OnQ Blog

Setting the record straight about LTE Unlicensed and Wi-Fi coexistence

Jul 24, 2015

Qualcomm products mentioned within this post are offered by Qualcomm Technologies, Inc. and/or its subsidiaries.

Qualcomm Incorporated, together with its subsidiaries Qualcomm Technologies, Inc. and Qualcomm Atheros, Inc., is working hard on LTE Unlicensed. On its own and in collaboration with many parties, the company is addressing the worldwide mobile broadband spectrum crunch. Increasing numbers of people are using smartphones, tablets, and other mobile devices on an anywhere/anytime 24/7 basis. To satisfy their increasing data demands, service providers need to deploy wireless technologies that make the most efficient use of each and every sliver of spectrum, be it licensed or unlicensed. Qualcomm Technologies is developing new versions of LTE Advanced for licensed spectrum as well as leading the industry at improving Wi-Fi services. But those efforts are not enough to meet the spectrum crunch. More is needed.

In the fall of 2013, Qualcomm began working on technologies to bring the benefits of 4G LTE to unlicensed spectrum. Any technology that meets a minimal set of technical rules is allowed in unlicensed spectrum, and no one using this spectrum has any priority over anyone else. LTE Unlicensed will offer consumers a substantially better mobile user experience than Wi-Fi—better throughput, better coverage, and increased capacity, while respecting incumbent technologies.

There are three forms of LTE Unlicensed (known as LTE-U, LAA, and MulteFire). From the outset—because of Qualcomm Atheros’ Wi-Fi business and its knowledge of Wi-Fi—Qualcomm worked closely with our collaborators to ensure that LTE Unlicensed will have no adverse impact on Wi-Fi. The company has done a great deal of technical design and development work to ensure that LTE Unlicensed will coexist very well with Wi-Fi, sharing the unlicensed spectrum fairly. As is typical whenever we launch a new technology, we’ve worked with companies and associations around the world, giving technical briefings, exchanging technical information, answering questions, and collaborating. In May, the U.S. Federal Communications Commission issued a Public Notice asking a series of questions about LTE Unlicensed, which Qualcomm and other parties answered.

Our comments and subsequent replies filed with the FCC contain the results of extensive coexistence tests performed by Qualcomm Research, the R&D arm of Qualcomm Technologies, and test results published by the LTE-U Forum, which is the group of companies who developed LTE-U. The company previously demonstrated LTE Unlicensed using coexistence techniques at the International CES and Mobile World Congress, and it has also given numerous demonstrations to key Wi-Fi equipment vendors and service providers in its lab and over the air on our San Diego campus in hyper-dense settings, all showing LTE Unlicensed successfully coexisting with Wi-Fi. These demonstrations prove that adding a neighboring LTE Unlicensed node does not impact an existing Wi-Fi node any more than would adding another Wi-Fi node. In fact, in many cases, replacing a Wi-Fi node with an LTE-U node improves the throughput for nearby Wi-Fi users.

For example, one of the tests measured average Wi-Fi throughput in an extremely dense deployment. The results of this test are depicted below. The base scenario used eight commercial off-the-shelf, carrier-grade Wi-Fi access points all operating in the same 5 GHz channel and each sending data to a different client device. When two of the Wi-Fi access points are replaced with LTE-U small cells operating in the same conditions, the average throughput of the remaining Wi-Fi nodes increased by 16%. When four of the eight Wi-Fi nodes are replaced with four LTE-U nodes, the gain increases 38% over the baseline.

In response to some FCC commenters claiming that LTE-U will interfere with Wi-Fi unless LTE-U operates with an energy detection level that is 100 times (20 dB) more sensitive than the level that Wi-Fi itself uses to detect non-Wi-Fi technologies and decide whether a channel is available for use, additional tests were performed and then detailed in the Qualcomm reply comments. These additional tests confirmed that LTE-U successfully shares spectrum with Wi-Fi when realistic assumptions are used. These tests likewise confirmed that LTE-U actually improves Wi-Fi performance when LTE-U is operating either above or below Wi-Fi’s Energy Detect (ED) level. In other words, LTE-U protects Wi-Fi to a greater degree than Wi-Fi protects itself.

