ystem things control 10 kbps Latency 100 ms 10 ms Latency Figure 1.10 5G use case areas. 1 Introduction 2019+ 10 Gbps & 1 ms Massive IoT 2018+ High reliability Low latency 2017+ Massive MIMO Cloud radio Gigabit LTE Unlicensed LTE 600 Mbps Public safety Figure 1.11 4G LTE evolution path toward 5G. Evolution Path from LTE to 5G A part of 5G capabilities can be provided on top of 4G networks with 4.5G, 4.5G Pro, and 4.9G enhancements, also known as LTE-Advanced Pro. 4.5G was commercially available in 2016 with support for 600 Mbps peak rates. 4.5G brings also the first set of IoT opti- mization and public safety capabilities to LTE networks. 4.5G Pro supports 1 Gbps with carrier aggregation and 4x4 MIMO. LTE evolution can coexist on the same frequency with legacy LTE devices, which makes the LTE evolution a smooth step toward 5G. LTE evolution can complement 5G, especially in the early phase, when 5G coverage is still limited. Figure 1.11 shows the high-level evolution path from 4G LTE toward 5G. Mobile Data Traffic Growth 3G and LTE have been successful technologies in making wireless data available globally with great practical end user performance. Mobile data is SO convenient that the data volumes have grown rapidly. The advanced markets have already more than 1 GB of mobile data per person per day, and the growth continues further with LTE evolution and 5G. Figure 1.12 shows a few examples that highlight the impressive growth of data traffic. When the first 3G networks started 2001, the total global fixed Internet traffic was 6000 TB per day. When the first LTE networks started in 2010, the total mobile traffic was 8000 TB per day. When the first 5G networks started 2019, the mobile data traffic of even a small country like Finland was 8000 TB per day. The target of 5G technology is to enable very high capacity, that is, terabits per second, in a single stadium, which corresponds to several thousands of terabytes during a single sports game. 5G will be able to deliver a similar data volume during a single game 