*1.2.1 5G NR RAN (gNB)*

5G NR (New Radio) is the global standard for the air interface of 5G networks developed by 3GPP with operation from below 1 GHz up to more than 40 GHz and massive MIMO beamforming capability [8].

**Figure 1.** *5G system architecture (vRAN approach).*

RAN stands for Radio Access Network. RAN provides radio access and coordinates network resources across User Equipment (UE). For more general, the RAN is divided into two parts. The first part is the lower layer RAN split including the antenna integrated Radio Unit (RU) and the Distributed Unit (DU). The second part is the higher layer RAN split, a 3GPP standard F1 interface between the DU and the Centralized Unit (CU). DU and CU constitute Baseband Unit (BBU) [9].

Legacy LTE uses Evolved Node B (eNodeB or eNB) like Base Station (BTS) in GSM networks. Similarly, gNodeB (gNB – next generation Node B) is 5G Base Station. gNB features Software Defined Radio (SDR) with various MIMO options described in session 3 of this chapter [10].

In 5G NR, RU handles digital front end (DFE), part of the physical layer (low physical) and multiple beamforming operation. RU consists of a Remote Radio Head (RRH) and Active Antenna System (AAS) [11]. Antennas in AAS for 5G NR make use of the shorter element sizes at high frequencies to incorporate a larger count of radiating elements. These antenna arrays are essential for MIMO beamforming operations that play a vital role in 5G systems [12]. The RRH performs all RF functions like ADC/DAC, digital up/down-conversion, filtering and transmitting and receiving signals to the BBU including beamforming. RRH can also provide monitoring and control functions to optimize system performance.

In LTE systems, RRH is connected to the antenna by RF coaxial cable and is usually mounted near the antenna to reduce transmission line losses. In 5G NR, RRH and AAS are integrated in a small and compact form factor [6].

Common Public Radio Interface (CPRI) is the standardized interface that sends data from the RRHs to the Base Band Unit (BBU). CPRI is a very high-speed connection on fiber optic cable. eCPRI is enhanced CPRI which is used to reduce the burden on the fiber. The connection between the RUs and the DU is called fronthaul and it is fiber optic cable.

DU stands for Distributed Unit. DU is placed close to RU and runs RLC, MAC, parts of the Physical layer. This function consists of signal processing, network access. DU is controlled by CU (Centralized Unit). DU also supports FFT/IFFT functions [13].

CU provides support for the higher layers of the protocol stack such as SDAP, PDCP and RRC. Practically, there is a single CU for each gNB. A CU can control multiple DUs (can be more than 100 DUs). Each RU corresponds to one cell. Each DU can support one or more RUs, so in 5G systems, one gNB can control hundreds of cells. 5G NR cell can be femtocell, smallcell or macrocell [14]. 5G Small Cell Radio Nodes can be installed on walls or ceilings with network connectivity and power are provided over Ethernet. Midhaul connects the CU with the DU via F1 interface. Backhaul connects the 5G core to the CU. The 5G core may be up to 200 km away from the CU.

RIC is RAN Intelligent Controller which is responsible for all RAN operation and optimization procedures such as radio and resource connection management, mobility management, QoS management to support the best effective network operation.

There are three different approaches to design a RAN as abstracted in **Table 1** [15].

### *1.2.2 5G Core network*

According to the definition of 3GPP, 5G has two networking modes: SA (Standalone) and NSA (Non-Standalone). 5G system Service-based


#### **Table 1.**

*RAN classification.*

**Figure 2.**

*5G system service-based architecture with core network functions.*

architecture is illustrated in **Figure 2** and corresponding functions are described in **Table 2** [16].

The EPC (Evolved Packet Core) network consists of MME (Mobility Management Entity), S-GW (Service Gateway) and PDN gateway. EPC performs functions such as mobility management, IP connection, QoS management, and billing management.

#### **1.3 Chapter structure and organization**

The structure and organization of this book chapter are illustrated in **Figure 3**.

### **2. Basic multiplexing techniques**

The term "multiplexing" refers to the sharing of a *system resource* (SR) to a set of users. There is a subtle distinction between multiplexing and multiple access, while multiplexing means the SR sharing is "fixed" (*static* multiplexing) or adaptive

*Multiplexing Techniques for Applications Based-on 5G Systems DOI: http://dx.doi.org/10.5772/intechopen.101780*


**Table 2.**

*Core network functions.*

#### **Figure 3.**

*Structure and organization of the book chapter.*

change (*dynamic* multiplexing), multiple access techniques are those techniques that enable multiple users to share limited SRs remotely.

Multiplexing allows multiple channels/users to share the same SR. Multiplexing helps to increase the efficiency of using the SR and the transmission capacity of the system. Dynamic multiplexing makes the allocation of the SR more efficient.

5G NR systems also use "duplexing schemes" for Uplink (UL) and Downlink (DL) data transmission.

The traditional multiplexing techniques are:

1.*Frequency Division Multiplexing (FDM):* Specified subbands of frequency are allocated. Suitable for analog signal transmission, widely used in analog broadcast radio and television.


We are now considering basic multiplexing techniques.
