## 3 Simple Model of Bandwidth Consumption Calculation in 5G Fronthaul Interfaces
### Bandwidth Consumption in A-RoF Interfaces  
Digital fronthaul/midhaul interfaces are very demanding in terms of throughput, which is why in this part of the work we will consider the implementation of A-RoF solutions. In the analog mode of the photonic carrier modulation, we can use a modulating signal located in the baseband, the intermediate band, or the radio frequency band [49]--Figure 8.  
In the case of photonic carrier modulation with a radio signal coming from the baseband, we have the largest saving of the photonic band. This technique requires the use of separate optical resources for each frequency BB channel. This causes complications in the need to use a separate optical channel or a separate optical fiber for each BB channel. As in the D-RoF interface, a modulator must be used on the gNB-DU/RRH side to allow the BB signal to be applied to the RF band. The second solution indicates the use of an IF intermediate frequency. In this technique, all frequency channels can be sent simultaneously to the selected RRH. In a remotely managed radio module, we convert the signal that transfers data from the intermediate band to the target RF band. This solution is quite economical, due to the possibility of optical transmission of many radio channels focused around one unified, in a given network, intermediate frequency, which can be selected depending on the needs. The solution that most occupies the optical band remains, that is, simultaneous transmission of all components of the radio signal, including the RF carrier. This solution is the least effective from the point of view of the FH network, but allows the use of maximally simplified AAU, whose tasks are reduced to optical modulation and demodulation, amplification, pre-amplification, and shaping the beam emitted by the antenna array. In comparison to the D-RoF solutions, the signals in the A-RoF format do not occupy too much bandwidth in the optical channel, however, they are characterized by much higher requirements for distortions of modulating signals. The modulation signal is specific, because it resembles an analog format in spite of the fact that it transfers digital data. For many years, scientists have been working on the optical OFDM (O-OFDM) technique, which is very similar to the A-RoF such as baseband-over-fiber (BBoF) solution, but the On/Off Keying (OOK) method with a direct detection is still popular and the cheapest one. The modulation of the photonic carrier with a signal from the BB is therefore similar to the O-OFDM, however, there is only one source of carrier surrounded by two bands (double-side band (DSB) mode), thus the orthogonality of subcarriers remains on the side of the modulating signal. Care for the orthogonality of radio subcarriers, during transport in the optical path, is not a problem due to their very low frequency distance and the occurrence of multi-path effects in a small range (chromatic dispersion and power penalty influence--DSB mode), which occur on a much larger scale on the side of the wireless interface. Thus, the only limitations here are signal attenuation, its delay and dispersion, which must be taken into account in particular when using a very broadband modulation signal. The use of high radio frequency allows the creation of more wider frequency channels (e.g., the need to use mmWave ranges in 5G); however, when using DSB modulation this results in a doubled increase in the width of the optical channel. This can be limited by using the SSB modulation technique by introducing Mach-Zehnder Modulation (MZM) in the Hilbert configuration or by filtering out one sideband. Such a treatment, however, weakens the modulating signal, at the expense of improving the bandwidth efficiency and reducing the impact of the chromatic dispersion of the fiber-optic paths. The large number of systems (2G-5G) supported by the base station causes its high degree of complexity and hinders its quick reconfiguration.