 4 X 4 mmWave, Metro- Outdoor Microware, 2 X 2 mmWave, Pico-cell Indoor/ 32-100 < 0.3 mmWave, outdoor 2 X 2 sub-6 GHz, relay Femto- Indoor < 0.1 Sub-6 GHz, 2 X 2 relay 94 Chapter 1 Narrowband channels Wider channels Ultra-wideband channels 3, 5, 40 MHz 3.5, 56, 112 MHz High-order modulation 64QAM, 250, 500, 5000 MHz Higher order modulation 256QAM Low-order modulation QPSK, 16QAM, 64QAM 64QAM, 256QAM, 1024QAM S, C band C, Ku, K, Ka band Q band V band E band Frequency (GHz) Sub-6 GHz Microwave mmWave Figure 1.41 Frequency spectrum, channel bandwidth, and modulation considerations for RF bands [79]. Table 1.3 summarizes different characteristics for each wireless backhaul method and fur- ther outlines the key factors to be considered in backhaul selection. Low-order modulation schemes such as QPSK can be used with wideband channels or for operation in poor atmospheric conditions with low SNR channel conditions. On the other hand, high-order modulation up to 2048 QAM can be used with narrowband channels or for operation in good channel quality and in clear atmospheric conditions. Depending on the link capacity requirements, deployment scenario, SNR, and atmospheric conditions, the data throughput can range from 100 Mbps to 10 Gbps. For macro-cell base station applications, the migration from indoor units to full outdoor units lowers the power, improves signal quality, and lowers OPEX. Macro-cells take advantage of full outdoor unit partition because RF loss in the waveguide or coaxial cable is minimized, or eliminated, which lowers RF power output and improves receiver input sensitivity. In small-cell base stations, the adop- tion of an integrated configuration means that systems can achieve a small footprint with lower equipment cost. Small cells benefit from an embedded partition because a single unit houses the wide and local area network connectivity, and wireless backhaul radio functions, resulting in reduced system size and simplified installation. Furthermore, since many small- cell deployments rely on E-band/