A mobile network provides wireless connectivity to devices on the move. These devices are most often smartphones, tablets or laptops, nowadays these devices also include cars, industrial robots, drones or, for example, home robots. All these devices are called UEs and in some cases they can also be UEs that do not move. Such a mobile network consists of two main parts. RAN (Radio Access Network) and MC (Mobile Core).

Zjednodušená architektúra 4G mobilnej bunkovej siete

Fig. V2: Simplified 4G Mobile Cellular Network Architecture [V12].

Radio Access Network

The RAN is the part of the mobile network connecting the UE to the cloud. 5G RAN uses 5G radio FDD (frequency-division duplexing) frequencies for wireless connection to devices. [L7] RAN has 3 main components, user equipment, gNodeB and distribution unit. UE is a device controlled by the user, such as a smartphone or tablet. The gNB is a base station that serves a certain area known as a cell and the DU performs user plane functions. RAN forwards UE signals that are wirelessly connected to the so-called network backhaul or CN. It sends them to different endpoints so they can travel through a different network. The mobile phone itself can be connected to several networks, which is called a dual-mode handset. Examples of some RAN types are GRAN (GSM RAN), GERAN (GRAN with EDGE packets), UTRAN (UMTS RAN) and E-UTRAN (LTE RAN). [L8] [L9]

Base station

It is the basic device of the 5G network. In 5G networks, the term gNodeB (Next Generation NodeB) is used. The base station realizes wireless signal transmission between the cable network and the wireless terminal and provides wireless coverage of the area. The density of base stations increases with frequency, in this phase 5G networks operate mainly in the 3000-5000 MHz band. Base stations can be divided into a 5G BBU (baseband unit) and one or more 5G RRHs (remote radio heads), or they can be combined into a single unit for a small cell with only 1 or 2 sectors. These units can be connected via CPRI (common public radio interface) or eCPRI (enhanced), which is important for 5G. CPRI is a serial interface that is a very fast connection. During the transition to 5G, there will be more and more traffic on the fiber between RRU and BBU, which complicates the implementation of the serial interface. Extreme 5G requests strain the fiber bandwidth limit. Then eCPRI is used, which can divide the baseband functions and give part of them to the RRU, while reducing the load on the fiber. [L10] 5G networks have different base stations with different architectures to support flexible network architecture and adapt to different scenarios. 5G base stations can be divided into different architectures. In terms of device form, 5g base stations can be divided into baseband devices, radio frequency devices, integrated gNB devices and other device forms. [L11] [L12]

RAN Controller
Rozdelenie CUPS

Fig. L6: Distribution of CUPS [L9]

RAN controller is software that controls the nodes that are connected to the RAN. It connects to the core network depending on the RAN type and is responsible for data encryption, radio resource management and mobility management. In modern RAN architectures, CP (control plane) and UP (user plane) are separated into different network elements. This is known as CUPS (Control and User Plane Separation). In this variant, the Ran controller exchanges user management data via the SDN (software-defined networking) switch, and the second set of data via the base stations via the second control interface. This division will be an important aspect of a flexible 5G RAN. [L12]

RAN process

The process in RAN is divided into several stages. These stages are together in the base station and each of them has a key role. These stages are RRC (Radio Resource Control), PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Media Access Control) and PHY (Physical Layer). The graphic representation and procedure can be seen in figure no. L7.

RAN proces

Fig. L7 RAN process [L9]

RRC works in CP RANky, it does not process packets on UP. Its main functions are connection establishment, release functions, RRC connection procedures, paging. [L13] PDCP has the task of compressing and decompressing headers, integrity protection, transmission of UP and CP data, and encryption. [14] RLC corrects errors using ARQ (Automatic Repeat Request), has the task of chaining, segmentation and reassembly of SDU (Service Data Unit). [L15] MAC is in charge of buffering, multiplexing and demultiplexing of segments, it is also designed to maximize the use of expensive licensed spectrum. [16] The PHY is responsible for coding, modulation and FEC (forward error correction).

