Google Says Carriers Shouldn't Use LTE in Unlicensed Spectrum Bands

By Jaikumar Vijayan  |  Posted 2015-06-15 Print this article Print
unlicensed spectrum

LTE in unlicensed spectrum bands could crowd out WiFi and other services; a better option is for mobile carriers to use underutilized 3.5GHz bands, Google said.

Mobile carriers' planned use of unlicensed spectrum bands for Long Term Evolution (LTE) services could crowd out other unlicensed services, such as WiFi, Bluetooth and ZigBee, that operate on the same bands, Google warned in a white paper that it submitted to the FCC last week.

The rapid growth of mobile data services and bandwidth-hungry applications has pushed mobile operators to look for more capacity in the 2.4GHz and 5GHz unlicensed frequency bands. Such "WiFi" offloading can benefit carriers by giving them additional capacity. It also helps consumers by enabling better performance, Google hardware engineer Nihar Jindal said in a blog posting.

Over the past few months, multiple carriers and suppliers have said they plan to use the unlicensed 5GHz band to deploy LTE services. Typically, such services have been deployed only in licensed frequencies with wireless carriers having the option to use unlicensed frequencies if they needed additional spectrum without the added expense of a license, Jindal said.

However, LTE in unlicensed (LTE-U) form poses several co-existence challenges. "LTE over unlicensed has the potential to crowd out unlicensed services," Jindal said. "Holders of licensed spectrum shouldn't be able to convert the unlicensed 5GHz band into a de facto licensed spectrum band, and certainly they should not have the ability to drive out other unlicensed users."

Google's 25-page paper to the FCC reports in, highly technical detail, on what the company said was its investigation of the co-existence between WiFi and LTE technology working across both the licensed and the unlicensed 5GHz spectrum.

The investigation showed that some services running on unlicensed spectrum, particularly WiFi, are susceptible to being crowded out by LTE in certain situations, Google said in its report.

LTE in unlicensed form co-exists poorly with WiFi because of the incompatibility of its so-called "duty-cycling" mechanism with WiFi, the report said. The lack of an effective co-existence mechanism in scenarios where WiFi and LTE in unlicensed form hear each other at moderate power levels, is another issue, the paper said.

"LTE in unlicensed [form] represents yet another innovative technology unleashed by accessibility to unlicensed spectrum," Google conceded. But given the vast scale of the technologies operating in the unlicensed space, further study is required to understand the full implications of the emerging trend, the paper said.

Some vendors have already begun that effort. In 2014, Verizon established an LTE-U Forum, along with Alcatel-Lucent, Ericsson, Qualcomm Technologies and Samsung, to develop specifications for better interoperability between LTE-U and technologies that use unlicensed spectrum.

In March the group released a technical report containing what it said were co-existence specifications and minimum performance specifications for operating LTE-U base stations on unlicensed bands in the 5GHz band.

A wide range of commercial products currently share unlicensed space, including WiFi, Bluetooth and garage door openers.  Verizon wants to work with the unlicensed community to ensure the best connectivity so LTE-U usage does not drown out the other technologies.

According to Google's Jindal, one way to avoid co-existence issues is for carriers to use the newly available spectrum in the 3.5GHz band and to leave the 5 GHz band as is. "The FCC recently identified the now-underutilized 3.5GHz band spectrum as ideal for this kind of use," he said.


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