If DoD operators are forced to share their bands of the spectrum, there is concern that this may reduce the performance of systems. The addition of commercial users would also increase the overall congestion of the sub-6 spectrum, increasing the risk of connectivity interruptions for DoD operators. There is precedent for successful spectrum-sharing - in 2010, the FCC opened up the 3550-3700 MHz bandwidth (known as Citizens Broadband Radio Service, or CBRS) to the commercial sector. However, this process took more than five years, a timeframe that is untenable in the current competitive environment. This paper will explore the CBRS case study in more detail in Chapter 3.
Given these benefits and challenges associated with mmWave and sub-6, the future of 5G may involve some combination of both. Sub-6 is optimized for broad area coverage, which will make up a large part of the network, but mmWave may ultimately be able to provide more exquisite coverage in specific scenarios, and has some distinct military advantages in some topographies by virtue of being harder to intercept. This will require further research and testing in the mmWave spectrum targeting the current physics challenges around propagation, which may in turn lower the capex required for mmWave infrastructure deployment. In the near term, 3 and 4 GHz spectrum will likely serve as the dominant global bands that drive volume in infrastructure and device deployments. In the current state of 5G development and spectrum usage, it is unlikely that the United States will be able to leverage such technology, much less lead the rest of the world in that band of spectrum deployment as it did with 4G almost a decade ago.
