Українська   Русский
DonNTU   Masters' portal

Abstract

At the time of writing this abstract, the master's work has not yet been completed. Final completion: June 2021. The full text of the work and materials on the topic can be obtained from the author after that date.

Content

Introduction

Today, due to the constant development of society, the need to communicate, transfer and store information continuously increases. Customer demand and technological innovations – this is the fundamental driving forces behind the development of telecommunications. In his turn, the development of telecommunication technologies is closely related to the capabilities of communication channels – from analog to high-speed digital fiber-optic communication lines – and the computerization of society. So Thus, the following stages in the development of telecommunications can be distinguished [1,2]:

In modern society, there is a tendency to replace wired newer wireless equipment items. It is much more convenient not only because of the mobility of devices, but also in terms of convenience in use.

Wireless technologies – it is a subclass of information technology, serving to transfer information from one device to another, which are at a certain distance, without the involvement of a wired connection. Infrared radiation can be used to transmit information, radio waves, optical or laser radiation.

Four types are distinguished depending on the nature of the transmission medium. wireless data transmission [3]:

  1. Cellular radio channels. Data transfer is carried out wirelessly from transmitter to receiver. The transmitter forms radio pulse of a certain frequency and amplitude, the vibration is emitted in space. The receiver filters and processes the signal, then the required information is extracted. Radio waves partially are absorbed by the atmosphere, so this connection can be distorted when high humidity or rain. Mobile communication works exactly on based on radio wave standards, wireless data transmission channels differ in information transfer speed and operating frequency range;
  2. Satellite channels. This way of transmitting information is to use a satellite with an antenna with special equipment. The signal comes from the subscriber to the nearest ground station, then the signal is forwarded to the satellite. From there, the information is sent to the receiver, another ground station. Satellite communications are used to provide television and radio broadcasting. A satellite phone can be used in any remote cellular stations point;
  3. Infrared channels. Communication is established between the receiver and transmitter that are close to each other. Such the channel for wireless data transmission works by means of an LED radiation. Communication can be bi-directional or broadcast;
  4. Laser channels. The principle of operation is the same as in the previous variant, only a laser beam is used instead of LEDs. Objects must be in close proximity to each other.

Currently, the most promising along with others global networks are the LTE (Long-Term Evolution) standard. Mobile broadband gives you the fastest wireless speeds packet data transmission. With regard to the operating frequency band, all ambiguous. The LTE standard is very flexible, networks can be based in frequency range from 1.4 to 20 MHz.

The range of the networks depends on the height of the base station and can reach 100 km. Network connectivity provided to a large number of gadgets: smartphones, tablets, laptops, game consoles and other devices that support this standard. The devices must have a built-in LTE module, which works in conjunction with the existing GSM and 3G standards. In case of breakage LTE connection, the device will switch to the available access to 3G or GSM networks without disconnection. Centralized network management technologies connections, high quality mobile communication and access to mobile Internet, wide territorial coverage are gradually becoming the usual parameters of infocommunication services. Subscribers no longer tolerate the need for waiting: they require instant access that's both convenient and efficient.

The above is a prerequisite for supplier development communication services. At the moment, work is underway to introduce and the launch of the 5G standard – the fifth generation of mobile communications operating on based on telecommunication standards following existing 4G / IMT-Advanced standards. This standard has many advantages such as high average speed up to 1 Gb / s, the number of connections – millions per square kilometer, reducing delays to 1 ms, 100 times more energy efficient, mobility up to 500 km / h. But, along with this, there are a number of disadvantages: the rise in prices for communication services and smartphones, security and privacy concerns, an increase in the number of cellular antennas, adverse consequences for health [4].

In this regard, it is advisable to improve the standard LTE, namely the quality of service it provides (transmission rate information, signal bandwidth, error probability, etc.). One of the methods for achieving this goal is a simulation modeling – research method in which the system under study is replaced by a model, with sufficient accuracy, describing the real system (the constructed model describes the processes as they would take place in reality), with which experiments are carried out in order to obtain information about this system [5,6]. Such a model can be played in time, both for one test and for a given set of them. Moreover, the results will be determined by the random nature of the processes. Based on these data, one can get fairly stable statistics.

From all of the above, we can conclude that to improve quality of service for LTE-networks, the most effective solution is analysis and research of simulation models of radio channels.

