## 3 Materials and Methods
### Analysis of Independent Research Variables and Data Collection
Data are sent in packets, i.e., in a Transport Block (TB) within one Transmission Time Interval (TTI), with its duration of 1 ms. The DL/UL retransmission rate can be defined as the ratio of retransmitted packets (packets sent with retransmission) to all packets sent via the DL/UL SCH transport [19]. DL IBLER & (7) UL IBLER  
Block Error Rate (BLER) shows as a percentage how many blocks with errors were received compared to the total number of blocks sent. The Initial Block Error Rate (IBLER) is an indicator used to evaluate network performance; it shows the relationship between the number of blocks with initial transmission errors and the total number of initially transmitted TBs in the DL and UL direction [19]. Cell Traffic Volume DL & (9) Cell Traffic Volume UL  
Cell Traffic Volume DL/UL represents the total aggregated DL/UL traffic in the cell in a period of one hour expressed in Gbit. In LTE networks, the total aggregated traffic represents the sum of traffic in 9 classes, which are identified by the QoS Class Identifier (QCI) [19]. The classes marked with QCI 1--QCI 4 are characterized by a defined and guaranteed throughput of Guaranteed Bit Rate (GBR), and examples of services that belong  
Figure 2: Layout of eNodeB locations with marked signal propagation in the research area. to them are QCI 1--Conversational Voice; QCI 2--Conversational Video; QCI 3--Real Time Gaming; QCI 4--Non-Conversational Video. Non-GBR classes are marked with QCI 5--QCI 9 and imply a certain risk of packet loss, especially in conditions of network congestion. Examples of services belonging to them are QCI 5--IMS Signaling; QCI 6--Video, TCP-based; QCI 7--Voice, Video, Interactive Gaming; QCI 8 and QCI 9--Video, TCP-based. 1. Cell Downlink Average Throughput & (11) Cell Uplink Average Throughput  
One of the most important indicators of network performance is Throughput, which can be defined as the ratio of the amount of data transferred and the time for which the transfer is made. The variable Cell Downlink/Uplink Average Throughput represents the average value of this indicator for a period of one hour, at the level of one cell in the DL and UL direction. The average throughput value can be determined not only geographically (per spatial unit-cell), but also logically (per service) [19]. 1. Average DL User Throughput & (13) Average UL User Throughput  
The average value of Throughput at the user level in the LTE network, in the observed space in the DL and UL direction, is determined by the value of the Average DL/UL User Throughput variable. This value is calculated for a period of one hour [19]. 1. UL Average Interference  
The total power of the noise floor and the interference of neighboring cells, received by each PRB, is measured during one TTI in the UL direction. The eNodeB divides the total power of the noise floor and the interference of neighboring cells by the number of PRBs, and the resulting value is used as the sampling result. At the end of the one-hour measurement period, the average of these sampling results expressed in dBm is used as the value of the UL Average Interference variable [21]. 1. DL.QPSK.TB.Retrans, (16) DL.16 QAM.TB.Retrans & (17) DL.64 QAM.TB.Retrans  
The variables DL.QPSK.TB.Retrans, DL.16 QAM.TB.Retrans and DL.64 QAM.TB.Retrans are related to the variable DL ReTrans Rate and refer to retransmission rates for certain modulation schemes. Their meaning is as follows:  
1. DL.QPSK.TB.Retrans--Number of retransmitted TBs in DL SCH at Quadrature Phase Shift Keying (QPSK) modulation;  
1. DL.16 QAM.TB.Retrans--Number of retransmitted TBs in DL SCH at Quadrature Amplitude Modulation (QAM) with 16 carrier states (16 QAM);  
1. DL.64 QAM.TB.Retrans--Number of retransmitted TBs in DL SCH at QAM with 64 carrier states (64 QAM).