The next step for a better understanding is picture no. 8. In the figure, the functionalities from Fig. L7 are divided between physical elements. This is called Split RAN. Such a split architecture allows us to coordinate performance characteristics such as responsiveness and cost. By separating the DU from the RU, for example, we save on costs because less intelligent RUs are cheaper. Videos, games or audio have different latency tolerances and such services depend on different deployment and traffic scenarios. This concept was introduced for 5G, but it can also be used with 2G, 3G and 4G. RAN is divided into CU (Central Unit), DU (Distributed Unit) and RU (Radio Unit). The RU is a hardware radio unit that converts the signals sent from the antennas into a digital signal. It takes care of DFE (digital front end) and lower PHY. The DU software is normally deployed close to the RU and runs the RLC, MAC and PHY parts. CU software operates RRC and PDCP layers. The split architecture allows the 5G network to use different protocol distributions between CUs and DUs, depending on the network design. Let's also be aware that Split RAN changes the nature of the so-called Backhaul network, which originally connected the base stations directly to the MC. With Split RAN we have multiple connections. RU-DU connection is called Fronthaul, DU-CU connection is called Midhaul and CU-MC is called Backhaul. [L9] [L17]

Split RAN

Obr. Fig. L8 Split RAN [L9]

Mobile Core

The 5G core is the heart of the 5G network, controlling DP (Data Plane) and CP operations. It is responsible for many different communication functions in the mobile network such as authentication, authorization and data management. MC provides an IP connection to the RAN and connects users to the Internet, while monitoring the movement of users between base stations and ensuring that the promised QoS (Quality of Service) connection is maintained. It can be said that MC is essentially a bundle of functions. 5G MC is called NG-Core (Next Generation) and uses SBA (servicebased architecture) architecture. MC can be viewed in two ways, from the 3GPP perspective and from the Internet. In the second version, the MC acts as a router that connects the physical RAN to the global Internet. In this way, IP addresses serve as a global identifier for us.

In the second perspective, the IMSI (International Mobile Station Identity) from the SIM (Subscriber Identity Module) card serves us as a global identifier, thanks to which communication between two mobiles is possible. [L9] [L18] [L19]

Components
5G Core Architektúra

Fig. L9 5G Core Architecture [L19]

MC consists of several functional blocks. AMF (Core Access and Mobility Management Function) is responsible for the management of registration, connectivity, reachability, mobility and various functions in protection and access. SMF (Session Management Function) is responsible for interacting with a separate data plane, creating, updating and deleting session PDUs (Protocol Data Unit) and managing the session context. PCF (Policy Control Function) guides control plane functions through usage rules. Through PCF, operators can manage and guide network behavior. UDM (Unified Data Management) is a centralized way of controlling network user data. Combines multiple data sources into a single data source. As a central repository of information, it is critical for user data and other network functions in the 5GC. AUSF (Authentication Server Function) is responsible for the protection procedure for SIM authentication. It handles routing based on SUCI (Subscription Concealed Identifier) and SUPI (Subscription Permanent Identifier). It supports the re-sync procedure. Maintains session states in an external centralized database. SDSF (Structured Data Storage Network Function) is a utility service used to store structured data. It is implemented through a SQL database. UDSF (Unstructured Data Storage Network Function) is a utility service used to store unstructured data, implemented via Key/Value Store. NEF (Network Exposure Function) is a function designed to act as a two-way gateway to allow trusted external organizations to access the CSP network to create a 5G innovative service. NRF (NF Repository Function) is a key element of 5g service-based architecture. It provides a single record of all network functions available in PLMN, along with the profiles and the services they support. [L9] [L18]

Differences between 4G and 5G

Changes at the core level are among countless architectural changes. 4G EPC (Evolved Packet Core) is largely different from 5G core. 5G uses virtualization and cloud design. 5G also uses a higher radio frequency. It was designed to guarantee high speeds, flexibility and low latency. Other changes include network slicing, massive MIMO and a move to millimeter waves that support multiple devices in an area. [L19] [L18]

Standalone a Non-standalone

There is SA and NSA architecture. Each has its advantages and disadvantages. The 5G NSA was already completed in 2017 and uses the 4G LTE RAN and core networks as a foundation, but with the addition of a 5G component carrier. SA uses 5G CN software for features and is essentially built from the ground up with 5G components and features. The disadvantage of SA is that it is not backward compatible with 4G, but it provides a high-speed connection and allows operators to save time and money. NSA is popular among operators for rapid deployment, but cannot provide advanced 5G NR features like SA. [L19]

Beam shaping

Another groundbreaking technology in 5G is beamforming, better known as beamforming. It is a type of radio frequency used to send strong, focused signals to a target device. In it, an access point uses multiple antennas to send the same signal to a specific receiving device. Normally, the signal would spread in multiple directions from the transmitting antenna. In this way, multiple signals are transmitted at the same time. The layering of the signal creates interference, which can be both constructive and destructive, depending on the correct deployment. With successful beamforming, the signal will be strong and focused on its target. The overall difference is that beamforming uses multiple antennas instead of one. As a result, these signals have a more direct connection that is faster and more reliable. Beamforming has several types, analog, hybrid, digital, Massive MIMO, and beam steering. In 5G, it is used to overcome common 5G problems such as range. Since 5G uses radio frequencies of 30 GHz - 300 GHz to communicate with devices, there is a greater chance of signal interference or difficulty passing through physical objects. This can be solved by several strategies such as using a very large number of antennas in a single 5G base station, but it can also be solved by beamforming. Other advantages are higher signal quality, faster transmission, less error rate, and analog beamforming is relatively easy to implement. [L19] [L20] [L21]

