## 4 Calculation Results and Partial Discussion

Table 2: Additional parameters of FH/MH radio streams for calculation of bandwidth consumption in the lower Split/Option interfaces [29; 32; 51]. Intermediate Splits/Options were introduced in all reference models (Figure 7), however, they function differently. In this analysis, additional calculations were made for the eCPRI Split I\({}_{\text{U}}\)/II\({}_{\text{D}}\) (directions UL and DL), which is functionally similar to 5 GPP Split B (Figure 7b,c). The results of calculations, carried out on the basis of (3), were placed in the form of diagrams in Figure 11. It can be noticed that in this Split/Option the demand for fronthaul/midhaul the bandwidth is increasing slightly. This increase is mainly due to the fact that each mapped OFDM subcarrier must be quantized. The number of quantization bits per IQ subcarrier can be found in Table 2. The increase of the speed of this Split/Option on the control plane (CP) will be significant, as it can reach even 30% of the UP flow. Two new Option 9/10, as well as the extension of the functionality of Option 8 split were proposed in the paper--Figure 8. To this end, a special design of an optical gNB-DU/RRH as a network node or network termination is proposed, which is equipped with appropriate radio components and photonics--Figures 2-4. Proposals are based on A-RoF solutions and are achievable if the  
Figure 11: Calculation results of optical resources needed to connect 4-sector gNB-DU/RRH to optical fronthaul/midhaul as a function of antenna elements number of massive-MIMO array (calculation parameters changing according to Tables 1 and 2)—there are overlapping lines in graphs for 20 MHz and 50 MHz, as well as 80 MHz and 100 MHz: (**a**) total bit-rate for radio BB channels digitized to eCPRI format—Splits I\({}_{\text{U}}\)/II\({}_{\text{D}}\) (Figure 7c); (**b**) number of DWDM-OOK 50 GHz-grid channels for radio BB channels digitized to eCPRI format—Splits I\({}_{\text{U}}\)/II\({}_{\text{D}}\) (Figure 7c). Figure 10: Calculation results of optical resources needed to connect 4-sector gNB-DU/RRH to optical FH/MH as a function of antenna elements number of massive-MIMO array (calculation parameters changing according to Tables 1 and 2): (**a**) total bit-rate for radio BB channels digitized to eCPRI format—3 GPP—Option 6/CPRI Forum—Split D (Figure 7a,c); (**b**) number of DWDM-OOK 50 GHz-grid channels for radio BB channels digitized to eCPRI format—3 GPP—Option 6/ CPRI Forum—Split D (Figure 7a,c). fronthaul/midhaul links are based on an all-optical network using WDM technique. The calculations were carried out on the basis of a derived relation (7), and their results are presented in the form of diagrams shown in Figure 12. In the Option/Split 10, the radio-frequency-over-fiber (RFoF) technique is used, which enables transporting radio signals through optical links exactly in the form in which they have be radiated in place of the radio-antenna device. However, this solution has significant limitations, as with the increase of RF frequencies, photonic resources in fronthaul/midhaul links are very quickly occupied. This is due there being more and more optical channels from the DWDM standard grid--Figure 12a. In the case of the RFoF, the use of photonic resources is effective when the radio carrier is located in the sub-6 (FR1) band--Figure 12a--area marked with the number 1. This technique fits very well in the simple and low energy analog beamforming (ABF) implementation on the AAU side, however, for each space beam (layer) a separate RFoF channel will have to be used. With Option 10, the DBF technique can only be implemented on the gNB-CU cloud side. Figure 12: Calculation results of needs for optical resources in optical A-RoF fronthaul/midhaul path from gNB-CU/BBU/DU to 4-sector gNB-DU/RRH/AAU presented as Optical Wavelength Spectrum (OWS)—count-down from 1675 nm optical carrier (band U): (**a**) Option 10 (proposition—Figure 8)—analog transport of RF over optical DWDM link (min.