现有的 4G LTE 设备将继续无缝连接到 4G LTE 无线接入网络，即便在它们将来演进并能够支持第一代 5G 网络时，也是如此。
When the members of the industry-led 3GPP consortium began drafting the standards that would eventually define the fifth generation of mobile communication technology, 5G, one point was clear off the bat: 5G technology would not replace 4G LTE. Instead, it would complement it, extending the potential scope of cellular technologies to a wide array of new applications targeting consumers, industrial and automotive markets, and more.
True to their commitment and wary not to stunt market growth for LTE-M and NB-IoT, 4G LTE’s two low power wide area cellular (LPWA) technologies, the 3GPP has since gone out of its way to enable the compatibility of 4G LPWA technologies with the 5G radio access networks. And with Rel 16 and Rel 17 still in the making and chipsets and devices not expected until 2023, LTE-M and NB-IoT will continue to serve their use cases well into the foreseeable future.
LTE-M and NB-IoT were defined in 3GPP Rel 13 and evolved with a handful of additional features in Rel 14. These 4G LTE air interface technologies were designed to enable an emerging class of applications that sporadically transmit small amounts of data using power constrained devices with increased coverage requirements. LTE-M and NB-IoT continue to expand their footprint, as networks around the world continue to roll out and mature.
With all the hype around the rollout of the first 5G networks, we have seen customers voice concerns over the compatibility of 4G LTE LPWA devices with this new infrastructure. Specifically, the confusion has centered on whether 3GPP Rel 13-compliant devices carry a disadvantage over those compliant with 3GPP Rel 14. Some clarification is clearly due.
Compatible with 5G radio access networks...
The first point worth making is that neither LTE-M nor NB-IoT use a 5G New Radio (NR) air interface. In fact, 5G NR, which optimizes the waveforms currently used by LTE technology, wasn’t even defined until 3GPP Rel 15, which was only frozen in 2019. Furthermore, NB-IoT and LTE-M devices that comply with 3GPP Releases 15 and 16 will continue to use a 4G LTE air interface. This is because 5G NR radio access networks offering in-band support for LTE-M and NB-IoT will only become optional (at the mobile network operator’s discretion) in 3GPP Rel 16 (expected to be completed in June 2020).
The 5G RAN can be designed to look like a 4G RAN to the LPWA devices, with 3GPP intending to make their 5G RAN compatible with legacy Rel 13-15 LPWA devices. Whether this pans out or, alternatively, the 5G RAN only works with Rel 16+ devices remains to be seen. We should have better visibility into this once 3GPP Rel 16 is frozen.
Another important point is that 5G NR-based RANs, as presently deployed, are built on top of existing 4G LTE radio access networks, effectively using the LTE network connection as an anchor. The fact that these LTE networks are expected to remain in place for many, many years to come - we know of no MNO that has announced an LTE sunset timeline – means that existing Rel 13 and Rel 14 LTE-M and NB-IoT devices, as well as the many billions of ‘legacy’ Rel 8-14 4G LTE devices will continue to connect seamlessly to them. This will remain true even as 5G networks deploy as overlays, mostly on different frequencies from their 4G LTE cousins .
...and any 4G compatible 5G core networks
Now, new 5G core networks are being deployed, with capabilities that outperform 4G Evolved Packet Core (EPC) networks. Whether or not these core networks offer backward compatibility with 4G LTE devices will depend on the MNO’s choice of architecture. 5G core networks could support both legacy 4G LTE devices connecting via 4G LTE RANs as well as 5G NR devices connecting via 5G NR RANs. But as in the case of compatibility with 5G radio access networks, there is no difference between Rel 13 and Rel 14 compliant devices in terms of interoperability with such a 5G core network. The backwards compatibility is built in to the network.
4G LPWA technology is (arguably) already 5G
To push the argument further, LTE-M and NB-IoT are already 5G technologies in that they meet the ITU’s IMT-2020 requirements for 5G massive IoT use cases. It’s a confusing assertion that should not be misunderstood to mean that these devices are built using a 5G NR air interface; they definitely are not now and will not be. But it shows that the 3GPP has little incentive to replace these technologies as they continue to gain traction.
5G NR-based IoT devices will see their day, but with 3GPP Rel 17 finalized in 2021, they are unlikely to hit the market before 2023. That said, they will not cover the same use cases as today’s LTE-M and NB-IoT devices, given that the 5G “NR-Light” spec these devices will be designed to is aimed at use cases served today with LTE Cat 1 or Cat 4 levels of performance.
To conclude, if you are confronted with the choice between LTE-M and NB-IoT devices that are designed to the 3GPP Rel 13 and Rel 14 standards, compatibility with tomorrow’s networks should not be the decisive factor. Today’s LTE-M and NB-IoT technologies, whether they meet Rel 13 or Rel 14, can be deployed with no fear of obsolescence.
Additionally, for at least the next five to ten years, every location with 5G coverage will offer 4G LTE coverage as well – even in the most aggressive 5G deployment markets.