## 2 An Overview of the Cellular Networks
### General Features of Cellular Networks
#### 2.1.1 Architecture  
Although the various technological solutions developed over the years differ from one another in several respects, they basically share the same network architecture, which conforms to the specifications of 3 GPP [32] and is described, for instance, in [29]. It consists of three main levels: mobile device, radio access network (RAN), and core network (see Figure 1).  
The mobile device level includes all the devices that use cellular services, such as phones, tablets, notebooks, and IoT appliances. Mobile devices are thus the part of the network which is directly managed by users. There are two types of device: a subscriber identity module (SIM), which contains information about users' numbers and accounts, and mobile equipment (ME)--that is, any device capable of accessing cellular services.  
The RAN level deals with the radio cells, which guarantee radio connectivity to the mobile devices. This level includes the base stations, which each control a set of cells and can be either omnidirectional (equipped with an antenna equally radiating in all directions) or sectoral (where each sector is generated by a different antenna). Sectored sites are the most common ones; there also exist mixed sites.  
\begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Acronym** & **Technology** & **Description** & **Acronym** & **Technology** & **Description** \\ \hline ARCN & GSM & Absolute Radio Frequency Channel Number & PCI & 4G & Physical Cell Identifier \\ BCC & GSM & Base station Color Code & PCU & GSM & Packet Control Unit \\ BSC & GSM & Base Station Controller & PMAN & All & Public Land Mobile Network \\ BSC & GSM & Base Station Id Code & PSC & UMTS & Primary Scrambling Code \\ BTS & GSM & Base Transceiver System & RA & GSM, UMTS & Routing Area \\ CCI & GSM, UMTS & Cell Global Identifier & RAC & GSM & Routing Area Code \\ CI & GSM, UMTS & Cell Identifier & RAI & GSM & Routing Area Identifier \\ EARFNC & LTE & Evolved ARFNC & RNC & UMTS & Radio Network Controller \\ ECI & LTE & E-UTRAN Cell Identifier & RSCP & UMTS & Received Signal Code Power \\ LA & GSM, UMTS & Location Area & RSRP & LTE & Reference Signal Received Power \\ LAC & GSM, UMTS & Location Area Code & ROLEV & GSM & Receiving Level \\ LAI & GSM, UMTS & Local Area Identifier & TA & LTE & Tracking Area \\ MCC & All & Mobile Country Code & TAC & LTE & Tracking Area Code \\ MNC & All & Mobile Network Code & TAI & LTE & Tracking Area Identifier \\ NCC & GSM & Network Control Code & UARCFN & UMTS & UTRA ARFCN \\ \hline \hline \end{tabular}
\end{table}
Table 1: Acronyms related to the specific network technologies used throughout the paper.  
Figure 1: A general architecture for cellular networks.  
The core network level provides all the interconnection services that ensure voice, messaging, and data to be delivered to the required destination. In addition, it guarantees various security and administrative services. It supports circuit switching (CS), which is needed for real time connections, packet switching (PS), to manage services which do not require a prior reserved channel between endpoints for transmitting, and the administration layer, for billing, managing network user databases, and similar tasks.