2019 will be the year of 5G. 5G will become real in 2019 as service operators around the world have already begun deploying 5G services. To date, mmWave deployments have been targeted to fixed wireless access, or in other words fiber to the home (FTTP) replacements. The early 5G sub 6 GHz rollouts are a milestone but mmWave is the pathway to the transformational impact needed for the 5G ecosystem.
mmWave spectrum has been a major focus for wireless researchers and 5G ecosystem suppliers because of the copious amount of spectrum available for mobile access in both the licensed and unlicensed bands. In fact, mmWave spectrum for 5G dwarfs the spectrum available for prior generation cellular, WiFI and Bluetooth combined! More spectrum equates to higher data rates and the ability to accommodate more users assuming similar spectral efficiencies.
Today, most 5G deployments target sub 6 GHz spectrum and the Non-StandAlone (NSA) architecture. NSA uses LTE as the anchor for the control plane, and the user plane flows directly to the EPC (4G) or NGC (5G) depending on the specific NSA architecture. 5G mmWave will likely follow mainly because the technology is still in its infancy. Sub 6 GHz 5G does increase bandwidth but not at the scale of 5G mmWave. The 5G mmWave deployments will rely on the NSA architecture and in thinking about this issue, a question arises, “Does 5G standalone (SA) make sense?”
Although there is quite a bit of spectrum earmarked for 5G mobile access in the mmWave bands, the propagation of waveforms at these frequencies is much shorter than the sub 6 GHz implementations. In addition, mmWave waveforms are highly directional and can be blocked causing disruptions to the link. The 3GPP has devoted a good portion of the specification to the concepts of beam management and beam recovery to address these scenarios that should work in theory, but the question is whether they will work in practice and at what efficiency?
Now, consider the configuration – NSA or SA for 5G mmWave. The advantages of SA for any 5G deployment include lower latency and lower cost as the network does not need to rely on 4G/LTE for the control information. However, NSA also makes a lot of sense for 5G mmWave because LTE deployments are available and robust. In the SA 5G mmWave scenario, the control channels utilize the same 5G mmWave spectrum as the data. For NSA 5G mmWave, LTE provides the anchor and the control information is transmitted over that link.
For example, when a 5G mmWave UE is connected to a gNodeB where both the control and user planes utilize a mmWave band, the control information is subjected to the same interference and blocking challenges as the data plane and thus the beam management and recovery will be engaged to maintain the link but these procedures take time and the likelihood of link disruption is quite high. NSA provides a more stable link for the control plane and may prove critical in terms of gNodeB handoff and cell selection for the mobility case. Handoff is very important because the rate of handover will be much higher in a mmWave network due to the greater density of base station deployments.
As the industry moves toward closer to a 5G reality, mmWave continues to be an important technology for mobile access to realize the goals and objectives of 5G. Architectural choices such as the tradeoffs between NSA and SA become more poignant and perhaps difficult. It will be interesting to see if service operators do, in fact, deploy 5G SA mmWave technologies, but I suspect we will see mmWave deployments dominated by NSA for the short-term.
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