5G communication technologies promise instant downloads of video content to mobile devices, online games with minimal delays, video communication without clutter and squares, and many other delightful things. These include smart factories, smart auto-pilot cars and trains, and countless IoT devices that improve human life in every corner of the planet. One of the 5G-related areas in which Toshiba engineers work is ultra-fast wireless technologies. Their implementation in the future will eliminate the need to lay a fiber-optic cable between base stations of fifth-generation networks. In this post, we will tell you how we managed to implement a wireless connection at a speed of 20 Gbps.
How does it work now?
The fifth generation communication system consists of subscriber devices that connect to base stations using wireless technologies (access level link), base stations that transmit a signal from the subscriber device to the network core (transit link), and the network core itself, in which processing is performed. signals and routing of data streams from subscriber to subscriber and from subscriber to the Internet.
The standard scheme of the cellular network. Source (hereinafter): Toshiba
The core of the network receives data and provides security management. Disruption of the link between the base station and the core of the network will lead to a break in the connection, so the backhaul connection must be very reliable and maintain a high speed so that there are no delays.
In 2016, when Toshiba first began work on increasing 5G speeds, most of the research in this area focused on improving the speed of the access channel. However, the ultra-high speed of 5G requires the simultaneous increase in the bandwidth of both the access channel and the backhaul channel.
What's on offer?
Traditionally, backhaul connections have been implemented using optical fiber. Compared to other countries, Japan has many fiber optic networks, but laying them in mountainous areas is difficult and very expensive, and in order to provide 5G communications in the mountains, new base stations would have to be installed in such areas, which would further increase costs. Therefore, Toshiba engineers focused on replacing fiber backhaul links with wireless ones.
Wireless backhaul network
The question was how to achieve the ultra-high speed required for 5G networks. The most common of all methods is to increase speed by expanding the bandwidth. Frequencies for 3G and 4G are no longer enough for this. It was necessary to move to higher frequencies - to millimeter waves.
Difficulties of transition to millimeter
Millimeter waves from 28 GHz have never been used for mobile communications before. The main problem faced by the developers is that millimeter waves can only travel a short distance. The first attempts to use them were a struggle to ensure that they finish off at least a kilometer. Building a network in which many base stations are located close to each other will require huge infrastructure costs, and this will nullify the savings from replacing fiber optic links with wireless ones.
To improve communication quality and data transfer rates, the Toshiba team decided to use Multiple Input Multiple Output (MIMO) technology. MIMO uses multiple antennas at the transmitter and receiver to increase speed by transmitting multiple signals at the same time. Radio waves bounce off buildings and other physical obstacles and reach the receiving antennas at different angles. MIMO technology provides fast and stable communications in these environments by using reflections from radio waves to improve performance.
However, in conditions of mountainous terrain, the antennas were planned to be installed at the highest points, which meant that there were practically no physical obstacles to the reflection of radio waves. The second difficulty was the need to focus the millimeter waves into a narrow beam to increase the distance of stable communication. This further reduced the reflection.
Given the limitations described, taking advantage of MIMO's advantages to increase speed and throughput has proven to be difficult. To solve the problem, Toshiba engineers decided to use polarized MIMO (Polarized MIMO) technology, which stabilizes and accelerates signal transmission by separating radio waves into waves with vertical and horizontal polarization.
Using Polarized MIMO for Backhaul
Splitting the signal into two waves allows two independent connections to be established and provides a stable link at double the speed. Toshiba was not the first company to try to use Polarized MIMO for organizing a communication channel, but all researchers reported that they could not provide a sufficiently high transmission speed at distances of more than one kilometer: the next problem was not signal attenuation, but a large amount of interference.
When transmitting signals at a standard 5G speed of 20 Gbit / s, the volume of transmitted information is much larger than in previous generation networks. Sending large amounts of data leads to the fact that even the slightest interference is a problem, especially in conditions of wide bandwidth in the millimeter wave range. Correction of wideband distortion was required when using Polarized MIMO. Broadband distortion correction technologies were pioneered in digital TV broadcasting, which Toshiba has been involved in for over 20 years in research and development in digital broadcasting and wireless LANs.
The combination of Polarized MIMO and wideband distortion correction methods was a breakthrough: tests showed that the technology of organizing wireless backhaul links is almost ready for use in a 5G environment - at least in laboratory conditions everything worked perfectly. It remained to conduct field tests in open areas, but this also arose difficulties: for the transmission of millimeter-wave waves, according to Japanese legislation, it was required to obtain a permit, and it is extremely difficult to obtain it. In this regard, it was decided to conduct field tests in the UK, at the Bristol Research & Innovation laboratory, which is run by Toshiba Europe.
Field trials
To test the development, the transmitter was installed on the roof of the University of Bristol, and the receiver was installed on a building 900 meters away. To simulate an actual distance of five kilometers, an attenuator was installed on the receiver side.
Location of the transmitter and receiver on the ground
Before the experiments, it was necessary to ensure a clear focusing of the transmitter and receiver. It had to be done by eye, and it was not easy, since even the searchlights are difficult to focus, and the radio waves are also invisible. In addition, every day in the morning, equipment had to be installed and re-configured, and removed from the roof in the evening.
Photos from the field test site of super speeds for 5G
Three days before the planned end of their stay in the UK, the researchers finally reached a stable speed of 20 Gbps.
What to expect in the future
Following the presentation of the technology at a scientific conference in December 2019, the Toshiba team continued to work to make the experimental designs commercially exploitable. This requires taking into account many factors, for example, the influence of wind and rain, temperature and humidity.
The evolution of mobile wireless technology is steadily moving forward. Engineers are already looking beyond 5G and are discussing a transition to 6G in the 2030s. Mobile coverage is projected to reach outer space in the 6G era. Toshiba will work with others in this process to create technologies for people around the world to provide stable, high-speed communications over long distances, wherever you are.