1. Relevance of the topic

Undoubtedly, at the present stage of development of science and technology, radio engineering systems significantly affect the life of society. The radio system can considered as a system consisting of technical means performing processing radio signals. The purpose of such a system is to extract and transmit information. Radio technical systems provide the following capabilities:

Regardless of the purposes of using the radio engineering system, the main a requirement for it is high-quality and reliable performance of its functions.

When designing radio engineering systems, developers face an important the task is to ensure and maintain high quality of these systems. For achievement a satisfactory result requires an optimal structure for this situation and system parameters, as well as acceptable methods of implementation and algorithms for its operation components. This decision can be based on a number of experimental studies of various variations in the implementation of radio engineering systems. However, with further assembly and implementation of various system options, significant an obstacle in the form of a proportional increase in the duration and cost of work on designing.

Based on the above, we can conclude that the most effective by searching for optimal solutions in the development of radio engineering systems is conducting research by the method of modeling. One of the advantages of this method is the ability to quickly and easily influence the structure and parameters of the system, thanks to which there is no need for significant financial costs when studies of the operation of radio engineering systems, taking into account the various options for their implementation. To solve the second no less significant problem of the duration of work on design, it is enough to introduce high-performance computing machines. Thus, modeling is not only efficient by research and design of radio engineering systems, providing high reliability and quality of work, but also allows you to reduce the time and cost of design and commissioning.

2. Purpose and objectives of the study, planned results

The aim of the study is to improve the accuracy of modeling LTE-networks by developing a simulation model of an LTE-radio channel.

To do this, it is necessary to solve the following tasks:

Object of study: broadband LTE radio channel.

Subject of research: simulation.

The results obtained in the course of this master's work, can be used to create models of LTE networks, when working with which you can get more accurate simulation results.

3.Analysis of problems arising in the simulation of cellular networks

3.1 Communication channel classification

Communication channel – is a system of technical means providing independent signal transmission with certain properties between subscribers on a common communication line. Communication channels can be classified as follows.

By purpose, the channels are:

Depending on the signal propagation environment:

Depending on the characteristics of the signals acting at the input and output of the channel:

By splitting method:

Depending on the bandwidth:

In fig. 1 is a generalized block diagram of a communication system.

Generalized block diagram of a communication system

Figure: 1 – Generalized block diagram of a communication system (animation: 6 frames, 6 repetitions, 48 KB)

The message of the information source a is encoded into a symbol X and, after modulation, is converted into a signal U arriving at the LAN. As a result, under the influence of interference Z on the receiving side, the signal differs from the original U. The receiving part contains a demodulator that transforms z into a Y symbol and a decoder that transforms the Y symbol into a message b, Which arrives at the information receiver.

The exact mathematical description of any real communication channel is usually quite complex. Instead, they usually use simplified mathematical models that reveal the most important patterns of a real channel.

3.2 Simulation process

Modeling is a research method in which the object under study is replaced by a model that reproduces the closest possible the original behavior is within certain assumptions and acceptable errors. IN In general, modeling consists of developing a model of a real object and further study of its properties by studying the model itself. It should also be clarified that it is advisable to carry out simulations only when it is simpler and cheaper creation of the original itself or, when the latter, for some reason, it is better not at all create.

In general, a model is a physical or abstract object, properties which, in a sense, copy the properties of the original object. Moreover, on the formulation of requirements for the model is influenced by the problem being solved and the available means.

The similarity of the developed model with the real object suggests compliance of this model with a number of basic requirements. The model should be:

Depending on the implementation method, the following classification is distinguished: physical, mathematical and semi-natural models.

Physical models – these are real physical objects that duplicate characteristics and properties of the original by preserving or applying a similar physical nature [8].

As such models, layouts that are based on the basic principles and algorithms of the system. Physical models are widely used when studying the environment of propagation of radio signals, which is an integral component of radio engineering systems.

Mathematical model – this is a generalized description of an object based on functional or logical operator relations, algorithms, algebraic, integro-differential or other equations, which can be both in an open (unresolved) and in closed (permitted) forms.

Since the operation of radio engineering systems is based on the use of radio signals, which are sufficiently fully described by functional dependencies of one (usually time) or several variables, mathematical modeling has received a wide dissemination in the modeling of these systems, and as their separate components and systems as a whole. Consequently, RTS are easily amenable to mathematical description. In turn, mathematical models are divided into analytical and imitation [9].

