## 3 Simple Model of Bandwidth Consumption Calculation in 5G Fronthaul Interfaces
### Bandwidth Consumption in D-RoF Interfaces
The rate consumption calculations that will occur at the Split D during the maximum load, according to the CPRI Forum [9], can be carried out on the basis of a simplified and adapted formula [2; 48]  
\[BR_{D}=\frac{S\cdot N_{L}\cdot N_{SC}\cdot N_{SY}\cdot R_{C}\cdot K\cdot HF \cdot LC}{T_{F}} \tag{2}\]  
where \(S\)--the number of sectors per gNB-DU/RRH, \(N_{L}\)--the number of layers (related to the number of layers needed to create and form space beams directed to mobile UE), \(N_{SC}\)--the number of active CP-OFDM subcarriers in BB channel (the number of subcarriers for the new waveform from the 5G-NR interface should be used--in the channel with a specified frequency bandwidth [MHz]), \(N_{SY}\)--the number of CP-OFDM symbols or newest waveform per standard time-frame (in the non-standalone 5G-Rel-15 interface a coherent value was assumed in relation to FDD-LTE), \(R_{C}\)--the factor of FEC code efficiency, \(K=\log_{2}M\)--bits per modulation symbol, where \(M\)--modulation order (usually for \(M\)-QAM format), \(HF\) (Headers Factor)--CPRI frame redundancy factor (redundancy at 1/15 for CPRI, so the ratio is 16/15--much smaller and variable for the eCPRI, depending on the size of the charge in a frame [32] matched to the Ethernet frame and/or OTN [36; 39]), \(LC\)--a line code also used as a scrambling (for faster streams it is 64B/66B, so the code rate is 66/64) and a physical Ethernet link control (also applicable to the RoE technology [32; 36]). The line code in the optical Ethernet link applies only to the LAN format. Ethernet WAN interface is devoid of this code, because physical layer functions are taken over by the transport system, e.g., OTN. When the radio samples are transported in the fronthaul/midhaul paths using Ethernet (RoE) frames only, the \(LC\) value is included in the \(HF\) redundancy. When the level of the Split/Option increases, the total data rate related to the user's data plane will increase, which results from the need to send additional data defining the radio signal. At Split I\({}_{\text{U}}\) and II\({}_{\text{D}}\) (Figure 7--eCPRI 1.2--yellow number 2) an additional parameter appears which determinesthe number of quanta in the process of converting the frequency sub-carriers. Thus, the coding and modulation rules will not be taken into account, as the frequency components will be quantized. In order to estimate the bit rate that will occur in the fronthaul/midhaul path type Split I\({}_{\text{U}}\)/II\({}_{\text{D}}\), an approximate formula [2] can be used  
\[BR_{I_{U}/II_{D}}=\frac{2\cdot S\cdot N_{P}\cdot N_{SC}\cdot N_{SY}\cdot N_{QF} \cdot HF}{T_{F}} \tag{3}\]  
where \(S\)--the number of sectors per gNB-DU/RRH/AAU, \(N_{P}\)--the number of ADC/DAC chains (used in digital beamforming (DBF)--special application in massive-MIMO mode), \(N_{SC}\)--the number of active CP-OFDM subcarriers in BB channel (the number of subcarriers for the 5G-NR waveform interface should be used), \(N_{SY}\)--the number of CP-OFDM or newest waveform symbols per standard 4G/5G time-frame, \(N_{QF}\)--the quantizer resolution in the frequency domain, \(HF\) (Headers Factor)--eCPRI frame header redundancy factor [32] and higher IP/Ethernet network layers, \(T_{F}\)--frame duration (4G/5G system parameter).