Microwave Journal
www.microwavejournal.com/blogs/23-5g-and-beyond-national-instruments/post/32588-unlicensed-spectrum-may-be-critical-to-5g

Unlicensed Spectrum May Be Critical to 5G

July 23, 2019

When the International Telecom Union (ITU) outlined the key objectives for 5G, the 3GPP faced a difficult task — expand the capabilities of the current wireless network under the constraint of limited spectrum.  Spectrum equates to bandwidth, and the industry needs more spectrum to increase data rates and address specific use cases beyond 4G.  Unfortunately, there is very little unoccupied spectrum below 6 GHz.  Because of this fact, the 3GPP introduced the concept of using mmWave frequencies as a mobile access vehicle early in the standardization process.

5G and mmWave have been linked since the beginning.  mmWave spectrum offers a path to realize 5G data rates on the order of 10x or more, compared to today’s networks.  It may come as no surprise for many, but mmWave for mobile access is difficult and comes with several challenges for mobile access.  Many may debate whether these challenges have already been cost-effectively addressed or not.  However, early 5G mmWave deployments target two specific use cases: indoor “hot spots” and fixed wireless access (FWA).  In other words, not mobile access in the LTE context. 

Although mmWave holds much promise, there is more work to be done, and the 3GPP continues to investigate other frequency options to unlock more spectrum for 5G use.  In addition to mmWave, the 3GPP has been investigating unlicensed spectrum with the NR-U study item.  In LTE or 4G, the 3GPP defined a coexistence path for WiFi and LTE using the unlicensed bands, where an LTE subscriber could use the unlicensed 2.4 or 5 GHz bands to supplement data throughput.  Known as LAA or license assisted access, LTE and WiFi can coexist, although it is unclear how many users take advantage of this technology today.  3GPP’s 5G NR-U proposals go way beyond the prior 4G work, and there is additional motivation to take NR-U further. 

Perhaps not coincidentally, the FCC has issued a notice of proposed rulemaking to investigate the use of the 6 GHz band covering 5.925-7.125 GHz as unlicensed and a possible home for 5G use.  This spectrum today is used by cable operators for distribution of services, radars, and dedicated microwave communication links.  By designating this spectrum as unlicensed, 5G operators and others could take advantage of this spectrum to create new networks or augment already deployed networks.  The combination of 2.4, 5 and now 6 GHz potentially creates over 1 GHz of spectrum for 5G use. 

However, unlicensed bands for 5G do not come for free. Any 5G device using unlicensed spectrum must embrace all these techniques:

  • Comply with lower power emission requirements that limit signal propagation and inband interference, constraining the coverage area. 
  • Share spectrum with incumbent users, adding technical complexity to 5G terminals, so that all devices can coexist. 
  • Make use of DFS (Dynamic Frequency Selection) and TPC (Transmit Power Control) techniques to facilitate coexistence, like WiFi devices do today.
  • Likely adopt the LTE or 4G coexistence techniques, such as LBT (Listen Before Talk) to achieve coexistence with WiFi devices. 

In cases where this spectrum is lightly used, 5G NR-U deployments could be strategically placed, enabling the creation of dedicated-use 5G NR networks offering benefits above and beyond current technologies to address the key performance objectives of the 3GPP — i.e., faster data rates, higher reliability, and low-latency — to further extend the 5G ecosystem, albeit in localized regions and perhaps explicitly for specific use cases.    

At first glance, NR-U adds complexity, and the 3GPP members will have to weigh the benefits, costs, and potential drawbacks of this approach.  On the other hand, it is a lot of spectrum, and spectrum is key to realizing the potential of 5G.  If the 3GPP is successful in moving forward with NR-U, there are copious amounts of unlicensed mmWave spectrum that can also benefit from this work once mmWave technologies have matured.  NR-U is just one of several study items for 3GPP Release 16 and beyond, but it may be critically important to the 5G initiative, and perhaps much more important than many of use initially thought. 

It’s clear that 5G NR, with new bands, wider bandwidth, and new beamforming technology, presents significant design and test challenges that require powerful tools to accelerate innovation. For more information on how to solve these challenges, go to ni.com/5g.