Analytical models are models in which the representation of the object under study is based on a system of mathematical equations of various types. Research with using analytical modeling is carried out by applying methods symbolic or numerical solutions of mathematical equations by a person or with using a computer. Simulation by this method allows you to identify general theoretical dependencies of the behavior of the original object.

A simulation model is a logical-mathematical description that repeats the internal structure of the system, the functions of its individual elements and most significant relationships between them.

With this modeling method, the created model reproduces the algorithm the functioning of the system in time: elementary phenomena are simulated taking into account their logical structure and sequence of actions. For simulation models it is possible achieve high consistency when describing the functioning of a real object.

One of the advantages of simulation is the ability to set the speed of the process: slow down in the case of fast processes and accelerate to simulate systems with slow variability. This feature has a significant impact in the modeling of radio engineering systems, since radio signals are processes rapidly changing in time and when they research in vivo presents a number of difficulties.

Semi-natural model – a model that uses elements to create real equipment of the investigated object. Inclusion of real equipment in the process modeling complex processes allows you to achieve a reduction in labor intensity modeling, as well as to increase the percentage of adequacy of the results.

The ultimate goal of modeling is to obtain a fundamentally new information about the studied object, which can expand and deepen its description. The modeling process can be considered complete if the information obtained sufficient to make a certain decision. Simulation can proceed like this [10]:

  1. problem statement;
  2. system definition;
  3. decision on the need for modeling;
  4. model formulation;
  5. model translation;
  6. model check;
  7. planning a study;
  8. experimenting;
  9. interpreting results
  10. implementation and documentation.

The statement of the problem consists in defining a number of questions to be answered, and also designate new information about the system that needs to be achieved during research.

System definition – formally placing the boundaries between the studied system and environment, in other words, defining what is an element system and what not. The separation of the system from the outside world, in turn, leads to designation of constraints and assumptions on which the designed model will be based. Also, taking into account the designated boundaries, the performance indicators required with further numerical assessment of the quality of the system, its compliance with the designated tasks.

Based on the first two stages, a decision is made about the need continue modeling. In some cases, a clear statement and analysis of the problem situations are able to give an idea of the weak points of the investigated object. In this case further modeling is impractical. Otherwise, work on model creation continues.

Model formulation – transition from a real object to some logical scheme. Due to the need to ensure the similarity of the model with the original, the construction models, as a rule, begins with an analysis of the system under study–the selection of individual component parts. In the process of such analysis, the structure of the object under study is indicated, the connection of the system components between themselves and the external environment is determined.

Model translation – process describing a model using language that is understandable the computer with which the model will be implemented.

Model check – this is a check of the correctness of the model transition to the language computer and checking the conformity of the developed model to the investigated object (assessment of adequacy).

Study planning – development of the proposed course of the experiment, the result of which should be the necessary information, determining the way conducting each series of tests.

Experimentation is the very process of performing experiments with model, the purpose of which is to obtain the desired data about the object of interest.

In the form of interpretation of the results, conclusions about the functioning of the object appear, built on the basis of data obtained earlier as a result of modeling. If a modeling results are useful, then they can be used to make decisions, in Otherwise, it is necessary to revise all previous stages of modeling. IN if the simulation results are useful, but the information obtained is insufficient to make a decision, it is necessary to continue modeling.

Implementation and documentation is the use of a model and simulation results in practice, as well as the creation of documentation of the entire process create and use the model.

The modeling process is shown schematically in fig. 2.

Simulation process

Figure 2 – Scheme of the simulation process

3.3 Problems of modeling cellular networks

Organizing a cellular communication system is a laborious process, which includes a number of stages, of which one of the most difficult and design is in charge. This stage is such for because of the need to ensure the closest to optimal building a network by the criterion of efficiency-cost. In the process design, such types of work as determining places for placement of base stations and the subsequent distribution of available frequency channels between cells in such a way that the served the territory had access to cellular communication with the required quality with the minimum number of base stations. An additional complication is the difficulty of analytically assessing the characteristics of the location of signals and calculation of the field strength, as well as the need to take into account the unevenness traffic within the served area.

Throughout the entire process of organization, the mobile network is constantly undergoing adjustment – changes are made to the already developed network diagram based on mandatory performance measurement experiments electromagnetic field, after which at the stage of network operation, taking into account the final evaluation of the project made at this stage, the network again undergoing revision. In the future, as the network is used and developed also often undergoes various modifications aimed at improving the quality of the network.

