## 3 Simple Model of Bandwidth Consumption Calculation in 5G Fronthaul Interfaces
### Bandwidth Consumption in D-RoF Interfaces  
In the classical FH variant, usually one gNB-CU/BBU center will support interworking with several gNB-DU/RRH or DU radio terminations. In this sense, the total bit rate needed to service the massive-MIMO radio equipment can significantly exceed 10 Tbps. A single CPRI interface (Figure 7: (a) Option 8, (b) Split A, (c) Split E--yellow number 1) represents one antenna module in one sector of the radio-antenna head. The digitized baseband signal must be delivered here independently to each antenna module so that MIMO techniques and spatial beamforming on the side of the wireless interface can function  
Figure 7: Models of Splits/Options and functions performed by 5G-FH/MH components in the scope of F1/F2 interfaces in the NG-RAN domain: (**a**) functional division according to 3 GPP [46], (**b**) functional division according to 5 GPP [1], (**c**) functional division according to CPRI Industry Forum—interface eCPRI v.2.0 [32]. effectively. The total bit rate needed to deliver the appropriate number of fast CPRI streams to the gNB-DU/RRH mast, via the F1/F2 interface (Figure 1), can be determined based on the formula [47]  
\[BR_{8}=S\cdot A\cdot f_{s}\cdot b_{s}\cdot IQ\cdot HF\cdot LC \tag{1}\]  
where \(S\)--the number of sectors per gNB-DU/RRH/AAU, \(A\)--the number of antenna modules in array per one sector, \(f_{s}\)--speed of sampling (in CPRI for 20 MHz radio baseband channel is equal to 30.72 MS/s \((3.84\cdot(20/5)\cdot 2)\), in wider BB radio channel is proportionally higher [8; 9]), \(b_{s}\)--number of bits per sample (depending on the format of the sampled signal: is equal 15 per one I/Q subcarrier for 4G/5G-Rel-15 (cyclic prefix orthogonal frequency division multiplexing (CP-OFDM))), \(IQ\)--a factor indicating a separate sub-sampling I as in-phase and Q as quadrature (is equal 2), \(HF\) (Headers Factor)--a factor indicating the redundancy of CPRI headers (redundancy is 1/15, therefore, amounts to 16/15), \(LC\)--alphabet nB/mB line code (8B/10B--ratio of 10/8--used in CPRI Options 1-7, 64B/66B--ratio of 66/64--used in CPRI Options 7A-10). The relocation of the need of signal processing power to specific parts of the radio network chain (CU or DU) depends on the network architecture and, in SDR mode, enables balancing the power consumption and dynamic selection of signal processing centers in the gNB-CU/BBU cloud or gNB-DU/RRH terminal/node. In the situation when we transfer more functions related to the processing of baseband signals to the signal processing cloud, the stream that will only transmit data regarding the actual transmission can be significantly reduced. In the context of this case, we will consider Option 6 according to the 3 GPP (Split C according to 5 GPP, Split D according to CPRI Forum--Figure 7--yellow number 3), which applies to both 'duplex' directions (uplink (UL) and downlink (DL)) and is located at the border between PHY and MAC layers. The division presented in Figure 7 indicates the places where the separation of the network elements functions can be made, which is also an important determinant of the directions of evolution and the emergence of NG-RAN Split/Option standards at the F1 and F2 interfaces [1; 32; 46].