Speed

5G can theoretically reach speeds of up to 20 Gbps, which is 20 times faster than 4G. However, we will have to wait a long time to reach this peak in the real world. The highest download speeds these days are from 1 Gbps to 10 Gbps with latency down to 1 ms, with average speeds of 50 Mbps and above. Actual speed depends on connected device and 5G coverage. The resulting speed also depends on the type of 5G and the number of people connected to the network. There are 3 types of connection, low-band, mid-band and high-band. Low-band is also called, it has the lowest speed but offers greater coverage and penetration. Mid-band is the most used and can provide speeds from 10 to 1000 Mbps. The highest speeds are achievable in high-band and can reach up to 4 Gbps. Currently, there are bigger speed differences between operators. T-Mobile has the highest speed with an average of 150 Mbps. While AT & T has the lowest with an average of 49.1 Mbps, which is only slightly more than a regular 4G network. [L24] [L23] [L25]

Rýchlosť

5G môže teoreticky dosiahnuť rýchlosť až 20 Gbps, čo je 20 krát viac ako pri 4G. Nato aby sme dosiahli tento vrchol v reálnom svete však budeme musieť ešte dlho čakať. Najvyššie rýchlosti sťahovania v dnešnej dobe sú od 1 Gbps do 10 Gbps s latenciou až po 1 ms, pričom priemerná rýchlosť je 50Mbps a vyššie. Skutočná rýchlosť závisí od pripojeného zariadenia a 5G pokrytia. Výsledná rýchlosť taktiež záleží od druhu 5G a od počtu ľudí pripojených na sieť. Sú 3 druhy pripojenia, low-band, mid-band a high-band. Low-band je taktiež nazývané, má najnižšiu rýchlosť, ale ponúka väčšie pokrytie a penetráciu. Mid-band je najpoužívanejším a dokáže poskytnúť rýchlosť od 10 do 1000 Mbps. Najvyššie rýchlosti sú dosiahnuteľné v high-band a môžu dosiahnúť až 4 Gbps. Momentálne sú väčšie rozdiely rýchlosti medzi operátormi. T-Mobile má najvyššiu rýchlosť s priemerom 150 Mbps. Pričom AT & T má najnižšiu s priemerom 49.1 Mbps, čo je len o málo viac ako bežná 4G sieť. [L24] [L23] [L25]

Latency

Latency is the biggest difference between 4G and 5G. The promised value is under 5 milliseconds and according to several sources it could be as high as 1 millisecond. The ideal over-the-air latency for 5G is 8 to 12 milliseconds, with this latency increasing with retransmissions and the like. This latency can be reduced to 10-15ms using edge servers near the transmitters. 4G latency currently ranges from 60 to 98 ms, which is approximately 5 times higher. [26] Such extremely low latency is good for VR (Virtual Reality) gaming, text translation and normal everyday use, but probably the biggest use is in V2X communication. The average human reaction time is 250 ms, your car can react 25 times faster than the average human, which can help prevent a traffic accident. [L24] [L23] [L25]

Disadvantages

Like any new technology, 5G also has its drawbacks. One of these disadvantages is backward compatibility. Older devices without 5G support are automatically useless as far as 5G is concerned. Another limitation occurs during deployment. 5G will mainly be deployed in large cities with a high population, meaning that rural areas and smaller cities will not have access to this technology in the near future. This is due to the fact that investment in infrastructure is not cheap. Another significant problem is range and natural interference. Buildings, trees and similar obstacles can absorb or disrupt the signal, and the connection distance is not very long, since the frequency waves travel only a short distance. 5G uses millimeter waves, which are much shorter than the waves of 4G. In addition to physical obstructions such as buildings and trees, high frequencies are susceptible to moisture and rain. 5G is a relatively new technology and has security and privacy issues that have yet to be resolved. People can still use IMSI catchers on 5G networks. Network Slicing also creates new vulnerabilities. Attackers can exploit a weakness in one network slice and then laterally move into others. [L27] [L28] [L29]