There are ongoing efforts to mitigate these physics challenges, such as massive MIMO (multiple-input, multiple-output) and beamforming. Massive MIMO is an antenna array that will greatly expand the number of simultaneous connections and throughput, and will give base stations the ability to send and receive signals from many more users at once and increase the capacity of networks significantly, assuming multiple RF paths to users exist. Beamforming is a technique for identifying the most efficient data-delivery route to a particular user and reducing interference for nearby users in the process. These options can improve the propagation of mmWaves, but challenges remain with maintaining connectivity across a broader area using this part of the spectrum. Significant time and R&D will have to be devoted to solving the mmWave propagation problem before it can be deployed as a more universal wireless network solution.
Sub-6
Sub-6 includes the range of spectrum below 6 GHz. Sub-6 can provide broad area network coverage with lower risk of interruption than mmWave due to its longer wavelength and greater capacity to penetrate obstacles. It therefore requires less capex and fewer base stations, as compared to mmWave. This, together with the ability to leverage existing 4G infrastructure, makes sub-6 the lower hanging fruit for a potential 5G sub-6 ecosystem. Faster time-to-rollout is particularly important given the speed at which China is pushing forward. While mmWave may ultimately be deployed in specific environments where its propagation and cost challenges are not prohibitive, sub-6 will likely provide the broader solution for more wide area 5G coverage in the near term. This in turn will drive product design and manufacturing for the 5G supply chain, given the larger quantity of equipment that will feed that sub-6 network.
Maximizing the potential of 5G requires hundreds of consecutive MHz of bandwidth in order to optimize performance, and the sub-6 spectrum is already crowded with existing systems and uses. In the United States, sub-6 5G technologies will likely be deployed in existing macrocell networks and infrastructure through existing LTE spectrum. This would give modest improvements to RF system performance, but would not yield a 10x performance improvement over modern versions of LTE operating in the same spectrum. This failure to deliver the same disruptive speed improvements that LTE had over 3G would mute the impact of 5G deployment in the United States.
An additional challenge in the United States is that the government owns large portions of the sub-6 spectrum and limits commercial access to them. It is possible to relocate Federal users or share these bandwidths to allow commercial sector to develop 5G capabilities on them, but both of these processes are time-intensive. The average time it takes to “clear” spectrum (relocate existing users and systems to other parts of the spectrum) and then release it to the civil sector, either through auction, direct assignment, or other methods, is typically upwards of ~10 years. Sharing spectrum is a slightly faster process because it doesn’t require a complete upheaval of existing federal users, but even that has historically taken upwards of five years.
There are also legitimate concerns within DoD that sharing its bandwidths in the sub-6 spectrum will create a number of operational issues, from spectrum optimization to security vulnerabilities.