The quality of services provided to the user is directly affected base station subsystem characteristics. Are put to the base station the following requirements:

Without ensuring the listed requirements, provision of services high quality is not possible.

Quality of service should be understood as the cumulative impact services provided per user, on the basis of which the degree of satisfaction of their subscribers. This definition should include both the technical side responsible for the quality of the network, and aspects, directly related to additional services, cost service, price and quality of mobile terminals, etc.

The number of mobile network subscribers, the volume of traffic and its distribution by the territory served by the network – these factors are not static and are constantly changing throughout the life of a cellular network. For this reason, the network configuration of the base station must adapt to the ongoing changes, as a result of which its planning is continuous process in which several stages can be distinguished:

In addition to the difficulties described above, a significant problem for signal transmissions are interference from artificial and natural origin.

In the general case, a hindrance should be understood as a random effect on a signal in the communication channel that makes it difficult or completely obstructs correct reception. It is worth highlighting that the greatest difficulties cause influences of a random nature, since theoretically dealing with regular interference is not difficult.

Among the natural disturbances, the most common receiver noise and atmospheric noise that generate electrical discharges during thunderstorms. In addition, interference can introduce such phenomena as static electricity, space and solar noise. In general, such interference is classified as additive noise.

Equally important is the fact that radio links in mobile communications often pass through uneven terrain. In such cases, it is necessary take into account the real profile of the track, which may undergo strong changes throughout its length: from smooth to strong rough terrain. You should also consider the presence of buildings, trees and other obstacles in the city.

To create an efficient cellular network that provides and maintaining high quality work during the design phase all of the above factors must be considered.

Conclusions

The definition of the communication channel is given. The classification of communication channels by purpose is given (voice frequency (PM) or telephone channel, sound broadcasting, television broadcasting, telegraph, data transmission, facsimile, newspaper transmission), depending on the signal transmission medium (wired, radio, waveguide, optical), depending on the characteristics of the signals acting at the input and output of the channel (continuous, discrete, discrete-continuous), according to the separation method (with frequency division, time division), depending on the bandwidth (narrowband, broadband, ultra-wideband). The generalized block diagram of the information transmission system is presented.

Definitions of modeling and model are given. The requirements for the model are set and the stages of modeling are listed. The problems arising in the modeling of cellular networks are listed. The main problem for any channel in signal transmission is indicated, which is interference. Examples of artificial and natural interference are given.

References

  1. Тенденции и стратегии развития телекоммуникаций [Электронный ресурс]. – Режим доступа: https://www.huawei.com/ru/industry-insights/outlook/perspectives/HW_147027 – Загл. с экрана.
  2. История развития телекоммуникационных систем и компьютерных сетей [Электронный ресурс]. – Режим доступа: https://studfiles.net/ – Загл. с экрана.
  3. Романчева, Н.И. Базовые Интернет-технологии [учебное пособие] / Н.И. Романчева. – М.: МГТУГА, 2008. – 96 с
  4. Tafazolli, R. Technologies for the Wireless Future.Vol.2. Wireless World Research Forum, 2006.
  5. Имитационные модели [Электронный ресурс]. – Режим доступа: https://studme.org/190916/ekonomika/imitatsionnye_modeli – Загл. с экрана.
  6. Diakoumis Gerakoulis, Evaggelos Geraniotis CDMA: Access and Switching: For Terrestrial and Satellite Networks (Hardcover) Diakoumis Gerakoulis, Evaggelos Geraniotis, 2001.
  7. Васильев, К. К. Математическое моделирование систем: учебное пособие / К. К. Васильев, М. Н. Служивый. – Ульяновск: УлГТУ, 2008. – 170 с.
  8. Галкин, А. П. Моделирование каналов систем связи / А. П. Галкин, А. Н. Лапин, А. Г. Самойлов. – М.: Связь, 1979. – 100 с.
  9. Борисов, Ю. П. Математическое моделирование радиотехнических систем и устройств / Ю. П. Борисов, В. В. Цветнов. – М.: Радио и связь, 1985. – 176 с.
  10. Jeruchim, Michel C. Simulation of Communication Systems Modeling, Methodology and Techniques / Michel C. Jeruchim, Philip Balaban, K. Sam Shanmugan. – 2-nd ed. – N. Y.: Kluwer Academic Publishers, 2002. – 937 p.