Further tests confirm that LTE-U has a negligible impact on Wi-Fi beacon delivery or latency sensitive Wi-Fi applications, such as VoIP. It was pointed out by Qualcomm’s reply comments to the FCC that it is totally improper to compare the coexistence test results of LTE-U/LAA and Wi-Fi to single-link, interference-free Wi-Fi throughput, like some parties opposed to LTE Unlicensed did. More test results show that when two neighboring Wi-Fi Access Points share a single channel, the Wi-Fi throughput drops below 50% of the single-link Wi-Fi throughput. Moreover, commercial Wi-Fi Access Points today often display unequal sharing behavior with each other, both in terms of throughput and medium utilization time. However, the Wi-Fi throughput when sharing a channel with an LTE-U session is often higher than the Wi-Fi throughput when it shares the same channel with another Wi-Fi communications session. Thus, the arguments put forth by opponents of LTE Unlicensed lack technical merit.

Qualcomm explains in detail in the technical appendix of its reply comments why LTE-U is such a friendly neighbor to Wi-Fi. LTE-U does not use all of the available 5 GHz band, over 200 MHz is exclusively available for Wi-Fi. And, LTE-U is a downlink-only technology, meaning LTE-U end devices will not generate any interference to Wi-Fi or any other technologies in the 5GHz band. An LTE-U small cell scans portions of 5 GHz looking for a vacant channel, and if there is no vacant channel, it finds the least occupied channel. It then takes turns using that channel with Wi-Fi users, ensuring that it never uses the channel more than its proportionate share of the time, and it vacates the channel when no longer needs it. Unlike Wi-Fi, which does not currently have a coexistence specification, the companies involved in developing LTE-U have adopted and will follow the very extensive coexistence specifications and testing requirements that have been published at www.lteuforum.org. Also in contrast to Wi-Fi, LTE-U’s protocol scales very well with node density since each LTE-U node deterministically clears the channel after using a fair share of the channel resources.

Qualcomm, on its own and with its collaborators in the industry, has worked closely with many other companies on bilateral and multilateral bases and through industry organizations, such as 3GPP, the LTE-U Forum, ATIS, IEEE 802 and the Wi-Fi Alliance on coexistence. There have been scores of presentations, demos, and meetings. The members of the LTE-U Forum hosted an all-day technical workshop in May 2015 attended by 96 people from 29 different companies and organizations including leading Wi-Fi equipment, chipset, device and OS vendors as well as the Wi-Fi Alliance and IEEE 802. More recently, members of the LTE-U Forum delivered a technical briefing at an IEEE 802 plenary session. With regard to LAA, there have been more than a dozen liaison statements between 3GPP and the IEEE; and in late August, 3GPP is holding a technical workshop for members of 3GPP, the IEEE, and other organizations around the world.

The FCC’s unlicensed regulatory regime has enabled LTE Unlicensed technology and will continue to deliver innovations in the important unlicensed spectrum bands. Contrary to claims by those opposed to LTE Unlicensed, there is absolutely no basis for any new regulation with respect to LTE Unlicensed. All versions of LTE Unlicensed will fully comply with FCC’s rules and any other regulations in those regions where it will be deployed. More importantly, LTE Unlicensed offers significant benefits for consumers by using many of the advanced technical innovations of 4G LTE Advanced and incorporating them into small cells that will support operations in both licensed and unlicensed spectrum to provide greater capacity for smartphones and tablets.

LTE Unlicensed is one of many innovations that the wireless industry is developing to enhance consumers’ user experience through using each sliver of spectrum in the most efficient manner possible. The record before the FCC demonstrates that LTE Unlicensed has no adverse impact on Wi-Fi and that deployments will enable each of the coexistence mechanisms discussed in Qualcomm’s comments and reply comments.

This unlicensed technology innovation and successful industry collaboration are a direct result of the FCC’s technology neutral approach to unlicensed spectrum. Thus, calls for FCC oversight are not only unnecessary, but they are designed to slow the deployment of an innovative technology that will provide improved services to mobile consumers.

In this blog post we refer to “Qualcomm” for ease of reference. However, in connection with our fiscal 2013 reorganization, Qualcomm Incorporated continues to operate QTL and own the vast majority of our patent portfolio, while Qualcomm Technologies, Inc., its wholly-owned subsidiary, now operates, along with its subsidiaries, substantially all of our products and services businesses, including QCT, and substantially all of our research and development functions.


Opinions expressed in the content posted here are the personal opinions of the original authors, and do not necessarily reflect those of Qualcomm Incorporated or its subsidiaries ("Qualcomm"). Qualcomm products mentioned within this post are offered by Qualcomm Technologies, Inc. and/or its subsidiaries. The content is provided for informational purposes only and is not meant to be an endorsement or representation by Qualcomm or any other party. This site may also provide links or references to non-Qualcomm sites and resources. Qualcomm makes no representations, warranties, or other commitments whatsoever about any non-Qualcomm sites or third-party resources that may be referenced, accessible from, or linked to this site.

Dean Brenner

Senior Vice President, Spectrum Strategy and Technology Policy