## 4 Analysis of Research Variables
### DL Cell Traffic Volume  
This variable represents the total aggregated DL traffic in the cell up to the moment of sampling and is expressed in Gbit. According to the standard 3 GPP TS 23.203 rel 8, the total aggregate traffic is grouped into nine classes by the quality of service, so that the _QoS Class Identifier_ (QCI) clearly identifies each traffic class with numbers from 1 to 9, which is the case in the M:tel LTE network. QCI definitions and explanations are given in [43; 44]. Each QCI defines the following four parameters, which are given in Table 5 in addition to the service examples for each QCI value [45]:  
1. Bit rate: guaranteed Bit Rate (GBR) or Non-Guaranteed Bit Rate (Non-GBR);
2. Priority level: a number in the range between 1 and 9, where 1 represents the highest priority;
3. Packet Delay Budget--PDB. Defines the upper limit of the allowed packet delay;
4. Packet Error and Loss Rate (PELR). Defined as the ratio of the number of packets with errors-lost packets and the total number of sent packets [46].  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Mark** & **Meaning** \\ \hline QPSK.ErrTB.Ibler & Number TB with initial errors under QPSK modulation \\
16 QAM.ErrTB.Ibler & Number TB with initial errors under 16 QAM modulation \\
64 QAM.ErrTB.Ibler & Number TB with initial errors under 64 QAM modulation \\ \hline \hline \end{tabular}
\end{table}
Table 4: Values by which the iBLER value is calculated.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Mark** & **Meaning** \\ \hline QPSK.TB.Retrans & No of retransmitted TB into DL-SCH under QPSK modulation \\
16 QAM.TB.Retrans & No of retransmitted TB into DL-SCH under 16 QAM modulation \\
64 QAM.TB.Retrans & No of retransmitted TB into DL-SCH under 64 QAM modulation \\ QPSK.TB & No of initially emitted TB into DL-SCH under QPSK modulation \\
16 QAM.TB & No of initially emitted TB into DL-SCH under 16 QAM modulation \\
64 QAM.TB & No of initially emitted TB into DL-SCH under 64 QAM modulation \\ \hline \hline \end{tabular}
\end{table}
Table 3: Values by which the DL retransmission rate is calculated.  
The examples of services are given in the following Table 5 and can be classified into traffic classes in a 3G mobile network, according to the definition of the Organization for the Development of International Telecommunication Standards (3 GPP), by QoS criteria: (1) conversational traffic (voice transmission--talks and lectures); (2) streaming traffic (audio/video streaming--video telephony, telnet, voice and video services); (3) interactive traffic (internet search--interactive applications such as interactive email and interactive web browsing); (4) background traffic (W3, email--background download, FTP, news and Telnet, download of background files). This clustering is usually used as a base in network traffic.  
The parameters listed in Table 5, among others, define the quality of an individual service from the aspect of the mobile operator, i.e., the service provider. Although the QoS is a well-defined and established research domain, it is often necessary, but also difficult, to distinguish it from the quality of the user experience. The QoE puts the person-user and his perception of the quality of experience in the foreground, but in general it can be said that with the increase of QoS, the operator can expect a higher value of QoE [47].