# Overview of Mobile Communications in Colombia and Introduction to 5G
## 1 Introduction
### 5G in Colombia  
Fourth-generation mobile systems offer enormous advantages over their predecessors, especially in terms of Internet connection speed. However, these networks are not capable of meeting the service needs of natural and industrial users. For example, they do not allow the connection of millions of devices that will be connected to the IoT. Some of the improvements that 5G has over 4G include 100 times faster data transmission, lower end-to-end latency, and higher capacity [22]. Another novelty of 5G is the variety of scenarios that are envisaged and that are related to different applications: enhanced mobile broadband (eMMB), massive machine-type communications (mMTC) and ultrareliable and low-latency communications (uRLLC). As for eMMB, it achieves mobile broadband thanks to high data rates, while uRLLC guarantees connection reliability thanks to low latency [23]. On the other hand, mMTC connects millions of devices (IoT elements) in a small geographic area [24]. Figure 3 presents the 5G application scenarios. Figure 2: Proportion of households with Internet connection. Source: DANE [20]. Of the three application scenarios, eMBB and uRRLC require more channel capacity than 4G. Since the radio spectrum below 1 GHz and from 1 to 6 GHz is saturated with wireless services at some intervals, a portion of the centimeter waves (above 6 GHz up to 30 GHz) and millimeter waves (between 30 and 300 GHz) will enable the bandwidth needed in 5G, as is the case with eMBMB aimed at offering high-speed, low-latency services. To this end, the United States auctioned spectrum blocks at 24, 28, 37, 39, and 47 GHz [25], and Brazil and Sweden at 26 GHz [26; 27]. The most prominent challenge to overcome in the efficient deployment of 5G using the centimeter and millimeter bands is the increase in radio signal attenuation as the frequency increases, requiring rigorous planning of the radio infrastructure. The monthly global mobile data volume will increase fivefold by 2024 compared to 2018, reaching 136 exabytes [28]. This amount is partly high due to orthogonal frequency division multiplexing (OFDM), the dominant waveform in 4G and 5G wireless communication systems that increases the data rate [29]. The third-generation partnership project (3 GPP) in the 5G new radio (NR) physical layer chose cyclic-prefix OFDM (CP-OFDM) as the waveform to support downlink (DL) and uplink (UL) transmission, while DL also uses DFT-s-OFDM (discrete Fourier transform spread based) in the frequency ranges of FR1 from 410 MHz to 7.125 GHz with bandwidth up to 100 MHz; and FR2 from 24.25 to 52.6 GHz with bandwidth up to 400 MHz [30; 31; 32]. DFT-s-OFDM closely resembles the single-carrier SC-FDMA waveforms used in LTE UL. DFT-s-OFDM, based on CP-OFDM, and operates DFT at the transmitter side to spread the signal among the allocated subcarriers, resulting in lower PAPR (peak to average power ratio) in coverage-limited user equipment (UE), because energy efficiency is a critical issue in transmissions for mobile users (MUs) battery [33; 34]. For their part, the CP-OFDM coding technique adds the tail portion of each OFDM symbol to the header, generating a guard band with a duration equal to the expected delay [35]. In this way, it reduces inter-symbol interference (ISI) in channels where bit errors occur due to delays caused by different propagation paths [36]. The introduction of 5G is often facilitated by sharing part of the radio spectrum of 4G-LTE cellular networks with 5G NR. Thus, choosing CP-OFDM at the PHY layer makes it complement, coexist, and adapt to each other's multiple similarities [37], even though LTE uses fixed 15 kHz subcarrier spacing for the network-wide data channel and 5G uses integral 15 kHz multiple subcarrier spacings given by \(15*2\eta\) (\(\eta\) integer) [38; 39]. Figure 3: 5G application scenarios. Fifth-generation technology increases channel capacity with more bandwidth per carrier (from 5 to 400 MHz) [40], being spectrally more efficient due to the higher orders of the modulation schemes [41; 42].