advantage we gain is reliable connection everywhere with high data rates, and we eliminate areas with very poor coverage. Printed electronics is cheap and easy to install”, says Emil Björnson.

Wireless technology at these high frequencies, however, is susceptible to disturbances: the signal can be easily blocked by, for example, a hand.
“Since we have so many antennas that are well-separated, it will be difficult or nearly impossible to bring them all down by disturbance at the same time”, Emil Björnson assures us.

An overview of the invention and the results of the research has been published in the Journal on Wireless Communications and Networking, with the title “Ubiquitous cell-free Massive MIMO communications”.

Ubiquitous cell-free Massive MIMO communications
Giovanni Interdonato, Emil Björnson, Hien Quoc Ngo, Pål Frenger & Erik G. Larsson
EURASIP Journal on Wireless Communications and Networking, volume 2019, Article number: 197 (2019) doi 10.1186/s13638-019-1507-0

Radio stripe with processing unitRadio stripe with antennas and processing units. Photo credit Anna Nilsen

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