# Fibre Wireless Distributed Antenna Systems for 5G and 6G Services
## 1 Introduction
Due to its cost-effective and easy paradigm, which improves the network's range, this transport approach is a significant option for high-capacity wireless transmission. Due to its straightforward and economical paradigm that increases the network's coverage, this transport strategy represents a substantial advancement for exceptionally high-capacity wireless transmission [16]. RoF links undergo nonlinear severities caused by the link components, which can be alleviated using linearization procedures [17; 18; 19]. Several types of RoF implementations include analog RoF (A-RoF) [20; 21; 22; 23; 24], digital RoF (D-RoF) [25; 26; 27], and sigma-delta RoF (\(\delta\)RoF) links [28; 29; 30]. Signal degradation affects A-RoF for tens of kilometres. To overcome these issues, the network's reach for D-RoF is cost-effective for longer links [25]; however, the system's cost rises, owing to the superior bandwidth resolution of the analog digital converter (ADC) and the need for extra signal processing. In fronthaul networks, the low efficiency and elevated data traffic demand are also problematic [28]. \(\delta\)RoF avoids the common public radio interface (CPRI) bottleneck with a 1-bit ADC. A 1-bit operation causes substantial quantization noise, necessitating the inclusion of a passband filter (BPF) on the receiver side, leading to increased complications of the techniques. Consequently, the A-RoF is a better alternative than digital and sigma-delta RoF [29; 30] as it is simple, reasonably economical and already has a widespread structure. Additionally, multichannel aggreggations enable the RoF to support many signals from the same or separate providers at once [31]. More specifically, utilizing RF circuits or digital signal processing (DSP), various mobile data are converted onto an intermediate frequency (IF) carrier; as a result, many signals are transported simultaneously on a single optical carrier. Therefore, the RoF transmission link makes it possible for the DAS network, which may have different architectural configurations, to distribute these multiple signals flexibly. Future access scenarios in which many airways, including mm-Wave and THz bands, coexist would greatly benefit from these features. As fewer optical transceivers (TRx), which make up most of the indoor DAS network's CAPEX and OPEX, are needed, the total ownership cost referred to as TCO is decreased by improving the efficiency of the optical transceivers. Figure 1: Block diagram showing a backhaul, the baseband unit (BBU) connected to an optical front haul (OFH). The base station connects the remote radio heads (RRHs), the distributed antenna system for industrial and indoor factory use case is also shown where RoF as an OFH is connected to the RRH and then DAS via source donor and receive antennas is integrated with hub unit for wireless connectivity. transport network. However, the effects of coexisting mm-Wave and THz services within an indoor environment have not been thoroughly studied. The 5G networks use sub-7 GHz bands, but these are congested and have limited bandwidth. To meet the growing demand for mobile data, it will be necessary to move to higher frequency bands, such as the millimetre-wave range. The 3 rd Generation Partnership Project (3 GPP) has defined two frequency ranges for 5G networks: FR1 (0.41-7.125 GHz) and FR2 (24.25-52.6 GHz) [32]. For example, the FR1 frequency range might be used for cellular, machine-type communication (MTC), ultra-reliable low-latency communication (URLLC), and enhanced machine-type communication (eMTC) applications. Meanwhile, the FR2 range has a lot of unused spectrum that can be used for high-speed broadband transmission for indoor applications, such as gigabit-per-second enhanced mobile broadband (eMBB). This study aims to provide the following:  
1. A RoF-based DAS network that is capable of supporting both 5G mm-Wave and 6G THz services at the same time is proposed. 2.