# Experimental Evaluation of Hybrid Fibre-Wireless System for 5G Networks
## 1 Introduction
### Motivation  
This transport approach is a significant innovation for extremely high-capacity wireless transmission by virtue of a simple and cost-effective paradigm that extends the network's reach [2, 3]. Despite their benefits, such as minimal electromagnetic intrusions, lower loss rates and larger bandwidth, RoF links suffer from channel and linear distortions caused by system components, which can be rectified using linearization methods [4, 5, 6, 7, 8, 9]. Analog radio over fibre (A-RoF) [1, 2, 3, 4, 5, 6, 7, 8, 9], digital radio over fibre (D-RoF) [11, 12] and sigma delta radio over fibre (S-DRoF) [13, 14, 15, 16, 17] are all different types of RoF implementations.  
A-RoF suffers from signal degradation and has a network expansion range of only a few tens of kilometres. The reach of the network for D-RoF is efficient for longer lengths [11], but due to the greater resolution bandwidth of the analogue digital converter (ADC) and the requirement of additional signal processing the system's cost increases. In fronthaul networks, inadequate spectral efficiency and high demand for data traffic are also undesirable [12; 17]. The Common Public Radio Interface (CPRI) bottleneck is bypassed in S-DRoF by employing sigma-delta modulation (SDM), which works as a 1-bit ADC. The high quantization noise is caused by a 1-bit operation, which necessitates the use of a bandpass filter on the receiver side, increasing the complexity of these systems. As a result, the A-RoF system is a better alternative than D-RoF and S-DRoF [18] since it is simple, inexpensive and already has a widespread infrastructure.  
Because of the limitations imposed by the optical and microwave components, analogue fronthaul applications are limited. Many linearization methods have been proposed to address these issues [4; 5; 6; 7; 8; 9], but these methodological solutions have been questioned due to limited bandwidth, high method complexity and the requirement of returning the output signal to the base station (feedback), which is a lengthy process [18].  
The 5G network is expected to provide Gbit/s of connection, acting as a connector for total connectivity and coverage. Enhanced mobile broadband is one of the most widely utilised scenarios (eMBB). By utilizing revolutionary technological solutions, such as new radios (NR), 5G enables multi-services and a wide range of capabilities. Because it affects the coexistence with other systems, 5G NR enables the used multiplexing mechanism [19; 20]. Multiple waveforms for multicarrier transmission have been proposed for 5G due to this coexistence capability (including 4G systems), including cyclic prefix-based orthogonal frequency division multiplexing (OFDM), filtered orthogonal frequency division  
Figure 1: Block diagram explaining backhaul connection to the baseband unit (BBU) connected to optical front haul (OFH), and then its transmission from the transceiver station. The base station further connects it to the remote radio heads (RRHs). Extending the network coverage via fibre and wireless infrastructure is shown w.r.t application scenarios such as picocell, stadiums, buildings, etc.  
multiplexing (F-OFDM) and generalised frequency division multiplexing (GFDM), which have been framed by the 3 GPP for the 5G NR Release 15 that describes the eMBB scenario.