# Multi-Technology Multi-Operator Site Sharing: Compliance Distance Analysis for EMF Exposure
## 1 Introduction  
Mobile networks are the fastest-growing wireless communication networks due to the massive increase in data service consumption, especially with the wide spread of smartphones and tablets. This leads to the generation of large data traffic over the mobile network that will reach very high figures by 2030 compared with 2020 [1, 2]. Expanding mobile networks necessitates the installation of additional BSs to increase network coverage and capacity. Most deployed sites involve the 2G Global System for Mobile Communication (GSM), 3G Universal Mobile Telecommunications System (UMTS), 4G Long-Term Evolution (LTE), and 5G NR, which has recently been introduced. The installation of more BSs raises electromagnetic field exposure levels, which has become a source of concern due to the effects on human health [3, 4, 5]. Several well-known international organizations have set standard guidelines, i.e., the International Commission on Non-Ionizing Radiation Protection (ICNIRP) [6, 7] and the Federal Communication Commission (FCC) in the USA [8]. These standards have been adopted by national regulators in many countries to control the installation of EMF transmitters. The ICNIRP and FCC guidelines distinguish between the general public and occupationally exposed individuals. The general public comprises normal individuals who are exposed to EMFs, and occupational personnel are the staff exposed to certain situations associated with EMFs and are well-trained for possible risks [6]. It is predicted that 5G technology will be the system for general purposes [9] because 5G provides a high capacity and enables many features [10]. This requires the installation of NR BSs at higher-frequency bands [11], and most are colocated with existing technologies (2G, 3G, and 4G). The group of solutions and technologies operating at one site causes an increase in EMF exposure, and investigation is needed to evaluate the total accumulated radiation and assess it versus the standard limits [12; 13; 14]. In many countries, the MNOs have started to share mobile sites to expand their network services in terms of coverage footprint and capacity resources [15]. Site sharing has become a good alternative and a key approach because of the following main reasons [16]:  
1. It is less expensive to share a site than to build a new one. According to [17], infrastructure sharing can result in significant cost savings--up to 40% of assets can be saved by site sharing, and cash flow can improve by 31% as a result. 2. The densification of the existing sites increases the difficulty of acquiring more physical sites within the required nominal locations and leads to fewer options. 3. Site sharing enables the rationalization of the legacy 2G and 3G networks, taking into account the declining revenues from 2G and 3G networks and the higher spectral efficiency of the next generation of 4G and 5G technologies. 4. Site sharing enables diverting the investment to other important innovations, such as the deployment of more 5G sites. 5. Site sharing has some social benefits because it lowers network costs, which lowers the customer's service fee. 6. Tower sharing benefits the environment by reducing the number of sites with better looks and views. Network sharing can proceed in many ways, starting from a small part of the infrastructure up to full sharing, including core parts [18]. Sharing can be classified into two groups. The first is passive sharing, which mainly involves sharing parts of the tower site, antennas, and/or the backhaul part (MW, transport, fiber, etc. ), as illustrated in Figure 1.  
The second group is active sharing, which consists primarily of sharing the Radio Access Network (RAN) component with a dedicated frequency spectrum for each operator as the Multi-Operator RAN (MORAN) and a shared frequency spectrum as the Multi-Operator Core Network (MOCN), as shown in Figure 2.  
Figure 1: Illustration of passive sharing between three operators.