 tion, beamforming antenna gain, and uplink solutions are discussed. 10.6.1 Signal Propagation at 3.5 GHz Band Higher frequency leads to higher signal attenuation and shorter propagation. The Okumura-Hata propagation models show a 10 dB difference in path loss between 3.5 and 1.8 GHz. Nokia has conducted propagation measurements at 3.5 GHz, and the results are summarized in Figure 10.21: the outdoor propagation difference is 5.8 dB in non-line-of-sight (NLOS) conditions and less in the line-of-sight (LOS) case. There is an additional 3-5 dB indoor penetration loss at 3.5 GHz, which makes the total path loss difference 9-11 dB in indoor conditions. For more details, see [7]. We can conclude that there is a propagation difference between 3.5 and 1.8 GHz of approximately 10 dB. The difference is less outdoors and can be more in deep indoors. 10.6.2 Beamforming Antenna Gain The physical size of the antenna becomes smaller when the frequency increases. Alter- natively, the antenna gain can be increased while maintaining the antenna size at higher bands. A 3.5 GHz antenna can therefore provide higher gain than a 1.8 GHz antenna in the same form factor. Figure 10.22 shows typical three-sector four-port passive antennas at 700-900 MHz bands and at 2 GHz bands. The antenna at 2 GHz gives an 18 dBi gain Pathloss difference 3.5 GHz VS. 1.8 GHz [dB] 6.0 Outdoor Indoor shops Indoor old Indoor modern building building Figure 10.21 Path loss difference between 3.5 and 1.8 GHz. 10.6 Coverage for Sub-6-GHz Band <1 GHz 2 GHz 3.5 GHz 7-10 dB gain 1.5 m 1.3 m 38 cm 32 cm <50 cm 15 dBi 18 dBi 25 dBi 0.57 m2 0.42 m2 <0.50 m2 Passive 4-port antenna Massive MIMO antenna Figure 10.22 Antenna gain and size benchmarking of low band passive antenna with mid-band massive MIMO antenna. with a frontal area of approximately 0.4 m². A massive MIMO antenna at 3.5 GHz has a similar area while providing 25 dBi antenna gain, that is, 7 dB more than at 1.8 GHz. A higher antenna gain means that the beams become narrower. Therefore, traditional sec- to