Hundreds of antennas per base station.
Future Networks

Swarms of Antennas

With hundreds of antennas per base station, mobile network data rates are increasing dramatically, and Massive MIMO is an important component of 5G.
Sports fans have been able to experience concerts, basketball games, a solar eclipse and even the 2018 Winter Olympics in virtual reality. Data for broadband applications of this kind is transmitted via mobile networks. Video and music streaming are also increasing mobile data traffic significantly, as is information from more and more machines that relay their status or request a technician. Between 2017 and 2021 mobile data traffic will increase by nearly 50 percent per year, according to the Cisco Visual Networking Index. How are networks to cope with this increasing volume of traffic?
One way, of course, is a higher bandwidth, or wider frequencies across which data can be transmitted. But there are limits to the bandwidth mobile networks can use: physical, statutory and by sharing between network operators. Fortunately, the networks have potential for optimization elsewhere – in their number of antennas. And there is a technology that both business and sciences currently consider to be highly promising and are developing intensively. It is Massive MIMO and the principle on which it is based is simple: the more antennas, the more data is transmitted.

Massive MIMO Increases Network Capacity

Today’s LTE base stations mostly have just two antennas, but they already use MIMO (Multiple Input, Multiple Output) multi-antenna technology, which is standard in modern domestic WiFi routers. A helpful MIMO function is that data to be transmitted can be distributed between separate transmitter antennas and received by several receiver antennas. This way several terminal devices can be supplied simultaneously on the same frequency and more data can be transmitted. This physical separation of data flows is called spatial multiplexing.
In order to cope with masses of future data using the next generation mobile standard 5G, telcos and scientists aim to further boost the potential of MIMO by using hundreds of antennas per mobile network base station. Each antenna increases the data rate and number of possible users in a mobile radio cell.
5G Optimal Transmission Research at the HfTL
The new transmission standard 5G provides even higher bandwidths for even more broadband customers. Extensive high frequency research is required to ensure successful coordinated operation of mobile network interfaces.

Beamforming for Targeted Power

In addition to spatial separation of data transmission there is another reason why this is possible. It is known as beamforming. "The more antennas I have, the more I can bundle the transmission power and aim it at the individual user," says Dr. Michael Einhaus, who is working on the mobile network of the future at the University of Telecommunication in Leipzig, Germany. Several antennas send signals to a terminal device. When and how strongly they arrive provides information about the position of the terminal device and obstacles on the transmission route. This information enables the antennas to bundle their transmission power optimally toward the recipient instead of continuing to spread the radio waves in concentric circles. This procedure not only increases the data rate; it also uses less energy.

Field Trials: Up to Ten Times More Data

How high the potential is, remains to be seen. Compared with LTE, in field trials the data rate has been increased eightfold with 64 antennas and tenfold with 128 antennas. In September 2017 Deutsche Telekom and Huawei carried out a joint Massive MIMO field trial in the 3.5-gigahertz band with a bandwidth of 20 megahertz. They reached a transmission speed of 750 megabits per second, which can otherwise only be achieved by combining frequencies. By comparison, with LTE Telekom reaches a maximum download speed of 300 megabits per second depending on device and network development area.

Interaction of Base Stations

With hundreds of antennas per base station much more data can be transmitted via the same bandwidth.
The antennas target the terminal device directly with their transmission power rather than transmitting their radio waves in concentric circles. They thereby increase the data throughput and use less energy.
A number of challenges remain to be solved, of course. They include, for example, how to synchronize adjacent Massive MIMO base stations. “In a mobile radio cell, focusing transmission power precisely on the user works wonderfully well, thanks to the many transmission antennas,” Dr. Einhaus says. “But if the neighboring radio cell does the same they can easily meet and shoot each other down.” So mechanisms and algorithms are needed that coordinate base stations so that they support rather than interfere with each other. By 2020 the ITU, the U.N. telecommunications agency, aims to standardize 5G. Rollout of the new mobile standard will then begin, and with it that of Massive MIMO.

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