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The Opportunities and Challenges of LTE Unlicensed in 5 GHz

The Opportunities and Challenges of LTE Unlicensed in 5 GHz

by David Witkowski, Executive Director Wireless Communications Initiative

In 1998, the Federal Communications Commission established the Unlicensed National Information Infrastructure or U-NII 5 GHz bands. These are used primarily for Wi-Fi networks in homes, offices, hotels, airports, and other public spaces and also consumer devices. U-NII is also used by wireless Internet Service Providers, linking public safety radio sites, and for monitoring and critical infrastructure such as gas/oil pipelines.

Data flows to laptops, smartphones, and tablets via a variety of paths. Mobile carriers such as Verizon, AT&T, T-Mobile, and Sprint purchase spectrum licenses and install 4G and 3G equipment sited on towers, poletops, and buildings. Seeking additional spectrum to feed our data-hungry smartphones, mobile carriers are deploying a modified form of LTE — the wireless standard often called “4G” — into unlicensed spectrum. Known as LTE Unlicensed or “LTE-U,” it’s designed to share spectrum and co-exist with the existing Wi-Fi signals — or at least that’s the intention.

Our appetite for wireless data is strong and growing quickly. Globally, we consumed 8 Exabytes per month in 2014 and by 2020 we’ll be consuming 71 Exabytes per month, and there isn’t enough licensed spectrum to support this growth.

Spectrum is both scarce and expensive. Early 4G systems used spectrum from a 2008 auction that cost $19.1 billion, and in 2015 carriers paid a record-breaking $44.9 billion for AWS-3 spectrum. Future auctions are expected to break those records. If carriers had to pay for access to the U-NII spectrum, it would cost $138 billion based upon the AWS-3 pricing.

These costs are just for spectrum — carriers must still buy the equipment, negotiate site leases for towers, and pay crews to build the system. Making efficient use of spectrum is a key strategic element for any mobile carrier, and LTE — which is very spectrum efficient – is a good solution.

Part of the beauty of unlicensed spectrum is that anyone can use it, but there can be issues with sharing — namely congestion and interference with existing users. Under the stewardship and standards set by the Wi-Fi Alliance and the IEEE, methods to allow technologies such as Wi-Fi, Bluetooth, and Zigbee to co-exist in the same spectrum with minimal loss of efficiency have been developed. Within the IEEE family of standards, there is good cooperation on co-channeled technologies.

That mobile carriers are deploying LTE-U in the same band with Wi-Fi is troubling to some. Google, which recently launched their Project Fi mobile phone service, is one of several companies known as “Wi-Fi First Carriers” who are building mobile telephone networks that primarily use Wi-Fi and only switch to mobile carriers when Wi-Fi is weak or nonexistent. Cable carriers are moving aggressively into public Wi-Fi, especially in dense urban cores where ubiquitous Wi-Fi coverage enables mobile use without traditional carriers. Ensuring that Wi-Fi continues to work well is key to this strategy.

In early 2015, the FCC asked for industry comments on LTE-U; the response was both large and polarized. Members of the LTE-U Forum (an industry group formed by Verizon in cooperation with Alcatel-Lucent, Ericsson, Qualcomm, and Samsung) have published measurement results that argue LTE-U can co-exist with Wi-Fi. Companies with a vested stake in Wi-Fi (such as Google, Comcast, and members of the Wi-Fi Alliance — which incidentally do not purchase spectrum licenses) have published measurements that argue LTE-U has an adverse and unfair impact on Wi-Fi systems.

The FCC says it doesn’t want to intervene and expects the industry to sort this out via the standards process. As of October 2015, the Wi-Fi Alliance and LTE-U Forum were still debating how co-existence should be tested, and neither side wants to hand certification control to the other. We recommend setting aside the question of certification and focusing on open discussion for a test plan, so that stakeholders can test independently and cross-verify the others’ results. Objective analysis is in everyone’s interest and will ensure LTE-U and Wi-Fi can co-exist and eliminate the need for FCC intervention.

David Witkowski is the Executive Director of the Wireless Communications Initiative at Joint Venture Silicon Valley (www.jointventure.org/wireless) and the founder of Oku Solutions (www.okusolutions.com).