Abstract

Content

Introduction

1. The problem statement

2. Simulation of coverage

3. The services

4. The selection criterion of the base station

5. Model algorithm

6. The analysis of the results of the simulation

The necessity of having the broadband access everywhere, where the modern man is, not only at home or in the office, but in transport and on the street as well, grows every day. Approximately 2/3 out of 1.8 billion people, who are expected to use broadband access by 2012, will use it in its mobile version. Notably, the majority of the users will be provided by HSPA (High Speed Packet Access) and LTE (Long Term Evolution) net-services.

1. The problem statement

It is typical of each mobile network, that the users are arranged among some territory not equally. It is caused by the huge amount of people gathered in public places. As the result, the load of the base stations appears to be irregular. Some of the base stations are used inefficiently.

Within LTE networks base stations have basic and peripheral areas. Basic areas do not cross. Peripheral areas are able to cross. Within peripheral areas it is possible to choose to which of the base station to connect the user. The selection criterion will be created in the given model.

The selection criterion must take into account the bandwidth of the user, attenuation, jitter and the delay of the signal. So the user will be connected to the less loaded base stations with the best service qualities.

2. Simulation of coverage.

For the creation of the model it is necessary to simulate coverage and the arrangement of the users. The number of stations is 225, the number of the users is 900.

To perform the calculation of the radius of basic and peripheral area, the model of distribution of SUI radio-wave will be used.

The result of the simulation of the coverage is shown on the fig.1.

In the picture the territory 30 x 30 kilometers is presented. Base stations are marked with the stars, the users are marked with dots. Each base station is surrounded by basic and peripheral areas:

Figure 1 – The Arrangement of the Base Stations and Coverage

3. The services

For the improving the quality factors it is necessary to divide services into several categories in order to improve the Qos factors in future, for each category separately and differently.

The main services for LTE networks are: VoIP, IPTV and the Internet. By the Internet service we mean loading of web-pages, files and others.

4. The selection criterion of the base station

First, it is obligatory to decide to which base station the user must be connected. For that purpose it is necessary to evaluate the communication channel parameters, the peculiarities of traffic, to choose the most favorable option of load distribution, keeping the proper quality of service.

Each traffic type is characterized by its requirements to the parameters of the communication channels. If voice traffic is picky about the delay and its rejection, the transfer of data - distortions and packet loss. Therefore, for each type of transmitted data is useful to introduce the so-called utility function, which is assessing the appropriateness of the communication channel for transmission of traffic at the moment.

Video transmission in real time is similar in characteristics to the voice, but when using adaptive coding and control jitter delay allowed a significant reduction in bandwidth.

Delay in the data delivery influences greatly the quality of service. As well as for bandwidth, each kind of traffic has its own dependence of the quality of service upon the delay. Streaming voice and video transmission is most critical to delays. Jitter influences basically voice and video streaming as well.

Therefore, the dependence of utility indicator upon the delay, jitter and bandwidth, while using each of them, is singled out. By means of resulting criterion will serve the multiplication of three factors by factor considering the attenuation.

where U_b – is the utility indicator for the bandwidth; U_t – is the utility indicator for the delay; U_j – is the utility indicator for the jitter ; and c – is the factor considering the attenuation.

5. Model algorithm

The algorithm of the basic program is shown on the figure 2. All the functions of the algorithm are described previously. We will concentrate basically on lowering of the bandwidth while overloading of the base station.

The highest possible bandwidth of the base station in the model is 40 Mbps. This number corresponds to the bandwidth of LTE-FDD (Frequency Division Duplex). The channel width – 20 MHz. If loading at the base station is more than 40 Mbps, the bandwidth of the users of IPTV and the Internet lows down.

Figure 2 – Model Algorithm

6. The analysis of the results of the simulation

As the result of the functioning of the algorithm all the users are connected to base stations with the best quality factors. All the base stations are loaded more regular. Two approaches are compared in the model. The first one is the traditional approach ( when the users are connected to the base stations depending on the correlation between noise and signal); the second approach is the given one. The root-mean-square error of loading of the base station is calculated in the model.

When using the method provided, the root-mean-square error goes down to 6%. The loading histograms of the base stations according to two methods are presented on the figure 3 below.

Figure 3 – The Loading Histograms of the Base Stations а - algoritm of using utility function б - without using utility function

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Note

In the process of abstract writing the master's work hasn't been finished yet. Date of finish: December, 2013. The full thesis of master's work and materials according to the theme may be received from the author or his scientific advisor after the pointed date.