# Optical Channel Selection Avoiding DIPP in DSB-RFoF Fronthaul Interface
## 1 Introduction  
The 4G and 5G cellular systems have gained independence in using the domain of packet switching. Bypassing telephone centrals when setting up connections has made it possible to provide broadband services based on wireless access. This kind of approach has resulted in an exponential growth in demand for packet mobile services, which were previously only provided over wired networks. It quickly turned out that the approach to designing mobile systems needed to be changed, as the architecture known from the first generations was no longer effective. As a result of the evolutionary changes, the boundary between the core part of the system and the section with radio resource management and multilevel processing of radio signals from baseband and beyond has been clearly marked. The original architecture of the network in the radio domain of the distributed radio access network (D-RAN) type, also known as an all-in-one macro base station, provides simplicity, as it consists in constructing base stations as single-device systems for processing and broadcasting the radio signals. The use of such a solution is appropriate when the use of the base station is uniform in time and the peak-load is well below the hardware capabilities of the equipment. As mentioned earlier, the rapidly growing demand for broadband Internet access has changed the paradigm in the approach to designing new wireless communication systems, especially those that can be used to provide more dynamic and sophisticated network services. In order to eliminate the disadvantages of the D-RAN solution, the centralized/cloud radio access network (C-RAN) architecture was introduced. In this solution, the user equipment (UE) is set at the center, which means that the provision of coordinated multi-point (CoMP) services becomes much simpler as spatial access aggregation can take place at the level of one base station. In addition, coverage of the area with a radio signal is much more effective, because the central unit, often locatedin a computing cloud, has greater coordination possibilities and easier access to the often different needs related to the software signal processing. The C-RAN concept was used in mobile networks from the second generation (2G), and the architecture related to it was disseminated only at the beginning of the 21 st century in order to increase the efficiency of next-generation cellular networks. In all cases, the implementation of this concept required the use of specific media that made it possible to transfer pre-prepared radio signals from a central unit (CU) to a radio unit (RU). With the current advances in transmission technologies, this can be done with a wireless microwave medium or a fiber-optic medium. The microwave radio-link was sufficient for the distribution of signals from 2G and 3G interfaces. The appearance on the global market of 4G systems solely with the domain of packet switching has revolutionized the approach to the methods of modernizing the C-RAN architecture. Optical fiber and networks using its transmission potential appeared in the foreground. In the case of 5G mobile systems, in both the core and radio domains, it is difficult to imagine the functioning of such demanding networks without solutions based on optical fibers. The concept of the Xhaul network [1; 2] proposed in the 5 GPP project shows exceptionally well the degree of integration of the fiber-optic and radio domains, which is widely used in 5G solutions [3]. In the paper, will pay particular attention to the use of fiber-optic networks in the radio domain of next generations of mobile systems. Next-generation radio access networks (NG-RANs) are very much based on optical networks, which ensures the construction of efficient and broadband interfaces for backhaul (BH), midhaul (MH) and fronthaul (FH) links. Backhaul networks are a very important broadband link between the core network (5 GC) and the NG-RAN domains.