MP), IoT optimization, and device-to-device (D2D) connectivity. Release 13 pro- vided LTE downlink operation on the unlicensed bands, also known as License Assisted Access (LAA), enhanced carrier aggregation beyond 100 MHz, three-dimensional (3D) beamforming, and support for Machine Type Communications (MTC) with LTE-M and narrowband IoT (NB-IoT). Release 14 brought very low latency operation as well as uplink LAA, and enhanced 3D beamforming to 64 antenna ports. Release 15 is considered as the last major LTE release, and provides a number of significant new features, including short Transmission Time Interval (TTI) and Ultra-Reliable Low Latency Communication (URLLC), Time Division Duplex (TDD) support for NB-IoT, additional enhancements to MTC, V2X, and many others. Release 16 brought high power broadcast solution to LTE. The main LTE features of each 3GPP release are summarized in Figure 16.3 The evolution of the LTE peak data rate in commercial devices and networks is illustrated in Figure 16.4. LTE started with 150 Mbps using 20 MHz spectrum and 2x2 MIMO. The main solution for increasing the data rate is carrier aggregation: 16 LTE-Advanced Evolution 2 Gbps 1.4 Gbps 1 Gbps 600 Mbps 450 Mbps 300 Mbps 150 Mbps Figure 16.4 LTE peak data rate evolution in commercial networks. Commercial LTE networks Figure 16.5 Number of commercial LTE networks [4]. 20 + 20 MHz gives 300 Mbps and 3x20 MHz (3CA) gives 450 Mbps. 600 Mbps is obtained with 3 X 20 MHz and 256-QAM. A data rate of 1 Gbps and higher can be obtained with a combination of carrier aggregation and 4x4 MIMO. Data rates of 300-600 Mbps became available during 2015 and the peak rate of 1 Gbps during 2017. The latest devices can already support 2 Gbps peak rate. Since the opening of the first LTE network in 2009, the number of commercial net- works has increased rapidly to over 700 in more than 200 countries by 2018. The rapid growth of launches occurred during 2012-2015. The number of launched networks shown in Figure 16.5. LTE-Advanced needs a lot of spectrum