Unlicensed Spectrum May Be Critical to 5G

 

The link between 5G and mmWave

 

5G and mmWave have been connected since the beginning. mmWave spectrum offers a path to realize 5G data rates on the order of 10X or more, in comparison to today’s networks. It may come as no surprise, but mmWave for mobile access is fraught with challenges. A lot of people debate whether these challenges have been addressed cost effectively. And yet, early 5G mmWave deployments target two unique use cases: indoor “hot spots” and fixed wireless access (FWA). This basically means, not mobile access in the context of LTE. 

 

Although mmWave contains much promise, more work must be done to actualize its potential, and the 3GPP continues to investigate other frequency options to unleash more spectrum for 5G use. Along with mmWave, the 3GPP is 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, the path proves LTE and WiFi can coexist, although it’s unclear how many users take advantage of this technology today. 3GPP’s 5G NR-U proposals go way beyond the prior work on 4G, and there is additional motivation to take NR-U further.

 

 

Maybe 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. Today, this spectrum 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 full advantage of it 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. 

 

Nevertheless, unlicensed bands for 5G come with stipulations. Any 5G device using unlicensed spectrum must:
 

• Comply with lower power emission requirements that limit signal propagation and in-band 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 Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) techniques to facilitate coexistence, like WiFi devices do today
• Likely adopt the LTE or 4G coexistence techniques, such as Listen Before Talk (LBT), to work side-by-side with WiFi devices

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

 

At first sight, NR-U adds complexity, and the 3GPP members must weigh the benefits, costs, and potential drawbacks of this approach. Nevertheless, it provides a large amount 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 abundant amounts of unlicensed mmWave spectrum that can also benefit from this work once mmWave technologies have matured. NR-U is just one of multiple study items for 3GPP Release 16 and beyond, but it may be critical to the 5G initiative—perhaps much more important than many of us initially thought. 

 

It is clear that 5G NR, with new bands, wider bandwidth, and new beamforming technology, presents important design and test challenges that require powerful tools to accelerate innovation.

 

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