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the base station and the home—FWA can actually perform very well in both urban and suburban settings. It's true that vegetation and interference are challenging, but these can be overcome with antenna arrays that provide high gain. • Sub-6 GHz. This lower-frequency spectrum helps overcome the problems caused by obstructions, but at a cost. Only 100MHz of contiguous spectrum is available, so data rates are lower. Efficient use of frequency range (sub-6GHz or mmWave) is critical to scaling deployments. The choice for any situation will depend on balancing the goals of speed and coverage. Achieving higher data rates with antenna arrays An FWA system will also need to employ active antenna systems (AAS) and massive MIMO (multiple input/multiple output) to deliver gigabit service. • AAS provides many directional antenna beams. These beams are redirected in less than a microsecond, enabling beamforming that offsets the greater path loss associated with high frequencies. • Massive MIMO uses arrays of dozens, hundreds, or even thousands of antennas, allowing simultaneous transmission of single or many data streams to each user. The results are improved capacity, reliability, high data rates, and low latency. Beamforming also enables less inter-cell interference and better signal coverage. Learn more about AAS and massive MIMO included in this eBook. All-digital or hybrid beamforming A third element to consider is the type of beamforming to employ—all-digital or hybrid. All-digital approach The most obvious choice in mmWave base station applications is to upgrade the current platform. You could explore extending all-digital beamforming massive MIMO platforms used for sub- 6GHz frequencies, but this isn't a plug-and-play solution An all-digital approach faces these design constraints: • Power consumption. Digital beamforming uses many low- resolution analog-to-digital converters (ADC). But ADCs with a high sampling frequency and a standard number of effective bits of resolution can consume a large amount of power. This power consumption can become the bottleneck of the receiver. A large AAS with massive bandwidth presents a huge challenge for an all-digital beamforming solution. Essentially, the power consumption will limit the design. • The need for two-dimensional scanning in dense urban environments. The required scanning range depends on the deployment scenario, as shown in the figure below. In a dense urban landscape, wide scan ranges are needed in both azimuth (~120°) and elevation (~90°). For suburban deployments, a fixed or limited scan range (< 20°) in the elevation plane may be enough. A suburban deployment requires limited scan range or half as many active channels to achieve the same effective isotropic radiated power (EIRP), which reduces power and cost. FWA Array Complexity Depends on the Scanning Range Needed for the Deployment Scenario To achieve the target EIRP of 75dBm and beamforming gain, an all-digital solution using today's technology would need 16 transceivers. This would equal a total power consumption of 440W. But for outdoor passive-cooled, tower-top electronics, it's challenging to thermally manage more than 300W from the RF subsystem. We need new technological solutions. | 7 | Remember: An array's size is dependent on: • The scanning range (azimuth and elevation) • Desired EIRP EIRP is the product of: • The number of active channels • Conducted transmit power of each channel • Beamforming gain (array factor) • Intrinsic antenna element gain #3 #2

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