, advanced digital signal- processing capabilities, and mmWave radio frequency integrated circuits (RFICs) have made it pos- sible to use these high-frequency bands as a part of the 5G network. At the same time, 5G will also use licensed and unlicensed spectrum below 6 GHz. These bands will play an important role providing the coverage needed for massive MTC and the reliability needed for critical MTC. Hence, to realize the full capabilities of a 5G network will require the new mmWave bands in combination with more conventional spectrum bands. 5G will implement a range of new technologies to support these new capabilities and the new mmWave spectrum band. These are described below. 11.5.2.1 Advanced Multielement Antenna Structures Figure 11.17 illustrates the concept of a phased array antenna. This is an essential technology needed in mmWave to overcome the propagation challenges. Conventional LTE systems typically use 2-4 antenna elements with independent signals in a multiple input multiple output (MIMO) configura- tion. Full dimension MIMO (FD-MIMO) extends this to tens of antenna elements, using techniques that are most effective in TDD spectrum bands. 5G will increase the effectiveness of FD-MIMO in FDD bands below 6 GHz, improving capacity and efficiency in sub 6 GHz spectrum. Due to the small size of antenna elements at mmWave frequencies, hundreds of antenna elements can fit in a reasonably sized antenna structure. This allows the system to compensate for propagation loss through beamforming, which can concentrate specific transmissions aimed at the location of each device. Because each beam can carry a different signal in the same frequency, this technology also enables a significant increase in capacity. Building the Network of the Future FIGURE 11.17 Phased array antenna with beam forming. With the very high bandwidths used in the mmWave frequency band, and the very high number of antenna elements used in both phased array and FD-MIMO antenna structures, the use of CPRI in a cRAN structure becomes impr