Scientists from RUDN University have created a mathematical model of reliable microwave communication for mobile phones and other devices. The results of the research have been published in the special issue of the IEEE Journal on Selected Areas in Communications (JSAC) devoted to microwave communication and will be presented at the "Enabling Technologies, Applications, and Methods for Emerging 5G Systems" international conference at the University Mediterranea of Reggio Calabria (9-11 October 2017).

5G refers to the newest, fifth generation of mobile communication technologies, international standards of which are yet under development and scheduled for release by the non-profit consortium 3GPP in 2020. 5G networks will provide extremely reliable communication with transmission delays not exceeding one millisecond. Such are the requirements of the so-called tactile Internet where not only data but also haptic sensations are transmitted over the network. For example, a surgeon can remotely perform an operation with an artificial hand and sense a feedback within a thousandth of a second. Similar ultra-low delays are necessary for self-driving vehicles or virtual reality applications, for instance, in order to transmit a hologram of an interlocutor - a 3D image that accurately conveys emotions and gestures. The second feature of fifth-generation networks is the ability to support high user density: up to a million devices per square kilometer can connect to each other at an average speed of about 100 megabits per second. Thirdly, the peak speed in 5G networks may reach tens of gigabits per second.

On the verge of the 5G era, research aimed at enabling gigabit-rate transmission via millimeter wave channels (mmWave) is of enormous interest. mmWave technology is already used in static environments with stationary devices, in particular indoors, however its implementation in mobile networks with moving transceiving devices and where the coordination of several moving devices is required is problematic for a number of reasons. The announcement of the JSAC special issue on mmWave provoked a staggering response of the scientific community: in less than four months JSAC received 96 papers, the majority of which came from the most prominent research groups in the field. After a rigorous selection, 38 papers were published in two issues of the journal in July and September of this year, including the study conducted by an international team of scientists from the Royal College, London (UK), Tampere University of Technology (Finland) and RUDN University (Moscow, Russia).

"JSAC is one of the most reputable journals on telecommunications; in its field it is comparable to journal Nature. The impact factor of JSAC is over eight. JSAC accepts only cutting-edge research and does not publish anything that deals with accomplished projects. The editors are interested in what will be implemented in the future, and even in what might not be implemented, might not happen, that is, as a matter of fact, negative results," commented one of the co-authors, Konstantin Samuylov, Doctor of Technical Sciences, Professor, Head of the Institute of Applied Mathematics & Communications Technology of RUDN University.

"In our paper, we analyze the use of the microwave range in high-density urban mobile networks. This range allows to provide both ultra-high speed and ultra-high throughput communication to devices in rapid motion and in high-density conditions, for example on a busy street or in a large shopping center. However, the use of millimeter waves in such environments faces serious problems related to the quality of wireless communication. These include signal attenuation at relatively small distances, up to hundreds of meters, and connection sensitivity to line-of-sight blocking. The ultrashort wave transmitter is directed toward the receiver, and the radio channel is like a narrow cone of light: whenever there is a foreign object on its way (a person, a car, even a lamp post) the communication is blocked. By means of a mathematical model we seek to find ways to use the microwave range despite its limitations while maintaining quality," Prof. Samuylov said.

While one part of the international research team was working on structural issues and long-term prospects, the other was making simulators - software tools that technically model the system of the future. These were used by the scientists to solve the problem of communication reliability: how to maintain the communication between devices despite the discontinuous nature of the connection.

"It is said that by means of their models mathematicians get a glimpse of the future, but I would put it another way: we, mathematicians, rather provide support to those who try to do so. First, a system is developed; second, it is studied from the technical point of view, and only then comes a mathematical research. These three components must be present in a paper for a high-ranking journal, and all three must be strong and cutting-edge. For example, at every step during the review period we had to prove that our work meets the ultramodern criteria," the scientist continued.

Besides signal loss, the researchers have been working on other problems that exist in 5G. One of them is effective radio resource (frequency range) allocation in the network. We have become accustomed to see the abbreviation LTE on our smartphone screens, it stands for Long-Term Evolution of mobile communication systems, the standard developed by the 3GPP consortium. The LTE standard is the base of 5G networks, however today its allocated frequency range is close to saturation, meaning that there are not enough radio frequencies to meet the requirements of 5G networks. The second problem is related to power consumption: in order to operate efficiently, the network requires a huge amount of electricity. A shortage may result in servers, cloud systems, routers and network components running out of coal, so to speak.

"Here are the challenges humanity faces: the first one is that the capacity of mobile communication frequencies will soon be exhausted, the second is that network equipment will face electricity deficit," Prof. Samuylov said.

Opening up a new frequency range, mmWave, to high-density mobile networks is an attempt to respond to one of these challenges. A solution to the aforementioned communication blocking problem in a heterogeneous mobile network has also been suggested: if an mmWave connection is blocked, then it can be transferred to a Wi-Fi network, or, if necessary, to an LTE network. This is a very simplified picture of the connection reliability measures in a 5G network. To analyze such a network, mathematicians solve optimization problems, for example, to minimize transceiver power consumption or to optimize the frequency range.

"Ultramodern 5G communications and various communication scenarios based upon them may be implemented in the future. Whether they will be implemented or not is a matter of collaboration between the academic community and the industry. It is going to be a long way, and the work done by scientists should be reflected in the standards developed by international organizations," the scholar added.

Among other achievements of his team, Prof. Samuylov mentioned their participation in the IEEE Globecom, a major worldwide conference on telecommunications. The selection for this conference is just as tough as for publication in JSAC, nonetheless the scientists from RUDN University have presented joint results with their European partners at IEEE Globecom for two years in a row now.

Prof. Samuylov noted that the competitiveness enhancement program "5-100", in which RUDN University is taking part, makes a significant contribution to the development of science in Russia. 20 universities participate in this megaproject, and five of them should enter the top 100 of the QS World University Rankings by 2020. In particular, thanks to this program RUDN University has been able to attract foreign researchers to work in Russia.

"This year, I have 20 people from abroad working with me, including our compatriots with PhD degrees. Now, we start to pay foreign scientists money, and not vice versa. It is difficult for us to compete with the West at the technology level, mainly because we do not produce hardware components. But we are engaged in mathematical modeling and are competitive due to the internationally high level of the Russian mathematical school. Today, the Institute of Applied Mathematics & Communications Technology of RUDN University employs about one hundred people, half of whom have high qualifications and wages above the Moscow average. This is unprecedented for Russian higher education nowadays," the scientist concluded.

###