## 2 Radio and Photonic Components in Optical Massive-MIMO gNB-DU/RRH
In addition to the optical and radio bus, along the radio-photonic module, a bus runs with a control channel (Figure 3a, red--optical, green--electric), which was delivered as a dedicated optical channel from the controller working at the gNB-CU/BBU. Through this digital channel, we can control any component in the photonic and radio signal processing chain. Its function will primarily be to determine and establish the path on which radio frequencies from a specific radio band or baseband channels (in analog or digitized form) will travel. Figure 2: Block configurations of integrated massive-MIMO optical gNB-DUs/RRHs with the same photonic and radio-photonic modules (devices): (**a**) 4-sectors gNB-DU/RRH containing microROADM; (**b**) 1-sector gNB-DU/RRH containing microOM/microOD; (**c**) 6-sectors gNB-DU/RRH containing microROADM (concept first time presented in proceedings [6]). Next block (Figure 3b) is connected to an electric bus that has a large number of transmission lines. The number of transmission lines depends on the number of media converters included in the radio-photonic block. The transmission bus provides signals to the ports of the signal switch, whose task is to direct the appropriate signal for initial preparation or separation, before entering them to the specific radio antenna subunit. The digital signals go to the DSP controller, which demultiplexes/ multiplexes streams in the time domain and organizes them so that they reach the appropriate transmission line connecting with a specific radio-antenna module. The analog signals go to the radio controller, where they are pre-prepared (e.g., adaptation to the transmission line, correction of time and frequency parameters, or pre-amplification in a small range). The analog radio signal (A-RoF format) can come from the following ranges: BB, IF, or RF. The control channel (Figures 3 and 4--green lines) enables the radio block subassemblies to operate and continues along the radio signal transmission bus. The functionality of the control channel does not terminate there. It is still appropriate to control the final radio systems closest to the antenna array assembly--Figure 4.  
Figure 4: Massive-MIMO antenna component of optical gNB-DU/RRH—example of single radio-antenna module. Proposition of gNB-DU/RRH construction with components controlled in SDR mode by the radio control channel (green line) (presented in proceedings [23]). Figure 3: Switching and processing devices of integrated optical gNB-DU/RRH: (**a**) block construction of the photonic part with microRNAOAM/microOM–microOD inside, (**b**) block construction of a common radio part with the digitized and analog radio signals switch (presented in proceedings [6]). The digital and analog buses are routed from the radio module to the radio-antenna head. Along the head with antennas, attachments should be placed to individual units converting radio signals prepared for emission in places of antennas. Digitized radio signals (Figure 4) go to the digital block, where their duplex directions are subjected to separation and they are converted (processed) from digital to analog and vice versa. Here, there is an encoding/decoding operation for the partial streams that have reached the gNB-DU/RRH optical interface in CPRI/eCPRI format [31; 32]. The signal from BB (uplink direction) gains its original form and is then transferred to the RF band. At this point, it is possible to use a greater number of the radio signal conversion degrees. It depends on the method of group transmission of baseband channels and the need for cooperation with analog signal transformation techniques. In the radio signal adaptation chain, there is also a section for forming the radiated beam. Each radio-antenna module is equipped with systems for two directions that allow analog beamforming and spatial beam control in cooperation with other radio-antenna modules. In the case when signals in a digitized form (prepared in gNB-CU/BBU) are delivered to the radio-antenna module, then DBF is additionally applied.